/**
 * Aim Trainer (Qualification Course) — deterministic, pure game-rules module.
 *
 * Framework-free and client-safe: no React, Next.js, or Payload imports, no
 * side effects. All randomness is injected via an `rng` callback so every
 * function is reproducible and unit-testable.
 */

export type AimTrainerDifficulty = "recruit" | "veteran" | "elite";

export interface AimTrainerTierConfig {
  readonly torsoW: number;
  readonly torsoH: number;
  readonly headRadius: number;
  readonly movingRatio: number;
  readonly speed: number;
  readonly maxConcurrentTargets: number;
  readonly targetLifetimeMs: number;
  readonly replacementDelayMs: number;
}

export const AIM_TRAINER_DIFFICULTIES: Readonly<
  Record<AimTrainerDifficulty, AimTrainerTierConfig>
> = {
  recruit: {
    torsoW: 76,
    torsoH: 118,
    headRadius: 21,
    movingRatio: 0.25,
    speed: 80,
    maxConcurrentTargets: 1,
    targetLifetimeMs: 2000,
    replacementDelayMs: 400,
  },
  veteran: {
    torsoW: 62,
    torsoH: 100,
    headRadius: 18,
    movingRatio: 0.55,
    speed: 140,
    maxConcurrentTargets: 2,
    targetLifetimeMs: 1500,
    replacementDelayMs: 300,
  },
  elite: {
    torsoW: 50,
    torsoH: 82,
    headRadius: 15,
    movingRatio: 0.8,
    speed: 220,
    maxConcurrentTargets: 2,
    targetLifetimeMs: 1100,
    replacementDelayMs: 200,
  },
};

export const COURSE_DURATION_MS = 30_000;
export const TORSO_POINTS = 100;
export const HEADSHOT_POINTS = 250;
export const ACCURACY_BONUS_MAX = 500;
export const POINTS_PER_XP = 500;
/** XP awarded per full POINTS_PER_XP score block — one XP per 4,000 score. */
export const SCORE_XP_RATE = 0.125;
export const COMPLETION_XP = 1;
export const NEW_TIER_RECORD_XP = 2;
export const XP_CAP = 50;

export const MAX_SHOTS_FIRED = 500;
export const MAX_HITS = 180;
export const MAX_DESPAWNED_TARGETS = 60;

const DIFFICULTY_VALUES: readonly AimTrainerDifficulty[] = ["recruit", "veteran", "elite"];

export function isAimTrainerDifficulty(value: unknown): value is AimTrainerDifficulty {
  return (
    typeof value === "string" &&
    (DIFFICULTY_VALUES as readonly string[]).includes(value)
  );
}

export function calculateAimTrainerAccuracy(
  hits: number,
  shotsFired: number,
  despawnedUnhitTargets: number,
): number {
  const denominator = shotsFired + despawnedUnhitTargets;
  if (denominator === 0) return 0;
  return Math.min(1, Math.max(0, hits / denominator));
}

export function calculateAimTrainerScore(
  headshots: number,
  torsoHits: number,
  shotsFired: number,
  despawnedUnhitTargets: number,
): number {
  const accuracy = calculateAimTrainerAccuracy(headshots + torsoHits, shotsFired, despawnedUnhitTargets);
  return (
    headshots * HEADSHOT_POINTS +
    torsoHits * TORSO_POINTS +
    Math.round(accuracy * ACCURACY_BONUS_MAX)
  );
}

export function calculateAimTrainerXp(score: number, isNewTierBest: boolean): number {
  const xp =
    COMPLETION_XP +
    Math.floor(score / POINTS_PER_XP) * SCORE_XP_RATE +
    (isNewTierBest ? NEW_TIER_RECORD_XP : 0);
  return Math.min(XP_CAP, xp);
}

export interface AimTrainerTarget {
  readonly x: number;
  readonly y: number;
  readonly vx: number;
  readonly vy: number;
  readonly moving: boolean;
  readonly torsoW: number;
  readonly torsoH: number;
  readonly headRadius: number;
}

export interface AimTrainerTargetHit {
  readonly index: number;
  readonly zone: "head" | "torso";
}

/**
 * Create a target whose whole body (torso rectangle plus the circular head
 * sitting above it) stays inside the canvas. The head circle is centered at
 * `(x, y - headRadius)` and the torso spans `[y, y + torsoH]`, so the target's
 * vertical extent is `[y - 2*headRadius, y + torsoH]`.
 */
export function createAimTrainerTarget(
  rng: () => number,
  canvasW: number,
  canvasH: number,
  difficulty: AimTrainerDifficulty,
): AimTrainerTarget {
  const config = AIM_TRAINER_DIFFICULTIES[difficulty];
  const minX = config.torsoW / 2;
  const maxX = canvasW - config.torsoW / 2;
  const minY = 2 * config.headRadius;
  const maxY = canvasH - config.torsoH;

  const x = minX + rng() * (maxX - minX);
  const y = minY + rng() * (maxY - minY);

  const moving = rng() < config.movingRatio;
  if (!moving) {
    return { x, y, vx: 0, vy: 0, moving, torsoW: config.torsoW, torsoH: config.torsoH, headRadius: config.headRadius };
  }

  const angle = rng() * 2 * Math.PI;
  const vx = Math.cos(angle) * config.speed;
  const vy = Math.sin(angle) * config.speed;
  return { x, y, vx, vy, moving, torsoW: config.torsoW, torsoH: config.torsoH, headRadius: config.headRadius };
}

/**
 * Advance a target by `dt` seconds, bouncing it off the playable bounds so the
 * whole body stays inside the canvas. Pure: returns a new target, never mutates
 * the input.
 */
export function stepAimTrainerTarget(
  target: AimTrainerTarget,
  dt: number,
  canvasW: number,
  canvasH: number,
): AimTrainerTarget {
  if (!target.moving) return target;

  let x = target.x + target.vx * dt;
  let y = target.y + target.vy * dt;
  let vx = target.vx;
  let vy = target.vy;

  const minX = target.torsoW / 2;
  const maxX = canvasW - target.torsoW / 2;
  const minY = 2 * target.headRadius;
  const maxY = canvasH - target.torsoH;

  if (x < minX) {
    x = minX;
    vx = -vx;
  } else if (x > maxX) {
    x = maxX;
    vx = -vx;
  }

  if (y < minY) {
    y = minY;
    vy = -vy;
  } else if (y > maxY) {
    y = maxY;
    vy = -vy;
  }

  return { ...target, x, y, vx, vy };
}

/**
 * Resolve a click at `(x, y)` against a target. The circular head zone is
 * checked first, then the torso rectangle. Returns `null` for a miss.
 */
export function resolveAimTrainerHitZone(
  target: AimTrainerTarget,
  x: number,
  y: number,
): "head" | "torso" | null {
  const headCx = target.x;
  const headCy = target.y - target.headRadius;
  const dx = x - headCx;
  const dy = y - headCy;
  if (dx * dx + dy * dy <= target.headRadius * target.headRadius) {
    return "head";
  }

  const halfW = target.torsoW / 2;
  if (
    x >= target.x - halfW &&
    x <= target.x + halfW &&
    y >= target.y &&
    y <= target.y + target.torsoH
  ) {
    return "torso";
  }

  return null;
}

/**
 * Resolve a click against the topmost matching target. Later targets are drawn
 * above earlier targets, so overlapping targets are checked from last to first.
 */
export function resolveAimTrainerTargetHit(
  targets: readonly AimTrainerTarget[],
  x: number,
  y: number,
): AimTrainerTargetHit | null {
  for (let targetIndex = targets.length - 1; targetIndex >= 0; targetIndex -= 1) {
    const target = targets[targetIndex];
    if (!target) continue;

    const zone = resolveAimTrainerHitZone(target, x, y);
    if (zone) return { index: targetIndex, zone };
  }

  return null;
}