"""
Strategy backtesting engine for A-share stocks.

Supports:
- Predefined strategies (MA crossover, momentum, mean reversion, etc.)
- Custom entry/exit rules
- Multi-strategy comparison
- Performance metrics (returns, drawdown, Sharpe, win rate)

Usage: python3 backtest_engine.py <function> <json_args>
"""

import sys
import json


def run(strategy_name=None, entry_rule=None, exit_rule=None,
        universe="hs300", symbols=None, start_date="20210101", end_date="20251231"):
    """Run a single backtest. Stub - to be implemented."""
    return json.dumps({
        "status": "stub",
        "message": f"Backtest (strategy={strategy_name or 'custom'}, universe={universe}) — not yet implemented",
        "metrics": {
            "cumulative_return": None,
            "annualized_return": None,
            "win_rate": None,
            "max_drawdown": None,
            "sharpe_ratio": None,
            "benchmark_return": None,
        },
    }, ensure_ascii=False)


def predefined():
    """List available predefined strategies."""
    strategies = [
        {
            "name": "ma_cross",
            "description": "MA Golden Cross: buy when 20-day MA crosses above 60-day MA",
            "params": {"fast": 20, "slow": 60},
        },
        {
            "name": "momentum_breakout",
            "description": "Momentum Breakout: buy when price breaks 20-day high with volume > 1.5x avg",
            "params": {"lookback": 20, "volume_multiplier": 1.5},
        },
        {
            "name": "mean_reversion",
            "description": "Mean Reversion: buy when price deviates >2 std below 20-day MA, sell at MA",
            "params": {"ma_period": 20, "std_dev": 2},
        },
        {
            "name": "turtle",
            "description": "Turtle Trading: breakout of 20-day high, exit at 10-day low",
            "params": {"entry_period": 20, "exit_period": 10},
        },
    ]
    return json.dumps({"strategies": strategies}, ensure_ascii=False)


def compare(strategies, universe="hs300", start_date="20210101", end_date="20251231"):
    """Compare multiple strategies. Stub - to be implemented."""
    return json.dumps({
        "status": "stub",
        "message": f"Strategy comparison ({strategies}) — not yet implemented",
        "comparison": [],
    }, ensure_ascii=False)


FUNCTIONS = {
    "run": run,
    "predefined": predefined,
    "compare": compare,
}

if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Usage: backtest_engine.py <function> [json_args]")
        sys.exit(1)

    func_name = sys.argv[1]
    args = json.loads(sys.argv[2]) if len(sys.argv) > 2 else {}

    if func_name not in FUNCTIONS:
        print(f"Unknown function: {func_name}")
        sys.exit(1)

    result = FUNCTIONS[func_name](**args)
    print(result)