feat: Support Reddit searching

Reddit API is rate limited and current stats are returned in response
headers.

Author: macie

README.md

@@ -6,7 +6,8 @@ Find opinions about given phrase (also URL) on social news websites:
 
 - _[Lemmy](https://en.wikipedia.org/wiki/Lemmy_(social_network))_
 - _[Lobsters](https://lobste.rs/about)_
-- _[Hacker News](https://en.wikipedia.org/wiki/Hacker_News)_.
+- _[Hacker News](https://en.wikipedia.org/wiki/Hacker_News)_
+- _[Reddit](https://en.wikipedia.org/wiki/Reddit)_.
 
 It can be used for [including discussions on static websites/blogs](#static-site-generators).
 
@@ -29,6 +30,8 @@ Hacker News	https://news.ycombinator.com/item?id=31840331	The Grug Brained Devel
 Hacker News	https://news.ycombinator.com/item?id=38076886	The Grug Brained Developer (2022)	https://grugbrain.dev/
 Lobsters	https://lobste.rs/s/ifaar4/grug_brained_developer	The Grug Brained Developer	https://grugbrain.dev/
 Lobsters	https://lobste.rs/s/pmpc9v/grug_brained_developer	The Grug Brained Developer	http://grugbrain.dev
+Reddit	https://reddit.com/r/programming/comments/16gt8w4/the_grug_brained_developer/	The grug brained developer	https://grugbrain.dev
+Reddit	https://reddit.com/r/brdev/comments/14jhm17/the_grug_brained_developer/	The Grug Brained Developer	https://grugbrain.dev
 ```
 
 The result is printed to stdout as rows in format: `<service_name><tab><URL><tab><title><tab><source_domain>`.

cmd/main.go

@@ -41,6 +41,7 @@ func main() {
 		opinions.SearchHackerNews,
 		opinions.SearchLemmy,
 		opinions.SearchLobsters,
+		opinions.SearchReddit,
 	}
 
 	wg := new(sync.WaitGroup)

reddit.go

@@ -0,0 +1,70 @@
+package opinions
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/url"
+
+	"github.com/macie/opinions/http"
+)
+
+// RedditResponse represents some interesting fields of response from Reddit API.
+type RedditResponse struct {
+	Data struct {
+		Children []struct {
+			Data struct {
+				ID          string `json:"permalink"`
+				Title       string `json:"title"`
+				URL         string `json:"url"`
+				NumComments int    `json:"num_comments"`
+			} `json:"data"`
+		} `json:"children"`
+	} `json:"data"`
+}
+
+// SearchReddit searches Reddit for given query and returns list of discussions
+// sorted by relevance.
+//
+// See: https://www.reddit.com/dev/api#GET_search
+func SearchReddit(ctx context.Context, client http.Client, query string) ([]Discussion, error) {
+	discussions := make([]Discussion, 0)
+	searchURL := "https://www.reddit.com/search.json?sort=relevance&t=all&q="
+
+	r, err := client.Get(ctx, searchURL+url.QueryEscape(query))
+	if err != nil {
+		return discussions, err
+	}
+	defer r.Body.Close()
+
+	if r.StatusCode != http.StatusOK {
+		if r.Header.Get("X-Ratelimit-Remaining") == "0" { // https://support.reddithelp.com/hc/en-us/articles/16160319875092-Reddit-Data-API-Wiki
+			return discussions, fmt.Errorf("cannot search Reddit: too many requests. Wait %s seconds", r.Header.Get("X-Ratelimit-Reset"))
+		}
+
+		return discussions, fmt.Errorf("cannot search Reddit: `GET %s` responded with status code %d", r.Request.URL, r.StatusCode)
+	}
+
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		return discussions, err
+	}
+
+	var response RedditResponse
+	if err := json.Unmarshal(body, &response); err != nil {
+		return discussions, err
+	}
+
+	for _, entry := range response.Data.Children {
+		discussions = append(discussions, Discussion{
+			Service:  "Reddit",
+			URL:      "https://reddit.com" + entry.Data.ID,
+			Title:    entry.Data.Title,
+			Source:   entry.Data.URL,
+			Comments: entry.Data.NumComments,
+		})
+	}
+
+	return discussions, nil
+}

reddit_test.go

@@ -0,0 +1,20 @@
+package opinions
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/macie/opinions/ensure"
+	"github.com/macie/opinions/http"
+)
+
+func ExampleSearchReddit() {
+	client := http.Client{}
+	query := "https://grugbrain.dev/"
+
+	opinions := ensure.MustReturn(SearchReddit(context.TODO(), client, query))
+
+	fmt.Println(opinions[0])
+	// Output:
+	// Reddit	https://reddit.com/r/hypeurls/comments/17k6i1l/the_grug_brained_developer_2022/	The Grug Brained Developer (2022)	https://grugbrain.dev/
+}