local oop = {}

local function super_call(self, method_name, ...)
    local class = getmetatable(self)
    if not class then
        error("super() called on non-instance")
    end
    local base = rawget(class, "__base")
    if not base then
        error("super() called but no base class")
    end
    local fn = base[method_name]
    if not fn then
        error("base class has no method '" .. tostring(method_name) .. "'")
    end
    return fn(self, ...)
end

local function_def_cache = setmetatable({}, { __mode = "k" })

function oop.setattr(target, key, value)
    target[key] = value
end

function oop.new(class, ...)
    local actual_class = class
    if type(class) == "function" then
        actual_class = function_def_cache[class]
        if not actual_class then
            actual_class = oop.class(class)
            function_def_cache[class] = actual_class
        end
    end
    local obj = setmetatable({}, actual_class)
    if actual_class.__init then
        actual_class.__init(obj, ...)
    end
    return obj
end

local function lookup_in_class(cls, key)
    local cur = cls
    while cur do
        local val = rawget(cur, key)
        if val ~= nil then
            return val
        end
        cur = rawget(cur, "__base")
    end
    return nil
end

function oop.class(def, base)
    local cls = {}
    cls.__name = "Anonymous"
    cls.__base = base
    cls.__index = function(self, key)
        local val = lookup_in_class(cls, key)
        if type(val) == "function" then
            return function(...)
                return val(self, ...)
            end
        end
        return val
    end

    function cls:super(method_name, ...)
        return super_call(self, method_name, ...)
    end
    function cls.setattr(target, key, value)
        return oop.setattr(target, key, value)
    end
    function cls.inherit(parent)
        cls.__base = parent
        cls.super = parent
        local mt = getmetatable(cls) or {}
        mt.__index = parent
        mt.__call = mt.__call or function(c, ...)
            return oop.new(c, ...)
        end
        setmetatable(cls, mt)
    end

    setmetatable(cls, {
        __index = base,
        __call = function(c, ...)
            return oop.new(c, ...)
        end
    })

    if type(def) == "string" then
        cls.__name = def
    elseif type(def) == "function" then
        def(cls)
    elseif def ~= nil then
        error("class definition must be a function or name string")
    end
    if base then
        cls.inherit(base)
    end

    return cls
end

function oop.isinstance(obj, class)
    local mt = getmetatable(obj)
    while mt do
        if mt == class then
            return true
        end
        mt = rawget(mt, "__base")
    end
    return false
end

function oop.issubclass(class, base)
    local mt = class
    while mt do
        if mt == base then
            return true
        end
        mt = rawget(mt, "__base")
    end
    return false
end

function oop.install(env)
    local target = env or _G
    target.class = oop.class
    target.new = oop.new
    target.setattr = oop.setattr
    target.isinstance = oop.isinstance
    target.issubclass = oop.issubclass
end

oop.install()

return oop