feat: return error

README.md

@@ -68,13 +68,19 @@ slog.SetDefault(slog.New(log.Default()))
 It is possible to request a specific theme.
 
 ```go
-log.SetStyles(redlog.Theme("catppuccin"))
+styles, _ := redlog.Theme("catppuccin")
+logger := log.New(os.Stderr)
+logger.SetStyles(styles)
 ```
 
 And with a specific variation of the theme.
 
 ```go
-log.SetStyles(redlog.Theme("catppuccin", redlog.WithVariant("mocha")))
+styles, err := redlog.Theme("catppuccin", redlog.WithVariant("mocha"))
+if err != nil {
+    log.Fatal(err)
+}
+log.SetStyles(styles)
 ```
 
 ## Specific theme

redlog.go

@@ -1,10 +1,17 @@
 package redlog
 
 import (
+	"errors"
+
 	"github.com/charmbracelet/log"
 	"github.com/op/redlog/internal/themes"
 )
 
+var (
+	ErrUnknownTheme   = errors.New("unknown theme")
+	ErrUnknownVariant = errors.New("unknown variant")
+)
+
 // Default is the default theme style.
 var Default = themes.Default.Default.Styles
 
@@ -15,23 +22,23 @@ func WithVariant(name string) func(*option) {
 
 // Theme returns the most suitable theme given the provided arguments.
 //
-// This function will fallback to the default theme or the found themes
-// variant, if the requested was not found.
-func Theme(name string, opts ...Option) *log.Styles {
+// This function will always return a usable style, together with an error if
+// the requested theme or variant was not found.
+func Theme(name string, opts ...Option) (*log.Styles, error) {
 	o := option{name: name}
 	for _, opt := range opts {
 		opt(&o)
 	}
 
 	t, ok := themes.ByName(o.name)
 	if !ok {
-		return Default
+		return Default, ErrUnknownTheme
 	}
 	v, ok := themes.VariantByName(t, o.variant)
 	if !ok {
-		return t.Default.Styles
+		return t.Default.Styles, ErrUnknownVariant
 	}
-	return v.Styles
+	return v.Styles, nil
 }
 
 type Option func(*option)