local Constraints = require "lib.simple_ui.constraints"
local SingleChildElement = require "lib.simple_ui.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 = "Placeholder"
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.constraints.maxHeight + self.top + self.bottom }
    self.child.offset = self.offset + Vec3 { self.left, self.top }
end

return element