finalize: io reader lecture

interfaces/14-io-reader/_database_save.go

@@ -1,133 +0,0 @@
-// 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"
-	"reflect"
-)
-
-type database struct {
-	list  *list
-	types map[string]item // the registry of the types
-}
-
-// load the list by decoding the data from a json file.
-func (db *database) load(path string) error { // #v1
-	data, err := ioutil.ReadFile(path)
-	if err != nil {
-		return err
-	}
-	return json.Unmarshal(data, db)
-}
-
-// save the list by encoding the data to a json file.
-func (db *database) save(path string) error { // #v1
-	out, err := json.MarshalIndent(db, "", "\t")
-	if err != nil {
-		return err
-	}
-	return ioutil.WriteFile(path, out, 0644)
-}
-
-// #v2
-// func (db *database) load(r io.Reader) error {
-//  data, err := ioutil.ReadAll(r)
-// 	if err != nil {
-// 		return err
-// 	}
-// 	return json.Unmarshal(data, db)
-// }
-
-// #v3
-// TODO: use decoder
-
-// #v2
-// func (db *database) save(w io.Writer) error {
-// 	data, err := json.MarshalIndent(db, "", "\t")
-// 	if err != nil {
-// 		return err
-// 	}
-
-// 	_, err = io.Copy(w, bytes.NewReader(data))
-// 	return err
-// }
-
-// #v3
-// TODO: use encoder
-
-func (db *database) MarshalJSON() ([]byte, error) {
-	type encodable struct {
-		Type 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
-		t := reflect.TypeOf(it).Elem().Name()
-		e = append(e, encodable{t, it})
-	}
-
-	return json.Marshal(e)
-}
-
-func (db *database) UnmarshalJSON(data []byte) error {
-	var decodables []struct {
-		Type string
-		Item json.RawMessage
-	}
-
-	if err := json.Unmarshal(data, &decodables); err != nil {
-		return err
-	}
-
-	for _, d := range decodables {
-		it, err := db.newItem(d.Item, d.Type)
-		if err != nil {
-			return err
-		}
-
-		*db.list = append(*db.list, it)
-	}
-
-	return nil
-}
-
-func (db *database) newItem(data []byte, typ string) (item, error) {
-	it, ok := db.types[typ]
-	if !ok {
-		return nil, fmt.Errorf("newItem: type (%q) does not exist", typ)
-	}
-
-	// get the dynamic type inside "it" like *book, *game, etc..
-	t := reflect.TypeOf(it)
-
-	// get the pointer type's element type like book, game, etc...
-	e := t.Elem()
-
-	// create a new pointer value of the type like new(book), new(game), etc...
-	v := reflect.New(e)
-
-	// get the interface value and cast it to the item type
-	it = v.Interface().(item)
-
-	return it, json.Unmarshal(data, &it)
-}
-
-func (db *database) register(typ string, it item) {
-	if db.types == nil {
-		db.types = make(map[string]item)
-	}
-	db.types[typ] = it
-}

interfaces/14-io-reader/_main_save.go

@@ -1,40 +0,0 @@
-// 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 (
-	"fmt"
-)
-
-func main() {
-	var store list
-
-	db := database{list: &store}
-
-	// db.register("book", new(book))
-	// db.register("book", new(book))
-	// db.register("game", new(game))
-	// db.register("puzzle", new(puzzle))
-	// db.register("toy", new(toy))
-
-	// db.load("database.json")
-
-	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.save("database.json")
-
-	fmt.Print(store)
-}

interfaces/14-io-reader/database.go

@@ -10,6 +10,7 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"reflect"
 )
@@ -19,27 +20,17 @@ type database struct {
 	types map[string]item // the registry of the types
 }
 
-// load the list by decoding the data from a json file.
+// load the list by decoding the data from any data source.
-func (db *database) load(path string) error { // #v1
+func (db *database) load(r io.Reader) error {
-	data, err := ioutil.ReadFile(path)
+	// ReadAll reads from `r` entirely into memory.
+	// `data` contains the entire data in memory.
+	data, err := ioutil.ReadAll(r)
 	if err != nil {
 		return err
 	}
 	return json.Unmarshal(data, db)
 }
 
-// #v2
-// func (db *database) load(r io.Reader) error {
-//  data, err := ioutil.ReadAll(r)
-// 	if err != nil {
-// 		return err
-// 	}
-// 	return json.Unmarshal(data, db)
-// }
-
-// #v3
-// TODO: use decoder
-
 func (db *database) MarshalJSON() ([]byte, error) {
 	type encodable struct {
 		Type string
@@ -49,9 +40,6 @@ func (db *database) MarshalJSON() ([]byte, error) {
 	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
 		t := reflect.TypeOf(it).Elem().Name()
 		e = append(e, encodable{t, it})
 	}
@@ -87,16 +75,9 @@ func (db *database) newItem(data []byte, typ string) (item, error) {
 		return nil, fmt.Errorf("newItem: type (%q) does not exist", typ)
 	}
 
-	// get the dynamic type inside "it" like *book, *game, etc..
 	t := reflect.TypeOf(it)
-
-	// get the pointer type's element type like book, game, etc...
 	e := t.Elem()
-
-	// create a new pointer value of the type like new(book), new(game), etc...
 	v := reflect.New(e)
-
-	// get the interface value and cast it to the item type
 	it = v.Interface().(item)
 
 	return it, json.Unmarshal(data, &it)

interfaces/14-io-reader/main.go

@@ -9,22 +9,10 @@ package main
 
 import (
 	"fmt"
+	"net/http"
 )
 
 func main() {
-	var store list
-
-	db := database{list: &store}
-	db.register("book", new(book))
-	db.register("book", new(book))
-	db.register("game", new(game))
-	db.register("puzzle", new(puzzle))
-	db.register("toy", new(toy))
-
-	db.load("database.json")
-
-	fmt.Print(store)
-
 	/*
 		store := list{
 			&book{product{"moby dick", 10}, toTimestamp(118281600)},
@@ -48,4 +36,32 @@ func main() {
 		// store.discount(.5)
 		// fmt.Print(store)
 	*/
+
+	var store list
+
+	db := database{list: &store}
+	db.register("book", new(book))
+	db.register("book", new(book))
+	db.register("game", new(game))
+	db.register("puzzle", new(puzzle))
+	db.register("toy", new(toy))
+
+	// load from a file
+	// f, _ := os.Open("database.json")
+	// db.load(f)
+	// f.Close()
+
+	// load from a string
+	// const data = `[
+	// { "Type": "book", "Item": { "Title": "1984", "Price": 8, "Published": -649641600 } },
+	// { "Type": "game", "Item": { "Title": "paperboy", "Price": 20 } }]`
+	// r := strings.NewReader(data)
+	// db.load(r)
+
+	// load from a web server
+	res, _ := http.Get("https://inancgumus.github.io/x/database.json")
+	db.load(res.Body)
+	res.Body.Close()
+
+	fmt.Print(store)
 }