added tests, add support for duration diff+add

.gitignore

@@ -30,3 +30,5 @@ go.work.sum
 # Editor/IDE
 # .idea/
 # .vscode/
+
+ts

README.md

@@ -2,7 +2,7 @@
 
 generic cli timestamp parser and calculator tool
 
-# Usage
+## Usage
 
 ```default
 This is ts, a timestamp tool.
@@ -21,6 +21,28 @@ Usage: ts <time string> [<time string>]
 -e --examples Show examples or supported inputs.
 ```
 
+## Examples
+
+```default
+# diff between to day and yesterday 10 am
+ts today "10am yesterday"
+14h0m0s
+
+# show timestamp from a couple days ago
+ts "3 days ago"
+2025-09-21 13:51:55.054754744 +0200 CEST
+
+# show timestamp of one hour and 45 minutes before (-d is the defaul)
+ts -d now 1h45m
+2025-09-24 12:07:45.072300157 +0200 CEST m=-6299.999710536
+
+# 10 hours from now
+ts now 10h
+2025-09-24 03:53:36.7095512 +0200 CEST m=-35999.999720767
+```
+
+To see a comprehensive list of supported inputs, call `ts -e`.
+
 ## Installation
 
 The tool does not have any dependencies.  Just download the binary for

cmd/config.go

@@ -36,7 +36,7 @@ const (
 
 Usage: ts <time string> [<time string>]
 -d --diff     Calculate difference between two timestamps (default)
--a --add      Add two timestamps (second parameter must be a time)
+-a --add      Add two timestamps (second parameter must be a duration)
 -f --format   For diffs: duration, hour, min, sec, msec
               For timestamps: datetime, rfc3339, date, time, unix, string
               string is a strftime(1) format string. datetime is
@@ -71,7 +71,11 @@ noon                   Yesterday at 10:15am                 Mon, 02 Jan 2006 15:
 1:05pm                 Next dec 22nd at 3pm                 3 days ago                            1999AD
 10:25:10am             Next December 25th at 7:30am UTC-7   Three days ago                        1999 AD
 1:05:10pm              Next December 23rd AT 5:25 PM        1 day from now                        2008CE
-10:25                  Last December 23rd AT 5:25 PM        1 week ago                            2008 CE`
+10:25                  Last December 23rd AT 5:25 PM        1 week ago                            2008 CE
+
+Example durations for second parameter:
+2d1h30m  2 days, one and a half hour
+30m      30 minutes`
 	ModeDiff int = iota
 	ModeAdd
 )
@@ -127,6 +131,15 @@ func InitConfig(output io.Writer) (*Config, error) {
 		return nil, fmt.Errorf("error unmarshalling: %w", err)
 	}
 
+	// want examples?
+	if conf.Examples {
+		_, err := fmt.Fprintln(output, Examples)
+		if err != nil {
+			Die(err)
+		}
+		os.Exit(0)
+	}
+
 	// args are timestamps
 	if len(flagset.Args()) == 0 {
 		return nil, errors.New("no timestamp argument[s] specified.\n" + Usage)

cmd/root.go

@@ -18,10 +18,8 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package cmd
 
 import (
-	"fmt"
 	"io"
 	"log"
-	"os"
 )
 
 func Die(err error) int {
@@ -36,14 +34,6 @@ func Main(output io.Writer) int {
 		return Die(err)
 	}
 
-	if conf.Examples {
-		_, err := fmt.Fprintln(output, Examples)
-		if err != nil {
-			Die(err)
-		}
-		os.Exit(0)
-	}
-
 	tp := NewTP(conf)
 
 	if err := tp.ProcessTimestamps(); err != nil {

cmd/times.go

@@ -18,8 +18,11 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"log"
+	"regexp"
+	"strconv"
 	"time"
 
 	"github.com/ijt/go-anytime"
@@ -97,6 +100,13 @@ func (tp *TimestampProccessor) Calc(timestampA, timestampB string) error {
 		return err
 	}
 
+	durB, err := duration2int(timestampB)
+	if err == nil {
+		// calculate with a duration
+		tp.CalcDuration(tsA, durB)
+		return nil
+	}
+
 	tsB, err := tp.Parse(timestampB)
 	if err != nil {
 		return err
@@ -125,9 +135,64 @@ func (tp *TimestampProccessor) Calc(timestampA, timestampB string) error {
 	return nil
 }
 
+func (tp *TimestampProccessor) CalcDuration(tsA time.Time, durB time.Duration) {
+	var datetime time.Time
+
+	switch tp.Mode {
+	case ModeDiff:
+		datetime = tsA.Add(-durB)
+	case ModeAdd:
+		datetime = tsA.Add(durB)
+	}
+
+	tp.Print(TPdatetime{TimestampProccessor: *tp, Data: datetime})
+}
+
 func (tp *TimestampProccessor) Print(ts TimestampWriter) {
 	_, err := fmt.Fprintln(tp.Output, ts.String())
 	if err != nil {
 		log.Fatalf("failed to print to given output handle: %s", err)
 	}
 }
+
+/*
+We could use time.ParseDuration(), but this doesn't support days.
+
+We  could also  use github.com/xhit/go-str2duration/v2,  which does
+the job,  but it's  just another dependency,  just for  this little
+gem. And  we don't need a  time.Time value.
+
+Convert a  duration into  seconds (int).
+
+	Valid  time units  are "s", "m", "h" and "d".
+
+	Valid inputs: 2h5m (2 hours and 5 min), 10d12h (10 and a half days)
+*/
+func duration2int(duration string) (time.Duration, error) {
+	re := regexp.MustCompile(`(\d+)([dhms])`)
+	seconds := 0
+	found := false
+
+	for _, match := range re.FindAllStringSubmatch(duration, -1) {
+		if len(match) == 3 {
+			found = true
+			v, _ := strconv.Atoi(match[1])
+			switch match[2][0] {
+			case 'd':
+				seconds += v * 86400
+			case 'h':
+				seconds += v * 3600
+			case 'm':
+				seconds += v * 60
+			case 's':
+				seconds += v
+			}
+		}
+	}
+
+	if !found {
+		return 0, errors.New("failed to parse duration")
+	}
+
+	return time.Duration(seconds) * time.Second, nil
+}

cmd/times_test.go

@@ -0,0 +1,148 @@
+/*
+Copyright © 2025 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package cmd
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// reference time for our tests
+var now = time.Date(2025, 9, 25, 12, 30, 00, 0, time.UTC)
+
+// return fixed date at given params
+func dateAtTime(dateFrom time.Time, hour int, min int, sec int) time.Time {
+	t := dateFrom
+	return time.Date(t.Year(), t.Month(), t.Day(), hour, min, sec, 0, t.Location())
+}
+
+func setUTC() {
+	// make sure to have a consistent environment
+	os.Setenv("TZ", "UTC")
+	loc, _ := time.LoadLocation("UTC")
+	time.Local = loc
+}
+
+func TestParseTimestamps(t *testing.T) {
+	setUTC()
+
+	var datetimes = []struct {
+		input string
+		want  time.Time
+	}{
+		// some timestamps from ijt/go-anytime/anytime_test.go
+		{`a minute from now`, now.Add(time.Minute)},
+		{`5 minutes ago`, now.Add(-5 * time.Minute)},
+		{`an hour from now`, now.Add(time.Hour)},
+		{`Yesterday 10am`, dateAtTime(now.AddDate(0, 0, -1), 10, 0, 0)},
+		{`Mon Jan  2 15:04:05 2006`, time.Date(2006, 1, 2, 15, 4, 5, 0, now.Location())},
+		{`1 day from now`, now.Add(24 * time.Hour)},
+		{`One year ago`, now.AddDate(-1, 0, 0)},
+		{`03:15`, dateAtTime(now, 3, 15, 0)},
+		{`Wed Sep 25 12:30:00 PM UTC 2025`, now},
+	}
+
+	for _, tt := range datetimes {
+		testname := fmt.Sprintf("parsetimestamp-%s", strings.ReplaceAll(tt.input, " ", "-"))
+		t.Run(testname, func(t *testing.T) {
+			var writer bytes.Buffer
+			tp := NewTP(&Config{Args: []string{tt.input}, Output: &writer}, now)
+
+			// writer.String()
+			ts, err := tp.Parse(tt.input)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, ts)
+
+			err = tp.ProcessTimestamps()
+			assert.NoError(t, err)
+			assert.EqualValues(t, tt.want.String()+"\n", writer.String())
+		})
+	}
+}
+
+func preDiff(tsA, tsB time.Time) time.Duration {
+	var diff time.Duration
+
+	// avoid negative results
+	if tsA.Unix() > tsB.Unix() {
+		diff = tsA.Sub(tsB)
+	} else {
+		diff = tsB.Sub(tsA)
+	}
+
+	return diff
+}
+
+func TestDiffTimestamps(t *testing.T) {
+	setUTC()
+
+	var datetimes = []struct {
+		A    string
+		B    string
+		want time.Duration
+	}{
+		{`now`, `11:30`, preDiff(now, dateAtTime(now, 11, 30, 00))},
+		{`11:30`, `now`, preDiff(now, dateAtTime(now, 11, 30, 00))},
+	}
+
+	for _, tt := range datetimes {
+		testname := fmt.Sprintf("diff-%s-%s", strings.ReplaceAll(tt.A, " ", "-"), strings.ReplaceAll(tt.B, " ", "-"))
+		t.Run(testname, func(t *testing.T) {
+			var writer bytes.Buffer
+			tp := NewTP(&Config{Args: []string{tt.A, tt.B}, Output: &writer, Mode: ModeDiff}, now)
+
+			err := tp.ProcessTimestamps()
+			assert.NoError(t, err)
+			assert.EqualValues(t, tt.want.String()+"\n", writer.String())
+		})
+	}
+}
+
+func TestAddTimestamps(t *testing.T) {
+	setUTC()
+
+	var datetimes = []struct {
+		A    string
+		B    string
+		want time.Time
+	}{
+		{`now`, `01:30`, dateAtTime(now, 14, 00, 00)},
+		{`now`, `2h`, dateAtTime(now, 14, 30, 00)},
+		{`now`, `12d4h`, dateAtTime(now.Add(time.Hour*24*12), 16, 30, 00)},
+		{`now`, `45m`, dateAtTime(now, 13, 15, 00)},
+		{`now`, `1d10s`, dateAtTime(now.Add(time.Hour*24*1), 12, 30, 10)},
+	}
+
+	for _, tt := range datetimes {
+		testname := fmt.Sprintf("diff-%s-%s", strings.ReplaceAll(tt.A, " ", "-"), strings.ReplaceAll(tt.B, " ", "-"))
+		t.Run(testname, func(t *testing.T) {
+			var writer bytes.Buffer
+			tp := NewTP(&Config{Args: []string{tt.A, tt.B}, Output: &writer, Mode: ModeAdd}, now)
+
+			err := tp.ProcessTimestamps()
+			assert.NoError(t, err)
+			assert.EqualValues(t, tt.want.String()+"\n", writer.String())
+		})
+	}
+}

cmd/writer.go

@@ -0,0 +1,94 @@
+/*
+Copyright © 2025 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package cmd
+
+import (
+	"fmt"
+	"time"
+)
+
+type TimestampWriter interface {
+	String() string
+}
+
+type TPduration struct {
+	TimestampProccessor
+	Data time.Duration
+}
+
+type TPdatetime struct {
+	TimestampProccessor
+	Data time.Time
+}
+
+func (duration TPduration) String() string {
+	var unit string
+
+	if duration.Unit {
+		switch duration.Format {
+		case "d", "day", "days":
+			unit = " days"
+		case "h", "hour", "hours":
+			unit = " hours"
+		case "m", "min", "mins", "minutes":
+			unit = " minutes"
+		case "s", "sec", "secs", "seconds":
+			unit = " seconds"
+		case "ms", "msec", "msecs", "milliseconds":
+			unit = " milliseconds"
+		}
+	}
+
+	// duration, days, hour, min, sec, msec
+	switch duration.Format {
+	case "d", "day", "days":
+		return fmt.Sprintf("%.02f%s", duration.Data.Hours()/24+(duration.Data.Minutes()/60), unit)
+	case "h", "hour", "hours":
+		return fmt.Sprintf("%.02f%s", duration.Data.Hours(), unit)
+	case "m", "min", "mins", "minutes":
+		return fmt.Sprintf("%.02f%s", duration.Data.Minutes(), unit)
+	case "s", "sec", "secs", "seconds":
+		return fmt.Sprintf("%.02f%s", duration.Data.Seconds(), unit)
+	case "ms", "msec", "msecs", "milliseconds":
+		return fmt.Sprintf("%d%s", duration.Data.Milliseconds(), unit)
+	case "dur", "duration":
+		fallthrough
+	default:
+		return duration.Data.String()
+	}
+}
+
+func (datetime TPdatetime) String() string {
+	// datetime(default), date, time, unix, string
+	switch datetime.Format {
+	case "rfc3339":
+		return datetime.Data.Format(time.RFC3339)
+	case "date":
+		return datetime.Data.Format("2006-01-02")
+	case "time":
+		return datetime.Data.Format("03:04:05")
+	case "unix":
+		return fmt.Sprintf("%d", datetime.Data.Unix())
+	case "datetime":
+		fallthrough
+	case "":
+		return datetime.Data.String()
+	default:
+		return datetime.Data.Format(datetime.Format)
+	}
+}