local Constraints = require "lib.simple_ui.core.constraints"
local SingleChildElement = require "lib.simple_ui.core.single_child_element"

--- @class Padding : SingleChildElement
--- @field left number
--- @field right number
--- @field top number
--- @field bottom number
local element = setmetatable({}, SingleChildElement)
element.__index = element
element.type = "Padding"
element.left = 0
element.right = 0
element.top = 0
element.bottom = 0

--- "When passing layout constraints to its child, padding shrinks the constraints by the given padding, causing the child to layout at a smaller size.
--- Padding then sizes itself to its child's size, inflated by the padding, effectively creating empty space around the child."
---
--- as in https://api.flutter.dev/flutter/widgets/Padding-class.html
function element:layout()
    if not self._child_ then return end
    local c = Constraints(self._constraints_)
    c.maxWidth = c.maxWidth - self.left - self.right
    c.maxHeight = c.maxHeight - self.top - self.bottom
    c.maxWidth = c.maxWidth > 0 and c.maxWidth or 0
    c.maxHeight = c.maxHeight > 0 and c.maxHeight or 0
    self._child_._constraints_ = c

    self._child_:layout()
    self._size_ = Vec3 { self._child_._size_.x + self.left + self.right, self._child_._size_.y + self.top + self.bottom }
    self._child_._offset_ = Vec3 { self.left, self.top }
end

--- @return Padding
--- @param values {left: number?, top: number?, right: number?, bottom: number?, child: UIElement?}
function element:new(values)
    return SingleChildElement.new(self, values)
end

return element