"""
Queue Position Model — estimates fill probability based on queue position.

The most impactful missing piece in the CWM. In real markets, 70-80% of limit
orders don't fill. Queue position determines fill probability.

This module models:
  - Queue position estimation (how many orders ahead of us)
  - Fill probability given queue position and market activity
  - Queue adverse selection (being at the front of a toxic queue)
"""
from __future__ import annotations

import math
from dataclasses import dataclass, field
from typing import Optional, Tuple

import numpy as np
from numba import njit


@dataclass(frozen=True, slots=True)
class QueueState:
    """Queue position state for a price level."""
    queue_position: int  # 0 = front of queue
    queue_depth: float   # total qty ahead of us
    fill_probability: float  # 0-1
    adverse_selection_risk: float  # 0-1


@njit(cache=True)
def estimate_queue_position(
    our_qty: float,
    level_qty: float,
    recent_trade_rate: float,
    time_in_queue_s: float,
) -> float:
    """
    Estimate queue position based on queue dynamics.

    Uses a simplified model:
      - Position = level_qty - our_qty (qty ahead)
      - Fill rate = recent_trade_rate / queue_depth
      - Time to fill = queue_depth / fill_rate

    Returns estimated queue depth ahead of us.
    """
    if level_qty <= 0:
        return 0.0
    queue_depth = max(0.0, level_qty - our_qty)
    if recent_trade_rate <= 0:
        return queue_depth
    # Adjust for time already in queue
    consumed = recent_trade_rate * time_in_queue_s
    return max(0.0, queue_depth - consumed)


@njit(cache=True)
def compute_fill_probability(
    queue_depth: float,
    our_qty: float,
    recent_trade_rate: float,
    time_horizon_s: float,
    toxicity: float,
) -> float:
    """
    Compute probability of fill given queue dynamics.

    Model:
      - Base fill rate = recent_trade_rate / (queue_depth + our_qty)
      - Adjusted for toxicity (toxic flow consumes queue faster)
      - Bounded by time horizon

    Returns 0.0-1.0 probability.
    """
    if our_qty <= 0 or queue_depth < 0:
        return 0.0
    if recent_trade_rate <= 0:
        return 0.0

    total_depth = queue_depth + our_qty
    if total_depth <= 0:
        return 1.0

    # Base fill rate: fraction of queue consumed per second
    base_rate = recent_trade_rate / total_depth

    # Toxicity adjustment: toxic flow fills queue faster (adverse for us)
    toxicity_factor = 1.0 + toxicity * 0.5

    # Probability of fill within time horizon
    fill_prob = 1.0 - math.exp(-base_rate * toxicity_factor * time_horizon_s)

    return min(1.0, max(0.0, fill_prob))


@njit(cache=True)
def compute_queue_adverse_selection(
    queue_position: int,
    recent_trade_rate: float,
    toxicity: float,
    spread_bps: float,
) -> float:
    """
    Compute adverse selection risk from queue position.

    Adverse selection is higher when:
      - We're near the front of the queue (more likely to be picked off)
      - Toxic flow is high (adverse fills more likely)
      - Spread is tight (less buffer against adverse moves)

    Returns 0.0-1.0 risk score.
    """
    if queue_position <= 0:
        position_risk = 1.0  # front of queue = highest risk
    else:
        position_risk = 1.0 / (1.0 + queue_position * 0.1)

    toxicity_risk = min(1.0, toxicity)
    spread_risk = max(0.0, 1.0 - spread_bps / 10.0)

    # Combined risk (weighted average)
    return 0.4 * position_risk + 0.4 * toxicity_risk + 0.2 * spread_risk


class QueuePositionModel:
    """
    Full queue position model for the CWM.

    Integrates with the CWM to provide:
      - Queue position estimation
      - Fill probability computation
      - Adverse selection risk scoring
    """

    def __init__(self, default_trade_rate: float = 0.5) -> None:
        self._default_trade_rate = default_trade_rate

    def estimate_fill_probability(
        self,
        our_qty: float,
        level_qty: float,
        toxicity: float = 0.0,
        spread_bps: float = 0.0,
        time_horizon_s: float = 300.0,
        recent_trade_rate: Optional[float] = None,
    ) -> float:
        """Estimate probability of fill at a price level."""
        trade_rate = recent_trade_rate or self._default_trade_rate
        queue_depth = estimate_queue_position(our_qty, level_qty, trade_rate, 0.0)
        return compute_fill_probability(queue_depth, our_qty, trade_rate, time_horizon_s, toxicity)

    def estimate_queue_position(
        self,
        our_qty: float,
        level_qty: float,
        recent_trade_rate: Optional[float] = None,
        time_in_queue_s: float = 0.0,
    ) -> float:
        """Estimate queue position ahead of us."""
        trade_rate = recent_trade_rate or self._default_trade_rate
        return estimate_queue_position(our_qty, level_qty, trade_rate, time_in_queue_s)

    def adverse_selection_risk(
        self,
        queue_position: int,
        toxicity: float = 0.0,
        spread_bps: float = 0.0,
    ) -> float:
        """Compute adverse selection risk from queue position."""
        return compute_queue_adverse_selection(queue_position, self._default_trade_rate, toxicity, spread_bps)