Add Collection endpoint (bold-commerce#115)

Co-authored-by: Geoffrey Chen <[email protected]>

collection.go

@@ -0,0 +1,82 @@
+package goshopify
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+)
+
+const collectionsBasePath = "collections"
+
+// CollectionService is an interface for interfacing with the collection endpoints
+// of the Shopify API.
+// See: https://help.shopify.com/api/reference/products/collection
+type CollectionService interface {
+	Get(collectionID int64, options interface{}) (*Collection, error)
+	ListProducts(collectionID int64, options interface{}) ([]Product, error)
+	ListProductsWithPagination(collectionID int64,options interface{}) ([]Product, *Pagination, error)
+}
+
+// CollectionServiceOp handles communication with the collection related methods of
+// the Shopify API.
+type CollectionServiceOp struct {
+	client *Client
+}
+
+// Collection represents a Shopify collection
+type Collection struct {
+	ID             int64       `json:"id"`
+	Handle         string      `json:"handle"`
+	Title          string      `json:"title"`
+	UpdatedAt      *time.Time  `json:"updated_at"`
+	BodyHTML       string      `json:"body_html"`
+	SortOrder      string      `json:"sort_order"`
+	TemplateSuffix string      `json:"template_suffix"`
+	Image          Image       `json:"image"`
+	PublishedAt    *time.Time  `json:"published_at"`
+	PublishedScope string      `json:"published_scope"`
+}
+
+// Represents the result from the collections/X.json endpoint
+type CollectionResource struct {
+	Collection *Collection `json:"collection"`
+}
+
+// Get individual collection
+func (s *CollectionServiceOp) Get(collectionID int64, options interface{}) (*Collection, error) {
+	path := fmt.Sprintf("%s/%d.json", collectionsBasePath, collectionID)
+	resource := new(CollectionResource)
+	err := s.client.Get(path, resource, options)
+	return resource.Collection, err
+}
+
+// List products for a collection
+func (s *CollectionServiceOp) ListProducts(collectionID int64, options interface{}) ([]Product, error) {
+	products, _, err := s.ListProductsWithPagination(collectionID, options)
+	if err != nil {
+		return nil, err
+	}
+	return products, nil
+}
+
+// List products for a collection and return pagination to retrieve next/previous results.
+func (s *CollectionServiceOp) ListProductsWithPagination(collectionID int64,options interface{}) ([]Product, *Pagination, error) {
+	path := fmt.Sprintf("%s/%d/products.json", collectionsBasePath, collectionID)
+	resource := new(ProductsResource)
+	headers := http.Header{}
+
+	headers, err := s.client.createAndDoGetHeaders("GET", path, nil, options, resource)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// Extract pagination info from header
+	linkHeader := headers.Get("Link")
+
+	pagination, err := extractPagination(linkHeader)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return resource.Products, pagination, nil
+}