// Inventory System -- package inventory (finished).

package inventory

import (
	"errors"
	"fmt"
)

// Item is one collectable thing. Make one with NewItem.
type Item struct {
	name   string
	weight float64
	value  int
}

// NewItem returns an item. The name must not be empty, and the weight and the
// value must not be below 0.
func NewItem(name string, weight float64, value int) (*Item, error) {
	if name == "" {
		return nil, errors.New("an item needs a name")
	}
	if weight < 0 {
		return nil, fmt.Errorf("item %s: weight %.1f is below 0", name, weight)
	}
	if value < 0 {
		return nil, fmt.Errorf("item %s: value %d is below 0", name, value)
	}
	return &Item{name: name, weight: weight, value: value}, nil
}

// Name returns the item's name.
func (it *Item) Name() string {
	return it.name
}

// Describe returns a one-line summary such as "sword (3.5kg, 50g)".
func (it *Item) Describe() string {
	return fmt.Sprintf("%s (%.1fkg, %dg)", it.name, it.weight, it.value)
}

// Inventory is a container of items. Make one with New.
type Inventory struct {
	items []*Item
}

// New returns an empty inventory.
func New() *Inventory {
	return &Inventory{}
}

// Add puts an item in the inventory.
func (inv *Inventory) Add(item *Item) {
	inv.items = append(inv.items, item)
}

// Remove takes out the first item with this name and returns it. It returns
// nil if no item has this name.
func (inv *Inventory) Remove(name string) *Item {
	for i, item := range inv.items {
		if item.name == name {
			inv.items = append(inv.items[:i], inv.items[i+1:]...)
			return item
		}
	}
	return nil
}

// TotalWeight returns the sum of the weights.
func (inv *Inventory) TotalWeight() float64 {
	total := 0.0
	for _, item := range inv.items {
		total = total + item.weight
	}
	return total
}

// TotalValue returns the sum of the values.
func (inv *Inventory) TotalValue() int {
	total := 0
	for _, item := range inv.items {
		total = total + item.value
	}
	return total
}

// Counts returns how many items there are with each name.
func (inv *Inventory) Counts() map[string]int {
	counts := map[string]int{}
	for _, item := range inv.items {
		counts[item.name]++
	}
	return counts
}

// List prints each item on its own line, then a line of totals.
func (inv *Inventory) List() {
	fmt.Printf("Inventory (%d items):\n", len(inv.items))
	for _, item := range inv.items {
		fmt.Println("  - " + item.Describe())
	}
	fmt.Printf("  Totals: %.2fkg, %dg\n", inv.TotalWeight(), inv.TotalValue())
}