StationPA

local LONG_PING = 5
local MEDIUM_PING = 1
local SHORT_PING = 0.2

local inst1 = "pling"
local inst2 = "iron_xylophone"
local inst3 = "bit"
local melody = {
    {duration=0.5, notes={{inst1, 5, 20}, {inst2, 5, 20}, {inst3, 5, 4}}},
    {duration=0.5, notes={{inst1, 5, 16}, {inst2, 5, 16}, {inst3, 5, 8}}},
    {duration=0.5, notes={{inst1, 5, 18}, {inst2, 5, 18}, {inst3, 5, 6}}},
    {duration=0.5, notes={{inst1, 5, 11}, {inst2, 5, 11}, {inst3, 5, 11}}}
}

local stations = {}
local speakers = {}
for _, name in pairs(peripheral.getNames()) do
    pType = peripheral.getType(name)
    if pType == "Create_Station" then
        local station = peripheral.wrap(name)
        local sName = station.getStationName()
        station.name=string.gfind(string.gsub(sName, "%s%d", ""), "[%a%s%p]+")()
        station.platform=tonumber(string.gfind(sName, "%d+$")())
        station.present=station.isTrainPresent()
        table.insert(stations, station)
    elseif pType == "speaker" then
        table.insert(speakers, peripheral.wrap(name))
    end
end

shell.run("clear")

local pingTimer = os.startTimer(SHORT_PING)
local noteTimer = nil
local noteIndex = 1
while true do
    local event, timerId = os.pullEvent("timer")
    local noteStart = false
    if timerId == pingTimer then
        local newTime = LONG_PING
        for i, station in pairs(stations) do
            if station.isTrainPresent() then
                if not station.present then
                    stations[i].present = true
                    newTime = math.min(newTime, MEDIUM_PING)
                    noteStart = true
                    local name = station.getTrainName()
                    print(name.." arrived on platform "..station.platform)
                end
            else
                stations[i].present = false
                if station.isTrainEnroute() then
                    newTime = math.min(newTime, MEDIUM_PING)
                elseif station.isTrainImminent() then
                    newTime = math.min(newTime, SHORT_PING)
                end
            end
        end
        pingTimer = os.startTimer(newTime)
    end
    if timerId == noteTimer or noteStart then
        local notes = melody[noteIndex]
        if notes == nil then
            noteIndex = 1
        else
            for _, note in pairs(notes.notes) do
                for _, speaker in pairs(speakers) do
                    speaker.playNote(unpack(note))
                end
            end
            noteIndex = noteIndex + 1
            noteTimer = os.startTimer(notes.duration)
        end
    end
end