/**
 * @module tests/unit/db/generationStore
 * @description Unit tests for the generational MVCC record layer
 * (`src/db/generationStore.ts`) against a real `MemoryStorage` adapter —
 * counter monotonicity, the commit protocol (staging → execute → manifest
 * rename → tx-log), point-in-time resolution from before-images, pin
 * refcounting, compaction retention rules, CAS conflicts, timestamp
 * resolution, and crash rollback of uncommitted generations.
 */

import { describe, it, expect, beforeEach, vi } from 'vitest'
import { MemoryStorage } from '../../../src/storage/adapters/memoryStorage.js'
import {
  GenerationStore,
  GENERATIONS_PREFIX,
  MANIFEST_PATH
} from '../../../src/db/generationStore.js'
import {
  GenerationCompactedError,
  GenerationConflictError
} from '../../../src/db/errors.js'
import { NounType } from '../../../src/types/graphTypes.js'

/** Stored-metadata fixture in the canonical shape the live write paths use. */
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
  }
}

// Entity ids must be UUID-shaped (the sharded storage layout derives the
// shard from the UUID hex). Fixed values keep assertions deterministic;
// suffix ordering (…aa < …bb < …cc) matches `changedBetween`'s sorted output.
const ID_A = '00000000-0000-4000-8000-0000000000aa'
const ID_B = '00000000-0000-4000-8000-0000000000bb'
const ID_C = '00000000-0000-4000-8000-0000000000cc'
const ID_SOLO = '00000000-0000-4000-8000-0000000000d0'
const ID_LATER = '00000000-0000-4000-8000-0000000000e0'

describe('db/GenerationStore', () => {
  let storage: MemoryStorage
  let store: GenerationStore

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

  /** Commit one transaction that writes `metadata` for `id`. */
  async function commitWrite(
    id: string,
    version: number,
    options?: { meta?: Record<string, unknown>; ifAtGeneration?: number }
  ): Promise<{ generation: number; timestamp: number }> {
    return store.commitTransaction({
      touched: { nouns: [id], verbs: [] },
      meta: options?.meta,
      ifAtGeneration: options?.ifAtGeneration,
      execute: async () => {
        await storage.saveNounMetadata(id, metadataFixture(version))
      }
    })
  }

  describe('generation counter', () => {
    it('starts at 0 on a fresh store', () => {
      expect(store.generation()).toBe(0)
      expect(store.committedGeneration()).toBe(0)
    })

    it('advances by exactly one per committed transaction', async () => {
      await commitWrite(ID_A, 1)
      expect(store.generation()).toBe(1)
      await commitWrite(ID_A, 2)
      expect(store.generation()).toBe(2)
      expect(store.committedGeneration()).toBe(2)
    })

    it('bumps on single-operation writes via the storage hook (suppressed inside transact)', async () => {
      // Single-op write outside any transaction → hook bumps.
      await storage.saveNounMetadata(ID_SOLO, metadataFixture(1))
      expect(store.generation()).toBe(1)
      expect(store.committedGeneration()).toBe(0) // no transact committed

      // A transact batch writing twice bumps ONCE (the batch is one generation).
      await store.commitTransaction({
        touched: { nouns: [ID_A, ID_B], verbs: [] },
        execute: async () => {
          await storage.saveNounMetadata(ID_A, metadataFixture(1))
          await storage.saveNounMetadata(ID_B, metadataFixture(1))
        }
      })
      expect(store.generation()).toBe(2)
    })

    it('survives close + reopen monotonically', async () => {
      await commitWrite(ID_A, 1)
      await storage.saveNounMetadata(ID_SOLO, metadataFixture(1)) // single-op bump
      const before = store.generation()
      await store.close()

      const reopened = new GenerationStore(storage)
      await reopened.open()
      expect(reopened.generation()).toBeGreaterThanOrEqual(before)
      expect(reopened.committedGeneration()).toBe(1)
    })
  })

  describe('CAS (ifAtGeneration)', () => {
    it('commits when the expectation matches and rejects with expected/actual when stale', async () => {
      await commitWrite(ID_A, 1)
      const pinned = store.generation()

      await commitWrite(ID_A, 2, { ifAtGeneration: pinned }) // fresh → commits
      expect(store.generation()).toBe(pinned + 1)

      try {
        await commitWrite(ID_A, 3, { ifAtGeneration: pinned }) // stale → rejects
        expect.unreachable('should have thrown GenerationConflictError')
      } catch (err) {
        expect(err).toBeInstanceOf(GenerationConflictError)
        expect((err as GenerationConflictError).expected).toBe(pinned)
        expect((err as GenerationConflictError).actual).toBe(pinned + 1)
      }
      expect(store.generation()).toBe(pinned + 1) // nothing moved
    })
  })

  describe('failed transactions', () => {
    it('removes the staging directory and returns the generation reservation', async () => {
      await commitWrite(ID_A, 1)
      const before = store.generation()

      await expect(
        store.commitTransaction({
          touched: { nouns: [ID_A], verbs: [] },
          execute: async () => {
            throw new Error('boom mid-batch')
          }
        })
      ).rejects.toThrow('boom mid-batch')

      expect(store.generation()).toBe(before)
      const leftovers = await storage.listRawObjects(`${GENERATIONS_PREFIX}/${before + 1}`)
      expect(leftovers).toEqual([])
    })
  })

  describe('point-in-time resolution', () => {
    it('resolves untouched ids to the live fast path', async () => {
      await commitWrite(ID_A, 1)
      const pinned = store.generation()
      await commitWrite(ID_B, 1) // later commit touches a DIFFERENT id

      expect(await store.resolveAt('noun', ID_A, pinned)).toEqual({ source: 'current' })
    })

    it('resolves changed ids from the first before-image after the pin', async () => {
      await commitWrite(ID_A, 1)
      const pinned = store.generation()
      await commitWrite(ID_A, 2)
      await commitWrite(ID_A, 3)

      const resolved = await store.resolveAt('noun', ID_A, pinned)
      expect(resolved.source).toBe('record')
      if (resolved.source === 'record') {
        expect(resolved.metadata.version).toBe(1) // state as of the pin
      }
    })

    it('resolves ids created after the pin as absent', async () => {
      await commitWrite(ID_A, 1)
      const pinned = store.generation()
      await commitWrite(ID_LATER, 1)

      expect(await store.resolveAt('noun', ID_LATER, pinned)).toEqual({ source: 'absent' })
    })

    it('changedBetween reports the ids touched in the interval', async () => {
      await commitWrite(ID_A, 1)
      const from = store.generation()
      await commitWrite(ID_B, 1)
      await commitWrite(ID_C, 1)
      const to = store.generation()

      const changed = await store.changedBetween(from, to)
      expect(changed.nouns).toEqual([ID_B, ID_C])
      expect(changed.verbs).toEqual([])
      expect(changed.fromGeneration).toBe(from)
      expect(changed.toGeneration).toBe(to)
    })
  })

  describe('timestamp resolution + tx-log', () => {
    it('records meta in the tx-log and resolves timestamps to generations', async () => {
      const t0 = Date.now() - 10
      const first = await commitWrite(ID_A, 1, { meta: { author: 'unit-test' } })
      // Distinct commit timestamps: resolution picks the NEWEST generation
      // committed at-or-before the instant, so same-millisecond commits tie.
      await new Promise((resolve) => setTimeout(resolve, 5))
      const second = await commitWrite(ID_A, 2)

      const lines = await storage.readTxLogLines()
      expect(lines.length).toBe(2)
      const firstEntry = JSON.parse(lines[0])
      expect(firstEntry.generation).toBe(first.generation)
      expect(firstEntry.meta).toEqual({ author: 'unit-test' })

      expect((await store.resolveTimestamp(t0)).generation).toBe(0)
      expect((await store.resolveTimestamp(first.timestamp)).generation).toBe(first.generation)
      expect((await store.resolveTimestamp(Date.now() + 1000)).generation).toBe(
        second.generation
      )
    })
  })

  describe('pins + compaction', () => {
    it('refcounts pins and never reclaims records a live pin needs', async () => {
      await commitWrite(ID_A, 1)
      const pinned = store.generation()
      store.pin(pinned)
      store.pin(pinned) // refcount 2
      await commitWrite(ID_A, 2)
      await commitWrite(ID_A, 3)

      // Pin at G protects every record-set ABOVE G (resolution reads
      // before-images from generations strictly greater than the pin).
      await store.compact()
      const resolved = await store.resolveAt('noun', ID_A, pinned)
      expect(resolved.source).toBe('record')
      if (resolved.source === 'record') {
        expect(resolved.metadata.version).toBe(1)
      }

      store.release(pinned)
      await store.compact()
      // Still one live pin — records above it still resolve correctly.
      const stillResolved = await store.resolveAt('noun', ID_A, pinned)
      expect(stillResolved.source).toBe('record')

      store.release(pinned)
      const result = await store.compact()
      expect(result.removedGenerations).toBeGreaterThan(0)
      // History record-sets only — the fact log (at `_generations/facts/`) is
      // deliberately NOT reclaimed by history compaction.
      const remaining = (await storage.listRawObjects(GENERATIONS_PREFIX)).filter(
        (p: string) => !p.startsWith(`${GENERATIONS_PREFIX}/facts/`)
      )
      expect(remaining).toEqual([])
    })

    it('maxGenerations cap keeps the most recent record-sets', async () => {
      await commitWrite(ID_A, 1)
      await commitWrite(ID_A, 2)
      await commitWrite(ID_A, 3)

      const result = await store.compact({ maxGenerations: 2 })
      expect(result.removedGenerations).toBe(1)
      expect(result.horizon).toBe(1)

      // Removing record-set N breaks pins BELOW N (their reads need N's
      // before-images) — the horizon itself stays reachable: state at the
      // horizon resolves from the retained record-sets above it.
      expect(() => store.assertReachable(0)).toThrow(GenerationCompactedError)
      expect(store.assertReachable(1)).toBe(1)
      expect(store.assertReachable(2)).toBe(2)
    })

    it('rejects future and negative generations', async () => {
      await commitWrite(ID_A, 1)
      expect(() => store.assertReachable(99)).toThrow(RangeError)
      expect(() => store.assertReachable(-1)).toThrow(RangeError)
      expect(() => store.assertReachable(1.5)).toThrow(RangeError)
    })
  })

  describe('crash recovery', () => {
    it('rolls back an uncommitted generation on open (manifest rename is the commit point)', async () => {
      await commitWrite(ID_A, 1)

      // Simulate a crash between record staging and the manifest rename: a
      // throwing fault injector skips the abort cleanup, exactly as a dead
      // process would, leaving canonical files mutated and the staging
      // directory present — but the manifest still at the prior generation.
      store.setCommitFaultInjector((phase) => {
        if (phase === 'before-manifest-rename') {
          throw new Error('simulated crash')
        }
      })
      await expect(commitWrite(ID_A, 2)).rejects.toThrow('simulated crash')
      store.setCommitFaultInjector(undefined)

      // The canonical file currently holds the EXECUTED (uncommitted) state.
      const dirty = await storage.readNounRaw(ID_A)
      expect((dirty.metadata as { version: number }).version).toBe(2)

      // Recovery on the next open restores the before-image byte-identically.
      const reopened = new GenerationStore(storage)
      const openResult = await reopened.open()
      expect(openResult.rolledBackGenerations).toBe(1)
      const repaired = await storage.readNounRaw(ID_A)
      expect((repaired.metadata as { version: number }).version).toBe(1)
      expect(reopened.committedGeneration()).toBe(1)
      // The crashed generation number is never reused.
      expect(reopened.generation()).toBeGreaterThanOrEqual(2)
    })

    it('keeps a transaction whose manifest rename landed (tx-log append is advisory)', async () => {
      await commitWrite(ID_A, 1)
      store.setCommitFaultInjector((phase) => {
        if (phase === 'after-manifest-rename') {
          throw new Error('simulated crash after commit point')
        }
      })
      await expect(commitWrite(ID_A, 2)).rejects.toThrow('simulated crash after commit point')
      store.setCommitFaultInjector(undefined)

      const reopened = new GenerationStore(storage)
      const openResult = await reopened.open()
      expect(openResult.rolledBackGenerations).toBe(0)
      expect(reopened.committedGeneration()).toBe(2)
      const kept = await storage.readNounRaw(ID_A)
      expect((kept.metadata as { version: number }).version).toBe(2)

      const manifest = await storage.readRawObject(MANIFEST_PATH)
      expect(manifest.generation).toBe(2)
    })
  })

  // ==========================================================================
  // Model-B single-op generation-stamping (per-write history + group-commit)
  // ==========================================================================
  describe('Model-B single-op generations', () => {
    /** Apply one single-op write as its own generation (live write + buffered history). */
    async function singleOpWrite(id: string, version: number): Promise<number> {
      const { generation } = await store.commitSingleOp({
        touched: { nouns: [id] },
        execute: async () => {
          await storage.saveNounMetadata(id, metadataFixture(version))
        }
      })
      return generation
    }

    it('each single-op write is its own generation, resolvable BEFORE any flush', async () => {
      const g1 = await singleOpWrite(ID_A, 1)
      const g2 = await singleOpWrite(ID_A, 2)
      expect(g1).toBe(1)
      expect(g2).toBe(2)
      // Counter advanced per write; nothing persisted to disk yet.
      expect(store.generation()).toBe(2)
      expect(store.committedGeneration()).toBe(0)
      // Reads resolve through the in-memory pending tier with NO forced flush:
      // the state as-of g1 is v1 (the before-image buffered by g2).
      const atG1 = await store.resolveAt('noun', ID_A, g1)
      expect(atG1.source).toBe('record')
      expect(((atG1 as { metadata: { version: number } }).metadata).version).toBe(1)
      // hasCommittedAfter counts pending → a now()-style pin at g1 is historical.
      expect(store.hasCommittedAfter(g1)).toBe(true)
    })

    it('range queries (changedBetween / generationsTouching) include un-flushed pending generations', async () => {
      // Two single-op writes to different ids, NEITHER flushed (still in the
      // pending tier). diff()/since()/history() are built on these, so they must
      // see un-flushed single-ops with NO forced flush.
      const g1 = await singleOpWrite(ID_A, 1)
      const g2 = await singleOpWrite(ID_B, 1)
      expect(store.committedGeneration()).toBe(0) // nothing on disk yet

      const changed = await store.changedBetween(0, store.generation())
      expect(changed.nouns).toEqual([ID_A, ID_B]) // resolves over committed ∪ pending
      expect(await store.generationsTouching('noun', ID_A, 0, store.generation())).toEqual([g1])
      expect(await store.generationsTouching('noun', ID_B, 0, store.generation())).toEqual([g2])

      // …and the range stays identical across the flush (now reading from disk).
      await store.flushPendingSingleOps()
      expect((await store.changedBetween(0, store.generation())).nouns).toEqual([ID_A, ID_B])
    })

    it('flush persists pending single-op generations (groupCommit-marked) and advances committed', async () => {
      await singleOpWrite(ID_A, 1)
      await singleOpWrite(ID_A, 2)
      await store.flushPendingSingleOps()
      expect(store.committedGeneration()).toBe(2)
      const delta = await storage.readRawObject(`${GENERATIONS_PREFIX}/2/tx.json`)
      expect(delta.groupCommit).toBe(true)
      expect(typeof delta.bytes).toBe('number')
      // asOf resolution survives the flush (now reading before-images from disk).
      const atG1 = await store.resolveAt('noun', ID_A, 1)
      expect(((atG1 as { metadata: { version: number } }).metadata).version).toBe(1)
    })

    it('🛑 a crash mid group-commit flush DROPS the generation WITHOUT reverting the live write', async () => {
      // gen 1: X = v1, flushed (durable).
      await singleOpWrite(ID_A, 1)
      await store.flushPendingSingleOps()
      expect(store.committedGeneration()).toBe(1)

      // gen 2: X = v2 acknowledged to canonical storage; its history is buffered.
      await singleOpWrite(ID_A, 2)
      expect((await storage.readNounRaw(ID_A)).metadata).toMatchObject({ version: 2 })

      // Crash before the manifest rename of the group-commit flush: the gen-2
      // dir (before-image v1) lands on disk; the manifest stays at gen 1.
      store.setCommitFaultInjector((phase) => {
        if (phase === 'before-manifest-rename') throw new Error('simulated crash mid-flush')
      })
      await expect(store.flushPendingSingleOps()).rejects.toThrow('simulated crash mid-flush')
      store.setCommitFaultInjector(undefined)
      expect(await storage.readRawObject(`${GENERATIONS_PREFIX}/2/tx.json`)).not.toBeNull()
      expect((await storage.readRawObject(MANIFEST_PATH)).generation).toBe(1)

      // Recover on a FRESH store (process restart: in-memory pending is gone).
      const reopened = new GenerationStore(storage)
      const result = await reopened.open()
      expect(result.rolledBackGenerations).toBe(1)
      expect(reopened.committedGeneration()).toBe(1)

      // THE CORRUPTION TRAP: drop-without-restore — the acknowledged live write
      // (v2) is NOT reverted to the before-image (v1). Only the crashed flush
      // window's HISTORY is lost; live data stays correct.
      expect((await storage.readNounRaw(ID_A)).metadata).toMatchObject({ version: 2 })
      // The orphan dir is gone and the dropped generation number is never reissued.
      expect(await storage.readRawObject(`${GENERATIONS_PREFIX}/2/tx.json`)).toBeNull()
      expect(reopened.generation()).toBeGreaterThanOrEqual(2)
    })

    it('a clean reopen replays committed single-op history (asOf survives restart)', async () => {
      await singleOpWrite(ID_A, 1)
      await singleOpWrite(ID_A, 2)
      await store.flushPendingSingleOps()

      const reopened = new GenerationStore(storage)
      await reopened.open()
      expect(reopened.committedGeneration()).toBe(2)
      const atG1 = await reopened.resolveAt('noun', ID_A, 1)
      expect(((atG1 as { metadata: { version: number } }).metadata).version).toBe(1)
    })
  })

  // ==========================================================================
  // Retention CAPS (Model-B `retention` knob)
  // ==========================================================================
  describe('retention caps', () => {
    async function manyGens(n: number): Promise<void> {
      for (let v = 1; v <= n; v++) await commitWrite(ID_A, v)
    }

    it('maxBytes reclaims the oldest generations until total history fits the budget', async () => {
      await manyGens(5)
      const total = await store.historyBytes()
      expect(total).toBeGreaterThan(0)
      const perGen = total / 5
      const budget = Math.floor(perGen * 2.5)
      const result = await store.compact({ maxBytes: budget })
      expect(result.removedGenerations).toBeGreaterThan(0)
      expect(await store.historyBytes()).toBeLessThanOrEqual(budget)
    })

    it('maxAge keeps generations within the window and reclaims older ones', async () => {
      await manyGens(3)
      // A wide window keeps everything.
      expect((await store.compact({ maxAge: 60_000 })).removedGenerations).toBe(0)
      // Advance the clock 10s past the commits, then a 1s window reclaims all
      // three (fake timers make the age comparison deterministic).
      vi.useFakeTimers()
      try {
        vi.setSystemTime(Date.now() + 10_000)
        expect((await store.compact({ maxAge: 1_000 })).removedGenerations).toBe(3)
      } finally {
        vi.useRealTimers()
      }
    })

    it('no caps reclaims every unpinned generation; a pin protects newer ones', async () => {
      await manyGens(3)
      store.pin(2) // protects generations > 2 (i.e. gen 3) from reclamation
      const result = await store.compact()
      // gens 1 and 2 are ≤ the pin → reclaimable; gen 3 is pin-protected.
      expect(result.removedGenerations).toBe(2)
      store.release(2)
    })

    it('timeBudgetMs bounds a pass; the next pass resumes the same prefix', async () => {
      await manyGens(4)
      // A spent budget (0ms) stops before reclaiming anything — an early stop
      // is a consistent prefix, never a partial generation.
      const bounded = await store.compact({ timeBudgetMs: 0 })
      expect(bounded.removedGenerations).toBe(0)
      expect(bounded.horizon).toBe(0)
      // The next (unbounded) pass picks up exactly where the bounded one
      // stopped and completes the same work.
      const resumed = await store.compact()
      expect(resumed.removedGenerations).toBe(4)
      expect(resumed.horizon).toBe(4)
    })
  })

  // ==========================================================================
  describe('history-bytes running total (the O(1) retention check)', () => {
    /** A fresh walk with the cache dropped — ground truth for the invariant. */
    async function groundTruthBytes(): Promise<number> {
      ;(store as any).historyBytesTotal = null
      return store.historyBytes()
    }

    it('is seeded once, then maintained through commits WITHOUT re-walks', async () => {
      await commitWrite(ID_A, 1)
      await commitWrite(ID_A, 2)
      const seeded = await store.historyBytes()
      expect(seeded).toBe(await groundTruthBytes())

      // From here every read must come from the running total, not a walk:
      // getDelta re-reads are the walk's cost — commits must not trigger any.
      const getDeltaSpy = vi.spyOn(store as any, 'getDelta')
      await commitWrite(ID_B, 1)
      const afterCommit = await store.historyBytes()
      expect(getDeltaSpy).not.toHaveBeenCalled()
      getDeltaSpy.mockRestore()
      expect(afterCommit).toBe(await groundTruthBytes())
    })

    it('stays exact through single-op group commits and compaction', async () => {
      await commitWrite(ID_A, 1)
      await store.historyBytes() // seed
      // Single-op path: buffered generations flushed as one group commit.
      await store.commitSingleOp({
        touched: { nouns: [ID_B] },
        execute: async () => {
          await storage.saveNounMetadata(ID_B, metadataFixture(1))
        }
      })
      await store.flushPendingSingleOps()
      expect(await store.historyBytes()).toBe(await groundTruthBytes())

      await store.historyBytes() // re-seed after ground-truth reset
      await store.compact({ maxGenerations: 1 })
      expect(await store.historyBytes()).toBe(await groundTruthBytes())
    })

    it('historyStats reports counts, bytes, range, and horizon read-only', async () => {
      await commitWrite(ID_A, 1)
      await commitWrite(ID_B, 1)
      const stats = await store.historyStats()
      expect(stats.generations).toBe(2)
      expect(stats.bytes).toBe(await store.historyBytes())
      expect(stats.oldestGeneration).toBe(1)
      expect(stats.newestGeneration).toBe(2)
      expect(stats.oldestTimestamp).toBeLessThanOrEqual(stats.newestTimestamp!)
      expect(stats.horizon).toBe(0)
      // Read-only: nothing was reclaimed by asking.
      expect(store.committedGeneration()).toBe(2)

      await store.compact({ maxGenerations: 1 })
      const after = await store.historyStats()
      expect(after.generations).toBe(1)
      expect(after.oldestGeneration).toBe(2)
      expect(after.horizon).toBe(1)
    })

    it('empty history reports null range and zero bytes', async () => {
      const stats = await store.historyStats()
      expect(stats).toMatchObject({
        generations: 0,
        bytes: 0,
        oldestGeneration: null,
        newestGeneration: null,
        oldestTimestamp: null,
        newestTimestamp: null,
        horizon: 0
      })
    })
  })
})