csv-align.lua

-- $ stylua csv-align.lua
-- $ luacheck csv-align.lua
-- $ cp csv-align.lua ~/.config/nvim/plugin/.

local M = {}

local ns = vim.api.nvim_create_namespace("csv-align")

function M.align()
	local lines = vim.api.nvim_buf_get_lines(0, 0, -1, false)

	local column_len = {}

	-- Calculate maximum width for each CSV column.
	for _, line in ipairs(lines) do
		local fields = vim.split(line, ",", { plain = true })

		for i, field in ipairs(fields) do
			-- Add one for the comma.
			local len = vim.fn.strdisplaywidth(field) + 1

			column_len[i] = math.max(column_len[i] or 0, len)
		end
	end

	-- Clear existing virtual text.
	vim.api.nvim_buf_clear_namespace(0, ns, 0, -1)

	-- Build virtual text with padding for each line.
	for line_number, line in ipairs(lines) do
		local fields = vim.split(line, ",", { plain = true })

		local col = 0

		for i, field in ipairs(fields) do
			col = col + #field + 1

			if col > #line then
				break
			end

			local len = vim.fn.strdisplaywidth(field) + 1

			local padding_len = column_len[i] - len

			if padding_len > 0 then
				vim.api.nvim_buf_set_extmark(0, ns, line_number - 1, col, {
					virt_text = { { string.rep(" ", padding_len), "Comment" } },
					virt_text_pos = "inline",
				})
			end
		end
	end
end

vim.api.nvim_create_autocmd({ "BufReadPost", "BufWritePost", "TextChanged", "InsertLeave" }, {
	pattern = { "*.csv" },
	callback = M.align,
})

return M