// ponytail: 5e DMG p.82 XP thresholds per character. Single source of truth
// for the encounter builder's budget math. The "Easy/Medium/Hard/Deadly"
// thresholds are *per character*; the table is indexed by character level.

export type Difficulty = "Easy" | "Medium" | "Hard" | "Deadly";

const THRESHOLDS: Record<number, Record<Difficulty, number>> = {
  1: { Easy: 25, Medium: 50, Hard: 75, Deadly: 100 },
  2: { Easy: 50, Medium: 100, Hard: 150, Deadly: 200 },
  3: { Easy: 75, Medium: 150, Hard: 225, Deadly: 400 },
  4: { Easy: 125, Medium: 250, Hard: 375, Deadly: 500 },
  5: { Easy: 250, Medium: 500, Hard: 750, Deadly: 1100 },
  6: { Easy: 300, Medium: 600, Hard: 900, Deadly: 1400 },
  7: { Easy: 350, Medium: 750, Hard: 1100, Deadly: 1700 },
  8: { Easy: 450, Medium: 900, Hard: 1400, Deadly: 2100 },
  9: { Easy: 550, Medium: 1100, Hard: 1600, Deadly: 2400 },
  10: { Easy: 600, Medium: 1200, Hard: 1900, Deadly: 2800 },
  11: { Easy: 800, Medium: 1600, Hard: 2400, Deadly: 3600 },
  12: { Easy: 1000, Medium: 2000, Hard: 3000, Deadly: 4500 },
  13: { Easy: 1100, Medium: 2200, Hard: 3400, Deadly: 5100 },
  14: { Easy: 1250, Medium: 2500, Hard: 3800, Deadly: 5700 },
  15: { Easy: 1400, Medium: 2800, Hard: 4300, Deadly: 6400 },
  16: { Easy: 1600, Medium: 3200, Hard: 4800, Deadly: 7200 },
  17: { Easy: 2000, Medium: 3900, Hard: 5900, Deadly: 8800 },
  18: { Easy: 2100, Medium: 4200, Hard: 6300, Deadly: 9500 },
  19: { Easy: 2400, Medium: 4900, Hard: 7300, Deadly: 10900 },
  20: { Easy: 2800, Medium: 5700, Hard: 8500, Deadly: 12700 },
};

export interface Budget {
  easy: number;
  medium: number;
  hard: number;
  deadly: number;
}

/** Compute per-difficulty XP budgets for a party. Clamps level to 1..20. */
export function encounterBudget(partyLevel: number, partySize: number): Budget {
  const lvl = Math.max(1, Math.min(20, Math.round(partyLevel)));
  const size = Math.max(1, Math.round(partySize));
  const t = THRESHOLDS[lvl];
  return {
    easy: t.Easy * size,
    medium: t.Medium * size,
    hard: t.Hard * size,
    deadly: t.Deadly * size,
  };
}

/** Map an XP total to a difficulty bucket. */
export function difficultyForXp(xp: number, budget: Budget): Difficulty {
  if (xp >= budget.deadly) return "Deadly";
  if (xp >= budget.hard) return "Hard";
  if (xp >= budget.medium) return "Medium";
  if (xp >= budget.easy) return "Easy";
  return "Easy";
}

export const DIFFICULTY_COLOR: Record<Difficulty, string> = {
  Easy: "var(--color-success)",
  Medium: "var(--color-info)",
  Hard: "var(--color-gold-bright)",
  Deadly: "var(--color-danger)",
};

// ─── Self-check (run: node scripts/check-encounter-budget.ts) ────
// ponytail: the smallest thing that fails if the budget math breaks. No
// framework — plain asserts. Verifies the per-level table scales, the
// party-size multiplier, level clamping, and the XP→difficulty bucketing
// (the boundary the DMG relies on: a budget-equal XP is the *next* tier).
function assert(cond: boolean, msg: string): void {
  if (!cond) throw new Error(`encounter-budget self-check failed: ${msg}`);
}

export function demo(): void {
  // Level 5, 4 PCs — DMG p.82 per-character: Easy 250 / Med 500 / Hard 750 / Deadly 1100.
  const b = encounterBudget(5, 4);
  assert(b.easy === 1000, "L5×4 easy = 250×4");
  assert(b.medium === 2000, "L5×4 medium = 500×4");
  assert(b.hard === 3000, "L5×4 hard = 750×4");
  assert(b.deadly === 4400, "L5×4 deadly = 1100×4");

  // Solo L1 character.
  const solo = encounterBudget(1, 1);
  assert(solo.easy === 25 && solo.deadly === 100, "L1×1 matches table");

  // Level clamps to 1..20; size clamps to >=1.
  const low = encounterBudget(0, 1);
  assert(low.easy === 25, "level clamps up to 1");
  const high = encounterBudget(99, 1);
  assert(high.deadly === 12700, "level clamps down to 20");
  const zero = encounterBudget(5, 0);
  assert(zero.medium === 500, "size clamps up to 1");

  // difficultyForXp: budget-equal XP lands in the *next* tier up (>=, not >),
  // and anything below the easy floor is still Easy (never undefined).
  const d = encounterBudget(5, 4);
  assert(difficultyForXp(999, d) === "Easy", "below easy floor stays Easy");
  assert(difficultyForXp(1000, d) === "Easy", "== easy budget is Easy");
  assert(difficultyForXp(2000, d) === "Medium", "== medium budget is Medium");
  assert(difficultyForXp(3000, d) === "Hard", "== hard budget is Hard");
  assert(difficultyForXp(4400, d) === "Deadly", "== deadly budget is Deadly");
  assert(difficultyForXp(9999, d) === "Deadly", "over deadly stays Deadly");

  console.log("encounter-budget self-check passed ✓");
}