'use strict';

const { devWarn } = require('./log');

// clips -> clips_fts 的同步触发器。v2 / v3 共用。
const FTS_TRIGGERS = `
  CREATE TRIGGER IF NOT EXISTS clips_ai AFTER INSERT ON clips BEGIN
    INSERT INTO clips_fts(rowid, text) VALUES (new.id, new.text);
  END;
  CREATE TRIGGER IF NOT EXISTS clips_ad AFTER DELETE ON clips BEGIN
    INSERT INTO clips_fts(clips_fts, rowid, text) VALUES('delete', old.id, old.text);
  END;
  -- 只在 text 真的变了才重建索引。没有这个 WHEN 的话，每次
  -- "UPDATE clips SET top_at = ?"（也就是每次复制/置顶）都会白白
  -- 把该行从 FTS 删掉再插回去。
  CREATE TRIGGER IF NOT EXISTS clips_au AFTER UPDATE ON clips
  WHEN old.text IS NOT new.text BEGIN
    INSERT INTO clips_fts(clips_fts, rowid, text) VALUES('delete', old.id, old.text);
    INSERT INTO clips_fts(rowid, text) VALUES (new.id, new.text);
  END;
`;

// STEPS[i] upgrades the schema from version (i + 1) to (i + 2).
// STEPS[0] therefore is the v1 -> v2 step.
const STEPS = [
  // v1 -> v2: add FTS5 table + triggers (idempotent).
  function v1_to_v2(db) {
    db.exec(`
      CREATE VIRTUAL TABLE IF NOT EXISTS clips_fts USING fts5(text, content='clips', content_rowid='id');
      ${FTS_TRIGGERS}
      INSERT INTO clips_fts(rowid, text) SELECT id, text FROM clips WHERE text IS NOT NULL;
    `);
  },

  // v2 -> v3: 换成 trigram 分词器。
  //
  // v2 用的是默认的 unicode61 分词器，它把一整串连续的中文当成**一个** token，
  // 而 FTS5 的 MATCH 是整 token 匹配、不做子串匹配。结果：搜"公园"在
  // "今天去公园散步"里一条都搜不到 —— 对一个中文剪贴板工具来说等于搜索全废。
  // （v2 这一步之前因为索引下标算错从没真正执行过，所以线上一直悄悄退回 LIKE，
  //   反而"正好"是对的；把 v2 修好之后这个坑才会暴露出来。）
  //
  // trigram 分词器按 3 字符滑窗切分，支持子串匹配，中文可用。
  // 代价：≤2 字符的查询它匹配不到，这部分由调用方退回 LIKE 处理。
  function v2_to_v3(db) {
    db.exec(`
      DROP TRIGGER IF EXISTS clips_ai;
      DROP TRIGGER IF EXISTS clips_ad;
      DROP TRIGGER IF EXISTS clips_au;
      DROP TABLE IF EXISTS clips_fts;
      CREATE VIRTUAL TABLE clips_fts USING fts5(
        text, content='clips', content_rowid='id', tokenize='trigram'
      );
      ${FTS_TRIGGERS}
      INSERT INTO clips_fts(rowid, text) SELECT id, text FROM clips WHERE text IS NOT NULL;
    `);
  },
];

/**
 * Applies each pending schema step in order.
 *
 * The DB's own `PRAGMA user_version` is the source of truth for what has already
 * been applied — not the config file, which only records the version the app
 * *wants*. Passing a config-derived `fromVersion` would re-run every step on
 * every launch (re-indexing the whole FTS table each time the app starts).
 *
 * Returns the version actually reached, so callers can tell whether a step was
 * skipped because of an error.
 */
function migrate(db, fromVersion, toVersion) {
  let current = fromVersion;
  try {
    const row = db.pragma('user_version', { simple: true });
    if (typeof row === 'number' && row > 0) current = row;
  } catch (e) {
    // Non-sqlite stub (tests) — fall back to the caller-supplied version.
  }

  for (let v = current + 1; v <= toVersion; v++) {
    const step = STEPS[v - 2];
    if (!step) continue;
    try {
      step(db);
      current = v;
      try { db.pragma(`user_version = ${v}`); } catch (e) {}
    } catch (e) {
      // Most likely FTS5 is not compiled into this SQLite build. Leave the
      // version marker where it is so a later launch can retry, and let the
      // caller fall back to LIKE-based search.
      devWarn('[migrate] step', v, 'failed, leaving schema at v' + current + ':', e.message);
      break;
    }
  }
  return current;
}

module.exports = { migrate, STEPS };