add: database to reflection decoder

interfaces/11-reflection-decoder/database.go

@@ -0,0 +1,107 @@
+// 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 (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"reflect"
+)
+
+type database struct {
+	list  *list
+	types map[string]item
+}
+
+func (db *database) save() error {
+	data, err := json.MarshalIndent(db, "", "\t")
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	return ioutil.WriteFile("database.json", data, os.ModePerm)
+}
+
+func (db *database) load() error {
+	data, err := ioutil.ReadFile("database.json")
+	if err != nil {
+		return err
+	}
+
+	if err = json.Unmarshal(data, db); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (db *database) MarshalJSON() ([]byte, error) {
+	type encodable struct {
+		Category string
+		Item     item
+	}
+
+	var e []encodable
+
+	for _, it := range *db.list {
+		// TypeOf -> finds the dynamic type of "it"
+		// Elem   -> returns the element type of the pointer
+		// Name   -> returns the type name as string
+		cat := reflect.TypeOf(it).Elem().Name()
+		e = append(e, encodable{cat, it})
+	}
+
+	return json.Marshal(e)
+}
+
+func (db *database) UnmarshalJSON(data []byte) error {
+	var decodables []struct {
+		Category string
+		Item     json.RawMessage
+	}
+
+	if err := json.Unmarshal(data, &decodables); err != nil {
+		return err
+	}
+
+	for _, d := range decodables {
+		it, err := db.newItem(d.Category)
+		if err != nil {
+			return err
+		}
+
+		if err := json.Unmarshal(d.Item, &it); err != nil {
+			return err
+		}
+
+		*db.list = append(*db.list, it)
+	}
+
+	return nil
+}
+
+func (db *database) register(category string, t item) {
+	if db.types == nil {
+		db.types = make(map[string]item)
+	}
+	db.types[category] = t
+}
+
+func (db *database) newItem(category string) (item, error) {
+	it, ok := db.types[category]
+	if !ok {
+		return nil, fmt.Errorf("register %q within database before decoding", category)
+	}
+
+	t := reflect.TypeOf(it).Elem()
+	v := reflect.New(t)
+	return v.Interface().(item), nil
+}

interfaces/11-reflection-decoder/database.json

@@ -51,4 +51,4 @@
 			"Price": 150
 		}
 	}
-]
+]

interfaces/11-reflection-decoder/list.go

@@ -8,9 +8,7 @@
 package main
 
 import (
-	"encoding/json"
 	"fmt"
-	"reflect"
 	"strings"
 )
 
@@ -19,103 +17,8 @@ type item interface {
 	fmt.Stringer
 }
 
-// itemEncode adds an additional category field
-// to the product types.
-type itemEncode struct {
-	// Category is the product category field.
-	Category string
-
-	// Item is an interface value.
-	// Here, we are embedding an interface value.
-	Item item
-}
-
-// itemDecode is used to decode the product types from json.
-type itemDecode struct {
-	// Category is the product category field.
-	Category string
-
-	// json.RawMessage is a special type of the json package.
-	// It prevents the json package functions encode/decode
-	// the specific parts of the json data.
-	Item json.RawMessage
-}
-
 type list []item
 
-func (l list) MarshalJSON() ([]byte, error) {
-	var eitems []itemEncode
-
-	for _, it := range l {
-		// TypeOf -> finds the dynamic type of "it"
-		// Elem   -> returns the element type of the pointer
-		// Name   -> returns the type name as string
-		cat := reflect.TypeOf(it).Elem().Name()
-		eitems = append(eitems, itemEncode{cat, it})
-	}
-
-	return json.Marshal(eitems)
-}
-
-func (l *list) UnmarshalJSON(data []byte) error {
-	var ditems []itemDecode
-
-	if err := json.Unmarshal(data, &ditems); err != nil {
-		return err
-	}
-
-	items, err := decode(ditems)
-	if err != nil {
-		return err
-	}
-
-	*l = items
-	return nil
-}
-
-// decode and return items as a list.
-func decode(data []itemDecode) (items list, err error) {
-	for _, d := range data {
-		item := newItem(d.Category)
-
-		if json.Unmarshal(d.Item, &item); err != nil {
-			return nil, err
-		}
-
-		items = append(items, item)
-	}
-	return items, nil
-}
-
-// newItem creates and returns an item depending on category.
-func newItem(category string) item {
-	// for each product you need to open this code
-	// and add a new case.
-	//
-	// dependency injection should be the responsibility
-	// of the user of this function.
-	switch category {
-	case "book":
-		// var b book
-		// return &b
-		return new(book)
-	case "game":
-		return new(game)
-	case "puzzle":
-		return new(puzzle)
-	case "toy":
-		return new(toy)
-	}
-	return nil
-}
-
-// type decoder map[string]interface{}
-// func (d decoder) newItem(kind string) item {
-// 	t := reflect.TypeOf(d[kind])
-// 	v := reflect.New(t)
-// 	return v.Interface().(item)
-// }
-
 func (l list) String() string {
 	if len(l) == 0 {
 		return "Sorry. We're waiting for delivery 🚚."

interfaces/11-reflection-decoder/main.go

@@ -15,36 +15,49 @@ import (
 )
 
 func main() {
-	// store := list{
-	// 	&book{product{"moby dick", 10}, toTimestamp(118281600)},
-	// 	&book{product{"odyssey", 15}, toTimestamp("733622400")},
-	// 	&book{product{"hobbit", 25}, unknown},
-	// 	&puzzle{product{"rubik's cube", 5}},
-	// 	&game{product{"minecraft", 20}},
-	// 	&game{product{"tetris", 5}},
-	// 	&toy{product{"yoda", 150}},
-	// }
+	var store list
 
-	// out, err := json.MarshalIndent(store, "", "\t")
-	// if err != nil {
+	// db := database{list: &store}
+	// db.register("book", new(book))
+	// db.register("game", new(game))
+	// db.register("puzzle", new(puzzle))
+	// db.register("toy", new(toy))
+
+	// if err := db.load(); err != nil {
 	// 	log.Fatalln(err)
 	// }
 
-	// fmt.Println(string(out))
-	//---
 	data, err := ioutil.ReadFile("database.json")
 	if err != nil {
 		log.Fatalln(err)
 	}
 
-	var store list
 	if err = json.Unmarshal(data, &store); err != nil {
 		log.Fatalln(err)
 	}
 
 	fmt.Print(store)
 
-	// for _, p := range store {
-	// 	fmt.Printf("%#v\n", p)
-	// }
+	/*
+		store := list{
+			&book{product{"moby dick", 10}, toTimestamp(118281600)},
+			&book{product{"odyssey", 15}, toTimestamp("733622400")},
+			&book{product{"hobbit", 25}, unknown},
+			&puzzle{product{"rubik's cube", 5}},
+			&game{product{"minecraft", 20}},
+			&game{product{"tetris", 5}},
+			&toy{product{"yoda", 150}},
+		}
+
+		db := &database{list: &store}
+		if err := db.save(); err != nil {
+			log.Fatalln(err)
+		}
+
+		// out, err := json.MarshalIndent(db, "", "\t")
+		// if err != nil {
+		// 	log.Fatalln(err)
+		// }
+		// fmt.Println(string(out))
+	*/
 }