/**
 * @module tests/integration/reprojection-doors-open
 * @description The reprojection engine against a REAL brain on filesystem
 * storage: a toy secondary projection (bucket counts with its own watermark
 * artifact, stamp-after-data per src/utils/projectionWatermark.ts) folds the
 * brain's committed facts through the engine, wired with the callback-form
 * {@link FactLogSource} over `brain.scanFacts`.
 *
 * Proves the three doors-open rows:
 * (i)   folding to caught-up matches ground-truth counts;
 * (ii)  mid-fold, `find()` and `get()` still answer, and a door bump
 *       preempts the advance at the next boundary (mechanism-pinned via
 *       batch counts, not wall-clock);
 * (iii) a crash mid-fold (abandon; reopen; re-advance) resumes from the
 *       durable stamp — never refolds from zero.
 */
import { describe, it, expect, beforeAll, afterAll } from 'vitest'
import { mkdtempSync, mkdirSync, readFileSync, writeFileSync, rmSync, existsSync } from 'node:fs'
import { tmpdir } from 'node:os'
import { join } from 'node:path'
import { Brainy } from '../../src/index.js'
import {
  ReprojectionEngine,
  type ProjectionAdapter
} from '../../src/reprojection/reprojectionEngine.js'
import { FactLogSource } from '../../src/reprojection/factLogSource.js'
import { makeProjectionStamp, readStampedWatermark } from '../../src/utils/projectionWatermark.js'
import type { CommitFact } from '../../src/db/factLog.js'

/** 50 rows, 5 buckets, 10 each. */
const ROWS = 50
const BUCKETS = 5
const GROUND_TRUTH: Record<string, number> = { b0: 10, b1: 10, b2: 10, b3: 10, b4: 10 }

/**
 * The toy secondary projection: latest bucket per entity id, persisted as a
 * data file plus a SEPARATE stamp artifact written stamp-after-data via the
 * shared projectionWatermark helpers. Idempotent by construction (latest-
 * state per id), so at-least-once redelivery on resume is harmless.
 */
class BucketCountProjection implements ProjectionAdapter {
  readonly family = 'bucket-counts'
  /** Every generation this INSTANCE applied — the refold detector for (iii). */
  readonly appliedGenerations: number[] = []
  private latest: Map<string, string | null>
  private wm: number | null

  private constructor(
    private readonly dir: string,
    wm: number | null,
    latest: Map<string, string | null>
  ) {
    this.wm = wm
    this.latest = latest
  }

  /** Load from the artifact dir — data is trusted only under a valid stamp. */
  static async open(dir: string): Promise<BucketCountProjection> {
    mkdirSync(dir, { recursive: true })
    const stampPath = join(dir, 'stamp.json')
    const dataPath = join(dir, 'data.json')
    let wm: number | null = null
    if (existsSync(stampPath)) {
      wm = readStampedWatermark(JSON.parse(readFileSync(stampPath, 'utf8')))
    }
    const latest = new Map<string, string | null>(
      wm !== null && existsSync(dataPath)
        ? (JSON.parse(readFileSync(dataPath, 'utf8')) as Array<[string, string | null]>)
        : []
    )
    return new BucketCountProjection(dir, wm, latest)
  }

  /** Non-null bucket tallies from the latest-state map. */
  counts(): Record<string, number> {
    const out: Record<string, number> = {}
    for (const bucket of this.latest.values()) {
      if (bucket !== null) out[bucket] = (out[bucket] ?? 0) + 1
    }
    return out
  }

  watermark(): number | null {
    return this.wm
  }

  async applyBatch(facts: CommitFact[], upTo: number): Promise<void> {
    for (const fact of facts) {
      this.appliedGenerations.push(fact.generation)
      for (const op of fact.ops) {
        if (op.kind !== 'noun') continue
        if (op.record === null) {
          this.latest.set(op.id, null) // tombstone
          continue
        }
        // The stored noun record nests user metadata under `.metadata`.
        const stored = op.record.metadata as Record<string, unknown> | null
        const user = (stored?.metadata ?? stored) as Record<string, unknown> | null
        const bucket = typeof user?.bucket === 'string' ? user.bucket : null
        this.latest.set(op.id, bucket)
      }
    }
    // Durability THEN stamp — the projectionWatermark law.
    writeFileSync(join(this.dir, 'data.json'), JSON.stringify([...this.latest]))
    writeFileSync(join(this.dir, 'stamp.json'), JSON.stringify(makeProjectionStamp(upTo)))
    this.wm = upTo
  }

  async discard(): Promise<void> {
    rmSync(this.dir, { recursive: true, force: true })
  }
}

describe('reprojection doors-open — a real brain, a toy secondary projection', () => {
  let brainDir: string
  let projRoot: string
  let brain: Brainy
  const ids: string[] = []

  const openBrain = async (dir: string): Promise<Brainy> => {
    const b = new Brainy({
      storage: { type: 'filesystem', path: dir },
      requireSubtype: false,
      silent: true,
      dimensions: 384
    })
    await b.init()
    return b
  }

  /**
   * The production wiring, callback form: the engine's `from` is an EXCLUSIVE
   * lower bound, `scanFacts` bounds are inclusive — hence `from + 1`; the
   * first batch is returned and the handle closed (short batches at segment
   * boundaries are legal — only EMPTY means caught up).
   */
  const sourceFor = (b: Brainy): FactLogSource =>
    new FactLogSource(async (from, limit) => {
      const scan = b.scanFacts({ fromGeneration: from + 1, batchSize: limit })
      if (!scan) throw new Error('this brain hosts no fact log — cannot reproject')
      const iterator = scan.batches()
      try {
        const first = await iterator.next()
        return first.done ? [] : first.value.facts
      } finally {
        if (typeof iterator.return === 'function') await iterator.return(undefined)
      }
    })

  beforeAll(async () => {
    brainDir = mkdtempSync(join(tmpdir(), 'brainy-reproj-'))
    projRoot = mkdtempSync(join(tmpdir(), 'brainy-reproj-artifacts-'))
    brain = await openBrain(brainDir)
    for (let i = 0; i < ROWS; i++) {
      ids.push(
        await brain.add({
          data: `record ${i} filed in bucket ${i % BUCKETS}`,
          type: 'document',
          metadata: { bucket: `b${i % BUCKETS}` }
        })
      )
    }
  }, 240_000)

  afterAll(async () => {
    await brain?.close().catch(() => {})
    rmSync(brainDir, { recursive: true, force: true })
    rmSync(projRoot, { recursive: true, force: true })
  })

  it('(i) folds to caught-up through the engine and matches ground-truth counts', async () => {
    const projection = await BucketCountProjection.open(join(projRoot, 'i'))
    const engine = new ReprojectionEngine({ source: sourceFor(brain), batchSize: 8 })
    engine.register(projection)

    const result = await engine.advance(projection.family, { budgetMs: 60_000 })

    expect(result.status).toBe('caught-up')
    expect(result.watermark).toBeGreaterThanOrEqual(ROWS) // one generation per add, at least
    expect(result.applied).toBeGreaterThanOrEqual(ROWS)
    expect(engine.quarantined(projection.family)).toEqual([])
    expect(projection.counts()).toEqual(GROUND_TRUTH)
    // The stamp on disk is the adapter's own — stamped exactly at the fold head.
    const reloaded = await BucketCountProjection.open(join(projRoot, 'i'))
    expect(reloaded.watermark()).toBe(result.watermark)
    expect(reloaded.counts()).toEqual(GROUND_TRUTH)
  })

  it('(ii) doors stay open mid-fold: find() and get() answer, and a bump preempts the advance', async () => {
    const projection = await BucketCountProjection.open(join(projRoot, 'ii'))
    const engine = new ReprojectionEngine({ source: sourceFor(brain), batchSize: 4 })
    engine.register(projection)
    const head = brain.scanFacts()!.headGeneration

    const inFlight = engine.advance(projection.family, { budgetMs: 60_000 })
    // The read hook: foreground door traffic announces itself, then reads —
    // both interleave with the running fold on the same event loop.
    engine.doorSignal.bump()
    const found = await brain.find({ query: 'record filed in bucket', limit: 3 })
    const got = await brain.get(ids[0])
    const result = await inFlight

    // The doors answered mid-fold.
    expect(found.length).toBeGreaterThan(0)
    expect(got).toBeTruthy()
    const gotMeta = got!.metadata as Record<string, unknown> | undefined
    expect((gotMeta?.bucket ?? (gotMeta?.metadata as Record<string, unknown>)?.bucket)).toBe('b0')

    // THE PREEMPTION PIN — mechanism, not wall-clock: the bump landed before
    // the first installment boundary, so the advance yielded after exactly
    // one batch (≤ batchSize facts), far short of the head.
    expect(result.status).toBe('preempted')
    expect(result.applied).toBeGreaterThan(0)
    expect(result.applied).toBeLessThanOrEqual(4)
    expect(projection.appliedGenerations.length).toBe(result.applied)
    expect(projection.watermark()).not.toBeNull()
    expect(projection.watermark()!).toBeLessThan(head)

    // Resuming folds the remainder; nothing was lost to the preemption.
    const resumed = await engine.advance(projection.family, { budgetMs: 60_000 })
    expect(resumed.status).toBe('caught-up')
    expect(projection.counts()).toEqual(GROUND_TRUTH)
  })

  it('(iii) crash mid-fold: reopen and re-advance resumes from the stamp, never refolds from zero', async () => {
    const projDir = join(projRoot, 'iii')
    const before = await BucketCountProjection.open(projDir)
    const engine1 = new ReprojectionEngine({ source: sourceFor(brain), batchSize: 4 })
    engine1.register(before)

    // A zero budget folds exactly one guaranteed batch, then stops.
    const partial = await engine1.advance(before.family, { budgetMs: 0 })
    expect(partial.status).toBe('budget-exhausted')
    const stamped = before.watermark()
    expect(stamped).not.toBeNull()
    expect(stamped!).toBeGreaterThan(0)

    // CRASH: abandon the engine and adapter mid-fold; reopen the brain cold.
    await brain.close()
    brain = await openBrain(brainDir)

    const after = await BucketCountProjection.open(projDir)
    expect(after.watermark()).toBe(stamped) // the stamp survived the crash

    const engine2 = new ReprojectionEngine({ source: sourceFor(brain), batchSize: 4 })
    engine2.register(after)
    const resumed = await engine2.advance(after.family, { budgetMs: 60_000 })
    expect(resumed.status).toBe('caught-up')

    // NEVER REFOLDS FROM ZERO: every generation the resumed instance applied
    // sits strictly above the crash stamp.
    expect(after.appliedGenerations.length).toBeGreaterThan(0)
    expect(Math.min(...after.appliedGenerations)).toBeGreaterThan(stamped!)
    // And the combined state — durable prefix plus resumed fold — is exact.
    expect(after.counts()).toEqual(GROUND_TRUTH)
  })
})