dotfiles/.config/nvim/lua/my/functions.lua

local M = {}

function M.remove_trailing_whitespace()
    local curpos = vim.api.nvim_win_get_cursor(0)
    vim.cmd([[keeppatterns %s/\s\+$//e]])
    vim.api.nvim_win_set_cursor(0, curpos)
end
vim.api.nvim_create_augroup('config_functions', { clear = true })
vim.api.nvim_create_autocmd(
    { 'BufWritePre' },
    {
        group = 'config_functions',
        pattern = {
            '*.lua', '*.cpp',
            '*.hpp', '*.conf', '*.cfg', '*.ini'
        },
        callback = M.remove_trailing_whitespace
    }
)

function M.insert_modeline()
    local comment_string = vim.o.commentstring
    local space_maybe = ''
    if string.match(comment_string, '%%s(.*)') ~= '' then
        space_maybe = ' '
    end

    local fenc = vim.o.fileencoding
    if fenc == '' then
        fenc = 'utf-8'
    end

    local modeline_elements = {
        ' vim: set',
        ' fenc=' .. fenc,
        ' ts=' .. vim.o.tabstop,
        ' sw=' .. vim.o.shiftwidth,
        (vim.o.expandtab and ' et' or ' noet'),
        ' tw=' .. vim.o.textwidth,
        ':',
        space_maybe
    }
    local modeline = comment_string:gsub('%%s', table.concat(modeline_elements))
    modeline = modeline:gsub('  ', ' ')

    local buffer = vim.api.nvim_win_get_buf(0)
    local current = vim.api.nvim_buf_get_lines(buffer, -2, -1, true)[1]
    if current == modeline then
        print('modeline already exists')
    elseif string.match(current, 'vim:') then
        vim.api.nvim_buf_set_lines(buffer, -2, -1, true, { modeline })
        print('modeline updated')
    else
        vim.api.nvim_buf_set_lines(buffer, -1, -1, true, { '', modeline })
        print('modeline inserted')
    end
end
vim.cmd([[command! ModelineInsert lua M.insert_modeline()]])

-- set colorcolumn to textwidth after buffer is displayed or option is changed
function M.set_colorcolumn()
    if vim.o.textwidth > 0 then
        vim.opt_local.colorcolumn = { vim.o.textwidth }
    else
        vim.opt_local.colorcolumn = ''
    end
end
vim.api.nvim_create_augroup('config_settings', { clear = true })
vim.api.nvim_create_autocmd(
    { 'BufEnter' },
    {
        group = 'config_settings',
        callback = M.set_colorcolumn
    }
)
vim.api.nvim_create_autocmd(
    { 'OptionSet' },
    {
        group = 'config_settings',
        pattern = { 'textwidth' },
        callback = M.set_colorcolumn
    }
)

function M.get_project_root()
    local path = vim.api.nvim_buf_get_name(0)
    local root_markers = {
        '.git', '.hg', '.svn', '.bzr', '_darcs',
        '.projectile', '.clang-format', '.luarc.json'
    }
    local sep = '/'

    repeat
        path = path:gsub(string.format('%s[^%s]*$', sep, sep), '')
        for _, marker in ipairs(root_markers) do
            if io.open(path .. sep .. marker) then
                return path
            end
        end
    until path == ''
    return nil
end

function M.shell_capture(command)
    local handle = io.popen(command)
    if not handle then return nil end
    local result = handle:read() or nil
    handle:close()
    return result
end

return M