from reportlab.lib.pagesizes import A4
from reportlab.lib import colors
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.units import cm, mm
from reportlab.platypus import (
    SimpleDocTemplate, Paragraph, Spacer, Table, TableStyle,
    HRFlowable, PageBreak, KeepTogether
)
from reportlab.lib.enums import TA_CENTER, TA_LEFT, TA_JUSTIFY
from reportlab.platypus import ListFlowable, ListItem
from reportlab.lib.colors import HexColor

OUTPUT_PATH = "/tmp/workspace/interbody-fusion-guide/Interbody_Fusion_Techniques_Guide.pdf"

# ─── COLOR PALETTE ───────────────────────────────────────────────────────────
C_DARK_BLUE   = HexColor("#1A3A5C")
C_MED_BLUE    = HexColor("#2E6DA4")
C_LIGHT_BLUE  = HexColor("#D6E8F7")
C_ALIF        = HexColor("#1B6CA8")  # blue
C_PLIF        = HexColor("#1E8449")  # green
C_TLIF        = HexColor("#B7770D")  # amber
C_XLIF        = HexColor("#7D3C98")  # purple
C_ALIF_LIGHT  = HexColor("#D6EAF8")
C_PLIF_LIGHT  = HexColor("#D5F5E3")
C_TLIF_LIGHT  = HexColor("#FEF9E7")
C_XLIF_LIGHT  = HexColor("#F5EEF8")
C_WHITE       = colors.white
C_LIGHT_GREY  = HexColor("#F2F2F2")
C_MID_GREY    = HexColor("#CCCCCC")
C_TEXT        = HexColor("#1A1A1A")

# ─── STYLES ──────────────────────────────────────────────────────────────────
styles = getSampleStyleSheet()

def make_style(name, parent='Normal', **kwargs):
    s = ParagraphStyle(name, parent=styles[parent], **kwargs)
    return s

TITLE_STYLE = make_style('DocTitle', fontSize=26, textColor=C_WHITE,
                         alignment=TA_CENTER, fontName='Helvetica-Bold',
                         spaceAfter=6)
SUBTITLE_STYLE = make_style('DocSubtitle', fontSize=13, textColor=HexColor("#C8DCF0"),
                             alignment=TA_CENTER, fontName='Helvetica',
                             spaceAfter=4)
AUTHOR_STYLE = make_style('Author', fontSize=10, textColor=HexColor("#90B8D8"),
                           alignment=TA_CENTER, fontName='Helvetica-Oblique')

SECTION_TITLE = make_style('SectionTitle', fontSize=18, textColor=C_WHITE,
                            fontName='Helvetica-Bold', alignment=TA_LEFT,
                            spaceBefore=0, spaceAfter=0)

H2 = make_style('H2', fontSize=13, textColor=C_DARK_BLUE,
                fontName='Helvetica-Bold', spaceBefore=10, spaceAfter=4)
H3 = make_style('H3', fontSize=11, textColor=C_MED_BLUE,
                fontName='Helvetica-Bold', spaceBefore=6, spaceAfter=3)

BODY = make_style('Body', fontSize=10, textColor=C_TEXT,
                  fontName='Helvetica', leading=15, spaceAfter=4,
                  alignment=TA_JUSTIFY)
BODY_BOLD = make_style('BodyBold', fontSize=10, textColor=C_TEXT,
                       fontName='Helvetica-Bold', leading=15)
STEP_NUM = make_style('StepNum', fontSize=11, textColor=C_WHITE,
                      fontName='Helvetica-Bold', alignment=TA_CENTER)
STEP_TEXT = make_style('StepText', fontSize=10, textColor=C_TEXT,
                       fontName='Helvetica', leading=14, spaceAfter=2)
STEP_TITLE = make_style('StepTitle', fontSize=10, textColor=C_DARK_BLUE,
                        fontName='Helvetica-Bold', leading=14)
CAUTION = make_style('Caution', fontSize=9.5, textColor=HexColor("#7E5109"),
                     fontName='Helvetica', leading=13, spaceAfter=3)
TIP = make_style('Tip', fontSize=9.5, textColor=HexColor("#145A32"),
                 fontName='Helvetica', leading=13, spaceAfter=3)
TABLE_HEADER = make_style('TH', fontSize=9, textColor=C_WHITE,
                          fontName='Helvetica-Bold', alignment=TA_CENTER)
TABLE_CELL = make_style('TC', fontSize=9, textColor=C_TEXT,
                        fontName='Helvetica', leading=12, alignment=TA_LEFT)
TABLE_CELL_C = make_style('TCC', fontSize=9, textColor=C_TEXT,
                           fontName='Helvetica', leading=12, alignment=TA_CENTER)
FOOTER_STYLE = make_style('Footer', fontSize=8, textColor=HexColor("#888888"),
                           alignment=TA_CENTER, fontName='Helvetica-Oblique')
TOC_TITLE = make_style('TOCTitle', fontSize=11, textColor=C_DARK_BLUE,
                       fontName='Helvetica-Bold', leading=14)
TOC_ENTRY = make_style('TOCEntry', fontSize=10, textColor=C_TEXT,
                       fontName='Helvetica', leading=14, leftIndent=12)

# ─── HELPERS ─────────────────────────────────────────────────────────────────

def section_header(title, color, subtitle=None):
    """A full-width colored banner for each section."""
    inner = [Paragraph(title, SECTION_TITLE)]
    if subtitle:
        inner.append(Paragraph(subtitle, make_style(
            'SH_Sub', fontSize=10, textColor=HexColor("#D0E8FF"),
            fontName='Helvetica-Oblique', alignment=TA_LEFT)))
    tbl = Table([[inner]], colWidths=[17*cm])
    tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), color),
        ('TOPPADDING', (0,0), (-1,-1), 10),
        ('BOTTOMPADDING', (0,0), (-1,-1), 10),
        ('LEFTPADDING', (0,0), (-1,-1), 14),
        ('RIGHTPADDING', (0,0), (-1,-1), 14),
        ('ROUNDEDCORNERS', [6,6,6,6]),
    ]))
    return tbl

def step_row(num, title, detail, color):
    """A single numbered step row."""
    num_cell = Table([[Paragraph(str(num), STEP_NUM)]], colWidths=[1.1*cm], rowHeights=[1.1*cm])
    num_cell.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), color),
        ('TOPPADDING', (0,0), (-1,-1), 0),
        ('BOTTOMPADDING', (0,0), (-1,-1), 0),
        ('LEFTPADDING', (0,0), (-1,-1), 0),
        ('RIGHTPADDING', (0,0), (-1,-1), 0),
        ('VALIGN', (0,0), (-1,-1), 'MIDDLE'),
        ('ROUNDEDCORNERS', [4,4,4,4]),
    ]))
    text_cell = [Paragraph(title, STEP_TITLE), Paragraph(detail, STEP_TEXT)]
    row_tbl = Table([[num_cell, text_cell]], colWidths=[1.3*cm, 15.7*cm])
    row_tbl.setStyle(TableStyle([
        ('VALIGN', (0,0), (-1,-1), 'TOP'),
        ('LEFTPADDING', (0,0), (0,-1), 0),
        ('RIGHTPADDING', (0,0), (0,-1), 6),
        ('TOPPADDING', (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING', (1,0), (1,-1), 8),
        ('BACKGROUND', (1,0), (1,-1), C_LIGHT_GREY),
        ('LINEBELOW', (0,0), (-1,-1), 0.5, C_MID_GREY),
    ]))
    return row_tbl

def info_box(text, bg_color, label="NOTE"):
    """A coloured info/caution/tip box."""
    tbl = Table([[Paragraph(f"<b>{label}:</b> {text}", BODY)]], colWidths=[17*cm])
    tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), bg_color),
        ('TOPPADDING', (0,0), (-1,-1), 7),
        ('BOTTOMPADDING', (0,0), (-1,-1), 7),
        ('LEFTPADDING', (0,0), (-1,-1), 10),
        ('RIGHTPADDING', (0,0), (-1,-1), 10),
        ('BOX', (0,0), (-1,-1), 0.8, C_MID_GREY),
    ]))
    return tbl

def comparison_table(header_row, data_rows, col_widths, header_color):
    table_data = []
    header_cells = [Paragraph(h, TABLE_HEADER) for h in header_row]
    table_data.append(header_cells)
    for row in data_rows:
        table_data.append([Paragraph(str(c), TABLE_CELL) for c in row])
    tbl = Table(table_data, colWidths=col_widths, repeatRows=1)
    style = [
        ('BACKGROUND', (0,0), (-1,0), header_color),
        ('TEXTCOLOR', (0,0), (-1,0), C_WHITE),
        ('FONTNAME', (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE', (0,0), (-1,-1), 9),
        ('ALIGN', (0,0), (-1,0), 'CENTER'),
        ('VALIGN', (0,0), (-1,-1), 'TOP'),
        ('GRID', (0,0), (-1,-1), 0.4, C_MID_GREY),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [C_WHITE, C_LIGHT_GREY]),
        ('TOPPADDING', (0,0), (-1,-1), 5),
        ('BOTTOMPADDING', (0,0), (-1,-1), 5),
        ('LEFTPADDING', (0,0), (-1,-1), 5),
        ('RIGHTPADDING', (0,0), (-1,-1), 5),
    ]
    tbl.setStyle(TableStyle(style))
    return tbl

# ─── COVER PAGE ──────────────────────────────────────────────────────────────

def build_cover():
    elems = []
    elems.append(Spacer(1, 2.5*cm))
    cover_tbl = Table([[
        Paragraph("LUMBAR INTERBODY FUSION", TITLE_STYLE),
    ]], colWidths=[17*cm])
    cover_tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), C_DARK_BLUE),
        ('TOPPADDING', (0,0), (-1,-1), 20),
        ('BOTTOMPADDING', (0,0), (-1,-1), 8),
        ('LEFTPADDING', (0,0), (-1,-1), 16),
        ('RIGHTPADDING', (0,0), (-1,-1), 16),
    ]))
    subtitle_tbl = Table([[
        Paragraph("Step-by-Step Surgical Guide", SUBTITLE_STYLE),
    ]], colWidths=[17*cm])
    subtitle_tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), C_MED_BLUE),
        ('TOPPADDING', (0,0), (-1,-1), 8),
        ('BOTTOMPADDING', (0,0), (-1,-1), 18),
        ('LEFTPADDING', (0,0), (-1,-1), 16),
        ('RIGHTPADDING', (0,0), (-1,-1), 16),
    ]))
    elems.append(cover_tbl)
    elems.append(subtitle_tbl)
    elems.append(Spacer(1, 0.6*cm))

    # 4 technique boxes
    tech_data = [
        [Paragraph("ALIF", make_style('T1', fontSize=16, textColor=C_WHITE,
                   fontName='Helvetica-Bold', alignment=TA_CENTER)),
         Paragraph("PLIF", make_style('T2', fontSize=16, textColor=C_WHITE,
                   fontName='Helvetica-Bold', alignment=TA_CENTER)),
         Paragraph("TLIF", make_style('T3', fontSize=16, textColor=C_WHITE,
                   fontName='Helvetica-Bold', alignment=TA_CENTER)),
         Paragraph("XLIF", make_style('T4', fontSize=16, textColor=C_WHITE,
                   fontName='Helvetica-Bold', alignment=TA_CENTER))],
        [Paragraph("Anterior<br/>Lumbar<br/>Interbody Fusion",
                   make_style('T1s', fontSize=9, textColor=HexColor("#C8DCF0"),
                   fontName='Helvetica', alignment=TA_CENTER)),
         Paragraph("Posterior<br/>Lumbar<br/>Interbody Fusion",
                   make_style('T2s', fontSize=9, textColor=HexColor("#C8DCF0"),
                   fontName='Helvetica', alignment=TA_CENTER)),
         Paragraph("Transforaminal<br/>Lumbar<br/>Interbody Fusion",
                   make_style('T3s', fontSize=9, textColor=HexColor("#C8DCF0"),
                   fontName='Helvetica', alignment=TA_CENTER)),
         Paragraph("Extreme Lateral<br/>Lumbar<br/>Interbody Fusion",
                   make_style('T4s', fontSize=9, textColor=HexColor("#C8DCF0"),
                   fontName='Helvetica', alignment=TA_CENTER))],
    ]
    tech_tbl = Table(tech_data, colWidths=[4.25*cm]*4, rowHeights=[1.5*cm, 1.5*cm])
    tech_tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (0,-1), C_ALIF),
        ('BACKGROUND', (1,0), (1,-1), C_PLIF),
        ('BACKGROUND', (2,0), (2,-1), C_TLIF),
        ('BACKGROUND', (3,0), (3,-1), C_XLIF),
        ('VALIGN', (0,0), (-1,-1), 'MIDDLE'),
        ('TOPPADDING', (0,0), (-1,-1), 8),
        ('BOTTOMPADDING', (0,0), (-1,-1), 8),
        ('INNERGRID', (0,0), (-1,-1), 1.5, C_WHITE),
    ]))
    elems.append(tech_tbl)
    elems.append(Spacer(1, 0.6*cm))
    elems.append(Paragraph("Reference: Campbell's Operative Orthopaedics 15th Ed 2026 · Grainger & Allison's Diagnostic Radiology · Gray's Anatomy for Students", AUTHOR_STYLE))
    elems.append(Spacer(1, 0.3*cm))
    elems.append(Paragraph("Compiled by Orris Medical AI · July 2026", AUTHOR_STYLE))
    return elems

# ─── TOC ─────────────────────────────────────────────────────────────────────

def build_toc():
    elems = []
    elems.append(PageBreak())
    elems.append(Paragraph("TABLE OF CONTENTS", H2))
    elems.append(HRFlowable(width="100%", thickness=1.5, color=C_DARK_BLUE, spaceAfter=8))
    entries = [
        ("1.  Overview & Concept", "3"),
        ("2.  Axial Anatomy & Approach Zones", "3"),
        ("3.  ALIF — Anterior Lumbar Interbody Fusion", "4"),
        ("      3.1  Indications & Contraindications", "4"),
        ("      3.2  Anatomy at Risk", "4"),
        ("      3.3  Step-by-Step Technique", "5"),
        ("      3.4  Complications", "6"),
        ("4.  PLIF — Posterior Lumbar Interbody Fusion", "7"),
        ("      4.1  Indications & Contraindications", "7"),
        ("      4.2  Anatomy at Risk", "7"),
        ("      4.3  Step-by-Step Technique", "8"),
        ("      4.4  Complications", "9"),
        ("5.  TLIF — Transforaminal Lumbar Interbody Fusion", "10"),
        ("      5.1  Indications & Contraindications", "10"),
        ("      5.2  Kambin's Triangle", "10"),
        ("      5.3  Step-by-Step Technique", "11"),
        ("      5.4  Complications", "12"),
        ("6.  XLIF/LLIF — Extreme Lateral Interbody Fusion", "13"),
        ("      6.1  Indications & Contraindications", "13"),
        ("      6.2  Safe Zone & EMG Monitoring", "13"),
        ("      6.3  Step-by-Step Technique", "14"),
        ("      6.4  Complications", "15"),
        ("7.  Master Comparison Table", "16"),
        ("8.  Cage Materials & Bone Graft Options", "17"),
        ("9.  Decision Algorithm by Level", "17"),
    ]
    for title, page in entries:
        row = Table([[Paragraph(title, TOC_ENTRY), Paragraph(page, make_style(
            'TOCP', fontSize=10, fontName='Helvetica', alignment=TA_CENTER,
            textColor=C_MED_BLUE))]],
            colWidths=[15*cm, 2*cm])
        row.setStyle(TableStyle([
            ('LINEBELOW', (0,0), (-1,-1), 0.3, C_MID_GREY),
            ('TOPPADDING', (0,0), (-1,-1), 3),
            ('BOTTOMPADDING', (0,0), (-1,-1), 3),
        ]))
        elems.append(row)
    return elems

# ─── OVERVIEW ────────────────────────────────────────────────────────────────

def build_overview():
    elems = []
    elems.append(PageBreak())
    elems.append(section_header("1.  OVERVIEW & CONCEPT", C_DARK_BLUE,
                                "Lumbar Interbody Fusion — Principles"))
    elems.append(Spacer(1, 0.4*cm))
    elems.append(Paragraph(
        "Lumbar interbody fusion (LIF) techniques access the intervertebral disc space "
        "to remove the disc, prepare the vertebral endplates, and insert an interbody "
        "cage packed with bone graft material. The goal is to achieve <b>circumferential "
        "fusion</b> (anterior + posterior column), restoring disc height, correcting "
        "sagittal alignment, and providing long-term stability.", BODY))
    elems.append(Spacer(1, 0.3*cm))

    elems.append(Paragraph("Core Surgical Goals", H3))
    goals = [
        ("Stability", "Eliminate painful motion at the diseased segment"),
        ("Decompression", "Restore foraminal height and canal dimensions"),
        ("Alignment", "Restore/improve lumbar lordosis and sagittal balance"),
        ("Fusion", "Achieve solid bony union — hardware alone will fatigue-fracture without fusion"),
    ]
    for g, d in goals:
        elems.append(Paragraph(f"<b>{g}:</b> {d}", BODY))

    elems.append(Spacer(1, 0.3*cm))
    elems.append(Paragraph("Two-Element Framework (Common to All LIF Techniques)", H3))
    fw_data = [
        ["Element", "Options", "Purpose"],
        ["Anchor\n(Vertebral Attachment)", "Pedicle screws\nTranslaminar screws", "Secure the construct to bone"],
        ["Interbody Device", "PEEK cage · Titanium cage\nCarbon composite cage", "Restore height · Promote fusion"],
        ["Graft Material", "Autologous bone · Allograft\nBMP-2 · Ceramic substitute", "Drive osteogenesis within the cage"],
    ]
    fw_tbl = comparison_table(fw_data[0], fw_data[1:],
                               [4*cm, 7*cm, 6*cm], C_DARK_BLUE)
    elems.append(fw_tbl)

    elems.append(Spacer(1, 0.5*cm))
    elems.append(section_header("2.  AXIAL ANATOMY & APPROACH ZONES", C_DARK_BLUE,
                                "Cross-sectional view of the lumbar spine showing surgical corridors"))
    elems.append(Spacer(1, 0.4*cm))
    elems.append(Paragraph(
        "Each technique uses a distinct corridor to reach the disc space. "
        "Understanding the axial anatomy prevents injury to vascular, neural, "
        "and visceral structures adjacent to each approach zone.", BODY))
    elems.append(Spacer(1, 0.2*cm))

    zone_data = [
        ["Approach", "Direction", "Key Corridor Structures", "Primary Risk"],
        ["ALIF", "Directly anterior", "Transperitoneal or retroperitoneal;\nAnterior to aorta & IVC", "Vascular, retrograde ejaculation"],
        ["PLIF", "Directly posterior", "Posterior midline through spinal canal", "Bilateral nerve root / dural injury"],
        ["TLIF", "Posterolateral", "Posterior midline; unilateral foramen\n(Kambin's triangle)", "Exiting nerve root injury"],
        ["XLIF/LLIF", "Directly lateral", "Retroperitoneal; through psoas muscle", "Lumbar plexus / genitofemoral nerve"],
        ["OLIF/ATP", "Oblique-anterior", "Between anterior vessels & psoas", "Sympathetic chain, vessels"],
    ]
    zone_tbl = comparison_table(zone_data[0], zone_data[1:],
                                 [2.5*cm, 3*cm, 6*cm, 5.5*cm], C_DARK_BLUE)
    elems.append(zone_tbl)
    elems.append(Spacer(1, 0.3*cm))
    elems.append(info_box(
        "The iliac crest blocks access to L5-S1 in XLIF/LLIF. "
        "ALIF is the preferred approach for L5-S1 interbody fusion requiring a large cage.",
        HexColor("#EBF5FB"), "KEY ANATOMY POINT"))
    return elems

# ─── ALIF ────────────────────────────────────────────────────────────────────

def build_alif():
    elems = []
    elems.append(PageBreak())
    elems.append(section_header(
        "3.  ALIF — ANTERIOR LUMBAR INTERBODY FUSION", C_ALIF,
        "Approach: Anterior (transperitoneal or retroperitoneal)  |  Position: Supine"))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("3.1  Indications & Contraindications", H2))
    ic_data = [
        ["INDICATIONS", "CONTRAINDICATIONS / CAUTIONS"],
        ["Degenerative disc disease (L4-5, L5-S1)\nSpondylolisthesis (grade I-II)\nSagittal imbalance / flatback correction\nPseudarthrosis (revision after posterior fusion)\nDiscogenic low back pain\nAdjacent segment disease",
         "Prior retroperitoneal surgery / extensive abdominal adhesions\nOsteoporosis (cage subsidence risk)\nMale patient desiring future fertility (retrograde ejaculation risk)\nNo available vascular/access surgeon\nMorbid obesity\nInflammatory bowel disease / stoma"],
    ]
    ic_tbl = Table([[Paragraph(ic_data[0][0], TABLE_HEADER),
                     Paragraph(ic_data[0][1], TABLE_HEADER)],
                    [Paragraph(ic_data[1][0], BODY),
                     Paragraph(ic_data[1][1], BODY)]],
                   colWidths=[8.5*cm, 8.5*cm])
    ic_tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), C_ALIF),
        ('BACKGROUND', (0,1), (0,1), C_ALIF_LIGHT),
        ('BACKGROUND', (1,1), (1,1), HexColor("#FDEDEC")),
        ('GRID', (0,0), (-1,-1), 0.4, C_MID_GREY),
        ('VALIGN', (0,0), (-1,-1), 'TOP'),
        ('TOPPADDING', (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING', (0,0), (-1,-1), 7),
        ('RIGHTPADDING', (0,0), (-1,-1), 7),
    ]))
    elems.append(ic_tbl)
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("3.2  Anatomy at Risk", H2))
    anat_data = [
        ["Structure", "Location", "Injury Consequence"],
        ["Aorta / iliac arteries", "Anterior to vertebral body", "Catastrophic haemorrhage"],
        ["IVC / iliac veins", "Right anterolateral to vertebra", "Major venous haemorrhage"],
        ["Superior hypogastric plexus", "Anterior to L5-S1 disc space", "Retrograde ejaculation (NOT impotence)"],
        ["Left ureter", "Crosses left iliac artery", "Ureteral injury, hydronephrosis"],
        ["Sympathetic chain", "Anterolateral to vertebral bodies", "Sympathetic dysfunction"],
        ["Lumbosacral trunk (L4-L5 nerve)", "Posterior to iliac vessels", "Motor weakness lower limb"],
    ]
    elems.append(comparison_table(anat_data[0], anat_data[1:],
                                   [4.5*cm, 5.5*cm, 7*cm], C_ALIF))
    elems.append(Spacer(1, 0.4*cm))
    elems.append(info_box(
        "Retrograde ejaculation occurs in 0.5–5% of male patients due to injury to the "
        "superior hypogastric plexus. It is distinct from impotence (erectile function is preserved). "
        "Minimise by using blunt dissection from left to right and avoiding electrocautery anterior to L5-S1.",
        HexColor("#FEF9E7"), "CAUTION"))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("3.3  Step-by-Step Technique (Transperitoneal — L5-S1)", H2))
    steps = [
        ("Patient Positioning", "Supine on a radiolucent table. Slight Trendelenburg to allow bowel to fall cephalad. "
         "Ensure fluoroscopy access for lateral and AP views. Secure both arms padded on armboards."),
        ("Skin Incision", "Vertical midline from umbilicus to pubis OR transverse Pfannenstiel incision (preferred — cosmetically superior, better exposure). "
         "Pfannenstiel requires transection of the rectus abdominis sheath."),
        ("Peritoneal Entry", "Identify and open posterior rectus sheath and abdominal fascia. Carefully open the peritoneum. "
         "Pack abdominal contents cephalad with moistened lap pads."),
        ("Posterior Peritoneum", "Identify the aortic bifurcation and sacral promontory by palpation through the posterior peritoneum. "
         "Make a longitudinal incision in the posterior peritoneum in the midline, around the aortic bifurcation."),
        ("Vessel Mobilisation", "Extend incision distally along the right common iliac artery to its bifurcation. "
         "Identify right ureter crossing the right iliac artery — curve incision medially to avoid it. "
         "Retract common iliac vessels laterally with vessel loops or retractors."),
        ("Middle Sacral Vessels", "Identify and ligate/clip the middle sacral artery and vein in the midline "
         "over the L5-S1 disc space (see Fig 44.36B)."),
        ("Disc Exposure", "AVOID electrocautery anterior to the L5-S1 disc space — protect the superior hypogastric plexus. "
         "Use blunt dissection left to right. Expose the anterior annulus of L5-S1 clearly."),
        ("Level Confirmation", "Confirm the correct disc level with lateral fluoroscopy using a needle or Kirschner wire in the disc space."),
        ("Discectomy", "Incise the anterior annulus with a scalpel (box or H-shaped annulotomy). "
         "Remove all disc material using curettes, rongeurs, and pituitary forceps. "
         "Achieve complete discectomy including cartilaginous endplates."),
        ("Endplate Preparation", "Use rasps, scrapers, and curettes to decorticate the endplates to bleeding bone. "
         "Avoid violating the cortical endplate (increases subsidence risk). "
         "Achieve flat, parallel endplates to accept the cage."),
        ("Trial Cage Sizing", "Insert trial cages of increasing height until the desired disc distraction is achieved. "
         "Confirm with lateral fluoroscopy. Choose the largest cage that fits without over-distraction."),
        ("Cage Insertion", "Pack the final cage with autologous bone graft, allograft, or BMP-2. "
         "Insert the cage in the anterior-central position to maximise lordosis and endplate contact. "
         "Confirm AP and lateral position with fluoroscopy."),
        ("Haemostasis & Closure", "Obtain haemostasis. Close the posterior peritoneum over the great vessels. "
         "Close the abdominal wall in layers (rectus sheath, subcutaneous tissue, skin). "
         "Insert a urinary catheter preoperatively; remove on day 1-2."),
        ("Supplemental Posterior Fixation", "For most indications, posterior percutaneous pedicle screw-rod fixation is added "
         "(same anaesthetic or staged). This converts ALIF to a 360° fusion construct."),
    ]
    for i, (title, detail) in enumerate(steps, 1):
        elems.append(step_row(i, title, detail, C_ALIF))
        elems.append(Spacer(1, 0.15*cm))

    elems.append(Spacer(1, 0.4*cm))
    elems.append(Paragraph("3.4  ALIF Complications", H2))
    comp_data = [
        ["Complication", "Incidence", "Prevention / Management"],
        ["Retrograde ejaculation", "0.5–5% males", "Blunt dissection; avoid electrocautery anterior to L5-S1"],
        ["Vascular injury (aorta/IVC/iliac)", "1–3%", "Gentle retraction; vascular access surgeon on standby"],
        ["Cage subsidence", "4–10%", "Avoid endplate violation; choose correct cage size"],
        ["Postoperative ileus", "3–5%", "Gentle bowel handling; early ambulation"],
        ["Wound infection (superficial/deep)", "1–2%", "Prophylactic antibiotics; sterile technique"],
        ["Approach-related nerve injury", "<1%", "Identify ureter; avoid deep retraction near L4-5 nerve"],
        ["Pseudarthrosis", "3–8%", "Ensure solid endplate preparation; use BMP-2 if needed"],
        ["Deep vein thrombosis/PE", "1–3%", "Sequential compression devices; early mobilisation"],
    ]
    elems.append(comparison_table(comp_data[0], comp_data[1:],
                                   [5*cm, 3*cm, 9*cm], C_ALIF))
    return elems

# ─── PLIF ────────────────────────────────────────────────────────────────────

def build_plif():
    elems = []
    elems.append(PageBreak())
    elems.append(section_header(
        "4.  PLIF — POSTERIOR LUMBAR INTERBODY FUSION", C_PLIF,
        "Approach: Posterior midline  |  Position: Prone"))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("4.1  Indications & Contraindications", H2))
    ic_data = [
        ["INDICATIONS", "CONTRAINDICATIONS / CAUTIONS"],
        ["Lumbar spondylolisthesis with neural compression\nDegenerative disc disease with instability\nRecurrent disc herniation (after previous discectomy)\nSpondylolysis with instability\nDegenerative scoliosis requiring decompression + fusion\nSegmental instability following laminectomy",
         "Severe epidural fibrosis (previous posterior surgery — consider TLIF instead)\nOsteoporosis (small cages + limited endplate contact)\nSevere canal stenosis with multiple adhesions\nActive infection at operative level\nMajor comorbidities precluding prolonged prone position"],
    ]
    ic_tbl = Table([[Paragraph(ic_data[0][0], TABLE_HEADER),
                     Paragraph(ic_data[0][1], TABLE_HEADER)],
                    [Paragraph(ic_data[1][0], BODY),
                     Paragraph(ic_data[1][1], BODY)]],
                   colWidths=[8.5*cm, 8.5*cm])
    ic_tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), C_PLIF),
        ('BACKGROUND', (0,1), (0,1), C_PLIF_LIGHT),
        ('BACKGROUND', (1,1), (1,1), HexColor("#FDEDEC")),
        ('GRID', (0,0), (-1,-1), 0.4, C_MID_GREY),
        ('VALIGN', (0,0), (-1,-1), 'TOP'),
        ('TOPPADDING', (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING', (0,0), (-1,-1), 7),
        ('RIGHTPADDING', (0,0), (-1,-1), 7),
    ]))
    elems.append(ic_tbl)
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("4.2  Anatomy at Risk", H2))
    anat_data = [
        ["Structure", "Location", "Injury Consequence"],
        ["Dural sac / cauda equina", "Central posterior to disc", "CSF leak, neural injury, arachnoiditis"],
        ["Traversing nerve roots (bilateral)", "Medial to pedicles bilaterally", "Radiculopathy, motor weakness, foot drop"],
        ["Epidural veins", "Surrounding dural sac", "Epidural haematoma, blood loss"],
        ["Segmental vessels", "Lateral to disc anteriorly", "Haemorrhage during discectomy"],
        ["Anterior dura / nerve sleeves", "Anterior to posterior longitudinal ligament", "Injury during disc removal"],
    ]
    elems.append(comparison_table(anat_data[0], anat_data[1:],
                                   [4.5*cm, 5.5*cm, 7*cm], C_PLIF))
    elems.append(Spacer(1, 0.3*cm))
    elems.append(info_box(
        "PLIF requires BILATERAL nerve root retraction to gain access to both sides of the disc space. "
        "This is the most significant disadvantage vs. TLIF (unilateral retraction). "
        "In the presence of previous posterior surgery with epidural scarring, "
        "TLIF through the foramen is strongly preferred.",
        HexColor("#EAFAF1"), "TECHNIQUE NOTE"))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("4.3  Step-by-Step Technique", H2))
    steps = [
        ("Patient Positioning", "Prone on a 4-post frame or Wilson frame. Hips and knees slightly flexed to reduce lumbar lordosis "
         "and open the interlaminar space. Abdomen hangs free (reduces epidural venous pressure and blood loss). "
         "Ensure no ocular pressure."),
        ("Skin Incision", "Standard posterior midline incision over the target level(s). Length depends on number of levels. "
         "Mark skin landmarks with fluoroscopy before incision."),
        ("Muscle Dissection", "Subperiosteal dissection of paraspinal muscles bilaterally. "
         "Expose laminae, facet joints, and transverse processes at the target level(s). "
         "Use Cobb elevator and electrocautery."),
        ("Pedicle Screw Placement", "Place bilateral pedicle screws above and below the target disc before neural work. "
         "This provides stability and allows distraction across the disc space. "
         "Confirm with AP and lateral fluoroscopy."),
        ("Laminectomy / Laminotomy", "Perform a wide bilateral laminectomy and medial facetectomy to expose the posterior disc. "
         "Remove ligamentum flavum. The dural sac and bilateral nerve roots must be visible."),
        ("Epidural Haemostasis", "Control epidural bleeding with bipolar diathermy and Gelfoam/Surgicel. "
         "Thorough haemostasis before neural retraction is essential."),
        ("Bilateral Nerve Root Retraction", "Using nerve root retractors, gently retract the dural sac medially AND both traversing "
         "nerve roots medially on each side. This creates bilateral corridors lateral to the dura. "
         "Limit retraction time — prolonged retraction causes nerve injury."),
        ("Annulotomy (Bilateral)", "Using a 15-blade or Kerrison rongeur, make annulotomy windows bilaterally. "
         "Access the disc space from both sides."),
        ("Discectomy", "Remove disc material bilaterally using curettes, pituitary rongeurs, and disc forceps. "
         "Achieve complete disc removal. Visualise the anterior annulus."),
        ("Endplate Preparation", "Use rasps and curettes to prepare the endplates bilaterally to bleeding cancellous bone. "
         "Match the endplate contour to the cage profile."),
        ("Trial Cage Sizing", "Insert bilateral trial sizers to determine correct cage dimensions. "
         "Distraction across the pedicle screws (using the rod and distractor) opens the disc space "
         "and facilitates cage insertion."),
        ("Cage Insertion (Bilateral)", "Pack two small PLIF cages (typically 10-12 mm wide, kidney-shaped) with bone graft. "
         "Insert one cage from each side, positioning them in the anterior one-third of the disc space. "
         "Confirm position with AP and lateral fluoroscopy."),
        ("Posterolateral Bone Grafting", "Decorticate transverse processes and facet joints. "
         "Apply autologous bone graft for posterolateral fusion."),
        ("Rod Insertion & Compression", "Insert connecting rods bilaterally. Apply compression across the construct "
         "to seat the cages and close the disc space. Tighten all screw caps."),
        ("Closure", "Irrigate wound thoroughly with antibiotic solution. Place suction drain(s). "
         "Close paraspinal fascia, subcutaneous tissue, and skin in layers."),
    ]
    for i, (title, detail) in enumerate(steps, 1):
        elems.append(step_row(i, title, detail, C_PLIF))
        elems.append(Spacer(1, 0.12*cm))

    elems.append(Spacer(1, 0.4*cm))
    elems.append(Paragraph("4.4  PLIF Complications", H2))
    comp_data = [
        ["Complication", "Incidence", "Prevention / Management"],
        ["Dural tear / CSF leak", "5–10%", "Primary repair with 6-0 Prolene; fibrin glue; flat bed rest 24–48h"],
        ["Bilateral nerve root injury", "2–5%", "Minimise retraction duration; careful technique"],
        ["Epidural haematoma", "1–3%", "Haemostasis before retraction; suction drain postop"],
        ["Cage migration / expulsion", "1–5%", "Size cage correctly; position anteriorly; compress construct"],
        ["Adjacent segment disease", "5–10%/year", "Minimise fusion levels; preserve motion where possible"],
        ["Pseudarthrosis", "5–10%", "Thorough endplate prep; adequate graft volume; stop NSAIDs/smoking"],
        ["Infection (deep)", "1–3%", "Prophylactic antibiotics; drain removal by 48h"],
        ["Foot drop / motor deficit", "<1%", "Immediate post-op exam; urgent MRI if new deficit"],
    ]
    elems.append(comparison_table(comp_data[0], comp_data[1:],
                                   [5*cm, 3*cm, 9*cm], C_PLIF))
    return elems

# ─── TLIF ────────────────────────────────────────────────────────────────────

def build_tlif():
    elems = []
    elems.append(PageBreak())
    elems.append(section_header(
        "5.  TLIF — TRANSFORAMINAL LUMBAR INTERBODY FUSION", C_TLIF,
        "Approach: Posterolateral through foramen (unilateral)  |  Position: Prone"))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("5.1  Indications & Contraindications", H2))
    ic_data = [
        ["INDICATIONS", "CONTRAINDICATIONS / CAUTIONS"],
        ["Spondylolisthesis grades I-II (gold standard)\nDegenerative disc disease with instability\nRecurrent disc herniation (after PLIF or discectomy)\nPost-laminectomy instability\nPrevious posterior surgery (TLIF avoids bilateral scar)\nSingle-level degenerative disease\nMinimally invasive surgery (MIS-TLIF)",
         "Bilateral foraminal stenosis requiring bilateral decompression\nSevere foraminal scarring at entry side\nConjoined nerve root anomaly at approach foramen\nActive discitis / infection\nSevere osteoporosis"],
    ]
    ic_tbl = Table([[Paragraph(ic_data[0][0], TABLE_HEADER),
                     Paragraph(ic_data[0][1], TABLE_HEADER)],
                    [Paragraph(ic_data[1][0], BODY),
                     Paragraph(ic_data[1][1], BODY)]],
                   colWidths=[8.5*cm, 8.5*cm])
    ic_tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), C_TLIF),
        ('BACKGROUND', (0,1), (0,1), C_TLIF_LIGHT),
        ('BACKGROUND', (1,1), (1,1), HexColor("#FDEDEC")),
        ('GRID', (0,0), (-1,-1), 0.4, C_MID_GREY),
        ('VALIGN', (0,0), (-1,-1), 'TOP'),
        ('TOPPADDING', (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING', (0,0), (-1,-1), 7),
        ('RIGHTPADDING', (0,0), (-1,-1), 7),
    ]))
    elems.append(ic_tbl)
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("5.2  Kambin's Triangle — The TLIF Safe Working Zone", H2))
    elems.append(Paragraph(
        "Kambin's triangle is the anatomical safe zone for posterolateral disc access used in TLIF. "
        "Working within this triangle avoids injury to the traversing and exiting nerve roots.", BODY))
    kb_data = [
        ["Side of Triangle", "Anatomical Structure"],
        ["Hypotenuse (lateral)", "Exiting nerve root in the foramen"],
        ["Base (inferior)", "Superior endplate of the lower vertebra"],
        ["Height (medial)", "Traversing nerve root / lateral border of dural sac"],
        ["Safe working area", "Within this triangle — typically 8-12 mm diameter space"],
    ]
    kb_tbl = comparison_table(kb_data[0], kb_data[1:],
                               [5.5*cm, 11.5*cm], C_TLIF)
    elems.append(kb_tbl)
    elems.append(Spacer(1, 0.3*cm))
    elems.append(info_box(
        "At L4-5 and L5-S1, the exiting nerve root (L4 or L5) runs in the superior portion "
        "of the foramen. Always identify and protect it before inserting the cage. "
        "The exiting root is at greater risk in TLIF than PLIF.",
        HexColor("#FEF9E7"), "CAUTION"))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("5.3  Step-by-Step Technique (Open TLIF)", H2))
    steps = [
        ("Patient Positioning", "Prone on a 4-post frame or Jackson table. Abdomen hanging free. "
         "Slight reverse Trendelenburg. Fluoroscopy set for lateral and AP views. "
         "If MIS-TLIF: tubular retractor system aligned over target foramen."),
        ("Skin Incision", "Posterior midline incision OR paramedian incision for MIS-TLIF. "
         "Length depends on number of levels and if bilateral decompression is planned. "
         "Confirm level with fluoroscopy before incising fascia."),
        ("Muscle Dissection", "Subperiosteal dissection of paraspinal muscles. "
         "For MIS-TLIF: sequential muscle dilation through tubular retractor. "
         "Expose the facet joint on the approach side (usually the symptomatic side)."),
        ("Bilateral Pedicle Screw Placement", "Place bilateral pedicle screws above and below the target level "
         "BEFORE facetectomy to maintain stability. Use fluoroscopy or navigation to confirm. "
         "For MIS-TLIF: percutaneous screws placed through stab incisions before/after interbody work."),
        ("Ipsilateral Laminotomy / Facetectomy", "On the approach side: perform a partial or complete ipsilateral "
         "facetectomy (superior articular process of lower level + inferior articular process of upper level). "
         "This opens the foramen and exposes Kambin's triangle. "
         "Also perform laminotomy for canal access if decompression is required."),
        ("Contralateral Decompression (if needed)", "Using angled curettes and Kerrison rongeurs, perform "
         "contralateral laminotomy and foraminotomy through the same ipsilateral approach by "
         "tilting the table and working 'over the top'. This avoids bilateral approach."),
        ("Nerve Root Identification", "Identify the exiting nerve root in the foramen (ipsilateral) and the "
         "traversing nerve root medially. Protect both. "
         "Use Woodson probe to palpate nerve root before inserting any instrument into the disc."),
        ("Annulotomy", "With the exiting nerve root retracted superolaterally and traversing root "
         "retracted medially, perform a unilateral annulotomy at the posterolateral corner of the disc. "
         "Use a 15-blade scalpel or Kerrison rongeur."),
        ("Discectomy", "Thorough disc removal using curettes, pituitary rongeurs, straight and angled instruments. "
         "Work from one side through the foramen. Achieve decompression of the anterior neural elements."),
        ("Endplate Preparation", "Rasps, disc space shavers, and curettes used to prepare both endplates "
         "to cancellous bone while preserving the cortical rim (cage support). "
         "Confirm with fluoroscopy — instrument should reach the anterior annulus."),
        ("Cage Selection & Packing", "Select a curved or kidney-shaped TLIF cage of appropriate height. "
         "Pack with bone graft (autologous bone from facetectomy + allograft or BMP-2)."),
        ("Cage Insertion", "Insert cage through the foramen using an inserter handle. "
         "Rotate/translate cage into the anterior-central position (anterior half of disc space). "
         "A cage sitting posteriorly risks nerve compression and provides less lordosis correction. "
         "Confirm with AP and lateral fluoroscopy."),
        ("Contralateral Bone Graft", "Pack bone graft into the contralateral side of the disc space through "
         "the same ipsilateral window using a curved bone graft funnel."),
        ("Posterolateral Graft", "Decorticate ipsilateral transverse processes. Apply autologous bone graft."),
        ("Rod Insertion & Compression", "Insert connecting rods bilaterally. Apply compression to seat "
         "the cage and close the disc height. Final tightening. Confirm final construct with fluoroscopy."),
        ("Closure", "Irrigate copiously. Place suction drain. Close fascia, subcutaneous, skin in layers."),
    ]
    for i, (title, detail) in enumerate(steps, 1):
        elems.append(step_row(i, title, detail, C_TLIF))
        elems.append(Spacer(1, 0.1*cm))

    elems.append(Spacer(1, 0.4*cm))
    elems.append(Paragraph("5.4  TLIF Complications", H2))
    comp_data = [
        ["Complication", "Incidence", "Prevention / Management"],
        ["Exiting nerve root injury", "1–5%", "Identify root before disc entry; gentle retraction; avoid overfilling foramen"],
        ["Dural tear", "3–7%", "Primary repair; fibrin glue; avoid CSF fistula"],
        ["Cage migration", "1–4%", "Position cage anteriorly; compress construct after cage placement"],
        ["Pseudarthrosis", "3–7%", "Thorough endplate prep; adequate graft; cease NSAIDs/smoking preop"],
        ["Adjacent segment disease", "5%/year", "Preserve motion segments; match fusion to pathology only"],
        ["Postop neurological deficit", "<2%", "Immediate neurological assessment; urgent MRI/CT if deficit"],
        ["Infection", "1–3%", "Prophylactic antibiotics; irrigation; drain by 48h"],
        ["Haematoma (epidural)", "0.5–1%", "Adequate haemostasis; drain; urgent decompression if dense deficit"],
    ]
    elems.append(comparison_table(comp_data[0], comp_data[1:],
                                   [5*cm, 3*cm, 9*cm], C_TLIF))
    return elems

# ─── XLIF ────────────────────────────────────────────────────────────────────

def build_xlif():
    elems = []
    elems.append(PageBreak())
    elems.append(section_header(
        "6.  XLIF/LLIF — EXTREME LATERAL INTERBODY FUSION", C_XLIF,
        "Approach: Direct lateral through psoas  |  Position: Lateral decubitus"))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("6.1  Indications & Contraindications", H2))
    ic_data = [
        ["INDICATIONS", "CONTRAINDICATIONS / CAUTIONS"],
        ["Degenerative disc disease L1-L4 (multi-level)\nDegenerative scoliosis correction\nSagittal imbalance (with posterior fixation)\nAdjacent segment disease (above L5-S1)\nRetroperitoneal approach contraindicated (prior ALIF)\nMinimally invasive multi-level fusion\nFailed prior posterior fusion (revision via lateral)",
         "L5-S1 disc (iliac crest obstruction — use ALIF)\nPrior ipsilateral retroperitoneal surgery (relative)\nPsoas abscess or tumour\nBilateral severe canal stenosis requiring direct decompression\nHigh-grade spondylolisthesis (anterior translation prevents lateral access)\nCoagulopathy"],
    ]
    ic_tbl = Table([[Paragraph(ic_data[0][0], TABLE_HEADER),
                     Paragraph(ic_data[0][1], TABLE_HEADER)],
                    [Paragraph(ic_data[1][0], BODY),
                     Paragraph(ic_data[1][1], BODY)]],
                   colWidths=[8.5*cm, 8.5*cm])
    ic_tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), C_XLIF),
        ('BACKGROUND', (0,1), (0,1), C_XLIF_LIGHT),
        ('BACKGROUND', (1,1), (1,1), HexColor("#FDEDEC")),
        ('GRID', (0,0), (-1,-1), 0.4, C_MID_GREY),
        ('VALIGN', (0,0), (-1,-1), 'TOP'),
        ('TOPPADDING', (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING', (0,0), (-1,-1), 7),
        ('RIGHTPADDING', (0,0), (-1,-1), 7),
    ]))
    elems.append(ic_tbl)
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("6.2  Safe Zone & EMG Monitoring", H2))
    elems.append(Paragraph(
        "The disc is divided into four zones (I-IV) from anterior (A) to posterior (P) per the Moro classification. "
        "The lumbar plexus migrates anteriorly at lower lumbar levels, "
        "making L4-5 the most dangerous level for XLIF.", BODY))
    sz_data = [
        ["Zone", "Location on Disc", "Contents / Risk", "Relevance to XLIF"],
        ["I (Anterior)", "Anterior quarter", "Anterior to psoas; great vessel zone", "ALIF territory — avoid in XLIF"],
        ["II (Anterior-mid)", "Second quarter from front", "Anterior to lumbar plexus", "OPTIMAL XLIF working zone"],
        ["III (Posterior-mid)", "Third quarter", "Lumbar plexus traverses here", "HIGH RISK — avoid if possible"],
        ["IV (Posterior)", "Posterior quarter", "Lumbar plexus and dural sac", "UNSAFE — do not enter"],
    ]
    elems.append(comparison_table(sz_data[0], sz_data[1:],
                                   [2.5*cm, 3.5*cm, 6*cm, 5*cm], C_XLIF))
    elems.append(Spacer(1, 0.3*cm))

    elems.append(Paragraph("EMG Thresholds (NVM5/NovaBay Monitoring):", H3))
    emg_data = [
        ["Threshold (mA)", "Interpretation", "Action"],
        [">10 mA", "Nerve at SAFE distance", "Continue dilator advancement"],
        ["5–10 mA", "Nerve NEAR — caution zone", "Slow down; redirect slightly anterior"],
        ["<5 mA", "Nerve VERY CLOSE — STOP", "Remove dilator; redirect significantly or abort"],
    ]
    elems.append(comparison_table(emg_data[0], emg_data[1:],
                                   [3.5*cm, 6.5*cm, 7*cm], C_XLIF))
    elems.append(Spacer(1, 0.3*cm))
    elems.append(info_box(
        "L4-5 is the most neurologically challenging level for XLIF. The lumbar plexus "
        "(particularly the femoral nerve) migrates to the anterior half of the psoas "
        "at this level, dramatically reducing the safe working zone. "
        "Some surgeons prefer TLIF or OLIF at L4-5 for this reason.",
        HexColor("#F5EEF8"), "CRITICAL POINT — L4-5 XLIF"))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("6.3  Step-by-Step Technique", H2))
    steps = [
        ("Patient Positioning", "Right lateral decubitus (left side up — approach from the left). "
         "The patient is placed perpendicular to the table and secured with kidney rest and tape. "
         "The operating table is flexed at the hip to open the lateral flank space. "
         "All bony prominences padded. Neuromonitoring (EMG) electrodes placed in lower extremity muscles."),
        ("Fluoroscopic Planning", "Obtain a true lateral fluoroscopic view — ensure the pedicles are perfectly "
         "superimposed. Mark the disc centre on the skin. Confirm the iliac crest is below the target disc "
         "(if iliac crest obstructs — XLIF not feasible; use ALIF or TLIF)."),
        ("Retroperitoneal Access (Flank Incision)", "Make a 2-3 cm transverse or oblique incision in the flank "
         "posterior to the anterior axillary line. Incise external oblique, internal oblique, and transverse "
         "abdominis along their fibres (muscle-splitting technique). "
         "Identify and enter the retroperitoneal space."),
        ("Peritoneal Sac Mobilisation", "Bluntly sweep the peritoneal sac anteriorly with the fingers. "
         "Use a finger to confirm the retroperitoneal corridor — "
         "feel the psoas muscle posteriorly and the peritoneal sac anteriorly."),
        ("Lateral Skin Incision", "With finger in the retroperitoneal space, turn the index finger laterally "
         "toward the lateral skin over the disc. Make a second 2-cm stab incision at this mark."),
        ("Initial Dilator Insertion", "Insert the initial dilator through the lateral incision under finger guidance. "
         "Use live EMG monitoring as the dilator contacts the psoas muscle. "
         "Advance slowly — <b>EMG must remain >10 mA throughout</b>. "
         "Confirm position with AP and lateral fluoroscopy."),
        ("Sequential Dilation of Psoas", "Pass sequential dilators of increasing diameter through the psoas muscle "
         "under continuous EMG monitoring. Monitor all lower limb muscle groups. "
         "Spread the psoas fibres longitudinally (parallel to nerve direction) "
         "rather than transversely to minimise plexus injury."),
        ("Retractor Placement", "Once the largest dilator reaches the disc surface, insert the expandable "
         "lateral retractor system. Expand the blades to create a working window over the disc. "
         "Attach to the table-mounted arm holder. Reconfirm position with fluoroscopy."),
        ("Level Confirmation", "Final AP and lateral fluoroscopy before disc work. "
         "A Kirschner wire or marker needle in the disc confirms the correct level."),
        ("Annulotomy", "Make a wide annulotomy on the lateral disc surface with a 15-blade scalpel "
         "or electrosurgical device. The annulotomy window should span the full anterior-posterior "
         "width of the disc to allow insertion of a wide cage."),
        ("Discectomy", "Complete disc removal using straight and angled curettes, rongeurs, and pituitary forceps. "
         "Work from the lateral window to reach the contralateral side. "
         "The XLIF cage will span the full width — both endplates must be cleared."),
        ("Endplate Preparation", "Use laterally-angled rasps and scrapers to prepare both endplates. "
         "The XLIF cage spans both apophyseal rings bilaterally — "
         "this is the biomechanical advantage over PLIF/TLIF cages. "
         "Preserve the cortical apophyseal ring for cage support."),
        ("Trial Sizing", "Insert lateral trial cages to determine the correct height and width. "
         "The cage footprint should span the full width of the endplate. "
         "Confirm with AP fluoroscopy — cage should reach the contralateral apophyseal ring."),
        ("Cage Packing & Insertion", "Pack the cage with bone graft (allograft/autograft/BMP-2). "
         "Insert the cage using a lateral inserter handle, advancing to the anterior-central position. "
         "AP view confirms cage spans full endplate width. Lateral view confirms anterior positioning."),
        ("Supplemental Fixation", "XLIF provides interbody support but inadequate rotational control alone. "
         "Options: (a) percutaneous posterior bilateral pedicle screws (standard), "
         "(b) lateral plate (standalone at single level if bone quality adequate). "
         "Patient may be repositioned prone for posterior fixation."),
        ("Retractor Removal & Closure", "Slowly remove the retractor while checking for bleeding. "
         "The psoas reconstitutes around the working corridor. "
         "Close lateral incision in layers: transverse abdominis, internal oblique, "
         "external oblique, subcutaneous, skin. No drain usually required."),
    ]
    for i, (title, detail) in enumerate(steps, 1):
        elems.append(step_row(i, title, detail, C_XLIF))
        elems.append(Spacer(1, 0.1*cm))

    elems.append(Spacer(1, 0.4*cm))
    elems.append(Paragraph("6.4  XLIF Complications", H2))
    comp_data = [
        ["Complication", "Incidence", "Prevention / Management"],
        ["Genitofemoral nerve injury\n(anterior thigh numbness)", "5–15%", "Most resolve spontaneously in 3–6 months; reassurance; gabapentin"],
        ["Lumbar plexus injury\n(thigh pain, hip flexor weakness)", "1–5%", "Strict EMG monitoring; limit retraction; avoid L4-5 if plexus not safe"],
        ["Femoral nerve injury\n(quadriceps weakness)", "<2%", "EMG monitoring; abort if threshold <5 mA; urgent MRI if postop weakness"],
        ["Approach-side hip flexor weakness", "10–30% transient", "Psoas retraction; resolves in 6–12 weeks in most"],
        ["Sympathetic chain injury", "<1%", "Retrograde ejaculation; careful anterior dissection"],
        ["Cage subsidence", "4–10%", "Preserve apophyseal ring; avoid endplate violation"],
        ["Inadequate decompression", "Variable", "Add posterior decompression if indirect decompression insufficient"],
        ["Peritoneal entry / bowel injury", "<0.5%", "Careful retroperitoneal dissection; surgical repair if entered"],
    ]
    elems.append(comparison_table(comp_data[0], comp_data[1:],
                                   [4.5*cm, 3*cm, 9.5*cm], C_XLIF))
    return elems

# ─── COMPARISON ──────────────────────────────────────────────────────────────

def build_comparison():
    elems = []
    elems.append(PageBreak())
    elems.append(section_header("7.  MASTER COMPARISON TABLE", C_DARK_BLUE,
                                "ALIF vs. PLIF vs. TLIF vs. XLIF"))
    elems.append(Spacer(1, 0.5*cm))
    data = [
        ["Feature", "ALIF", "PLIF", "TLIF", "XLIF/LLIF"],
        ["Approach direction", "Anterior", "Posterior (bilateral)", "Posterolateral (unilateral)", "Direct lateral through psoas"],
        ["Patient position", "Supine", "Prone", "Prone", "Lateral decubitus"],
        ["Access surgeon needed", "Yes (vascular / gen surg)", "No", "No", "No"],
        ["Levels accessible", "L4-S1 (best L5-S1)", "L3-S1", "L3-S1", "L1-L4 ONLY (not L5-S1)"],
        ["Cage footprint", "Largest (lordotic)", "Smallest (2 bilateral)", "Intermediate (1 unilateral)", "Widest (spans full endplate)"],
        ["Lordosis restoration", "Best", "Least", "Good", "Good"],
        ["Direct decompression", "No", "Yes (bilateral)", "Yes (unilateral)", "No (indirect only)"],
        ["Neural retraction needed", "None", "Bilateral", "Unilateral", "None"],
        ["Neuromonitoring required", "Optional", "SSEP/MEP optional", "SSEP/MEP optional", "EMG MANDATORY"],
        ["Unique complication", "Retrograde ejaculation; vascular injury", "Bilateral nerve injury; dural tear", "Exiting nerve root injury", "Lumbar plexus / genitofemoral nerve"],
        ["MIS option available", "Mini-ALIF", "Limited", "MIS-TLIF (standard)", "Standard MIS"],
        ["Blood loss", "Moderate", "Moderate-high", "Low-moderate", "Low"],
        ["Hospital stay", "2–4 days", "3–5 days", "2–4 days", "1–3 days"],
        ["360° fusion", "Yes (+ posterior screws)", "Yes (all-posterior)", "Yes (all-posterior)", "Yes (+ posterior screws)"],
    ]
    header = data[0]
    rows = data[1:]
    tbl_data = [[Paragraph(h, TABLE_HEADER) for h in header]]
    for row in rows:
        cells = [Paragraph(row[0], BODY_BOLD)]
        colors_row = [C_ALIF_LIGHT, C_PLIF_LIGHT, C_TLIF_LIGHT, C_XLIF_LIGHT]
        for j, cell in enumerate(row[1:]):
            cells.append(Paragraph(cell, TABLE_CELL))
        tbl_data.append(cells)

    tbl = Table(tbl_data, colWidths=[4*cm, 3.25*cm, 3.25*cm, 3.25*cm, 3.25*cm], repeatRows=1)
    style = [
        ('BACKGROUND', (0,0), (-1,0), C_DARK_BLUE),
        ('BACKGROUND', (1,1), (1,-1), C_ALIF_LIGHT),
        ('BACKGROUND', (2,1), (2,-1), C_PLIF_LIGHT),
        ('BACKGROUND', (3,1), (3,-1), C_TLIF_LIGHT),
        ('BACKGROUND', (4,1), (4,-1), C_XLIF_LIGHT),
        ('BACKGROUND', (0,1), (0,-1), C_LIGHT_GREY),
        ('FONTNAME', (0,1), (0,-1), 'Helvetica-Bold'),
        ('FONTSIZE', (0,0), (-1,-1), 8.5),
        ('GRID', (0,0), (-1,-1), 0.4, C_MID_GREY),
        ('VALIGN', (0,0), (-1,-1), 'TOP'),
        ('TOPPADDING', (0,0), (-1,-1), 5),
        ('BOTTOMPADDING', (0,0), (-1,-1), 5),
        ('LEFTPADDING', (0,0), (-1,-1), 4),
        ('RIGHTPADDING', (0,0), (-1,-1), 4),
        ('TEXTCOLOR', (0,0), (-1,0), C_WHITE),
    ]
    tbl.setStyle(TableStyle(style))
    elems.append(tbl)
    return elems

# ─── CAGE MATERIALS ──────────────────────────────────────────────────────────

def build_cage_and_algorithm():
    elems = []
    elems.append(PageBreak())
    elems.append(section_header("8.  CAGE MATERIALS & BONE GRAFT OPTIONS", C_DARK_BLUE))
    elems.append(Spacer(1, 0.4*cm))
    cage_data = [
        ["Material", "Radiopacity", "Key Properties", "Common Use"],
        ["PEEK\n(Polyether ether ketone)", "Radiolucent\n(with markers)", "Modulus close to bone; reduces stress shielding;\nRadiolucent — fusion assessment easy", "Most common; all techniques"],
        ["Titanium (mesh/solid)", "Radiopaque", "Excellent osseointegration; high strength;\nCan cause artefact on MRI/CT", "Revision; corpectomy cages"],
        ["Carbon composite", "Radiolucent", "Radiolucent; strong; good biocompatibility", "ALIF, TLIF"],
        ["Bioabsorbable (PLA)", "Radiolucent", "Resorbs over time; avoids permanent implant;\nLimited long-term data", "Experimental / paediatric"],
    ]
    elems.append(comparison_table(cage_data[0], cage_data[1:],
                                   [3.5*cm, 3*cm, 6*cm, 4.5*cm], C_DARK_BLUE))
    elems.append(Spacer(1, 0.4*cm))

    elems.append(Paragraph("Bone Graft Options", H2))
    graft_data = [
        ["Graft Type", "Source", "Properties", "Limitations"],
        ["Autologous\nIliac crest bone", "Patient's iliac crest", "Gold standard; osteogenic + osteoconductive + osteoinductive", "Donor site pain; limited volume"],
        ["Local autograft\n(facet/lamina bone)", "Laminectomy/facetectomy chips", "Readily available; no donor site morbidity", "Lower volume; variable quality"],
        ["Allograft\n(bone bank)", "Cadaveric bone bank", "No donor site; available in large quantities;\nFemoral rings, fibular strut, chips", "No live cells; infection risk (small); slower fusion"],
        ["BMP-2\n(Infuse, Medtronic)", "Recombinant human", "Strong osteoinductive signal; high fusion rates;\nReduces autograft need", "Expensive; ectopic bone; oedema; cancer risk debate"],
        ["Ceramics\n(TCP, HA, CaSO4)", "Synthetic", "Osteoconductive scaffold; readily available;\nNo infection risk", "Not osteoinductive; brittle"],
        ["DBM (Demineralised\nBone Matrix)", "Processed allograft", "Some osteoinductivity; easy to use", "Variable efficacy; cost"],
    ]
    elems.append(comparison_table(graft_data[0], graft_data[1:],
                                   [3.5*cm, 3*cm, 5.5*cm, 5*cm], C_DARK_BLUE))
    elems.append(Spacer(1, 0.5*cm))

    elems.append(section_header("9.  DECISION ALGORITHM BY LEVEL", C_DARK_BLUE,
                                "Choosing the right approach based on level and patient factors"))
    elems.append(Spacer(1, 0.4*cm))
    algo_data = [
        ["Level", "First-Choice Approach", "Rationale / Key Factors"],
        ["L5-S1", "ALIF", "Largest cage; best lordosis; iliac crest does not obstruct; L5-S1 most accessible anteriorly"],
        ["L5-S1\n(ALIF not feasible)", "TLIF", "Previous abdominal surgery; male requesting fertility preservation; no vascular surgeon available"],
        ["L4-5", "TLIF or ALIF", "TLIF if prior retroperitoneal surgery or high iliac crest; ALIF if large cage + lordosis needed"],
        ["L4-5\n(low iliac crest, good psoas anatomy)", "XLIF", "MIS approach; low blood loss; if direct decompression not needed"],
        ["L2-4\n(multi-level, deformity)", "XLIF + posterior fixation", "Efficient multi-level corridor; good cage footprint; combine with posterior correction"],
        ["L1-4\n(need direct decompression)", "TLIF", "Canal/foraminal stenosis requiring direct neural decompression"],
        ["Any level\n(prior posterior surgery)", "ALIF or XLIF", "Avoids epidural scar tissue; anterior/lateral virgin corridor"],
        ["Any level\n(sagittal imbalance)", "ALIF or XLIF + PSO/SPO", "Lordotic ALIF cage or lateral cage + posterior osteotomy for major deformity"],
    ]
    elems.append(comparison_table(algo_data[0], algo_data[1:],
                                   [3.5*cm, 4.5*cm, 9*cm], C_DARK_BLUE))
    elems.append(Spacer(1, 0.5*cm))
    elems.append(info_box(
        "All interbody fusion constructs will eventually fail by hardware loosening or fracture "
        "if solid bony fusion does not occur. The cage is a temporary scaffold — "
        "fusion is the ultimate goal. Smoking cessation, optimisation of diabetes/osteoporosis, "
        "and avoidance of NSAIDs in the post-fusion period are essential to achieve solid fusion.",
        HexColor("#EBF5FB"), "FINAL NOTE — CRITICAL PRINCIPLE"))
    elems.append(Spacer(1, 0.4*cm))
    elems.append(Paragraph(
        "Reference: Campbell's Operative Orthopaedics 15th Ed 2026 · "
        "Grainger & Allison's Diagnostic Radiology · Gray's Anatomy for Students 4th Ed · "
        "Schwartz's Principles of Surgery 11th Ed",
        make_style('Ref', fontSize=8, textColor=HexColor("#666666"),
                   fontName='Helvetica-Oblique', alignment=TA_CENTER)))
    return elems

# ─── PAGE TEMPLATE ───────────────────────────────────────────────────────────

def on_later_pages(canvas, doc):
    canvas.saveState()
    canvas.setFont('Helvetica', 8)
    canvas.setFillColor(HexColor("#888888"))
    canvas.drawString(2*cm, 1.2*cm,
                      "Lumbar Interbody Fusion — Step-by-Step Surgical Guide   |   Orris Medical AI")
    canvas.drawRightString(19*cm, 1.2*cm, f"Page {doc.page}")
    canvas.setStrokeColor(HexColor("#CCCCCC"))
    canvas.line(2*cm, 1.5*cm, 19*cm, 1.5*cm)
    canvas.restoreState()

def on_first_page(canvas, doc):
    canvas.saveState()
    canvas.restoreState()

# ─── BUILD PDF ───────────────────────────────────────────────────────────────

def build_pdf():
    doc = SimpleDocTemplate(
        OUTPUT_PATH,
        pagesize=A4,
        topMargin=2*cm,
        bottomMargin=2*cm,
        leftMargin=2*cm,
        rightMargin=2*cm,
        title="Lumbar Interbody Fusion — Step-by-Step Surgical Guide",
        author="Orris Medical AI",
        subject="ALIF PLIF TLIF XLIF Surgical Technique Guide",
    )
    elements = []
    elements += build_cover()
    elements += build_toc()
    elements += build_overview()
    elements += build_alif()
    elements += build_plif()
    elements += build_tlif()
    elements += build_xlif()
    elements += build_comparison()
    elements += build_cage_and_algorithm()

    doc.build(elements,
              onFirstPage=on_first_page,
              onLaterPages=on_later_pages)
    print(f"PDF saved to: {OUTPUT_PATH}")

if __name__ == "__main__":
    build_pdf()