class SingleStopVehicleLoader:
    """
    Optimize loading for single-destination delivery

    Uses 3D bin packing with vehicle-specific constraints
    """

    def __init__(self, vehicle_length, vehicle_width, vehicle_height,
                 weight_capacity, front_axle_limit=13000, rear_axle_limit=34000):
        """
        Initialize vehicle loader

        Parameters:
        - vehicle_length, vehicle_width, vehicle_height: cargo area dimensions (inches)
        - weight_capacity: max payload weight (lbs)
        - front_axle_limit, rear_axle_limit: axle weight limits (lbs)
        """

        self.vehicle_dims = (vehicle_length, vehicle_width, vehicle_height)
        self.weight_capacity = weight_capacity
        self.front_axle_limit = front_axle_limit
        self.rear_axle_limit = rear_axle_limit

        self.items = []
        self.solution = None

    def add_item(self, length, width, height, weight, item_id=None):
        """Add item to load"""
        if item_id is None:
            item_id = f"Item_{len(self.items)}"

        self.items.append({
            'id': item_id,
            'dims': (length, width, height),
            'weight': weight
        })

    def optimize_loading(self, algorithm='weight_balanced'):
        """
        Optimize vehicle loading

        Algorithms:
        - 'weight_balanced': Prioritize weight distribution
        - 'space_efficient': Maximize space utilization
        - 'easy_unload': Place items for easy access
        """

        L, W, H = self.vehicle_dims

        if algorithm == 'weight_balanced':
            # Sort by weight (heaviest first)
            sorted_items = sorted(self.items,
                                 key=lambda x: x['weight'],
                                 reverse=True)
        elif algorithm == 'space_efficient':
            # Sort by volume
            sorted_items = sorted(self.items,
                                 key=lambda x: x['dims'][0] * x['dims'][1] * x['dims'][2],
                                 reverse=True)
        else:
            sorted_items = self.items

        loaded_items = []
        current_weight = 0

        # Simple layer-based loading
        current_y = 0
        current_z = 0
        current_x = 0

        for item in sorted_items:
            l, w, h = item['dims']
            weight = item['weight']

            # Check weight
            if current_weight + weight > self.weight_capacity:
                continue  # Skip item if too heavy

            # Try to place item
            if current_x + l <= L:
                # Place in current row
                loaded_items.append({
                    'item': item,
                    'position': (current_x, current_y, current_z),
                    'dims': (l, w, h)
                })
                current_x += l
                current_weight += weight

            elif current_y + w <= W:
                # Start new row
                current_x = 0
                current_y += w
                loaded_items.append({
                    'item': item,
                    'position': (current_x, current_y, current_z),
                    'dims': (l, w, h)
                })
                current_x += l
                current_weight += weight

            elif current_z + h <= H:
                # Start new layer
                current_x = 0
                current_y = 0
                current_z += h
                loaded_items.append({
                    'item': item,
                    'position': (current_x, current_y, current_z),
                    'dims': (l, w, h)
                })
                current_x += l
                current_weight += weight

        # Check axle weights
        axle_check = self.check_axle_weights(loaded_items)

        self.solution = {
            'loaded_items': loaded_items,
            'total_weight': current_weight,
            'items_loaded': len(loaded_items),
            'items_not_loaded': len(self.items) - len(loaded_items),
            'utilization': self.calculate_utilization(loaded_items),
            'axle_weights': axle_check
        }

        return self.solution

    def check_axle_weights(self, loaded_items):
        """
        Calculate axle weight distribution

        Assumes:
        - Front axle at 0 (front of vehicle)
        - Rear axle at 60% of vehicle length
        """

        L = self.vehicle_dims[0]
        rear_axle_position = L * 0.6

        front_axle_weight = 0
        rear_axle_weight = 0

        for item_data in loaded_items:
            pos = item_data['position']
            dims = item_data['dims']
            weight = item_data['item']['weight']

            # Calculate center of mass
            com_x = pos[0] + dims[0] / 2

            # Distance from axles
            distance_from_rear = rear_axle_position - com_x

            if distance_from_rear > 0:
                # Weight forward of rear axle - distributes to both
                front_ratio = distance_from_rear / rear_axle_position
                front_axle_weight += weight * front_ratio
                rear_axle_weight += weight * (1 - front_ratio)
            else:
                # Weight behind rear axle - all on rear
                rear_axle_weight += weight

        return {
            'front_axle': front_axle_weight,
            'rear_axle': rear_axle_weight,
            'front_limit': self.front_axle_limit,
            'rear_limit': self.rear_axle_limit,
            'front_ok': front_axle_weight <= self.front_axle_limit,
            'rear_ok': rear_axle_weight <= self.rear_axle_limit,
            'balanced': abs(front_axle_weight - rear_axle_weight) / (front_axle_weight + rear_axle_weight) < 0.3
        }

    def calculate_utilization(self, loaded_items):
        """Calculate volume utilization"""
        L, W, H = self.vehicle_dims
        vehicle_volume = L * W * H

        loaded_volume = sum(
            item_data['dims'][0] * item_data['dims'][1] * item_data['dims'][2]
            for item_data in loaded_items
        )

        return (loaded_volume / vehicle_volume * 100) if vehicle_volume > 0 else 0

    def print_solution(self):
        """Print loading solution"""
        if not self.solution:
            print("No solution available")
            return

        print("=" * 70)
        print("VEHICLE LOADING SOLUTION")
        print("=" * 70)
        print(f"Vehicle: {self.vehicle_dims[0]}L x {self.vehicle_dims[1]}W x {self.vehicle_dims[2]}H in")
        print(f"Weight Capacity: {self.weight_capacity:,} lbs")
        print()
        print(f"Items Loaded: {self.solution['items_loaded']} / {len(self.items)}")
        print(f"Total Weight: {self.solution['total_weight']:,} lbs")
        print(f"Utilization: {self.solution['utilization']:.1f}%")
        print()
        print("Axle Weight Distribution:")
        axle = self.solution['axle_weights']
        print(f"  Front Axle: {axle['front_axle']:,.0f} lbs "
              f"({'OK' if axle['front_ok'] else 'OVER LIMIT'})")
        print(f"  Rear Axle: {axle['rear_axle']:,.0f} lbs "
              f"({'OK' if axle['rear_ok'] else 'OVER LIMIT'})")
        print(f"  Balanced: {'Yes' if axle['balanced'] else 'No - adjust load'}")


# Example usage
if __name__ == "__main__":
    # 26ft box truck
    loader = SingleStopVehicleLoader(
        vehicle_length=312,  # 26ft in inches
        vehicle_width=96,    # 8ft
        vehicle_height=96,   # 8ft
        weight_capacity=10000  # lbs
    )

    # Add items
    loader.add_item(48, 40, 60, 800, "Pallet_1")
    loader.add_item(48, 40, 50, 700, "Pallet_2")
    loader.add_item(48, 40, 55, 750, "Pallet_3")
    loader.add_item(36, 30, 40, 500, "Box_1")
    loader.add_item(36, 30, 40, 500, "Box_2")

    # Optimize
    solution = loader.optimize_loading(algorithm='weight_balanced')
    loader.print_solution()

class MultiStopVehicleLoader:
    """
    Optimize vehicle loading for multi-stop delivery routes

    Ensures items are accessible in delivery sequence
    """

    def __init__(self, vehicle_dims, weight_capacity):
        self.vehicle_dims = vehicle_dims
        self.weight_capacity = weight_capacity
        self.stops = []  # List of delivery stops
        self.solution = None

    def add_stop(self, stop_id, items, delivery_sequence):
        """
        Add delivery stop with items

        Parameters:
        - stop_id: stop identifier
        - items: list of item dicts with 'dims' and 'weight'
        - delivery_sequence: order in route (1, 2, 3, ...)
        """

        self.stops.append({
            'id': stop_id,
            'items': items,
            'sequence': delivery_sequence
        })

    def optimize_loading(self):
        """
        Optimize loading for multi-stop delivery

        Strategy:
        - Zone vehicle by delivery sequence
        - Last stop loaded first (at door)
        - Earlier stops loaded deeper in vehicle
        """

        # Sort stops by reverse delivery sequence
        sorted_stops = sorted(self.stops,
                            key=lambda s: s['sequence'],
                            reverse=True)

        L, W, H = self.vehicle_dims

        # Calculate zones
        num_stops = len(sorted_stops)
        zone_length = L / num_stops

        zones = []
        current_weight = 0

        for idx, stop in enumerate(sorted_stops):
            zone_start = idx * zone_length
            zone_end = (idx + 1) * zone_length

            zone_items = []

            # Load items for this stop in this zone
            for item in stop['items']:
                if current_weight + item['weight'] <= self.weight_capacity:
                    # Simple placement (could be more sophisticated)
                    zone_items.append({
                        'item': item,
                        'stop_id': stop['id'],
                        'zone': (zone_start, zone_end)
                    })
                    current_weight += item['weight']

            zones.append({
                'stop': stop,
                'zone': (zone_start, zone_end),
                'items': zone_items
            })

        self.solution = {
            'zones': zones,
            'total_weight': current_weight,
            'stops_loaded': len(zones),
            'total_items': sum(len(z['items']) for z in zones)
        }

        return self.solution

    def print_solution(self):
        """Print multi-stop loading plan"""
        if not self.solution:
            print("No solution available")
            return

        print("=" * 70)
        print("MULTI-STOP VEHICLE LOADING PLAN")
        print("=" * 70)
        print(f"Total Weight: {self.solution['total_weight']:,} lbs")
        print(f"Stops: {self.solution['stops_loaded']}")
        print(f"Total Items: {self.solution['total_items']}")
        print()

        for zone_data in self.solution['zones']:
            stop = zone_data['stop']
            zone = zone_data['zone']
            print(f"Stop {stop['sequence']}: {stop['id']}")
            print(f"  Zone: {zone[0]:.0f}-{zone[1]:.0f} inches from front")
            print(f"  Items: {len(zone_data['items'])}")
            print()

def optimize_fleet_loading(orders, vehicles):
    """
    Optimize loading across multiple vehicles

    Assigns orders to vehicles to minimize:
    - Number of vehicles used
    - Total distance traveled
    - Loading/unloading complexity

    Parameters:
    - orders: list of order dicts with items, destination, priority
    - vehicles: list of available vehicle specs

    Returns: assignment of orders to vehicles
    """

    from pulp import *

    n_orders = len(orders)
    n_vehicles = len(vehicles)

    # Create problem
    prob = LpProblem("Fleet_Loading", LpMinimize)

    # Decision variables
    # x[i,j] = 1 if order i assigned to vehicle j
    x = LpVariable.dicts("assign",
                        [(i, j) for i in range(n_orders) for j in range(n_vehicles)],
                        cat='Binary')

    # y[j] = 1 if vehicle j is used
    y = LpVariable.dicts("use_vehicle", range(n_vehicles), cat='Binary')

    # Objective: Minimize vehicles used + routing cost
    prob += lpSum([y[j] * vehicles[j]['cost']
                   for j in range(n_vehicles)]), "Total_Cost"

    # Constraints

    # 1. Each order assigned to exactly one vehicle
    for i in range(n_orders):
        prob += lpSum([x[i,j] for j in range(n_vehicles)]) == 1, f"Order_{i}"

    # 2. Vehicle capacity (weight)
    for j in range(n_vehicles):
        prob += (lpSum([orders[i]['weight'] * x[i,j] for i in range(n_orders)]) <=
                vehicles[j]['weight_capacity']), f"Weight_{j}"

    # 3. Vehicle capacity (volume)
    for j in range(n_vehicles):
        prob += (lpSum([orders[i]['volume'] * x[i,j] for i in range(n_orders)]) <=
                vehicles[j]['volume_capacity']), f"Volume_{j}"

    # 4. Vehicle used if orders assigned
    for j in range(n_vehicles):
        for i in range(n_orders):
            prob += x[i,j] <= y[j], f"VehicleUsed_{i}_{j}"

    # Solve
    prob.solve(PULP_CBC_CMD(msg=0))

    # Extract solution
    assignments = [[] for _ in range(n_vehicles)]

    for i in range(n_orders):
        for j in range(n_vehicles):
            if x[i,j].varValue and x[i,j].varValue > 0.5:
                assignments[j].append(i)

    return {
        'status': LpStatus[prob.status],
        'vehicles_used': sum(1 for a in assignments if a),
        'assignments': assignments
    }