/**
 * Multi-process safety + read-only mode integration tests.
 *
 * Covers the surface added in 7.21.0:
 *   - Brainy.openReadOnly() enforces ReaderMode on every mutation entry.
 *   - Two concurrent writers on the same filesystem directory: second throws.
 *   - { force: true } overrides a live writer lock.
 *   - Flush-request RPC: in-process shortcut + cross-process round-trip.
 *   - stats(), explain(), health() return useful diagnostics in read-only mode.
 *
 * Uses a temp directory per `describe` block so tests don't share state.
 */

import { describe, it, expect, beforeEach, afterEach } from 'vitest'
import { mkdtempSync, rmSync } from 'node:fs'
import { tmpdir } from 'node:os'
import { join } from 'node:path'
import { Brainy } from '../../src/brainy.js'
import { NounType } from '../../src/types/graphTypes.js'

function makeTempDir(): string {
  return mkdtempSync(join(tmpdir(), 'brainy-mp-'))
}

describe('Multi-process safety + read-only mode', () => {
  let dir: string
  let writer: Brainy | null = null
  let reader: Brainy | null = null

  beforeEach(() => {
    dir = makeTempDir()
  })

  afterEach(async () => {
    if (writer) {
      try { await writer.close() } catch { /* may already be closed */ }
      writer = null
    }
    if (reader) {
      try { await reader.close() } catch { /* may already be closed */ }
      reader = null
    }
    try { rmSync(dir, { recursive: true, force: true }) } catch { /* ignore */ }
  })

  describe('ReaderMode enforcement', () => {
    it('rejects every mutation when opened via openReadOnly()', async () => {
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()
      await writer.add({ data: 'seed entity', type: NounType.Concept })
      await writer.flush()
      await writer.close()
      writer = null

      reader = await Brainy.openReadOnly({
        storage: { type: 'filesystem', path: dir }
      })

      expect(reader.isReadOnly).toBe(true)
      await expect(reader.add({ data: 'x', type: NounType.Concept })).rejects.toThrow(/read-only/i)
      await expect(reader.addMany({ items: [] })).rejects.toThrow(/read-only/i)
      await expect(reader.update({ id: 'x', data: 'y' })).rejects.toThrow(/read-only/i)
      await expect(reader.remove('x')).rejects.toThrow(/read-only/i)
      await expect(reader.removeMany({ ids: ['x'] } as any)).rejects.toThrow(/read-only/i)
      await expect(reader.relate({ from: 'x', to: 'y' } as any)).rejects.toThrow(/read-only/i)
      await expect(reader.unrelate('x')).rejects.toThrow(/read-only/i)
    })

    it('flush() and close() are safe to call in read-only mode', async () => {
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()
      await writer.add({ data: 'thing', type: NounType.Concept })
      await writer.flush()
      await writer.close()
      writer = null

      reader = await Brainy.openReadOnly({
        storage: { type: 'filesystem', path: dir }
      })
      await expect(reader.flush()).resolves.toBeUndefined()
      await expect(reader.close()).resolves.toBeUndefined()
      reader = null
    })
  })

  describe('Writer lock', () => {
    it('blocks a writer when a different live PID holds the directory', async () => {
      // Simulate a cross-process lock holder by writing the lock file by hand
      // with a real PID that is not ours. Node itself (PID 1 on most container
      // hosts is `init`; on dev hosts it's an existing process) is always
      // alive for the duration of this test.
      const { mkdirSync, writeFileSync } = await import('node:fs')
      const { join } = await import('node:path')
      const os = await import('node:os')
      mkdirSync(join(dir, 'locks'), { recursive: true })
      // Use a PID we know is alive but isn't ours: the parent of our own
      // process. On every Unix this is the shell or test runner.
      const otherPid = (process as any).ppid || 1
      writeFileSync(join(dir, 'locks', '_writer.lock'), JSON.stringify({
        pid: otherPid,
        hostname: os.hostname(),
        startedAt: new Date().toISOString(),
        lastHeartbeat: new Date().toISOString(),
        version: '7.21.0',
        rootDir: dir
      }))

      const blocked = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await expect(blocked.init()).rejects.toThrow(/another writer holds/i)
      // Don't track `blocked` for afterEach cleanup since init failed.
    })

    it('takes over a STALE foreign lock (dead PID + old heartbeat) and claims atomically', async () => {
      const { mkdirSync, writeFileSync, readFileSync } = await import('node:fs')
      const { join } = await import('node:path')
      const os = await import('node:os')
      mkdirSync(join(dir, 'locks'), { recursive: true })
      const tenMinutesAgo = new Date(Date.now() - 10 * 60 * 1000).toISOString()
      writeFileSync(join(dir, 'locks', '_writer.lock'), JSON.stringify({
        pid: 999999999, // no such process — provably dead
        hostname: os.hostname(),
        startedAt: tenMinutesAgo,
        lastHeartbeat: tenMinutesAgo,
        version: '8.0.0',
        rootDir: dir
      }))

      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init() // stale takeover must succeed

      const lock = JSON.parse(readFileSync(join(dir, 'locks', '_writer.lock'), 'utf-8'))
      expect(lock.pid).toBe(process.pid) // the atomic wx claim installed OUR lock
    })

    it('the writer-locked error carries the machine-readable contract (code + lockInfo)', async () => {
      const { mkdirSync, writeFileSync } = await import('node:fs')
      const { join } = await import('node:path')
      const os = await import('node:os')
      mkdirSync(join(dir, 'locks'), { recursive: true })
      const otherPid = (process as any).ppid || 1
      writeFileSync(join(dir, 'locks', '_writer.lock'), JSON.stringify({
        pid: otherPid,
        hostname: os.hostname(),
        startedAt: new Date().toISOString(),
        lastHeartbeat: new Date().toISOString(),
        version: '8.7.0',
        rootDir: dir
      }))

      const blocked = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      const err: any = await blocked.init().catch((e) => e)
      expect(err.code).toBe('BRAINY_WRITER_LOCKED')
      expect(err.lockInfo?.pid).toBe(otherPid)
    })

    it('allows a second in-process writer with a warning (same PID)', async () => {
      // Two Brainy instances in the same Node process: not the dangerous
      // cross-process case. Should succeed (with a console warning).
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()

      const second = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await expect(second.init()).resolves.toBeUndefined()
      await second.close()
    })

    it('lets a reader open while a writer is live', async () => {
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()
      await writer.add({ data: 'concurrent', type: NounType.Concept })
      await writer.flush()

      reader = await Brainy.openReadOnly({
        storage: { type: 'filesystem', path: dir }
      })
      const stats = await reader.stats()
      expect(stats.mode).toBe('reader')
      expect(stats.writerLock).toBeDefined()
      expect(stats.writerLock!.pid).toBe(process.pid)
    })

    it('honors { force: true } to override an existing lock', async () => {
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()

      const second = new Brainy({ requireSubtype: false,
        storage: { type: 'filesystem', path: dir },
        force: true
      })
      await expect(second.init()).resolves.toBeUndefined()
      await second.close()
    })
  })

  describe('Flush-request RPC', () => {
    it('in-process call just flushes', async () => {
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()
      const ok = await writer.requestFlush({ timeoutMs: 1000 })
      expect(ok).toBe(true)
    })

    it('cross-instance request reaches the writer (same-process simulation)', async () => {
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()
      await writer.add({ data: 'pre-request', type: NounType.Concept })

      // openReadOnly() in the same Node process — the storage will still hit
      // the writer's flush watcher via the shared filesystem.
      reader = await Brainy.openReadOnly({
        storage: { type: 'filesystem', path: dir }
      })
      const acked = await reader.requestFlush({ timeoutMs: 3000 })
      expect(acked).toBe(true)
    })

    it('returns false when no writer is running', async () => {
      // Seed some data, then close the writer. The data dir exists but no
      // writer is listening for flush requests.
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()
      await writer.add({ data: 'orphan', type: NounType.Concept })
      await writer.flush()
      await writer.close()
      writer = null

      reader = await Brainy.openReadOnly({
        storage: { type: 'filesystem', path: dir }
      })
      const acked = await reader.requestFlush({ timeoutMs: 1500 })
      expect(acked).toBe(false)
    })
  })

  describe('Diagnostics on a reader', () => {
    beforeEach(async () => {
      writer = new Brainy({ requireSubtype: false, storage: { type: 'filesystem', path: dir } })
      await writer.init()
      await writer.add({ data: 'one', type: NounType.Concept, metadata: { tag: 'a' } })
      await writer.add({ data: 'two', type: NounType.Concept, metadata: { tag: 'b' } })
      await writer.flush()
    })

    it('stats() reports counts, mode, and writer lock metadata', async () => {
      reader = await Brainy.openReadOnly({
        storage: { type: 'filesystem', path: dir }
      })
      const stats = await reader.stats()
      expect(stats.mode).toBe('reader')
      // Both Concept entities the writer added should be visible to the
      // reader, classified correctly as 'concept' (not 'thing'). This is
      // the BR-FIND-WHERE-ZERO regression test: stats() must read from the
      // column store via idMapper.size, and getNounType() must use the
      // write-time type cache instead of the old hardcoded 'thing'.
      expect(stats.entityCount).toBeGreaterThanOrEqual(2)
      expect(stats.entitiesByType.concept).toBeGreaterThanOrEqual(2)
      expect(stats.writerLock).toBeDefined()
      expect(stats.writerLock!.pid).toBe(process.pid)
      expect(stats.version).toBeTruthy()
    })

    it('explain() flags a field with no index entries', async () => {
      reader = await Brainy.openReadOnly({
        storage: { type: 'filesystem', path: dir }
      })
      const plan = await reader.explain({ where: { entityTypeXYZ: 'never-registered' } })
      expect(plan.fieldPlan).toHaveLength(1)
      expect(plan.fieldPlan[0].path).toBe('none')
      expect(plan.warnings.length).toBeGreaterThan(0)
    })

    it('health() returns checks with a pass/warn/fail overall', async () => {
      reader = await Brainy.openReadOnly({
        storage: { type: 'filesystem', path: dir }
      })
      const report = await reader.health()
      expect(report.checks.length).toBeGreaterThan(0)
      expect(['pass', 'warn', 'fail']).toContain(report.overall)
    })
  })
})