defmodule Editor do

    def copy("") do
        {"", ""}
    end

    def copy(string) do
        f = String.first string
        s = string_tail(string)
        {f, s}
    end

    defp string_tail(string) do
        String.slice(string, 1..-1)
    end

    def insert(string, character) do
        insert(string, character, is_character(character))
    end

    defp insert(string, character, true) do
        string <> character
    end

    defp insert(_string, _character, false) do
        :error
    end

    defp is_character(string) do
        String.length(string) == 1
    end

    def delete(string) do
        string_tail(string)
    end

    def edit(string, commands) do
        trimmed_commands = Enum.map(commands, &String.trim/1)
        edit(string, trimmed_commands, "")
    end


    defp edit(string, ["копировать"|rest], res) do
        {next_string, to_res} = copy(string)
        edit(to_res, rest, res <> next_string)
    end

    defp edit(string, ["удалить"|rest], res) do
        next_string = delete(string)
        edit(next_string, rest, res)
    end

    defp edit(string, [command|rest], res) do
        has = String.contains?(command, "вставить")
        case has do
            true ->
            a = String.split(command)
            symbol = List.last a
            next_res = insert(res, symbol)
            edit(string, rest, next_res)
            false -> :error
        end
    end

    defp edit(_string, [], res) do
        res
    end

    def main do
        c = "копировать "
        IO.puts(edit("helo wosld", [c, c, c, "вставить l  ", c, c, c, c, "вставить r", "  удалить  ", c, c]))
    end
end


Editor.main