Weekly Challenge #22: Credit Card Validator

-- The function get_name() should return a single string that is the name of the puzzle.
--
function get_name()
    return "CREDIT CARD VERIFIER"
end

-- The function get_description() should return an array of strings, where each string is
-- a line of description for the puzzle. Surrounding text with asterisks will cause it to
-- be rendered in bold, something we use when mentioning a signal by name.
--
-- By using the syntax that we use in our puzzle descriptions, you can also create tables:
--
--       "| This is a table. | This is a second column. | This is a column with "
--       "|                  |                          | multiple line of text."
--       "----------------------------------------------------------------------"
--       "| This is a second |                          | More text here!       "
--       "| table row.       |                          |                       "
--
-- Puzzle descriptions are not automatically paginated, so you can use the string "<PAGE>"
-- to start a new page of text. If you don't it will overflow and make Zach sad.
--
function get_description()
    return {
        "*card#* are XBus inputs connected to numeric keypads.",
        "*error* is a simple output connected to a LED next to the keypad.",
        "15-digit credit card numbers are entered on the keypads connected to *card#*.",
        "Verfiy whether the card number was entered correctly, using the *Luhn algorithm*.",
        "Send 100 to *error* to make the LED turn on when the card number is incorrect.",
        "There will never be two card numbers entered during the same time unit.",
        "<PAGE>",
        "*The Luhn algorithm* works like this:",
        "Counting from the right, double every second digit of the number",
        "Take the sum of all digits. If you ended up with a value above 9 in the previous step, use the sum of the digits of that number",
        "If the sum is divisible by 10, the number passes the Luhn algorithm",
        "See the next page for an example.",
        "<PAGE>",
        "Take a number:",
        "|2|8|8|5|7|1|6|6|1|9|1|8|1|1|3",
        "Double every second digit, counting from the right:",
        "|2|*16*|8|*10*|7|*2*|6|*12*|1|*18*|1|*16*|1|*2*|3",
        "Add the digits together: 2+1+6+8+1+0+7+2+6+1+2+1+1+8+1+1+6+1+2+3=60",
        "The number passes because 60 is divisible by 10"
    }
end

-- The function get_board() allows you to specify an 18x7 "ASCII art" grid to customize
-- the layout of the board and the placement of the input and output terminals. Generally
-- speaking, inputs are placed on the left of boards, while outputs are placed on the right.
--
-- For empty space, use the '.' character.
-- For buildable board space, use the '#' character.
-- For an input or output terminal, use characters '0' through '9' no more than once each.
-- For the bottom-left corner of the radio, use the 'R' character.
-- For the bottom-left corners of dials, use characters 'A', 'B', and 'C'.
--
function get_board()
    return [[
        .0123##########...
        .....##########...
        .###############..
        .################4
        .###############..
        .##############...
        .##############...
    ]]
end

-- The function get_data() is called both to establish information about the puzzle (such as what
-- the inputs and outputs are) and to generate the random test cases. Signal levels and XBus data
-- should change from call to call, but information like the names and types of terminals should
-- not change at all.
--
-- To create a standard input or output terminal, call create_terminal(). Valid terminal types are
-- TYPE_SIMPLE, TYPE_XBUS, and TYPE_XBUS_NONBLOCKING. Valid terminal directions are DIR_INPUT and
-- DIR_OUTPUT. Valid data for a simple I/O signal is an array of integers, 0 - 100 inclusive. Valid
-- data for an XBus signal is an array of integer arrays, each with values -999 to 999 inclusive.
--
--       create_terminal(name, board_character, type, direction, data)
--
-- To create a radio (C2S-RF901), call create_radio(). You may only create one radio in each puzzle.
-- Since radios are XBus-only, the only valid data for data_rx and data_tx are arrays of integer arrays,
-- each with values -999 to 999 inclusive. You cannot customize the signal names for a radio.
--
-- By default the radio will be placed in the bottom-left corner of the screen. However, if you use an
-- 'R' character in your board layout, the bottom-left corner of the radio will be placed there instead.
--
--       create_radio(data_rx, data_tx)
--
-- To create a dial (N4DL-1000), call create_dial(). You may create up to three dials in each puzzle.
-- The names of dials should be kept short, as there is not much room to display them visually. A valid
-- value is an integer between 0 and 99, inclusive.
--
-- By default dials will be placed in the bottom-left corner of the screen. However, if you use an
-- 'A', 'B', or 'C' character in your board layout, the bottom-left corners of the first, second, and
-- third dials will be placed there, respectively.
--
--       create_dial(name, value)
--
-- NOTE: To generate random values you should use math.random(). However, you SHOULD NOT seed
--       the random number generator with a new seed value, as that is how the game ensures that
--       the first test run is consistent for all users, and thus something that allows for the
--       comparison of cycle scores.
--
-- NOTE: Fun fact! Arrays in Lua are implemented as tables (dictionaries) with integer keys that
--       start at 1 by convention. Contrast this with nearly every other programming language, in
--       which arrays start with an index of 0. Because of this, the 60 "time slices" that make
--       up a test case are indexed from 1 to 60 inclusive.
--
function random_sequence(length)
    local result = {}
    for i = 1, length do
        result[i] = math.random(0, 9)
    end
    return result
end

function get_luhn_digit(seq)
    local checksum = 0
    for i = 1, #seq do
        local digit = seq[#seq - i + 1]
        if i % 2 == 1 then
            digit = digit * 2
        end
        if digit < 10 then
            checksum = checksum + digit
        else
            checksum = checksum + 1 + (digit - 10)
        end
    end
    return (10 - checksum % 10) % 10
end

function get_data()
    local inputs = {{}, {}, {}, {}}
    local output = {}
    local current_lane = 1
    local time = 1

    while time <= 60 do
        local seq = random_sequence(14)
        local correct_luhn = get_luhn_digit(seq)
        local last_digit
        if math.random(1, 5) == 1 then
            last_digit = math.random(0, 9)
        else
            last_digit = correct_luhn
        end
        seq[15] = last_digit
        inputs[current_lane][time] = seq
        if last_digit != correct_luhn then
            output[time] = 100
        end
        if current_lane < 4 then
            current_lane = current_lane + 1
        else
            current_lane = 1
        end
        time = time + 4
    end

    create_terminal("card#", "0", TYPE_XBUS, DIR_INPUT, inputs[1])
    create_terminal("card#", "1", TYPE_XBUS, DIR_INPUT, inputs[2])
    create_terminal("card#", "2", TYPE_XBUS, DIR_INPUT, inputs[3])
    create_terminal("card#", "3", TYPE_XBUS, DIR_INPUT, inputs[4])
    create_terminal("error", "4", TYPE_SIMPLE, DIR_OUTPUT, output)
end