Fix: Garmin Connect authentication and profile fetching (profile URL and GarminTime parsing)

internal/types/garmin.go

@@ -1,12 +1,45 @@
 package types
 
-import "time"
+import (
+	"fmt"
+	"strings"
+	"time"
+)
 
 // GarminTime represents Garmin's timestamp format with custom JSON parsing
 type GarminTime struct {
 	time.Time
 }
 
+// UnmarshalJSON implements the json.Unmarshaler interface.
+// It parses Garmin's specific timestamp format.
+func (gt *GarminTime) UnmarshalJSON(b []byte) (err error) {
+	s := strings.Trim(string(b), `"`)
+	if s == "null" {
+		return nil
+	}
+
+	// Try parsing with milliseconds (e.g., "2018-09-01T00:13:25.000")
+	// Garmin sometimes returns .0 for milliseconds, which Go's time.Parse handles as .000
+	// The 'Z' in the layout indicates a UTC time without a specific offset, which is often how these are interpreted.
+	// If the input string does not contain 'Z', it will be parsed as local time.
+	// For consistency, we'll assume UTC if no timezone is specified.
+	layouts := []string{
+		"2006-01-02T15:04:05.0", // Example: 2018-09-01T00:13:25.0
+		"2006-01-02T15:04:05",   // Example: 2018-09-01T00:13:25
+		"2006-01-02",            // Example: 2018-09-01
+	}
+
+	for _, layout := range layouts {
+		if t, err := time.Parse(layout, s); err == nil {
+			gt.Time = t
+			return nil
+		}
+	}
+
+	return fmt.Errorf("cannot parse %q into a GarminTime", s)
+}
+
 // SessionData represents saved session information
 type SessionData struct {
 	Domain    string `json:"domain"`