WIP: load more comments for a post

Signed-off-by: Vartan Benohanian <vartanbeno@gmail.com>

comment.go

@@ -2,6 +2,7 @@ package reddit
 
 import (
 	"context"
+	"errors"
 	"net/http"
 	"net/url"
 )
@@ -63,3 +64,69 @@ func (s *CommentService) Edit(ctx context.Context, id string, text string) (*Com
 
 	return root, resp, nil
 }
+
+// LoadMoreReplies retrieves more replies that were left out when initially fetching the comment.
+func (s *CommentService) LoadMoreReplies(ctx context.Context, comment *Comment) (*Response, error) {
+	if comment == nil {
+		return nil, errors.New("comment: must not be nil")
+	}
+
+	if !comment.hasMore() {
+		return nil, nil
+	}
+
+	postID := comment.PostID
+	commentIDs := comment.Replies.MoreComments.Children
+
+	type query struct {
+		PostID  string   `url:"link_id"`
+		IDs     []string `url:"children,comma"`
+		APIType string   `url:"api_type"`
+	}
+
+	path := "api/morechildren"
+	path, err := addOptions(path, query{postID, commentIDs, "json"})
+	if err != nil {
+		return nil, err
+	}
+
+	req, err := s.client.NewRequest(http.MethodGet, path, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	type rootResponse struct {
+		JSON struct {
+			Data struct {
+				Things Things `json:"things"`
+			} `json:"data"`
+		} `json:"json"`
+	}
+
+	root := new(rootResponse)
+	resp, err := s.client.Do(ctx, req, root)
+	if err != nil {
+		return resp, err
+	}
+
+	comments := root.JSON.Data.Things.Comments
+	for _, c := range comments {
+		addCommentToReplies(comment, c)
+	}
+
+	comment.Replies.MoreComments = nil
+	return resp, nil
+}
+
+// addCommentToReplies traverses the comment tree to find the one
+// that the 2nd comment is replying to. It then adds it to its replies.
+func addCommentToReplies(parent *Comment, comment *Comment) {
+	if parent.FullID == comment.ParentID {
+		parent.Replies.Comments = append(parent.Replies.Comments, comment)
+		return
+	}
+
+	for _, reply := range parent.Replies.Comments {
+		addCommentToReplies(reply, comment)
+	}
+}