import { ghExecFileAsync } from './gh-utils'
import { noteRepositoryRateLimitSpend, repositoryRateLimitGuard } from './rate-limit'
import { githubHostExecOptions } from './github-api-repository'
import { githubRepoIdentityKey } from '../../shared/github/repository-identity-key'
import type { OwnerRepo } from './github-repository-identity'

type GhExecOptions = Parameters<typeof ghExecFileAsync>[1]

// Why: a merged PR's commit set is immutable, so definitive answers — member
// or not — never change; that TTL only bounds memory. Errors (a commit not on
// GitHub yet, network) get a short TTL so a future push can flip the answer
// without the checks-panel poll re-probing every cycle.
const MEMBERSHIP_CACHE_MAX_ENTRIES = 200
const MEMBERSHIP_DEFINITIVE_TTL_MS = 6 * 60 * 60 * 1000
const MEMBERSHIP_ERROR_TTL_MS = 5 * 60 * 1000
const COMMIT_PULLS_PAGE_SIZE = 100
// Why: a worktree HEAD is associated with ~1 PR, so page 1 is short in practice
// and this cap is never reached; it only bounds the pathological case of a commit
// linked to hundreds of PRs, where staying 'unknown' is the safe answer.
const COMMIT_PULLS_MAX_PAGES = 5

export type MergedPRCommitMembership = 'contained' | 'not-contained' | 'unknown'

const membershipCache = new Map<string, { value: MergedPRCommitMembership; expiresAt: number }>()

function pruneMergedPRCommitMembershipCache(now = Date.now()): void {
  for (const [cacheKey, cached] of membershipCache) {
    if (cached.expiresAt <= now) {
      membershipCache.delete(cacheKey)
    }
  }
  while (membershipCache.size > MEMBERSHIP_CACHE_MAX_ENTRIES) {
    const oldestKey = membershipCache.keys().next().value
    if (oldestKey === undefined) {
      break
    }
    membershipCache.delete(oldestKey)
  }
}

export function resetMergedPRCommitMembershipCacheForTest(): void {
  membershipCache.clear()
}

/**
 * Whether `commitOid` is part of pull request `prNumber` on GitHub — i.e. the
 * commit belongs to that PR's history rather than merely sharing a branch name.
 * A worktree sitting on such a commit is on the PR's own line of work (for
 * example behind web-committed suggestions or an update-branch merge), not a
 * reused branch name. Conservative on any failure: returns unknown.
 */
export async function isCommitPartOfMergedPR(args: {
  ownerRepo: OwnerRepo
  prNumber: number
  commitOid: string
  ghOptions: GhExecOptions
}): Promise<MergedPRCommitMembership> {
  const oid = args.commitOid.trim().toLowerCase()
  if (!/^[0-9a-f]{4,64}$/.test(oid) || !Number.isInteger(args.prNumber)) {
    return 'unknown'
  }
  const owner = args.ownerRepo.owner
  const repo = args.ownerRepo.repo
  const cacheKey = `${githubRepoIdentityKey(args.ownerRepo)}#${args.prNumber}@${oid}`
  const ghOptions = { ...args.ghOptions, ...githubHostExecOptions(args.ownerRepo) }
  const now = Date.now()
  pruneMergedPRCommitMembershipCache(now)
  const cached = membershipCache.get(cacheKey)
  if (cached && cached.expiresAt > now) {
    return cached.value
  }
  // Why blocked stays unknown: hiding a transient branch match is safe, but
  // callers must not clear a durable linked PR when the probe never ran.
  if (repositoryRateLimitGuard(args.ownerRepo, 'core', ghOptions).blocked) {
    return 'unknown'
  }
  try {
    // Why paginate: a full page that omits the target PR may just be truncated (a
    // commit can belong to many PRs). Reading only page 1 and calling it
    // 'not-contained' would wrongly clear a durable link; calling it 'unknown'
    // would never clear one that genuinely diverged. Walk pages until the PR is
    // found (contained) or a short page proves absence (not-contained); only the
    // pathological all-full case up to the cap stays 'unknown'.
    for (let page = 1; page <= COMMIT_PULLS_MAX_PAGES; page += 1) {
      if (page > 1 && repositoryRateLimitGuard(args.ownerRepo, 'core', ghOptions).blocked) {
        membershipCache.set(cacheKey, {
          value: 'unknown',
          expiresAt: now + MEMBERSHIP_ERROR_TTL_MS
        })
        return 'unknown'
      }
      noteRepositoryRateLimitSpend(args.ownerRepo, 'core', 1, ghOptions)
      const { stdout } = await ghExecFileAsync(
        [
          'api',
          `repos/${owner}/${repo}/commits/${oid}/pulls?per_page=${COMMIT_PULLS_PAGE_SIZE}&page=${page}`
        ],
        ghOptions
      )
      const parsed = JSON.parse(stdout) as unknown
      // Why: a non-array success payload is a shape mismatch, not an empty page;
      // caching it as definitive not-contained could wrongly clear a durable link.
      if (!Array.isArray(parsed)) {
        membershipCache.set(cacheKey, {
          value: 'unknown',
          expiresAt: now + MEMBERSHIP_ERROR_TTL_MS
        })
        return 'unknown'
      }
      const entries = parsed
      const contained = entries.some(
        (entry) =>
          typeof entry === 'object' &&
          entry !== null &&
          (entry as { number?: unknown }).number === args.prNumber
      )
      if (contained) {
        membershipCache.set(cacheKey, {
          value: 'contained',
          expiresAt: now + MEMBERSHIP_DEFINITIVE_TTL_MS
        })
        return 'contained'
      }
      if (entries.length < COMMIT_PULLS_PAGE_SIZE) {
        membershipCache.set(cacheKey, {
          value: 'not-contained',
          expiresAt: now + MEMBERSHIP_DEFINITIVE_TTL_MS
        })
        return 'not-contained'
      }
    }
    membershipCache.set(cacheKey, {
      value: 'unknown',
      expiresAt: now + MEMBERSHIP_ERROR_TTL_MS
    })
    return 'unknown'
  } catch {
    // Why: 422 often means "new local work" today, but a later push can make
    // the answer knowable; preserve durable links until a probe succeeds.
    membershipCache.set(cacheKey, {
      value: 'unknown',
      expiresAt: now + MEMBERSHIP_ERROR_TTL_MS
    })
    return 'unknown'
  }
}