"""Order execution service (REQ-013, REQ-014, dcy-003).

A single background execution loop (invariant A single writer, invariant B
single broker session) that, per tick:
  dispatch: claim pending slots with broker_order_id IS NULL (option A queue),
            submit the order, record broker_order_id (idempotency guard).
  poll:     observe fills on dispatched pending slots and transition the slot
            (pending_buy->holding / pending_sell->closed), or roll back on reject.
reconcile() re-polls dispatched slots on restart so a crash after dispatch
converges without duplicate orders (REQ-014).

All slot writes go through SlotService (advisory lock). The broker is touched
only here, never by the domain or the HTTP API.
"""
from __future__ import annotations

from dataclasses import dataclass

from trex_core.application.broker_port import BrokerPort, OrderRequest
from trex_core.domain.slot import SlotService, SlotState, SlotStateMismatchError

_MAX_DISPATCH_PER_TICK = 64


@dataclass
class ExecutionResult:
    dispatched: int = 0
    filled: int = 0
    rolled_back: int = 0


class ExecutionService:
    def __init__(self, slot_service: SlotService, repo, broker: BrokerPort) -> None:
        self._svc = slot_service
        self._repo = repo
        self._broker = broker

    # ------------------------------------------------------------
    def run_once(self) -> ExecutionResult:
        r = ExecutionResult()
        self._dispatch(r)
        self._poll(r)
        return r

    def reconcile(self) -> ExecutionResult:
        """Restart recovery: re-poll dispatched-but-pending slots (REQ-014).

        Undispatched pending slots (broker_order_id IS NULL) are simply picked
        up by the next dispatch, so a crash before dispatch causes no duplicate.
        """
        r = ExecutionResult()
        self._poll(r)
        return r

    # ------------------------------------------------------------
    def _dispatch(self, r: ExecutionResult) -> None:
        for _ in range(_MAX_DISPATCH_PER_TICK):
            slot = self._repo.find_pending_for_dispatch()
            if slot is None:
                return
            side = "buy" if slot.status is SlotState.PENDING_BUY else "sell"
            qty = int(slot.qty or 0)
            limit = int(slot.entry_price) if slot.entry_price else None
            ack = self._broker.submit_order(
                OrderRequest(
                    slot_id=str(slot.slot_id),
                    side=side,
                    symbol=slot.symbol or "",
                    qty=qty,
                    limit_price=limit,
                    order_type="00" if limit is not None else "01",
                )
            )
            if ack.accepted and ack.broker_order_id:
                self._repo.mark_dispatched(slot.slot_id, ack.broker_order_id)
                r.dispatched += 1
            else:
                self._rollback(slot, reason=ack.reason or "order_rejected")
                r.rolled_back += 1

    def _poll(self, r: ExecutionResult) -> None:
        for slot in self._repo.list_dispatched_pending():
            side = "buy" if slot.status is SlotState.PENDING_BUY else "sell"
            fs = self._broker.poll_fill(slot.broker_order_id, side=side, symbol=slot.symbol or "")
            if fs.is_filled:
                self._on_filled(slot, fs)
                r.filled += 1
            elif fs.is_terminal_reject:
                self._rollback(slot, reason=f"order_{fs.state}")
                r.rolled_back += 1
            # accepted / partially_filled -> leave for next tick

    # ------------------------------------------------------------
    def _on_filled(self, slot, fs) -> None:
        try:
            if slot.status is SlotState.PENDING_BUY:
                self._svc.transit_slot(
                    slot.slot_id, SlotState.PENDING_BUY, SlotState.HOLDING,
                    reason="buy_filled", actor="execution_loop",
                    avg_price=fs.avg_price, qty=float(fs.filled_qty) or slot.qty,
                )
            else:  # PENDING_SELL
                self._svc.transit_slot(
                    slot.slot_id, SlotState.PENDING_SELL, SlotState.CLOSED,
                    reason="sell_filled", actor="execution_loop",
                )
        except SlotStateMismatchError:
            return  # slot moved concurrently; next tick reconciles
        self._repo.clear_dispatch(slot.slot_id)  # done with this order

    def _rollback(self, slot, *, reason: str) -> None:
        try:
            if slot.status is SlotState.PENDING_BUY:
                self._svc.transit_slot(
                    slot.slot_id, SlotState.PENDING_BUY, SlotState.IDLE,
                    reason=reason, actor="execution_loop",
                )  # idle reset clears broker_order_id in the domain
            else:  # PENDING_SELL rejected -> back to holding, clear order for re-dispatch
                self._svc.transit_slot(
                    slot.slot_id, SlotState.PENDING_SELL, SlotState.HOLDING,
                    reason=reason, actor="execution_loop",
                )
                self._repo.clear_dispatch(slot.slot_id)
        except SlotStateMismatchError:
            return