feat: add the 'fmt' command to reformat a date/time

.gitignore

@@ -20,4 +20,6 @@
 # Go workspace file
 go.work
 go.work.sum
+
+# Project exclusions
 cmd/dtmate/cmd/README.md

DateTimeMate.go

@@ -2,6 +2,8 @@ package DateTimeMate
 
 import (
 	"github.com/golang-module/carbon/v2"
+	"github.com/lestrrat-go/strftime"
+	"github.com/tkuchiki/parsetime"
 	"strings"
 )
 
@@ -34,9 +36,9 @@ var abbrevMap = [][]string{
 	{"year", "Y"},
 }
 
-// convertRelativeDateToActual converts "yesterday", "today", "tomorrow"
+// ConvertRelativeDateToActual converts "yesterday", "today", "tomorrow"
 // into actual dates; yesterday and tomorrow are -/+ 24 hours of current time
-func convertRelativeDateToActual(from string) string {
+func ConvertRelativeDateToActual(from string) string {
 	switch strings.ToLower(from) {
 	case "now":
 		return carbon.Now().String()
@@ -66,3 +68,23 @@ func shrinkPeriod(period string) string {
 func removeTrailingS(s string) string {
 	return strings.TrimSuffix(s, "s")
 }
+
+// Reformat the source string to match the strftime outputFormat
+// Ex: "2024-07-22 08:21:44", "%v %r" => "22-Jul-2024 08:21:44 AM"
+func Reformat(source string, outputFormat string) (string, error) {
+	source = ConvertRelativeDateToActual(source)
+	f, err := strftime.New(outputFormat)
+	if err != nil {
+		return "", err
+	}
+	p, err := parsetime.NewParseTime()
+	if err != nil {
+		return "", err
+	}
+	s, err := p.Parse(source)
+	if err != nil {
+		return "", err
+
+	}
+	return f.FormatString(s), nil
+}

DateTimeMate_test.go

@@ -22,3 +22,43 @@ func TestShrinkPeriod(t *testing.T) {
 		}
 	}
 }
+
+func testFormat(t *testing.T, source, outputFormat, correct string) {
+	t.Helper()
+	computed, err := Reformat(source, outputFormat)
+	if err != nil {
+		t.Error(err)
+	}
+	if computed != correct {
+		t.Errorf("[computed: %v] != [correct: %v]", computed, correct)
+	}
+}
+
+func TestFormatCommand(t *testing.T) {
+	source := "2024-07-22 08:21:44"
+	fmt := "%T %D"
+	correct := "08:21:44 07/22/24"
+	testFormat(t, source, fmt, correct)
+
+	fmt = "%v %r"
+	correct = "22-Jul-2024 08:21:44 AM"
+	testFormat(t, source, fmt, correct)
+
+	fmt = "%Y%m%d.%H%M%S"
+	correct = "20240722.082144"
+	testFormat(t, source, fmt, correct)
+
+	source = "2024-02-29T23:59:59Z"
+	fmt = "%Y%m%d.%H%M%S"
+	correct = "20240229.235959"
+	testFormat(t, source, fmt, correct)
+
+	fmt = "%Z"
+	correct = "UTC"
+	testFormat(t, source, fmt, correct)
+
+	source = "Mon Jul 22 08:40:33 EDT 2024"
+	fmt = "%Z %z"
+	correct = "EDT -0400"
+	testFormat(t, source, fmt, correct)
+}

cmd/dtmate/cmd/fmt.go

@@ -0,0 +1,89 @@
+package cmd
+
+import (
+	"fmt"
+	"github.com/jftuga/DateTimeMate"
+	"github.com/spf13/cobra"
+	"os"
+)
+
+var fmtCmd = &cobra.Command{
+	Use:   "fmt [date/time] [format specifiers]",
+	Short: "reformat a date/time",
+	Run: func(cmd *cobra.Command, args []string) {
+		if optFmtList {
+			listConversionsSpecifiers()
+			return
+		}
+		reformat(args[0], args[1])
+	},
+}
+
+var optFmtList bool
+
+func init() {
+	rootCmd.AddCommand(fmtCmd)
+	fmtCmd.Flags().BoolVarP(&optFmtList, "list", "l", false, "list supported conversion specifiers")
+}
+
+// listConversionsSpecifiers the list was copied from:
+// https://github.com/lestrrat-go/strftime
+func listConversionsSpecifiers() {
+	list := [][]string{
+		[]string{`%A`, `national representation of the full weekday name`},
+		[]string{`%a`, `national representation of the abbreviated weekday`},
+		[]string{`%B`, `national representation of the full month name`},
+		[]string{`%b`, `national representation of the abbreviated month name`},
+		[]string{`%C`, `(year / 100) as decimal number; single digits are preceded by a zero`},
+		[]string{`%c`, `national representation of time and date`},
+		[]string{`%D`, `equivalent to %m/%d/%y`},
+		[]string{`%d`, `day of the month as a decimal number (01-31)`},
+		[]string{`%e`, `the day of the month as a decimal number (1-31); single digits are preceded by a blank`},
+		[]string{`%F`, `equivalent to %Y-%m-%d`},
+		[]string{`%H`, `the hour (24-hour clock) as a decimal number (00-23)`},
+		[]string{`%h`, `same as %b`},
+		[]string{`%I`, `the hour (12-hour clock) as a decimal number (01-12)`},
+		[]string{`%j`, `the day of the year as a decimal number (001-366)`},
+		[]string{`%k`, `the hour (24-hour clock) as a decimal number (0-23); single digits are preceded by a blank`},
+		[]string{`%l`, `the hour (12-hour clock) as a decimal number (1-12); single digits are preceded by a blank`},
+		[]string{`%M`, `the minute as a decimal number (00-59)`},
+		[]string{`%m`, `the month as a decimal number (01-12)`},
+		[]string{`%n`, `a newline`},
+		[]string{`%p`, `national representation of either 'ante meridiem' (a.m.)  or 'post meridiem' (p.m.)  as appropriate.`},
+		[]string{`%R`, `equivalent to %H:%M`},
+		[]string{`%r`, `equivalent to %I:%M:%S %p`},
+		[]string{`%S`, `the second as a decimal number (00-60)`},
+		[]string{`%T`, `equivalent to %H:%M:%S`},
+		[]string{`%t`, `a tab`},
+		[]string{`%U`, `the week number of the year (Sunday as the first day of the week) as a decimal number (00-53)`},
+		[]string{`%u`, `the weekday (Monday as the first day of the week) as a decimal number (1-7)`},
+		[]string{`%V`, `the week number of the year (Monday as the first day of the week) as a decimal number (01-53)`},
+		[]string{`%v`, `equivalent to %e-%b-%Y`},
+		[]string{`%W`, `the week number of the year (Monday as the first day of the week) as a decimal number (00-53)`},
+		[]string{`%w`, `the weekday (Sunday as the first day of the week) as a decimal number (0-6)`},
+		[]string{`%X`, `national representation of the time`},
+		[]string{`%x`, `national representation of the date`},
+		[]string{`%Y`, `the year with century as a decimal number`},
+		[]string{`%y`, `the year without century as a decimal number (00-99)`},
+		[]string{`%Z`, `the time zone name`},
+		[]string{`%z`, `the time zone offset from UTC`},
+		[]string{`%%`, `a '%'`},
+	}
+
+	for i := 0; i < len(list); i++ {
+		fmt.Printf("%s  %s\n", list[i][0], list[i][1])
+	}
+}
+
+func reformat(source, outputFormat string) {
+	result, err := DateTimeMate.Reformat(source, outputFormat)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	if optRootNoNewline {
+		fmt.Print(result)
+	} else {
+		fmt.Println(result)
+	}
+}

diff.go

@@ -51,7 +51,7 @@ func (diff *Diff) String() string {
 func (diff *Diff) CalculateDiff() (string, time.Duration, error) {
 	var start, end time.Time
 
-	alpha := carbon.Parse(convertRelativeDateToActual(diff.Start))
+	alpha := carbon.Parse(ConvertRelativeDateToActual(diff.Start))
 	if alpha.Error != nil {
 		// fmt.Println("alpha:", alpha.Error)
 		p, err := parsetime.NewParseTime()
@@ -66,7 +66,7 @@ func (diff *Diff) CalculateDiff() (string, time.Duration, error) {
 		start = alpha.StdTime()
 	}
 
-	omega := carbon.Parse(convertRelativeDateToActual(diff.End))
+	omega := carbon.Parse(ConvertRelativeDateToActual(diff.End))
 	if omega.Error != nil {
 		// fmt.Println("omega:", omega.Error)
 		p, err := parsetime.NewParseTime()

dur.go

@@ -134,7 +134,7 @@ func (dur *Dur) addOrSub(op int) ([]string, error) {
 		var f, u time.Time
 		var err error
 
-		until := convertRelativeDateToActual(dur.Until)
+		until := ConvertRelativeDateToActual(dur.Until)
 		p, err := parsetime.NewParseTime()
 		if err != nil {
 			return nil, err
@@ -144,7 +144,7 @@ func (dur *Dur) addOrSub(op int) ([]string, error) {
 			return nil, err
 		}
 
-		from := convertRelativeDateToActual(dur.From)
+		from := ConvertRelativeDateToActual(dur.From)
 		for {
 			from, err = calculate(from, dur.Period, op)
 			if err != nil {
@@ -222,7 +222,7 @@ func calculate(from, period string, index int) (string, error) {
 		}
 	}
 
-	from = convertRelativeDateToActual(from)
+	from = ConvertRelativeDateToActual(from)
 	p, err := parsetime.NewParseTime()
 	if err != nil {
 		return "", err