#!/usr/bin/env python3
"""
Test script to demonstrate the updated _add_stock logic.
This shows how duplicates are prevented by updating existing stock items.
"""

def simulate_add_stock(part_id, location_id, quantity, existing_stock_items):
    """
    Simulate the add stock workflow.

    Args:
        part_id: Part ID
        location_id: Location ID
        quantity: Quantity to add
        existing_stock_items: List of existing stock items (for simulation)

    Returns:
        Tuple of (action, stock_id, old_stock, new_stock)
    """
    # Find existing stock item for this part at this location
    existing = None
    for item in existing_stock_items:
        if item['part'] == part_id and item['location'] == location_id:
            existing = item
            break

    if existing:
        # Stock item exists - add to it
        stock_id = existing['pk']
        old_stock = existing['quantity']
        new_stock = old_stock + quantity

        # Update the existing item (simulate)
        existing['quantity'] = new_stock

        return ('updated', stock_id, old_stock, new_stock)
    else:
        # No existing stock - create new item
        new_item = {
            'pk': len(existing_stock_items) + 100,  # Simulate new ID
            'part': part_id,
            'location': location_id,
            'quantity': quantity
        }
        existing_stock_items.append(new_item)

        return ('created', new_item['pk'], 0, quantity)


print("Testing Add Stock Duplicate Prevention\n")
print("=" * 60)

# Simulate existing stock items
stock_items = []

print("\nScenario 1: Adding stock when NO existing item exists")
print("-" * 60)
action, sid, old, new = simulate_add_stock(part_id=456, location_id=476, quantity=150, existing_stock_items=stock_items)
print(f"Action: {action}")
print(f"Stock ID: {sid}")
print(f"Stock change: {old} -> {new} (+{new - old})")
print(f"Total stock items: {len(stock_items)}")
print(f"Expected: Created new stock item PASS" if action == 'created' else "FAIL")

print("\n" + "=" * 60)
print("\nScenario 2: Adding MORE stock to EXISTING item (should UPDATE, not duplicate)")
print("-" * 60)
print(f"Current stock items before scan: {len(stock_items)}")
action, sid, old, new = simulate_add_stock(part_id=456, location_id=476, quantity=100, existing_stock_items=stock_items)
print(f"Action: {action}")
print(f"Stock ID: {sid}")
print(f"Stock change: {old} -> {new} (+{new - old})")
print(f"Total stock items: {len(stock_items)}")
print(f"Expected: Updated existing item, NO duplicate PASS" if action == 'updated' and len(stock_items) == 1 else "FAIL")

print("\n" + "=" * 60)
print("\nScenario 3: Adding stock AGAIN (should continue to UPDATE)")
print("-" * 60)
print(f"Current stock items before scan: {len(stock_items)}")
action, sid, old, new = simulate_add_stock(part_id=456, location_id=476, quantity=50, existing_stock_items=stock_items)
print(f"Action: {action}")
print(f"Stock ID: {sid}")
print(f"Stock change: {old} -> {new} (+{new - old})")
print(f"Total stock items: {len(stock_items)}")
print(f"Expected: Updated existing item, still NO duplicate PASS" if action == 'updated' and len(stock_items) == 1 else "FAIL")

print("\n" + "=" * 60)
print("\nScenario 4: Adding same part to DIFFERENT location (should create new)")
print("-" * 60)
print(f"Current stock items before scan: {len(stock_items)}")
action, sid, old, new = simulate_add_stock(part_id=456, location_id=999, quantity=75, existing_stock_items=stock_items)
print(f"Action: {action}")
print(f"Stock ID: {sid}")
print(f"Stock change: {old} -> {new} (+{new - old})")
print(f"Total stock items: {len(stock_items)}")
print(f"Expected: Created new item for different location PASS" if action == 'created' and len(stock_items) == 2 else "FAIL")

print("\n" + "=" * 60)
print("\nFinal Summary:")
print("-" * 60)
for i, item in enumerate(stock_items, 1):
    print(f"Stock Item {i}: ID={item['pk']}, Part={item['part']}, Location={item['location']}, Qty={item['quantity']}")

print("\nSUCCESS All scenarios demonstrate proper duplicate prevention!")
print("   - Same part + same location = UPDATE existing")
print("   - Same part + different location = CREATE new")