lora_route_py/sim/radio/channel.py

"""
Wireless Channel Model.

Implements:
- Broadcast propagation to all nodes in range
- Airtime occupation tracking
- Collision detection (time overlap + |RSSI1 - RSSI2| < 6 dB)
- Transmission statistics for efficiency analysis
"""

import simpy
from typing import Dict, List, Optional, Callable
from dataclasses import dataclass, field

from sim.core.packet import Packet
from sim.radio import propagation, airtime as airtime_calc


@dataclass
class Transmission:
    """Represents an ongoing transmission on the channel."""

    packet: Packet
    sender_id: int
    start_time: float
    end_time: float
    rssi: float
    channel_busy_until: float
    airtime: float = 0.0  # Add airtime field


@dataclass
class ReceivedPacket:
    """Represents a packet received by a node."""

    packet: Packet
    sender_id: int
    rssi: float
    rx_time: float
    collision: bool = False


class Channel:
    """
    Wireless channel with collision detection.

    Manages:
    - Transmissions and their time slots
    - Collision detection based on time overlap and RSSI difference
    - Packet delivery to nodes within range
    - Transmission statistics for efficiency analysis
    """

    COLLISION_RSSI_DIFF_DB = 6.0  # RSSI difference threshold for collision

    def __init__(self, env: simpy.Environment):
        """
        Initialize channel.

        Args:
            env: SimPy environment
        """
        self.env = env
        self.transmissions: List[Transmission] = []
        self.collision_count = 0

        # Efficiency metrics
        self.total_transmissions = 0
        self.total_airtime = 0.0
        self.hello_transmissions = 0
        self.data_transmissions = 0
        self.ack_transmissions = 0

        # Callback for packet reception (set by node manager)
        self.receive_callback: Optional[Callable[[int, ReceivedPacket], None]] = None

        # Node positions {node_id: (x, y)}
        self.node_positions: Dict[int, tuple] = {}

    def register_node(self, node_id: int, x: float, y: float):
        """Register node position for propagation calculation."""
        self.node_positions[node_id] = (x, y)

    def transmit(self, packet: Packet, sender_id: int) -> float:
        """
        Transmit a packet on the channel.

        Args:
            packet: Packet to transmit
            sender_id: ID of sending node

        Returns:
            Airtime in seconds
        """
        # Calculate packet size and airtime
        if packet.is_hello:
            pkt_airtime = airtime_calc.get_hello_airtime()
            self.hello_transmissions += 1
        elif packet.is_ack:
            pkt_airtime = airtime_calc.get_ack_airtime()
            self.ack_transmissions += 1
        else:  # DATA
            payload_size = len(packet.payload) if packet.payload else 16
            pkt_airtime = airtime_calc.get_data_airtime(payload_size)
            self.data_transmissions += 1

        # Track transmission statistics
        self.total_transmissions += 1
        self.total_airtime += pkt_airtime

        start_time = self.env.now
        end_time = start_time + pkt_airtime

        # Get sender position and calculate RSSI for each potential receiver
        sender_pos = self.node_positions.get(sender_id)

        # Check for collisions with ongoing transmissions
        colliding = self._check_collision(start_time, end_time)

        # Create transmission record
        if sender_pos:
            # Calculate RSSI at sender's own position (not really used)
            tx_power = packet.rssi if packet.rssi else 14.0
            sender_rssi = tx_power  # At transmitter, RSSI = TX power
        else:
            sender_rssi = 14.0

        transmission = Transmission(
            packet=packet,
            sender_id=sender_id,
            start_time=start_time,
            end_time=end_time,
            rssi=sender_rssi,
            channel_busy_until=end_time,
            airtime=pkt_airtime,
        )

        if colliding:
            self.collision_count += 1
            # All packets involved in collision are dropped
            # Don't deliver to receivers
        else:
            self.transmissions.append(transmission)
            # Deliver to all nodes in range
            self._deliver_packet(packet, sender_id, start_time, end_time)

        # Clean up old transmissions
        self._cleanup_transmissions()

        return pkt_airtime

    def _check_collision(self, start_time: float, end_time: float) -> bool:
        """
        Check if transmission overlaps with any ongoing transmission.

        Collision condition:
        - Time overlap AND
        - |RSSI1 - RSSI2| < 6 dB

        Args:
            start_time: Start time of new transmission
            end_time: End time of new transmission

        Returns:
            True if collision detected
        """
        for trans in self.transmissions:
            # Check time overlap
            if not (end_time <= trans.start_time or start_time >= trans.end_time):
                # Time overlaps - check RSSI difference
                # Since we're checking at the sender, we assume similar RSSI
                # at nearby receivers (simplified model)
                # In real scenario, would need per-receiver RSSI calculation
                return True
        return False

    def _deliver_packet(
        self, packet: Packet, sender_id: int, start_time: float, end_time: float
    ):
        """
        Deliver packet to all nodes within communication range.

        Args:
            packet: Packet to deliver
            sender_id: ID of sending node
            start_time: Transmission start time
            end_time: Transmission end time
        """
        if not self.receive_callback:
            return

        sender_pos = self.node_positions.get(sender_id)
        if not sender_pos:
            return

        for node_id, pos in self.node_positions.items():
            if node_id == sender_id:
                continue  # Don't deliver to sender

            # Calculate distance and RSSI
            dist = propagation.calculate_distance(
                sender_pos[0], sender_pos[1], pos[0], pos[1]
            )
            rssi = propagation.calculate_rssi(14.0, dist)  # Use default TX power

            # Check if packet can be received
            if propagation.can_receive(rssi):
                # Check if this reception is affected by collision
                collision = self._is_reception_collided(
                    node_id, start_time, end_time, rssi
                )

                received = ReceivedPacket(
                    packet=packet,
                    sender_id=sender_id,
                    rssi=rssi,
                    rx_time=start_time,
                    collision=collision,
                )

                # Deliver to node
                self.receive_callback(node_id, received)

    def _is_reception_collided(
        self, receiver_id: int, start_time: float, end_time: float, signal_rssi: float
    ) -> bool:
        """
        Check if reception is affected by collision from other transmitters.

        Args:
            receiver_id: ID of receiving node
            start_time: Packet start time
            end_time: Packet end time
            signal_rssi: RSSI of the signal we want to receive

        Returns:
            True if collision detected
        """
        for trans in self.transmissions:
            if trans.sender_id == receiver_id:
                continue  # Ignore self-transmissions in list

            # Check time overlap
            if not (end_time <= trans.start_time or start_time >= trans.end_time):
                # Time overlaps - calculate RSSI of interfering signal
                receiver_pos = self.node_positions.get(receiver_id)
                sender_pos = self.node_positions.get(trans.sender_id)

                if receiver_pos and sender_pos:
                    dist = propagation.calculate_distance(
                        sender_pos[0], sender_pos[1], receiver_pos[0], receiver_pos[1]
                    )
                    interference_rssi = propagation.calculate_rssi(14.0, dist)

                    # Check RSSI difference
                    rssi_diff = abs(signal_rssi - interference_rssi)
                    if rssi_diff < self.COLLISION_RSSI_DIFF_DB:
                        return True
        return False

    def _cleanup_transmissions(self):
        """Remove old transmissions that have ended."""
        current_time = self.env.now
        self.transmissions = [
            t for t in self.transmissions if t.end_time > current_time
        ]

    def get_channel_busy_until(self) -> float:
        """Get the time until which channel is busy."""
        if not self.transmissions:
            return self.env.now
        return max(t.channel_busy_until for t in self.transmissions)

    def get_efficiency_metrics(self) -> dict:
        """Get efficiency metrics for analysis."""
        return {
            "total_transmissions": self.total_transmissions,
            "total_airtime": self.total_airtime,
            "hello_transmissions": self.hello_transmissions,
            "data_transmissions": self.data_transmissions,
            "ack_transmissions": self.ack_transmissions,
        }

    def reset(self):
        """Reset channel state."""
        self.transmissions.clear()
        self.collision_count = 0
        self.total_transmissions = 0
        self.total_airtime = 0.0
        self.hello_transmissions = 0
        self.data_transmissions = 0
        self.ack_transmissions = 0