function get_name()
    return "ADVANCED DISK DRIVE CONTROLLER"
end

NUM_TRACKS = 8
NUM_SECTORS = 8

function get_description()
    return {
        "*input* is a non-blocking XBus input connected to a computer.",
        "*output* is an XBus output connected to the same computer.",
        "*motor* is a simple output connected to a stepper motor.",
        "*read* is a simple input connected to the read/write head.",
        "*write* is a simple output connected to the read/write head.",
        "<PAGE>",
        "The purpose of this device is to read data from, and write data to, a rotating data disk.",
        "The disk is divided into " .. NUM_TRACKS .. " tracks and " .. NUM_SECTORS .. " sectors.",
        "(For a visual representation, refer to the 'Disk sector' article on Wikipedia.)",
        "The outermost track is track zero, then numbering increases inwards.",
        "The read/write head of the drive can be moved between tracks via *motor*. 50 makes the head stay still, 0 moves it one track outwards, 100 moves it one track inwards. The head will complete the requested movement by the start of the *next* time unit.",
        "The disk is rotating at the fixed speed of one sector per time unit.",
        "<PAGE>",
        "Input consists of data packets <track>,<sector>,<data>.",
        "Move the head to the specified track via *motor*, then wait until the correct sector gets rotated below the head.",
        "Then, if <data> is -1, send the value of *read* to *output*.",
        "Otherwise, send <data> to *write* to write the new value to the disk.",
        "*write* must be kept zero when not writing, to avoid overwriting unrelated data.",
        "The head starts at track zero. Rotation starts at sector zero."
    }
end

function get_board()
    return [[
        #.##############.#
        #################2
        0#################
        #################3
        1#################
        #################4
        #.##############.#
    ]]
end

function get_data()
    math.random()   -- this is just to force nicer values for test case #1
    local disk_contents = {}
    for i=0,NUM_TRACKS-1 do
        disk_contents[i] = {}
        for j=0,NUM_SECTORS-1 do
            disk_contents[i][j] = math.random(1, 100)
        end
    end

    local current_track = 0
    local next_input_time = math.random(1, 2)
    local target_track = 0
    local target_sector = -1
    local target_value = 0
    local input = {}
    local output = {}
    local motor = {}
    local read_arr = {}
    local write_arr = {}
    for time = 1,60 do
        local current_sector = (time-1)%NUM_SECTORS
        read_arr[time] = disk_contents[current_track][current_sector]
        if time == next_input_time then
            target_track = math.random(0, NUM_TRACKS-1)
            target_sector = math.random(0, NUM_SECTORS-1)
            if math.random(0, 1) == 0 then
                target_value = -1
            else
                target_value = math.random(1, 100)
            end
            input[time] = {target_track, target_sector, target_value}
        end
        if current_track < target_track then
            motor[time] = 100
        elseif current_track > target_track then
            motor[time] = 0
        else
            motor[time] = 50
        end
        write_arr[time] = 0
        if current_track == target_track and current_sector == target_sector then
            if target_value < 0 then
                output[time] = {read_arr[time]}
            else
                write_arr[time] = target_value
                disk_contents[target_track][target_sector] = target_value
            end
            target_sector = -1
            next_input_time = math.max(time + math.random(1, 2), next_input_time+3)
        end
        if motor[time] == 100 then
            current_track = current_track + 1
        elseif motor[time] == 0 then
            current_track = current_track - 1
        end
    end

    create_terminal('input', '0', TYPE_XBUS_NONBLOCKING, DIR_INPUT, input)
    create_terminal('output', '1', TYPE_XBUS, DIR_OUTPUT, output)
    create_terminal('motor', '2', TYPE_SIMPLE, DIR_OUTPUT, motor)
    create_terminal('read', '3', TYPE_SIMPLE, DIR_INPUT, read_arr)
    create_terminal('write', '4', TYPE_SIMPLE, DIR_OUTPUT, write_arr)
end