Move functions into their own, separate files & add docs

category.go

@@ -1,5 +1,38 @@
 package crunchyroll
 
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+)
+
+// Categories returns all available categories and possible subcategories.
+func (c *Crunchyroll) Categories(includeSubcategories bool) (ca []*Category, err error) {
+	tenantCategoriesEndpoint := fmt.Sprintf("https://beta.crunchyroll.com/content/v1/tenant_categories?include_subcategories=%t&locale=%s",
+		includeSubcategories, c.Locale)
+	resp, err := c.request(tenantCategoriesEndpoint, http.MethodGet)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	var jsonBody map[string]interface{}
+	if err = json.NewDecoder(resp.Body).Decode(&jsonBody); err != nil {
+		return nil, fmt.Errorf("failed to parse 'tenant_categories' response: %w", err)
+	}
+
+	for _, item := range jsonBody["items"].([]interface{}) {
+		category := &Category{}
+		if err := decodeMapToStruct(item, category); err != nil {
+			return nil, err
+		}
+
+		ca = append(ca, category)
+	}
+
+	return ca, nil
+}
+
 // Category contains all information about a category.
 type Category struct {
 	Category string `json:"tenant_category"`
@@ -18,19 +51,8 @@ type Category struct {
 	} `json:"sub_categories"`
 
 	Images struct {
-		Background []struct {
-			Width  int    `json:"width"`
-			Height int    `json:"height"`
-			Type   string `json:"type"`
-			Source string `json:"source"`
-		} `json:"background"`
-
-		Low []struct {
-			Width  int    `json:"width"`
-			Height int    `json:"height"`
-			Type   string `json:"type"`
-			Source string `json:"source"`
-		} `json:"low"`
+		Background []Image `json:"background"`
+		Low        []Image `json:"low"`
 	} `json:"images"`
 
 	Localization struct {