package main

import (
    "encoding/json"
    "fmt"
    "log"
    "net/http"

    "github.com/julienschmidt/httprouter"
)

func Index(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
    fmt.Fprint(w, "Welcome!\n")
}

type Book struct {
    ISDN   string `json:"isdn"`
    Title  string `json:"title"`
    Author string `json:"author"`
    Pages  int    `json:"pages"`
}

type JsonResponse struct {
    Meta interface{} `json:"metat"`
    Data interface{} `jsoin:"data"`
}

type JsonErrorResponse struct {
    Error *ApiError `json:"error"`
}

type ApiError struct {
    Status int16  `json:"status"`
    Title  string `json:"title"`
}

var bookstore = make(map[string]*Book, 0)

func BookIndex(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
    books := []*Book{}
    for _, book := range bookstore {
        books = append(books, book)
    }
    response := &JsonResponse{Data: &books}
    w.Header().Set("Content-Type", "application/json; charset=UTF-8")
    w.WriteHeader(http.StatusOK)
    if err := json.NewEncoder(w).Encode(response); err != nil {
        panic(err)
    }
}

func BookShow(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
    isdn := params.ByName("isdn")
    book, ok := bookstore[isdn]
    w.Header().Set("Content-Type", "application/json; charset=UTF-8")
    if !ok {
        w.WriteHeader(http.StatusNotFound)
        response := JsonErrorResponse{Error: &ApiError{Status: 404, Title: "Record Not Found"}}
        if err := json.NewEncoder(w).Encode(response); err != nil {
            panic(err)
        }

    }
    response := JsonResponse{Data: book}
    if err := json.NewEncoder(w).Encode(response); err != nil {
        panic(err)
    }
}

func main() {
    router := httprouter.New()
    router.GET("/", Index)
    router.GET("/books", BookIndex)
    router.GET("/books/:isdn", BookShow)

    bookstore["123"] = &Book{
        ISDN:   "123",
        Title:  "Silence of the Lambs",
        Author: "Thomas Harris",
        Pages:  367,
    }

    bookstore["124"] = &Book{
        ISDN:   "124",
        Title:  "To Kill a Mocking Bird",
        Author: "Harper Lee",
        Pages:  320,
    }

    log.Fatal(http.ListenAndServe(":8081", router))
}