-- This script relies on a modular framework I wrote. Since I use modules it's harder to get a 200 line+ script, so I wrote up this one in around 40 minutes without any tutorials. My post on my framework is below.
-- https://devforum.roblox.com/t/code-framework-and-structure/3059321

-- [ SERVICES ]
local Players = game:GetService("Players")
local Teams = game:GetService("Teams")
local ContextActionService = game:GetService("ContextActionService")
local StarterGui = game:GetService("StarterGui")
local TweenService = game:GetService("TweenService")
local UserInputService = game:GetService("UserInputService")

-- [ FOLDER ]
local Assets = script:WaitForChild("Assets")

-- [ MODULES ]
local Settings = require(script:WaitForChild("Settings"))

-- [ VARIABLES ]
local LocalPlayer : Player = game.Players.LocalPlayer
local PlayerGui = LocalPlayer:WaitForChild("PlayerGui")

local LeaderboardHandler = {}
local TeamConnections = {}
local LatestTeamIndexList = {}
local LeaderboardOpen = true

local PlayerFrame = Assets:WaitForChild("PlayerFrame")
local TeamFrame = Assets:WaitForChild("Team")
local LeaderboardUI
local MainFrame
local OpenCloseButton



-- [ FUNCTIONS ]
local function ClearList()
    for _, frame in pairs(MainFrame:GetChildren()) do
        if frame:IsA("Frame") then
            frame:Destroy()
        end
    end
end

local function PlayerToFrame(player : Player, index : number) : Frame
    local playerFrame = PlayerFrame:Clone()

    -- Setup the player's name and image.
    playerFrame.Image.Image = Players:GetUserThumbnailAsync(player.UserId, Enum.ThumbnailType.HeadShot, Enum.ThumbnailSize.Size420x420)
    playerFrame.DisplayName.Text = player.DisplayName
    playerFrame.Username.Text = "@"..player.Name
    playerFrame.LayoutOrder = index
    playerFrame.Name = player.UserId

    -- Check if the user is in settings.
    if Settings.CustomIcons[player.UserId] then
        playerFrame.Icon.Image = "http://www.roblox.com/asset/?id="..tostring(Settings.CustomIcons[player.UserId].ID)
        playerFrame.Icon.ImageColor3 = Settings.CustomIcons[player.UserId].ImageColor
        playerFrame.Icon.Visible = true
    end

    -- Return
    return playerFrame
end

local function TeamToFrame(team : Team, index : number) : Frame
    local teamFrame = TeamFrame:Clone()

    -- Setup the team text.
    teamFrame.TeamName.Text = team.Name
    teamFrame.TeamName.TextColor = team.TeamColor
    teamFrame.LayoutOrder = index

    -- Return
    return teamFrame
end

local function FindPlayerFrameInList(player : Player)
    for index, frame : Frame in pairs(MainFrame:GetChildren()) do
        if frame.Name == tostring(player.UserId) then
            return frame
        end
    end
    return nil
end

local function GetPlayerLocationInTeams(player : Player, teamIndexTable : {[string]: number}) : number
    -- Find the team.
    local team = player.Team

    -- Search through the index table to find their index.
    for key, index in pairs(teamIndexTable) do
        if key == team then
            return index
        end
    end

    -- Return nil if they weren't in any of the found tables.
    return -1
end

local function UserChangedTeam(player : Player)
    -- Find the users frame in the list.
    local frame = FindPlayerFrameInList(player)

    -- Check if it exists.
    if frame then
        -- Grab the users index position in the teams.
        local indexPosition = GetPlayerLocationInTeams(player, LatestTeamIndexList)

        -- Check if the index position exists and update the frame layout order.
        if indexPosition > -1 then
            frame.LayoutOrder = indexPosition
        end
    end
end

local function RefreshUI()
    -- Clear the previous list.
    ClearList()

    -- Get the players.
    local PlayerTable = Players:GetPlayers()
    local TeamTable = Teams:GetTeams()
    local TeamIndexTable = {}

    -- Create frames for the teams.
    for index, team : Team in ipairs(TeamTable) do
        -- Grab the correct index. Multiply by 1000 so that more than 1 user can be in that list.
        local correctIndex = index * 1000

        -- Add the team to the index table so we can sort the UI later.
        TeamIndexTable[team] = correctIndex

        -- Create the team frame.
        local teamFrame = TeamToFrame(team, correctIndex)
        teamFrame.Visible = true
        teamFrame.Parent = MainFrame
    end

    -- Update the team index table.
    LatestTeamIndexList = TeamIndexTable

    -- Create frames for each of the players.
    for index, player : Player in ipairs(PlayerTable) do
        -- Grab the users index in the team table.
        local usersIndex = GetPlayerLocationInTeams(player, TeamIndexTable)

        -- Check if the index exists.
        if usersIndex > -1 then
            -- Create the frame and parent it.
            local playerFrame = PlayerToFrame(player, usersIndex + index)
            playerFrame.Parent = MainFrame
            playerFrame.Visible = true
        end
    end
end

local function OpenCloseLeaderboard(actionName, inputState : Enum.UserInputState)
    -- Check if the user is beginning the press.
    if inputState ~= Enum.UserInputState.Begin then return end

    -- Check if the leaderboard is already open.
    LeaderboardOpen = not LeaderboardOpen

    -- We hold the tween's properties here.
    local propertyTable = {}

    -- Check if the user is mobile to update the button.
    if OpenCloseButton.Visible == true then
        OpenCloseButton.Text = if LeaderboardOpen then "CLOSE" else "OPEN"
    end

    -- Check if the leaderboard is open.
    if LeaderboardOpen then
        -- The leaderboard needs to be opened.
        propertyTable.Position = Settings.TweeningStyle.OpenPosition
    else
        -- The leaderboard needs to be closed.
        propertyTable.Position = Settings.TweeningStyle.ClosedPosition
    end

    -- Create the tween and play it.
    local lbInfo = Settings.TweeningStyle.LeaderboardTweenInfo
    local tween = TweenService:Create(MainFrame.Parent, lbInfo, propertyTable)
    tween:Play()
end

local function SetupUI()
    -- Place the leaderboard UI on the playergui.
    LeaderboardUI = Assets:WaitForChild("Leaderboard"):Clone()
    LeaderboardUI.Parent = PlayerGui


    -- Set up the variables for the frames.
    MainFrame = LeaderboardUI:WaitForChild("Frame"):WaitForChild("MainFrame")
    OpenCloseButton = LeaderboardUI:WaitForChild("Frame"):WaitForChild("OpenClose")

    -- Check if the user is mobile.
    if UserInputService.TouchEnabled then
        -- Enable the close button and listen for touches.
        OpenCloseButton.Visible = true
        OpenCloseButton.Text = if LeaderboardOpen then "CLOSE" else "OPEN"
        OpenCloseButton.MouseButton1Up:Connect(function()
            OpenCloseLeaderboard(nil, Enum.UserInputState.Begin)
        end)
    else
        -- Disable the close button.
        OpenCloseButton.Visible = false
    end

    -- Loop through all the current players and connect to them.
    for index, player : Player in pairs(Players:GetPlayers()) do
        -- Check if the user is already connected.
        if not TeamConnections[player.UserId] then
            -- Check if the user changed teams.
            TeamConnections[player.UserId] = player:GetPropertyChangedSignal("Team"):Connect(function()
                UserChangedTeam(player)
            end)
        end
    end
end

local function PlayerAdded(player : Player)
    -- Connect to the player changing teams.
    TeamConnections[player.UserId] = player:GetPropertyChangedSignal("Team"):Connect(function()
        UserChangedTeam(player)
    end)
end

local function PlayerRemoving(player : Player)
    -- Disconnect listening for the team change on leave.
    if TeamConnections[player.UserId] then
        TeamConnections[player.UserId]:Disconnect()
        print("Disconnected from player "..player.DisplayName)
    end
end



-- [ INITIALIZATION ]
function LeaderboardHandler.__init()
    -- Disable the old ui.
    StarterGui:SetCoreGuiEnabled(Enum.CoreGuiType.PlayerList, false)

    -- Bind the opening and closing keys.
    ContextActionService:BindAction("Leaderboard", OpenCloseLeaderboard, false, Enum.KeyCode.Tab)
    ContextActionService:SetPosition("Leaderboard", UDim2.new(0.3, 0,-1.2, 0))
    ContextActionService:SetTitle("Leaderboard", "Leaderboard")

    -- Setup the UI and refresh it.
    SetupUI()
    RefreshUI()
end

-- [ CONNECTIONS ]
Players.PlayerAdded:Connect(PlayerAdded)
Players.PlayerRemoving:Connect(PlayerRemoving)


-- [ RETURNING ]
return LeaderboardHandler