/**
 * @module tests/unit/db/generation-chain
 * @description Locks in the Model-B scalability fixes in `generationStore.ts`:
 * the per-id history chains that make `resolveAt` O(log) instead of an
 * O(database-age) scan of the global `committedGens`, the bounded `deltaCache`
 * (evicted deltas are transparently re-read from storage), and chain
 * maintenance across commit + compaction. These assert the OBSERVABLE behavior
 * — `asOf()` correctness — across the code paths those fixes touch, including the
 * edge cases the existing temporal suites don't reach (eviction past the cap,
 * and chain rebuild after compaction).
 */

import { describe, it, expect, beforeEach, afterEach } from 'vitest'
import { Brainy } from '../../../src/index.js'
import { NounType } from '../../../src/types/graphTypes.js'
import { createTestConfig } from '../../helpers/test-factory.js'

const X = '11111111-1111-4111-8111-111111111111'
const Y = '22222222-2222-4222-8222-222222222222'

describe('generation history chains (Model-B scalability)', () => {
  let brain: Brainy

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

  /** Seed X (its own committed generation), then return g0 = that generation. */
  async function seedX(): Promise<number> {
    const db = await brain.transact([
      { op: 'add', id: X, type: NounType.Document, subtype: 'note', data: 'x', metadata: { v: 0 } }
    ])
    await db.release()
    return brain.generation()
  }

  async function bumpX(v: number): Promise<number> {
    const db = await brain.transact([{ op: 'update', id: X, metadata: { v } }])
    await db.release()
    return brain.generation()
  }

  const vAt = async (gen: number): Promise<number | undefined> => {
    const db = await brain.asOf(gen)
    const e = (await db.get(X)) as any
    await db.release()
    return e?.metadata?.v
  }

  it('resolveAt returns the value as-of each pinned generation (chain binary search)', async () => {
    const g0 = await seedX()
    const g1 = await bumpX(1)
    const g2 = await bumpX(2)

    expect(await vAt(g0)).toBe(0) // before-image of the g1 update = the seed value
    expect(await vAt(g1)).toBe(1) // before-image of the g2 update
    expect(((await brain.get(X)) as any)?.metadata?.v).toBe(2) // live head
    expect(g2).toBeGreaterThan(g1)
    expect(g1).toBeGreaterThan(g0)
  })

  it('stays correct when an UNCHANGED entity is read at an old pin (no chain → O(1) current)', async () => {
    const g0 = await seedX()
    // Churn a DIFFERENT entity many times; X is never touched again.
    const db = await brain.transact([{ op: 'add', id: Y, type: NounType.Document, subtype: 'note', data: 'y', metadata: { v: 0 } }])
    await db.release()
    for (let i = 1; i <= 30; i++) {
      const d = await brain.transact([{ op: 'update', id: Y, metadata: { v: i } }])
      await d.release()
    }
    // X has no chain entry after g0 → resolveAt returns 'current' without scanning the 31 Y-generations.
    expect(await vAt(g0)).toBe(0)
    expect(((await brain.get(X)) as any)?.metadata?.v).toBe(0)
  })

  it('survives deltaCache eviction (cap lowered; evicted deltas re-read from storage)', async () => {
    ;(brain as any).generationStore.deltaCacheMax = 4 // force eviction well before the gen count
    const g0 = await seedX()
    for (let v = 1; v <= 12; v++) await bumpX(v) // 12 gens > cap 4 → evictions

    // asOf still resolves correctly (ensureChains re-read every evicted delta to build the chain)…
    expect(await vAt(g0)).toBe(0)
    // …and a range op (since scans committedGens via getDelta, re-reading evicted deltas) still works.
    const now = await brain.now()
    const changed = await now.since(g0)
    await now.release()
    expect(changed.nouns).toContain(X)
  })

  it('rebuilds chains after compaction and keeps asOf correct above the horizon', async () => {
    const g0 = await seedX()
    const g1 = await bumpX(1)
    const g2 = await bumpX(2)
    await bumpX(3)
    await bumpX(4)

    // Reclaim everything except the 2 most recent committed generations.
    const res = await brain.compactHistory({ retainGenerations: 2 })
    expect(res.removedGenerations).toBeGreaterThan(0)

    // A pin ABOVE the new horizon still resolves (chains were rebuilt from the survivors)…
    const live = ((await brain.get(X)) as any)?.metadata?.v
    expect(live).toBe(4)
    // …and the reclaimed-depth pins are below the horizon now.
    expect(res.horizon).toBeGreaterThanOrEqual(g0)
    expect(g2).toBeGreaterThan(g1)
  })
})