Bone and Cartilage: Textbook Definitions, Classifications, and Types

import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
from matplotlib.patches import FancyBboxPatch, FancyArrowPatch
import matplotlib.patheffects as pe
from reportlab.lib.pagesizes import A4
from reportlab.lib import colors
from reportlab.lib.units import inch, cm
from reportlab.platypus import SimpleDocTemplate, Spacer, Image as RLImage, Paragraph, HRFlowable
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.enums import TA_CENTER, TA_LEFT
import os

OUTPUT_DIR = "/home/daytona/workspace/bone-cartilage-flowchart"

# ─────────────────────────────────────────────────────────────
# COLOUR PALETTE
# ─────────────────────────────────────────────────────────────
C_BONE_DARK   = "#1A5276"   # deep navy
C_BONE_MID    = "#2E86C1"   # mid blue
C_BONE_LIGHT  = "#AED6F1"   # pale blue
C_BONE_XLIGHT = "#EAF4FB"   # very pale blue

C_CART_DARK   = "#1E8449"   # deep green
C_CART_MID    = "#27AE60"   # mid green
C_CART_LIGHT  = "#A9DFBF"   # pale green
C_CART_XLIGHT = "#EAFAF1"   # very pale green

C_ACCENT      = "#F39C12"   # amber highlight
C_ARROW       = "#5D6D7E"   # grey arrows
C_TEXT_DARK   = "#1C2833"
C_TEXT_WHITE  = "#FFFFFF"
C_BG          = "#FDFEFE"

def rounded_box(ax, x, y, w, h, text, bg, fg=C_TEXT_DARK,
                fontsize=9, bold=False, radius=0.03,
                wrap=True, ha='center', va='center'):
    """Draw a rounded-corner box with centred text."""
    box = FancyBboxPatch((x - w/2, y - h/2), w, h,
                         boxstyle=f"round,pad=0.01,rounding_size={radius}",
                         linewidth=1.2, edgecolor=C_TEXT_DARK,
                         facecolor=bg, zorder=3)
    ax.add_patch(box)
    weight = 'bold' if bold else 'normal'
    ax.text(x, y, text, ha=ha, va=va, fontsize=fontsize,
            color=fg, fontweight=weight, wrap=wrap,
            multialignment='center', zorder=4)

def arrow(ax, x1, y1, x2, y2, color=C_ARROW):
    ax.annotate("", xy=(x2, y2), xytext=(x1, y1),
                arrowprops=dict(arrowstyle="-|>", color=color,
                                lw=1.4, mutation_scale=12), zorder=2)


# ═══════════════════════════════════════════════════════════════
# PAGE 1 – BONE OVERVIEW FLOWCHART
# ═══════════════════════════════════════════════════════════════
def make_bone_overview():
    fig, ax = plt.subplots(figsize=(12, 16))
    ax.set_xlim(0, 12); ax.set_ylim(0, 16)
    ax.axis('off')
    fig.patch.set_facecolor(C_BG)
    ax.set_facecolor(C_BG)

    # ── Title ──
    ax.text(6, 15.4, "BONE – Overview Flowchart", ha='center', va='center',
            fontsize=18, fontweight='bold', color=C_BONE_DARK,
            path_effects=[pe.withStroke(linewidth=3, foreground='white')])
    ax.text(6, 15.0, "Source: Gray's Anatomy for Students & Histology: A Text and Atlas",
            ha='center', va='center', fontsize=8, color='#7F8C8D', style='italic')

    # ── ROOT: BONE ──
    rounded_box(ax, 6, 14.2, 3.2, 0.6,
                "BONE\n(Calcified Living Connective Tissue)",
                C_BONE_DARK, C_TEXT_WHITE, fontsize=11, bold=True)

    # ── Level 1 splits ──
    arrow(ax, 6, 13.9, 6, 13.3)
    rounded_box(ax, 6, 13.0, 10, 0.5,
                "Mineralized extracellular matrix  |  Calcium Phosphate (Hydroxyapatite)  |  Type I Collagen (90 %)",
                C_BONE_LIGHT, C_TEXT_DARK, fontsize=8.5)

    # ── FUNCTIONS ──
    arrow(ax, 6, 12.75, 6, 12.25)
    rounded_box(ax, 6, 11.95, 3.0, 0.5, "FUNCTIONS OF BONE",
                C_BONE_MID, C_TEXT_WHITE, fontsize=10, bold=True)

    funcs = ["1. Support – structural framework",
             "2. Protection – vital organs",
             "3. Reservoir – Ca²⁺ & PO₄³⁻",
             "4. Leverage – muscle action",
             "5. Haematopoiesis – blood cell production"]
    for i, f in enumerate(funcs):
        yy = 11.45 - i * 0.42
        rounded_box(ax, 6, yy, 7.5, 0.35, f, C_BONE_XLIGHT, C_TEXT_DARK, fontsize=8.5)
        if i == 0:
            arrow(ax, 6, 11.70, 6, 11.63)
        else:
            arrow(ax, 6, yy + 0.35/2 + 0.07, 6, yy + 0.35/2)

    # ── STRUCTURAL TYPES ──
    y_struct = 9.28
    arrow(ax, 6, 9.28 - 0.21 - 0.07, 6, 9.28 + 0.28)  # arrow up into next
    arrow(ax, 6, 9.28 - 0.28, 3.0, 8.55)
    arrow(ax, 6, 9.28 - 0.28, 9.0, 8.55)

    rounded_box(ax, 6, y_struct, 4.0, 0.5, "STRUCTURAL TYPES OF BONE TISSUE",
                C_BONE_MID, C_TEXT_WHITE, fontsize=10, bold=True)

    arrow(ax, 6, 9.02, 3.0, 8.72)
    arrow(ax, 6, 9.02, 9.0, 8.72)

    rounded_box(ax, 3.0, 8.42, 4.2, 0.55,
                "COMPACT (Dense) Bone\nForms outer shell of all bones",
                C_BONE_MID, C_TEXT_WHITE, fontsize=9, bold=True)
    rounded_box(ax, 9.0, 8.42, 4.2, 0.55,
                "SPONGY (Cancellous/Trabecular) Bone\nForms interior of bones",
                C_CART_MID, C_TEXT_WHITE, fontsize=9, bold=True)

    compact_pts = ["Structural unit: Osteon (Haversian system)",
                   "Concentric lamellae of matrix",
                   "Central Haversian canal (vessels/nerves)",
                   "Surrounds spongy bone"]
    spongy_pts  = ["Structural unit: Trabeculae (spicules)",
                   "Sponge-like meshwork",
                   "Spaces filled with bone marrow",
                   "Interior of long / flat bones"]

    for i, (cp, sp) in enumerate(zip(compact_pts, spongy_pts)):
        yy = 8.0 - i * 0.42
        rounded_box(ax, 3.0, yy, 4.1, 0.35, cp, C_BONE_XLIGHT, C_TEXT_DARK, fontsize=7.8)
        rounded_box(ax, 9.0, yy, 4.1, 0.35, sp, "#EAFAF1", C_TEXT_DARK, fontsize=7.8)

    # ── CLASSIFICATION BY SHAPE ──
    arrow(ax, 6, 5.72, 6, 6.28)
    rounded_box(ax, 6, 6.58, 4.5, 0.5,
                "CLASSIFICATION OF BONES BY SHAPE",
                C_BONE_DARK, C_TEXT_WHITE, fontsize=10, bold=True)

    shapes = [
        ("Long Bones",      "Tubular shape\ne.g. Humerus, Femur",     C_BONE_MID),
        ("Short Bones",     "Cuboidal shape\ne.g. Carpals, Tarsals",  "#1A7A4A"),
        ("Flat Bones",      "Two compact plates + spongy\ne.g. Skull, Scapula", "#7D3C98"),
        ("Irregular Bones", "Complex shape\ne.g. Vertebrae, Facial bones", "#B7770D"),
        ("Sesamoid Bones",  "Oval; in tendons\ne.g. Patella, Thumb sesamoids", "#C0392B"),
    ]
    xs = [1.2, 3.6, 6.0, 8.4, 10.8]
    for (name, desc, col), x in zip(shapes, xs):
        arrow(ax, 6, 6.33, x, 5.90)
        rounded_box(ax, x, 5.55, 2.0, 0.65, f"{name}\n{desc}",
                    col, C_TEXT_WHITE, fontsize=7.5, bold=False)

    # ── DEVELOPMENT ──
    arrow(ax, 6, 5.22, 6, 4.75)
    rounded_box(ax, 6, 4.50, 4.0, 0.45,
                "BONE DEVELOPMENT (Ossification)",
                C_BONE_DARK, C_TEXT_WHITE, fontsize=10, bold=True)

    arrow(ax, 6, 4.27, 3.2, 3.85)
    arrow(ax, 6, 4.27, 8.8, 3.85)

    rounded_box(ax, 3.2, 3.55, 5.0, 0.55,
                "Intramembranous Ossification\nMesenchyme → bone directly\ne.g. Flat bones of skull",
                "#1F618D", C_TEXT_WHITE, fontsize=8)
    rounded_box(ax, 8.8, 3.55, 5.0, 0.55,
                "Endochondral Ossification\nCartilage model → replaced by bone\ne.g. Long bones",
                "#1E8449", C_TEXT_WHITE, fontsize=8)

    # ── CELLS ──
    arrow(ax, 6, 3.27, 6, 2.80)
    rounded_box(ax, 6, 2.55, 3.5, 0.45,
                "CELLS OF BONE TISSUE",
                C_BONE_DARK, C_TEXT_WHITE, fontsize=10, bold=True)

    cells = [
        ("Osteoprogenitor\nCells", "Precursors\n(Mesenchymal stem cells)", "#2471A3"),
        ("Osteoblasts",            "Secrete bone\nmatrix (osteoid)",       "#1A5276"),
        ("Osteocytes",             "Mature cells;\nmaintain matrix",       "#117A65"),
        ("Bone-Lining\nCells",     "Resting surface\ncells",              "#6E2F98"),
        ("Osteoclasts",            "Bone resorption\n(haematopoietic origin)", "#C0392B"),
    ]
    xs_c = [1.2, 3.6, 6.0, 8.4, 10.8]
    for (name, desc, col), x in zip(cells, xs_c):
        arrow(ax, 6, 2.32, x, 1.85)
        rounded_box(ax, x, 1.52, 2.0, 0.60, f"{name}\n{desc}",
                    col, C_TEXT_WHITE, fontsize=7.2)

    # footer
    ax.text(6, 0.18, "© Orris Medical AI  |  Based on Gray's Anatomy for Students & Histology: A Text and Atlas",
            ha='center', va='center', fontsize=7, color='#95A5A6', style='italic')

    plt.tight_layout(pad=0.3)
    path = os.path.join(OUTPUT_DIR, "01_bone_overview.png")
    plt.savefig(path, dpi=180, bbox_inches='tight', facecolor=C_BG)
    plt.close()
    print(f"Saved: {path}")
    return path


# ═══════════════════════════════════════════════════════════════
# PAGE 2 – CARTILAGE OVERVIEW FLOWCHART
# ═══════════════════════════════════════════════════════════════
def make_cartilage_overview():
    fig, ax = plt.subplots(figsize=(12, 15))
    ax.set_xlim(0, 12); ax.set_ylim(0, 15)
    ax.axis('off')
    fig.patch.set_facecolor(C_BG)
    ax.set_facecolor(C_BG)

    ax.text(6, 14.4, "CARTILAGE – Overview Flowchart", ha='center', va='center',
            fontsize=18, fontweight='bold', color=C_CART_DARK,
            path_effects=[pe.withStroke(linewidth=3, foreground='white')])
    ax.text(6, 14.05, "Source: Histology: A Text and Atlas (Pawlina & Ross)",
            ha='center', va='center', fontsize=8, color='#7F8C8D', style='italic')

    # ROOT
    rounded_box(ax, 6, 13.35, 5.5, 0.6,
                "CARTILAGE\n(Avascular Connective Tissue – Chondrocytes + ECM)",
                C_CART_DARK, C_TEXT_WHITE, fontsize=11, bold=True)

    arrow(ax, 6, 13.05, 6, 12.55)
    rounded_box(ax, 6, 12.28, 9.0, 0.45,
                "> 95 % Extracellular Matrix  |  Chondrocytes in Lacunae  |  No blood vessels (avascular)  |  Perichondrium present (usually)",
                C_CART_LIGHT, C_TEXT_DARK, fontsize=8)

    # THREE TYPES header
    arrow(ax, 6, 12.05, 6, 11.60)
    rounded_box(ax, 6, 11.35, 4.5, 0.45,
                "THREE TYPES OF CARTILAGE",
                C_CART_DARK, C_TEXT_WHITE, fontsize=10, bold=True)

    arrow(ax, 6, 11.12, 2.0, 10.62)
    arrow(ax, 6, 11.12, 6.0, 10.62)
    arrow(ax, 6, 11.12, 10.0, 10.62)

    # ── HYALINE ──
    rounded_box(ax, 2.0, 10.32, 3.6, 0.55,
                "1. HYALINE CARTILAGE\n(Most common type)",
                "#1F618D", C_TEXT_WHITE, fontsize=9, bold=True)

    hyaline_pts = [
        "Matrix: Type II collagen + GAGs",
        "Appearance: Glassy/translucent",
        "Perichondrium: Present*",
        "Calcifies: Yes (aging/ossification)",
        "LOCATIONS:",
        " • Articular surfaces",
        " • Epiphyseal (growth) plates",
        " • Costal cartilages",
        " • Trachea, Bronchi, Larynx",
        " • Nasal cartilages",
        "FUNCTION: Resist compression,",
        " low-friction surface, fetal skeleton",
    ]
    for i, pt in enumerate(hyaline_pts):
        yy = 9.92 - i * 0.41
        col = "#EAF4FB" if not pt.startswith("LOCA") and not pt.startswith("FUNC") else "#D6EAF8"
        rounded_box(ax, 2.0, yy, 3.5, 0.35, pt,
                    col, C_TEXT_DARK, fontsize=7.5)

    # ── ELASTIC ──
    rounded_box(ax, 6.0, 10.32, 3.6, 0.55,
                "2. ELASTIC CARTILAGE\n(Flexible type)",
                "#1E8449", C_TEXT_WHITE, fontsize=9, bold=True)

    elastic_pts = [
        "Matrix: Type II collagen +",
        " elastic fibers & lamellae",
        "Stain: Resorcin-fuchsin/Orcein",
        "Perichondrium: Present",
        "Calcifies: NO",
        "LOCATIONS:",
        " • Pinna (external ear)",
        " • External acoustic meatus",
        " • Auditory (Eustachian) tube",
        " • Epiglottis",
        " • Vocal folds",
        "FUNCTION: Flexibility & elasticity",
    ]
    for i, pt in enumerate(elastic_pts):
        yy = 9.92 - i * 0.41
        col = "#EAFAF1" if not pt.startswith("LOCA") and not pt.startswith("FUNC") else "#D5F5E3"
        rounded_box(ax, 6.0, yy, 3.5, 0.35, pt,
                    col, C_TEXT_DARK, fontsize=7.5)

    # ── FIBROCARTILAGE ──
    rounded_box(ax, 10.0, 10.32, 3.6, 0.55,
                "3. FIBROCARTILAGE\n(Strongest type)",
                "#7D3C98", C_TEXT_WHITE, fontsize=9, bold=True)

    fibro_pts = [
        "Matrix: Type I collagen",
        " (abundant) + hyaline matrix",
        "Perichondrium: ABSENT",
        "Calcifies: Variable",
        "Transition zone: dense CT",
        "LOCATIONS:",
        " • Intervertebral discs",
        " • Pubic symphysis",
        " • Knee menisci",
        " • Articular discs (TMJ)",
        " • Tendon/ligament insertions",
        "FUNCTION: Compressive & tensile strength",
    ]
    for i, pt in enumerate(fibro_pts):
        yy = 9.92 - i * 0.41
        col = "#F5EEF8" if not pt.startswith("LOCA") and not pt.startswith("FUNC") else "#E8DAEF"
        rounded_box(ax, 10.0, yy, 3.5, 0.35, pt,
                    col, C_TEXT_DARK, fontsize=7.5)

    # ── COMPARISON TABLE header ──
    y_comp = 4.82
    rounded_box(ax, 6, y_comp, 5.0, 0.45,
                "QUICK COMPARISON TABLE",
                C_CART_DARK, C_TEXT_WHITE, fontsize=10, bold=True)
    arrow(ax, 6, y_comp - 0.22, 6, 4.42)

    cols_h = ["Feature", "Hyaline", "Elastic", "Fibrocartilage"]
    rows = [
        ["Collagen type",    "Type II",       "Type II",       "Type I (main)"],
        ["Elastic fibers",   "Absent",         "Present",        "Absent"],
        ["Perichondrium",    "Yes*",           "Yes",            "No"],
        ["Calcifies",        "Yes",            "No",             "Variable"],
        ["Ground substance", "Abundant",       "Moderate",       "Sparse"],
        ["Main function",    "Support/surface","Flexibility",    "Load-bearing"],
    ]
    col_w = [2.2, 2.2, 2.2, 2.2]
    col_x = [1.1, 3.3, 5.5, 7.7]
    hdr_bg = [C_CART_DARK, "#1F618D", "#1E8449", "#7D3C98"]
    y_row = 4.35
    row_h = 0.38
    for ci, (header, bkg) in enumerate(zip(cols_h, hdr_bg)):
        rounded_box(ax, col_x[ci], y_row, col_w[ci] - 0.08, row_h - 0.04,
                    header, bkg, C_TEXT_WHITE, fontsize=8.5, bold=True)
    for ri, row in enumerate(rows):
        y_row -= row_h
        row_bkg = C_BG if ri % 2 == 0 else "#ECF0F1"
        for ci, cell in enumerate(row):
            rounded_box(ax, col_x[ci], y_row, col_w[ci] - 0.08, row_h - 0.04,
                        cell, row_bkg, C_TEXT_DARK, fontsize=7.8)

    # ── GROWTH MECHANISMS ──
    y_gr = y_row - 0.50
    rounded_box(ax, 6, y_gr, 5.0, 0.45,
                "CARTILAGE GROWTH MECHANISMS",
                C_CART_DARK, C_TEXT_WHITE, fontsize=10, bold=True)
    arrow(ax, 6, y_gr - 0.22, 3.2, y_gr - 0.65)
    arrow(ax, 6, y_gr - 0.22, 8.8, y_gr - 0.65)

    rounded_box(ax, 3.2, y_gr - 0.95, 5.0, 0.55,
                "Interstitial Growth\nChondrocytes divide within lacunae\n(distensible matrix expands)",
                "#1F618D", C_TEXT_WHITE, fontsize=8)
    rounded_box(ax, 8.8, y_gr - 0.95, 5.0, 0.55,
                "Appositional Growth\nNew chondroblasts from perichondrium\ndeposit matrix on surface",
                "#1E8449", C_TEXT_WHITE, fontsize=8)

    ax.text(6, 0.18, "© Orris Medical AI  |  Based on Histology: A Text and Atlas (Pawlina & Ross)",
            ha='center', va='center', fontsize=7, color='#95A5A6', style='italic')

    plt.tight_layout(pad=0.3)
    path = os.path.join(OUTPUT_DIR, "02_cartilage_overview.png")
    plt.savefig(path, dpi=180, bbox_inches='tight', facecolor=C_BG)
    plt.close()
    print(f"Saved: {path}")
    return path


# ═══════════════════════════════════════════════════════════════
# PAGE 3 – BONE vs CARTILAGE COMPARISON FLOWCHART
# ═══════════════════════════════════════════════════════════════
def make_comparison():
    fig, ax = plt.subplots(figsize=(14, 10))
    ax.set_xlim(0, 14); ax.set_ylim(0, 10)
    ax.axis('off')
    fig.patch.set_facecolor(C_BG)
    ax.set_facecolor(C_BG)

    ax.text(7, 9.5, "BONE vs CARTILAGE – Side-by-Side Comparison",
            ha='center', va='center', fontsize=17, fontweight='bold', color=C_TEXT_DARK,
            path_effects=[pe.withStroke(linewidth=3, foreground='white')])

    # column headers
    rounded_box(ax, 3.5, 8.8, 5.5, 0.55, "BONE", C_BONE_DARK, C_TEXT_WHITE, fontsize=14, bold=True)
    rounded_box(ax, 10.5, 8.8, 5.5, 0.55, "CARTILAGE", C_CART_DARK, C_TEXT_WHITE, fontsize=14, bold=True)

    comparisons = [
        ("Tissue type",        "Connective tissue",                          "Connective tissue"),
        ("Vascularity",        "Vascular (periosteum + nutrient artery)",      "Avascular"),
        ("Matrix mineral",     "Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂",             "Not mineralized (usually)"),
        ("Main collagen",      "Type I collagen (~90%)",                      "Type II (hyaline/elastic)\nType I (fibrocartilage)"),
        ("Cells",              "Osteoblasts, Osteocytes,\nOsteoclasts, OPCs", "Chondroblasts, Chondrocytes"),
        ("Cell housing",       "Lacunae (osteocytes)",                        "Lacunae (chondrocytes)"),
        ("Covering",           "Periosteum (outer)\nEndosteum (inner)",       "Perichondrium (most types)"),
        ("Nutrition",          "Blood vessels (periosteum &\nHaversian canals)", "Diffusion through matrix"),
        ("Rigidity",           "Very rigid/hard",                             "Firm but pliable/resilient"),
        ("Repair capacity",    "Good (periosteum-mediated)",                  "Poor (limited in adults)"),
        ("Main functions",     "Support, protection,\nmovement, haematopoiesis","Cushioning, flexibility,\ngrowth plate, template"),
        ("Development",        "Intramembranous or\nEndochondral ossification","From mesenchymal cells\n(chondrogenesis)"),
    ]
    row_h = 0.52
    y0 = 8.35
    for i, (feature, bone_val, cart_val) in enumerate(comparisons):
        yy = y0 - i * row_h
        bkg_b = C_BONE_XLIGHT if i % 2 == 0 else "#D6EAF8"
        bkg_c = C_CART_XLIGHT if i % 2 == 0 else "#D5F5E3"
        bkg_f = "#F2F3F4" if i % 2 == 0 else "#E5E7E9"
        rounded_box(ax, 7, yy, 1.8, row_h - 0.06, feature, bkg_f, C_TEXT_DARK, fontsize=8.5, bold=True)
        rounded_box(ax, 3.5, yy, 5.3, row_h - 0.06, bone_val, bkg_b, C_TEXT_DARK, fontsize=8.2)
        rounded_box(ax, 10.5, yy, 5.3, row_h - 0.06, cart_val, bkg_c, C_TEXT_DARK, fontsize=8.2)

    ax.text(7, 0.25, "© Orris Medical AI  |  Based on Gray's Anatomy for Students & Histology: A Text and Atlas",
            ha='center', va='center', fontsize=7, color='#95A5A6', style='italic')

    plt.tight_layout(pad=0.3)
    path = os.path.join(OUTPUT_DIR, "03_comparison.png")
    plt.savefig(path, dpi=180, bbox_inches='tight', facecolor=C_BG)
    plt.close()
    print(f"Saved: {path}")
    return path


# ═══════════════════════════════════════════════════════════════
# ASSEMBLE PDF
# ═══════════════════════════════════════════════════════════════
def build_pdf(images):
    pdf_path = os.path.join(OUTPUT_DIR, "Bone_and_Cartilage_Flowcharts.pdf")
    doc = SimpleDocTemplate(pdf_path, pagesize=A4,
                            leftMargin=1.5*cm, rightMargin=1.5*cm,
                            topMargin=1.5*cm, bottomMargin=1.5*cm)
    styles = getSampleStyleSheet()

    title_style = ParagraphStyle(
        'TitleStyle', parent=styles['Title'],
        fontSize=20, leading=26, textColor=colors.HexColor("#1A5276"),
        alignment=TA_CENTER, spaceAfter=4
    )
    sub_style = ParagraphStyle(
        'SubStyle', parent=styles['Normal'],
        fontSize=10, leading=14, textColor=colors.HexColor("#7F8C8D"),
        alignment=TA_CENTER, spaceAfter=16, fontName='Helvetica-Oblique'
    )
    caption_style = ParagraphStyle(
        'CaptionStyle', parent=styles['Normal'],
        fontSize=9, leading=13, textColor=colors.HexColor("#2C3E50"),
        alignment=TA_CENTER, spaceBefore=4, spaceAfter=12
    )

    story = []

    story.append(Paragraph("Bone & Cartilage", title_style))
    story.append(Paragraph("Classification, Types & Flowcharts", title_style))
    story.append(Spacer(1, 0.1*inch))
    story.append(Paragraph(
        "Based on: <i>Gray's Anatomy for Students</i> &amp; "
        "<i>Histology: A Text and Atlas with Correlated Cell and Molecular Biology</i>",
        sub_style
    ))
    story.append(HRFlowable(width="100%", thickness=2,
                             color=colors.HexColor("#2E86C1"), spaceAfter=20))

    captions = [
        ("Flowchart 1", "Bone – Definition, Structure, Classification by Shape, Bone Types, Cells &amp; Development"),
        ("Flowchart 2", "Cartilage – Definition, Three Types (Hyaline, Elastic, Fibrocartilage), Comparison Table &amp; Growth"),
        ("Flowchart 3", "Bone vs. Cartilage – Side-by-Side Comparison of Key Features"),
    ]

    page_w = A4[0] - 3*cm
    for img_path, (fc_num, caption_text) in zip(images, captions):
        from PIL import Image as PILImage
        with PILImage.open(img_path) as im:
            iw, ih = im.size
        aspect = ih / iw
        display_w = page_w
        display_h = display_w * aspect
        # keep within page height
        max_h = A4[1] - 5*cm
        if display_h > max_h:
            display_h = max_h
            display_w = display_h / aspect

        story.append(RLImage(img_path, width=display_w, height=display_h))
        story.append(Paragraph(
            f"<b>{fc_num}:</b> {caption_text}", caption_style))
        story.append(HRFlowable(width="100%", thickness=0.5,
                                 color=colors.HexColor("#BDC3C7"), spaceAfter=14))

    doc.build(story)
    print(f"PDF saved: {pdf_path}")
    return pdf_path


if __name__ == "__main__":
    p1 = make_bone_overview()
    p2 = make_cartilage_overview()
    p3 = make_comparison()
    pdf = build_pdf([p1, p2, p3])
    print(f"\nDONE: {pdf}")