import fs from 'node:fs/promises';
import path from 'node:path';
import pg from 'pg';

const databaseUrl = process.env.DATABASE_URL || 'postgresql://postgres:postgres@127.0.0.1:54322/postgres';
const outputDir = process.env.PG_TUNING_OUTPUT_DIR || 'docs/refactor/launch-artifacts';

const settingNames = [
  'max_connections',
  'shared_buffers',
  'effective_cache_size',
  'work_mem',
  'maintenance_work_mem',
  'autovacuum_work_mem',
  'wal_buffers',
  'min_wal_size',
  'max_wal_size',
  'checkpoint_timeout',
  'checkpoint_completion_target',
  'effective_io_concurrency',
  'random_page_cost',
  'jit',
  'log_min_duration_statement',
  'idle_in_transaction_session_timeout',
  'statement_timeout',
  'lock_timeout',
];

function shanghaiStamp(date = new Date()) {
  const parts = Object.fromEntries(
    new Intl.DateTimeFormat('en-CA', {
      timeZone: 'Asia/Shanghai',
      year: 'numeric',
      month: '2-digit',
      day: '2-digit',
      hour: '2-digit',
      minute: '2-digit',
      second: '2-digit',
      hour12: false,
    }).formatToParts(date).map(part => [part.type, part.value]),
  );
  return `${parts.year}${parts.month}${parts.day}-${parts.hour}${parts.minute}${parts.second}`;
}

async function query(pool, sql, params = []) {
  const result = await pool.query(sql, params);
  return result.rows;
}

async function maybeQuery(pool, sql, params = []) {
  try {
    return await query(pool, sql, params);
  } catch (error) {
    return { unavailable: true, message: error?.message || String(error) };
  }
}

function redactUrl(value) {
  return value.replace(/:\/\/([^:]+):([^@]+)@/, '://$1:[redacted]@');
}

function explainSetting(setting) {
  const value = `${setting.setting}${setting.unit || ''}`;
  return {
    name: setting.name,
    value,
    source: setting.source,
    pendingRestart: setting.pending_restart,
  };
}

function evaluate(settingsRows) {
  const byName = new Map(settingsRows.map(row => [row.name, row]));
  const warnings = [];
  const maxConnections = Number(byName.get('max_connections')?.setting || 0);
  const jit = String(byName.get('jit')?.setting || '').toLowerCase();
  const statementTimeout = String(byName.get('statement_timeout')?.setting || '');
  const idleTimeout = String(byName.get('idle_in_transaction_session_timeout')?.setting || '');
  const lockTimeout = String(byName.get('lock_timeout')?.setting || '');

  if (maxConnections > 150) warnings.push('max_connections is high for a 4 vCPU database; prefer API/pooler limits over direct connections.');
  if (jit === 'on') warnings.push('jit is on; short OLTP-style question-bank API queries usually start safer with jit=off.');
  if (statementTimeout === '0') warnings.push('statement_timeout is disabled; production API should have a bounded global timeout and import jobs should override per session.');
  if (idleTimeout === '0') warnings.push('idle_in_transaction_session_timeout is disabled; long idle transactions can block migrations and writes.');
  if (lockTimeout === '0') warnings.push('lock_timeout is disabled; ordinary API requests may wait too long behind locks.');
  if (settingsRows.some(row => row.pending_restart)) warnings.push('Some PostgreSQL settings have pending_restart=true; restart is required before capacity testing.');

  return {
    status: warnings.length ? 'warn' : 'pass',
    warnings,
  };
}

function markdown(report) {
  const lines = [
    '# PostgreSQL 调参与运行证据',
    '',
    `生成时间：${new Date(report.generatedAt).toLocaleString('zh-CN', { timeZone: 'Asia/Shanghai' })}`,
    '',
    `数据库：${report.databaseUrl}`,
    '',
    `评估：${report.evaluation.status}`,
    '',
  ];
  if (report.evaluation.warnings.length) {
    lines.push('## 警告');
    lines.push('');
    for (const warning of report.evaluation.warnings) lines.push(`- ${warning}`);
    lines.push('');
  }
  lines.push('## 关键参数');
  lines.push('');
  lines.push('| 参数 | 当前值 | 来源 | 待重启 |');
  lines.push('| --- | ---: | --- | --- |');
  for (const item of report.settings) {
    lines.push(`| ${item.name} | ${item.value} | ${item.source} | ${item.pendingRestart ? '是' : '否'} |`);
  }
  lines.push('');
  lines.push('## 连接与等待');
  lines.push('');
  lines.push('| state | wait_event_type | wait_event | count |');
  lines.push('| --- | --- | --- | ---: |');
  for (const item of report.activityByWait) {
    lines.push(`| ${item.state || '-'} | ${item.wait_event_type || '-'} | ${item.wait_event || '-'} | ${item.count} |`);
  }
  lines.push('');
  lines.push('## 缓存与事务');
  lines.push('');
  lines.push('| datname | commits | rollbacks | cache_hit_ratio |');
  lines.push('| --- | ---: | ---: | ---: |');
  for (const item of report.databaseStats) {
    lines.push(`| ${item.datname} | ${item.xact_commit} | ${item.xact_rollback} | ${item.cache_hit_ratio ?? '-'} |`);
  }
  lines.push('');
  lines.push('## 大表规模');
  lines.push('');
  lines.push('| 表 | 估算行数 | 总大小 | 索引大小 |');
  lines.push('| --- | ---: | ---: | ---: |');
  for (const item of report.largeRelations) {
    lines.push(`| ${item.relation} | ${item.estimated_rows} | ${item.total_size} | ${item.index_size} |`);
  }
  lines.push('');
  if (Array.isArray(report.pgStatStatements)) {
    lines.push('## pg_stat_statements Top SQL');
    lines.push('');
    lines.push('| calls | total_exec_ms | mean_exec_ms | rows | query |');
    lines.push('| ---: | ---: | ---: | ---: | --- |');
    for (const item of report.pgStatStatements) {
      lines.push(`| ${item.calls} | ${item.total_exec_ms} | ${item.mean_exec_ms} | ${item.rows} | ${String(item.query || '').replaceAll('|', '\\|')} |`);
    }
    lines.push('');
  } else {
    lines.push('## pg_stat_statements');
    lines.push('');
    lines.push(`未采集：${report.pgStatStatements?.message || 'extension/view unavailable'}`);
    lines.push('');
  }
  return `${lines.join('\n')}\n`;
}

async function main() {
  const pool = new pg.Pool({ connectionString: databaseUrl, max: 2 });
  try {
    const settingsRaw = await query(
      pool,
      `
      select name, setting, unit, source, pending_restart
      from pg_settings
      where name = any($1::text[])
      order by array_position($1::text[], name)
      `,
      [settingNames],
    );
    const activityByWait = await query(
      pool,
      `
      select state, wait_event_type, wait_event, count(*)::int as count
      from pg_stat_activity
      where datname = current_database()
      group by state, wait_event_type, wait_event
      order by count desc, state nulls last
      `,
    );
    const databaseStats = await query(
      pool,
      `
      select datname,
             xact_commit::text,
             xact_rollback::text,
             blks_read::text,
             blks_hit::text,
             round(blks_hit * 100.0 / nullif(blks_hit + blks_read, 0), 2)::text as cache_hit_ratio
      from pg_stat_database
      where datname = current_database()
      `,
    );
    const bgwriter = await maybeQuery(
      pool,
      `
      select checkpoints_timed::text, checkpoints_req::text,
             checkpoint_write_time::text, checkpoint_sync_time::text
      from pg_stat_bgwriter
      `,
    );
    const largeRelations = await query(
      pool,
      `
      select relid::regclass::text as relation,
             n_live_tup::bigint::text as estimated_rows,
             pg_size_pretty(pg_total_relation_size(relid)) as total_size,
             pg_size_pretty(pg_indexes_size(relid)) as index_size
      from pg_stat_user_tables
      where schemaname = 'public'
      order by pg_total_relation_size(relid) desc
      limit 20
      `,
    );
    const pgStatStatements = await maybeQuery(
      pool,
      `
      select calls::bigint::text,
             round(total_exec_time::numeric, 2)::text as total_exec_ms,
             round(mean_exec_time::numeric, 2)::text as mean_exec_ms,
             rows::bigint::text,
             left(regexp_replace(query, '\\s+', ' ', 'g'), 180) as query
      from pg_stat_statements
      order by total_exec_time desc
      limit 10
      `,
    );
    const report = {
      generatedAt: new Date().toISOString(),
      databaseUrl: redactUrl(databaseUrl),
      evaluation: evaluate(settingsRaw),
      settings: settingsRaw.map(explainSetting),
      activityByWait,
      databaseStats,
      bgwriter,
      largeRelations,
      pgStatStatements,
    };
    await fs.mkdir(outputDir, { recursive: true });
    const jsonPath = path.join(outputDir, `postgres-tuning-evidence-${shanghaiStamp()}.json`);
    const mdPath = jsonPath.replace(/\.json$/, '.md');
    await fs.writeFile(jsonPath, `${JSON.stringify(report, null, 2)}\n`, 'utf8');
    await fs.writeFile(mdPath, markdown(report), 'utf8');
    console.log(`[pg-evidence] status=${report.evaluation.status}`);
    for (const warning of report.evaluation.warnings) console.log(`[pg-evidence] warning: ${warning}`);
    console.log(`[pg-evidence] wrote ${jsonPath}`);
    console.log(`[pg-evidence] wrote ${mdPath}`);
  } finally {
    await pool.end();
  }
}

main().catch(error => {
  console.error(error);
  process.exit(1);
});