Added tests and fixed timestamp handling

cmds/timestamps/ast.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"errors"
-	"strings"
 	"time"
 )
 
@@ -10,51 +9,66 @@ type TimeComponent struct {
 	TS *string `parser:"@Time"`
 }
 
-func (t TimeComponent) Time() (time.Time, error) {
-	if strings.HasSuffix(*t.TS, "Z") {
-		return time.ParseInLocation("15:04:05Z", *t.TS, time.UTC)
-	}
-	return time.ParseInLocation("15:04:05", *t.TS, time.Local)
+func (t TimeComponent) Time(loc *time.Location) (time.Time, error) {
+	return time.ParseInLocation("15:04:05", *t.TS, loc)
 }
 
 func (t TimeComponent) RequiresRefreshing() bool {
 	return false
 }
 
+type TimeInZoneComponent struct {
+	TS    *string `parser:"@Time"`
+	InUTC bool    `parser:"@Z?"`
+}
+
+func (t TimeInZoneComponent) Time() (time.Time, error) {
+	loc := time.Local
+	if t.InUTC {
+		loc = time.UTC
+	}
+
+	return time.ParseInLocation("15:04:05", *t.TS, loc)
+}
+
+func (t TimeInZoneComponent) RequiresRefreshing() bool {
+	return false
+}
+
 type DateWithTimeComponents struct {
 	Date      *string        `parser:"@Date"`
-	MaybeTime *TimeComponent `parser:" @@?"`
+	MaybeTime *TimeComponent `parser:"(T? @@)?"`
+	InUTC     bool           `parser:"(@Z)?"`
 }
 
 func (d DateWithTimeComponents) Time() (time.Time, error) {
-	t, err := time.Parse("2006-01-02", *d.Date)
+	loc := time.Local
+	if d.InUTC {
+		loc = time.UTC
+	}
+
+	t, err := time.ParseInLocation("2006-01-02", *d.Date, loc)
 	if err != nil {
 		return time.Time{}, err
 	}
 	if d.MaybeTime != nil {
-		tt, err := d.MaybeTime.Time()
+		tt, err := d.MaybeTime.Time(loc)
 		if err != nil {
 			return time.Time{}, err
 		}
-		t = t.Add(tt.Sub(tt.Truncate(24 * time.Hour)))
+		t = time.Date(t.Year(), t.Month(), t.Day(), tt.Hour(), tt.Minute(), tt.Second(), 0, loc)
 	}
 	return t, nil
 }
 
 type Timestamp struct {
-	Full      *string                 `parser:"@Timestamp"`
-	DT        *DateWithTimeComponents `parser:"| @@"`
-	TimeToday *TimeComponent          `parser:" | @@"`
+	DT        *DateWithTimeComponents `parser:"@@"`
+	TimeToday *TimeInZoneComponent    `parser:" | @@"`
 	Int       *int                    `parser:" | @Int"`
 }
 
 func (t Timestamp) Time() (time.Time, error) {
 	switch {
-	case t.Full != nil:
-		if strings.HasSuffix(*t.Full, "Z") {
-			return time.ParseInLocation("2006-01-02T15:04:05Z", *t.Full, time.UTC)
-		}
-		return time.ParseInLocation("2006-01-02T15:04:05", *t.Full, time.Local)
 	case t.DT != nil:
 		return t.DT.Time()
 	case t.TimeToday != nil:

cmds/timestamps/input.go

@@ -8,17 +8,19 @@ import (
 )
 
 var basicLexer = lexer.MustSimple([]lexer.SimpleRule{
-	{"Identifier", `[a-zA-Z_][a-zA-Z0-9_]*`},
+	{"Identifier", `[a-z][a-zA-Z0-9_]*`},
 	{"Date", `\d{4}-\d{2}-\d{2}`},
-	{"Timestamp", `\d{4}-\d{2}-\d{2}T?\d{2}:\d{2}:\d{2}Z?`},
-	{"Time", `\d{2}:\d{2}:\d{2}Z?`},
+	{"Time", `\d{2}:\d{2}:\d{2}`},
 	{"Int", `\d+`},
+	{"T", `T`},
+	{"Z", `Z`},
 	{"Whitespace", `[ ]+`},
 })
 
 var parser = participle.MustBuild[Atom](
 	participle.Lexer(basicLexer),
 	participle.Elide("Whitespace"),
+	participle.UseLookahead(2),
 )
 
 func Parse(expr string) (TimeResult, error) {

cmds/timestamps/input_test.go

@@ -0,0 +1,113 @@
+package main
+
+import (
+	"testing"
+	"time"
+)
+
+func TestParse(t *testing.T) {
+	// Reference time: 2025-11-19T11:07:13Z
+	// Unix: 1763550433
+	refTime := time.Date(2025, 11, 19, 11, 7, 13, 0, time.UTC)
+
+	tests := []struct {
+		input    string
+		expected func() time.Time
+		desc     string
+	}{
+		{
+			input: "1763550433",
+			expected: func() time.Time {
+				return refTime
+			},
+			desc: "Unix timestamp",
+		},
+		{
+			input: "2025-11-19T11:07:13Z",
+			expected: func() time.Time {
+				return refTime
+			},
+			desc: "ISO 8601 UTC",
+		},
+		{
+			input: "2025-11-19T11:07:13",
+			expected: func() time.Time {
+				return time.Date(2025, 11, 19, 11, 7, 13, 0, time.Local)
+			},
+			desc: "ISO 8601 Local",
+		},
+		{
+			input: "2025-11-19 11:07:13Z",
+			expected: func() time.Time {
+				return refTime
+			},
+			desc: "Date Space Time Z",
+		},
+		{
+			input: "2025-11-19",
+			expected: func() time.Time {
+				return time.Date(2025, 11, 19, 0, 0, 0, 0, time.Local)
+			},
+			desc: "Date only Local",
+		},
+		{
+			input: "2025-11-19Z",
+			expected: func() time.Time {
+				return time.Date(2025, 11, 19, 0, 0, 0, 0, time.UTC)
+			},
+			desc: "Date only UTC",
+		},
+		{
+			input: "11:07:13",
+			expected: func() time.Time {
+				now := time.Now()
+				return time.Date(now.Year(), now.Month(), now.Day(), 11, 7, 13, 0, time.Local)
+			},
+			desc: "Time only Local",
+		},
+		{
+			input: "11:07:13Z",
+			expected: func() time.Time {
+				now := time.Now().In(time.UTC)
+				return time.Date(now.Year(), now.Month(), now.Day(), 11, 7, 13, 0, time.UTC)
+			},
+			desc: "Time only UTC",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.desc, func(t *testing.T) {
+			res, err := Parse(tc.input)
+			if err != nil {
+				t.Fatalf("Parse(%q) error: %v", tc.input, err)
+			}
+			got, err := res.Time()
+			if err != nil {
+				t.Fatalf("res.Time() error: %v", err)
+			}
+
+			want := tc.expected()
+
+			// For "Time only" tests, there might be a slight race condition if the day changes between test execution and expected value generation.
+			// But practically it's fine.
+
+			if !got.Truncate(time.Second).Equal(want) {
+				t.Errorf("Parse(%q) = %v, want %v", tc.input, got, want)
+			}
+		})
+	}
+
+	t.Run("now", func(t *testing.T) {
+		res, err := Parse("now")
+		if err != nil {
+			t.Fatalf("Parse('now') error: %v", err)
+		}
+		got, err := res.Time()
+		if err != nil {
+			t.Fatalf("res.Time() error: %v", err)
+		}
+		if time.Since(got) > time.Second {
+			t.Errorf("Parse('now') = %v, want close to now", got)
+		}
+	})
+}

site/index.html

@@ -1,15 +1,14 @@
 <!DOCTYPE html>
 <html lang="en">
+
 <head>
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <meta name="color-scheme" content="light dark">
   <title>Tools</title>
-    <link
-      rel="stylesheet"
-      href="https://cdn.jsdelivr.net/npm/@picocss/pico@2/css/pico.min.css"
-    >
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@picocss/pico@2/css/pico.min.css">
 </head>
+
 <body class="container">
   <header>
     <hgroup>
@@ -24,7 +23,9 @@
       <li><a href="/gotemplate/">Go Template Playground</a></li>
       <li><a href="/gradient-bands/">Gradient Bands</a></li>
       <li><a href="/2lcc/">Two-letter Country Codes</a></li>
+      <li><a href="/timestamps/">Timestamp Converter</a></li>
     </ul>
   </main>
 </body>
+
 </html>