/// <summary>
/// Build a token for component default value. This will look up the component in the catalog, and if it finds an entry, it will
/// build a JSON structure that would be parsed into the default value.
///
/// This is an inherently fragile setup in case when the factory is not trivial, but it will work well for 'property bag' factories
/// that we are currently using.
/// </summary>
private static JToken BuildComponentToken(IExceptionContext ectx, IComponentFactory value, ModuleCatalog catalog)
{
Contracts.AssertValueOrNull(ectx);
ectx.AssertValue(value);
ectx.AssertValue(catalog);
var type = value.GetType();
ModuleCatalog.ComponentInfo componentInfo;
if (!catalog.TryFindComponent(type, out componentInfo))
{
// The default component is not in the catalog. This is, technically, allowed, but it means that there's no JSON representation
// for the default value. We will emit the one the won't parse back.
return(new JValue("(custom component)"));
}
ectx.Assert(componentInfo.ArgumentType == type);
// Try to invoke default ctor for the factory to obtain defaults.
object defaults;
try
{
defaults = Activator.CreateInstance(type);
}
catch (MissingMemberException ex)
{
// There was no default constructor found.
// This should never happen, since ModuleCatalog would error out if there is no default ctor.
ectx.Assert(false);
throw ectx.Except(ex, "Couldn't find default constructor");
}
var jResult = new JObject();
var jSettings = new JObject();
jResult[FieldNames.Name] = componentInfo.Name;
// Iterate over all fields of the factory object, and compare the values with the defaults.
// If the value differs, insert it into the settings object.
bool anyValue = false;
foreach (var fieldInfo in type.GetFields())
{
var attr = fieldInfo.GetCustomAttributes(typeof(ArgumentAttribute), false).FirstOrDefault()
as ArgumentAttribute;
if (attr == null || attr.Visibility == ArgumentAttribute.VisibilityType.CmdLineOnly)
{
continue;
}
ectx.Assert(!fieldInfo.IsStatic && !fieldInfo.IsInitOnly && !fieldInfo.IsLiteral);
bool needValue = false;
object actualValue = fieldInfo.GetValue(value);
if (attr.IsRequired)
{
needValue = true;
}
else
{
object defaultValue = fieldInfo.GetValue(defaults);
needValue = !Equals(actualValue, defaultValue);
}
if (!needValue)
{
continue;
}
jSettings[attr.Name ?? fieldInfo.Name] = BuildValueToken(ectx, actualValue, fieldInfo.FieldType, catalog);
anyValue = true;
}
if (anyValue)
{
jResult[FieldNames.Settings] = jSettings;
}
return(jResult);
}