import { pool } from '../pool.js';

// FTS-only search across pages / refs / source_docs / messages, unioned
// with a `kind` discriminator and ranked by ts_rank. Each branch's
// to_tsvector expression matches the GIN index on its table so the
// indexes are used. Vector / hybrid RRF search lands in Plan 3.
//
// Notes:
// - messages have no space_id → the messages branch is dropped when a
//   space_id filter is present.
// - source_docs inherit space_id from their owning resource via join.

const PAGES_TSV = `to_tsvector('english', p.title || ' ' || coalesce(p.body_md,''))`;
const REFS_TSV  = `to_tsvector('english', coalesce(r.title,'') || ' ' || coalesce(r.summary,'') || ' ' || coalesce(r.body_text,''))`;
const SD_TSV    = `to_tsvector('english', sd.name || ' ' || coalesce(sd.body_text,''))`;
const MSG_TSV   = `to_tsvector('english', m.body)`;

function buildBranches({ kinds, spaceFilterPresent }) {
  const branches = [];
  const wantPage = !kinds || kinds.includes('page');
  const wantRef  = !kinds || kinds.includes('ref');
  const wantSD   = !kinds || kinds.includes('source_doc');
  const wantMsg  = (!kinds || kinds.includes('message')) && !spaceFilterPresent;

  if (wantPage) {
    branches.push(`
      SELECT 'page'::text AS kind, p.id, p.space_id, p.title AS title_or_snippet,
             ts_rank(${PAGES_TSV}, q.tsq) AS rank
        FROM pages p, q
        WHERE ${PAGES_TSV} @@ q.tsq
          AND ($2::uuid IS NULL OR p.space_id = $2)
    `);
  }
  if (wantRef) {
    branches.push(`
      SELECT 'ref'::text AS kind, r.id, r.space_id,
             coalesce(r.title, r.source_url, '(untitled)') AS title_or_snippet,
             ts_rank(${REFS_TSV}, q.tsq) AS rank
        FROM refs r, q
        WHERE ${REFS_TSV} @@ q.tsq
          AND ($2::uuid IS NULL OR r.space_id = $2)
    `);
  }
  if (wantSD) {
    branches.push(`
      SELECT 'source_doc'::text AS kind, sd.id, res.space_id, sd.name AS title_or_snippet,
             ts_rank(${SD_TSV}, q.tsq) AS rank
        FROM source_docs sd
        JOIN resources res ON res.id = sd.resource_id, q
        WHERE ${SD_TSV} @@ q.tsq
          AND ($2::uuid IS NULL OR res.space_id = $2)
    `);
  }
  if (wantMsg) {
    branches.push(`
      SELECT 'message'::text AS kind, m.id, NULL::uuid AS space_id,
             substring(m.body, 1, 200) AS title_or_snippet,
             ts_rank(${MSG_TSV}, q.tsq) AS rank
        FROM messages m, q
        WHERE ${MSG_TSV} @@ q.tsq
    `);
  }
  return branches;
}

export async function fts({ q, space_id = null, kinds = null, limit = 50, offset = 0 } = {}) {
  if (!q || typeof q !== 'string') return [];
  const normalizedKinds = Array.isArray(kinds) && kinds.length ? kinds : null;
  const spaceFilterPresent = space_id !== null && space_id !== undefined;
  const branches = buildBranches({ kinds: normalizedKinds, spaceFilterPresent });
  if (branches.length === 0) return [];

  const sql = `
    WITH q AS (SELECT plainto_tsquery('english', $1) AS tsq)
    SELECT * FROM (
      ${branches.join('\n      UNION ALL\n      ')}
    ) u
    ORDER BY rank DESC
    LIMIT $3 OFFSET $4
  `;
  const { rows } = await pool.query(sql, [q, space_id, limit, offset]);
  return rows;
}