screens = screens or {}
screens.active_screens = screens.active_screens or {}
screens.lock_player = false
screens.mouse_delta = Vector(0, 0, 0)
screens.focused_screen = screens.focused_screen or NULL

do -- meta
    local SCREEN = {}
    SCREEN.__index = SCREEN

    function SCREEN:Remove()
        self:KillFocus()

        for _, ent in pairs(self.entities) do
            SafeRemoveEntity(ent)
        end

        function self:IsValid()
            return false
        end

        screens.active_screens[self.screen_id] = nil

        setmetatable(self, getmetatable(NULL))
    end

    function SCREEN:IsValid()
        return true
    end

    AccessorFunc(SCREEN, "terrain_mat", "TerrainMaterial")
    AccessorFunc(SCREEN, "rt_tex", "RTTexture")
    AccessorFunc(SCREEN, "fps", "FPS", FORCE_NUMBER)
    AccessorFunc(SCREEN, "width", "Width")
    AccessorFunc(SCREEN, "height", "Height")
    AccessorFunc(SCREEN, "water_level", "WaterLevel")

    AccessorFunc(SCREEN, "cam_pos", "CameraPos")
    AccessorFunc(SCREEN, "cam_ang", "CameraAngles")
    AccessorFunc(SCREEN, "cam_fov", "CameraFOV")

    function SCREEN:IsPaused()
        return self.paused
    end

    function SCREEN:Pause()
        self.paused = true
    end

    function SCREEN:Resume()
        self.paused = false
    end

    do -- input
        function SCREEN:RequestFocus()
            screens.EnableKeyMonitor(true)
            screens.focused_screen = self
        end

        function SCREEN:KillFocus()
            if screens.focused_screen == self then
                screens.EnableKeyMonitor(false)
                screens.focused_screen = NULL
            end
        end

        function SCREEN:IsFocused()
            return screens.focused_screen == self
        end

        function SCREEN:GetMouseDelta()
            return screens.mouse_delta
        end

        function SCREEN:OnInput(key, press)
            if key == IN_USE and press then
                self:KillFocus()
            end
        end
    end

    do -- entities
        function SCREEN:CreateEntity(mdl)
            local ent = ClientsideModel(mdl)
            ent:SetNoDraw(true)

            table.insert(self.entities, ent)

            return ent
        end

        function SCREEN:DrawEntities()
            render.SuppressEngineLighting(true)

            render.SetBlend(1)
            render.SetColorModulation(1,1,1)
            render.SetAmbientLight(0,0,0)
            render.ResetModelLighting(0.2,0.2,0.2)

            render.SetModelLighting(3, 1,1,1) -- global_light.r / 255, global_light.g / 255, global_light.b / 255)

            for _, ent in pairs(self.entities) do
                ent:DrawModel()
            end

            render.SuppressEngineLighting(false)
        end
    end

    if pac then
        function SCREEN:GetTextureFromURL(url, size, callback)
            pac.urltex.GetMaterialFromURL(url, function(mat, tex)
                callback(mat, tex)
            end, false, nil, size, false)
        end
    end

    do -- terrain
        local W, H = ScrW(), ScrH()

        local function start_height(tex)
            local mat = CreateMaterial("screens_heightmap_" .. os.clock(), "UnlitGeneric", {["$basetexture"] = "dev/hemisphere_height.vtf"})

            if tex then
                mat:SetTexture("$basetexture", tex)
            end

            cam.Start2D()

            surface.SetMaterial(mat)
            surface.SetDrawColor(255, 255, 255, 255)

            -- this kinda sucks but using a heightmap resolution higher than screen resolution will cause undesired results..
            surface.DrawTexturedRect(0, 0, W, H)

            render.CapturePixels()
        end

        local function get_height(x, y)
            local r,g,b = render.ReadPixel(math.ceil(x*W), math.ceil(y*H))

            return ((r+g+b) / 3) / 255
        end

        local function end_height()
            cam.End2D()
        end

        function SCREEN:CreateTerrainFromHeightmap(tex, size, res, height)
            local mesh = Mesh()

            start_height(tex)

            size = size or 32768
            res = res or 64
            height = height or 8192

            local data = {}
            local _size = size / res

            for y = 0, res do
                for x = 0, res do
                    local z1 = get_height(x/res, (y+1)/res) * height -- bottom left
                    local z2 = get_height(x/res, y/res) * height -- top left
                    local z3 = get_height((x+1)/res, y/res) * height -- top right
                    local z4 = get_height((x+1)/res, (y+1)/res) * height -- bottom right

                    table.insert(data, {pos = Vector(x * _size + _size, y * _size, z3)})
                    table.insert(data, {pos = Vector(x * _size, y * _size, z2)})
                    table.insert(data, {pos = Vector(x * _size, y * _size + _size, z1)})

                    table.insert(data, {pos = Vector(x * _size, y * _size + _size, z1)})
                    table.insert(data, {pos = Vector(x * _size + _size, y * _size + _size, z4)})
                    table.insert(data, {pos = Vector(x * _size + _size, y * _size, z3)})
                end
            end

            end_height()

            local height_cache = {}

            for _, vertex in pairs(data) do
                -- vertex.normal = VectorRand()
                vertex.u = (vertex.pos.x / size)
                vertex.v = (vertex.pos.y / size)
            end

            start_height(tex)
            for x = 0, W do
                for y = 0, H do
                    local r,g,b = render.ReadPixel(x, y)
                    local z = ((r+g+b) / 3) / 255

                    height_cache[x] = height_cache[x] or {}
                    height_cache[x][y] = height_cache[x][y] or z * height
                end
            end
            end_height()

            self.height_cache = height_cache

            mesh:BuildFromTriangles(data)

            SafeRemoveEntity(self.terrain_ent)
            local ent = self:CreateEntity("error.mdl")

            self.terrain_mat = Material("models/wireframe")
            self.terrain_size = size

            ent.RenderOverride = function(ent)
                render.MaterialOverride(self.terrain_mat)

                ent:SetModelScale(0, 0)
                ent:DrawModel()

                local mat = Matrix()

                mat:SetAngles(ent:GetAngles())
                mat:SetTranslation(ent:GetPos())

                cam.PushModelMatrix(mat)
                    mesh:Draw()
                cam.PopModelMatrix()

                render.MaterialOverride()
            end
        end

        function SCREEN:GetTerrainHeight(pos)
            if self.height_cache then
                local x = math.floor((pos.x / self.terrain_size) * W)
                local y = math.floor((pos.y / self.terrain_size) * H)

                return self.height_cache[x] and self.height_cache[x][y] or 0
            end

            return 0
        end
    end

    function SCREEN:SetFog(start, _end, max_density, r,g,b)
        if start and _end and max_density and r and g and b then
            self.fog_params =
            {
                start = start,
                _end = _end,
                max_density = max_density,
                color = {r,g,b},
            }
        else
            self.fog_params = nil
        end
    end

    function SCREEN:CreateWorldScreen()
        SafeRemoveEntity(self.world_screen)

        local ent = ClientsideModel("models/hunter/plates/plate1x1.mdl")

        local mat = Matrix()
        mat:Scale(Vector(self.height / self.width, 1, 1))
        ent:EnableMatrix("RenderMultiply", mat)

        ent.RenderOverride = function(s)

            if not self:IsValid() then
                timer.Simple(0, function()
                    s:Remove()
                end)
            end

            render.SetBlend(1)
            render.SetColorModulation(1, 1, 1)

            render.PushFilterMag(TEXFILTER.POINT)
            render.PushFilterMin(TEXFILTER.POINT)

                render.MaterialOverride(self.screen_mat)
                    s:DrawModel()
                render.MaterialOverride()

            render.PopFilterMag()
            render.PopFilterMin()
        end

        self.world_screen = ent

        return ent
    end

    -- events

    function SCREEN:UpdateFreeroamCamera()
        local speed = 100

        local delta = screens.mouse_delta * 0.1
        local cam_pos = self.cam_pos
        local cam_ang = self.cam_ang

        cam_ang.p = cam_ang.p + delta.y
        cam_ang.y = cam_ang.y - delta.x
        cam_ang.p = math.clamp(cam_ang.p, -90, 90)

        if input.IsKeyDown(KEY_LSHIFT) then
            speed = speed * 4
        elseif input.IsKeyDown(KEY_LCONTROL) then
            speed = speed / 4
        end

        if input.IsKeyDown(KEY_SPACE) then
            cam_pos = cam_pos - Vector(0, 0, -speed)
        end

        local offset = cam_ang:Forward() * speed

        if input.IsKeyDown(KEY_W) then
            cam_pos = cam_pos + offset
        elseif input.IsKeyDown(KEY_S) then
            cam_pos = cam_pos - offset
        end

        offset = cam_ang:Right() * speed
        offset.z = -offset.z

        if input.IsKeyDown(KEY_D) then
            cam_pos = cam_pos + offset
        elseif input.IsKeyDown(KEY_A) then
            cam_pos = cam_pos - offset
        end

        self.cam_pos = cam_pos
        self.cam_ang = cam_ang
    end

    function SCREEN:UpdateWalkCamera()
        self.cam_vel = self.cam_vel or Vector(0,0,0)
        local speed = 10

        local delta = screens.mouse_delta * 0.1
        local cam_pos = self.cam_pos
        local cam_ang = self.cam_ang

        cam_ang.p = cam_ang.p + delta.y
        cam_ang.y = cam_ang.y - delta.x
        cam_ang.p = math.clamp(cam_ang.p, -90, 90)

        if input.IsKeyDown(KEY_LSHIFT) then
            speed = speed * 4
        elseif input.IsKeyDown(KEY_LCONTROL) then
            speed = speed / 4
        end

        if input.IsKeyDown(KEY_SPACE) then
            if not self.jumped then
                self.cam_vel.z = self.cam_vel.z + 500
                self.jumped = true
            end
        else
            self.jumped = false
        end

        local offset = cam_ang:Forward() * speed

        if input.IsKeyDown(KEY_W) then
            cam_pos = cam_pos + offset
        elseif input.IsKeyDown(KEY_S) then
            cam_pos = cam_pos - offset
        end

        offset = cam_ang:Right() * speed
        offset.z = -offset.z

        if input.IsKeyDown(KEY_D) then
            cam_pos = cam_pos + offset
        elseif input.IsKeyDown(KEY_A) then
            cam_pos = cam_pos - offset
        end

        cam_pos.z = math.max(cam_pos.z - 100, self:GetTerrainHeight(cam_pos) + 72)

        self.cam_vel = (self.cam_vel + (cam_pos - self.cam_pos)) * 0.35

        self.cam_pos = cam_pos + self.cam_vel
        self.cam_ang = cam_ang
    end

    function SCREEN:UpdateCamera()
        if not self:IsFocused() then return end

        self:UpdateFreeroamCamera()
    end

    function SCREEN:Think()
        self:UpdateCamera()
    end

    local skybox_ent = ClientsideModel("models/XQM/Rails/gumball_1.mdl")
    skybox_ent:SetMaterial("models/debug/debugwhite")

    function SCREEN:DrawSkyBox()
        render.SetColorModulation(0.4,0.7,1)
        render.SetBlend(1)
        render.SuppressEngineLighting(true)
            skybox_ent:SetPos(self.cam_pos)
            skybox_ent:SetModelScale(-1, 0)
            skybox_ent:DrawModel()
        render.SuppressEngineLighting(false)
        render.ClearDepth()
    end

    do -- water
        local water_mat = CreateMaterial("screens_water_"..RealTime(), "Refract",
        {
            ["$model"] = 1,
            ["$nocull"] = 1,
            ["$translucent"] = 1,
            ["$bluramount"] = 50,
            ["$refractamount"] = 0.1,
            ["$refracttint"] = "0.5 0.5 1",
            ["$dudvmap"] = "water/dx80_tfwater001_dudv",
            ["$normalmap"] = "water/tfwater001_normal",

            Proxies =
            {
                AnimatedTexture =
                {
                    animatedtexturevar = "$normalmap",
                    animatedtextureframenumvar = "$bumpframe",
                    animatedtextureframerate = 30,
                },
            },
        })

        local water_mesh = Mesh()
        local data = {}
        local size = 32768 / 8

        for y = 0, 128 do
            for x = 0, 128 do
                table.insert(data, {pos = Vector(x * size + size, y * size)})
                table.insert(data, {pos = Vector(x * size, y * size)})
                table.insert(data, {pos = Vector(x * size, y * size + size)})

                table.insert(data, {pos = Vector(x * size, y * size + size)})
                table.insert(data, {pos = Vector(x * size + size, y * size + size)})
                table.insert(data, {pos = Vector(x * size + size, y * size)})
            end
        end

        local up = Vector(0,0,1)
        for k,v in pairs(data) do
            v.normal = up
            v.v = v.pos.x / size
            v.u = v.pos.y / size
        end

        water_mesh:BuildFromTriangles(data)

        function SCREEN:DrawWater()
            render.UpdateRefractTexture()

            render.SetBlend(1)
            render.SuppressEngineLighting(true)

            local mat = Matrix()

            mat:Translate(Vector(self.cam_pos.x - 32768*8, self.cam_pos.y - 32768*8,self.water_level))

            cam.PushModelMatrix(mat)

            render.SetMaterial(water_mat)
            water_mesh:Draw()

            cam.PopModelMatrix()
            render.SuppressEngineLighting(false)
        end

    end

    function SCREEN:Draw3D()
        self:DrawEntities()
    end

    function SCREEN:Draw2D()

    end

    function SCREEN:DrawPostProcess()
        if self.cam_pos.z < self.water_level then
            surface.SetDrawColor(20,50,100,100)
            surface.DrawRect(0,0,self.width,self.height)
        end
    end

    function SCREEN:Update()
        self:Think()

        local old_rt, old_w, old_h = render.GetRenderTarget(), ScrW(), ScrH()
        render.SetRenderTarget(self.rt_tex)
        render.SetViewPort(0, 0, self.width, self.height)
        render.Clear(0,0,0,0, true)

        local params = {}

        params.origin = self.cam_pos
        params.angles = self.cam_ang
        params.fob = self.cam_fov
        params.x = 0
        params.y = 0
        params.w = self.width
        params.h = self.height
        params.zfar = 32000*4
        params.aspect = self.width/self.height

        cam.Start(params)
            self:DrawSkyBox()

            local params = self.fog_params
            if params then
                render.FogMode(1)
                render.FogStart(params.start)
                render.FogEnd(params._end)
                render.FogMaxDensity(params.max_density)
                render.FogColor(unpack(params.color))
            end

            self:Draw3D()

            self:DrawWater()
        cam.End()

        cam.Start2D()
            self:Draw2D()
            self:DrawPostProcess()
        cam.End2D()

        render.SetRenderTarget(old_rt)
        render.SetViewPort(0, 0, old_w, old_h)
    end

    screens.ScreenMeta = SCREEN
end

function screens.GetAll()
    return screens.active_screens
end

function screens.Remove(id)
    local self = screens.active_screens[id] or NULL
    if self:IsValid() then
        self:Remove()
    end
end

function screens.Create(id, w, h, fps)
    w = w or 320
    h = h or 240
    fps = fps or 10

    screens.Remove(id)

    local self = setmetatable({}, screens.ScreenMeta)

    self.screen_id = id

    self.width = w
    self.height = h
    self.fps = fps

    self.cam_pos = Vector(0, 0, 0)
    self.cam_ang = Angle(0, 0, 0)
    self.cam_fov = 90

    self.rt_tex = GetRenderTarget(id, w, h, true)
    self.screen_mat = CreateMaterial(id, "UnlitGeneric")
    self.screen_mat:SetTexture("$basetexture", self.rt_tex)

    self.water_level = 1000
    self.world_screen = NULL

    self.entities = {}

    screens.active_screens[id] = self

    return self
end

function screens.EnableKeyMonitor(b)
    if b then
        screens.lock_player = LocalPlayer():EyeAngles()
    else
        screens.lock_player = false
    end
end

do -- hooks
    hook.Add("Think", "screens_update", function()
        local time = RealTime()

        for _, screen in pairs(screens.active_screens) do
            if not screen.paused and (not screen.last_update or screen.last_update < time) then
                screen:Update()
                screen.last_update = time + (1/screen.fps)
            end
        end
    end)

    hook.Add("CreateMove", "screens_camera", function(ucmd)
        if screens.lock_player then
            ucmd:SetForwardMove(0)
            ucmd:SetSideMove(0)
            ucmd:SetViewAngles(screens.lock_player)

            screens.mouse_delta.x = ucmd:GetMouseX()
            screens.mouse_delta.y = ucmd:GetMouseY()
        end
    end)

    local SIGH = {}

    hook.Add("KeyPress", "screens", function(ply, key)

        if key == IN_USE then
            for _, screen in pairs(screens.active_screens) do
                if screen.world_screen:IsValid() and screen.world_screen:GetPos():Distance(ply:EyePos()) < 100 then
                    if not screens.last_focus or screens.last_focus  < RealTime()  then
                        screen:RequestFocus()
                        screens.last_focus = RealTime() + 0.5
                    end
                end
            end
        end

        local screen = screens.focused_screen
        if screen:IsValid() then
            if not SIGH[key] then
                screen:OnInput(key, true)
                SIGH[key] = true
            end
        end
    end)

    hook.Add("KeyRelease", "screens", function(ply, key)
        local screen = screens.focused_screen
        if screen:IsValid() then
            if SIGH[key] then
                screen:OnInput(key, false)
                SIGH[key] = false
            end
        end
    end)
end

do -- test
    local size = 32768 * 4

    local screen = screens.Create("forest")

    screen:SetCameraPos(Vector(37032, 33568, 2500))
    screen:SetCameraAngles(Angle(0,45,0))

    local ent = screen:CreateWorldScreen()
    ent:SetPos(Vector(10724.440429688, -1749.2056884766, 64.03125))
    ent:SetAngles(Angle(90,0,0))

    screen:SetFog(0, size, 0.5, 80, 170, 255)
    screen:SetWaterLevel(1500)

    local trees = {
        "models/props_foliage/tree_pine01.mdl",
        "models/props_foliage/tree_pine01_8cluster.mdl",
        "models/props_foliage/tree_pine01_4cluster.mdl",
        "models/props_foliage/tree_pine_huge.mdl",
        "models/props_foliage/tree_pine_small.mdl",
    }

    screen:GetTextureFromURL("https://dl.dropbox.com/u/244444/ShareX/2013-07/2013-07-12_16-32-18.jpg", 2048, function(mat, tex)
        screen:CreateTerrainFromHeightmap(tex, size)

        --[[for i = 1, 1000 do
            local pos = Vector(math.random(), math.random(), 0) * size
            pos.z = screen:GetTerrainHeight(pos)

            if pos.z > screen:GetWaterLevel() + 500 and pos.z < 3000 then
                local ent = screen:CreateEntity(table.Random(trees))
                ent:SetModelScale(math.Rand(0.5, 2), 0)
                ent:SetPos(pos)
            end
        end]]
    end)

    screen:GetTextureFromURL("https://dl.dropbox.com/u/244444/ShareX/2013-07/2013-07-12_16-32-18.jpg", 2048, function(mat)
        screen:SetTerrainMaterial(mat)
    end)


    function screen:Draw2D()
        local t = RealTime()
        local w, h = screen:GetWidth(), screen:GetHeight()

        surface.SetFont("DermaDefault")

        surface.SetTextColor(255, 255, 255, 255)

        local pos = self:GetCameraPos()

        surface.SetTextPos(5, 5)
        surface.DrawText(tostring(pos))

        local height = self:GetTerrainHeight(pos)
        surface.SetTextPos(5, 20)
        surface.DrawText(height)
    end

    LOL_SCREEN = screen
end