#!/usr/bin/env node
// session-start-load-handoff.mjs — graceful-handoff v2.0
// SessionStart hook: on `source: resume` or `source: compact`, find
// NEXT-SESSION-PROMPT.local.md (or NEXT-SESSION-*.local.md) in cwd and up
// to 3 levels above, inject contents into the new session's context, then
// archive the file to prevent stale-load in subsequent sessions.

import { readFileSync, existsSync, readdirSync, renameSync } from 'node:fs';
import { dirname, join } from 'node:path';

function readStdin() {
  try {
    return readFileSync(0, 'utf-8');
  } catch {
    return '';
  }
}

// Find NEXT-SESSION-*.local.md in dir; returns path or null
function findHandoffIn(dir) {
  try {
    const entries = readdirSync(dir);
    // Prefer NEXT-SESSION-PROMPT.local.md, then any NEXT-SESSION-*.local.md
    const exact = entries.find(e => e === 'NEXT-SESSION-PROMPT.local.md');
    if (exact) return join(dir, exact);
    const match = entries.find(e => /^NEXT-SESSION-.*\.local\.md$/.test(e) && !/\.archived\./.test(e));
    if (match) return join(dir, match);
  } catch { /* ignore */ }
  return null;
}

// Walk up from start, max 3 levels, looking for handoff
function findHandoffUpwards(start) {
  let cur = start;
  for (let i = 0; i < 4; i++) { // 0,1,2,3 — start + 3 ancestors
    const found = findHandoffIn(cur);
    if (found) return found;
    const parent = dirname(cur);
    if (parent === cur) break;
    cur = parent;
  }
  return null;
}

function main() {
  const raw = readStdin();
  if (!raw.trim()) process.exit(0);
  let payload;
  try {
    payload = JSON.parse(raw);
  } catch {
    process.exit(0);
  }

  const source = payload?.source;
  if (source !== 'resume' && source !== 'compact') {
    process.exit(0);
  }

  const cwd = payload?.cwd || process.cwd();
  const handoffPath = findHandoffUpwards(cwd);
  if (!handoffPath) {
    process.exit(0);
  }

  let content;
  try {
    content = readFileSync(handoffPath, 'utf-8');
  } catch {
    process.exit(0);
  }

  // Inject via additionalContext for clean structured output
  const output = {
    hookSpecificOutput: {
      hookEventName: 'SessionStart',
      additionalContext: `<session-handoff source="${handoffPath}" loaded-by="graceful-handoff">\n${content}\n</session-handoff>`,
    },
  };
  process.stdout.write(JSON.stringify(output));

  // Archive to prevent stale-load in subsequent sessions
  try {
    const archived = handoffPath.replace(/\.local\.md$/, '.archived.local.md');
    if (!existsSync(archived)) {
      renameSync(handoffPath, archived);
    }
  } catch { /* archival is best-effort, never block injection */ }

  process.exit(0);
}

main();