/**
 * @file source-filter.js
 * @description Shared helper for the "data scope" feature: restricting a query
 * to sessions collected from a chosen set of machines (see server/db.js
 * `sessions.source` and server/lib/remote-sync.js).
 *
 * The client passes `?sources=local,src_abc,...` on any data endpoint. Absent or
 * empty means "all sources" (no filter) so every existing caller and the
 * zero-config default are unaffected. This module turns that query param into a
 * SQL fragment that is safe to append to any WHERE clause — either directly on
 * `sessions.source`, or, for tables that only carry a `session_id`, as a
 * subquery so complex aggregate SQL (stats, analytics) needs only one extra AND.
 *
 * `?tool=<id>` (an AI Tools catalog id, matched against `sessions.tool`) narrows
 * the same way; `parseScope` folds both into one predicate over `sessions`.
 *
 * `?from=&to=` (local `YYYY-MM-DD`, inclusive, read with `tz_offset`) is a date
 * range: `parseRange` turns it into the UTC instants a timestamp column is
 * compared with, and `inRange` tests a local date (a cost row's `date`).
 *
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

/**
 * Parse the `sources` query param into a de-duplicated list, or null for
 * "all sources" (no filtering).
 * @param {import("express").Request} req
 * @returns {string[]|null}
 */
function parseSources(req) {
  const raw = req.query ? req.query.sources : undefined;
  if (typeof raw !== "string") return null;
  const list = [
    ...new Set(
      raw
        .split(",")
        .map((s) => s.trim())
        .filter(Boolean)
    ),
  ];
  return list.length > 0 ? list : null;
}

/**
 * Filter directly on a `source` column (used when `sessions` is in the query).
 * @param {string[]|null} sources result of parseSources
 * @param {string} [col] the qualified source column (default "s.source")
 * @returns {{clause:string, params:string[]}} `clause` is "" when no filter
 */
function sourceColumnClause(sources, col = "s.source") {
  if (!sources || sources.length === 0) return { clause: "", params: [] };
  const placeholders = sources.map(() => "?").join(",");
  return { clause: `${col} IN (${placeholders})`, params: sources };
}

/**
 * Filter by session origin when only a `session_id` column is available, via a
 * subquery against `sessions`. Lets stats/analytics/events/agents scope by
 * source with a single extra AND and no FROM/GROUP BY changes.
 * @param {string[]|null} sources result of parseSources
 * @param {string} sessionIdCol the qualified session-id column (e.g. "e.session_id")
 * @returns {{clause:string, params:string[]}} `clause` is "" when no filter
 */
function sessionIdInSourcesClause(sources, sessionIdCol) {
  if (!sources || sources.length === 0) return { clause: "", params: [] };
  const placeholders = sources.map(() => "?").join(",");
  return {
    clause: `${sessionIdCol} IN (SELECT id FROM sessions WHERE source IN (${placeholders}))`,
    params: sources,
  };
}

// An AI Tools catalog id shape; the value is only ever a bound parameter.
const TOOL_RE = /^[a-z0-9][a-z0-9._-]{0,63}$/i;

/**
 * Parse `?tool=`: null when absent, false when malformed (the route answers 400).
 * @param {import("express").Request} req
 * @returns {string|null|false}
 */
function parseTool(req) {
  const raw = req.query ? req.query.tool : undefined;
  if (raw === undefined || raw === "") return null;
  return typeof raw === "string" && TOOL_RE.test(raw) ? raw : false;
}

/**
 * The data scope (sources and/or tool) as ONE predicate over `sessions` with
 * unqualified columns, or null for "everything". Callers check `parseTool` for
 * false first.
 * @param {import("express").Request} req
 * @returns {{where:string, params:string[]}|null}
 */
function parseScope(req) {
  const sources = parseSources(req);
  const tool = parseTool(req);
  const where = [];
  const params = [];
  if (sources) {
    where.push(`source IN (${sources.map(() => "?").join(",")})`);
    params.push(...sources);
  }
  if (tool) {
    where.push("tool = ?");
    params.push(tool);
  }
  return where.length ? { where: where.join(" AND "), params } : null;
}

const DATE_RE = /^\d{4}-\d{2}-\d{2}$/;
const DAY_MS = 86_400_000;

/** A real calendar date in `YYYY-MM-DD` form (2026-02-30 is not), before
 *  year 9999 (whose next day no longer prints as a comparable ISO string). */
function isDate(s) {
  if (typeof s !== "string" || !DATE_RE.test(s) || s >= "9999") return false;
  const ms = Date.parse(`${s}T00:00:00Z`);
  return Number.isFinite(ms) && new Date(ms).toISOString().slice(0, 10) === s;
}

/**
 * Parse `?from=&to=`: null when both are absent, false when either is not a
 * date or `from` is after `to` (the route answers 400). Either end may be open.
 * `start`/`end` are the local midnights of `from` and of the day after `to`,
 * as UTC ISO instants (`end` exclusive), for `col >= start AND col < end`.
 * @param {import("express").Request} req
 * @returns {{from:string|null, to:string|null, start:string|null, end:string|null}|null|false}
 */
function parseRange(req) {
  const q = req.query || {};
  const from = q.from === undefined || q.from === "" ? null : q.from;
  const to = q.to === undefined || q.to === "" ? null : q.to;
  if (from === null && to === null) return null;
  if ((from !== null && !isDate(from)) || (to !== null && !isDate(to))) return false;
  if (from !== null && to !== null && from > to) return false;
  const tz = parseInt(q.tz_offset, 10);
  const off = Number.isFinite(tz) ? tz * 60_000 : 0;
  const instant = (day, plus) =>
    new Date(Date.parse(`${day}T00:00:00Z`) + plus * DAY_MS + off).toISOString();
  return {
    from,
    to,
    start: from === null ? null : instant(from, 0),
    end: to === null ? null : instant(to, 1),
  };
}

/** Whether a local `YYYY-MM-DD` falls in a `parseRange` result (null = all). */
function inRange(range, date) {
  return !range || ((!range.from || date >= range.from) && (!range.to || date <= range.to));
}

/** The 400 every ranged route answers for a malformed `?from=`/`?to=`. */
const BAD_RANGE = {
  error: { code: "INVALID_INPUT", message: "from/to must be YYYY-MM-DD dates, from <= to" },
};

/** The 400 every scoped route answers for a malformed `?tool=`. */
const BAD_TOOL = { error: { code: "INVALID_INPUT", message: "tool must be an AI Tools id" } };

module.exports = {
  parseSources,
  parseTool,
  parseScope,
  BAD_TOOL,
  isDate,
  parseRange,
  inRange,
  BAD_RANGE,
  sourceColumnClause,
  sessionIdInSourcesClause,
};