main.go

package main

import(
	"net/http"
	"github.com/gin-gonic/gin"
	"errors"
)
//to store our books we gng to use struct
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},
}

//Create a router which allow us ro handle different books
// gin.context is all the information came in with the request
func getBooks(c *gin.Context){
	c.IndentedJSON(http.StatusOK, books)
}

func creatBook(c *gin.Context){
	var newBook book
    //BindJson is used to bind the info we got in the request to newBook which is of type struct book
	//now, assign this to the error and check if the error is nil, if it's not nill return
	if err := c.BindJSON(&newBook); err != nil{
		return

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

}

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 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 checkoutBook(c *gin.Context) {
	id, ok := c.GetQuery("id") //query parameter ex: ?x=2

	if ok == false {
		c.IndentedJSON(http.StatusBadRequest, gin.H{"message": "Missing id query parameter."})
		return
	}

	book, err := getBookById(id)

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

	if book.Quantity <= 0 {
		c.IndentedJSON(http.StatusBadRequest, 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 {
		c.IndentedJSON(http.StatusBadRequest, gin.H{"message": "Missing id query parameter."})
		return
	}

	book, err := getBookById(id)

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

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


func main(){
	router := gin.Default()
	router.GET("/books",getBooks)
	router.GET("/books/:id",bookById) // add : to make id as parameter
	router.POST("/books",creatBook)
	router.PATCH("/checkout", checkoutBook) // as we are updating that currently exists so  use patchh
	router.PATCH("/return", returnBook)
	router.Run("localhost:8000")
}