"""
migration_legacy_attendance_remote_indexes.py
================================================
Adds missing indexes to the REMOTE legacy database (the one described by
QrCodeLtServices.sql — contract / employee / locations / records) so the
Legacy Attendance feature's live queries don't full-table-scan on every
page load.

As shipped, that schema has NO index on:
    records.employeeId, records.locationId, records.time, records.contractId
    employee.id           (only the meaningless auto-increment `index` is indexed)
    locations.location

Adding an index does not change or risk any existing data — it only
speeds up reads. Safe to re-run: each ALTER is skipped if the index
already exists.

Uses pymysql directly (never SQLAlchemy ORM), consistent with every other
migration script in tools/ — this connects to REMOTE_DB_* (the legacy
server), not the app's own local database.

Run once per server (LT and GOV each point at their own legacy DB):
    python3 tools/migration_legacy_attendance_remote_indexes.py
"""

import os
import sys

sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))

from dotenv import load_dotenv
load_dotenv()

import pymysql

# (table, column, index_name)
INDEXES_TO_ADD = [
    ('records',   'employeeId', 'idx_records_employeeId'),
    ('records',   'locationId', 'idx_records_locationId'),
    ('records',   'time',       'idx_records_time'),
    ('records',   'contractId', 'idx_records_contractId'),
    ('employee',  'id',         'idx_employee_id'),
    ('locations', 'location',   'idx_locations_location'),
]


def get_connection():
    host = os.environ.get('REMOTE_DB_HOST', '')
    port = int(os.environ.get('REMOTE_DB_PORT', '3306'))
    user = os.environ.get('REMOTE_DB_USERNAME', '')
    password = os.environ.get('REMOTE_DB_PASSWORD', '')
    database = os.environ.get('REMOTE_DB_NAME', '')

    if not host or not database:
        print("[ERROR] REMOTE_DB_HOST / REMOTE_DB_NAME not set in .env — aborting.")
        sys.exit(1)

    print(f"[INFO] Connecting to legacy DB {user}@{host}:{port}/{database} ...")
    return pymysql.connect(
        host=host, port=port, user=user, password=password, database=database,
        charset='utf8mb4', connect_timeout=10
    )


def index_exists(cursor, table, index_name):
    cursor.execute("""
        SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS
        WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = %s AND INDEX_NAME = %s
    """, (table, index_name))
    return cursor.fetchone()[0] > 0


def main():
    conn = get_connection()
    try:
        with conn.cursor() as cur:
            for table, column, index_name in INDEXES_TO_ADD:
                if index_exists(cur, table, index_name):
                    print(f"[SKIP] {table}.{index_name} already exists")
                    continue
                print(f"[ADD]  {table}.{index_name} ON ({column}) ...")
                cur.execute(f"ALTER TABLE `{table}` ADD INDEX `{index_name}` (`{column}`)")
                conn.commit()
                print(f"[OK]   {table}.{index_name} created")
        print("[DONE] Legacy database indexes are up to date.")
    except pymysql.MySQLError as e:
        print(f"[ERROR] {e}")
        sys.exit(1)
    finally:
        conn.close()


if __name__ == '__main__':
    main()