"""migrations/data_split.py — 预算数据拆分迁移：budget_data → expense_data

旧结构：budget_data = [{month, rev, gross, payment, cost, paid}]
新结构：expense_data = [{month, expense_type, cost, paid, exp_note}]

部署时自动：检测未拆分的旧数据，将 cost/paid 从 budget_data 迁移到 expense_data。
幂等：只处理 expense_data 为空的记录。
"""


def migrate_data_split():
    """一次性数据拆分迁移"""
    from db import db, _exec
    import json

    conn = db()
    try:
        # 查询未迁移的记录
        cur = conn.cursor(dictionary=True)
        cur.execute(
            "SELECT id, budget_data, expense_data FROM project_finances "
            "WHERE (expense_data IS NULL OR expense_data = '' OR expense_data = '[]') "
            "AND budget_data IS NOT NULL AND budget_data != '' AND budget_data != '[]'"
        )
        rows = cur.fetchall()
        cur.close()

        migrated = 0
        for row in rows:
            try:
                budget = json.loads(row.get("budget_data") or "[]")
            except (json.JSONDecodeError, TypeError):
                continue

            expense_rows = []
            for b in budget:
                expense_rows.append({
                    "month": b.get("month", ""),
                    "expense_type": "",
                    "cost": float(b.get("cost") or 0),
                    "paid": float(b.get("paid") or 0),
                    "exp_note": "",
                })

            if expense_rows:
                _exec(
                    conn,
                    "UPDATE project_finances SET expense_data = ? WHERE id = ?",
                    (json.dumps(expense_rows, ensure_ascii=False), row["id"]),
                )
                migrated += 1

        conn.commit()
        print(f"[migrate] 数据拆分迁移完成：{migrated} 条记录已从 budget_data 提取 cost/paid 到 expense_data")
    finally:
        conn.close()