#!/usr/bin/env python3
"""kpi_alerts 去重键结构变更（幂等执行器，A2 方案）

用法：
  ddl_kpi_alerts_dedupe.py --check     # 只读：打印列/索引是否存在（默认）
  ddl_kpi_alerts_dedupe.py --apply     # 幂等执行：缺列则加列，缺索引则建索引
  ddl_kpi_alerts_dedupe.py --rollback  # 回退：删索引 + 删列（数据无需恢复：本改造无 UPDATE/DELETE）

特性：
  * information_schema 判存在后再执行 ⇒ 重复跑安全（第二次全 NOOP）
  * 只加可空列 + 唯一索引；历史行 dedupe_key 全 NULL ⇒ 建索引必然无冲突
  * root 本机 socket 连接（与 migrate_map_connections.py 同口径），不读 .env
"""
from __future__ import annotations

import argparse
import sys

from sqlalchemy import create_engine, text

URL = "mysql+pymysql://root@localhost/cma?unix_socket=/var/run/mysqld/mysqld.sock&charset=utf8mb4"
TABLE = "kpi_alerts"
COLUMN = "dedupe_key"
INDEX = "uk_kpi_alerts_dedupe"

ADD_COLUMN_SQL = (
    "ALTER TABLE kpi_alerts "
    "ADD COLUMN dedupe_key VARCHAR(160) NULL "
    "COMMENT '生成侧幂等键 period|scope|ident，仅 alert_type=overdue 填充；历史行为 NULL' "
    "AFTER alert_type"
)
ADD_INDEX_SQL = (
    "CREATE UNIQUE INDEX uk_kpi_alerts_dedupe "
    "ON kpi_alerts (entity_id, kpi_id, alert_type, dedupe_key)"
)
DROP_INDEX_SQL = "DROP INDEX uk_kpi_alerts_dedupe ON kpi_alerts"
DROP_COLUMN_SQL = "ALTER TABLE kpi_alerts DROP COLUMN dedupe_key"


def col_exists(eng) -> bool:
    with eng.connect() as c:
        n = c.execute(text(
            "SELECT COUNT(*) FROM information_schema.columns "
            "WHERE table_schema=DATABASE() AND table_name=:t AND column_name=:c"
        ), {"t": TABLE, "c": COLUMN}).scalar()
    return int(n or 0) > 0


def idx_exists(eng) -> bool:
    with eng.connect() as c:
        n = c.execute(text(
            "SELECT COUNT(*) FROM information_schema.statistics "
            "WHERE table_schema=DATABASE() AND table_name=:t AND index_name=:i"
        ), {"t": TABLE, "i": INDEX}).scalar()
    return int(n or 0) > 0


def main() -> int:
    ap = argparse.ArgumentParser()
    g = ap.add_mutually_exclusive_group()
    g.add_argument("--check", action="store_true", help="只读检查（默认）")
    g.add_argument("--apply", action="store_true", help="幂等执行")
    g.add_argument("--rollback", action="store_true", help="回退结构")
    a = ap.parse_args()
    if not (a.check or a.apply or a.rollback):
        a.check = True

    eng = create_engine(URL, future=True)
    col, idx = col_exists(eng), idx_exists(eng)
    print("[state] %s.%s=%s  index %s=%s" % (TABLE, COLUMN, col, INDEX, idx))

    if a.check:
        print("[check] %s" % ("结构就绪（无操作）" if (col and idx) else
                              ("缺列" if not col else "") + ("缺索引" if not idx else "")))
        return 0

    if a.rollback:
        with eng.begin() as c:
            if idx:
                c.execute(text(DROP_INDEX_SQL))
                print("[rollback] DROP INDEX %s ✅" % INDEX)
            if col:
                c.execute(text(DROP_COLUMN_SQL))
                print("[rollback] DROP COLUMN %s ✅" % COLUMN)
        print("[state] 回退后 col=%s idx=%s" % (col_exists(eng), idx_exists(eng)))
        return 0

    # --apply
    done = []
    if not col:
        with eng.begin() as c:
            c.execute(text(ADD_COLUMN_SQL))
        done.append("ADD COLUMN %s" % COLUMN)
        print("[apply] ADD COLUMN %s ✅" % COLUMN)
    else:
        print("[apply] column %s 已存在 → NOOP" % COLUMN)
    if not idx:
        with eng.begin() as c:
            c.execute(text(ADD_INDEX_SQL))
        done.append("CREATE INDEX %s" % INDEX)
        print("[apply] CREATE UNIQUE INDEX %s ✅" % INDEX)
    else:
        print("[apply] index %s 已存在 → NOOP" % INDEX)

    col2, idx2 = col_exists(eng), idx_exists(eng)
    print("[state] 执行后 col=%s idx=%s" % (col2, idx2))
    payload = {"changed": done, "column_exists": col2, "index_exists": idx2}
    print("[result] %s" % payload)
    return 0 if (col2 and idx2) else 5


if __name__ == "__main__":
    sys.exit(main())