simulation.py

# simulation.py — Dynamic time-based traffic simulation for UrbanFlow

def run_simulation(network, traffic_input, time_steps=10):
    """
    Simulates traffic flow over time.
    At each step:
      1. New vehicles enter from lanes
      2. Vehicles move one hop per step, limited by edge capacity
      3. Unmoved vehicles stay in queue
      4. Delay = total queued vehicles at end of step
    """
    queues = {node: 0 for node in network.keys()}
    total_delay = 0

    for t in range(time_steps):
        print(f"\n--- Time Step {t+1} ---")

        # New vehicles enter
        for lane, vehicles in traffic_input.items():
            queues[lane] += vehicles

        next_queues = {node: queues[node] for node in queues}

        # Process flow — distribute across ALL valid edges, not just first
        for node, connections in network.items():
            if queues[node] == 0:
                continue

            remaining = queues[node]
            for dest, capacity in sorted(connections.items(), key=lambda x: -x[1]):
                if remaining == 0:
                    break
                flow = min(remaining, capacity)
                next_queues[node] -= flow
                next_queues[dest] += flow
                remaining -= flow

        queues = next_queues

        step_delay = sum(v for v in queues.values() if v > 0)
        total_delay += step_delay

        print(f"Queues: {queues}")
        print(f"Step Delay: {step_delay}")

    print(f"\nTotal delay over simulation: {total_delay}")
    return total_delay