feature: Add logger for debugging (#18)

lua/auto-save/utils/logging.lua

@@ -0,0 +1,42 @@
+-- inspired from https://github.com/nvim-lua/plenary.nvim/blob/master/lua/plenary/log.lua
+
+local M = {}
+
+local outfile = string.format("%s/auto-save.log", vim.api.nvim_call_function("stdpath", { "cache" }))
+
+-- it could be that the directory of the file does not exist
+-- this would require further checks, see https://github.com/nvim-lua/plenary.nvim/blob/master/lua/plenary/log.lua#L138
+--- @param message string
+local write_to_outfile = function(message)
+  local f = assert(io.open(outfile, "a"))
+  f:write(message)
+  f:close()
+end
+
+M.new = function(options)
+  local enabled = options.debug
+
+  --- @param buf number | nil
+  --- @param message string
+  local log = function(buf, message)
+    if not enabled then
+      return
+    end
+
+    local log_message
+    if buf ~= nil then
+      local filename = vim.api.nvim_buf_get_name(buf)
+      log_message = string.format("[%s] [%s] - %s\n", os.date(), filename, message)
+    else
+      log_message = string.format("[%s] - %s\n", os.date(), message)
+    end
+
+    write_to_outfile(log_message)
+  end
+
+  return {
+    log = log,
+  }
+end
+
+return M