refactor(nvim): rewrite the buffer formatting flow

1 files changed, 67 insertions, 0 deletions

diff --git a/plugin/50-format.lua b/plugin/50-format.lua
new file mode 100644
index 0000000..46a245c
--- /dev/null
+++ b/plugin/50-format.lua
@@ -0,0 +1,67 @@
+--
+-- 50-format.lua
+--
+-- Specifies the formatters to use for different file types and sets up a global autocommand to trigger them.
+--
+-- User commands:
+--   FormatToggle: toggle formatting on save on/off for the current buffer
+
+local function toggle_format()
+	vim.b.format = not vim.b.format
+end
+
+local function format_impl(cmd, lines)
+	local r = vim.system(cmd, { stdin = lines, text = true }):wait()
+	if r.code ~= 0 then
+		vim.notify(cmd[1] .. " error:\n" .. r.stderr, vim.log.levels.WARN)
+		return nil
+	end
+	return vim.split(r.stdout, "\n", { trimempty = true })
+end
+
+local formatters = {
+	["sh"] = function(lines)
+		return format_impl({ "shfmt", "-" }, lines)
+	end,
+	["lua"] = function(lines)
+		return format_impl({ "stylua", "--search-parent-directories", "-" }, lines)
+	end,
+	["markdown"] = function(lines)
+		return format_impl({ "mdformat", "-" }, lines)
+	end,
+	["python"] = function(lines)
+		return format_impl({ "black", "-" }, lines)
+	end,
+}
+formatters.bash = formatters.sh
+
+--- Format the buffer `ev.buf` with the formatter for its filetype.
+--- This function is meant to be an event handler for `vim.api.nvim_create_autocmd()`
+--- @param ev table `ev` argument passed from `vim.api.nvim_create_autocmd()`
+local function on_format(ev)
+	if vim.b[ev.buf].format ~= true then
+		return
+	end
+	local ft = vim.bo[ev.buf].filetype
+	local format = formatters[ft]
+	if not format then
+		vim.notify("No formatter registered for " .. ft, vim.log.levels.ERROR)
+		return
+	end
+	local lines_in = vim.api.nvim_buf_get_lines(ev.buf, 0, -1, false)
+	local lines_out = format(lines_in)
+	if not lines_out or vim.deep_equal(lines_in, lines_out) then
+		return
+	end
+	local view = vim.fn.winsaveview()
+	vim.api.nvim_buf_set_lines(ev.buf, 0, -1, false, lines_out)
+	vim.fn.winrestview(view)
+end
+
+vim.api.nvim_create_autocmd("BufWritePre", {
+	desc = "Format buffer",
+	group = vim.g.dotfiles.augroup,
+	callback = on_format,
+})
+
+vim.api.nvim_create_user_command("FormatToggle", toggle_format, { desc = "Toggle format on save" })