/**
 * @module tests/unit/db/pending-flush-durability
 * @description Finding 8: the async group-commit flush that persists single-op
 * generation HISTORY must not swallow persist failures. Before the fix a failed
 * background flush was a bare `prodLog.warn` — writes kept succeeding while their
 * before-images silently piled up in memory, never durable and unbounded.
 *
 * The contract now:
 *  - a single transient flush failure does NOT trip the alarm (tolerance), and
 *  - after PENDING_FLUSH_FAILURE_THRESHOLD consecutive failures the store LATCHES
 *    and REFUSES further writes with a typed PendingFlushDurabilityError rather
 *    than accumulate un-durable history, and
 *  - it self-heals: once a flush finally succeeds the latch lifts and writes resume.
 * Live canonical data is never touched — only the immutable history is stuck.
 *
 * Fake timers keep the background retry/coalesce timers from firing, so the exact
 * number of flush attempts (and thus the latch point) is deterministic — the test
 * drives every flush explicitly.
 */
import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest'
import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
import { GenerationStore } from '../../../src/db/generationStore.js'
import { PendingFlushDurabilityError } from '../../../src/db/errors.js'
import { NounType } from '../../../src/types/graphTypes.js'

const ID = (suffix: string): string => `00000000-0000-4000-8000-0000000000${suffix}`
const meta = (v: number): Record<string, unknown> => ({
  noun: NounType.Document,
  subtype: 'note',
  data: `payload-v${v}`,
  version: v,
  _rev: v
})

describe('db/GenerationStore pending-flush durability (finding 8)', () => {
  let storage: MemoryStorage
  let store: GenerationStore

  beforeEach(async () => {
    vi.useFakeTimers()
    storage = new MemoryStorage()
    await storage.init()
    store = new GenerationStore(storage)
    await store.open()
    // High size threshold so single-ops never auto-flush — the test owns every flush.
    ;(store as any).pendingFlushThreshold = 1000
  })

  afterEach(() => {
    vi.useRealTimers()
  })

  /** One single-op write that buffers a pending generation. */
  const singleOp = (id: string, v: number) =>
    store.commitSingleOp({
      touched: { nouns: [id], verbs: [] },
      execute: async () => {
        await storage.saveNounMetadata(id, meta(v))
      }
    })

  it('latches after repeated flush failures, refuses writes, then self-heals', async () => {
    // Buffer a pending generation while storage is healthy.
    await singleOp(ID('aa'), 1)

    // Fault the HISTORY flush (raw generation-record writes) — NOT the live
    // canonical write, which uses a different path (saveNounMetadata).
    const fault = Object.assign(new Error('EIO simulated'), { code: 'EIO' })
    const spy = vi.spyOn(storage as any, 'writeRawObject').mockRejectedValue(fault)

    // Each explicit flush fails and is accounted; the third trips the latch.
    for (let i = 0; i < 3; i++) {
      await expect(store.flushPendingSingleOps()).rejects.toThrow('EIO simulated')
    }

    // Writes are now refused LOUDLY rather than piling up un-durable history.
    await expect(singleOp(ID('bb'), 1)).rejects.toBeInstanceOf(PendingFlushDurabilityError)
    // The live counter did not advance for the refused write (no generation consumed).
    expect(store.generation()).toBe(1)

    // Storage recovers → an explicit flush drains the retained tier and lifts the latch.
    spy.mockRestore()
    await expect(store.flushPendingSingleOps()).resolves.toBeUndefined()

    // Writes resume; the next single-op commits normally.
    const receipt = await singleOp(ID('cc'), 1)
    expect(receipt.generation).toBe(2)
  })

  it('a single transient flush failure does NOT latch — writes continue', async () => {
    await singleOp(ID('aa'), 1)

    const spy = vi.spyOn(storage as any, 'writeRawObject').mockRejectedValue(new Error('blip'))
    await expect(store.flushPendingSingleOps()).rejects.toThrow('blip') // failure #1, below threshold
    spy.mockRestore()

    // Below the latch threshold → the store still accepts writes.
    const receipt = await singleOp(ID('bb'), 1)
    expect(receipt.generation).toBe(2)

    // A subsequent healthy flush drains the tier and resets the failure counter.
    await expect(store.flushPendingSingleOps()).resolves.toBeUndefined()
    expect((store as any).pendingFlushFailures).toBe(0)
    expect((store as any).pendingFlushError).toBeNull()
  })
})