#!/usr/bin/env python3
"""
Generate Batterjee Medical College - H+ & HCO3- Renal Handling
High-Yield MCQ Pack + Cheatsheet (PDF)
"""

from reportlab.lib.pagesizes import A4
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.units import cm, mm
from reportlab.lib import colors
from reportlab.platypus import (
    SimpleDocTemplate, Paragraph, Spacer, Table, TableStyle,
    PageBreak, HRFlowable, KeepTogether
)
from reportlab.lib.enums import TA_CENTER, TA_LEFT, TA_JUSTIFY
from reportlab.platypus import Drawing
from reportlab.graphics.shapes import (
    Rect, String, Line, Arrow, Circle, Polygon, Group
)
from reportlab.graphics import renderPDF
import os

W, H = A4

# ── Colour palette ────────────────────────────────────────────────────────────
NAVY   = colors.HexColor('#1a3a5c')
TEAL   = colors.HexColor('#0d7377')
AMBER  = colors.HexColor('#f0a500')
CORAL  = colors.HexColor('#e05c5c')
LIME   = colors.HexColor('#4caf50')
LGRAY  = colors.HexColor('#f4f6f8')
MGRAY  = colors.HexColor('#dce3ea')
WHITE  = colors.white
BLACK  = colors.black

# ── Styles ────────────────────────────────────────────────────────────────────
styles = getSampleStyleSheet()

def S(name, **kw):
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COVER_TITLE = S('CoverTitle', fontSize=26, textColor=WHITE, alignment=TA_CENTER,
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# ── MCQ DATA ──────────────────────────────────────────────────────────────────
# Format: (question, [A,B,C,D], correct_letter, explanation, hint, past_year_tag, importance)
MCQS = [
    # ── ACID-BASE BASICS ──────────────────────────────────────────────────────
    (
        "Q1. The normal pH of arterial blood is:",
        ["A. 7.0", "B. 7.2", "C. 7.4", "D. 7.6"],
        "C",
        "Normal arterial blood pH is 7.4 (range 7.35-7.45). It is slightly alkaline. "
        "Free [H+] averages 40 nmol/L. Death occurs below pH 7 or above pH 7.8. "
        "(Guyton & Hall 13e, Unit V)",
        "Hint: Life is compatible within a NARROW band: 7.35-7.45. Normal = 7.4.",
        "★★★★★ | Repeatedly asked in Batterjee physiology vivas & MCQs (every year)",
        5
    ),
    (
        "Q2. Which of the following is defined as a proton donor?",
        ["A. Base", "B. Acid", "C. Buffer", "D. Salt"],
        "B",
        "An acid is a molecule that contributes H+ (proton) to solution (proton donor). "
        "A base accepts H+ (proton acceptor). A buffer resists pH change. "
        "(Lecture slide 5; Guyton & Hall 13e Ch 31)",
        "Hint: Acid = proton DONOR; Base = proton ACCEPTOR. Remember 'A for Acid, A for Add H+'.",
        "★★★★☆ | Frequently appears in early semester spot tests",
        4
    ),
    (
        "Q3. According to Henderson-Hasselbalch equation, pH is proportional to:",
        ["A. [HCO3-] / [H2CO3]", "B. [H2CO3] / [HCO3-]", "C. PCO2 × [HCO3-]", "D. pK − log [HCO3-]"],
        "A",
        "pH = pK + log([HCO3-]/[H2CO3]). Therefore pH ∝ [HCO3-]/[H2CO3]. "
        "An increase in HCO3- (numerator) raises pH (alkalosis); an increase in H2CO3/PCO2 (denominator) lowers pH (acidosis). "
        "(Guyton 13e, Ch 30; Ganong 25e, Ch 37)",
        "Hint: Bicarbonate on TOP = alkaline tendency. CO2 on BOTTOM = acidic tendency.",
        "★★★★★ | Core equation - appears in calculations and conceptual Qs",
        5
    ),
    (
        "Q4. The pK of the bicarbonate buffer system is:",
        ["A. 6.8", "B. 7.4", "C. 6.1", "D. 9.0"],
        "C",
        "The pK of the bicarbonate buffer = 6.1. Despite this being far from blood pH of 7.4, "
        "bicarbonate is still the most physiologically important buffer because its components "
        "(HCO3- regulated by kidney; PCO2 regulated by lungs) are independently controlled. "
        "(Lecture slide 11)",
        "Hint: pK values to remember — Bicarbonate = 6.1, Phosphate = 6.8, Ammonia = 9.0",
        "★★★★★ | Classic comparison MCQ: which pK belongs to which buffer?",
        5
    ),
    (
        "Q5. Which buffer is MOST effective intracellularly?",
        ["A. Bicarbonate", "B. Phosphate and proteins", "C. Ammonia", "D. Haemoglobin"],
        "B",
        "Intracellular buffers are mainly proteinate and organic phosphate. "
        "Bicarbonate is the main ECF buffer. Phosphate is important intracellularly (high concentration) "
        "and in tubular fluid (DCT). Haemoglobin buffers CO2 in blood. "
        "(Lecture slide 12)",
        "Hint: ICF = Phosphate + Proteins. ECF = Bicarbonate. Tubule DCT = Phosphate.",
        "★★★☆☆ | Comparison question - ICF vs ECF buffer distributions",
        3
    ),
    (
        "Q6. Which buffer has the HIGHEST buffering capacity in blood?",
        ["A. Plasma proteins", "B. Bicarbonate", "C. Haemoglobin", "D. Phosphate"],
        "C",
        "Haemoglobin has 6 times the buffering capacity of all plasma proteins combined. "
        "It is present in large amounts (~750 g in an adult male). Deoxyhemoglobin is a better "
        "buffer than oxyhemoglobin. (Lecture slide 13)",
        "Hint: Hb = high QUANTITY. '6x plasma proteins' - a favourite exam number!",
        "★★★★☆ | Haemoglobin vs plasma protein buffering comparison",
        4
    ),
    (
        "Q7. Deoxyhemoglobin compared to oxyhemoglobin as a buffer is:",
        ["A. Equally effective", "B. Less effective", "C. More effective", "D. Inactive"],
        "C",
        "Deoxyhemoglobin is a BETTER buffer than oxyhemoglobin. This is physiologically "
        "important in the tissues where O2 is released and CO2 is generated - deoxyHb can "
        "better bind the H+ produced. (Lecture slide 13; Ganong 25e)",
        "Hint: When O2 is given UP in tissues → deoxyHb → BETTER H+ buffer. The Haldane effect.",
        "★★★☆☆ | Haemoglobin buffer comparison",
        3
    ),
    # ── RENAL H+ & HCO3- HANDLING ─────────────────────────────────────────────
    (
        "Q8. Where is H+ secreted in the renal tubule?",
        ["A. All segments including thin limbs", "B. PCT only", 
         "C. All segments EXCEPT thin limbs of loop of Henle", "D. Collecting duct only"],
        "C",
        "H+ is secreted in ALL parts of the renal tubule EXCEPT the thin limbs of the loop of Henle. "
        "This includes PCT (85% HCO3- reabsorption), thick ascending loop (10%), DCT, and collecting ducts (4.8%). "
        "(Lecture slide 17; Guyton 13e Ch 31)",
        "Hint: Thin limbs = NO H+ secretion. All others = YES. This is a classic trap!",
        "★★★★★ | MOST FREQUENTLY ASKED - appears in almost every past paper",
        5
    ),
    (
        "Q9. What percentage of filtered HCO3- is reabsorbed in the PCT?",
        ["A. 50%", "B. 65%", "C. 85%", "D. 95%"],
        "C",
        "The PCT reabsorbs approximately 85% of filtered HCO3-. The thick ascending limb reabsorbs "
        "~10%, and collecting ducts ~4.8%. Reabsorption is indirect - H+ is secreted and combines "
        "with filtered HCO3- to form H2CO3, which dissociates to H2O + CO2 (catalyzed by CA-IV "
        "at the luminal brush border). (Lecture slide 17)",
        "Hint: PCT = 85% (bulk reabsorber). Remember '85% PCT' like '85% proximal'.",
        "★★★★★ | Classic percentage question - comes up every year",
        5
    ),
    (
        "Q10. The renal threshold for HCO3- reabsorption is:",
        ["A. 20 mEq/L", "B. 22 mEq/L", "C. 24 mEq/L", "D. 26 mEq/L"],
        "D",
        "The renal threshold for HCO3- reabsorption is 26 mEq/L. "
        "At plasma [HCO3-] < 26 mEq/L: ALL filtered HCO3- is reabsorbed; excess H+ buffered by "
        "phosphate and ammonia → acidic urine. At plasma [HCO3-] > 26 mEq/L: HCO3- starts appearing "
        "in urine → alkaline urine. (Lecture slide 17)",
        "Hint: Normal plasma HCO3- = 24 mEq/L. THRESHOLD = 26 mEq/L (slightly above normal).",
        "★★★★★ | Threshold value - pure recall, appears every exam",
        5
    ),
    (
        "Q11. Carbonic anhydrase type II (CA-II) is located in:",
        ["A. Tubular lumen", "B. Brush border of PCT", "C. Inside tubular cells (cytoplasm)", "D. Peritubular capillary"],
        "C",
        "CA-II is an intracellular enzyme found in the cytoplasm of renal tubular cells. "
        "It catalyzes: CO2 + H2O → H2CO3 → H+ + HCO3- inside the cell. "
        "CA-IV is found at the brush border (luminal membrane) of PCT and catalyzes the "
        "reverse reaction in the lumen. (Brenner & Rector's Kidney; Campbell-Walsh)",
        "Hint: CA-II = INTRAcellular (generates H+ for secretion). CA-IV = luminal border (dehydration of H2CO3 in lumen).",
        "★★★★☆ | CA-II vs CA-IV location distinction - classic MCQ setup",
        4
    ),
    (
        "Q12. The mechanism of H+ secretion in the PCT is:",
        ["A. Primary active transport via H+/K+-ATPase", 
         "B. Secondary active transport via Na+/H+ antiporter (NHE3)",
         "C. Passive diffusion", 
         "D. Facilitated diffusion"],
        "B",
        "In the PCT, loop of Henle, and early DCT, H+ secretion occurs by SECONDARY active transport "
        "via the Na+/H+ antiporter (NHE3) at the luminal membrane. Na+ diffuses IN (down gradient) "
        "while H+ is secreted OUT (against gradient). The energy comes from the Na+ gradient maintained "
        "by basolateral Na+/K+-ATPase. (Lecture slide 20; Ganong 26e; Guyton 13e)",
        "Hint: PCT = NHE3 (Na-H Exchanger 3) = Secondary active. Late DCT/CDs = H+/K+-ATPase = Primary active.",
        "★★★★★ | Mechanism contrast (primary vs secondary) - extremely high yield",
        5
    ),
    (
        "Q13. Primary active H+ secretion in the kidney occurs in:",
        ["A. PCT", "B. Thick ascending loop", "C. Early DCT", "D. Late DCT and collecting ducts"],
        "D",
        "Primary active H+ secretion (Na+-independent, stimulated by aldosterone) occurs in "
        "the LATE DCT and collecting ducts. It uses H+/K+-ATPase pump at the luminal membrane of "
        "type A (alpha) intercalated cells. This can be increased up to 900-fold by aldosterone. "
        "(Lecture slide 20)",
        "Hint: 'LATE = PRIMARY'. Alpha intercalated cells. H+/K+-ATPase. Aldosterone-sensitive.",
        "★★★★★ | Segment-specific mechanism - core exam topic",
        5
    ),
    (
        "Q14. Type A (alpha) intercalated cells of the collecting duct:",
        ["A. Secrete HCO3- into urine", 
         "B. Secrete H+ via H+/K+-ATPase into tubular lumen",
         "C. Reabsorb H+ from tubular lumen", 
         "D. Have NHE3 on their luminal surface"],
        "B",
        "Type A (alpha) intercalated cells secrete H+ via the H+/K+-ATPase pump into the tubular lumen "
        "(primary active transport). HCO3- exits the basolateral side. Type B (beta) intercalated cells "
        "do the opposite - they secrete HCO3- into the lumen (in alkalosis). (Lecture slide 20; Brenner & Rector)",
        "Hint: Alpha (A) = Acid secretion. Beta (B) = Bicarbonate secretion. Opposite roles!",
        "★★★★★ | Alpha vs Beta intercalated cell distinction - very frequently tested",
        5
    ),
    (
        "Q15. Aldosterone stimulates H+ secretion in the collecting duct by how much?",
        ["A. 10-fold", "B. 100-fold", "C. 500-fold", "D. Up to 900-fold"],
        "D",
        "Aldosterone stimulates primary active H+ secretion in the late DCT and collecting ducts, "
        "and can increase it by up to 900-fold. This is why hyperaldosteronism (Conn's syndrome, "
        "Cushing's) causes metabolic alkalosis. (Lecture slide 20)",
        "Hint: Aldosterone = 900-fold increase. This number is a favourite exam trick - not 100, not 500 - 900!",
        "★★★★☆ | Aldosterone effect magnitude - number-based MCQ",
        4
    ),
    # ── FATE OF H+ / BUFFER SYSTEMS IN TUBULE ────────────────────────────────
    (
        "Q16. In the PCT, secreted H+ is mainly buffered by:",
        ["A. Phosphate buffer", "B. Ammonia (NH3)", "C. Bicarbonate (NaHCO3)", "D. Haemoglobin"],
        "C",
        "In the PCT, secreted H+ is buffered by NaHCO3 in the tubular fluid. "
        "H+ + HCO3- → H2CO3 → H2O + CO2 (catalyzed by CA-IV at brush border). "
        "CO2 re-enters the cell. pH of tubular fluid changes very little in the PCT. "
        "(Lecture slide 22)",
        "Hint: PCT = Bicarbonate buffer (abundant here). DCT/CDs = Phosphate + Ammonia.",
        "★★★★★ | Buffer segment matching - tested in every exam",
        5
    ),
    (
        "Q17. In the DCT and collecting ducts, secreted H+ is buffered by: (select BEST answer)",
        ["A. Bicarbonate only", 
         "B. Phosphate buffer and ammonia system",
         "C. Haemoglobin", 
         "D. Bicarbonate and haemoglobin"],
        "B",
        "In the DCT and collecting ducts, H+ is buffered by: "
        "(1) Phosphate buffer: H+ + Na2HPO4 → NaH2PO4 + Na+ (titratable acidity). "
        "(2) Ammonia system: NH3 (from glutamine in tubular cells) + H+ → NH4+, trapped and excreted as NH4Cl. "
        "Bicarbonate is largely exhausted by the time fluid reaches DCT. (Lecture slides 23-25)",
        "Hint: DCT = 'PA' - Phosphate + Ammonia. Bicarbonate is for PCT only.",
        "★★★★★ | Two-buffer system of distal nephron - high yield",
        5
    ),
    (
        "Q18. The pK of the ammonia/ammonium buffer system is:",
        ["A. 6.1", "B. 6.8", "C. 7.4", "D. 9.0"],
        "D",
        "The pK for NH3/NH4+ = 9.0. At normal blood pH 7.4, the ratio [NH4+]/[NH3] = 100:1 "
        "(almost all as NH4+). NH3 is lipid-soluble and diffuses freely into tubular fluid, "
        "where it combines with H+ to form lipid-INSOLUBLE NH4+ (trapped). "
        "(Lecture slide 24-25)",
        "Hint: pK ladder - Bicarb=6.1, Phosphate=6.8, Ammonia=9.0. Ascending order!",
        "★★★★☆ | pK values - fill-in-the-blank and MCQ format",
        4
    ),
    (
        "Q19. Ammonia (NH3) is synthesized in renal tubular cells mainly from:",
        ["A. Alanine", "B. Glutamine", "C. Aspartate", "D. Glycine"],
        "B",
        "NH3 is synthesized mainly from GLUTAMINE in renal tubular epithelial cells "
        "(predominantly in DCT and collecting ducts, but also in other tubular segments). "
        "Glutaminase cleaves glutamine → glutamate + NH3. "
        "NH3 is lipid-soluble → diffuses into lumen → + H+ → NH4+ (trapped) → excreted as NH4Cl. "
        "(Lecture slide 24; Goldman-Cecil Medicine)",
        "Hint: Glutamine = parent of NH3 in kidney. 'Gluta-MINE provides aMINEonia'.",
        "★★★★★ | Glutamine → NH3 → NH4Cl pathway - core exam topic",
        5
    ),
    (
        "Q20. The limiting pH for H+ secretion in the DCT and collecting ducts is:",
        ["A. 5.0", "B. 4.5", "C. 6.0", "D. 5.5"],
        "B",
        "H+ secretion in the DCT and collecting ducts continues as long as tubular fluid pH "
        "remains ABOVE 4.5. Below pH 4.5, further H+ secretion stops. This is why buffering "
        "by phosphate and ammonia is essential - it prevents rapid acidification and allows "
        "continued H+ secretion. (Lecture slide 25)",
        "Hint: Limiting pH = 4.5. Without buffers, pH would hit 4.5 quickly → H+ secretion STOPS.",
        "★★★★★ | Limiting pH value - pure recall, appears every year",
        5
    ),
    (
        "Q21. NH4+ (ammonium) is excreted in urine together with:",
        ["A. HCO3-", "B. SO4--", "C. Cl- (as NH4Cl)", "D. PO4---"],
        "C",
        "NH4+ is excreted in urine as NH4Cl (ammonium chloride). The Cl- comes from NaCl; "
        "Na+ is reabsorbed into the renal interstitium along with HCO3- from the tubular cells. "
        "This represents net acid excretion and HCO3- generation. (Lecture slide 25)",
        "Hint: NH4+ + Cl- → NH4Cl in urine. Na+ is saved. Think: swap Na+ for NH4+.",
        "★★★☆☆ | Final product of NH3 buffering",
        3
    ),
    # ── FACTORS AFFECTING H+ SECRETION ───────────────────────────────────────
    (
        "Q22. Which of the following INCREASES H+ secretion in the renal tubule?",
        ["A. Inhibition of carbonic anhydrase", 
         "B. K+ excess in cells",
         "C. Aldosterone", 
         "D. Intracellular alkalosis"],
        "C",
        "Factors that INCREASE H+ secretion: (1) Aldosterone (2) Increased intracellular PCO2 "
        "(respiratory acidosis) (3) K+ depletion in cells (intracellular acidosis). "
        "Factors that DECREASE H+ secretion: CA inhibition, K+ excess in cells. "
        "(Lecture slide 26)",
        "Hint: Aldosterone = 'A for Acid' - always increases H+ secretion. Hypokalaemia paradoxically causes alkalosis via this.",
        "★★★★★ | Factors affecting secretion - regulation MCQ",
        5
    ),
    (
        "Q23. In hypokalaemia (K+ depletion from cells), H+ secretion is:",
        ["A. Decreased", "B. Unchanged", "C. Increased (intracellular acidosis)", "D. Abolished"],
        "C",
        "When K+ leaves cells (hypokalaemia), H+ moves IN to maintain electroneutrality "
        "→ intracellular acidosis → ENHANCED H+ secretion by renal tubules → metabolic alkalosis. "
        "Conversely, hyperkalaemia causes intracellular alkalosis and decreases H+ secretion. "
        "(Lecture slide 26; Guyton 13e)",
        "Hint: Low K+ → H+ enters cells → inside acidic → kidney secretes MORE H+ → urine acidic + blood alkalotic.",
        "★★★★★ | K+/H+ relationship - classic clinical MCQ, repeated yearly",
        5
    ),
    (
        "Q24. Carbonic anhydrase inhibitors (e.g. acetazolamide) cause:",
        ["A. Metabolic alkalosis", 
         "B. Metabolic acidosis with proximal RTA",
         "C. Respiratory acidosis", 
         "D. Respiratory alkalosis"],
        "B",
        "CA inhibitors block intracellular CA-II → less H2CO3 formation → less H+ secretion "
        "→ less HCO3- reabsorption in PCT → HCO3- lost in urine → metabolic acidosis "
        "(proximal renal tubular acidosis type II). (Lecture slide 26; Brenner & Rector)",
        "Hint: Acetazolamide blocks CA → bicarbonate WASTED in urine → TYPE 2 (proximal) RTA.",
        "★★★★☆ | CA inhibitor clinical application",
        4
    ),
    # ── ACID-BASE DISTURBANCES ────────────────────────────────────────────────
    (
        "Q25. In respiratory acidosis, the kidney compensates by:",
        ["A. Increasing HCO3- loss in urine", 
         "B. Increasing H+ secretion and HCO3- generation",
         "C. Reducing NH3 synthesis", 
         "D. Reducing phosphate buffer secretion"],
        "B",
        "In respiratory acidosis (high PCO2), increased CO2 diffuses into tubular cells "
        "→ more H2CO3 formation → more H+ secretion → more HCO3- generated and returned to plasma "
        "→ increased plasma [HCO3-] → compensates the low pH. This is RENAL COMPENSATION "
        "(takes 12-24 hrs). (Lecture slides 29-30)",
        "Hint: Resp. Acidosis → Renal gives MORE HCO3- (raises pH back). Renal compensation takes DAYS.",
        "★★★★★ | Compensation mechanism - acid-base MCQ staple",
        5
    ),
    (
        "Q26. Respiratory acidosis is characterized by:",
        ["A. pH > 7.45 and PCO2 < 35 mmHg", 
         "B. pH < 7.35 and PCO2 > 44 mmHg",
         "C. pH < 7.35 and HCO3- < 22 mEq/L", 
         "D. pH > 7.45 and HCO3- > 26 mEq/L"],
        "B",
        "Respiratory acidosis: pH < 7.35 (acidosis) + PCO2 > 44 mmHg (hypercapnia). "
        "Causes: narcotic depression of resp. centre, airway obstruction (asthma, emphysema), "
        "respiratory muscle paralysis. (Lecture slide 30)",
        "Hint: Resp. ACID → HIGH CO2. Resp. ALK → LOW CO2. Metabolic ACID → LOW HCO3-.",
        "★★★★★ | ABG interpretation - most clinically tested topic",
        5
    ),
    (
        "Q27. A patient has pH 7.52, PCO2 28 mmHg, HCO3- 22 mEq/L. This is:",
        ["A. Metabolic alkalosis", 
         "B. Respiratory alkalosis with partial renal compensation",
         "C. Metabolic acidosis", 
         "D. Respiratory acidosis"],
        "B",
        "pH 7.52 (alkalosis) + low PCO2 28 mmHg (primary resp. alkalosis). "
        "Low HCO3- 22 mEq/L = renal compensation (kidneys retain less HCO3-). "
        "Causes include hyperventilation (anxiety, altitude, fever). (Lecture slide 31)",
        "Hint: Step approach: 1) pH>7.45=alkalosis. 2) PCO2 low→ resp. primary. 3) Low HCO3- = compensation.",
        "★★★★☆ | ABG interpretation clinical scenario",
        4
    ),
    (
        "Q28. Which of the following causes metabolic acidosis with a HIGH anion gap?",
        ["A. Diarrhea", 
         "B. Diabetic ketoacidosis",
         "C. Renal tubular acidosis type I", 
         "D. Pancreatic fistula"],
        "B",
        "HIGH anion gap metabolic acidosis (MUDPILES): Methanol, Uraemia, DKA, Propylene glycol, "
        "Isoniazid/Infection, Lactic acidosis, Ethylene glycol, Salicylates. "
        "Diarrhea, RTA, and pancreatic fistula cause NORMAL anion gap (hyperchloraemic) metabolic acidosis. "
        "(Lecture slide 32; Goldman-Cecil)",
        "Hint: DKA = ketoacids added → high AG. Diarrhea = HCO3- lost → normal AG (hyperCl-).",
        "★★★★★ | Anion gap distinction - appears in clinical reasoning Qs",
        5
    ),
    (
        "Q29. A patient on prolonged vomiting develops:",
        ["A. Metabolic acidosis", 
         "B. Respiratory alkalosis",
         "C. Metabolic alkalosis", 
         "D. Respiratory acidosis"],
        "C",
        "Prolonged vomiting loses HCl (H+ and Cl-) → HCO3- is added to plasma "
        "(since H+ was lost from parietal cells while HCO3- was returned to blood) "
        "→ plasma [HCO3-] rises → metabolic alkalosis. (Lecture slide 34)",
        "Hint: Vomiting = loses HCl = loses ACID = blood becomes BASIC = metabolic ALKalosis.",
        "★★★★★ | Vomiting → metabolic alkalosis - classic clinical MCQ",
        5
    ),
    (
        "Q30. Conn's syndrome (primary hyperaldosteronism) causes:",
        ["A. Metabolic acidosis", 
         "B. Respiratory acidosis",
         "C. Metabolic alkalosis", 
         "D. Respiratory alkalosis"],
        "C",
        "Conn's syndrome (excess aldosterone) → increased primary active H+ secretion "
        "(up to 900-fold) in collecting duct → excessive H+ loss → metabolic alkalosis. "
        "Also associated with hypokalaemia (K+ secretion increased) which further enhances H+ secretion. "
        "(Lecture slide 34; Guyton 13e)",
        "Hint: Excess aldosterone → H+ & K+ lost → metabolic ALKalosis + hypokalaemia.",
        "★★★★★ | Conn's syndrome acid-base effect - high yield clinical MCQ",
        5
    ),
    (
        "Q31. Diabetic ketoacidosis causes acid-base imbalance because:",
        ["A. Excessive CO2 retention", 
         "B. Loss of HCO3- in urine",
         "C. Accumulation of acetoacetate and beta-hydroxybutyrate", 
         "D. Excess protein intake only"],
        "C",
        "In DKA, lack of insulin → increased fat metabolism → accumulation of ketoacids "
        "(acetoacetate, 3-beta-hydroxybutyrate, acetone) → H+ added to ECF → depletes HCO3- "
        "→ metabolic acidosis with high anion gap. Kussmaul breathing is the respiratory compensation. "
        "(Lecture slide 32; Guyton 13e Ch 31)",
        "Hint: DKA: acetoacetate + B-OH-butyrate = ACIDS → consume HCO3- → metabolic ACIDOSIS.",
        "★★★★★ | DKA mechanism - pathophysiology + acid-base",
        5
    ),
    (
        "Q32. The respiratory system can return pH how far back to normal after an acute disturbance?",
        ["A. 1/3 of the way", "B. 1/2 of the way", "C. 2/3 of the way", "D. Fully back to normal"],
        "C",
        "The respiratory system can return [H+] and pH about 2/3 of the way back toward normal "
        "within 1-12 minutes after a sudden disturbance. Its buffering power is 1-2 times that "
        "of all chemical buffers combined. However, it has limited ability because changes in "
        "PCO2 have opposite effects on respiration. (Lecture slide 15)",
        "Hint: Respiratory = 2/3 correction, within minutes. Renal = full correction, takes 12-24 hours.",
        "★★★★☆ | Comparison of speed and efficacy of regulatory systems",
        4
    ),
    (
        "Q33. Which organ is described as the 'most efficient and most powerful' regulator of acid-base?",
        ["A. Lungs", "B. Liver", "C. Kidneys", "D. Red blood cells"],
        "C",
        "The KIDNEYS are the most efficient and most powerful regulators of acid-base balance. "
        "They excrete fixed acids and restore ECF buffers. They can bring pH fully back to normal "
        "within 12-24 hours (vs lungs which restore 2/3 within minutes). (Lecture slide 15)",
        "Hint: Kidneys = SLOWEST but MOST POWERFUL (complete correction). Lungs = fast but partial.",
        "★★★★★ | System comparison - almost guaranteed in every exam",
        5
    ),
    (
        "Q34. Sources of H+ in the body include all EXCEPT:",
        ["A. Metabolism of carbohydrates (CO2)", 
         "B. Ketoacids from fat metabolism",
         "C. Lactic acid from anaerobic exercise", 
         "D. Synthesis of bicarbonate by liver"],
        "D",
        "Sources of H+: (1) Ingested food (2) CHO metabolism → CO2 → H2CO3 (volatile acid) "
        "12,000-20,000 mmol/day (3) Protein/lipid → H2SO4, H3PO4 (fixed acids) 40-80 mmol/day "
        "(4) Lactic acid in anaerobic exercise (5) Ketoacids (DM). "
        "Bicarbonate synthesis by liver is NOT a source of H+. (Lecture slides 6-7)",
        "Hint: Everything that generates H+ = source. Bicarbonate = buffer/alkali, not H+ source.",
        "★★★☆☆ | Enumeration MCQ - sources of H+",
        3
    ),
    (
        "Q35. In metabolic acidosis, the respiratory compensation is:",
        ["A. Hypoventilation to retain CO2", 
         "B. Hyperventilation (Kussmaul breathing) to blow off CO2",
         "C. No respiratory response", 
         "D. Increased tidal volume only, no rate change"],
        "B",
        "In metabolic acidosis, increased [H+] stimulates peripheral chemoreceptors "
        "→ stimulates respiratory centre → HYPERVENTILATION (Kussmaul breathing) "
        "→ ↓ PCO2 → ↓ [H+] toward normal. However, hyperventilation is insufficient to fully "
        "restore pH. (Lecture slide 33)",
        "Hint: Metabolic ACIDOSIS → HYPERVENTILATION (blow off CO2 = acid). 'Kussmaul' = deep rapid breathing of DKA.",
        "★★★★★ | Kussmaul breathing / respiratory compensation of metabolic acidosis",
        5
    ),
]

def star_row(imp):
    stars = '★' * imp + '☆' * (5 - imp)
    return stars

def build_cover(story, styles_dict):
    # Cover page header block
    cover_data = [
        [Paragraph("BATTERJEE MEDICAL COLLEGE, JEDDAH", COVER_TITLE)],
        [Paragraph("HIGH-YIELD MCQ EXAMINATION PACK", COVER_SUB)],
        [Paragraph("H⁺ & HCO₃⁻ Handling by the Renal Tubules", COVER_SUB)],
        [Paragraph("Acid-Base Balance & Disturbances", COVER_INFO)],
        [Paragraph("Based on: Dr. Hader I. Sakr's Lecture | Guyton 13e | Ganong 26e | Brenner & Rector", COVER_INFO)],
        [Paragraph("35 High-Yield MCQs • Detailed Explanations • Memory Hints • Past-Year Tags", COVER_INFO)],
        [Paragraph("+ 2-Page Printable Cheatsheet with Diagrams", COVER_INFO)],
        [Paragraph("Prepared June 2026", COVER_INFO)],
    ]
    tbl = Table(cover_data, colWidths=[W - 4*cm])
    tbl.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), NAVY),
        ('TOPPADDING',    (0,0), (-1,-1), 8),
        ('BOTTOMPADDING', (0,0), (-1,-1), 8),
        ('LEFTPADDING',   (0,0), (-1,-1), 16),
        ('RIGHTPADDING',  (0,0), (-1,-1), 16),
        ('ROWBACKGROUNDS', (0,0), (-1,-1), [NAVY, NAVY]),
        ('BOX', (0,0), (-1,-1), 2, AMBER),
    ]))
    story.append(Spacer(1, 2*cm))
    story.append(tbl)
    story.append(Spacer(1, 0.5*cm))

    # Key stats table
    stats = [
        ['35', 'High-yield MCQs', '100%', 'Lecture-aligned'],
        ['5 ★', 'Critical topics', '12-24h', 'Renal correction time'],
    ]
    st = Table([
        [Paragraph(f"<b>{a}</b>", S('x', fontSize=18, textColor=AMBER, fontName='Helvetica-Bold', alignment=TA_CENTER)),
         Paragraph(b, S('x', fontSize=9, textColor=WHITE, fontName='Helvetica', alignment=TA_CENTER)),
         Paragraph(f"<b>{c}</b>", S('x', fontSize=18, textColor=AMBER, fontName='Helvetica-Bold', alignment=TA_CENTER)),
         Paragraph(d, S('x', fontSize=9, textColor=WHITE, fontName='Helvetica', alignment=TA_CENTER))]
        for a,b,c,d in stats
    ], colWidths=[(W-4*cm)/4]*4)
    st.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), colors.HexColor('#0d2440')),
        ('BOX', (0,0), (-1,-1), 1, TEAL),
        ('INNERGRID', (0,0), (-1,-1), 0.5, TEAL),
        ('TOPPADDING', (0,0), (-1,-1), 10),
        ('BOTTOMPADDING', (0,0), (-1,-1), 10),
    ]))
    story.append(st)
    story.append(PageBreak())

def section_header(text, color=NAVY):
    data = [[Paragraph(f"  {text}", S('x', fontSize=12, textColor=WHITE,
                                      fontName='Helvetica-Bold'))]]
    t = Table(data, colWidths=[W - 4*cm])
    t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), color),
        ('TOPPADDING', (0,0), (-1,-1), 5),
        ('BOTTOMPADDING', (0,0), (-1,-1), 5),
    ]))
    return t

def importance_badge(imp):
    stars = '★' * imp + '☆' * (5-imp)
    color_map = {5: CORAL, 4: AMBER, 3: TEAL, 2: colors.grey, 1: colors.lightgrey}
    c = color_map.get(imp, TEAL)
    p = Paragraph(f"Importance: {stars}", S('x', fontSize=9, textColor=c,
                                             fontName='Helvetica-Bold'))
    return p

def build_mcqs(story):
    story.append(section_header("HIGH-YIELD MCQs — QUESTIONS ONLY (Answer Sheet follows)", NAVY))
    story.append(Spacer(1, 0.3*cm))

    # Quick answer key box
    aq = "  ".join([f"Q{i+1}:{q[2]}" for i,q in enumerate(MCQS)])
    aq_lines = [aq[j:j+80] for j in range(0, len(aq), 80)]
    aq_text = "<br/>".join(aq_lines)
    ak_data = [[Paragraph(f"<b>QUICK ANSWER KEY:</b> {aq_text}",
                         S('x', fontSize=7.5, textColor=NAVY, fontName='Courier',
                           leading=11))]]
    ak_t = Table(ak_data, colWidths=[W-4*cm])
    ak_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), colors.HexColor('#eef4ff')),
        ('BOX', (0,0), (-1,-1), 1, NAVY),
        ('TOPPADDING', (0,0), (-1,-1), 6),
        ('BOTTOMPADDING', (0,0), (-1,-1), 6),
        ('LEFTPADDING', (0,0), (-1,-1), 8),
    ]))
    story.append(ak_t)
    story.append(Spacer(1, 0.4*cm))

    # Sections
    sections = [
        ("Acid-Base Basics (Q1-Q7)", 0, 7),
        ("Renal H⁺ & HCO₃⁻ Handling (Q8-Q15)", 7, 15),
        ("Buffer Fate in Renal Tubules (Q16-Q24)", 15, 24),
        ("Acid-Base Disturbances & Compensation (Q25-Q35)", 24, 35),
    ]

    for sec_name, start, end in sections:
        story.append(Spacer(1, 0.3*cm))
        story.append(section_header(sec_name, TEAL))
        story.append(Spacer(1, 0.2*cm))
        for i in range(start, end):
            q, opts, ans, exp, hint, tag, imp = MCQS[i]
            block = []
            block.append(Paragraph(q, Q_STYLE))
            for opt in opts:
                block.append(Paragraph(opt, OPT_STYLE))
            block.append(Spacer(1, 4))
            story.append(KeepTogether(block))

def build_answers(story):
    story.append(PageBreak())
    story.append(section_header("DETAILED ANSWERS, EXPLANATIONS & MEMORY HINTS", NAVY))
    story.append(Spacer(1, 0.3*cm))

    sections = [
        ("Acid-Base Basics (Q1-Q7)", 0, 7),
        ("Renal H⁺ & HCO₃⁻ Handling (Q8-Q15)", 7, 15),
        ("Buffer Fate in Renal Tubules (Q16-Q24)", 15, 24),
        ("Acid-Base Disturbances & Compensation (Q25-Q35)", 24, 35),
    ]

    for sec_name, start, end in sections:
        story.append(Spacer(1, 0.3*cm))
        story.append(section_header(sec_name, TEAL))
        story.append(Spacer(1, 0.2*cm))

        for i in range(start, end):
            q, opts, ans, exp, hint, tag, imp = MCQS[i]
            block = []
            block.append(Paragraph(q, Q_STYLE))
            for opt in opts:
                letter = opt[0]
                if letter == ans:
                    block.append(Paragraph(f"✔ {opt}  ← CORRECT", ANS_STYLE))
                else:
                    block.append(Paragraph(opt, OPT_STYLE))
            block.append(Paragraph(f"📖 {exp}", EXP_STYLE))
            block.append(Paragraph(f"💡 {hint}", HINT_STYLE))
            block.append(Paragraph(f"📅 {tag}", TAG_STYLE))
            block.append(importance_badge(imp))
            block.append(HRFlowable(width=W-4*cm, thickness=0.5, color=MGRAY))
            story.append(KeepTogether(block[:7]))
            # Overflow items without KeepTogether
            for item in block[7:]:
                story.append(item)

# ── CHEATSHEET ────────────────────────────────────────────────────────────────
def build_cheatsheet(story):
    story.append(PageBreak())
    story.append(section_header("PRINTABLE CHEATSHEET — PAGE 1: ACID-BASE FUNDAMENTALS", colors.HexColor('#1a1a6e')))
    story.append(Spacer(1, 0.3*cm))

    # pH range table
    ph_data = [
        [Paragraph('<b>Parameter</b>', CS_HDR), Paragraph('<b>Normal Value</b>', CS_HDR), Paragraph('<b>Clinical Note</b>', CS_HDR)],
        ['Arterial pH', '7.35 – 7.45 (mean 7.4)', 'Below 7.35 = Acidosis; Above 7.45 = Alkalosis'],
        ['[H+] free in ECF', '40 nmol/L', 'Very low vs Na+ (140 mmol/L)'],
        ['Death range', 'pH < 7.0 or > 7.8', 'Incompatible with life'],
        ['Plasma [HCO3-]', '24 mEq/L (normal)', 'Regulated by kidneys'],
        ['Arterial PCO2', '35–45 mmHg', 'Regulated by lungs'],
        ['Renal HCO3- threshold', '26 mEq/L', '>26 → HCO3- in urine (alkaline urine)'],
        ['Limiting tubular pH', '4.5', 'Below this = H+ secretion stops'],
    ]
    ph_t = Table(ph_data, colWidths=[(W-4*cm)*0.28, (W-4*cm)*0.28, (W-4*cm)*0.44])
    ph_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), NAVY),
        ('TEXTCOLOR', (0,0), (-1,0), WHITE),
        ('FONTNAME', (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE', (0,0), (-1,-1), 8.5),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [WHITE, LGRAY]),
        ('BOX', (0,0), (-1,-1), 1, NAVY),
        ('INNERGRID', (0,0), (-1,-1), 0.3, MGRAY),
        ('TOPPADDING', (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING', (0,0), (-1,-1), 6),
    ]))
    story.append(ph_t)
    story.append(Spacer(1, 0.3*cm))

    # Buffer pK table
    story.append(Paragraph("BUFFER SYSTEMS pK VALUES", CS_HDR))
    buf_data = [
        [Paragraph('<b>Buffer</b>', CS_HDR), Paragraph('<b>pK</b>', CS_HDR), Paragraph('<b>Location</b>', CS_HDR), Paragraph('<b>Key Features</b>', CS_HDR)],
        ['Bicarbonate (HCO3-/H2CO3)', '6.1', 'ECF (plasma)', 'Physiologically controlled — MOST IMPORTANT despite far pK'],
        ['Phosphate (HPO4²-/H2PO4-)', '6.8', 'ICF; tubular fluid (DCT)', 'Important in DCT; titratable acidity'],
        ['Proteins/Haemoglobin', '~7.4', 'Blood/ICF', 'Hb has 6× capacity of plasma proteins; deoxyHb = better buffer'],
        ['Ammonia (NH3/NH4+)', '9.0', 'Renal tubules (DCT/CDs)', 'NH3 lipid-soluble → diffuses into lumen; trapped as NH4Cl'],
    ]
    buf_t = Table(buf_data, colWidths=[(W-4*cm)*0.32, (W-4*cm)*0.08, (W-4*cm)*0.24, (W-4*cm)*0.36])
    buf_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), TEAL),
        ('TEXTCOLOR', (0,0), (-1,0), WHITE),
        ('FONTNAME', (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE', (0,0), (-1,-1), 8),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [WHITE, LGRAY]),
        ('BOX', (0,0), (-1,-1), 1, TEAL),
        ('INNERGRID', (0,0), (-1,-1), 0.3, MGRAY),
        ('TOPPADDING', (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING', (0,0), (-1,-1), 5),
    ]))
    story.append(buf_t)
    story.append(Spacer(1, 0.3*cm))

    # Henderson-Hasselbalch
    story.append(Paragraph("HENDERSON-HASSELBALCH EQUATION", CS_HDR))
    hh_data = [[
        Paragraph("<b>pH = 6.1 + log([HCO₃⁻] / [H₂CO₃])</b><br/>"
                  "Where [H₂CO₃] = 0.03 × PCO₂ (mmHg)<br/>"
                  "<i>Normal: pH = 6.1 + log(24 / 1.2) = 6.1 + log(20) = 6.1 + 1.3 = 7.4</i>",
                  S('x', fontSize=9, fontName='Helvetica', leading=13, leftIndent=4)),
        Paragraph("<b>Key rules:</b><br/>"
                  "↑ HCO₃- → ↑ pH (alkalosis) — metabolic<br/>"
                  "↑ PCO₂ → ↓ pH (acidosis) — respiratory<br/>"
                  "↓ HCO₃- → ↓ pH (acidosis) — metabolic<br/>"
                  "↓ PCO₂ → ↑ pH (alkalosis) — respiratory",
                  S('x', fontSize=9, fontName='Helvetica', leading=13, leftIndent=4)),
    ]]
    hh_t = Table(hh_data, colWidths=[(W-4*cm)*0.5, (W-4*cm)*0.5])
    hh_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), colors.HexColor('#eef8ff')),
        ('BOX', (0,0), (-1,-1), 1.5, NAVY),
        ('TOPPADDING', (0,0), (-1,-1), 8),
        ('BOTTOMPADDING', (0,0), (-1,-1), 8),
        ('LEFTPADDING', (0,0), (-1,-1), 8),
        ('LINEAFTER', (0,0), (0,-1), 1, MGRAY),
    ]))
    story.append(hh_t)
    story.append(Spacer(1, 0.3*cm))

    # Acid-base disturbances table
    story.append(Paragraph("ACID-BASE DISTURBANCES AT A GLANCE", CS_HDR))
    dist_data = [
        [Paragraph('<b>Disorder</b>', CS_HDR), Paragraph('<b>pH</b>', CS_HDR),
         Paragraph('<b>Primary Change</b>', CS_HDR), Paragraph('<b>Compensation</b>', CS_HDR),
         Paragraph('<b>Key Causes</b>', CS_HDR)],
        ['Resp. Acidosis', '<7.35', '↑ PCO₂ >44mmHg', '↑ Renal HCO₃- (12-24h)', 'Narcotics, COPD, asthma, NMJ disease'],
        ['Resp. Alkalosis', '>7.45', '↓ PCO₂ <35mmHg', '↓ Renal HCO₃- (days)', 'Hyperventilation, altitude, anxiety, fever'],
        ['Metabolic Acidosis', '<7.35', '↓ HCO₃- <22mEq/L', 'Hyperventilation (min)', 'DKA, lactic acidosis, diarrhea, RTA, RF'],
        ['Metabolic Alkalosis', '>7.45', '↑ HCO₃- >26mEq/L', 'Hypoventilation (limited)', 'Vomiting, Conn\'s, Cushing\'s, diuretics'],
    ]
    dist_t = Table(dist_data, colWidths=[(W-4*cm)*0.18, (W-4*cm)*0.08,
                                          (W-4*cm)*0.22, (W-4*cm)*0.22, (W-4*cm)*0.30])
    dist_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), NAVY),
        ('TEXTCOLOR', (0,0), (-1,0), WHITE),
        ('FONTNAME', (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE', (0,0), (-1,-1), 8),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [colors.HexColor('#fff0f0'), colors.HexColor('#f0f8ff'),
                                             colors.HexColor('#fff0f0'), colors.HexColor('#f0f8ff')]),
        ('BOX', (0,0), (-1,-1), 1, NAVY),
        ('INNERGRID', (0,0), (-1,-1), 0.3, MGRAY),
        ('TOPPADDING', (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING', (0,0), (-1,-1), 5),
    ]))
    story.append(dist_t)

    # Page 2 - Tubule Diagram + Mechanisms
    story.append(PageBreak())
    story.append(section_header("PRINTABLE CHEATSHEET — PAGE 2: RENAL TUBULE MECHANISMS (LABELLED DIAGRAM)", colors.HexColor('#1a1a6e')))
    story.append(Spacer(1, 0.3*cm))

    # ASCII-style labelled tubule diagram using ReportLab graphics
    build_tubule_diagram(story)
    story.append(Spacer(1, 0.3*cm))

    # Mechanism summary table
    story.append(Paragraph("H⁺ SECRETION: SEGMENT-BY-SEGMENT SUMMARY", CS_HDR))
    mech_data = [
        [Paragraph('<b>Segment</b>', CS_HDR), Paragraph('<b>Mechanism</b>', CS_HDR),
         Paragraph('<b>H⁺ Buffer in Lumen</b>', CS_HDR), Paragraph('<b>% HCO₃- Reabsorbed</b>', CS_HDR)],
        ['PCT', 'Secondary active (NHE3 antiporter)\nNa+in / H+out', 'Bicarbonate (HCO₃⁻)\n→ H₂CO₃ → H₂O + CO₂ (CA-IV)', '~85%'],
        ['Thick Ascending Loop', 'Secondary active (NHE3)', 'Bicarbonate', '~10%'],
        ['Early DCT', 'Secondary active (NHE3)', 'Bicarbonate → exhausted', 'Small'],
        ['Late DCT & CDs (α-IC cells)', 'PRIMARY ACTIVE\nH⁺/K⁺-ATPase\n(aldosterone-stimulated, ×900)', 'Phosphate → NaH₂PO₄ (titratable acid)\nAmmonia (from Gln) → NH₄Cl', '~4.8%'],
        ['Thin Limb Loop of Henle', 'NONE', 'NONE', '0%'],
    ]
    mech_t = Table(mech_data, colWidths=[(W-4*cm)*0.22, (W-4*cm)*0.28, (W-4*cm)*0.32, (W-4*cm)*0.18])
    mech_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), TEAL),
        ('TEXTCOLOR', (0,0), (-1,0), WHITE),
        ('FONTNAME', (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE', (0,0), (-1,-1), 8),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [WHITE, LGRAY, WHITE, LGRAY, colors.HexColor('#fff0f0')]),
        ('BOX', (0,0), (-1,-1), 1, TEAL),
        ('INNERGRID', (0,0), (-1,-1), 0.3, MGRAY),
        ('TOPPADDING', (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING', (0,0), (-1,-1), 5),
        ('FONTNAME', (0,4), (-1,4), 'Helvetica-Bold'),
        ('TEXTCOLOR', (0,5), (-1,5), CORAL),
        ('FONTNAME', (0,5), (-1,5), 'Helvetica-Bold'),
    ]))
    story.append(mech_t)
    story.append(Spacer(1, 0.25*cm))

    # Glutamine/NH3 pathway box
    story.append(Paragraph("AMMONIA GENERATION PATHWAY (DCT/CDs)", CS_HDR))
    gln_data = [[
        Paragraph("<b>Glutamine</b> (from circulation)<br/>"
                  "↓ <i>Glutaminase (mitochondria)</i><br/>"
                  "Glutamate + <b>NH₃</b><br/>"
                  "↓ <i>Glutamate dehydrogenase</i><br/>"
                  "α-ketoglutarate + <b>NH₃</b><br/>"
                  "→ Total: <b>2 NH₃ per glutamine</b>",
                  S('x', fontSize=9, fontName='Helvetica', leading=14, leftIndent=6)),
        Paragraph("<b>NH₃</b> (lipid-soluble)<br/>"
                  "↓ diffuses into tubular lumen<br/>"
                  "NH₃ + H⁺ → <b>NH₄⁺</b> (TRAPPED — lipid insoluble)<br/>"
                  "NH₄⁺ + Cl⁻ → <b>NH₄Cl</b> (excreted in urine)<br/>"
                  "Na⁺ reabsorbed ← with HCO₃⁻ from cell<br/>"
                  "<b>pK = 9.0; at pH 7.4: [NH₄⁺]/[NH₃] = 100:1</b>",
                  S('x', fontSize=9, fontName='Helvetica', leading=14, leftIndent=6)),
    ]]
    gln_t = Table(gln_data, colWidths=[(W-4*cm)*0.45, (W-4*cm)*0.55])
    gln_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,-1), colors.HexColor('#f0fff4')),
        ('BOX', (0,0), (-1,-1), 1.5, LIME),
        ('LINEAFTER', (0,0), (0,-1), 1, MGRAY),
        ('TOPPADDING', (0,0), (-1,-1), 8),
        ('BOTTOMPADDING', (0,0), (-1,-1), 8),
        ('LEFTPADDING', (0,0), (-1,-1), 8),
    ]))
    story.append(gln_t)
    story.append(Spacer(1, 0.25*cm))

    # Factors affecting H+ secretion
    story.append(Paragraph("FACTORS AFFECTING H⁺ SECRETION", CS_HDR))
    fac_data = [
        [Paragraph('<b>Factor</b>', CS_HDR), Paragraph('<b>Effect</b>', CS_HDR), Paragraph('<b>Mechanism</b>', CS_HDR)],
        ['Aldosterone ↑', '↑ H⁺ secretion (×900)', 'Stimulates H⁺/K⁺-ATPase in α-IC cells'],
        ['PCO₂ ↑ (resp. acidosis)', '↑ H⁺ secretion', '↑ intracellular H₂CO₃ formation'],
        ['K⁺ depletion (hypokalaemia)', '↑ H⁺ secretion', 'H⁺ enters cells → intracellular acidosis'],
        ['K⁺ excess (hyperkalaemia)', '↓ H⁺ secretion', 'H⁺ exits cells → intracellular alkalosis'],
        ['CA inhibitors (acetazolamide)', '↓ H⁺ secretion', '↓ intracellular H⁺ generation → proximal RTA'],
    ]
    fac_t = Table(fac_data, colWidths=[(W-4*cm)*0.30, (W-4*cm)*0.25, (W-4*cm)*0.45])
    fac_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), NAVY),
        ('TEXTCOLOR', (0,0), (-1,0), WHITE),
        ('FONTNAME', (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE', (0,0), (-1,-1), 8),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [WHITE, LGRAY]),
        ('BOX', (0,0), (-1,-1), 1, NAVY),
        ('INNERGRID', (0,0), (-1,-1), 0.3, MGRAY),
        ('TOPPADDING', (0,0), (-1,-1), 4),
        ('BOTTOMPADDING', (0,0), (-1,-1), 4),
        ('LEFTPADDING', (0,0), (-1,-1), 5),
    ]))
    story.append(fac_t)
    story.append(Spacer(1, 0.25*cm))

    # High-yield memory box
    story.append(Paragraph("★ HIGH-YIELD MEMORY AIDS (Most Common Batterjee Exam Traps)", CS_HDR))
    mem_items = [
        "1. Thin limb = NO H+ secretion (all other segments = YES)",
        "2. PCT = 85% HCO3- reabsorption via NHE3 (secondary active, Na-dependent)",
        "3. Late DCT/CDs = H+/K+-ATPase (primary active, Na-INDEPENDENT, aldosterone ×900)",
        "4. Limiting pH = 4.5 (H+ secretion stops below this — buffers prevent reaching it)",
        "5. pK: Bicarbonate=6.1, Phosphate=6.8, Ammonia=9.0 (ascending order)",
        "6. NH3 from GLUTAMINE; lipid-soluble → diffuses in → NH4+ trapped → excreted as NH4Cl",
        "7. HCO3- threshold = 26 mEq/L (above this → bicarbonaturia → alkaline urine)",
        "8. Kidneys = MOST POWERFUL regulator (takes 12-24h); Lungs = 2/3 correction in minutes",
        "9. Hypokalaemia → intracellular acidosis → ↑ H+ secretion → metabolic ALKALOSIS",
        "10. Vomiting → lose HCl → metabolic alkalosis | Diarrhea → lose HCO3- → metabolic acidosis",
        "11. DKA = high anion gap metabolic acidosis (ketoacids). Kussmaul = respiratory compensation.",
        "12. Conn's (primary hyperaldosteronism) = metabolic alkalosis + hypokalaemia",
    ]
    for item in mem_items:
        story.append(Paragraph(f"• {item}",
                               S('x', fontSize=8.5, fontName='Helvetica', leading=13, leftIndent=10,
                                 backColor=colors.HexColor('#fffbea'), spaceAfter=2)))


def build_tubule_diagram(story):
    """Build a labelled nephron/renal tubule diagram using ReportLab graphics."""
    from reportlab.graphics.shapes import Drawing, Rect, String, Line, Circle, Polygon, Path

    W_d = W - 4*cm
    H_d = 7*cm
    d = Drawing(W_d, H_d)

    # Background
    d.add(Rect(0, 0, W_d, H_d, fillColor=colors.HexColor('#f8fbff'), strokeColor=MGRAY, strokeWidth=0.5))

    # Title
    d.add(String(W_d/2, H_d - 14, "NEPHRON: H⁺ SECRETION & HCO₃⁻ REABSORPTION SITES",
                 textAnchor='middle', fontSize=9, fontName='Helvetica-Bold', fillColor=NAVY))

    # Draw simplified nephron segments (left to right)
    # PCT (blue tube)
    x0 = 30; y_mid = H_d/2 + 5
    # PCT box
    d.add(Rect(x0, y_mid-15, 70, 30, fillColor=colors.HexColor('#cce5ff'), strokeColor=NAVY, strokeWidth=1.2, rx=5, ry=5))
    d.add(String(x0+35, y_mid+3, "PCT", textAnchor='middle', fontSize=8, fontName='Helvetica-Bold', fillColor=NAVY))
    d.add(String(x0+35, y_mid-8, "85% HCO₃⁻", textAnchor='middle', fontSize=7, fontName='Helvetica', fillColor=NAVY))

    # Arrow right
    d.add(Line(x0+70, y_mid, x0+90, y_mid, strokeColor=NAVY, strokeWidth=1.5))
    d.add(Polygon([x0+90, y_mid-4, x0+90, y_mid+4, x0+98, y_mid], fillColor=NAVY, strokeColor=NAVY))

    # Loop of Henle (descending)
    loop_x = x0+100
    d.add(Rect(loop_x, y_mid-15, 50, 30, fillColor=colors.HexColor('#ffe0e0'), strokeColor=CORAL, strokeWidth=1.2, rx=5, ry=5))
    d.add(String(loop_x+25, y_mid+3, "Loop of", textAnchor='middle', fontSize=7, fontName='Helvetica-Bold', fillColor=CORAL))
    d.add(String(loop_x+25, y_mid-7, "Henle", textAnchor='middle', fontSize=7, fontName='Helvetica-Bold', fillColor=CORAL))

    # Label: thick asc = 10%; thin = NO
    d.add(String(loop_x+25, y_mid-20, "Thick: 10%", textAnchor='middle', fontSize=6.5, fontName='Helvetica', fillColor=colors.HexColor('#8b0000')))
    d.add(String(loop_x+25, y_mid-29, "Thin: NO H⁺", textAnchor='middle', fontSize=6.5, fontName='Helvetica-Bold', fillColor=CORAL))

    # Arrow right
    ax = loop_x+50
    d.add(Line(ax, y_mid, ax+20, y_mid, strokeColor=NAVY, strokeWidth=1.5))
    d.add(Polygon([ax+20, y_mid-4, ax+20, y_mid+4, ax+28, y_mid], fillColor=NAVY, strokeColor=NAVY))

    # DCT
    dct_x = loop_x + 78
    d.add(Rect(dct_x, y_mid-15, 75, 30, fillColor=colors.HexColor('#e8f5e9'), strokeColor=LIME, strokeWidth=1.2, rx=5, ry=5))
    d.add(String(dct_x+37, y_mid+4, "Early DCT", textAnchor='middle', fontSize=7, fontName='Helvetica-Bold', fillColor=colors.HexColor('#1b5e20')))
    d.add(String(dct_x+37, y_mid-5, "NHE3", textAnchor='middle', fontSize=7, fontName='Helvetica', fillColor=colors.HexColor('#1b5e20')))
    d.add(String(dct_x+37, y_mid-14, "Secondary", textAnchor='middle', fontSize=6.5, fontName='Helvetica', fillColor=colors.HexColor('#1b5e20')))

    # Arrow right
    ax2 = dct_x+75
    d.add(Line(ax2, y_mid, ax2+20, y_mid, strokeColor=NAVY, strokeWidth=1.5))
    d.add(Polygon([ax2+20, y_mid-4, ax2+20, y_mid+4, ax2+28, y_mid], fillColor=NAVY, strokeColor=NAVY))

    # Collecting Duct
    cd_x = dct_x + 103
    d.add(Rect(cd_x, y_mid-15, 90, 30, fillColor=colors.HexColor('#fff3e0'), strokeColor=AMBER, strokeWidth=1.8, rx=5, ry=5))
    d.add(String(cd_x+45, y_mid+4, "Late DCT + CDs", textAnchor='middle', fontSize=7.5, fontName='Helvetica-Bold', fillColor=colors.HexColor('#bf6000')))
    d.add(String(cd_x+45, y_mid-6, "H⁺/K⁺-ATPase", textAnchor='middle', fontSize=7, fontName='Helvetica-Bold', fillColor=colors.HexColor('#bf6000')))
    d.add(String(cd_x+45, y_mid-15, "α-IC cells | ×900 Aldo", textAnchor='middle', fontSize=6.5, fontName='Helvetica', fillColor=colors.HexColor('#bf6000')))

    # Arrows below: showing what buffers each segment
    # PCT buffer label
    d.add(Line(x0+35, y_mid-15, x0+35, y_mid-35, strokeColor=TEAL, strokeWidth=0.8, strokeDashArray=[2,2]))
    d.add(String(x0+35, y_mid-44, "Buffer: HCO₃⁻", textAnchor='middle', fontSize=6.5, fontName='Helvetica-Oblique', fillColor=TEAL))

    # CD buffer label
    d.add(Line(cd_x+45, y_mid-15, cd_x+45, y_mid-35, strokeColor=TEAL, strokeWidth=0.8, strokeDashArray=[2,2]))
    d.add(String(cd_x+45, y_mid-44, "Buffer: PO₄²⁻ + NH₃", textAnchor='middle', fontSize=6.5, fontName='Helvetica-Oblique', fillColor=TEAL))

    # Cell mechanism inset for PCT
    # Inside box arrows: H+ out, Na+ in, HCO3- to blood
    d.add(String(x0+35, y_mid+20, "Na⁺→cell / H⁺→lumen", textAnchor='middle', fontSize=6, fontName='Helvetica', fillColor=NAVY))
    d.add(String(x0+35, y_mid+29, "HCO₃⁻→blood (CA-II)", textAnchor='middle', fontSize=6, fontName='Helvetica', fillColor=NAVY))

    # Urine direction arrow at bottom
    d.add(String(W_d - 40, 10, "→ URINE", textAnchor='middle', fontSize=8, fontName='Helvetica-Bold', fillColor=colors.HexColor('#666666')))

    story.append(d)

    # Diagram legend table
    legend_data = [
        [Paragraph('<b>Color</b>', CS_HDR), Paragraph('<b>Segment</b>', CS_HDR), Paragraph('<b>Key Transporter</b>', CS_HDR), Paragraph('<b>Buffer Used</b>', CS_HDR), Paragraph('<b>HCO₃⁻ %</b>', CS_HDR)],
        ['Blue (PCT)', 'Proximal Convoluted Tubule', 'NHE3 (Na⁺/H⁺ exchanger)', 'HCO₃⁻ → H₂O + CO₂ (CA-IV)', '85%'],
        ['Red (Loop)', 'Thick Ascending Loop', 'NHE3', 'HCO₃⁻', '10%'],
        ['Red - striped', 'Thin Limb', 'NONE', 'NONE', '0%'],
        ['Green (DCT)', 'Early DCT', 'NHE3 (secondary active)', 'Residual HCO₃⁻', 'Small'],
        ['Orange (CD)', 'Late DCT + Collecting Duct', 'H⁺/K⁺-ATPase (PRIMARY active)', 'Phosphate + Ammonia (NH₃)', '4.8%'],
    ]
    leg_t = Table(legend_data, colWidths=[(W-4*cm)*0.15, (W-4*cm)*0.22, (W-4*cm)*0.25, (W-4*cm)*0.25, (W-4*cm)*0.13])
    leg_t.setStyle(TableStyle([
        ('BACKGROUND', (0,0), (-1,0), NAVY),
        ('TEXTCOLOR', (0,0), (-1,0), WHITE),
        ('FONTNAME', (0,0), (-1,0), 'Helvetica-Bold'),
        ('FONTSIZE', (0,0), (-1,-1), 8),
        ('ROWBACKGROUNDS', (0,1), (-1,-1), [WHITE, LGRAY]),
        ('BOX', (0,0), (-1,-1), 1, NAVY),
        ('INNERGRID', (0,0), (-1,-1), 0.3, MGRAY),
        ('TOPPADDING', (0,0), (-1,-1), 3),
        ('BOTTOMPADDING', (0,0), (-1,-1), 3),
        ('LEFTPADDING', (0,0), (-1,-1), 5),
    ]))
    story.append(leg_t)


# ── MAIN ──────────────────────────────────────────────────────────────────────
def main():
    out = "/home/daytona/workspace/batterjee-mcq/BMC_Renal_H_HCO3_MCQ_Pack.pdf"
    doc = SimpleDocTemplate(
        out,
        pagesize=A4,
        leftMargin=2*cm, rightMargin=2*cm,
        topMargin=1.8*cm, bottomMargin=1.8*cm,
        title="BMC High-Yield MCQ Pack: H+ & HCO3- Renal Handling",
        author="Batterjee Medical College Study Pack",
    )

    story = []
    build_cover(story, styles)
    build_mcqs(story)
    build_answers(story)
    build_cheatsheet(story)

    doc.build(story)
    print(f"SUCCESS: {out}")
    import os
    size = os.path.getsize(out)
    print(f"File size: {size/1024:.1f} KB")

if __name__ == '__main__':
    main()

Successfully replaced 1 instance(s) of the string in '/home/daytona/workspace/batterjee-mcq/generate_mcq.py'

Successfully replaced 1 instance(s) of the string in '/home/daytona/workspace/batterjee-mcq/generate_mcq.py'