Extension-Druid/druid/system/middleclass.lua

-- Source: https://github.com/kikito/middleclass
local middleclass = {}

local function _createIndexWrapper(aClass, f)
  if f == nil then
    return aClass.__instanceDict
  else
    return function(self, name)
      local value = aClass.__instanceDict[name]

      if value ~= nil then
        return value
      elseif type(f) == "function" then
        return (f(self, name))
      else
        return f[name]
      end
    end
  end
end

local function _propagateInstanceMethod(aClass, name, f)
  f = name == "__index" and _createIndexWrapper(aClass, f) or f
  aClass.__instanceDict[name] = f

  for subclass in pairs(aClass.subclasses) do
    if rawget(subclass.__declaredMethods, name) == nil then
      _propagateInstanceMethod(subclass, name, f)
    end
  end
end

local function _declareInstanceMethod(aClass, name, f)
  aClass.__declaredMethods[name] = f

  if f == nil and aClass.super then
    f = aClass.super.__instanceDict[name]
  end

  _propagateInstanceMethod(aClass, name, f)
end

local function _tostring(self) return "class " .. self.name end
local function _call(self, ...) return self:instantiate(...) end

local function _createClass(name, super)
  local dict = {}
  dict.__index = dict

  local aClass = { name = name, super = super, static = {},
                   __instanceDict = dict, __declaredMethods = {},
                   subclasses = setmetatable({}, {__mode='k'})  }

  if super then
    setmetatable(aClass.static, {
      __index = function(_,k)
        local result = rawget(dict,k)
        if result == nil then
          return super.static[k]
        end
        return result
      end
    })
  else
    setmetatable(aClass.static, { __index = function(_,k) return rawget(dict,k) end })
  end

  setmetatable(aClass, { __index = aClass.static, __tostring = _tostring,
                         __call = _call, __newindex = _declareInstanceMethod })

  return aClass
end

local function _includeMixin(aClass, mixin)
  assert(type(mixin) == 'table', "mixin must be a table")

  for name,method in pairs(mixin) do
    if name ~= "included" and name ~= "static" then aClass[name] = method end
  end

  for name,method in pairs(mixin.static or {}) do
    aClass.static[name] = method
  end

  if type(mixin.included)=="function" then mixin:included(aClass) end
  return aClass
end

local DefaultMixin = {
  __tostring   = function(self) return "instance of " .. tostring(self.class) end,

  initialize   = function(self, ...) end,

  isInstanceOf = function(self, aClass)
    return type(aClass) == 'table'
       and type(self) == 'table'
       and (self.class == aClass
            or type(self.class) == 'table'
            and type(self.class.isSubclassOf) == 'function'
            and self.class:isSubclassOf(aClass))
  end,

  static = {
    allocate = function(self)
      assert(type(self) == 'table', "Make sure that you are using 'Class:allocate' instead of 'Class.allocate'")
      return setmetatable({ class = self }, self.__instanceDict)
    end,

    instantiate = function(self, ...)
      assert(type(self) == 'table', "Make sure that you are using 'Class:instantiate' instead of 'Class.instantiate'")
      local instance = self:allocate()
      instance:initialize(...)
      return instance
    end,

    subclass = function(self, name)
      assert(type(self) == 'table', "Make sure that you are using 'Class:subclass' instead of 'Class.subclass'")
      assert(type(name) == "string", "You must provide a name(string) for your class")

      local subclass = _createClass(name, self)

      for methodName, f in pairs(self.__instanceDict) do
        _propagateInstanceMethod(subclass, methodName, f)
      end
      subclass.initialize = function(instance, ...) return self.initialize(instance, ...) end

      self.subclasses[subclass] = true
      self:subclassed(subclass)

      return subclass
    end,

    subclassed = function(self, other) end,

    isSubclassOf = function(self, other)
      return type(other)      == 'table' and
             type(self.super) == 'table' and
             ( self.super == other or self.super:isSubclassOf(other) )
    end,

    include = function(self, ...)
      assert(type(self) == 'table', "Make sure you that you are using 'Class:include' instead of 'Class.include'")
      for _,mixin in ipairs({...}) do _includeMixin(self, mixin) end
      return self
    end
  }
}

function middleclass.class(name, super)
  assert(type(name) == 'string', "A name (string) is needed for the new class")
  return super and super:subclass(name) or _includeMixin(_createClass(name), DefaultMixin)
end

setmetatable(middleclass, { __call = function(_, ...) return middleclass.class(...) end })

return middleclass