tidy.nvim/lua/tidy/init.lua

local M = {
    config = {
        eof_quant = -1,
        fmts = {
            "sof",
            "eof",
            "multi",
            "ws"
        }
    }
}

function M.setup(user_config)

    -- integrate user configuration
    M.config = vim.tbl_deep_extend("force", M.config, user_config or {})

    vim.cmd[[
    augroup Tidy
        au!
        au BufWritePre * lua require( "tidy" ).tidy_up()
    augroup END
    ]]
end

function M.tidy_up()
    local cmd_mods = ":keepjumps keeppatterns silent! "

    local patterns = {
        -- delete all new lines at beginning of file

        sof = [[%s/\%^\n*/]],
        -- delete all lines at end of buffer, see source 2

        eof = [[0;/^\%(\n*.\)\@!/ + ]] .. M.config.eof_quant ..  ",$d",
        -- compress all instances of multiple newlines into one

        multi = [[:%s/\n\{2,}/\r\r/e]],
        -- delete all whitespace, see source 1
        ws = [[%s/\s\+$//e]]
    }

    -- get tuple of cursor position before making changes
    local pos = vim.api.nvim_win_get_cursor(0)

    for _, fmt_type in ipairs(M.config.fmts) do
        vim.cmd(cmd_mods .. patterns[fmt_type])
    end

    -- get row count after line deletion
    local end_row = vim.api.nvim_buf_line_count(0)

    --[[
        if the row value in the original cursor
        position tuple is greater than the
        line count after empty line deletion
        (meaning that the cursor was inside of
        the group of empty lines at the end of
        the file when they were deleted), set
        the cursor row to the last line
    ]]
    if pos[1] > end_row then
        pos[1] = end_row
    end

    vim.api.nvim_win_set_cursor(0, pos)
end

return M