Allow config defaults to be sourced from ENV

This allows the default config to source values from ENV variables if
they are set. With this change we don't have to modify the docker CMD or
edit the config.yml and then relaunch.

spec/config_spec.cr

@@ -1,14 +1,31 @@
 require "./spec_helper"
 
 describe Config do
-  it "creates config if it does not exist" do
-    with_default_config do |_, path|
+  it "creates default config if it does not exist" do
+    with_default_config do |config, path|
       File.exists?(path).should be_true
+      config.port.should eq 9000
     end
   end
 
   it "correctly loads config" do
     config = Config.load "spec/asset/test-config.yml"
     config.port.should eq 3000
+    config.base_url.should eq "/"
+  end
+
+  it "correctly reads config defaults from ENV" do
+    ENV["LOG_LEVEL"] = "debug"
+    config = Config.load "spec/asset/test-config.yml"
+    config.log_level.should eq "debug"
+    config.base_url.should eq "/"
+  end
+
+  it "correctly handles ENV truthiness" do
+    ENV["CACHE_ENABLED"] = "false"
+    config = Config.load "spec/asset/test-config.yml"
+    config.cache_enabled.should be_false
+    config.cache_log_enabled.should be_true
+    config.disable_login.should be_false
   end
 end

src/config.cr

@@ -4,28 +4,34 @@ class Config
   include YAML::Serializable
 
   @[YAML::Field(ignore: true)]
-  property path = ""
-  property host = "0.0.0.0"
-  property port : Int32 = 9000
-  property base_url = "/"
-  property session_secret = "mango-session-secret"
-  property library_path = "~/mango/library"
-  property library_cache_path = "~/mango/library.yml.gz"
-  property db_path = "~/mango/mango.db"
-  property queue_db_path = "~/mango/queue.db"
-  property scan_interval_minutes : Int32 = 5
-  property thumbnail_generation_interval_hours : Int32 = 24
-  property log_level = "info"
-  property upload_path = "~/mango/uploads"
-  property plugin_path = "~/mango/plugins"
-  property download_timeout_seconds : Int32 = 30
-  property cache_enabled = true
-  property cache_size_mbs = 50
-  property cache_log_enabled = true
-  property disable_login = false
-  property default_username = ""
-  property auth_proxy_header_name = ""
-  property plugin_update_interval_hours : Int32 = 24
+  property path : String = ""
+  property host : String = (ENV["LISTEN_HOST"]? || "0.0.0.0")
+  property port : Int32 = (ENV["LISTEN_PORT"]? || 9000).to_i
+  property base_url : String = (ENV["BASE_URL"]? || "/")
+  property session_secret : String = \
+        (ENV["SESSION_SECRET"]? || "mango-session-secret")
+  property library_path : String = (ENV["LIBRARY_PATH"]? || "~/mango/library")
+  property library_cache_path : String = \
+        (ENV["LIBRARY_CACHE_PATH"]? || "~/mango/library.yml.gz")
+  property db_path : String = (ENV["DB_PATH"]? || "~/mango/mango.db")
+  property queue_db_path : String = \
+        (ENV["QUEUE_DB_PATH"]? || "~/mango/queue.db")
+  property scan_interval_minutes : Int32 = (ENV["SCAN_INTERVAL"]? || 5).to_i
+  property thumbnail_generation_interval_hours : Int32 = \
+        (ENV["THUMBNAIL_INTERVAL"]? || 24).to_i
+  property log_level : String = (ENV["LOG_LEVEL"]? || "info")
+  property upload_path : String = (ENV["UPLOAD_PATH"]? || "~/mango/uploads")
+  property plugin_path : String = (ENV["PLUGIN_PATH"]? || "~/mango/plugins")
+  property download_timeout_seconds : Int32 = \
+        (ENV["DOWNLOAD_TIMEOUT"]? || 30).to_i
+  property cache_enabled : Bool = env_is_true?("CACHE_ENABLED", true)
+  property cache_size_mbs : Int32 = (ENV["CACHE_SIZE"]? || 50).to_i
+  property cache_log_enabled : Bool = env_is_true?("CACHE_LOG_ENABLED", true)
+  property disable_login : Bool = env_is_true?("DISABLE_LOGIN", false)
+  property default_username : String = (ENV["DEFAULT_USERNAME"]? || "")
+  property auth_proxy_header_name : String = (ENV["AUTH_PROXY_HEADER"]? || "")
+  property plugin_update_interval_hours : Int32 = \
+        (ENV["PLUGIN_UPDATE_INTERVAL"]? || 24).to_i
 
   @@singlet : Config?
 
@@ -38,7 +44,7 @@ class Config
   end
 
   def self.load(path : String?)
-    path = "~/.config/mango/config.yml" if path.nil?
+    path = (ENV["CONFIG_PATH"]? || "~/.config/mango/config.yml") if path.nil?
     cfg_path = File.expand_path path, home: true
     if File.exists? cfg_path
       config = self.from_yaml File.read cfg_path

src/util/util.cr

@@ -95,9 +95,9 @@ class String
   end
 end
 
-def env_is_true?(key : String) : Bool
+def env_is_true?(key : String, default : Bool = false) : Bool
   val = ENV[key.upcase]? || ENV[key.downcase]?
-  return false unless val
+  return default unless val
   val.downcase.in? "1", "true"
 end