Add config environment variables

The config file can now be specified with `INVIDIOUS_CONFIG_FILE`.
A YAML formatted string can still be passed with `INVIDIOUS_CONFIG`, replacing
the config file.

Additionally all options can now be specified as environment variables.
The syntax for variable names is `INVIDIOUS_` followed by the option name in
upper case. The values are parsed as YAML.

These new env vars only update the provided main configuration, but it is
possible to point the config file at the example config and then use env vars
for all config options:
```
INVIDIOUS_CONFIG_FILE=./config/config.example.yml \
INVIDIOUS_CHANNEL_THREADS=10 \
./invidious
```

src/invidious.cr

@@ -30,11 +30,8 @@ require "./invidious/*"
 require "./invidious/routes/**"
 require "./invidious/jobs/**"
 
-ENV_CONFIG_NAME = "INVIDIOUS_CONFIG"
+CONFIG   = Config.load
-
+HMAC_KEY = CONFIG.hmac_key || Random::Secure.hex(32)
-CONFIG_STR = ENV.has_key?(ENV_CONFIG_NAME) ? ENV.fetch(ENV_CONFIG_NAME) : File.read("config/config.yml")
-CONFIG     = Config.from_yaml(CONFIG_STR)
-HMAC_KEY   = CONFIG.hmac_key || Random::Secure.hex(32)
 
 PG_URL = URI.new(
   scheme: "postgres",

src/invidious/helpers/helpers.cr

@@ -115,6 +115,63 @@ class Config
       return false
     end
   end
+
+  def self.load
+    # Load config from file or YAML string env var
+    env_config_file = "INVIDIOUS_CONFIG_FILE"
+    env_config_yaml = "INVIDIOUS_CONFIG"
+
+    config_file = ENV.has_key?(env_config_file) ? ENV.fetch(env_config_file) : "config/config.yml"
+    config_yaml = ENV.has_key?(env_config_yaml) ? ENV.fetch(env_config_yaml) : File.read(config_file)
+
+    config = Config.from_yaml(config_yaml)
+
+    # Update config from env vars (upcased and prefixed with "INVIDIOUS_")
+    {% for ivar in Config.instance_vars %}
+        {% env_id = "INVIDIOUS_#{ivar.id.upcase}" %}
+
+        if ENV.has_key?({{env_id}})
+            # puts %(Config.{{ivar.id}} : Loading from env var {{env_id}})
+            env_value = ENV.fetch({{env_id}})
+            success = false
+
+            # Use YAML converter if specified
+            {% ann = ivar.annotation(::YAML::Field) %}
+            {% if ann && ann[:converter] %}
+                puts %(Config.{{ivar.id}} : Parsing "#{env_value}" as {{ivar.type}} with {{ann[:converter]}} converter)
+                config.{{ivar.id}} = {{ann[:converter]}}.from_yaml(YAML::ParseContext.new, YAML::Nodes.parse(ENV.fetch({{env_id}})).nodes[0])
+                puts %(Config.{{ivar.id}} : Set to #{config.{{ivar.id}}})
+                success = true
+
+            # Use regular YAML parser otherwise
+            {% else %}
+                {% ivar_types = ivar.type.union? ? ivar.type.union_types : [ivar.type] %}
+                # Sort types to avoid parsing nulls and numbers as strings
+                {% ivar_types = ivar_types.sort_by { |ivar_type| ivar_type == Nil ? 0 : ivar_type == Int32 ? 1 : 2 } %}
+                {{ivar_types}}.each do |ivar_type|
+                    if !success
+                        begin
+                            # puts %(Config.{{ivar.id}} : Trying to parse "#{env_value}" as #{ivar_type})
+                            config.{{ivar.id}} = ivar_type.from_yaml(env_value)
+                            puts %(Config.{{ivar.id}} : Set to #{config.{{ivar.id}}} (#{ivar_type}))
+                            success = true
+                        rescue
+                            # nop
+                        end
+                    end
+                end
+            {% end %}
+
+            # Exit on fail
+            if !success
+                puts %(Config.{{ivar.id}} failed to parse #{env_value} as {{ivar.type}})
+                exit(1)
+            end
+        end
+    {% end %}
+
+    return config
+  end
 end
 
 struct DBConfig