add: json encoding/decoding quiz and exercises

24-structs/exercises/05-decode/solution/main.go

@@ -0,0 +1,157 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const data = `
+[
+        {
+                "id": 1,
+                "name": "god of war",
+                "genre": "action adventure",
+                "price": 50
+        },
+        {
+                "id": 2,
+                "name": "x-com 2",
+                "genre": "strategy",
+                "price": 40
+        },
+        {
+                "id": 3,
+                "name": "minecraft",
+                "genre": "sandbox",
+                "price": 20
+        }
+]`
+
+func main() {
+	type item struct {
+		id    int
+		name  string
+		price int
+	}
+
+	type game struct {
+		item
+		genre string
+	}
+
+	// ----------------------------------------------------------
+	// DECODING SOLUTION:
+
+	// encodable and decodable game type
+	type jsonGame struct {
+		ID    int    `json:"id"`
+		Name  string `json:"name"`
+		Genre string `json:"genre"`
+		Price int    `json:"price"`
+	}
+
+	// load the initial data from json
+	var decoded []jsonGame
+	if err := json.Unmarshal([]byte(data), &decoded); err != nil {
+		fmt.Println("Sorry, there is a problem:", err)
+		return
+	}
+
+	// load the data into usual game values
+	var games []game
+	for _, dg := range decoded {
+		games = append(games, game{item{dg.ID, dg.Name, dg.Price}, dg.Genre})
+	}
+	// ----------------------------------------------------------
+
+	// index the games by id
+	byID := make(map[int]game)
+	for _, g := range games {
+		byID[g.id] = g
+	}
+
+	fmt.Printf("Inanc's game store has %d games.\n", len(games))
+
+	in := bufio.NewScanner(os.Stdin)
+	for {
+		fmt.Printf(`
+  > list   : lists all the games
+  > id N   : queries a game by id
+  > save   : exports the data to json and quits
+  > quit   : quits
+
+`)
+
+		if !in.Scan() {
+			break
+		}
+
+		fmt.Println()
+
+		cmd := strings.Fields(in.Text())
+		if len(cmd) == 0 {
+			continue
+		}
+
+		switch cmd[0] {
+		case "quit":
+			fmt.Println("bye!")
+			return
+
+		case "list":
+			for _, g := range games {
+				fmt.Printf("#%d: %-15q %-20s $%d\n",
+					g.id, g.name, "("+g.genre+")", g.price)
+			}
+
+		case "id":
+			if len(cmd) != 2 {
+				fmt.Println("wrong id")
+				continue
+			}
+
+			id, err := strconv.Atoi(cmd[1])
+			if err != nil {
+				fmt.Println("wrong id")
+				continue
+			}
+
+			g, ok := byID[id]
+			if !ok {
+				fmt.Println("sorry. i don't have the game")
+				continue
+			}
+
+			fmt.Printf("#%d: %-15q %-20s $%d\n",
+				g.id, g.name, "("+g.genre+")", g.price)
+
+		case "save":
+			// load the data into the encodable game values
+			var encodable []jsonGame
+			for _, g := range games {
+				encodable = append(encodable,
+					jsonGame{g.id, g.name, g.genre, g.price})
+			}
+
+			out, err := json.MarshalIndent(encodable, "", "\t")
+			if err != nil {
+				fmt.Println("Sorry:", err)
+				continue
+			}
+
+			fmt.Println(string(out))
+			return
+		}
+	}
+}