/**
 * pi-loom: Temporal Query Parser
 *
 * Zero-LLM regex-based time-aware query parsing, aligned with Mem0 v3's
 * Temporal Reasoning feature. Extracts temporal intent from natural language
 * queries and maps them to SQL-compatible date ranges.
 *
 * Supported patterns:
 *   - "last week/month/year"     → relative date ranges
 *   - "today/yesterday"          → specific day ranges
 *   - "this week/month"          → current period
 *   - "recently"                 → last 7 days
 *   - "as of March 2025"         → absolute date anchor
 *   - "upcoming" / "planned"     → future/unexpired
 *   - "right now" / "currently"   → active + recent
 */

/** Result of temporal query parsing. null means no temporal intent detected. */
export interface TemporalFilter {
  /** ISO 8601 start date for created_at range (inclusive). */
  startDate?: string;
  /** ISO 8601 end date for created_at range (exclusive). */
  endDate?: string;
  /** Only include memories without an expiration (upcoming/active). */
  unexpiredOnly?: boolean;
  /** The query with temporal phrases removed for cleaner keyword matching. */
  cleanQuery: string;
}

/** Relative date helpers */
function daysAgoISO(days: number): string {
  const d = new Date(Date.now() - days * 86400000);
  return d.toISOString().slice(0, 10);
}

function todayISO(daysOffset = 0): string {
  const d = new Date(Date.now() + daysOffset * 86400000);
  return d.toISOString().slice(0, 10);
}

function mondayThisWeekISO(): string {
  const now = new Date();
  const day = now.getDay(); // 0=Sun, 1=Mon
  const diff = day === 0 ? 6 : day - 1; // days since Monday
  const mon = new Date(now.getFullYear(), now.getMonth(), now.getDate() - diff);
  return mon.toISOString().slice(0, 10);
}

function firstOfMonthISO(offsetMonths = 0): string {
  const now = new Date();
  const d = new Date(now.getFullYear(), now.getMonth() + offsetMonths, 1);
  return d.toISOString().slice(0, 10);
}

/** Parse month name + year like "March 2025", "Jan 2026" */
const MONTH_NAMES = [
  "january",
  "february",
  "march",
  "april",
  "may",
  "june",
  "july",
  "august",
  "september",
  "october",
  "november",
  "december",
];

const MONTH_ABBR: Record<string, number> = {
  jan: 0,
  feb: 1,
  mar: 2,
  apr: 3,
  may: 4,
  jun: 5,
  jul: 6,
  aug: 7,
  sep: 8,
  oct: 9,
  nov: 10,
  dec: 11,
};

function parseMonthYear(s: string): Date | null {
  // "March 2025", "Mar 2025"
  const m = s.match(/^([a-z]{3,9})\s+(\d{4})$/i);
  if (!m) return null;
  const monthStr = m[1].toLowerCase();
  const year = parseInt(m[2], 10);
  let month: number | undefined;
  if (monthStr.length === 3) {
    month = MONTH_ABBR[monthStr];
  } else {
    const idx = MONTH_NAMES.indexOf(monthStr);
    if (idx >= 0) month = idx;
  }
  if (month === undefined) return null;
  return new Date(year, month, 1);
}

/**
 * Parse a natural language query and extract temporal intent.
 * Returns null if no temporal pattern is detected.
 */
export function parseTemporalQuery(query: string): TemporalFilter | null {
  const q = query.toLowerCase().trim();

  // ─── "as of DATE" — absolute anchor ────────────────────
  // "as of March 2025", "as of 2025-03-15"
  let m = q.match(/as\s+of\s+([a-z]{3,9}\s+\d{4}|\d{4}-\d{2}-\d{2})/i);
  if (m) {
    const dateStr = m[1];
    let endDate: string;
    if (/^\d{4}-\d{2}-\d{2}$/.test(dateStr)) {
      endDate = dateStr;
    } else {
      const ym = parseMonthYear(dateStr);
      if (!ym) return null;
      // End of that month
      const lastDay = new Date(ym.getFullYear(), ym.getMonth() + 1, 0);
      endDate = lastDay.toISOString().slice(0, 10);
    }
    return {
      endDate,
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "last week" / "past week" ─────────────────────────
  m = q.match(/(?:last|past|previous)\s+week/);
  if (m) {
    return {
      startDate: daysAgoISO(7),
      endDate: todayISO(1), // up to now
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "last month" / "past month" ───────────────────────
  m = q.match(/(?:last|past|previous)\s+month/);
  if (m) {
    return {
      startDate: daysAgoISO(30),
      endDate: todayISO(1),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "last year" / "past year" ─────────────────────────
  m = q.match(/(?:last|past|previous)\s+year/);
  if (m) {
    return {
      startDate: daysAgoISO(365),
      endDate: todayISO(1),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "today" ───────────────────────────────────────────
  m = /\btoday\b/.exec(q);
  if (m) {
    return {
      startDate: todayISO(),
      endDate: todayISO(1),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "yesterday" ───────────────────────────────────────
  m = /\byesterday\b/.exec(q);
  if (m) {
    return {
      startDate: daysAgoISO(1),
      endDate: todayISO(),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "this week" ───────────────────────────────────────
  m = /\bthis\s+week\b/.exec(q);
  if (m) {
    return {
      startDate: mondayThisWeekISO(),
      endDate: todayISO(1),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "this month" ──────────────────────────────────────
  m = /\bthis\s+month\b/.exec(q);
  if (m) {
    return {
      startDate: firstOfMonthISO(),
      endDate: todayISO(1),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "recently" ────────────────────────────────────────
  m = /\brecently\b/.exec(q);
  if (m) {
    return {
      startDate: daysAgoISO(7),
      endDate: todayISO(1),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "upcoming" / "planned" / "next week" ──────────────
  m = q.match(/\b(upcoming|planned|next\s+week)\b/);
  if (m) {
    return {
      unexpiredOnly: true, // exclude expired, keep everything else
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "right now" / "currently" / "current" ─────────────
  m = q.match(/\b(right\s+now|currently|current)\b/);
  if (m) {
    return {
      startDate: daysAgoISO(7),
      endDate: todayISO(1),
      unexpiredOnly: true,
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "before DATE" ─────────────────────────────────────
  m = q.match(/before\s+([a-z]{3,9}\s+\d{4}|\d{4}-\d{2}-\d{2})/i);
  if (m) {
    const ym = parseMonthYear(m[1]);
    const endDate = ym ? ym.toISOString().slice(0, 10) : m[1];
    return {
      endDate,
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "after DATE" ──────────────────────────────────────
  m = q.match(/after\s+([a-z]{3,9}\s+\d{4}|\d{4}-\d{2}-\d{2})/i);
  if (m) {
    const ym = parseMonthYear(m[1]);
    const startDate = ym ? ym.toISOString().slice(0, 10) : m[1];
    return {
      startDate,
      endDate: todayISO(1),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  // ─── "since DATE" ──────────────────────────────────────
  m = q.match(/since\s+([a-z]{3,9}\s+\d{4}|\d{4}-\d{2}-\d{2})/i);
  if (m) {
    const ym = parseMonthYear(m[1]);
    const startDate = ym ? ym.toISOString().slice(0, 10) : m[1];
    return {
      startDate,
      endDate: todayISO(1),
      cleanQuery: q.replace(m[0], "").trim(),
    };
  }

  return null;
}

/** Normalize whitespace in a query string (collapse runs → single space). */
export function normalizeQuery(q: string): string {
  return q.replace(/\s+/g, " ").trim();
}