simple_collision

local M = {}

--
function M.aabb(x1, y1, w1, h1, x2, y2, w2, h2)
    return not ((x2 > x1 + w1) or (x2 + w2 < x1) or
                (y2 > y1 + h1) or (y2 + h2 < y1))
end

function M.aabbPoint(x1, y1, x2, y2, w2, h2)
    return ((x1 > x2) and (x1 < x2 + w2) and
            (y1 > y2) and (y1 < y2 + h2))
end



function M.intersect(x1, y1, w1, h1, x2, y2, w2, h2)
    local mx1 = x1
    local my1 = y1
    local Mx1 = x1 + w1
    local My1 = y1 + h1

    if mx1 > Mx1 then
        mx1, Mx1 = Mx1, mx1
    end

    if my1 > My1 then
        mx1, Mx1 = Mx1, mx1
    end

    local mx2 = x2
    local my2 = y2
    local Mx2 = x2 + w2
    local My2 = y2 + h2

    if mx2 > Mx2 then
        mx2, Mx2 = Mx2, mx2
    end

    if my2 > My2 then
        mx2, Mx2 = Mx2, mx2
    end

    local rx = math.max(mx1, mx2)
    local ry = math.max(my1, my2)
    local rw = math.min(Mx1, Mx2)
    local rh = math.min(My1, My2)

    rw = rw - rx
    rh = rh - ry

    return rw > 0 and rh > 0, rx, ry, rw, rh
end

function M.collide(x1, y1, w1, h1, x2, y2, w2, h2)
  if not M.aabb(x1, y1, w1, h1, x2, y2, w2, h2) then
    return false, 0, 0
  end
  local vx = x1 + w1 * .5 - x2 - w2 * .5
  local vy = y1 + h1 * .5 - y2 - h2 * .5

  vx = vx > 0 and x2 + w2 - x1 or x2 - x1 - w1
  vy = vy > 0 and y2 + h2 - y1 or y2 - y1 - h1
  local xAxis = math.abs(vx) < math.abs(vy)

  return true, xAxis and vx or 0, xAxis and 0 or vy
end

return M