name: close-stale-prs

on:
  workflow_dispatch:
    inputs:
      dryRun:
        description: "Log actions without closing PRs"
        type: boolean
        default: false
  schedule:
    - cron: "0 6 * * *"

permissions:
  contents: read
  issues: write
  pull-requests: write

jobs:
  close-stale-prs:
    runs-on: ubuntu-latest
    timeout-minutes: 15
    steps:
      - name: Close inactive PRs
        uses: actions/github-script@v8
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const DAYS_INACTIVE = 60
            const MAX_RETRIES = 3

            // Adaptive delay: fast for small batches, slower for large to respect
            // GitHub's 80 content-generating requests/minute limit
            const SMALL_BATCH_THRESHOLD = 10
            const SMALL_BATCH_DELAY_MS = 1000  // 1s for daily operations (≤10 PRs)
            const LARGE_BATCH_DELAY_MS = 2000  // 2s for backlog (>10 PRs) = ~30 ops/min, well under 80 limit

            const startTime = Date.now()
            const cutoff = new Date(Date.now() - DAYS_INACTIVE * 24 * 60 * 60 * 1000)
            const { owner, repo } = context.repo
            const dryRun = context.payload.inputs?.dryRun === "true"

            core.info(`Dry run mode: ${dryRun}`)
            core.info(`Cutoff date: ${cutoff.toISOString()}`)

            function sleep(ms) {
              return new Promise(resolve => setTimeout(resolve, ms))
            }

            async function withRetry(fn, description = 'API call') {
              let lastError
              for (let attempt = 0; attempt < MAX_RETRIES; attempt++) {
                try {
                  const result = await fn()
                  return result
                } catch (error) {
                  lastError = error
                  const isRateLimited = error.status === 403 &&
                    (error.message?.includes('rate limit') || error.message?.includes('secondary'))

                  if (!isRateLimited) {
                    throw error
                  }

                  // Parse retry-after header, default to 60 seconds
                  const retryAfter = error.response?.headers?.['retry-after']
                    ? parseInt(error.response.headers['retry-after'])
                    : 60

                  // Exponential backoff: retryAfter * 2^attempt
                  const backoffMs = retryAfter * 1000 * Math.pow(2, attempt)

                  core.warning(`${description}: Rate limited (attempt ${attempt + 1}/${MAX_RETRIES}). Waiting ${backoffMs / 1000}s before retry...`)

                  await sleep(backoffMs)
                }
              }
              core.error(`${description}: Max retries (${MAX_RETRIES}) exceeded`)
              throw lastError
            }

            const query = `
              query($owner: String!, $repo: String!, $cursor: String) {
                repository(owner: $owner, name: $repo) {
                  pullRequests(first: 100, states: OPEN, after: $cursor) {
                    pageInfo {
                      hasNextPage
                      endCursor
                    }
                    nodes {
                      number
                      title
                      author {
                        login
                      }
                      createdAt
                      commits(last: 1) {
                        nodes {
                          commit {
                            committedDate
                          }
                        }
                      }
                      comments(last: 1) {
                        nodes {
                          createdAt
                        }
                      }
                      reviews(last: 1) {
                        nodes {
                          createdAt
                        }
                      }
                    }
                  }
                }
              }
            `

            const allPrs = []
            let cursor = null
            let hasNextPage = true
            let pageCount = 0

            while (hasNextPage) {
              pageCount++
              core.info(`Fetching page ${pageCount} of open PRs...`)

              const result = await withRetry(
                () => github.graphql(query, { owner, repo, cursor }),
                `GraphQL page ${pageCount}`
              )

              allPrs.push(...result.repository.pullRequests.nodes)
              hasNextPage = result.repository.pullRequests.pageInfo.hasNextPage
              cursor = result.repository.pullRequests.pageInfo.endCursor

              core.info(`Page ${pageCount}: fetched ${result.repository.pullRequests.nodes.length} PRs (total: ${allPrs.length})`)

              // Delay between pagination requests (use small batch delay for reads)
              if (hasNextPage) {
                await sleep(SMALL_BATCH_DELAY_MS)
              }
            }

            core.info(`Found ${allPrs.length} open pull requests`)

            const stalePrs = allPrs.filter((pr) => {
              const dates = [
                new Date(pr.createdAt),
                pr.commits.nodes[0] ? new Date(pr.commits.nodes[0].commit.committedDate) : null,
                pr.comments.nodes[0] ? new Date(pr.comments.nodes[0].createdAt) : null,
                pr.reviews.nodes[0] ? new Date(pr.reviews.nodes[0].createdAt) : null,
              ].filter((d) => d !== null)

              const lastActivity = dates.sort((a, b) => b.getTime() - a.getTime())[0]

              if (!lastActivity || lastActivity > cutoff) {
                core.info(`PR #${pr.number} is fresh (last activity: ${lastActivity?.toISOString() || "unknown"})`)
                return false
              }

              core.info(`PR #${pr.number} is STALE (last activity: ${lastActivity.toISOString()})`)
              return true
            })

            if (!stalePrs.length) {
              core.info("No stale pull requests found.")
              return
            }

            core.info(`Found ${stalePrs.length} stale pull requests`)

            // ============================================
            // Close stale PRs
            // ============================================
            const requestDelayMs = stalePrs.length > SMALL_BATCH_THRESHOLD
              ? LARGE_BATCH_DELAY_MS
              : SMALL_BATCH_DELAY_MS

            core.info(`Using ${requestDelayMs}ms delay between operations (${stalePrs.length > SMALL_BATCH_THRESHOLD ? 'large' : 'small'} batch mode)`)

            let closedCount = 0
            let skippedCount = 0

            for (const pr of stalePrs) {
              const issue_number = pr.number
              const closeComment = `Closing this pull request because it has had no updates for more than ${DAYS_INACTIVE} days. If you plan to continue working on it, feel free to reopen or open a new PR.`

              if (dryRun) {
                core.info(`[dry-run] Would close PR #${issue_number} from ${pr.author?.login || 'unknown'}: ${pr.title}`)
                continue
              }

              try {
                // Add comment
                await withRetry(
                  () => github.rest.issues.createComment({
                    owner,
                    repo,
                    issue_number,
                    body: closeComment,
                  }),
                  `Comment on PR #${issue_number}`
                )

                // Close PR
                await withRetry(
                  () => github.rest.pulls.update({
                    owner,
                    repo,
                    pull_number: issue_number,
                    state: "closed",
                  }),
                  `Close PR #${issue_number}`
                )

                closedCount++
                core.info(`Closed PR #${issue_number} from ${pr.author?.login || 'unknown'}: ${pr.title}`)

                // Delay before processing next PR
                await sleep(requestDelayMs)
              } catch (error) {
                skippedCount++
                core.error(`Failed to close PR #${issue_number}: ${error.message}`)
              }
            }

            const elapsed = Math.round((Date.now() - startTime) / 1000)
            core.info(`\n========== Summary ==========`)
            core.info(`Total open PRs found: ${allPrs.length}`)
            core.info(`Stale PRs identified: ${stalePrs.length}`)
            core.info(`PRs closed: ${closedCount}`)
            core.info(`PRs skipped (errors): ${skippedCount}`)
            core.info(`Elapsed time: ${elapsed}s`)
            core.info(`=============================`)
