Add database package

pkg/database/db.go

@@ -0,0 +1,88 @@
+package database
+
+import "fmt"
+
+// Database interface
+type Database interface {
+	// Set the key to given value
+	Set(key string, value int)
+
+	// Get the value for the given key, set 'ok' to true if key exists
+	Get(key string) (value int, ok bool)
+
+	// Unset the key, making it just like that key was never set
+	Unset(key string)
+
+	// Begin opens a new transaction
+	Begin()
+
+	// Commit closes all open transaction blocks, permanently apply the
+	// changes made in them.
+	Commit() error
+
+	// Rollback undoes all of the commands issued in the most recent
+	// transaction block, and closes the block.
+	Rollback() error
+}
+
+type db struct {
+	data map[string]int
+	logs []map[string]int
+}
+
+// NewDatabase returns the Database interface
+func NewDatabase() Database {
+	return &db{data: make(map[string]int)}
+}
+
+// Set the key to given value
+func (d *db) Set(key string, value int) {
+	d.data[key] = value
+}
+
+// Get the value for the given key, set 'ok' to true if key exists
+func (d *db) Get(key string) (int, bool) {
+	value, ok := d.data[key]
+	return value, ok
+}
+
+// Unset the key, making it just like that key was never set
+func (d *db) Unset(key string) {
+	delete(d.data, key)
+}
+
+// Begin opens a new transaction
+func (d *db) Begin() {
+	// Save a snapshot of the current state of the data to the logs.
+	snapshot := make(map[string]int)
+	for k, v := range d.data {
+		snapshot[k] = v
+	}
+	d.logs = append(d.logs, snapshot)
+}
+
+// Commit closes all open transaction blocks, permanently apply the
+// changes made in them.
+func (d *db) Commit() error {
+	// Check if there is anything to commit.
+	if len(d.logs) == 0 {
+		return fmt.Errorf("nothing to commit")
+	}
+
+	d.logs = nil
+	return nil
+}
+
+// Rollback undoes all of the commands issued in the most recent
+// transaction block, and closes the block.
+func (d *db) Rollback() error {
+	// Check if there is anything to rollback.
+	if len(d.logs) == 0 {
+		return fmt.Errorf("nothing to rollback")
+	}
+
+	// Restore the data to the last snapshot in the logs.
+	d.data = d.logs[len(d.logs)-1]
+	d.logs = d.logs[:len(d.logs)-1]
+	return nil
+}

pkg/database/db_test.go

@@ -0,0 +1,168 @@
+package database
+
+import (
+	"testing"
+)
+
+func TestUnset(t *testing.T) {
+	db := NewDatabase()
+
+	db.Set("ex", 10)
+	assertValue(t, db, "ex", 10)
+
+	db.Unset("ex")
+	assertUnset(t, db, "ex")
+}
+
+func TestRollback(t *testing.T) {
+	db := NewDatabase()
+
+	db.Begin()
+	db.Set("a", 10)
+	assertValue(t, db, "a", 10)
+
+	db.Begin()
+	db.Set("a", 20)
+	assertValue(t, db, "a", 20)
+
+	err := db.Rollback()
+	assertNoError(t, err)
+	assertValue(t, db, "a", 10)
+
+	err = db.Rollback()
+	assertNoError(t, err)
+	assertUnset(t, db, "a")
+}
+
+func TestNestedCommit(t *testing.T) {
+	db := NewDatabase()
+
+	db.Begin()
+	db.Set("a", 30)
+
+	db.Begin()
+	db.Set("a", 40)
+
+	err := db.Commit()
+	assertNoError(t, err)
+
+	assertValue(t, db, "a", 40)
+
+	err = db.Rollback()
+	assertError(t, err)
+
+	err = db.Commit()
+	assertError(t, err)
+}
+
+func TestTransactionInterleavedKeys(t *testing.T) {
+	db := NewDatabase()
+
+	db.Set("a", 10)
+	db.Set("b", 10)
+	assertValue(t, db, "a", 10)
+	assertValue(t, db, "b", 10)
+
+	db.Begin()
+	db.Set("a", 20)
+	assertValue(t, db, "a", 20)
+	assertValue(t, db, "b", 10)
+
+	db.Begin()
+	db.Set("b", 30)
+	assertValue(t, db, "a", 20)
+	assertValue(t, db, "b", 30)
+
+	db.Rollback()
+	assertValue(t, db, "a", 20)
+	assertValue(t, db, "b", 10)
+
+	db.Rollback()
+	assertValue(t, db, "a", 10)
+	assertValue(t, db, "b", 10)
+}
+
+func TestTransactionRollbackUnset(t *testing.T) {
+	db := NewDatabase()
+
+	db.Set("a", 10)
+	assertValue(t, db, "a", 10)
+
+	db.Begin()
+	assertValue(t, db, "a", 10)
+	db.Set("a", 20)
+	assertValue(t, db, "a", 20)
+
+	db.Begin()
+	db.Unset("a")
+	assertUnset(t, db, "a")
+
+	err := db.Rollback()
+	assertNoError(t, err)
+	assertValue(t, db, "a", 20)
+
+	err = db.Commit()
+	assertNoError(t, err)
+	assertValue(t, db, "a", 20)
+}
+
+func TestTransactionCommitUnset(t *testing.T) {
+	db := NewDatabase()
+
+	db.Set("a", 10)
+	assertValue(t, db, "a", 10)
+
+	db.Begin()
+	assertValue(t, db, "a", 10)
+	db.Unset("a")
+	assertUnset(t, db, "a")
+
+	err := db.Rollback()
+	assertNoError(t, err)
+	assertValue(t, db, "a", 10)
+
+	db.Begin()
+	db.Unset("a")
+	assertUnset(t, db, "a")
+
+	db.Commit()
+	assertUnset(t, db, "a")
+
+	db.Begin()
+	assertUnset(t, db, "a")
+	db.Set("a", 20)
+	assertValue(t, db, "a", 20)
+
+	db.Commit()
+	assertValue(t, db, "a", 20)
+}
+
+func assertUnset(t *testing.T, db Database, key string) {
+	t.Helper()
+	_, ok := db.Get(key)
+	if ok {
+		t.Fatalf("key %q should not exist", key)
+	}
+}
+
+func assertValue(t *testing.T, db Database, key string, value int) {
+	t.Helper()
+	v, ok := db.Get(key)
+	if !ok || value != v {
+		t.Fatalf("db.Get(%q) should return %d, true: got %d, %v", key, value, v, ok)
+	}
+}
+
+func assertNoError(t *testing.T, err error) {
+	t.Helper()
+	if err != nil {
+		t.Fatalf("expected no error, got: %v", err)
+	}
+}
+
+func assertError(t *testing.T, err error) {
+	t.Helper()
+	if err == nil {
+		t.Fatal("expected an error, got: nil")
+	}
+}