import json
from dataclasses import asdict
from pathlib import Path
from typing import Callable, Mapping

from okx_codex_trader.models import PaperOrderResult, PaperPosition, PaperState, TradeSignal


def default_state() -> PaperState:
    return PaperState(
        cash_usdt=10_000.0,
        realized_pnl=0.0,
        positions=[],
        updated_at="1970-01-01T00:00:00Z",
    )


def load_state(path: Path) -> PaperState:
    if not path.exists():
        return default_state()
    try:
        payload = json.loads(path.read_text())
    except json.JSONDecodeError as exc:
        raise ValueError("paper state is invalid") from exc
    return parse_state(payload)


def parse_state(payload: Mapping[str, object]) -> PaperState:
    try:
        cash_usdt = float(payload["cash_usdt"])
        realized_pnl = float(payload["realized_pnl"])
        updated_at = payload["updated_at"]
        positions_payload = payload["positions"]
    except (KeyError, TypeError, ValueError) as exc:
        raise ValueError("paper state is invalid") from exc
    if not isinstance(updated_at, str) or not isinstance(positions_payload, list):
        raise ValueError("paper state is invalid")
    positions: list[PaperPosition] = []
    for entry in positions_payload:
        if not isinstance(entry, Mapping):
            raise ValueError("paper state is invalid")
        try:
            symbol = entry["symbol"]
            side = entry["side"]
            quantity = float(entry["quantity"])
            avg_entry_price = float(entry["avg_entry_price"])
            margin_used = float(entry["margin_used"])
        except (KeyError, TypeError, ValueError) as exc:
            raise ValueError("paper state is invalid") from exc
        if not isinstance(symbol, str) or side not in {"long", "short"}:
            raise ValueError("paper state is invalid")
        positions.append(
            PaperPosition(
                symbol=symbol,
                side=side,
                quantity=quantity,
                avg_entry_price=avg_entry_price,
                margin_used=margin_used,
            )
        )
    return PaperState(
        cash_usdt=cash_usdt,
        realized_pnl=realized_pnl,
        positions=positions,
        updated_at=updated_at,
    )


def save_state(path: Path, state: PaperState) -> None:
    path.write_text(json.dumps(asdict(state), indent=2))


def apply_signal(
    *,
    state: PaperState,
    symbol: str,
    signal: TradeSignal,
    margin_usdt: float,
    price: float,
    now: Callable[[], str],
) -> tuple[PaperState, PaperOrderResult]:
    if signal.action == "flat":
        return state, PaperOrderResult(
            status="noop",
            symbol=symbol,
            side=None,
            price=None,
            quantity=None,
            margin_used=None,
            cash_usdt=state.cash_usdt,
        )
    if state.cash_usdt < margin_usdt:
        raise ValueError("insufficient local cash")
    quantity = margin_usdt * signal.leverage / price
    positions = list(state.positions)
    for index, position in enumerate(positions):
        if position.symbol != symbol or position.side != signal.action:
            continue
        total_quantity = position.quantity + quantity
        avg_entry_price = (
            position.quantity * position.avg_entry_price + quantity * price
        ) / total_quantity
        positions[index] = PaperPosition(
            symbol=symbol,
            side=signal.action,
            quantity=total_quantity,
            avg_entry_price=avg_entry_price,
            margin_used=position.margin_used + margin_usdt,
        )
        break
    else:
        positions.append(
            PaperPosition(
                symbol=symbol,
                side=signal.action,
                quantity=quantity,
                avg_entry_price=price,
                margin_used=margin_usdt,
            )
        )
    next_state = PaperState(
        cash_usdt=state.cash_usdt - margin_usdt,
        realized_pnl=state.realized_pnl,
        positions=positions,
        updated_at=now(),
    )
    return next_state, PaperOrderResult(
        status="filled",
        symbol=symbol,
        side=signal.action,
        price=price,
        quantity=quantity,
        margin_used=margin_usdt,
        cash_usdt=next_state.cash_usdt,
    )