/**
 * Enforce RFC headers, lifecycle-specific sections, alternatives, and retired
 * marker rules. Classification and filenames belong to the sibling tree gate;
 * translation structure belongs to the pairing gate. Exact format and
 * grandfathering rules live in `docs/rfc/README.md`.
 */

import { readFileSync } from 'node:fs'
import { resolve } from 'node:path'
import { rfcRoot, walkRfcTree } from './rfc-index.ts'

/** The date the format contract landed; the grandfather comment is valid only before it. */
const FORMAT_ADOPTED = '2026-07-05'

/** The exact comment a pre-format RFC carries in place of `## Alternatives considered`. */
const GRANDFATHER = '<!-- rfc-format: alternatives-not-recorded (pre-format RFC) -->'

/** The retired debt marker that flagged pre-format bodies; banned so it cannot creep back. */
const LEGACY_MARKER = 'XXX: legacy ADR/RFC body format'

/** Status-line grammar per lifecycle folder. */
const STATUS: Record<string, RegExp> = {
  proposed: /^Status: proposed$/,
  implemented: /^Status: implemented$/,
  rejected: /^Status: rejected — .+$/,
}

/** Required `##` headings per lifecycle, beyond the universal `## Problem` opener. */
const REQUIRED: Record<string, string[]> = {
  proposed: ['## Proposal', '## Acceptance criteria', '## Risks'],
  implemented: ['## Decision', '## Consequences'],
  rejected: ['## Proposal'],
}

/** Headings banned in `implemented/` — proposal-era spec-speak per the slop checklist. */
const BANNED_IMPLEMENTED = /^## (?:Proposal\b|Plan\b|Migration plan\b|Acceptance criteria\b)/i

const { rfcs, errors } = walkRfcTree()

for (const rfc of rfcs) {
  const fail = (msg: string): void => {
    errors.push(`format: ${rfc.rel} — ${msg}`)
  }
  const lines = readFileSync(resolve(rfcRoot, rfc.rel), 'utf8').split('\n')
  // Format tokens inside fenced examples are not document structure.
  let inFence = false
  const prose = lines.filter((l) => {
    if (l.startsWith('```')) {
      inFence = !inFence
      return false
    }
    return !inFence
  })

  if (!/^# RFC: \S/.test(lines[0] ?? '')) fail('line 1 must be `# RFC: <title>`')
  if (lines[1] !== '') fail('line 2 must be blank')
  const status = STATUS[rfc.lifecycle]
  if (status !== undefined && !status.test(lines[2] ?? '')) {
    fail(`line 3 must match the ${rfc.lifecycle} status grammar (${String(status)})`)
  }
  if (lines[3] !== '') fail('line 4 must be blank')
  const statusLines = prose.filter(l => l.startsWith('Status:') && l !== lines[2])
  if (statusLines.length > 0 || prose.filter(l => l === lines[2]).length > 1) {
    fail('the line-3 `Status:` line must be the only one in the file')
  }

  const h2s = prose.filter(l => l.startsWith('## ')).map(l => l.trimEnd())
  if (h2s[0] !== '## Problem') fail(`the first section must be \`## Problem\` (got ${JSON.stringify(h2s[0] ?? '<none>')})`)
  for (const required of REQUIRED[rfc.lifecycle] ?? []) {
    if (!h2s.includes(required)) fail(`missing the required \`${required}\` section`)
  }
  if (rfc.lifecycle === 'implemented') {
    for (const h2 of h2s.filter(h => BANNED_IMPLEMENTED.test(h))) {
      fail(`\`${h2}\` is a proposal-era heading; an implemented RFC states what is (fold it into Decision/Consequences/Testing)`)
    }
  }

  const hasSection = h2s.includes('## Alternatives considered')
  const hasGrandfather = prose.includes(GRANDFATHER)
  if (hasSection && hasGrandfather) fail('carries both `## Alternatives considered` and the grandfather comment — drop the comment')
  if (!hasSection && !hasGrandfather) fail('missing `## Alternatives considered` (a pre-format RFC whose alternatives are not reconstructible carries the grandfather comment instead — see docs/rfc/README.md § The file format)')
  if (hasGrandfather && rfc.date >= FORMAT_ADOPTED) fail(`the grandfather comment is only valid for RFCs dated before ${FORMAT_ADOPTED}`)

  if (prose.some(l => l.includes(LEGACY_MARKER))) fail('carries the retired legacy-format debt marker')
}

if (errors.length === 0) {
  console.log(`verify-rfc-format: ${rfcs.length} RFC(s) checked, all conform to docs/rfc/README.md § The file format.`)
  process.exit(0)
}

console.error('verify-rfc-format: violations found:')
for (const e of errors) console.error(`  ${e}`)
process.exit(1)