Videos: Use start time and end time for clips (#4264)

This PR parses the start and end time for clips.

It also adds a new, dedicated API endpoint (`/api/v1/clips/{id}`) for
retrieving the start and end time of a clip.

Here is a sample response from that new endpoint (`video` is a video object,
as described in https://docs.invidious.io/api/common_types/#videoobject):

GET `/api/v1/clips/UgkxxPM3BRphCAPLP88YoUGuj79KXPfpNNO_?pretty=1`

Response:
```
{
  "startTime": 8842.645,
  "endTime": 8855.856,
  "clipTitle": "✂️ Kirby is pink!",
  "video": {}
}
```

Closes issue 3921

4 files changed, 72 insertions, 0 deletions

diff --git a/src/invidious/routes/api/v1/videos.cr b/src/invidious/routes/api/v1/videos.cr
index 1017ac9d..9281f4dd 100644
--- a/src/invidious/routes/api/v1/videos.cr
+++ b/src/invidious/routes/api/v1/videos.cr
@@ -363,4 +363,47 @@ module Invidious::Routes::API::V1::Videos
       end
     end
   end
+
+  def self.clips(env)
+    locale = env.get("preferences").as(Preferences).locale
+
+    env.response.content_type = "application/json"
+
+    clip_id = env.params.url["id"]
+    region = env.params.query["region"]?
+    proxy = {"1", "true"}.any? &.== env.params.query["local"]?
+
+    response = YoutubeAPI.resolve_url("https://www.youtube.com/clip/#{clip_id}")
+    return error_json(400, "Invalid clip ID") if response["error"]?
+
+    video_id = response.dig?("endpoint", "watchEndpoint", "videoId").try &.as_s
+    return error_json(400, "Invalid clip ID") if video_id.nil?
+
+    start_time = nil
+    end_time = nil
+    clip_title = nil
+
+    if params = response.dig?("endpoint", "watchEndpoint", "params").try &.as_s
+      start_time, end_time, clip_title = parse_clip_parameters(params)
+    end
+
+    begin
+      video = get_video(video_id, region: region)
+    rescue ex : NotFoundException
+      return error_json(404, ex)
+    rescue ex
+      return error_json(500, ex)
+    end
+
+    return JSON.build do |json|
+      json.object do
+        json.field "startTime", start_time
+        json.field "endTime", end_time
+        json.field "clipTitle", clip_title
+        json.field "video" do
+          Invidious::JSONify::APIv1.video(video, json, locale: locale, proxy: proxy)
+        end
+      end
+    end
+  end
 end
diff --git a/src/invidious/routes/watch.cr b/src/invidious/routes/watch.cr
index 3d935f0a..aabe8dfc 100644
--- a/src/invidious/routes/watch.cr
+++ b/src/invidious/routes/watch.cr
@@ -275,6 +275,12 @@ module Invidious::Routes::Watch
     return error_template(400, "Invalid clip ID") if response["error"]?
 
     if video_id = response.dig?("endpoint", "watchEndpoint", "videoId")
+      if params = response.dig?("endpoint", "watchEndpoint", "params").try &.as_s
+        start_time, end_time, _ = parse_clip_parameters(params)
+        env.params.query["start"] = start_time.to_s if start_time != nil
+        env.params.query["end"] = end_time.to_s if end_time != nil
+      end
+
       return env.redirect "/watch?v=#{video_id}&#{env.params.query}"
     else
       return error_template(404, "The requested clip doesn't exist")
diff --git a/src/invidious/routing.cr b/src/invidious/routing.cr
index d6bd991c..ba05da19 100644
--- a/src/invidious/routing.cr
+++ b/src/invidious/routing.cr
@@ -235,6 +235,7 @@ module Invidious::Routing
       get "/api/v1/captions/:id", {{namespace}}::Videos, :captions
       get "/api/v1/annotations/:id", {{namespace}}::Videos, :annotations
       get "/api/v1/comments/:id", {{namespace}}::Videos, :comments
+      get "/api/v1/clips/:id", {{namespace}}::Videos, :clips
 
       # Feeds
       get "/api/v1/trending", {{namespace}}::Feeds, :trending
diff --git a/src/invidious/videos/clip.cr b/src/invidious/videos/clip.cr
new file mode 100644
index 00000000..29c57182
--- /dev/null
+++ b/src/invidious/videos/clip.cr
@@ -0,0 +1,22 @@
+require "json"
+
+# returns start_time, end_time and clip_title
+def parse_clip_parameters(params) : {Float64?, Float64?, String?}
+  decoded_protobuf = params.try { |i| URI.decode_www_form(i) }
+    .try { |i| Base64.decode(i) }
+    .try { |i| IO::Memory.new(i) }
+    .try { |i| Protodec::Any.parse(i) }
+
+  start_time = decoded_protobuf
+    .try(&.["50:0:embedded"]["2:1:varint"].as_i64)
+    .try { |i| i/1000 }
+
+  end_time = decoded_protobuf
+    .try(&.["50:0:embedded"]["3:2:varint"].as_i64)
+    .try { |i| i/1000 }
+
+  clip_title = decoded_protobuf
+    .try(&.["50:0:embedded"]["4:3:string"].as_s)
+
+  return start_time, end_time, clip_title
+end