-- look into actual drawing functionality!~
-- the client drawing code requires manual memory management:
-- we have to allocate a buffer and draw pixels to it
-- this code can't deal with that problem...
-- lib_gui will have to provide a layer that takes the abstract APIs here and adds drawing functions
-- on top. the abstract API can assist by adding a "dirty" flag so that cache management is straightforward.

-- sketch listener and collision system:
--    rect and layers detection (derive layers from hierarchy)
--    onDown onUp onMove onClick(down+up inside collision) onDrag(down inside collision, movement) onKeyboard
--    when will mouse cursor be visible? important engine consideration!

-- with min_width(), min_height(), and inner() we should have all the tools necessary for packing.
-- 1. estimate the size of all the children. (recursive)
-- 2. sort the children in the order specified by the packer's manifest.
-- 3. iterate through the children, moving them to the positions and sizes desired as specified by the packing mode.

-- also something to note - when we draw we have to pass a clip rectangle upwards so that scrolling is possible.
-- this isn't strictly necessary, but if the possibility is there, use it!

local P = {}

local widget_mt = {}
function widget_mt.__add(a, b) a.add_child(b) return a end
function widget_mt.__sub(a, b) a.remove_child(b) return a end
function widget_mt.__tostring(a)
    return a.x.."x "..a.y.."y "..a.relx().."rx "..a.rely().."ry" 
end

function P.widget(options)

    local this = {x = options.x or 0, y = options.y or 0, 
        parent = options.parent or nil, 
        children = options.children or {}, 
        align_x = options.align_x or 0.5, align_y = options.align_y or 0.5}
    
    local width = options.width or 0
    local height = options.height or 0
    local margin_left = options.margin_left or 0
    local margin_right = options.margin_right or 0
    local margin_top = options.margin_top or 0
    local margin_bottom = options.margin_bottom or 0
    
    -- align 0 = top-left
    -- align 1 = bottom-right
    -- align 0.5 = center
    
    function this.width() return width end
    function this.height() return height end
    
    function this.margin_left() return margin_left end
    function this.margin_top() return margin_top end
    function this.margin_right() return margin_right end
    function this.margin_bottom() return margin_bottom end
    
    function this.min_width() return width end
    function this.min_height() return height end
    
    function this.relx()
        local pos = this.x - (this.width() * this.align_x)
        if this.parent == nil then return pos
        else return pos + this.parent.relx() end
    end
    
    function this.rely()
        local pos = this.y - (this.height() * this.align_y)
        if this.parent == nil then return pos
        else return pos + this.parent.rely() end
    end
    
    function this.l() return this.relx() end
    function this.t() return this.rely() end
    function this.r() return this.relx() + this.width() end    
    function this.b() return this.rely() + this.height() end    
    function this.cx() return this.relx() + this.width() * 0.5 end        
    function this.cy() return this.rely() + this.height() * 0.5 end
    
    function this.inner()
        local l = this.l() + this.margin_left()
        local t = this.t() + this.margin_top()
        local r = this.r() - this.margin_right()
        local b = this.b() - this.margin_bottom()
        return {x=l, y=t, left=l, top=t, right=r, bottom=b, 
            width=r-l, height=b-t, cx=l+(r-l)*0.5, cy=t+(b-t)*0.5}
    end
    
    function this.aabb(x, y, w, h)
        return not (this.l()>x or this.r()<x+w or this.t()>y or this.b()<y+h)
    end
    
    function this.collide(x, y, w, h)
        -- very simple aabb collision for mousing. returns the "first and deepest child".
        w = w or 1
        h = h or 1
        local hit = this.aabb(x, y, w, h)
        local result = this
        for k, v in pairs(this.children) do
            result = v.collide(x, y, w, h) or this
        end
        return result
    end
    
    function this.detach() if this.parent then table.remove(this.parent.children, this) this.parent = nil end end
    function this.add_child(child) child.detach(); child.parent = this; this.children[child] = child end
    function this.remove_child(child) child.detach() end
    function this.remove_all_children() for k,child in pairs(this.children) do this.remove_child(child) end end
    function this.set_parent(parent) this.detach(); this.parent = parent; parent.children[this] = this end
    function this.despawn() 
        for k,child in pairs(this.children) do child.despawn() end this.remove_all_children()
    end
    
    setmetatable(this, widget_mt)

    return this
end

if _REQUIREDNAME == nil then
    widgets = P
else
    _G[_REQUIREDNAME] = P
end

local test = P.widget{x=100, y=100, width=100, height=100}
print(test)
local test2 = P.widget{x=100, y=100, width=100, height=100}
test2.set_parent(test)
print(test2)
print(test.collide(150,150))

return P