Minor breaking change: replace separators with callbacks

I don't think anyone ever changed these settings.
Using callbacks opens up a much larger number of use cases.
Closes #64.

lua/session_manager/config.lua

@@ -1,6 +1,9 @@
 local Path = require('plenary.path')
 local Enum = require('plenary.enum')
 
+local path_replacer = '__'
+local colon_replacer = '++'
+
 local config = {
   AutoloadMode = Enum({
     'Disabled',
@@ -9,10 +12,32 @@ local config = {
   }),
 }
 
+--- Replaces symbols into separators and colons to transform filename into a session directory.
+---@param filename string: Filename with expressions to replace.
+---@return table: Session directory
+local function session_filename_to_dir(filename)
+  -- Get session filename.
+  local dir = filename:sub(#tostring(config.sessions_dir) + 2)
+
+  dir = dir:gsub(colon_replacer, ':')
+  dir = dir:gsub(path_replacer, Path.path.sep)
+  return Path:new(dir)
+end
+
+--- Replaces separators and colons into special symbols to transform session directory into a filename.
+---@param dir table?: Path to session directory. Defaults to the current working directory if `nil`.
+---@return table: Session filename.
+local function dir_to_session_filename(dir)
+  local filename = dir and dir.filename or vim.loop.cwd()
+  filename = filename:gsub(':', colon_replacer)
+  filename = filename:gsub(Path.path.sep, path_replacer)
+  return Path:new(config.sessions_dir):joinpath(filename)
+end
+
 config.defaults = {
   sessions_dir = Path:new(vim.fn.stdpath('data'), 'sessions'),
-  path_replacer = '__',
-  colon_replacer = '++',
+  session_filename_to_dir = session_filename_to_dir,
+  dir_to_session_filename = dir_to_session_filename,
   autoload_mode = config.AutoloadMode.LastSession,
   autosave_last_session = true,
   autosave_ignore_not_normal = true,

lua/session_manager/init.lua

@@ -37,14 +37,14 @@ end
 
 --- Loads a session for the current working directory.
 function session_manager.load_current_dir_session(discard_current)
-  local session_name = utils.dir_to_session_filename(vim.loop.cwd())
+  local session_name = config.dir_to_session_filename(vim.loop.cwd())
   if session_name:exists() then
     utils.load_session(session_name.filename, discard_current)
   end
 end
 
 --- Saves a session for the current working directory.
-function session_manager.save_current_session() utils.save_session(utils.dir_to_session_filename().filename) end
+function session_manager.save_current_session() utils.save_session(config.dir_to_session_filename().filename) end
 
 --- Loads a session based on settings. Executed after starting the editor.
 function session_manager.autoload_session()

lua/session_manager/utils.lua

@@ -37,7 +37,7 @@ function utils.get_last_session_filename()
   local most_recent_filename = nil
   local most_recent_timestamp = 0
   for _, session_filename in ipairs(scandir.scan_dir(tostring(config.sessions_dir))) do
-    if utils.session_filename_to_dir(session_filename):is_dir() then
+    if config.session_filename_to_dir(session_filename):is_dir() then
       local timestamp = vim.fn.getftime(session_filename)
       if most_recent_timestamp < timestamp then
         most_recent_timestamp = timestamp
@@ -114,7 +114,7 @@ end
 function utils.get_sessions()
   local sessions = {}
   for _, session_filename in ipairs(scandir.scan_dir(tostring(config.sessions_dir))) do
-    local dir = utils.session_filename_to_dir(session_filename)
+    local dir = config.session_filename_to_dir(session_filename)
     if dir:is_dir() then
       table.insert(sessions, { timestamp = vim.fn.getftime(session_filename), filename = session_filename, dir = dir })
     else
@@ -124,35 +124,13 @@ function utils.get_sessions()
   table.sort(sessions, function(a, b) return a.timestamp > b.timestamp end)
 
   -- If the last session is the current one, then preselect the previous one.
-  if #sessions >= 2 and sessions[1].filename == utils.dir_to_session_filename().filename then
+  if #sessions >= 2 and sessions[1].filename == config.dir_to_session_filename().filename then
     sessions[1], sessions[2] = sessions[2], sessions[1]
   end
 
   return sessions
 end
 
---- Replaces symbols into separators and colons to transform filename into a session directory.
----@param filename string: Filename with expressions to replace.
----@return table: Session directory
-function utils.session_filename_to_dir(filename)
-  -- Get session filename.
-  local dir = filename:sub(#tostring(config.sessions_dir) + 2)
-
-  dir = dir:gsub(config.colon_replacer, ':')
-  dir = dir:gsub(config.path_replacer, Path.path.sep)
-  return Path:new(dir)
-end
-
---- Replaces separators and colons into special symbols to transform session directory into a filename.
----@param dir table?: Path to session directory. Defaults to the current working directory if `nil`.
----@return table: Session filename.
-function utils.dir_to_session_filename(dir)
-  local filename = dir and dir.filename or vim.loop.cwd()
-  filename = filename:gsub(':', config.colon_replacer)
-  filename = filename:gsub(Path.path.sep, config.path_replacer)
-  return Path:new(config.sessions_dir):joinpath(filename)
-end
-
 ---@param buffer number: buffer ID.
 ---@return boolean: `true` if this buffer could be restored later on loading.
 function utils.is_restorable(buffer)