factorio-scenario-ExpCluster/exp_legacy/module/modules/commands/rainbow.lua

--[[-- Commands Module - Rainbow
    - Adds a command that prints your message in rainbow font
    @commands Rainbow
]]

local ExpUtil = require("modules/exp_util")
local Commands = require("modules.exp_legacy.expcore.commands") --- @dep expcore.commands
local format_chat_colour = ExpUtil.format_rich_text_color --- @dep expcore.common

local function step_component(c1, c2)
    if c1 < 0 then
        return 0, c2 + c1
    elseif c1 > 1 then
        return 1, c2 - c1 + 1
    else
        return c1, c2
    end
end

local function step_color(color)
    color.r, color.g = step_component(color.r, color.g)
    color.g, color.b = step_component(color.g, color.b)
    color.b, color.r = step_component(color.b, color.r)
    color.r = step_component(color.r, 0)
    return color
end

local function next_color(color, step)
    step = step or 0.1
    local new_color = { r = 0, g = 0, b = 0 }
    if color.b == 0 and color.r ~= 0 then
        new_color.r = color.r - step
        new_color.g = color.g + step
    elseif color.r == 0 and color.g ~= 0 then
        new_color.g = color.g - step
        new_color.b = color.b + step
    elseif color.g == 0 and color.b ~= 0 then
        new_color.b = color.b - step
        new_color.r = color.r + step
    end
    return step_color(new_color)
end

--- Sends an rainbow message in the chat
-- @command rainbow
-- @tparam string message the message that will be printed in chat
Commands.new_command("rainbow", { "expcom-rainbow.description" }, "Sends an rainbow message in the chat")
    :add_param("message", false)
    :enable_auto_concat()
    :register(function(player, message)
        local player_name = player and player.name or "<Server>"
        local player_color = player and player.color or nil
        local color_step = 3 / message:len()
        if color_step > 1 then color_step = 1 end
        local current_color = { r = 1, g = 0, b = 0 }
        local output = format_chat_colour(player_name .. ": ", player_color)
        output = output .. message:gsub("%S", function(letter)
            local rtn = format_chat_colour(letter, current_color)
            current_color = next_color(current_color, color_step)
            return rtn
        end)
        game.print(output)
    end)