# tasks/online-compute/FlinkSQL/flinksql_007/gt/rewrite_sql.py
"""SQL rewriter for flinksql_007 grading.

Swaps datagen connector -> filesystem (read seed CSV) and print connector -> filesystem
(write output CSV). Preserves computed columns, WATERMARK, SELECT/JOIN/INSERT.

Implementation: targeted regex on WITH(...) blocks.
"""
import re

SEED_TABLE_MAP = {
    "user_source": "users.csv",
}

_WITH_RE = re.compile(r"WITH\s*\(([^)]*)\)", re.IGNORECASE | re.DOTALL)
_CREATE_RE = re.compile(r"CREATE\s+TABLE\s+(\w+)", re.IGNORECASE)
_CONN_RE = re.compile(r"'connector'\s*=\s*'(\w+)'", re.IGNORECASE)
# 方案 B：把 datagen 源表的计算列 `X AS LOCALTIMESTAMP` 改写为普通 `X TIMESTAMP(3)`
# 列（读 seed CSV 的时间戳列）。agent 若已用普通 TIMESTAMP(3) 则保持不变。
# 两方向都归一到 TIMESTAMP(3)，使 GT 与 agent 的 CSV schema 一致。
# 仅作用于 WITH 块之前的列定义区，不影响 WATERMARK / INSERT / SELECT。
_AS_LT_RE = re.compile(r"(\w+)\s+AS\s+LOCALTIMESTAMP", re.IGNORECASE)
_PLAIN_TS_RE = re.compile(r"(\w+)\s+TIMESTAMP(?:\(\d+\))?", re.IGNORECASE)


def rewrite_sql(sql_text, seed_dir, out_dir, out_prefix):
    """Rewrite SQL: datagen -> filesystem seed, print -> filesystem output.

    Args:
        sql_text: original SQL string
        seed_dir: directory containing seed CSV files
        out_dir: directory for output CSV (print sink replacement)
        out_prefix: "pred" or "gt" — output goes to {out_dir}/{out_prefix}/

    Returns:
        (rewritten_sql, ok, diagnostic)
    """
    out_path = f"{out_dir}/{out_prefix}"
    found_datagen = False
    found_print = False
    print_idx = 0
    rewritten = []

    for stmt in sql_text.split(";"):
        cm = _CREATE_RE.search(stmt)
        wm = _WITH_RE.search(stmt)
        if cm and wm:
            tname = cm.group(1)
            conn_m = _CONN_RE.search(wm.group(1))
            if conn_m:
                ctype = conn_m.group(1).lower()
                if ctype == "datagen":
                    found_datagen = True
                    seed_file = SEED_TABLE_MAP.get(tname.lower())
                    if not seed_file:
                        return "", False, f"no seed mapping for table '{tname}'"
                    new_with = (
                        f"WITH ('connector' = 'filesystem', "
                        f"'path' = '{seed_dir}/{seed_file}', "
                        f"'format' = 'csv', "
                        f"'csv.ignore-parse-errors' = 'true')"
                    )
                    # 方案 B：AS LOCALTIMESTAMP -> TIMESTAMP(3)；普通 TIMESTAMP(3) 保持
                    pre = stmt[:wm.start()]
                    pre = _AS_LT_RE.sub(r"\1 TIMESTAMP(3)", pre)
                    # 普通 TIMESTAMP(3) 列无需改动（已是目标形态）
                    stmt = pre + new_with + stmt[wm.end():]
                elif ctype == "print":
                    found_print = True
                    sink_id = f"sink{print_idx}"
                    print_idx += 1
                    # 保留 print connector, 加 print-identifier (changelog 归约用)
                    existing = wm.group(1).rstrip()
                    if existing.endswith(','):
                        existing = existing[:-1]
                    new_with = f"WITH ({existing}, 'print-identifier' = '{sink_id}')"
                    stmt = stmt[:wm.start()] + new_with + stmt[wm.end():]
        rewritten.append(stmt)

    if not found_datagen and not found_print:
        return "", False, "no datagen/print connector found"

    return ";".join(rewritten), True, "ok"