Add amend command

README.md

@@ -12,6 +12,7 @@ go install github.com/okaryo/dlog@latest
 
 ```bash
 dlog "task progress update"
+dlog amend "corrected task progress update"
 dlog
 dlog log
 dlog log --date 2026-04-12
@@ -22,12 +23,76 @@ dlog md --date 2026-04-12
 ## Behavior
 
 - `dlog "text"` appends a log entry for today with the current local timestamp.
+- `dlog amend "text"` replaces today's most recent log entry while keeping its original timestamp.
 - `dlog` and `dlog log` show today's logs in reverse chronological order.
 - `dlog log --date YYYY-MM-DD` shows logs for the specified date.
 - `dlog md` prints today's logs in Markdown order from oldest to newest.
 - `dlog md --date YYYY-MM-DD` prints logs for the specified date in Markdown order.
 - Displayed times use the timezone recorded in each log entry, not the viewer's current local timezone.
 
+## Examples
+
+Record logs for today:
+
+```bash
+$ dlog "task progress update"
+$ dlog "api design"
+$ dlog "bug fix"
+```
+
+Amend the most recent log entry:
+
+```bash
+$ dlog amend "bug fix (retry with test case)"
+```
+
+Show today's logs in reverse chronological order with `dlog` or `dlog log`:
+
+```bash
+$ dlog
+2026-04-12
+
+11:10 bug fix (retry with test case)
+10:25 api design
+10:03 task progress update
+```
+
+```bash
+$ dlog log
+2026-04-12
+
+11:10 bug fix (retry with test case)
+10:25 api design
+10:03 task progress update
+```
+
+Show a specific date:
+
+```bash
+$ dlog log --date 2026-04-11
+2026-04-11
+
+18:45 previous day task
+```
+
+Output logs as Markdown in chronological order:
+
+```bash
+$ dlog md
+# 2026-04-12
+- 10:03 task progress update
+- 10:25 api design
+- 11:10 bug fix (retry with test case)
+```
+
+Output a specific date as Markdown:
+
+```bash
+$ dlog md --date 2026-04-11
+# 2026-04-11
+- 18:45 previous day task
+```
+
 ## Storage
 
 - Logs are stored under `~/.dlog`.

cmd/root.go

@@ -39,7 +39,7 @@ func NewRootCmd(svc *service.Service, out io.Writer, errOut io.Writer) *cobra.Co
 
 	cmd.SetOut(out)
 	cmd.SetErr(errOut)
-	cmd.AddCommand(newLogCmd(svc, out), newMarkdownCmd(svc, out))
+	cmd.AddCommand(newLogCmd(svc, out), newMarkdownCmd(svc, out), newAmendCmd(svc))
 
 	return cmd
 }
@@ -117,3 +117,16 @@ func newMarkdownCmd(svc *service.Service, out io.Writer) *cobra.Command {
 
 	return cmd
 }
+
+func newAmendCmd(svc *service.Service) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "amend [text]",
+		Short: "Replace today's most recent log entry",
+		Args:  cobra.ExactArgs(1),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return svc.AmendTodayLog(args[0])
+		},
+	}
+
+	return cmd
+}

cmd/root_test.go

@@ -189,6 +189,58 @@ func TestRootCommandRejectsEmptyText(t *testing.T) {
 	}
 }
 
+func TestAmendSubcommandReplacesMostRecentLog(t *testing.T) {
+	current := time.Date(2026, 4, 12, 10, 3, 0, 0, time.FixedZone("JST", 9*60*60))
+	root, _, _, store := newTestRootCmd(t, func() time.Time { return current })
+
+	root.SetArgs([]string{"first task"})
+	if err := root.Execute(); err != nil {
+		t.Fatalf("seed first log: %v", err)
+	}
+
+	current = time.Date(2026, 4, 12, 11, 10, 0, 0, time.FixedZone("JST", 9*60*60))
+	root.SetArgs([]string{"second task"})
+	if err := root.Execute(); err != nil {
+		t.Fatalf("seed second log: %v", err)
+	}
+
+	root.SetArgs([]string{"amend", "corrected second task"})
+	if err := root.Execute(); err != nil {
+		t.Fatalf("execute amend command: %v", err)
+	}
+
+	data, err := os.ReadFile(filepath.Join(store.BaseDir(), "2026-04-12.json"))
+	if err != nil {
+		t.Fatalf("read saved file: %v", err)
+	}
+
+	content := string(data)
+	if !strings.Contains(content, `"text": "first task"`) {
+		t.Fatalf("saved file missing first text: %s", content)
+	}
+	if !strings.Contains(content, `"text": "corrected second task"`) {
+		t.Fatalf("saved file missing amended text: %s", content)
+	}
+	if strings.Contains(content, `"text": "second task"`) {
+		t.Fatalf("saved file still has old text: %s", content)
+	}
+}
+
+func TestAmendSubcommandFailsWithoutExistingLogs(t *testing.T) {
+	now := time.Date(2026, 4, 12, 10, 3, 21, 0, time.FixedZone("JST", 9*60*60))
+	root, _, _, _ := newTestRootCmd(t, func() time.Time { return now })
+
+	root.SetArgs([]string{"amend", "corrected task"})
+	err := root.Execute()
+	if err == nil {
+		t.Fatalf("expected error")
+	}
+
+	if !strings.Contains(err.Error(), "no logs to amend for today") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 func newTestRootCmd(t *testing.T, now func() time.Time) (*cobra.Command, *bytes.Buffer, *bytes.Buffer, *storage.Store) {
 	t.Helper()
 

internal/service/service.go

@@ -55,6 +55,32 @@ func (s *Service) AddTodayLog(text string) error {
 	return s.store.SaveDay(dayLog)
 }
 
+func (s *Service) AmendTodayLog(text string) error {
+	text = strings.TrimSpace(text)
+	if text == "" {
+		return fmt.Errorf("log text cannot be empty")
+	}
+
+	now := s.now()
+	dayLog, err := s.store.LoadDay(now)
+	if err != nil {
+		return err
+	}
+
+	expectedDate := now.Format(dayLayout)
+	if dayLog.Date != expectedDate {
+		return fmt.Errorf("day log date mismatch: expected %s, got %s", expectedDate, dayLog.Date)
+	}
+
+	if len(dayLog.Logs) == 0 {
+		return fmt.Errorf("no logs to amend for today")
+	}
+
+	dayLog.Logs[len(dayLog.Logs)-1].Text = text
+
+	return s.store.SaveDay(dayLog)
+}
+
 func (s *Service) GetTodayLog() (*model.DayLog, error) {
 	return s.getLogByTime(s.now())
 }

internal/service/service_test.go

@@ -66,6 +66,59 @@ func TestAddTodayLogFailsOnCorruptJSONWithoutChangingFile(t *testing.T) {
 	}
 }
 
+func TestAmendTodayLogReplacesMostRecentEntryText(t *testing.T) {
+	now := time.Date(2026, 4, 12, 10, 3, 21, 0, time.FixedZone("JST", 9*60*60))
+	store := storage.NewStore(t.TempDir())
+	svc := NewWithNow(store, func() time.Time { return now })
+
+	if err := svc.AddTodayLog("first entry"); err != nil {
+		t.Fatalf("add first log: %v", err)
+	}
+
+	now = time.Date(2026, 4, 12, 11, 10, 0, 0, time.FixedZone("JST", 9*60*60))
+	if err := svc.AddTodayLog("second entry"); err != nil {
+		t.Fatalf("add second log: %v", err)
+	}
+
+	if err := svc.AmendTodayLog("  corrected second entry  "); err != nil {
+		t.Fatalf("amend log: %v", err)
+	}
+
+	data, err := os.ReadFile(filepath.Join(store.BaseDir(), "2026-04-12.json"))
+	if err != nil {
+		t.Fatalf("read day log file: %v", err)
+	}
+
+	content := string(data)
+	if !strings.Contains(content, `"text": "first entry"`) {
+		t.Fatalf("first log text changed unexpectedly: %s", content)
+	}
+	if !strings.Contains(content, `"timestamp": "2026-04-12T11:10:00+09:00"`) {
+		t.Fatalf("most recent timestamp changed unexpectedly: %s", content)
+	}
+	if !strings.Contains(content, `"text": "corrected second entry"`) {
+		t.Fatalf("most recent text was not amended: %s", content)
+	}
+	if strings.Contains(content, `"text": "second entry"`) {
+		t.Fatalf("old most recent text still present: %s", content)
+	}
+}
+
+func TestAmendTodayLogFailsWhenNoLogsExist(t *testing.T) {
+	now := time.Date(2026, 4, 12, 10, 3, 21, 0, time.FixedZone("JST", 9*60*60))
+	store := storage.NewStore(t.TempDir())
+	svc := NewWithNow(store, func() time.Time { return now })
+
+	err := svc.AmendTodayLog("corrected")
+	if err == nil {
+		t.Fatalf("expected error")
+	}
+
+	if !strings.Contains(err.Error(), "no logs to amend for today") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 func TestGetLogByDateReturnsSpecifiedDayLog(t *testing.T) {
 	now := time.Date(2026, 4, 11, 18, 45, 0, 0, time.FixedZone("JST", 9*60*60))
 	store := storage.NewStore(t.TempDir())