// A reference rider, good enough to be the yardstick for every track.
//
// The generator uses it to set qualifying times, and the verifier uses it to
// prove those times are beatable. Both must judge a track the same way, which
// is why this lives in src/ and not inside either tool — the same rider, and
// the same seed, from both directions.

import {
  SURFACE, surfaceAt, groundAngleAt, isLaunchEdge, curvatureAt, LANE_COUNT,
} from './ExcitebikeTrack.js';
import {
  createRace, step, neutralInput, finalizeRace, mulberry32, STATE, STEP_MS, MODE,
} from './ExcitebikeLogic.js';

/**
 * The reference riders, from the ceiling down to the floor.
 *
 *   expert  perfect information, no lag. What the track can theoretically give.
 *   human   the yardstick the qualifying times are actually set from: it looks
 *           ahead less far, reacts on a delay, and cannot place the nose
 *           exactly. A track is fair when this rider can qualify on it.
 *   steady  a cautious human, low on the throttle.
 *   naive   holds the throttle down and steers at nothing. The difficulty
 *           floor: a track this rider can qualify on is asking nothing.
 */
// `heatOff` is where a rider lifts off turbo and `heatOn` where they get back
// on it. The gap between them matters more than either number: the throttle
// bleeds the moment you release turbo, so feathering B around a single
// threshold spends the whole race accelerating and never reaches turbo pace.
// Riding it in long bursts is what the heat model rewards, and it is how a
// person actually plays.
export const AUTO_SKILL = {
  expert: {
    heatOff: 0.94, heatOn: 0.52, lookahead: 190, pitchDeadzone: 0.04, reactionFrames: 1, jitter: 0,
  },
  human: {
    heatOff: 0.82, heatOn: 0.54, lookahead: 140, pitchDeadzone: 0.11, reactionFrames: 7, jitter: 0.09,
  },
  steady: {
    heatOff: 0.66, heatOn: 0.58, lookahead: 120, pitchDeadzone: 0.16, reactionFrames: 11, jitter: 0.14,
  },
  naive: null,
};

// How high to carry the nose into a landing. The tolerance is lopsided, so the
// safe place to sit is a little above the ground angle, not exactly on it.
const LAND_BIAS = 0.14;

function laneScore(model, lane, x, lookahead) {
  let cost = 0;
  for (let d = 0; d < lookahead; d += 8) {
    const s = surfaceAt(model, lane, x + d);
    const w = 1 - d / (lookahead * 1.35);
    if (s === SURFACE.GAP) cost += 900 * w;
    else if (s === SURFACE.OBSTACLE) cost += 900 * w;
    else if (s === SURFACE.MUD) cost += 130 * w;
    else if (s === SURFACE.ROUGH) cost += 85 * w;
    else if (s === SURFACE.COOL) cost -= 28 * w;
  }
  return cost;
}

/**
 * Cost of running up behind a slower bike in a lane.
 *
 * Without this the reference rider rams the back of the pack all race: the
 * contact rule puts the bike that closes from behind on the floor, so a rider
 * who ignores traffic spends SELECTION B crashing. Weighted by how fast it is
 * closing, because a rival pulling away is not in the way.
 */
function trafficAhead(state, self, lane) {
  if (state.bikes.length < 2) return 0;
  let cost = 0;
  for (const other of state.bikes) {
    if (other === self || other.state === STATE.FINISHED) continue;
    if (Math.abs(other.lane - lane) > 0.7) continue;
    const gap = other.x - self.x;
    if (gap < -24 || gap > 150) continue;
    const closing = Math.max(0, self.vx - other.vx);
    cost += (90 + closing * 3) * (1 - gap / 150);
  }
  return cost;
}

function memo(state) {
  if (!state._auto) {
    state._auto = {
      frame: 0, lane: null, onTurbo: true, rng: mulberry32(state.seed ^ 0x9e3779b9),
    };
  }
  return state._auto;
}

/** One frame of input from the reference rider. */
export function autoInput(state, skill = AUTO_SKILL.expert) {
  const inp = neutralInput();
  const b = state.player;
  const m = state.model;
  inp.a = true;
  if (!skill) return inp; // the naive rider: throttle only

  const mem = memo(state);
  mem.frame += 1;
  const lane = Math.max(0, Math.min(LANE_COUNT - 1, Math.round(b.lane)));

  if (b.state === STATE.AIRBORNE) {
    // Point the bike at the ground it is about to meet, with the nose held a
    // little high — landing rear wheel first is safe and going over the bars is
    // not, so the whole margin sits on the nose-up side. A less able rider
    // misjudges that target, and is slower to act on it.
    const want = groundAngleAt(m, lane, b.x + b.vx * 0.25) + LAND_BIAS
      + (skill.jitter ? (mem.rng() - 0.5) * skill.jitter : 0);
    const err = want - b.pitch;
    // Reaction lag: hold the previous decision between glances at the ground.
    if (mem.frame % skill.reactionFrames === 0 || mem.air == null) {
      mem.air = err > skill.pitchDeadzone ? 'up' : (err < -skill.pitchDeadzone ? 'down' : 'hold');
    }
    if (mem.air === 'up') inp.left = true;
    else if (mem.air === 'down') inp.right = true;
    return inp;
  }
  mem.air = null;

  if (b.state === STATE.RUNNING) {
    inp.a = Math.floor(state.elapsedMs / STEP_MS) % 2 === 0;
    return inp;
  }

  const here = surfaceAt(m, lane, b.x);
  if (b.temp >= skill.heatOff) mem.onTurbo = false;
  else if (b.temp <= skill.heatOn) mem.onTurbo = true;
  // A cool zone is free heat: hold turbo across it regardless.
  inp.b = mem.onTurbo || here === SURFACE.COOL;

  if (mem.frame % skill.reactionFrames === 0 || mem.lane == null) {
    let best = lane;
    let bestCost = Infinity;
    for (let l = 0; l < LANE_COUNT; l += 1) {
      const cost = laneScore(m, l, b.x, skill.lookahead)
        + trafficAhead(state, b, l)
        + Math.abs(l - b.lane) * 9;
      if (cost < bestCost) { bestCost = cost; best = l; }
    }
    mem.lane = best;
  }
  if (mem.lane < Math.round(b.lane)) inp.up = true;
  else if (mem.lane > Math.round(b.lane)) inp.down = true;

  // Loft the front wheel just before anything that will throw the bike up, so
  // it leaves the ground level rather than nose-down.
  if (isLaunchEdge(m, lane, b.x + 10) || curvatureAt(m, lane, b.x + 10) < -0.02) inp.left = true;

  return inp;
}

/**
 * Drive a whole race and report the outcome. `maxSeconds` is a safety net: a
 * track that cannot be finished must fail loudly rather than hang the tool.
 */
export function runAuto(model, {
  mode = MODE.SOLO, skill = AUTO_SKILL.expert, seed = 1, rivalCount = 5, maxSeconds = 600,
} = {}) {
  const state = createRace({ model, mode, rivalCount, seed });
  const limit = Math.ceil((maxSeconds * 1000) / STEP_MS);
  const counts = {};
  let frames = 0;
  while (state.phase !== STATE.FINISHED && frames < limit) {
    for (const ev of step(state, autoInput(state, skill))) {
      counts[ev.type] = (counts[ev.type] ?? 0) + 1;
    }
    frames += 1;
  }
  const result = finalizeRace(state);
  return { ...result, events: counts, frames, timedOut: frames >= limit, state };
}

const PROBE_SEEDS = [3, 9, 17, 23, 31];

/**
 * Measure a track the way both the generator and the verifier need it measured.
 *
 * The `human` rider is jittered, so a single run says very little; this takes
 * the median finish time across several seeds and the mean crash rate. Those
 * two numbers are what a qualifying time is set from and what the difficulty
 * curve is asserted against — keeping them in one place is what stops the tool
 * that writes the tracks and the tool that checks them from disagreeing.
 */
export function probeTrack(model, { skill = AUTO_SKILL.human, seeds = PROBE_SEEDS } = {}) {
  const runs = seeds.map((seed) => runAuto(model, { skill, seed }));
  const finished = runs.filter((r) => r.finished && !r.timedOut);
  const times = finished.map((r) => r.ms).sort((a, b) => a - b);
  const crashes = runs.reduce((s, r) => s + (r.events.crash ?? 0), 0) / runs.length;
  return {
    runs,
    finishedCount: finished.length,
    medianMs: times.length ? times[Math.floor(times.length / 2)] : null,
    worstMs: times.length ? times[times.length - 1] : null,
    bestMs: times.length ? times[0] : null,
    crashesPerKpx: (crashes / model.length) * 1000,
  };
}

export { PROBE_SEEDS };