Add prometheus metrics at /api/v1/metrics

src/invidious/helpers/helpers.cr

@@ -225,3 +225,11 @@ def get_playback_statistic
 
   return tracker.as(Hash(String, Int64 | Float64))
 end
+
+def to_prometheus_metrics(metrics_struct : Hash(String, Number)) : String
+  return String.build do |str|
+    metrics_struct.each.each do |key, value|
+      str << key << " " << value << "\n"
+    end
+  end
+end

src/invidious/jobs/statistics_refresh_job.cr

@@ -27,6 +27,11 @@ class Invidious::Jobs::StatisticsRefreshJob < Invidious::Jobs::BaseJob
     "playback" => {} of String => Int64 | Float64,
   }
 
+  STATISTICS_PROMETHEUS = {
+    "invidious_updated_at"                => Time.utc.to_unix,
+    "invidious_last_channel_refreshed_at" => 0_i64,
+  }
+
   private getter db : DB::Database
 
   def initialize(@db, @software_config : Hash(String, String))
@@ -59,6 +64,9 @@ class Invidious::Jobs::StatisticsRefreshJob < Invidious::Jobs::BaseJob
     users["activeHalfyear"] = Invidious::Database::Statistics.count_users_active_1m
     users["activeMonth"] = Invidious::Database::Statistics.count_users_active_6m
 
+    STATISTICS_PROMETHEUS["invidious_updated_at"] = Time.utc.to_unix
+    STATISTICS_PROMETHEUS["invidious_last_channel_refreshed_at"] = Invidious::Database::Statistics.channel_last_update.try &.to_unix || 0_i64
+
     STATISTICS["metadata"] = {
       "updatedAt"              => Time.utc.to_unix,
       "lastChannelRefreshedAt" => Invidious::Database::Statistics.channel_last_update.try &.to_unix || 0_i64,

src/invidious/routes/api/v1/misc.cr

@@ -26,6 +26,11 @@ module Invidious::Routes::API::V1::Misc
     end
   end
 
+  def self.metrics(env)
+    env.response.content_type = "text/plain"
+    return to_prometheus_metrics(Invidious::Jobs::StatisticsRefreshJob::STATISTICS_PROMETHEUS)
+  end
+
   # APIv1 currently uses the same logic for both
   # user playlists and Invidious playlists. This means that we can't
   # reasonably split them yet. This should be addressed in APIv2

src/invidious/routing.cr

@@ -310,6 +310,9 @@ module Invidious::Routing
 
       # Misc
       get "/api/v1/stats", {{namespace}}::Misc, :stats
+      if CONFIG.statistics_enabled
+        get "/api/v1/metrics", {{namespace}}::Misc, :metrics
+      end
       get "/api/v1/playlists/:plid", {{namespace}}::Misc, :get_playlist
       get "/api/v1/auth/playlists/:plid", {{namespace}}::Misc, :get_playlist
       get "/api/v1/mixes/:rdid", {{namespace}}::Misc, :mixes