Initial MVP commit

internal/platform/timeparse/parse.go

@@ -0,0 +1,30 @@
+package timeparse
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"gitea.maximumdirect.net/ejr/weatherapi/internal/platform/constants"
+)
+
+func ParseTimestamp(raw string) (time.Time, error) {
+	raw = strings.TrimSpace(raw)
+	if raw == "" {
+		return time.Time{}, fmt.Errorf("timestamp is required")
+	}
+
+	var lastErr error
+	for _, layout := range constants.SupportedTimestampLayouts {
+		ts, err := time.Parse(layout, raw)
+		if err == nil {
+			return ts, nil
+		}
+		lastErr = err
+	}
+
+	if lastErr == nil {
+		lastErr = fmt.Errorf("invalid timestamp")
+	}
+	return time.Time{}, fmt.Errorf("timestamp must be RFC3339 (example: 2026-03-17T12:30:00Z): %w", lastErr)
+}

internal/platform/timeparse/parse_test.go

@@ -0,0 +1,29 @@
+package timeparse
+
+import "testing"
+
+func TestParseTimestamp(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		wantErr bool
+	}{
+		{name: "rfc3339", input: "2026-03-17T12:30:00Z", wantErr: false},
+		{name: "rfc3339nano", input: "2026-03-17T12:30:00.123456789Z", wantErr: false},
+		{name: "missing timezone", input: "2026-03-17T12:30:00", wantErr: true},
+		{name: "invalid", input: "not-a-time", wantErr: true},
+		{name: "empty", input: "", wantErr: true},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := ParseTimestamp(tc.input)
+			if tc.wantErr && err == nil {
+				t.Fatalf("expected error")
+			}
+			if !tc.wantErr && err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+		})
+	}
+}