--- Helper function for tabulating messages.
local function tab(n) return string.rep(" ", n) end


--- Generates a multi-line string representing a lightning bolt
local function bolt()
    local bolt_lines = {}
    for n = 29, 21, -1 do
        table.insert(bolt_lines, tab(n) .. "x x")
    end
    table.insert(bolt_lines, tab(20) .. "x xxx")
    table.insert(bolt_lines, tab(19) .. "x   x")
    table.insert(bolt_lines, tab(18) .. "xx x")
    for n = 19, 12, -1 do
        table.insert(bolt_lines, tab(n) .. "x x")
    end
    table.insert(bolt_lines, tab(11) .. "xx")
    table.insert(bolt_lines, tab(10) .. "x")
    table.insert(bolt_lines, tab(9) .. "*\n")
    table.insert(bolt_lines, string.rep("#", 25) .. "\n")
    return table.concat(bolt_lines, "\n")
end


--- Print the prompt and read a yes/no answer from stdin.
local function ask_yes_or_no(prompt)
    io.stdout:write(prompt .. " ")
    local answer = string.lower(io.stdin:read("*l"))
    -- any line starting with a 'y' or 'Y' is considered a 'yes'
    return answer:sub(1, 1) == "y"
end


--- Print the prompt and read a valid number from stdin.
local function ask_number(prompt)
    io.stdout:write(prompt .. " ")
    while true do
        local n = tonumber(io.stdin:read("*l"))
        if n then
            return n
        else
            print("Enter a valid number.")
        end
    end
end


--- Explain the solution to persuade the player.
local function explain_solution()
    local k = ask_number("What was your original number?")
    -- For clarity we kept the same variable names of the original BASIC version
    local f = k + 3
    local g = f / 5
    local h = g * 8
    local i = h / 5 + 5
    local j = i - 1
    print("So you think you're so smart, eh?")
    print("Now watch.")
    print(k .. " plus 3 equals " .. f .. ". This divided by 5 equals " .. g .. ";")
    print("this times 8 equals " .. h .. ". If we divide by 5 and add 5,")
    print("we get " .. i .. ", which, minus 1, equals " .. j .. ".")
end


--- Main game function.
local function chief_game()
    --- Print game introduction and challenge
    print(tab(29) .. "Chief")
    print(tab(14) .. "Creative Computing  Morristown, New Jersey\n\n")
    print("I am Chief Numbers Freek, the great math god.")
    if not ask_yes_or_no("Are you ready to take the test you called me out for?") then
        print("Shut up, wise tongue.")
    end

    -- Print how to obtain the end result.
    print(" Take a number and add 3. Divide this number by 5 and")
    print("multiply by 8. Divide by 5 and add the same. Subtract 1.")

    -- Ask the result end and reverse calculate the original number.
    local end_result = ask_number(" What do you have?")
    local original_number = (end_result + 1 - 5) * 5 / 8 * 5 - 3

    -- If it is an integer we do not want to print any zero decimals.
    local int_part, dec_part = math.modf(original_number)
    if dec_part == 0 then original_number = int_part end

    -- If the player challenges the answer, print the explanation.
    if not ask_yes_or_no("I bet your number was " .. original_number .. ". Am I right?") then
        explain_solution()
        -- If the player does not accept the explanation, zap them.
        if not ask_yes_or_no("Now do you believe me?") then
            print("YOU HAVE MADE ME MAD!!!")
            print("THERE MUST BE A GREAT LIGHTNING BOLT!\n\n")
            print(bolt())
            print("I hope you believe me now, for your sake!!")
        end
    end
end

--- Run the game.
chief_game()