/**
 * @module tests/unit/db/generationStore-commit-guard
 * @description Pins the commit-order guard on
 * `GenerationStore.commitTransaction()` (`src/db/generationStore.ts`).
 *
 * `reservedGensAsc()`'s own doc comment states an invariant it never
 * enforced: pending single-op generations are always greater than every
 * committed one, because the store's only two sanctioned callers —
 * `Brainy.transact()` and `Brainy.compactHistory()` — flush the pending tier
 * before committing. Nothing stopped a caller from invoking
 * `commitTransaction()` directly while single-ops were still buffered: the
 * fresh commit would land in `committedRanges` ABOVE those lower,
 * still-pending generations, so the committed-then-pending concatenation
 * `reservedGensAsc()` yields is no longer ascending — and `resolveManyAt`
 * (which walks committed ranges before pending ones) would silently report a
 * WRONG before-image for a point-in-time read. `commitTransaction()` now
 * refuses loudly (`PendingSingleOpsUnflushedError`) instead of assuming.
 *
 * Four pins:
 * 1. A direct `commitTransaction()` call while single-ops are pending throws
 *    and commits NOTHING.
 * 2. The same commit succeeds once the pending tier is flushed first.
 * 3. `Brainy.transact()` — which already flushes first — is unaffected
 *    (mirrors `tests/unit/db/generation-chain.test.ts`'s `seedX()`/`bumpX()`
 *    transact pin: add, then transact-update, generation advances by one
 *    each time, the update lands).
 * 4. `reservedGensAsc()` stays ascending across a real add+transact+delete
 *    workload — proven by point-in-time reads (`asOf`) staying correct
 *    throughout, which is exactly what an ordering break would corrupt.
 */

import { describe, it, expect, beforeEach, afterEach } from 'vitest'
import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
import {
  GenerationStore,
  GENERATIONS_PREFIX,
  MANIFEST_PATH
} from '../../../src/db/generationStore.js'
import { PendingSingleOpsUnflushedError } from '../../../src/db/errors.js'
import { Brainy } from '../../../src/index.js'
import { NounType } from '../../../src/types/graphTypes.js'
import { createTestConfig, generateTestVector } from '../../helpers/test-factory.js'

/** Precomputed embedding so Brainy-level adds skip the (slow) embedding model —
 *  these tests exercise the generation layer, not semantics. */
const VEC = generateTestVector()

// Entity ids must be UUID-shaped (the sharded storage layout derives the
// shard from the UUID hex) — same fixture convention as generationStore.test.ts.
const ID_A = '00000000-0000-4000-8000-0000000000aa'
const ID_B = '00000000-0000-4000-8000-0000000000bb'

/** Stored-metadata fixture in the canonical shape the live write paths use
 *  (matches generationStore.test.ts's fixture exactly). */
function metadataFixture(version: number): Record<string, unknown> {
  return {
    noun: NounType.Document,
    subtype: 'note',
    data: `payload-v${version}`,
    version,
    createdAt: 1000,
    updatedAt: 1000 + version,
    _rev: version
  }
}

describe('db/GenerationStore — commitTransaction pending-tier guard (store level)', () => {
  let storage: MemoryStorage
  let store: GenerationStore

  beforeEach(async () => {
    storage = new MemoryStorage()
    await storage.init()
    store = new GenerationStore(storage)
    await store.open()
  })

  /** Buffer one single-op generation via commitSingleOp WITHOUT flushing —
   *  the pending tier that must be drained before commitTransaction(). */
  async function pendingSingleOp(id: string, version: number): Promise<number> {
    const { generation } = await store.commitSingleOp({
      touched: { nouns: [id] },
      execute: async () => {
        await storage.saveNounMetadata(id, metadataFixture(version))
      }
    })
    return generation
  }

  /** A direct transact commit — exactly what a caller bypassing
   *  Brainy.transact()'s flush-first step would issue. */
  function directCommit(id: string, version: number): Promise<{ generation: number; timestamp: number }> {
    return store.commitTransaction({
      touched: { nouns: [id], verbs: [] },
      execute: async () => {
        await storage.saveNounMetadata(id, metadataFixture(version))
      }
    })
  }

  it('PIN 1: refuses a direct commitTransaction() while single-ops are pending, and commits NOTHING', async () => {
    const g1 = await pendingSingleOp(ID_A, 1)
    expect(g1).toBe(1)
    expect(store.committedGeneration()).toBe(0) // nothing flushed to disk yet

    let caught: unknown
    try {
      await directCommit(ID_B, 1)
      expect.unreachable('should have thrown PendingSingleOpsUnflushedError')
    } catch (err) {
      caught = err
    }
    expect(caught).toBeInstanceOf(PendingSingleOpsUnflushedError)
    expect((caught as PendingSingleOpsUnflushedError).pendingCount).toBe(1)

    // Nothing committed: the head + committed ranges are unchanged, and the
    // counter never advanced for the refused attempt (the guard fires before
    // a generation is even reserved).
    expect(store.committedGeneration()).toBe(0)
    expect(store.generation()).toBe(1) // still just the pending single-op's gen
    expect(await storage.readRawObject(MANIFEST_PATH)).toBeNull()
    // The guard fires BEFORE a generation is reserved (`gen = ++this.counter`
    // never runs), so the refused attempt's would-be directory (generation 2,
    // the next number after the pending single-op's 1) was never created.
    expect(await storage.listRawObjects(`${GENERATIONS_PREFIX}/2`)).toEqual([])

    // The refused write never touched canonical storage.
    expect((await storage.readNounRaw(ID_B)).metadata).toBeNull()

    // The pending tier itself is untouched by the refused attempt — flushing
    // now still commits the ORIGINAL single-op cleanly.
    await store.flushPendingSingleOps()
    expect(store.committedGeneration()).toBe(1)
    const atG0 = await store.resolveAt('noun', ID_A, 0)
    expect(atG0).toEqual({ source: 'absent' }) // the create sentinel before g1's write
  })

  it('PIN 2: the same commit succeeds once the pending tier is flushed first', async () => {
    await pendingSingleOp(ID_A, 1)
    await expect(directCommit(ID_B, 1)).rejects.toBeInstanceOf(PendingSingleOpsUnflushedError)

    await store.flushPendingSingleOps()
    expect(store.committedGeneration()).toBe(1)

    const { generation } = await directCommit(ID_B, 1)
    expect(generation).toBe(2)
    expect(store.committedGeneration()).toBe(2)
    expect((await storage.readNounRaw(ID_B)).metadata).toMatchObject({ version: 1 })
  })
})

describe('Brainy public API — commitTransaction pending-tier guard is behavior-neutral', () => {
  let brain: Brainy

  beforeEach(async () => {
    brain = new Brainy(createTestConfig())
    await brain.init()
  })
  afterEach(async () => {
    await brain.close()
  })

  it('PIN 3: Brainy.transact() still commits normally over pending single-ops (mirrors generation-chain.test.ts\'s seedX()/bumpX() transact pin)', async () => {
    const store = (brain as any).generationStore as GenerationStore
    // Relative, not absolute: under the adopt-at-open default the open-time
    // baseline backfill takes a generation of its own (see
    // bounded-chains.test.ts's identical note), so the first user add is not
    // necessarily generation 1.
    const baseGen = brain.generation()
    const baseCommitted = store.committedGeneration()

    const id = await brain.add({
      data: 'x',
      type: NounType.Document,
      subtype: 'note',
      metadata: { v: 1 },
      vector: VEC
    })
    // The add is a pending single-op generation — NOT yet flushed.
    expect(brain.generation()).toBe(baseGen + 1)
    expect(store.committedGeneration()).toBe(baseCommitted)

    // Brainy.transact() flushes the pending tier FIRST (src/brainy.ts:
    // `await this.generationStore.flushPendingSingleOps()`, immediately
    // before its `generationStore.commitTransaction()` call), so the guard
    // never fires on this path — same shape as generation-chain.test.ts's
    // seedX() (add) → bumpX() (transact update) → generation advances by one.
    const db = await brain.transact([{ op: 'update', id, metadata: { v: 2 } }])
    await db.release()

    expect(brain.generation()).toBe(baseGen + 2)
    expect(store.committedGeneration()).toBe(baseGen + 2) // the flushed add + the transact update
    const entity = (await brain.get(id)) as any
    expect(entity.metadata.v).toBe(2)
  })

  it('PIN 4: reservedGensAsc() stays ascending across a real add+transact+delete workload — point-in-time reads stay correct', async () => {
    const store = (brain as any).generationStore as GenerationStore
    const baseGen = brain.generation()
    const baseCommitted = store.committedGeneration()

    const idX = await brain.add({
      data: 'x',
      type: NounType.Document,
      subtype: 'note',
      metadata: { v: 1 },
      vector: VEC
    })
    expect(brain.generation()).toBe(baseGen + 1) // pending (un-flushed)

    const idY = await brain.add({
      data: 'y',
      type: NounType.Document,
      subtype: 'note',
      metadata: { v: 1 },
      vector: VEC
    })
    // Pin right after BOTH adds — before the transact update — so X reads v1
    // and Y still exists at this pin, unlike the live head after the rest of
    // the workload runs.
    const pinAfterBothAdds = brain.generation()
    expect(pinAfterBothAdds).toBe(baseGen + 2) // ALSO pending — two un-flushed single-ops
    expect(store.committedGeneration()).toBe(baseCommitted)

    // A transact() flushes baseGen+1 and baseGen+2 first, then commits its
    // own update as baseGen+3. If committed-vs-pending ordering ever broke,
    // this is exactly the step that would land a commit ABOVE still-pending
    // generations.
    const db = await brain.transact([{ op: 'update', id: idX, metadata: { v: 3 } }])
    await db.release()
    expect(brain.generation()).toBe(baseGen + 3)
    expect(store.committedGeneration()).toBe(baseGen + 3)

    // A single-op delete, pending again (un-flushed).
    await brain.remove(idY)
    expect(brain.generation()).toBe(baseGen + 4)

    // A point-in-time read pinned right after the two adds (before the
    // transact update) must see X's PRE-update value and Y still present.
    // This is precisely what resolveManyAt/resolveAt get WRONG if committed
    // and pending generations were ever interleaved out of ascending order.
    const past = await brain.asOf(pinAfterBothAdds)
    const xAtPin = (await past.get(idX)) as any
    expect(xAtPin?.metadata?.v).toBe(1)
    const yAtPin = (await past.get(idY)) as any
    expect(yAtPin?.metadata?.v).toBe(1) // not yet removed, as of this pin
    await past.release()

    // Live state reflects every later write, in the right order.
    const xNow = (await brain.get(idX)) as any
    expect(xNow.metadata.v).toBe(3)
    expect(await brain.get(idY)).toBeNull()
  })
})