jdhao-nvim-config/lua/custom-autocmd.lua

local fn = vim.fn
local api = vim.api

local utils = require("utils")

-- Display a message when the current file is not in utf-8 format.
-- Note that we need to use `unsilent` command here because of this issue:
-- https://github.com/vim/vim/issues/4379
api.nvim_create_autocmd({ "BufRead" }, {
  pattern = "*",
  group = api.nvim_create_augroup("non_utf8_file", { clear = true }),
  callback = function()
    if vim.bo.fileencoding ~= "utf-8" then
      vim.notify("File not in UTF-8 format!", vim.log.levels.WARN, { title = "nvim-config" })
    end
  end,
})

-- highlight yanked region, see `:h lua-highlight`
local yank_group = api.nvim_create_augroup("highlight_yank", { clear = true })
api.nvim_create_autocmd({ "TextYankPost" }, {
  pattern = "*",
  group = yank_group,
  callback = function()
    vim.highlight.on_yank { higroup = "YankColor", timeout = 300 }
  end,
})

api.nvim_create_autocmd({ "CursorMoved" }, {
  pattern = "*",
  group = yank_group,
  callback = function()
    vim.g.current_cursor_pos = vim.fn.getcurpos()
  end,
})

api.nvim_create_autocmd("TextYankPost", {
  pattern = "*",
  group = yank_group,
  callback = function(ev)
    if vim.v.event.operator == "y" then
      vim.fn.setpos(".", vim.g.current_cursor_pos)
    end
  end,
})

-- Auto-create dir when saving a file, in case some intermediate directory does not exist
api.nvim_create_autocmd({ "BufWritePre" }, {
  pattern = "*",
  group = api.nvim_create_augroup("auto_create_dir", { clear = true }),
  callback = function(ctx)
    local dir = fn.fnamemodify(ctx.file, ":p:h")
    utils.may_create_dir(dir)
  end,
})

api.nvim_create_autocmd({ "BufWritePre" }, {
  pattern = {"*.c", "*.cc", "*.cpp", "*.h", "*.rs", "*.py"},
  callback = function()
    vim.lsp.buf.format { asnyc = false }
  end,
})

-- Automatically reload the file if it is changed outside of Nvim, see https://unix.stackexchange.com/a/383044/221410.
-- It seems that `checktime` does not work in command line. We need to check if we are in command
-- line before executing this command, see also https://vi.stackexchange.com/a/20397/15292 .
api.nvim_create_augroup("auto_read", { clear = true })

api.nvim_create_autocmd({ "FileChangedShellPost" }, {
  pattern = "*",
  group = "auto_read",
  callback = function()
    vim.notify("File changed on disk. Buffer reloaded!", vim.log.levels.WARN, { title = "nvim-config" })
  end,
})

api.nvim_create_autocmd({ "FocusGained", "CursorHold" }, {
  pattern = "*",
  group = "auto_read",
  callback = function()
    if fn.getcmdwintype() == "" then
      vim.cmd("checktime")
    end
  end,
})

-- Resize all windows when we resize the terminal
api.nvim_create_autocmd("VimResized", {
  group = api.nvim_create_augroup("win_autoresize", { clear = true }),
  desc = "autoresize windows on resizing operation",
  command = "wincmd =",
})

local function open_nvim_tree(data)
  -- check if buffer is a directory
  local directory = vim.fn.isdirectory(data.file) == 1

  if not directory then
    return
  end

  -- create a new, empty buffer
  vim.cmd.enew()

  -- wipe the directory buffer
  vim.cmd.bw(data.buf)

  -- open the tree
  require("nvim-tree.api").tree.open()
end

api.nvim_create_autocmd({ "VimEnter" }, { callback = open_nvim_tree })

-- Do not use smart case in command line mode, extracted from https://vi.stackexchange.com/a/16511/15292.
api.nvim_create_augroup("dynamic_smartcase", { clear = true })
api.nvim_create_autocmd("CmdLineEnter", {
  group = "dynamic_smartcase",
  pattern = ":",
  callback = function()
    vim.o.smartcase = false
  end,
})

api.nvim_create_autocmd("CmdLineLeave", {
  group = "dynamic_smartcase",
  pattern = ":",
  callback = function()
    vim.o.smartcase = true
  end,
})

api.nvim_create_autocmd("TermOpen", {
  group = api.nvim_create_augroup("term_start", { clear = true }),
  pattern = "*",
  callback = function()
    -- Do not use number and relative number for terminal inside nvim
    vim.wo.relativenumber = false
    vim.wo.number = false

    -- Go to insert mode by default to start typing command
    vim.cmd("startinsert")
  end,
})

local number_toggle_group = api.nvim_create_augroup("numbertoggle", { clear = true })
api.nvim_create_autocmd({ "BufEnter", "FocusGained", "InsertLeave", "WinEnter" }, {
  pattern = "*",
  group = number_toggle_group,
  desc = "togger line number",
  callback = function()
    if vim.wo.number then
      vim.wo.relativenumber = true
    end
  end,
})

api.nvim_create_autocmd({ "BufLeave", "FocusLost", "InsertEnter", "WinLeave" }, {
  group = number_toggle_group,
  desc = "togger line number",
  callback = function()
    if vim.wo.number then
      vim.wo.relativenumber = false
    end
  end,
})

api.nvim_create_autocmd("ColorScheme", {
  group = api.nvim_create_augroup("custom_highlight", { clear = true }),
  pattern = "*",
  desc = "Define or overrride some highlight groups",
  callback = function()
    -- For yank highlight
    vim.api.nvim_set_hl(0, "YankColor", { fg = "#34495E", bg = "#2ECC71", ctermfg = 59, ctermbg = 41 })

    -- For cursor colors
    vim.api.nvim_set_hl(0, "Cursor", { fg = "black", bg = "#00c918", bold = true })
    vim.api.nvim_set_hl(0, "Cursor2", { fg = "red", bg = "red" })

    -- For floating windows border highlight
    vim.api.nvim_set_hl(0, "FloatBorder", { fg = "LightGreen" })

    -- highlight for matching parentheses
    vim.api.nvim_set_hl(0, "MatchParen", { bold = true, underline = true })
  end,
})

api.nvim_create_autocmd("BufEnter", {
  pattern = "*",
  group = api.nvim_create_augroup("auto_close_win", { clear = true }),
  desc = "Quit Nvim if we have only one window, and its filetype match our pattern",
  callback = function(ev)
    local quit_filetypes = { "qf", "vista", "NvimTree" }

    local should_quit = true
    local tabwins = api.nvim_tabpage_list_wins(0)

    for _, win in pairs(tabwins) do
      local buf = api.nvim_win_get_buf(win)
      local bf = fn.getbufvar(buf, "&filetype")

      if fn.index(quit_filetypes, bf) == -1 then
        should_quit = false
      end
    end

    if should_quit then
      vim.cmd("qall")
    end
  end,
})

api.nvim_create_autocmd({ "VimEnter", "DirChanged" }, {
  group = api.nvim_create_augroup("git_repo_check", { clear = true }),
  pattern = "*",
  desc = "check if we are inside Git repo",
  callback = function()
    utils.inside_git_repo()
  end,
})

-- ref: https://vi.stackexchange.com/a/169/15292
api.nvim_create_autocmd("BufReadPre", {
  group = api.nvim_create_augroup("large_file", { clear = true }),
  pattern = "*",
  desc = "optimize for large file",
  callback = function(ev)
    local file_size_limit = 524288 -- 0.5MB
    local f = ev.file

    if fn.getfsize(f) > file_size_limit or fn.getfsize(f) == -2 then
      vim.o.eventignore = "all"
      --  turning off relative number helps a lot
      vim.wo.relativenumber = false

      vim.bo.swapfile = false
      vim.bo.bufhidden = "unload"
      vim.bo.undolevels = -1
    end
  end,
})