require "core.strict"
require "core.regex"
local common = require "core.common"
local config = require "core.config"
local style = require "core.style"
local command
local keymap
local dirwatch
local RootView
local StatusView
local TitleView
local CommandView
local NagView
local DocView
local Doc

local core = {}

local function load_session()
  local ok, t = pcall(dofile, USERDIR .. "/session.lua")
  return ok and t or {}
end


local function save_session()
  local fp = io.open(USERDIR .. "/session.lua", "w")
  if fp then
    fp:write("return {recents=", common.serialize(core.recent_projects),
      ", window=", common.serialize(table.pack(system.get_window_size())),
      ", window_mode=", common.serialize(system.get_window_mode()),
      ", previous_find=", common.serialize(core.previous_find),
      ", previous_replace=", common.serialize(core.previous_replace),
      "}\n")
    fp:close()
  end
end


local function update_recents_project(action, dir_path_abs)
  local dirname = common.normalize_volume(dir_path_abs)
  if not dirname then return end
  local recents = core.recent_projects
  local n = #recents
  for i = 1, n do
    if dirname == recents[i] then
      table.remove(recents, i)
      break
    end
  end
  if action == "add" then
    table.insert(recents, 1, dirname)
  end
end


function core.set_project_dir(new_dir, change_project_fn)
  local chdir_ok = pcall(system.chdir, new_dir)
  if chdir_ok then
    if change_project_fn then change_project_fn() end
    core.project_dir = common.normalize_volume(new_dir)
    core.project_directories = {}
  end
  return chdir_ok
end


local function reload_customizations()
  -- The logic is:
  -- - the core.style and config modules are reloaded with the purpose of applying
  --   the new user's and project's module configs
  -- - inside the core.config the existing fields in config.plugins are preserved
  --   because they are reserved to plugins configuration and plugins are already
  --   loaded.
  -- - plugins are not reloaded or unloaded
  local plugins_save = {}
  for k, v in pairs(config.plugins) do
    plugins_save[k] = v
  end
  core.reload_module("core.style")
  core.reload_module("core.config")
  core.load_user_directory()
  core.load_project_module()
  for k, v in pairs(plugins_save) do
    config.plugins[k] = v
  end
end


function core.open_folder_project(dir_path_abs)
  if core.set_project_dir(dir_path_abs, core.on_quit_project) then
    core.root_view:close_all_docviews()
    reload_customizations()
    update_recents_project("add", dir_path_abs)
    core.add_project_directory(dir_path_abs)
    core.on_enter_project(dir_path_abs)
  end
end


local function strip_leading_path(filename)
    return filename:sub(2)
end

local function strip_trailing_slash(filename)
  if filename:match("[^:][/\\]$") then
    return filename:sub(1, -2)
  end
  return filename
end



function core.project_subdir_is_shown(dir, filename)
  return not dir.files_limit or dir.shown_subdir[filename]
end


local function show_max_files_warning(dir)
  local message = dir.slow_filesystem and
    "Filesystem is too slow: project files will not be indexed." or
    "Too many files in project directory: stopped reading at "..
    config.max_project_files.." files. For more information see "..
    "usage.md at https://github.com/lite-xl/lite-xl."
  if core.status_view then
    core.status_view:show_message("!", style.accent, message)
  end
end


local function file_search(files, info)
  local filename, type = info.filename, info.type
  local inf, sup = 1, #files
  while sup - inf > 8 do
    local curr = math.floor((inf + sup) / 2)
    if system.path_compare(filename, type, files[curr].filename, files[curr].type) then
      sup = curr - 1
    else
      inf = curr
    end
  end
  while inf <= sup and not system.path_compare(filename, type, files[inf].filename, files[inf].type) do
    if files[inf].filename == filename then
      return inf, true
    end
    inf = inf + 1
  end
  return inf, false
end


local function files_info_equal(a, b)
  return a.filename == b.filename and a.type == b.type
end

-- for "a" inclusive from i1 + 1 and i1 + n
local function files_list_match(a, i1, n, b)
  if n ~= #b then return false end
  for i = 1, n do
    if not files_info_equal(a[i1 + i], b[i]) then
      return false
    end
  end
  return true
end

-- arguments like for files_list_match
local function files_list_replace(as, i1, n, bs, hook)
  local m = #bs
  local i, j = 1, 1
  while i <= m or i <= n do
    local a, b = as[i1 + i], bs[j]
    if i > n or (j <= m and not files_info_equal(a, b) and
      not system.path_compare(a.filename, a.type, b.filename, b.type))
    then
      table.insert(as, i1 + i, b)
      i, j, n = i + 1, j + 1, n + 1
      if hook and hook.insert then hook.insert(b) end
    elseif j > m or system.path_compare(a.filename, a.type, b.filename, b.type) then
      if hook and hook.remove then hook.remove(as[i1 + i]) end
      table.remove(as, i1 + i)
      n = n - 1
    else
      i, j = i + 1, j + 1
    end
  end
end


local function project_subdir_bounds(dir, filename)
  local index, n = 0, #dir.files
  for i, file in ipairs(dir.files) do
    local file = dir.files[i]
    if file.filename == filename then
      index, n = i, #dir.files - i
      for j = 1, #dir.files - i do
        if not common.path_belongs_to(dir.files[i + j].filename, filename) then
          n = j - 1
          break
        end
      end
      return index, n, file
    end
  end
end


-- Predicate function to inhibit directory recursion in get_directory_files
-- based on a time limit and the number of files.
local function timed_max_files_pred(dir, filename, entries_count, t_elapsed)
  local n_limit = entries_count <= config.max_project_files
  local t_limit = t_elapsed < 20 / config.fps
  return n_limit and t_limit and core.project_subdir_is_shown(dir, filename)
end



-- Should be called on any directory that registers a change.
-- Uses relative paths at the project root.
local function refresh_directory(topdir, target, expanded)
  local index, n, directory
  if target == "" then
    index, n = 1, #topdir.files
    directory = ""
  else
    index, n = project_subdir_bounds(topdir, target)
    index = index + 1
    n = index + n - 1
    directory =  (PATHSEP .. target)
  end
  if index then
    local files
    local change = false
    if topdir.files_limit then
      -- If we have the folders literally open on the side panel.
      files = expanded and dirwatch.get_directory_files(topdir, topdir.name, directory, {}, 0, core.project_subdir_is_shown) or {}
      change = true
    else
      -- If we're expecting to keep track of everything, go through the list and iteratively deal with directories.
      files = dirwatch.get_directory_files(topdir, topdir.name, directory, {}, 0, function() return false end)
    end
    
    local new_idx, old_idx = 1, index
    local new_directories = {}
    local last_dir = nil
    while old_idx <= n or new_idx <= #files do 
      local old_info, new_info = topdir.files[old_idx], files[new_idx]
      if not new_info or not old_info or not last_dir or old_info.filename:sub(1, #last_dir + 1) ~= last_dir .. "/" then
        if not new_info or not old_info or not files_info_equal(new_info, old_info) then
          change = true
          if not old_info or (new_info and system.path_compare(new_info.filename, new_info.type, old_info.filename, old_info.type)) then
            table.insert(topdir.files, old_idx, new_info)
            new_idx = new_idx + 1
            old_idx = old_idx + 1
            if new_info.type == "dir" then
              table.insert(new_directories, new_info)
            end
            n = n + 1
          else
            table.remove(topdir.files, old_idx)
            if old_info.type == "dir" then
              topdir.watch:unwatch(target .. PATHSEP .. old_info.filename)
            end
            n = n - 1
          end
        else
          new_idx = new_idx + 1
          old_idx = old_idx + 1
        end
        if old_info and old_info.type == "dir" then
          last_dir = old_info.filename
        end
      else
        old_idx = old_idx + 1
      end
    end
    for i, v in ipairs(new_directories) do
      topdir.watch:watch(target)
      if refresh_directory(topdir, target .. PATHSEP .. v.filename) then
        change = true
      end
    end
    if change then
      core.redraw = true
      topdir.is_dirty = true
    end    
    return change
  end
end

function core.add_project_directory(path)
  -- top directories has a file-like "item" but the item.filename
  -- will be simply the name of the directory, without its path.
  -- The field item.topdir will identify it as a top level directory.
  path = common.normalize_volume(path)
  local topdir = {
    name = path,
    item = {filename = common.basename(path), type = "dir", topdir = true},
    files_limit = false,
    is_dirty = true,
    shown_subdir = {},
    watch_thread = nil,
    watch = dirwatch.new()
  }
  table.insert(core.project_directories, topdir)  
  
  local fstype = PLATFORM == "Linux" and system.get_fs_type(topdir.name) or "unknown"
  topdir.force_scans = (fstype == "nfs" or fstype == "fuse")
  local t, complete, entries_count = dirwatch.get_directory_files(topdir, topdir.name, "", {}, 0, timed_max_files_pred)
  topdir.files = t
  if not complete then
    topdir.slow_filesystem = not complete and (entries_count <= config.max_project_files)
    topdir.files_limit = true
    show_max_files_warning(topdir)
    refresh_directory(topdir, "", true)
  else
    for i,v in ipairs(t) do
      if v.type == "dir" then topdir.watch:watch(path .. PATHSEP .. v.filename) end
    end
  end
  topdir.watch:watch(topdir.name)
  -- each top level directory gets a watch thread. if the project is small, or
  -- if the ablity to use directory watches hasn't been compromised in some way
  -- either through error, or amount of files, then this should be incredibly 
  -- quick; essentially one syscall per check. Otherwise, this may take a bit of
  -- time; the watch will yield in this coroutine after 0.01 second, for 0.1 seconds.
  topdir.watch_thread = core.add_thread(function()
    while true do
      topdir.watch:check(function(target)
        if target == topdir.name then return refresh_directory(topdir, "", true) end	
        local dirpath = target:sub(#topdir.name + 2)
        local abs_dirpath = topdir.name .. PATHSEP .. dirpath
        if dirpath then
          -- check if the directory is in the project files list, if not exit.
          local dir_index, dir_match = file_search(topdir.files, {filename = dirpath, type = "dir"})
          if not dir_match or not core.project_subdir_is_shown(topdir, topdir.files[dir_index].filename) then return end
        end
        return refresh_directory(topdir, dirpath, true)
      end, 0.01, 0.01)
      coroutine.yield(0.05)
    end
  end)
  
  if path == core.project_dir then
    core.project_files = topdir.files
  end
  core.redraw = true
  return topdir
end


-- The function below is needed to reload the project directories
-- when the project's module changes.
local function rescan_project_directories()
  local save_project_dirs = {}
  local n = #core.project_directories
  for i = 1, n do
    local dir = core.project_directories[i]
    save_project_dirs[i] = {name = dir.name, shown_subdir = dir.shown_subdir}
  end
  core.project_directories = {}
  for i = 1, n do -- add again the directories in the project
    local dir = core.add_project_directory(save_project_dirs[i].name)
    if dir.files_limit then
      -- We need to sort the list of shown subdirectories so that higher level
      -- directories are populated first. We use the function system.path_compare
      -- because it order the entries in the appropriate order.
      -- TODO: we may consider storing the table shown_subdir as a sorted table
      -- since the beginning.
      local subdir_list = {}
      for subdir in pairs(save_project_dirs[i].shown_subdir) do
        table.insert(subdir_list, subdir)
      end
      table.sort(subdir_list, function(a, b) return system.path_compare(a, "dir", b, "dir") end)
      for _, subdir in ipairs(subdir_list) do
        local show = save_project_dirs[i].shown_subdir[subdir]
        for j = 1, #dir.files do
          if dir.files[j].filename == subdir then
            -- The instructions below match when happens in TreeView:on_mouse_pressed.
            -- We perform the operations only once iff the subdir is in dir.files.
            -- In theory set_show below may fail and return false but is it is listed
            -- there it means it succeeded before so we are optimistically assume it
            -- will not fail for the sake of simplicity.
            core.update_project_subdir(dir, subdir, show)
            break
          end
        end
      end
    end
  end
end


function core.project_dir_by_name(name)
  for i = 1, #core.project_directories do
    if core.project_directories[i].name == name then
      return core.project_directories[i]
    end
  end
end


function core.update_project_subdir(dir, filename, expanded)
  assert(dir.files_limit, "function should be called only when directory is in files limit mode")
  dir.shown_subdir[filename] = expanded
  local index, n, file = project_subdir_bounds(dir, filename)
  if index then
    local new_files = expanded and dirwatch.get_directory_files(dir, dir.name, PATHSEP .. filename, {}, 0, core.project_subdir_is_shown) or {}
    files_list_replace(dir.files, index, n, new_files)
    dir.is_dirty = true
    return true
  end
end


-- Find files and directories recursively reading from the filesystem.
-- Filter files and yields file's directory and info table. This latter
-- is filled to be like required by project directories "files" list.
local function find_files_rec(root, path)
  local all = system.list_dir(root .. path) or {}
  for _, file in ipairs(all) do
    local file = path .. PATHSEP .. file
    local info = system.get_file_info(root .. file)
    if info then
      info.filename = strip_leading_path(file)
      if info.type == "file" then
        coroutine.yield(root, info)
      elseif not common.match_pattern(common.basename(info.filename), config.ignore_files) then
        find_files_rec(root, PATHSEP .. info.filename)
      end
    end
  end
end


-- Iterator function to list all project files
local function project_files_iter(state)
  local dir = core.project_directories[state.dir_index]
  if state.co then
    -- We have a coroutine to fetch for files, use the coroutine.
    -- Used for directories that exceeds the files nuumber limit.
    local ok, name, file = coroutine.resume(state.co, dir.name, "")
    if ok and name then
      return name, file
    else
      -- The coroutine terminated, increment file/dir counter to scan
      -- next project directory.
      state.co = false
      state.file_index = 1
      state.dir_index = state.dir_index + 1
      dir = core.project_directories[state.dir_index]
    end
  else
    -- Increase file/dir counter
    state.file_index = state.file_index + 1
    while dir and state.file_index > #dir.files do
      state.dir_index = state.dir_index + 1
      state.file_index = 1
      dir = core.project_directories[state.dir_index]
    end
  end
  if not dir then return end
  if dir.files_limit then
    -- The current project directory is files limited: create a couroutine
    -- to read files from the filesystem.
    state.co = coroutine.create(find_files_rec)
    return project_files_iter(state)
  end
  return dir.name, dir.files[state.file_index]
end


function core.get_project_files()
  local state = { dir_index = 1, file_index = 0 }
  return project_files_iter, state
end


function core.project_files_number()
  local n = 0
  for i = 1, #core.project_directories do
    if core.project_directories[i].files_limit then return end
    n = n + #core.project_directories[i].files
  end
  return n
end


-- create a directory using mkdir but may need to create the parent
-- directories as well.
local function create_user_directory()
  local success, err = common.mkdirp(USERDIR)
  if not success then
    error("cannot create directory \"" .. USERDIR .. "\": " .. err)
  end
  for _, modname in ipairs {'plugins', 'colors', 'fonts'} do
    local subdirname = USERDIR .. PATHSEP .. modname
    if not system.mkdir(subdirname) then
      error("cannot create directory: \"" .. subdirname .. "\"")
    end
  end
end


local function write_user_init_file(init_filename)
  local init_file = io.open(init_filename, "w")
  if not init_file then error("cannot create file: \"" .. init_filename .. "\"") end
  init_file:write([[
-- put user settings here
-- this module will be loaded after everything else when the application starts
-- it will be automatically reloaded when saved

local core = require "core"
local keymap = require "core.keymap"
local config = require "core.config"
local style = require "core.style"

------------------------------ Themes ----------------------------------------

-- light theme:
-- core.reload_module("colors.summer")

--------------------------- Key bindings -------------------------------------

-- key binding:
-- keymap.add { ["ctrl+escape"] = "core:quit" }


------------------------------- Fonts ----------------------------------------

-- customize fonts:
-- style.font = renderer.font.load(DATADIR .. "/fonts/FiraSans-Regular.ttf", 14 * SCALE)
-- style.code_font = renderer.font.load(DATADIR .. "/fonts/JetBrainsMono-Regular.ttf", 14 * SCALE)
--
-- font names used by lite:
-- style.font          : user interface
-- style.big_font      : big text in welcome screen
-- style.icon_font     : icons
-- style.icon_big_font : toolbar icons
-- style.code_font     : code
--
-- the function to load the font accept a 3rd optional argument like:
--
-- {antialiasing="grayscale", hinting="full"}
--
-- possible values are:
-- antialiasing: grayscale, subpixel
-- hinting: none, slight, full

------------------------------ Plugins ----------------------------------------

-- enable or disable plugin loading setting config entries:

-- enable plugins.trimwhitespace, otherwise it is disable by default:
-- config.plugins.trimwhitespace = true
--
-- disable detectindent, otherwise it is enabled by default
-- config.plugins.detectindent = false
]])
  init_file:close()
end


function core.write_init_project_module(init_filename)
  local init_file = io.open(init_filename, "w")
  if not init_file then error("cannot create file: \"" .. init_filename .. "\"") end
  init_file:write([[
-- Put project's module settings here.
-- This module will be loaded when opening a project, after the user module
-- configuration.
-- It will be automatically reloaded when saved.

local config = require "core.config"

-- you can add some patterns to ignore files within the project
-- config.ignore_files = {"^%.", <some-patterns>}

-- Patterns are normally applied to the file's or directory's name, without
-- its path. See below about how to apply filters on a path.
--
-- Here some examples:
--
-- "^%." match any file of directory whose basename begins with a dot.
--
-- When there is an '/' or a '/$' at the end the pattern it will only match
-- directories. When using such a pattern a final '/' will be added to the name
-- of any directory entry before checking if it matches.
--
-- "^%.git/" matches any directory named ".git" anywhere in the project.
--
-- If a "/" appears anywhere in the pattern except if it appears at the end or
-- is immediately followed by a '$' then the pattern will be applied to the full
-- path of the file or directory. An initial "/" will be prepended to the file's
-- or directory's path to indicate the project's root.
--
-- "^/node_modules/" will match a directory named "node_modules" at the project's root.
-- "^/build.*/" match any top level directory whose name begins with "build"
-- "^/subprojects/.+/" match any directory inside a top-level folder named "subprojects".

-- You may activate some plugins on a pre-project base to override the user's settings.
-- config.plugins.trimwitespace = true
]])
  init_file:close()
end


function core.load_user_directory()
  return core.try(function()
    local stat_dir = system.get_file_info(USERDIR)
    if not stat_dir then
      create_user_directory()
    end
    local init_filename = USERDIR .. "/init.lua"
    local stat_file = system.get_file_info(init_filename)
    if not stat_file then
      write_user_init_file(init_filename)
    end
    dofile(init_filename)
  end)
end


function core.remove_project_directory(path)
  -- skip the fist directory because it is the project's directory
  for i = 2, #core.project_directories do
    local dir = core.project_directories[i]
    if dir.name == path then
      table.remove(core.project_directories, i)
      return true
    end
  end
  return false
end


local function configure_borderless_window()
  system.set_window_bordered(not config.borderless)
  core.title_view:configure_hit_test(config.borderless)
  core.title_view.visible = config.borderless
end


local function add_config_files_hooks()
  -- auto-realod style when user's module is saved by overriding Doc:Save()
  local doc_save = Doc.save
  local user_filename = system.absolute_path(USERDIR .. PATHSEP .. "init.lua")
  function Doc:save(filename, abs_filename)
    local module_filename = system.absolute_path(".lite_project.lua")
    doc_save(self, filename, abs_filename)
    if self.abs_filename == user_filename or self.abs_filename == module_filename then
      reload_customizations()
      rescan_project_directories()
      configure_borderless_window()
    end
  end
end


function core.init()
  command = require "core.command"
  keymap = require "core.keymap"
  dirwatch = require "core.dirwatch"
  RootView = require "core.rootview"
  StatusView = require "core.statusview"
  TitleView = require "core.titleview"
  CommandView = require "core.commandview"
  NagView = require "core.nagview"
  DocView = require "core.docview"
  Doc = require "core.doc"

  if PATHSEP == '\\' then
    USERDIR = common.normalize_volume(USERDIR)
    DATADIR = common.normalize_volume(DATADIR)
    EXEDIR  = common.normalize_volume(EXEDIR)
  end

  do
    local session = load_session()
    if session.window_mode == "normal" then
      system.set_window_size(table.unpack(session.window))
    elseif session.window_mode == "maximized" then
      system.set_window_mode("maximized")
    end
    core.recent_projects = session.recents or {}
    core.previous_find = session.previous_find or {}
    core.previous_replace = session.previous_replace or {}
  end

  local project_dir = core.recent_projects[1] or "."
  local project_dir_explicit = false
  local files = {}
  local delayed_error
  for i = 2, #ARGS do
    local arg_filename = strip_trailing_slash(ARGS[i])
    local info = system.get_file_info(arg_filename) or {}
    if info.type == "file" then
      local file_abs = system.absolute_path(arg_filename)
      if file_abs then
        table.insert(files, file_abs)
        project_dir = file_abs:match("^(.+)[/\\].+$")
      end
    elseif info.type == "dir" then
      project_dir = arg_filename
      project_dir_explicit = true
    else
      -- on macOS we can get an argument like "-psn_0_52353" that we just ignore.
      if not ARGS[i]:match("^-psn") then
        delayed_error = string.format("error: invalid file or directory %q", ARGS[i])
      end
    end
  end

  core.frame_start = 0
  core.clip_rect_stack = {{ 0,0,0,0 }}
  core.log_items = {}
  core.docs = {}
  core.cursor_clipboard = {}
  core.cursor_clipboard_whole_line = {}
  core.window_mode = "normal"
  core.threads = setmetatable({}, { __mode = "k" })
  core.blink_start = system.get_time()
  core.blink_timer = core.blink_start
  
  local got_user_error, got_project_error = not core.load_user_directory()

  local project_dir_abs = system.absolute_path(project_dir)
  -- We prevent set_project_dir below to effectively add and scan the directory becaese tha
  -- project module and its ignore files is not yet loaded.
  local set_project_ok = project_dir_abs and core.set_project_dir(project_dir_abs)
  if set_project_ok then
    if project_dir_explicit then
      update_recents_project("add", project_dir_abs)
    end
  else
    if not project_dir_explicit then
      update_recents_project("remove", project_dir)
    end
    project_dir_abs = system.absolute_path(".")
    if not core.set_project_dir(project_dir_abs, function() 
      got_project_error = not core.load_project_module()
    end) then
      system.show_fatal_error("Lite XL internal error", "cannot set project directory to cwd")
      os.exit(1)
    end
  end

  core.redraw = true
  core.visited_files = {}
  core.restart_request = false
  core.quit_request = false

  core.root_view = RootView()
  core.command_view = CommandView()
  core.status_view = StatusView()
  core.nag_view = NagView()
  core.title_view = TitleView()

  local cur_node = core.root_view.root_node
  cur_node.is_primary_node = true
  cur_node:split("up", core.title_view, {y = true})
  cur_node = cur_node.b
  cur_node:split("up", core.nag_view, {y = true})
  cur_node = cur_node.b
  cur_node = cur_node:split("down", core.command_view, {y = true})
  cur_node = cur_node:split("down", core.status_view, {y = true})

  command.add_defaults()
  local plugins_success, plugins_refuse_list = core.load_plugins()

  do
    local pdir, pname = project_dir_abs:match("(.*)[/\\\\](.*)")
    core.log("Opening project %q from directory %s", pname, pdir)
  end

  -- We add the project directory now because the project's module is loaded.
  core.add_project_directory(project_dir_abs)

  -- We assume we have just a single project directory here. Now that StatusView
  -- is there show max files warning if needed.
  if core.project_directories[1].files_limit then
    show_max_files_warning(core.project_directories[1])
  end

  for _, filename in ipairs(files) do
    core.root_view:open_doc(core.open_doc(filename))
  end

  if delayed_error then
    core.error(delayed_error)
  end

  if not plugins_success or got_user_error or got_project_error then
    command.perform("core:open-log")
  end

  configure_borderless_window()

  if #plugins_refuse_list.userdir.plugins > 0 or #plugins_refuse_list.datadir.plugins > 0 then
    local opt = {
      { font = style.font, text = "Exit", default_no = true },
      { font = style.font, text = "Continue" , default_yes = true }
    }
    local msg = {}
    for _, entry in pairs(plugins_refuse_list) do
      if #entry.plugins > 0 then
        msg[#msg + 1] = string.format("Plugins from directory \"%s\":\n%s", common.home_encode(entry.dir), table.concat(entry.plugins, "\n"))
      end
    end
    core.nag_view:show(
      "Refused Plugins",
      string.format(
        "Some plugins are not loaded due to version mismatch.\n\n%s.\n\n" ..
        "Please download a recent version from https://github.com/lite-xl/lite-xl-plugins.",
        table.concat(msg, ".\n\n")),
      opt, function(item)
        if item.text == "Exit" then os.exit(1) end
      end)
  end

  add_config_files_hooks()
end


function core.confirm_close_docs(docs, close_fn, ...)
  local dirty_count = 0
  local dirty_name
  for _, doc in ipairs(docs or core.docs) do
    if doc:is_dirty() then
      dirty_count = dirty_count + 1
      dirty_name = doc:get_name()
    end
  end
  if dirty_count > 0 then
    local text
    if dirty_count == 1 then
      text = string.format("\"%s\" has unsaved changes. Quit anyway?", dirty_name)
    else
      text = string.format("%d docs have unsaved changes. Quit anyway?", dirty_count)
    end
    local args = {...}
    local opt = {
      { font = style.font, text = "Yes", default_yes = true },
      { font = style.font, text = "No" , default_no = true }
    }
    core.nag_view:show("Unsaved Changes", text, opt, function(item)
      if item.text == "Yes" then close_fn(table.unpack(args)) end
    end)
  else
    close_fn(...)
  end
end

local temp_uid = math.floor(system.get_time() * 1000) % 0xffffffff
local temp_file_prefix = string.format(".lite_temp_%08x", tonumber(temp_uid))
local temp_file_counter = 0

local function delete_temp_files()
  for _, filename in ipairs(system.list_dir(EXEDIR)) do
    if filename:find(temp_file_prefix, 1, true) == 1 then
      os.remove(EXEDIR .. PATHSEP .. filename)
    end
  end
end

function core.temp_filename(ext)
  temp_file_counter = temp_file_counter + 1
  return USERDIR .. PATHSEP .. temp_file_prefix
      .. string.format("%06x", temp_file_counter) .. (ext or "")
end

-- override to perform an operation before quitting or entering the
-- current project
do
  local do_nothing = function() end
  core.on_quit_project = do_nothing
  core.on_enter_project = do_nothing
end


local function quit_with_function(quit_fn, force)
  if force then
    delete_temp_files()
    core.on_quit_project()
    save_session()
    quit_fn()
  else
    core.confirm_close_docs(core.docs, quit_with_function, quit_fn, true)
  end
end

function core.quit(force)
  quit_with_function(function() core.quit_request = true end, force)
end


function core.restart()
  quit_with_function(function() core.restart_request = true end)
end


local function check_plugin_version(filename)
  local info = system.get_file_info(filename)
  if info ~= nil and info.type == "dir" then
    filename = filename .. "/init.lua"
    info = system.get_file_info(filename)
  end
  if not info or not filename:match("%.lua$") then return false end
  local f = io.open(filename, "r")
  if not f then return false end
  local version_match = false
  for line in f:lines() do
    local mod_version = line:match('%-%-.*%f[%a]mod%-version%s*:%s*(%d+)')
    if mod_version then
      version_match = (mod_version == MOD_VERSION)
      break
    end
    -- The following pattern is used for backward compatibility only
    -- Future versions will look only at the mod-version tag.
    local version = line:match('%-%-%s*lite%-xl%s*(%d+%.%d+)$')
    if version then
      -- we consider the version tag 2.0 equivalent to mod-version:2
      version_match = (version == '2.0' and MOD_VERSION == "2")
      break
    end
  end
  f:close()
  return true, version_match
end


function core.load_plugins()
  local no_errors = true
  local refused_list = {
    userdir = {dir = USERDIR, plugins = {}},
    datadir = {dir = DATADIR, plugins = {}},
  }
  local files, ordered = {}, {}
  for _, root_dir in ipairs {DATADIR, USERDIR} do
    local plugin_dir = root_dir .. "/plugins"
    for _, filename in ipairs(system.list_dir(plugin_dir) or {}) do
      if not files[filename] then table.insert(ordered, filename) end
      files[filename] = plugin_dir -- user plugins will always replace system plugins
    end
  end
  table.sort(ordered)

  for _, filename in ipairs(ordered) do
    local plugin_dir, basename = files[filename], filename:match("(.-)%.lua$") or filename
    local is_lua_file, version_match = check_plugin_version(plugin_dir .. '/' .. filename)
    if is_lua_file then
      if not version_match then
        core.log_quiet("Version mismatch for plugin %q from %s", basename, plugin_dir)
        local list = refused_list[plugin_dir:find(USERDIR, 1, true) == 1 and 'userdir' or 'datadir'].plugins
        table.insert(list, filename)
      end
      if version_match and config.plugins[basename] ~= false then
        local ok = core.try(require, "plugins." .. basename)
        if ok then core.log_quiet("Loaded plugin %q from %s", basename, plugin_dir) end
        if not ok then
          no_errors = false
        end
      end
    end
  end
  return no_errors, refused_list
end


function core.load_project_module()
  local filename = ".lite_project.lua"
  if system.get_file_info(filename) then
    return core.try(function()
      local fn, err = loadfile(filename)
      if not fn then error("Error when loading project module:\n\t" .. err) end
      fn()
      core.log_quiet("Loaded project module")
    end)
  end
  return true
end


function core.reload_module(name)
  local old = package.loaded[name]
  package.loaded[name] = nil
  local new = require(name)
  if type(old) == "table" then
    for k, v in pairs(new) do old[k] = v end
    package.loaded[name] = old
  end
end


function core.set_visited(filename)
  for i = 1, #core.visited_files do
    if core.visited_files[i] == filename then
      table.remove(core.visited_files, i)
      break
    end
  end
  table.insert(core.visited_files, 1, filename)
end


function core.set_active_view(view)
  assert(view, "Tried to set active view to nil")
  if view ~= core.active_view then
    if core.active_view and core.active_view.force_focus then
      core.next_active_view = view
      return
    end
    core.next_active_view = nil
    if view.doc and view.doc.filename then
      core.set_visited(view.doc.filename)
    end
    core.last_active_view = core.active_view
    core.active_view = view
  end
end


function core.show_title_bar(show)
  core.title_view.visible = show
end


function core.add_thread(f, weak_ref, ...)
  local key = weak_ref or #core.threads + 1
  local args = {...}
  local fn = function() return core.try(f, table.unpack(args)) end
  core.threads[key] = { cr = coroutine.create(fn), wake = 0 }
  return key
end


function core.push_clip_rect(x, y, w, h)
  local x2, y2, w2, h2 = table.unpack(core.clip_rect_stack[#core.clip_rect_stack])
  local r, b, r2, b2 = x+w, y+h, x2+w2, y2+h2
  x, y = math.max(x, x2), math.max(y, y2)
  b, r = math.min(b, b2), math.min(r, r2)
  w, h = r-x, b-y
  table.insert(core.clip_rect_stack, { x, y, w, h })
  renderer.set_clip_rect(x, y, w, h)
end


function core.pop_clip_rect()
  table.remove(core.clip_rect_stack)
  local x, y, w, h = table.unpack(core.clip_rect_stack[#core.clip_rect_stack])
  renderer.set_clip_rect(x, y, w, h)
end


function core.normalize_to_project_dir(filename)
  filename = common.normalize_path(filename)
  if common.path_belongs_to(filename, core.project_dir) then
    filename = common.relative_path(core.project_dir, filename)
  end
  return filename
end


-- The function below works like system.absolute_path except it
-- doesn't fail if the file does not exist. We consider that the
-- current dir is core.project_dir so relative filename are considered
-- to be in core.project_dir.
-- Please note that .. or . in the filename are not taken into account.
-- This function should get only filenames normalized using
-- common.normalize_path function.
function core.project_absolute_path(filename)
  if filename:match('^%a:\\') or filename:find('/', 1, true) == 1 then
    return filename
  else
    return core.project_dir .. PATHSEP .. filename
  end
end


function core.open_doc(filename)
  local new_file = not filename or not system.get_file_info(filename)
  local abs_filename
  if filename then
    -- normalize filename and set absolute filename then
    -- try to find existing doc for filename
    filename = core.normalize_to_project_dir(filename)
    abs_filename = core.project_absolute_path(filename)
    for _, doc in ipairs(core.docs) do
      if doc.abs_filename and abs_filename == doc.abs_filename then
        return doc
      end
    end
  end
  -- no existing doc for filename; create new
  local doc = Doc(filename, abs_filename, new_file)
  table.insert(core.docs, doc)
  core.log_quiet(filename and "Opened doc \"%s\"" or "Opened new doc", filename)
  return doc
end


function core.get_views_referencing_doc(doc)
  local res = {}
  local views = core.root_view.root_node:get_children()
  for _, view in ipairs(views) do
    if view.doc == doc then table.insert(res, view) end
  end
  return res
end


local function log(level, show, fmt, ...)
  local text = string.format(fmt, ...)
  if show then
    local s = style.log[level]
    core.status_view:show_message(s.icon, s.color, text)
  end

  local info = debug.getinfo(2, "Sl")
  local at = string.format("%s:%d", info.short_src, info.currentline)
  local item = {
    level = level,
    text = text,
    time = os.time(),
    at = at
  }
  table.insert(core.log_items, item)
  if #core.log_items > config.max_log_items then
    table.remove(core.log_items, 1)
  end
  return item
end


function core.log(...)
  return log("INFO", true, ...)
end


function core.log_quiet(...)
  return log("INFO", false, ...)
end


function core.error(...)
  return log("ERROR", true, ...)
end


function core.get_log(i)
  if i == nil then
    local r = {}
    for _, item in ipairs(core.log_items) do
      table.insert(r, core.get_log(item))
    end
    return table.concat(r, "\n")
  end
  local item = type(i) == "number" and core.log_items[i] or i
  local text = string.format("%s [%s] %s at %s", os.date(nil, item.time), item.level, item.text, item.at)
  if item.info then
    text = string.format("%s\n%s\n", text, item.info)
  end
  return text
end


function core.try(fn, ...)
  local err
  local ok, res = xpcall(fn, function(msg)
    local item = core.error("%s", msg)
    item.info = debug.traceback(nil, 2):gsub("\t", "")
    err = msg
  end, ...)
  if ok then
    return true, res
  end
  return false, err
end

local scheduled_rescan = {}

function core.has_pending_rescan()
  for _ in pairs(scheduled_rescan) do
    return true
  end
end

function core.on_event(type, ...)
  local did_keymap = false
  if type == "textinput" then
    core.root_view:on_text_input(...)
  elseif type == "keypressed" then
    did_keymap = keymap.on_key_pressed(...)
  elseif type == "keyreleased" then
    keymap.on_key_released(...)
  elseif type == "mousemoved" then
    core.root_view:on_mouse_moved(...)
  elseif type == "mousepressed" then
    if not core.root_view:on_mouse_pressed(...) then
      did_keymap = keymap.on_mouse_pressed(...)
    end
  elseif type == "mousereleased" then
    core.root_view:on_mouse_released(...)
  elseif type == "mousewheel" then
    if not core.root_view:on_mouse_wheel(...) then
      did_keymap = keymap.on_mouse_wheel(...)
    end
  elseif type == "resized" then
    core.window_mode = system.get_window_mode()
  elseif type == "minimized" or type == "maximized" or type == "restored" then
    core.window_mode = type == "restored" and "normal" or type
  elseif type == "filedropped" then
    if not core.root_view:on_file_dropped(...) then
      local filename, mx, my = ...
      local info = system.get_file_info(filename)
      if info and info.type == "dir" then
        system.exec(string.format("%q %q", EXEFILE, filename))
      else
        local ok, doc = core.try(core.open_doc, filename)
        if ok then
          local node = core.root_view.root_node:get_child_overlapping_point(mx, my)
          node:set_active_view(node.active_view)
          core.root_view:open_doc(doc)
        end
      end
    end
  elseif type == "focuslost" then
    core.root_view:on_focus_lost(...)
  elseif type == "quit" then
    core.quit()
  end
  return did_keymap
end


local function get_title_filename(view)
  local doc_filename = view.get_filename and view:get_filename() or view:get_name()
  return (doc_filename ~= "---") and doc_filename or ""
end


function core.compose_window_title(title)
  return title == "" and "Lite XL" or title .. " - Lite XL"
end


function core.step()
  -- handle events
  local did_keymap = false

  for type, a,b,c,d in system.poll_event do
    if type == "textinput" and did_keymap then
      did_keymap = false
    elseif type == "mousemoved" then
      core.try(core.on_event, type, a, b, c, d)
    else
      local _, res = core.try(core.on_event, type, a, b, c, d)
      did_keymap = res or did_keymap
    end
    core.redraw = true
  end

  local width, height = renderer.get_size()

  -- update
  core.root_view.size.x, core.root_view.size.y = width, height
  core.root_view:update()
  if not core.redraw then return false end
  core.redraw = false

  -- close unreferenced docs
  for i = #core.docs, 1, -1 do
    local doc = core.docs[i]
    if #core.get_views_referencing_doc(doc) == 0 then
      table.remove(core.docs, i)
      doc:on_close()
    end
  end

  -- update window title
  local current_title = get_title_filename(core.active_view)
  if current_title ~= core.window_title then
    system.set_window_title(core.compose_window_title(current_title))
    core.window_title = current_title
  end

  -- draw
  renderer.begin_frame()
  core.clip_rect_stack[1] = { 0, 0, width, height }
  renderer.set_clip_rect(table.unpack(core.clip_rect_stack[1]))
  core.root_view:draw()
  renderer.end_frame()
  return true
end


local run_threads = coroutine.wrap(function()
  while true do
    local max_time = 1 / config.fps - 0.004
    local need_more_work = false

    for k, thread in pairs(core.threads) do
      -- run thread
      if thread.wake < system.get_time() then
        local _, wait = assert(coroutine.resume(thread.cr))
        if coroutine.status(thread.cr) == "dead" then
          if type(k) == "number" then
            table.remove(core.threads, k)
          else
            core.threads[k] = nil
          end
        elseif wait then
          thread.wake = system.get_time() + wait
        else
          need_more_work = true
        end
      end

      -- stop running threads if we're about to hit the end of frame
      if system.get_time() - core.frame_start > max_time then
        coroutine.yield(true)
      end
    end

    if not need_more_work then coroutine.yield(false) end
  end
end)


function core.run()
  local idle_iterations = 0
  while true do
    core.frame_start = system.get_time()
    local did_redraw = core.step()
    local need_more_work = run_threads() or core.has_pending_rescan()
    if core.restart_request or core.quit_request then break end
    if not did_redraw and not need_more_work then
      idle_iterations = idle_iterations + 1
      -- do not wait of events at idle_iterations = 1 to give a chance at core.step to run
      -- and set "redraw" flag.
      if idle_iterations > 1 then
        if system.window_has_focus() then
          -- keep running even with no events to make the cursor blinks
          local t = system.get_time() - core.blink_start
          local h = config.blink_period / 2
          local dt = math.ceil(t / h) * h - t
          system.wait_event(dt + 1 / config.fps)
        else
          system.wait_event()
        end
      end
    else
      idle_iterations = 0
      local elapsed = system.get_time() - core.frame_start
      system.sleep(math.max(0, 1 / config.fps - elapsed))
    end
  end
end


function core.blink_reset()
  core.blink_start = system.get_time()
end


function core.request_cursor(value)
  core.cursor_change_req = value
end


function core.on_error(err)
  -- write error to file
  local fp = io.open(USERDIR .. "/error.txt", "wb")
  fp:write("Error: " .. tostring(err) .. "\n")
  fp:write(debug.traceback(nil, 4) .. "\n")
  fp:close()
  -- save copy of all unsaved documents
  for _, doc in ipairs(core.docs) do
    if doc:is_dirty() and doc.filename then
      doc:save(doc.filename .. "~")
    end
  end
end


return core