package main

import (
	"encoding/json"
	"fmt"
	"math/rand"
	"net/http"
	"time"
)

type OrderItem struct {
	ProductID string  `json:"product_id"`
	Name      string  `json:"name"`
	Price     float64 `json:"price"`
	Qty       int     `json:"qty"`
}

type OrderRequest struct {
	UserID   string      `json:"user_id"`
	Items    []OrderItem `json:"items"`
	PayToken string      `json:"pay_token"`
	Address  string      `json:"address"`
}

type OrderResponse struct {
	Status    string      `json:"status"`
	OrderID   string      `json:"order_id"`
	UserID    string      `json:"user_id"`
	Items     []OrderItem `json:"items"`
	Total     float64     `json:"total"`
	CreatedAt string      `json:"created_at"`
	EstDays   int         `json:"estimated_delivery_days"`
}

func generateOrderID() string {
	const chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	r := rand.New(rand.NewSource(time.Now().UnixNano()))
	b := make([]byte, 10)
	for i := range b {
		b[i] = chars[r.Intn(len(chars))]
	}
	return "ORD-" + string(b)
}

func calcTotal(items []OrderItem) float64 {
	total := 0.0
	for _, item := range items {
		total += item.Price * float64(item.Qty)
	}
	// Округление до 2 знаков
	return float64(int(total*100)) / 100
}

func Handler(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")

	if r.Method != http.MethodPost {
		w.WriteHeader(http.StatusMethodNotAllowed)
		fmt.Fprintln(w, `{"error":"method not allowed"}`)
		return
	}

	var req OrderRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		w.WriteHeader(http.StatusBadRequest)
		fmt.Fprintf(w, `{"error":"invalid JSON: %s"}`, err.Error())
		return
	}

	if req.UserID == "" {
		w.WriteHeader(http.StatusUnprocessableEntity)
		fmt.Fprintln(w, `{"error":"user_id required"}`)
		return
	}
	if len(req.Items) == 0 {
		w.WriteHeader(http.StatusUnprocessableEntity)
		fmt.Fprintln(w, `{"error":"items cannot be empty"}`)
		return
	}
	if req.PayToken == "" {
		w.WriteHeader(http.StatusUnprocessableEntity)
		fmt.Fprintln(w, `{"error":"pay_token required"}`)
		return
	}

	resp := OrderResponse{
		Status:    "created",
		OrderID:   generateOrderID(),
		UserID:    req.UserID,
		Items:     req.Items,
		Total:     calcTotal(req.Items),
		CreatedAt: time.Now().UTC().Format(time.RFC3339),
		EstDays:   3 + rand.Intn(5),
	}

	w.WriteHeader(http.StatusCreated)
	json.NewEncoder(w).Encode(resp)
}