/**
 * The measurement machinery itself.
 *
 * These tests exist because a measurement tool that is quietly wrong is worse than no tool: it does
 * not fail, it just produces numbers that decide what the bot becomes. Each one guards a property
 * the paired method depends on.
 */

import { describe, it } from 'node:test';
import assert from 'node:assert/strict';

import { pump } from '../src/engine/advance.ts';
import { createGame } from '../src/engine/setup.ts';
import { adTrackCount } from '../src/engine/state.ts';
import type { GameConfig, GameState } from '../src/engine/state.ts';
import type { BotPolicy } from '../src/sim/bot.ts';
import { developerBot, makeDeveloperBot, playGame } from '../src/sim/bot.ts';
import { compare, parseTweaks } from '../src/sim/compare.ts';
import { makeFunnelProbe, summarize } from '../src/sim/stats.ts';

const config: GameConfig = {
  mode: 'solitaire',
  victory: 'highestAfterDays',
  length: 'standard',
  optionalRules: {
    reducedVisibility: false,
    sisterTrains: false,
    employeeRotation: false,
    emergencyToolbox: false,
  },
};

const game = (seed: number): GameState =>
  createGame({ id: `h${seed}`, seed, config, playerNames: ['bot'] });

/** One game, reduced to a string: every event type in order, plus the final revenue. */
function fingerprint(policy: BotPolicy, seed: number): string {
  const s = game(seed);
  const r = playGame(s, policy, pump);
  return `${r.revenue[0]}|${r.events.map((e) => e.type).join(',')}`;
}

describe('the paired method rests on determinism', () => {
  it('plays the identical game twice from one seed', () => {
    /**
     * THE PROPERTY EVERYTHING ELSE DEPENDS ON. A paired comparison subtracts two games that share a
     * deal; if the same policy on the same seed can diverge, the difference is measuring the engine's
     * own noise and every heuristic verdict is worthless.
     *
     * It is also the engine's central claim — pure, seeded, no ambient randomness — and the failure
     * mode is silent: one `Math.random`, one Map iterated in a different order, and this is the only
     * thing that would notice.
     */
    for (const seed of [1000, 8919, 775569289]) {
      assert.equal(fingerprint(developerBot, seed), fingerprint(developerBot, seed), `seed ${seed} diverged`);
    }
  });

  it('gives the untweaked variant the identical game too', () => {
    // `developerBot` IS `makeDeveloperBot({})`, and the refactor that introduced tweaks must not
    // have changed a single decision. If this fails, every number measured before it is unusable.
    for (const seed of [1000, 8919, 775569289]) {
      assert.equal(
        fingerprint(developerBot, seed),
        fingerprint(makeDeveloperBot({}), seed),
        `seed ${seed}: the untweaked variant plays a different game`,
      );
    }
  });
});

describe('a tweak has to actually do something', () => {
  it('actually holds the trains it says it holds', () => {
    /**
     * REGRESSION, and the reason this file exists. The first `trainCapSlack` gated the two branches
     * whose comments say they exist to play a train card — and measured **exactly zero difference
     * over 400 paired seeds**, because `followThrough` ends with a generic "play what is in hand"
     * fallback that played the card anyway.
     *
     * ASSERT THE CONTRACT, NOT MERELY A DIFFERENCE. A first version of this test only checked that
     * some decision changed somewhere, and it passed against the broken bot: with a tight cap the
     * gated branches do change which Local Operations option is chosen, they just fail to stop the
     * card being played two steps later. "Something moved" is not the promise. The promise is that
     * committed trains never exceed what the Office can hold.
     *
     * Office tiers only ever go up, so the final A/D count is the most generous the cap ever was.
     */
    const committed = (s: GameState): number =>
      s.timetable.filter((t) => t !== null).length + s.pendingExtras.length;

    for (const slack of [0, 1]) {
      const capped = makeDeveloperBot({ trainCapSlack: slack });
      let cappedWorst = 0;
      let baseWorst = 0;
      for (const seed of [1000, 8919, 16838, 24757, 32676, 40595, 48514]) {
        const a = game(seed);
        playGame(a, capped, pump);
        const roomA = adTrackCount(a, 0) + slack;
        cappedWorst = Math.max(cappedWorst, committed(a) - roomA);

        const b = game(seed);
        playGame(b, developerBot, pump);
        baseWorst = Math.max(baseWorst, committed(b) - (adTrackCount(b, 0) + slack));
      }
      assert.ok(
        cappedWorst <= 0,
        `trainCapSlack=${slack} let the bot commit ${cappedWorst} train(s) more than the Office can hold`,
      );
      // And the cap is not vacuous: the uncapped bot really does overshoot on these seeds.
      assert.ok(
        baseWorst > 0,
        `slack=${slack}: the baseline never overshoots on these seeds, so the test proves nothing`,
      );
    }
  });

  it('names itself so a report cannot confuse two runs', () => {
    assert.equal(developerBot.name, 'developer');
    assert.equal(makeDeveloperBot({}).name, 'developer');
    assert.equal(makeDeveloperBot({ trainCapSlack: 1 }).name, 'developer+trainCapSlack=1');
  });

  it('refuses a tweak name it does not know', () => {
    // A typo silently parsed as "no tweaks" would compare the bot against itself and report a
    // confident zero — the most expensive possible failure of this tool.
    assert.deepEqual(parseTweaks(['400', 'trainCapSlack=2']), { trainCapSlack: 2 });
    assert.throws(() => parseTweaks(['trainCapSlok=1']), /unknown tweak/);
  });
});

describe('the funnel counts what it claims to count', () => {
  it('keeps every gate inside the total it is a fraction of', () => {
    const s = game(430);
    const probe = makeFunnelProbe(0);
    const r = playGame(s, developerBot, pump, 50_000, probe.onEvent, probe.onTurn);
    const f = probe.funnel;

    assert.ok(f.arrivals > 0, 'no train reached an Office in a whole game');
    for (const [name, n] of [
      ['at a passenger office', f.arrivalsAtPassengerOffice],
      ['with an empty coach', f.arrivalsWithEmptyCoach],
      ['with a loaded coach', f.arrivalsWithLoadedCoach],
      ['with a wanted car', f.arrivalsWithWantedCar],
    ] as const) {
      assert.ok(n <= f.arrivals, `${name} (${n}) exceeds arrivals (${f.arrivals})`);
    }

    assert.ok(f.cargoPhases > 0, 'no Cargo phase was sampled');
    for (const [name, n] of [
      ['with a facility', f.cargoWithFacility],
      ['green stocked', f.cargoGreenStocked],
      ['car spotted', f.cargoCarSpotted],
      ['laborer free', f.cargoLaborerFree],
      ['ready', f.cargoReady],
    ] as const) {
      assert.ok(n <= f.cargoPhases, `${name} (${n}) exceeds Cargo phases (${f.cargoPhases})`);
    }
    // "All three at one industry" cannot exceed any of the three it is made of.
    assert.ok(f.cargoReady <= Math.min(f.cargoGreenStocked, f.cargoCarSpotted, f.cargoLaborerFree));
    assert.ok(f.buriedWithDigAvailable <= f.buriedTurns);

    // Sampled once per Cargo phase, never once per decision: 5 Days x 12 Stages is the ceiling.
    assert.ok(f.cargoPhases <= 60, `${f.cargoPhases} Cargo phases in a 5-Day game`);

    // And the arrivals it counted are the arrivals that happened.
    const arrived = r.events.filter((e) => e.type === 'trainArrived').length;
    assert.equal(f.arrivals, arrived, 'the probe and the event log disagree about arrivals');
  });

  it('rides along on the harness summary', () => {
    const s = game(202);
    const probe = makeFunnelProbe(0);
    const r = playGame(s, developerBot, pump, 50_000, probe.onEvent, probe.onTurn);
    const stats = summarize(202, r.events, r.intents, s, probe.funnel);
    assert.ok(stats.funnel, 'summarize dropped the funnel');
    assert.equal(stats.funnel!.arrivals, probe.funnel.arrivals);
    // Optional, so a caller with no probe still gets a summary.
    assert.equal(summarize(202, r.events, r.intents, s).funnel, undefined);
  });
});

describe('the comparison arithmetic', () => {
  it('reports a dead heat as a dead heat', () => {
    // Comparing the bot with itself must produce exactly zero, no games differing, and a t of 0 —
    // if the machinery has any asymmetry in it, this is where it shows.
    const r = compare({}, 12);
    assert.equal(r.mean, 0);
    assert.equal(r.identical, 12);
    assert.equal(r.better, 0);
    assert.equal(r.worse, 0);
    assert.equal(r.t, 0);
  });

  it('pairs by seed, and deals the same seeds the harness does', () => {
    const r = compare({ trainCapSlack: 1 }, 5);
    assert.deepEqual(
      r.deltas.map((d) => d.seed),
      [0, 1, 2, 3, 4].map((i) => 1000 + i * 7919),
      'compare and the harness must talk about the same games',
    );
    for (let i = 0; i < r.deltas.length; i++) {
      assert.equal(r.baseStats[i]!.seed, r.deltas[i]!.seed);
      assert.equal(r.variantStats[i]!.seed, r.deltas[i]!.seed);
      assert.equal(r.deltas[i]!.delta, r.variantStats[i]!.revenue.net - r.baseStats[i]!.revenue.net);
    }
  });

  it('computes the standard error from the PAIRED difference', () => {
    // The whole gain of pairing is that σ of the difference is smaller than σ of either side. Using
    // the level's σ by mistake would quietly restore the ±1.0 noise floor this exists to escape.
    const r = compare({ trainCapSlack: 1 }, 40);
    const d = r.deltas.map((x) => x.delta);
    const m = d.reduce((p, c) => p + c, 0) / d.length;
    const sd = Math.sqrt(d.reduce((p, c) => p + (c - m) ** 2, 0) / (d.length - 1));
    assert.ok(Math.abs(r.mean - m) < 1e-9);
    assert.ok(Math.abs(r.sd - sd) < 1e-9);
    assert.ok(Math.abs(r.stderr - sd / Math.sqrt(d.length)) < 1e-9);
  });
});