Simple checkpoints

-- Initialize GameData, cross-playthrough variables, for this level. This avoids conflicts with GameData of other levels.
GameData[Level.filename()] = GameData[Level.filename()] or {}
-- Initialize the checkpoint variable
GameData[Level.filename()].checkpoint = GameData[Level.filename()].checkpoint or 0

-- When the level starts, trigger a SMBX event by name, based on which checkpoint we are at.
function onStart()
    local checkpoint = GameData[Level.filename()].checkpoint

    if checkpoint == 0 then
        triggerEvent("startFight")
    elseif checkpoint == 1 then
        triggerEvent("startCP1")
    elseif checkpoint == 2 then
        triggerEvent("startCP2")
    end
end

-- In a SMBX event, trigger the events named below to collect a checkpoint.
function onEvent(eventName)
    if eventName == "collectCP1" then
        GameData[Level.filename()].checkpoint = 1
    elseif eventName == "collectCP2" then
        GameData[Level.filename()].checkpoint = 2
    end
end

-- Reset the checkpoint after winning
function onExit()
    if Level.winState() > 0 then
        GameData[Level.filename()].checkpoint = 0
    end
end