main.go

package main

import (
	"net/http"
	"github.com/gin-gonic/gin"
	"errors"
)

type book struct {
	ID 			string	`json:"id"`
	Title 		string	`json:"title"`
	Author 		string	`json:"author"`
	Quantity 	int		`json:"quantity"`
}

var books = []book{
	{ID: "1", Title: "In Search of Lost Time", Author: "Marcel Proust", Quantity: 2},
	{ID: "2", Title: "The Great Gatsby", Author: "F. Scott Fitzgerald", Quantity: 5},
	{ID: "3", Title: "War and Peace", Author: "Leo Tolstoy", Quantity: 6},
}


func getBooks(c *gin.Context){
	c.IndentedJSON(http.StatusOK, books)
}

func bookById(c *gin.Context){
	id := c.Param("id")
	book, err := getBookById(id)

	if err != nil {
		c.IndentedJSON(http.StatusNotFound,gin.H{"message":"Book not found."})
		return
	}

	c.IndentedJSON(http.StatusOK, book)
}

func checkoutBook(c *gin.Context){
	id, ok := c.GetQuery("id")

	if !ok { // 修正: err を ok に変更
		c.IndentedJSON(http.StatusBadRequest,gin.H{"message":"Missing id query parametor"})
		return
	}


	book,err := getBookById(id)

	if err != nil{
		c.IndentedJSON(http.StatusBadRequest,gin.H{"message":"Book Not Found."})
		return
	}

	if book.Quantity == 0 {
		c.IndentedJSON(http.StatusNotFound,gin.H{"message":"Book Not available."})
		return
	}

	book.Quantity -= 1
	c.IndentedJSON(http.StatusOK, book)
}

func returnBook(c *gin.Context){
	id, ok := c.GetQuery("id")

	if !ok { // 修正: err を ok に変更
		c.IndentedJSON(http.StatusBadRequest,gin.H{"message":"Missing id query parametor"})
		return
	}


	book,err := getBookById(id)

	if err != nil{
		c.IndentedJSON(http.StatusBadRequest,gin.H{"message":"Book Not Found."})
		return
	}

	book.Quantity += 1
	c.IndentedJSON(http.StatusOK,book)
}

func getBookById(id string)(*book,error){
	for i,b := range books {
		if b.ID == id {
			return &books[i],nil
		}
	}

	return nil, errors.New("book not found")
}

func createBook(c *gin.Context) {
	var newBook book

	if err := c.BindJSON(&newBook); err != nil{
		return
	}

	books = append(books,newBook)
	c.IndentedJSON(http.StatusCreated,newBook)
}

func main(){
	router := gin.Default()
	router.GET("/books", getBooks)
	router.GET("/books/:id",bookById)
	router.POST("/books", createBook)
	router.PATCH("/checkout", checkoutBook)
	router.PATCH("/return", returnBook)
	router.Run("localhost:8080")
}