package main

import (
	"fmt"
)

// a new type named Category that can hold integer values
type Category int

// The go equivalent of an enum that enumerates different named Categories
const (
	Electronics Category = iota //0
	Groceries                   //1
	Clothes                     //2
)

// implementation of the fmt.Stringer interface. In that way, Categories can be printed using the fmt.Print* functions
func (c Category) String() string {
	switch c {
	case Electronics:
		return "Electronics"
	case Groceries:
		return "Groceries"
	case Clothes:
		return "Clothes"
	default:
		return "Unknown"
	}
}

type Product struct {
	Name     string
	Price    float64
	Quantity int
	Category Category
}

// implementation of the fmt.Stringer interface for printing products
func (p Product) String() string {
	return fmt.Sprintf("%s (%s, Price: $%.2f, Quantity: %d)", p.Name, p.Category, p.Price, p.Quantity)
}

func addProduct(inventory map[string]Product, name string, price float64, quantity int, category Category) {

	//do not create a new product in case a product with the name already exists
	if _, exists := inventory[name]; exists {
		fmt.Printf("Unable to add new Product %s: Product already exists.\n", name)
		return
	}

	//create a new product...
	p := Product{name, price, quantity, category}
	inventory[name] = p // ...and insert it into the map
}

func removeProduct(inventory map[string]Product, name string) {
	//no checks required. Does nothing if the product doesn't exist.
	delete(inventory, name)
}

func updateQuantity(inventory map[string]Product, name string, newQuantity int) {
	p := inventory[name]     //read from the map
	p.Quantity = newQuantity //update value
	inventory[name] = p      //store back into the map
}

func displayInventory(inventory map[string]Product) {
	//Iterate over the inventory
	i := 1
	for _, p := range inventory { //don't care about the key (_), only the value (p) is relevant
		fmt.Printf("%d. %s\n", i, p)
		i++
	}
}

func main() {

	fmt.Println("Welcome to the Inventory Manager!")

	// Store a fixed list of initial product names in an array.
	initialProductNames := [...]string{"Laptop"}

	// Convert the array into a slice so the inventory can grow or shrink dynamically.
	productNames := initialProductNames[:]
	productNames = append(productNames, "Apples", "T-shirt")

	// Use a map to associate product names with details like quantity, price, and category.
	prices := []float64{1000.0, 2.0, 10.0}
	quantities := []int{5, 50, 20}
	categories := []Category{Electronics, Groceries, Clothes}

	inventory := make(map[string]Product)
	for i, name := range productNames {
		inventory[name] = Product{name, prices[i], quantities[i], categories[i]}
	}

	// Display initial inventory
	fmt.Println("\nInitial Inventory:")
	displayInventory(inventory)

	// Add a new product
	fmt.Println("\nAdding a new product: Phone (Electronics, Price: $800, Quantity: 10)")
	addProduct(inventory, "Phone", 800, 10, Electronics)

	// Display updated inventory
	fmt.Println("\nUpdated Inventory:")
	displayInventory(inventory)

	// Update the quantity of an existing product
	fmt.Println("\nUpdating quantity for Apples: New Quantity = 30")
	updateQuantity(inventory, "Apples", 30)

	// Remove a product
	fmt.Println("\nRemoving product: T-shirt")
	removeProduct(inventory, "T-shirt")

	// Display final inventory
	fmt.Println("\nFinal Inventory:")
	displayInventory(inventory)
}