// lib/validators/intent-approval.mjs
// Intent approval marker — the gate /trekplan passes before it plans anything.
//
// A brief carries two optional frontmatter fields once the operator has
// approved its intent in /trekbrief (Phase 4h, or `/trekbrief --approve`):
//
//   intent_approved_hash: "sha256:<64 hex>"   hash over ## Intent + ## Goal
//   intent_approved_at:   "<ISO-8601>"        when the stamp was written
//
// The hash binds the approval to the EXACT intent text: each section is
// normalized (lines trimmed, whitespace runs collapsed, blank lines dropped)
// and the pair is hashed. Reflowing a paragraph keeps the approval; changing
// a word in ## Intent or ## Goal after approval makes it stale, and /trekplan
// stops until the operator approves the new text.
//
// WHAT THE MARKER DOES NOT PROVE. Same user, same machine: any session with
// write access to the brief can run `--stamp` itself, or write the two fields
// by hand. The marker is a TRACE that the approval step ran against this text,
// NOT a signature binding a person — the same limit as the order queue's
// `--from`. It catches drift (intent edited after approval) and omission (no
// approval step at all); it does not catch a session that approves on the
// operator's behalf.
//
// trekreview briefs are exempt: they are produced from a review of an already
// planned brief and carry no ## Intent of their own.
//
// CLI:
//   node lib/validators/intent-approval.mjs --check [--json] <brief.md>
//     exit 0 = approved and current; exit 1 = stop (errors); exit 2 = usage
//   node lib/validators/intent-approval.mjs --stamp <brief.md>
//     writes the marker and emits `brief-approved`; exit 0 stamped, 1 refused
//   node lib/validators/intent-approval.mjs --resolve <project-dir | brief-file>
//     what `/trekbrief --approve` approves: {brief_path, project_dir, plan_command}; exit 1 = no brief

import { createHash } from 'node:crypto';
import { existsSync, readFileSync, renameSync, statSync, writeFileSync } from 'node:fs';
import { basename, dirname, join } from 'node:path';
import { parseDocument } from '../util/frontmatter.mjs';
import { issue } from '../util/result.mjs';
import { emit } from '../stats/event-emit.mjs';
import { resolveStatsDir } from '../stats/stats-append.mjs';

export const INTENT_HASH_FIELD = 'intent_approved_hash';
export const INTENT_APPROVED_AT_FIELD = 'intent_approved_at';
export const INTENT_SECTIONS = Object.freeze(['Intent', 'Goal']);
const HASH_RE = /^sha256:[0-9a-f]{64}$/;
const STATS_FILENAME = 'trekexecute-stats.jsonl'; // where event-emit writes lifecycle events

const APPROVE_HINT = 'Run /trekbrief --approve <project-dir | brief-file> — the operator reads ## Intent + ## Goal and answers "Approve".';

/**
 * Line indexes of the `## ` headings that are real headings: a `## ` line
 * inside a fenced code block or an HTML comment is text, not a heading. Seeing
 * it as one let an example `## Intent` capture the hash, or cut the real
 * section short (M1).
 */
function headingLines(lines) {
  const out = [];
  let fence = null; // { ch, len } of the open fence
  let inComment = false;
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    if (fence) {
      const close = /^ {0,3}(`{3,}|~{3,})\s*$/.exec(line);
      if (close && close[1][0] === fence.ch && close[1].length >= fence.len) fence = null;
      continue;
    }
    if (inComment) {
      if (line.includes('-->')) inComment = false;
      continue;
    }
    const open = /^ {0,3}(`{3,}|~{3,})/.exec(line);
    if (open) { fence = { ch: open[1][0], len: open[1].length }; continue; }
    if (/^##\s/.test(line)) out.push(i);
    const c = line.lastIndexOf('<!--');
    if (c >= 0 && line.indexOf('-->', c + 4) < 0) inComment = true;
  }
  return out;
}

/** Every `## <heading>` section's text (one entry per occurrence). */
function extractSections(lines, heads, heading) {
  const re = new RegExp(`^##\\s+${heading}\\b`);
  return heads.filter((i) => re.test(lines[i])).map((i) => {
    const next = heads.find((j) => j > i);
    return lines.slice(i + 1, next === undefined ? lines.length : next).join('\n');
  });
}

function normalize(text) {
  return text.split(/\r?\n/)
    .map((l) => l.trim().replace(/\s+/g, ' '))
    .filter(Boolean)
    .join('\n');
}

/**
 * Hash ## Intent + ## Goal of a brief body.
 * @returns {{ hash: string|null, missing: string[], duplicate: string[] }} hash is null when a
 *   section is absent or empty, or appears more than once (which one would the approval cover?).
 */
export function computeIntentHash(body) {
  const lines = (body || '').split('\n');
  const heads = headingLines(lines);
  const parts = [];
  const missing = [];
  const duplicate = [];
  for (const h of INTENT_SECTIONS) {
    const found = extractSections(lines, heads, h);
    if (found.length > 1) duplicate.push(h);
    const n = found.length === 1 ? normalize(found[0]) : '';
    if (!n && found.length <= 1) missing.push(h);
    parts.push(n);
  }
  if (missing.length || duplicate.length) return { hash: null, missing, duplicate };
  const hex = createHash('sha256').update(JSON.stringify(parts), 'utf8').digest('hex');
  return { hash: `sha256:${hex}`, missing, duplicate };
}

/** Why the approval cannot bind, in words. */
function unbindable({ missing, duplicate }) {
  const why = [];
  if (duplicate.length) why.push(`## ${duplicate.join(' and ## ')} appears more than once`);
  if (missing.length) why.push(`## ${missing.join(' and ## ')} is missing or empty`);
  return why.join('; ');
}

/** Check the approval marker of a brief's text. Returns a validator Result. */
export function checkIntentApprovalContent(text) {
  const doc = parseDocument(text);
  if (!doc.valid) return doc;
  const fm = doc.parsed.frontmatter || {};
  const body = doc.parsed.body || '';
  const errors = [];
  const result = () => ({ valid: errors.length === 0, errors, warnings: [], parsed: { frontmatter: fm } });

  if (fm.type === 'trekreview') return result();

  if (!(INTENT_HASH_FIELD in fm)) {
    errors.push(issue(
      'BRIEF_INTENT_NOT_APPROVED',
      'The brief\'s intent has not been approved — /trekplan does not plan against an unapproved intent.',
      APPROVE_HINT,
    ));
    return result();
  }
  const recorded = String(fm[INTENT_HASH_FIELD]);
  if (!HASH_RE.test(recorded)) {
    errors.push(issue(
      'BRIEF_INTENT_APPROVAL_INVALID',
      `${INTENT_HASH_FIELD} "${recorded}" is not "sha256:<64 hex>" — the marker is malformed.`,
      APPROVE_HINT,
    ));
    return result();
  }
  const bound = computeIntentHash(body);
  const { hash } = bound;
  if (!hash) {
    errors.push(issue(
      'BRIEF_INTENT_APPROVAL_INVALID',
      `The approval cannot bind: ${unbindable(bound)}.`,
      'Leave exactly one non-empty ## Intent and one ## Goal, then ' + APPROVE_HINT,
    ));
    return result();
  }
  if (hash !== recorded) {
    errors.push(issue(
      'BRIEF_INTENT_APPROVAL_STALE',
      '## Intent or ## Goal changed after the intent was approved — the approval covers the old text, not this one.',
      APPROVE_HINT,
    ));
  }
  return result();
}

/**
 * Write the approval marker into a brief's frontmatter (replacing any prior one).
 * @returns {{ stamped: boolean, text: string, hash?: string, approvedAt?: string, reason?: string }}
 */
export function stampIntentApproval(text, now = new Date()) {
  const doc = parseDocument(text);
  if (!doc.valid) return { stamped: false, text, reason: 'frontmatter does not parse' };
  const bound = computeIntentHash(doc.parsed.body || '');
  const { hash } = bound;
  if (!hash) return { stamped: false, text, reason: unbindable(bound) };
  const m = /^(?---\r?\n)([\s\S]*?)(\r?\n---)/.exec(text);
  if (!m) return { stamped: false, text, reason: 'no frontmatter block' };
  const approvedAt = now.toISOString();
  const kept = m[2].split(/\r?\n/).filter((l) =>
    !l.startsWith(`${INTENT_HASH_FIELD}:`) && !l.startsWith(`${INTENT_APPROVED_AT_FIELD}:`));
  kept.push(`${INTENT_HASH_FIELD}: "${hash}"`, `${INTENT_APPROVED_AT_FIELD}: "${approvedAt}"`);
  const out = m[1] + kept.join('\n') + m[3] + text.slice(m.index + m[0].length);
  return { stamped: true, text: out, hash, approvedAt };
}

/**
 * Where the brief-approved record goes. CLAUDE_PLUGIN_DATA when the harness
 * provides it; otherwise the plugin data dir the hooks write to and
 * scripts/yardstick.mjs reads — the Bash tool env carries no CLAUDE_PLUGIN_DATA,
 * and event-emit's own fallback is a silent skip, which is how brief-approved
 * reached 0 records. One resolver for every stats writer: lib/stats/stats-append.mjs.
 */
export function resolveApprovalDataDir(env = process.env) {
  return resolveStatsDir(env);
}

/**
 * What `/trekbrief --approve <arg>` approves. A directory means `<dir>/brief.md`
 * (a /trekplan --project brief); a file is itself (a /trekplan --brief brief,
 * whatever its name). Before M2 only `<dir>/brief.md` was reachable.
 * @returns {{ brief_path: string, project_dir: string, plan_command: string } | { error: string }}
 */
export function resolveApproveTarget(arg) {
  const target = String(arg || '').replace(/\/+$/, '');
  if (!target) return { error: 'no brief given — /trekbrief --approve <project-dir | brief-file>' };
  let isDir = false;
  try { isDir = statSync(target).isDirectory(); } catch { /* absent */ }
  const briefPath = isDir ? join(target, 'brief.md') : target;
  if (!existsSync(briefPath) || statSync(briefPath).isDirectory()) {
    return { error: `no brief at ${briefPath} — run /trekbrief first` };
  }
  const projectDir = dirname(briefPath);
  const planCommand = basename(briefPath) === 'brief.md'
    ? `/trekplan --project ${projectDir}`
    : `/trekplan --brief ${briefPath}`;
  return { brief_path: briefPath, project_dir: projectDir, plan_command: planCommand };
}

if (import.meta.url === `file://${process.argv[1]}`) {
  const args = process.argv.slice(2);
  const file = args.find((a) => !a.startsWith('--'));
  if (args.includes('--resolve')) {
    const r = resolveApproveTarget(file);
    process.stdout.write(JSON.stringify(r) + '\n');
    process.exit(r.error ? 1 : 0);
  }
  const mode = args.includes('--stamp') ? 'stamp' : args.includes('--check') ? 'check' : null;
  if (!file || !mode) {
    process.stderr.write('Usage: intent-approval.mjs --check [--json] <brief.md> | --stamp <brief.md> | --resolve <project-dir | brief-file>\n');
    process.exit(2);
  }
  let text = null;
  if (existsSync(file)) {
    try { text = readFileSync(file, 'utf8'); } catch { text = null; }
  }

  if (mode === 'check') {
    const r = text === null
      ? { valid: false, errors: [issue('BRIEF_NOT_FOUND', `Cannot read brief: ${file}`)], warnings: [] }
      : checkIntentApprovalContent(text);
    if (args.includes('--json')) {
      process.stdout.write(JSON.stringify({ valid: r.valid, errors: r.errors, warnings: r.warnings }, null, 2) + '\n');
    } else {
      process.stdout.write(`intent-approval: ${r.valid ? 'APPROVED' : 'STOP'} ${file}\n`);
      for (const e of r.errors) process.stderr.write(`  ERROR  [${e.code}] ${e.message}\n         ${e.hint || ''}\n`);
    }
    process.exit(r.valid ? 0 : 1);
  }

  // --stamp
  if (text === null) {
    process.stdout.write(JSON.stringify({ stamped: false, reason: `cannot read ${file}` }) + '\n');
    process.exit(1);
  }
  const s = stampIntentApproval(text);
  if (!s.stamped) {
    process.stdout.write(JSON.stringify({ stamped: false, reason: s.reason }) + '\n');
    process.exit(1);
  }
  const tmp = join(dirname(file), `.${basename(file)}.approve.tmp`);
  writeFileSync(tmp, s.text);
  renameSync(tmp, file);
  const fm = parseDocument(s.text).parsed.frontmatter || {};
  const record = emit('brief-approved',
    { project: dirname(file), slug: fm.slug ?? null, intent_hash: s.hash },
    { path: join(resolveApprovalDataDir(), STATS_FILENAME) });
  process.stdout.write(JSON.stringify({
    stamped: true, intent_hash: s.hash, approved_at: s.approvedAt, record,
  }) + '\n');
  process.exit(0);
}