decoupling with interface and concrete data

Author: meowpunch

Ultimate Go Programming/decoupling/go.mod

@@ -0,0 +1,3 @@
+module decoupling
+
+go 1.21.1

Ultimate Go Programming/decoupling/migration.go

@@ -0,0 +1,140 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"math/rand"
+	"time"
+)
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
+// =============================================================================
+
+// Data is the structure of the data we are copying.
+type Data struct {
+	Line string
+}
+
+// =============================================================================
+
+// Puller declares behavior for pulling data.
+type Puller interface {
+	Pull(d *Data) error
+}
+
+// Storer declares behavior for storing data.
+type Storer interface {
+	Store(d *Data) error
+}
+
+// PullStorer declares behavior for both pulling and storing.
+type PullStorer interface {
+	Puller
+	Storer
+}
+
+// =============================================================================
+
+// Xenia is a system we need to pull data from.
+type Xenia struct {
+	Host    string
+	Timeout time.Duration
+}
+
+// Pull knows how to pull data out of Xenia.
+func (*Xenia) Pull(d *Data) error {
+	switch rand.Intn(10) {
+	case 1, 9:
+		return io.EOF
+
+	case 5:
+		return errors.New("error reading data from Xenia")
+
+	default:
+		d.Line = "Data"
+		fmt.Println("In:", d.Line)
+		return nil
+	}
+}
+
+// Pillar is a system we need to store data into.
+type Pillar struct {
+	Host    string
+	Timeout time.Duration
+}
+
+// Store knows how to store data into Pillar.
+func (*Pillar) Store(d *Data) error {
+	fmt.Println("Out:", d.Line)
+	return nil
+}
+
+// =============================================================================
+
+// System wraps Pullers and Stores together into a single system.
+type System struct {
+	Puller
+	Storer
+}
+
+// =============================================================================
+
+// pull knows how to pull bulks of data from any Puller.
+func pull(p Puller, data []Data) (int, error) {
+	for i := range data {
+		if err := p.Pull(&data[i]); err != nil {
+			return i, err
+		}
+	}
+
+	return len(data), nil
+}
+
+// store knows how to store bulks of data from any Storer.
+func store(s Storer, data []Data) (int, error) {
+	for i := range data {
+		if err := s.Store(&data[i]); err != nil {
+			return i, err
+		}
+	}
+
+	return len(data), nil
+}
+
+// Copy knows how to pull and store data
+func Copy(p Puller, s Storer, batch int) error {
+	data := make([]Data, batch)
+
+	for {
+		i, err := pull(p, data)
+		if i > 0 {
+			if _, err := store(s, data[:i]); err != nil {
+				return err
+			}
+		}
+
+		if err != nil {
+			return err
+		}
+	}
+}
+
+// =============================================================================
+
+func main() {
+	x := &Xenia{
+		Host:    "localhost:8000",
+		Timeout: time.Second}
+	p := &Pillar{
+		Host:    "localhost:9000",
+		Timeout: time.Second,
+	}
+
+	if err := Copy(x, p, 3); err != io.EOF {
+		fmt.Println(err)
+	}
+}