/**
 * Section 10 — ranking semantics.
 *
 * The other ten spec files prove the deployment answers: TLS, auth, quorum
 * commit, convergence, isolation, dashboards, backups. Not one of them writes a
 * signal and observes an order change, so tidalDB's actual thesis — `VISION.md:17`
 * "Ranking is not a feature. It is a primitive." — was unverified.
 *
 * These five checks verify it against a throwaway standalone node this suite
 * boots and seeds itself (60 items, 4 categories, deterministic vectors from
 * `tidal-stress`'s own generator). Hermetic: no cluster, no credential, no
 * network. Run with `npm run test:e2e:semantics`.
 *
 * Two of the five report a product gap rather than a success, because that is
 * what the measurement said. They are written as tripwires in the honest
 * direction — the same shape as the inert-feature checks in
 * `09-operator-authority.spec.ts` — so the day the gap closes, the test fails
 * with an instruction instead of the gap persisting silently.
 */

import { expect, test, type APIRequestContext } from '@playwright/test';
import { recordJson } from '../support/evidence.ts';
import { PROBE_IDS } from '../app/fixture-contract.ts';
import { startApp, type RunningApp } from '../app/harness.ts';

/** One row of a ranked response (`tidal-server/src/dto.rs:269`). */
type FeedItem = {
  entity_id: number;
  score: number;
  rank: number;
  /** Absent, not `[]`, when a profile reports nothing (`dto.rs:373`). */
  signals?: { name: string; value: number }[];
};

/** The whole catalog in one read, so "last" means globally worst, not page-worst. */
const FULL_CORPUS = 60;

/**
 * `for_you`, never `trending`. Measured on this schema, `trending` reports
 * `view_velocity` and `share_velocity` — and `share` is not a declared signal
 * here, so that term is permanently 0. An unknown profile name is answered with
 * 500 rather than 400, so profile names are pinned to ones probed as live.
 */
const PROFILE = 'for_you';

async function readFeed(
  request: APIRequestContext,
  app: RunningApp,
  limit = FULL_CORPUS,
): Promise<FeedItem[]> {
  const response = await request.get(`${app.url}/api/feed?profile=${PROFILE}&limit=${limit}`);
  expect(response.status(), 'the feed must answer before anything is concluded from it').toBe(200);
  const body = (await response.json()) as { items?: FeedItem[] };
  const items = body.items ?? [];
  expect(items.length, 'an empty feed cannot support any ranking assertion').toBeGreaterThan(0);
  return items;
}

async function writeSignal(
  request: APIRequestContext,
  app: RunningApp,
  entityId: number,
  signal: string,
): Promise<void> {
  const response = await request.post(`${app.url}/api/signals`, {
    data: { entity_id: entityId, signal, weight: 1.0 },
  });
  expect(response.status(), `POST /signals ${signal} on ${entityId} must be accepted`).toBe(204);
}

const positionOf = (items: FeedItem[], entityId: number): number =>
  items.findIndex((item) => item.entity_id === entityId);

const signalValue = (item: FeedItem | undefined, name: string): number | undefined =>
  item?.signals?.find((signal) => signal.name === name)?.value;

test.describe('section 10 — ranking semantics', () => {
  test('a like moves the item up, immediately — no ETL in between', async ({
    request,
  }, testInfo) => {
    const app = await startApp();
    try {
      const before = await readFeed(request, app);
      const target = before[before.length - 1]!.entity_id;
      const beforeIndex = positionOf(before, target);

      await writeSignal(request, app, target, 'like');

      // No sleep and no retry between the write and the read. VISION.md:166
      // claims the next query reflects the write with "no Kafka consumer to lag,
      // no feature store sync to schedule". Polling here would be testing our
      // patience rather than that claim.
      const after = await readFeed(request, app);
      const afterIndex = positionOf(after, target);

      await recordJson(testInfo, 'like-moves-up', {
        entityId: target,
        beforeIndex,
        afterIndex,
        likeBoost: signalValue(after[afterIndex], 'like_boost'),
        profile: PROFILE,
      });

      // Position, not score. Scores are floats a profile owns and re-normalises
      // across the candidate set (measured: unliked items go 0.5 -> 0.0 once one
      // item is boosted). Position is the contract a user actually experiences.
      expect(
        afterIndex,
        `a like must improve position immediately; ${target} went ${beforeIndex} -> ${afterIndex}`,
      ).toBeLessThan(beforeIndex);
      expect(afterIndex, 'a single like on the worst item should reach the top').toBe(0);
    } finally {
      await app.close();
    }
  });

  test('a skip is durably accepted and then ignored by every built-in profile', async ({
    request,
  }, testInfo) => {
    const app = await startApp();
    try {
      // Every profile this deployment exposes and which resolves (`top` returns
      // 500 despite existing in engine source, so it is not probed).
      const profiles = [
        'for_you',
        'trending',
        'hot',
        'new',
        'shuffle',
        'hidden_gems',
        'controversial',
      ];
      const baseline = await readFeed(request, app);
      const target = baseline[20]!.entity_id;

      const positionsBefore: Record<string, number> = {};
      for (const profile of profiles) {
        const response = await request.get(
          `${app.url}/api/feed?profile=${profile}&limit=${FULL_CORPUS}`,
        );
        const body = (await response.json()) as { items?: FeedItem[] };
        positionsBefore[profile] = positionOf(body.items ?? [], target);
      }

      // Five skips, not one: a single write could plausibly fall below a rounding
      // threshold. Five cannot.
      for (let n = 0; n < 5; n += 1) await writeSignal(request, app, target, 'skip');

      const positionsAfter: Record<string, number> = {};
      const reported: Record<string, string[]> = {};
      for (const profile of profiles) {
        const response = await request.get(
          `${app.url}/api/feed?profile=${profile}&limit=${FULL_CORPUS}`,
        );
        const body = (await response.json()) as { items?: FeedItem[] };
        const items = body.items ?? [];
        positionsAfter[profile] = positionOf(items, target);
        reported[profile] = (items[positionsAfter[profile]]?.signals ?? []).map((s) => s.name);
      }

      await recordJson(testInfo, 'skip-is-inert', {
        entityId: target,
        skipsWritten: 5,
        declaredDecay: app.declaredDecay,
        positionsBefore,
        positionsAfter,
        signalNamesReported: reported,
      });

      // The schema declares `skip` (permanent), and the write is accepted, so the
      // event is durably recorded. But `Penalty` — the mechanism that would let it
      // demote anything (`tidal/src/ranking/profile.rs:227`, applied at
      // `tidal/src/ranking/executor/signal_values.rs:183`, labelled `{signal}_penalty`
      // at `tidal/src/ranking/executor/mod.rs:65`) — is never populated: every
      // built-in profile is built from `skeleton()`, which sets
      // `penalties: vec![]` (`tidal/src/ranking/builtins.rs:62`), and no built-in
      // overrides it. So `VISION.md:187` "Negative signals are equal citizens" does
      // not hold for any shipped profile: a skip is stored and query-time inert.
      expect(app.declaredDecay.skip, 'the schema must still declare skip').toBe('permanent');
      for (const profile of profiles) {
        expect(
          positionsAfter[profile],
          `${profile} moved ${target} after 5 skips (${positionsBefore[profile]} -> ` +
            `${positionsAfter[profile]}). Good news: a profile now applies a skip ` +
            `penalty. Rewrite this test as a demotion assertion and close the ` +
            `"negative signals are inert" finding.`,
        ).toBe(positionsBefore[profile]);
        expect(
          reported[profile],
          `${profile} now reports a skip term. Same good news as above.`,
        ).not.toContain('skip_penalty');
      }
    } finally {
      await app.close();
    }
  });

  test('decay is applied continuously at query time, at each signal\u2019s declared half-life', async ({
    request,
  }, testInfo) => {
    const app = await startApp();
    try {
      const viewItem = 900_000_300;
      const likeItem = 900_000_301;

      // Written concurrently so both carry the same elapsed time, which makes the
      // ratio of their decay rates depend only on their declared half-lives.
      await Promise.all([
        writeSignal(request, app, viewItem, 'view'),
        writeSignal(request, app, likeItem, 'like'),
      ]);

      const first = await readFeed(request, app);
      const readOne = Date.now();

      // A real interval, deliberately. This is not a sleep to make an assertion
      // pass — elapsed time IS the independent variable of the property under
      // test. `CODING_GUIDELINES.md:88` says "decay is a type, not a formula you
      // call"; the observable consequence is that the SAME stored event reports a
      // smaller value on a later read, with no writes in between.
      await new Promise((resolve) => setTimeout(resolve, 4_000));

      const second = await readFeed(request, app);
      const readTwo = Date.now();
      const elapsedSeconds = (readTwo - readOne) / 1_000;

      const viewFirst = signalValue(first[positionOf(first, viewItem)], 'view_boost');
      const viewSecond = signalValue(second[positionOf(second, viewItem)], 'view_boost');
      const likeFirst = signalValue(first[positionOf(first, likeItem)], 'like_boost');
      const likeSecond = signalValue(second[positionOf(second, likeItem)], 'like_boost');

      // Guard the measurement before concluding anything from it: an absent value
      // would otherwise read as "no decay".
      for (const [label, value] of Object.entries({ viewFirst, viewSecond, likeFirst, likeSecond })) {
        expect(value, `${label} must be reported before decay can be measured`).toBeDefined();
      }

      // Recover each signal's half-life from the two readings:
      //   value(t) = value(0) * 2^(-t/H)  =>  H = t * ln2 / -ln(v2/v1)
      const impliedHalfLife = (v1: number, v2: number): number =>
        (elapsedSeconds * Math.LN2) / -Math.log(v2 / v1);
      const viewHalfLife = impliedHalfLife(viewFirst!, viewSecond!);
      const likeHalfLife = impliedHalfLife(likeFirst!, likeSecond!);

      const declaredView = app.declaredDecay.view;
      const declaredLike = app.declaredDecay.like;
      expect(typeof declaredView, 'view must declare an exponential half-life').toBe('number');
      expect(typeof declaredLike, 'like must declare an exponential half-life').toBe('number');

      await recordJson(testInfo, 'decay-recovers-declared-half-life', {
        elapsedSeconds,
        declaredDecay: app.declaredDecay,
        view: { first: viewFirst, second: viewSecond, impliedHalfLifeSeconds: viewHalfLife },
        like: { first: likeFirst, second: likeSecond, impliedHalfLifeSeconds: likeHalfLife },
        impliedDays: { view: viewHalfLife / 86_400, like: likeHalfLife / 86_400 },
      });

      expect(viewSecond!, 'the same stored view must report lower on a later read').toBeLessThan(
        viewFirst!,
      );
      expect(likeSecond!, 'the same stored like must report lower on a later read').toBeLessThan(
        likeFirst!,
      );

      // +/-20% is generous against a 4-second observation window and still
      // separates the two decisively: 7d x 1.2 = 8.4d sits well below 14d x 0.8 = 11.2d.
      const tolerance = 0.2;
      expect(
        Math.abs(viewHalfLife - (declaredView as number)) / (declaredView as number),
        `view decayed as if its half-life were ${(viewHalfLife / 86_400).toFixed(2)}d, but the ` +
          `loaded schema declares ${((declaredView as number) / 86_400).toFixed(2)}d`,
      ).toBeLessThan(tolerance);
      expect(
        Math.abs(likeHalfLife - (declaredLike as number)) / (declaredLike as number),
        `like decayed as if its half-life were ${(likeHalfLife / 86_400).toFixed(2)}d, but the ` +
          `loaded schema declares ${((declaredLike as number) / 86_400).toFixed(2)}d`,
      ).toBeLessThan(tolerance);

      // Note on scope: `skip` is declared permanent, and permanence is the one
      // decay claim this surface cannot show — no built-in profile reports a skip
      // term at all (see the inertness check above), so there is no value to watch
      // hold still. Recorded rather than faked.
      expect(app.declaredDecay.skip, 'skip remains declared permanent').toBe('permanent');
    } finally {
      await app.close();
    }
  });

  test('vector search returns the true nearest neighbours, not an approximation', async ({
    request,
  }, testInfo) => {
    const app = await startApp();
    try {
      const observations: Record<string, unknown>[] = [];

      for (const probe of PROBE_IDS) {
        const vector = app.groundTruth.probeVectors[String(probe)];
        expect(vector, `ground truth carries no query vector for probe ${probe}`).toBeDefined();
        expect(vector!.length, 'the query vector must match the declared width').toBe(
          app.groundTruth.dim,
        );

        // Field is `vector`, not `values` — a wrong name is answered 422, which
        // reads like a malformed body. Response field is `items`, not `matches`.
        const response = await request.post(`${app.url}/api/vector_search`, {
          data: { vector, k: 10 },
        });
        expect(response.status(), `vector_search for ${probe} must answer`).toBe(200);
        const body = (await response.json()) as {
          items?: { entity_id: number; distance: number }[];
        };
        const items = body.items ?? [];
        expect(
          items.length,
          'an empty result cannot distinguish a perfect index from a broken one',
        ).toBeGreaterThan(0);

        const truth = app.groundTruth.neighboursByItem[String(probe)] ?? [];
        const returned = items.map((item) => item.entity_id);
        const compared = Math.min(truth.length, returned.length);

        observations.push({
          probe,
          selfDistance: items[0]?.distance,
          returned: returned.slice(0, compared),
          truth: truth.slice(0, compared),
        });

        // An item's own vector must find the item itself, at ~zero distance.
        expect(items[0]?.entity_id, `${probe}'s own vector must rank ${probe} first`).toBe(probe);
        expect(
          items[0]!.distance,
          `${probe} found itself at distance ${items[0]!.distance}, beyond the f32 round-trip ` +
            `tolerance of ${app.groundTruth.selfDistanceTolerance}`,
        ).toBeLessThan(app.groundTruth.selfDistanceTolerance);

        // And the whole top-k must equal brute-force cosine over the same corpus,
        // computed by `tidal-stress`'s own oracle from the same generator that
        // produced the indexed vectors.
        expect(
          returned.slice(0, compared),
          `ANN top-${compared} for ${probe} diverged from brute-force cosine`,
        ).toEqual(truth.slice(0, compared));
      }

      await recordJson(testInfo, 'ann-matches-brute-force', {
        dim: app.groundTruth.dim,
        tolerance: app.groundTruth.selfDistanceTolerance,
        observations,
      });
    } finally {
      await app.close();
    }
  });

  test('reported signal values reconcile with what was written, and rank is sequential', async ({
    request,
  }, testInfo) => {
    const app = await startApp();
    try {
      const likedTwice = 900_000_200;
      const viewedOnce = 900_000_201;

      await writeSignal(request, app, likedTwice, 'like');
      await writeSignal(request, app, likedTwice, 'like');
      await writeSignal(request, app, viewedOnce, 'view');

      const items = await readFeed(request, app);
      const liked = items[positionOf(items, likedTwice)];
      const viewed = items[positionOf(items, viewedOnce)];

      const likeBoost = signalValue(liked, 'like_boost');
      const viewCount = signalValue(viewed, 'view');
      const viewBoost = signalValue(viewed, 'view_boost');
      const ranks = items.map((item) => item.rank);
      const expectedRanks = items.map((_unused, index) => index + 1);

      await recordJson(testInfo, 'explainability-reconciles', {
        likedTwice: { entityId: likedTwice, likeBoost },
        viewedOnce: { entityId: viewedOnce, viewCount, viewBoost },
        ranks,
      });

      // Two unit-weight likes report a boost of 2 per like. Decay over the few
      // milliseconds since the write makes this marginally short of 4, so the
      // comparison is a tolerance rather than an equality.
      expect(likeBoost, 'two unit likes must be reported, not silently dropped').toBeDefined();
      expect(
        Math.abs(likeBoost! - 4),
        `two unit-weight likes reported like_boost ${likeBoost}, expected ~4 (2 per like)`,
      ).toBeLessThan(0.01);

      // The raw `view` term is a count, and it must equal the number of writes.
      expect(viewCount, 'the raw view count must be reported').toBe(1);
      expect(
        Math.abs(viewBoost! - 1),
        `one unit-weight view reported view_boost ${viewBoost}, expected ~1`,
      ).toBeLessThan(0.01);

      // Rank must be a dense 1..n sequence. This is the assertion that caught the
      // duplicate-rank defect on the deployed cluster, where `scatter_merge`
      // returns a merged slice without re-stamping rank
      // (`tidal-server/src/cluster/node.rs:7542`). Standalone numbers ranks at
      // `tidal/src/query/executor/pipeline.rs:611` and is unaffected — the pair of
      // results is what localises the defect to the merge.
      // See 11-ranking-integrity.spec.ts for the cluster half.
      expect(
        ranks,
        'rank must be a dense 1..n sequence; duplicates mean a merge did not re-stamp it',
      ).toEqual(expectedRanks);
    } finally {
      await app.close();
    }
  });
});