local DEFAULT_PLATFORM_COLOR = {255,255,255}

local GRAVITY_CONSTANT  =  300
local AIR_RES_CONSTANT  =  1
local VERY_SMALL_NUM    =  0.01

local function platform_below_platform (platform, system)
    return system:isPointOccupied(platform.x, platform.y + platform.h + VERY_SMALL_NUM, platform) or system:isPointOccupied(platform.x + platform.w, platform.y + platform.h + VERY_SMALL_NUM, platform)
end

--------------------------------------------------------------------------------

local PlayerController = {}
      PlayerController.__index = PlayerController

function PlayerController.new (target, controls)
    assert(controls.jump and controls.left and controls.right )
    local  self = setmetatable({}, PlayerController)
           self.target    = target
           self.controls  = controls
    return self
end

function PlayerController:update (dt, system)
    local not_jumping = platform_below_platform(self.target, system)
    if love.keyboard.isDown( self.controls.jump ) then
        self.target.dy = self.target.dy + (not_jumping and -260 or (-280 * dt))
    end
    if love.keyboard.isDown( self.controls.left ) then
        self.target.dx = self.target.dx - 15
    end
    if love.keyboard.isDown( self.controls.right ) then
        self.target.dx = self.target.dx + 15
    end
end

--------------------------------------------------------------------------------

local Platform = {}
      Platform.__index = Platform

function Platform.new (t)
    local  self = setmetatable(t, Platform)
    assert(self.x and self.y and self.w and self.y)
           self.color = self.color or DEFAULT_PLATFORM_COLOR
    return self
end

--------------------------------------------------------------------------------

local PlatformSystem = {}
      PlatformSystem.__index = PlatformSystem

function PlatformSystem.new ()
    local  self = setmetatable({}, PlatformSystem)
           self.platforms   = {}
           self.controllers = {}
    return self
end

function PlatformSystem:addPlatform (x, y, w, h)
    self.platforms[#self.platforms + 1] = Platform.new {
        x = x, y = y, w = w, h = h
    }
end

function PlatformSystem:addPlayer ( x, y, w, h, controls )
    local platform = Platform.new {
        x = x, y = y, w = w, h = h,
        movable = true, dx = 0, dy = 0
    }
    self.platforms[#self.platforms + 1] = platform
    self.controllers[#self.controllers + 1] = PlayerController.new(platform, controls)
    return platform
end

function PlatformSystem:isPointOccupied (x, y, except)
    for _, platform in ipairs(self.platforms) do
        if platform.x <= x and x <= platform.x + platform.w and platform.y <= y and y <= platform.y + platform.h and platform ~= except then
            return platform
        end
    end
    return false
end

function PlatformSystem:updatePlatform (platform, dt)
    local ndx, ndy  =  platform.dx * (1 - AIR_RES_CONSTANT * dt), platform.dy + GRAVITY_CONSTANT * dt
    local nx, ny    =  platform.x + ndx * dt, platform.y + ndy * dt
    if true then
        if not self:isPointOccupied(platform.x, ny, platform) and not self:isPointOccupied(platform.x + platform.w, ny, platform) and not self:isPointOccupied(platform.x, ny + platform.h, platform) and not self:isPointOccupied(platform.x + platform.w, ny + platform.h, platform) then
            platform.y, platform.dy = ny, ndy
        else
            ndx = ndx * (1 - AIR_RES_CONSTANT * dt)
            platform.dy = 0
        end
        if not self:isPointOccupied(nx, platform.y, platform) and not self:isPointOccupied(nx + platform.w, platform.y, platform) and not self:isPointOccupied(nx, platform.y + platform.h, platform) and not self:isPointOccupied(nx + platform.w, platform.y + platform.h, platform) then
            platform.x, platform.dx = nx, ndx
        else
            platform.dx = 0
        end
    end
end

function PlatformSystem:update (dt)
    -- Update movable platforms
    for _, platform in ipairs(self.platforms) do
        if platform.movable then
            platform.moved = self:updatePlatform(platform, dt) or self:updatePlatform(platform, dt * 0.5) or self:updatePlatform(platform, dt * 0.25)
        end
    end
    -- Update controllers
    for _, controller in ipairs(self.controllers) do
        controller:update(dt, self)
    end
end

function PlatformSystem:draw (dt, offset_x, offset_y)
    local offset_x, offset_y  =  offset_x or 0, offset_y or 0
    for _, platform in ipairs(self.platforms) do
        love.graphics.setColor(platform.color)
        love.graphics.rectangle('fill', platform.x - offset_y, platform.y - offset_x, platform.w, platform.h)
    end
end

--------------------------------------------------------------------------------

return {
    PlatformSystem = PlatformSystem,
    Player = Player,
}