"""
migration_attendance_indexes.py
===============================
Adds the secondary indexes `attendance_data` has been missing.

Without them the Attendance Report (ORDER BY date/time, filters), the check-in
cooldown lookup, the check-out work-type suggestion and the Verification Review
scan and sort the whole table, so they slow down as history grows.

Uses pymysql directly (no Flask app / ORM import). Indexes are built with online
DDL (ALGORITHM=INPLACE, LOCK=NONE) so check-ins keep working while they build;
if the server refuses that, the plain ALTER TABLE is used instead.

Run once on each server (LT and GOV) — before or after deploying the code:
    python3 tools/migration_attendance_indexes.py

Safe to re-run — an index is skipped when one with the same name, or an
existing index that already starts with the same columns, is present.
"""

import os, sys, re

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

from dotenv import load_dotenv
load_dotenv()

import pymysql

TABLE = 'attendance_data'

# (index name, columns, what it speeds up)
INDEXES = [
    ('idx_ad_date_time',     ('check_in_date', 'check_in_time'),
     'Attendance Report sort and date filters'),
    ('idx_ad_emp_date_time', ('employee_id', 'check_in_date', 'check_in_time'),
     'employee filter, check-out work-type suggestion'),
    ('idx_ad_qr_emp_date',   ('qr_code_id', 'employee_id', 'check_in_date'),
     'check-in cooldown guard'),
    ('idx_ad_location_name', ('location_name',),
     'location filter and dropdown'),
    ('idx_ad_verif_status',  ('verification_status',),
     'Verification Review status filter'),
]


def parse_db_url(url):
    """
    Parse DATABASE_URL robustly using regex to handle special characters
    (including @ or : ) in the password.
    """
    url = re.sub(r'^mysql\+pymysql://', '', url)
    url = re.sub(r'^mysql://', '', url)
    m = re.match(
        r'^(?P<user>[^:]+):(?P<password>.+)@(?P<host>[^@:/]+)(?::(?P<port>\d+))?/(?P<db>[^?]+)',
        url
    )
    if not m:
        print(f"[ERROR] Could not parse DATABASE_URL. Raw (redacted): {url[:30]}...")
        sys.exit(1)
    return {
        'host':     m.group('host'),
        'port':     int(m.group('port')) if m.group('port') else 3306,
        'user':     m.group('user'),
        'password': m.group('password'),
        'database': m.group('db'),
    }


def get_connection():
    db_url = os.environ.get('DATABASE_URL', '')
    if not db_url:
        print("[ERROR] DATABASE_URL not set in .env")
        sys.exit(1)
    params = parse_db_url(db_url)
    return pymysql.connect(charset='utf8mb4', autocommit=True, **params)


def existing_indexes(cur):
    """{index_name: (col1, col2, ...)} for the table."""
    cur.execute(
        "SELECT INDEX_NAME, COLUMN_NAME FROM information_schema.STATISTICS "
        "WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = %s "
        "ORDER BY INDEX_NAME, SEQ_IN_INDEX",
        (TABLE,)
    )
    indexes = {}
    for index_name, column_name in cur.fetchall():
        indexes.setdefault(index_name, []).append(column_name)
    return {name: tuple(cols) for name, cols in indexes.items()}


def existing_columns(cur):
    cur.execute(
        "SELECT COLUMN_NAME FROM information_schema.COLUMNS "
        "WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = %s",
        (TABLE,)
    )
    return {row[0] for row in cur.fetchall()}


def run():
    conn = get_connection()
    created = skipped = failed = 0
    try:
        with conn.cursor() as cur:
            columns = existing_columns(cur)
            if not columns:
                print(f"[ERROR] Table '{TABLE}' not found in this database.")
                sys.exit(1)

            for name, cols, purpose in INDEXES:
                indexes = existing_indexes(cur)

                missing = [c for c in cols if c not in columns]
                if missing:
                    print(f"[SKIP] {name}: column(s) {', '.join(missing)} not present on '{TABLE}'.")
                    skipped += 1
                    continue

                if name in indexes:
                    print(f"[SKIP] {name}: already exists.")
                    skipped += 1
                    continue

                covering = [n for n, existing in indexes.items() if existing[:len(cols)] == cols]
                if covering:
                    print(f"[SKIP] {name}: already covered by index '{covering[0]}' {indexes[covering[0]]}.")
                    skipped += 1
                    continue

                column_sql = ', '.join(f"`{c}`" for c in cols)
                print(f"[ADD]  {name} ({', '.join(cols)}) — {purpose} ...")
                try:
                    cur.execute(
                        f"ALTER TABLE `{TABLE}` ADD INDEX `{name}` ({column_sql}), "
                        f"ALGORITHM=INPLACE, LOCK=NONE"
                    )
                except pymysql.MySQLError as online_error:
                    print(f"       Online DDL not available ({online_error}); retrying with a plain ALTER TABLE ...")
                    try:
                        cur.execute(f"ALTER TABLE `{TABLE}` ADD INDEX `{name}` ({column_sql})")
                    except pymysql.MySQLError as error:
                        print(f"[FAIL] {name}: {error}")
                        failed += 1
                        continue

                if name in existing_indexes(cur):
                    print(f"[OK]   {name} created.")
                    created += 1
                else:
                    print(f"[FAIL] {name} was not created — check DB permissions.")
                    failed += 1
    finally:
        conn.close()

    print(f"\nDone: {created} created, {skipped} skipped, {failed} failed.")
    if failed:
        sys.exit(1)


if __name__ == '__main__':
    run()