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module Configurate
# This object builds a chain of configuration providers to try to find
# the value of a setting.
class LookupChain
def initialize
@provider = []
end
# Adds a provider to the chain. Providers are tried in the order
# they are added, so the order is important.
#
# @param provider [#lookup]
# @param *args the arguments passed to the providers constructor
# @raise [ArgumentError] if an invalid provider is given
# @return [void]
def add_provider(provider, *args)
unless provider.respond_to?(:instance_methods) && provider.instance_methods.include?(:lookup)
raise ArgumentError, "the given provider does not respond to lookup"
end
@provider << provider.new(*args)
end
# Tries all providers in the order they were added to provide a response
# for setting.
#
# @param setting [SettingPath,String] nested settings as strings should
# be separated by a dot
# @param ... further args passed to the provider
# @return [Array,Hash,String,Boolean,nil] whatever the responding
# provider provides is casted to a {String}, except for some special values
def lookup(setting, *args)
setting = SettingPath.new setting if setting.is_a? String
@provider.each do |provider|
begin
return special_value_or_string(provider.lookup(setting.clone, *args))
rescue SettingNotFoundError; end
end
nil
end
alias_method :[], :lookup
private
def special_value_or_string(value)
if [TrueClass, FalseClass, NilClass, Array, Hash].include?(value.class)
return value
elsif value.is_a?(String)
return case value.strip
when "true" then true
when "false" then false
when "", "nil" then nil
else value
end
elsif value.respond_to?(:to_s)
return value.to_s
else
return value
end
end
end
end
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