keypath-description.swift

extension KeyPathObject: CustomStringConvertible {
  public var description: String {
    let components = self.components
    
    assert(heapObject.metadata.kind == .class,
           "KeyPath class object that's not a class?")
    let classMetadata = heapObject.metadata as! ClassMetadata
    assert(classMetadata.genericTypes.count == 2,
           "KeyPath type without 2 generic types? Root and Leaf?")
    let root = classMetadata.genericTypes[0]
    
    guard components.allSatisfy({ $0.kind == .struct ||
                                  $0.kind == .class }) else {
      return "\(classMetadata.type)"
    }
    
    var currentRoot = reflect(root) as! TypeMetadata
    var fields = currentRoot.contextDescriptor.fields
    var fieldOffsets = currentRoot.fieldOffsets
    var result = "\(root)."
    
    for component in components {
      for (i, fieldOffset) in fieldOffsets.enumerated() {
        if component.storedOffset == fieldOffset {
          let field = fields.records[i]
          let fieldName = field.name
          result += "\(fieldName)."
          
          let fieldType = currentRoot.type(of: field.mangledTypeName)!
          currentRoot = reflect(fieldType) as! TypeMetadata
          fields = currentRoot.contextDescriptor.fields
          fieldOffsets = currentRoot.fieldOffsets
        }
      }
    }
    
    result.removeLast()
    
    return result
  }
}