GeanyLua: get selected filename

-- Get selected filename
-- 2018.10.16
--
-- Based on "on_menu_open_selected_file1_activate()" (Ctrl+Shift+O) and "document_open_file_full()"

local function path_is_absolute(p)
  if (geany.dirsep == '\\') then
    if (string.match(string.sub(p, 1, 3), '[A-Za-z]:[\\\/]') ~= nil) then
      return true;
    end
  else
    if (string.sub(p, 1, 1) == geany.dirsep) then return true end;
  end
  return false;
end

local function file_is_exists(p)
  local f = geany.stat(p);
  if (f ~= nil) then
    if (f.type == 'r') then return true end;
  end
  return false;
end

local function  tidy_path(fp)
  local c1, c2, ii, fd, td
  -- Remove relative junk
  if (geany.dirsep == '\\') then
    fp = string.gsub(fp, '/', geany.dirsep);
  end
  -- Replace "/./" and "//"
  fp = string.gsub(fp, geany.dirsep .. '%.' .. geany.dirsep, geany.dirsep);
  fp = string.gsub(fp, geany.dirsep .. geany.dirsep, geany.dirsep);
  -- Replace "/../"
  while true do
    c1 = string.find(fp, geany.dirsep .. '..' .. geany.dirsep, 1, true);
    if (c1 == nil) then break end;
    if (c1 <= 4) then return nil end; -- Bad path
    fd = string.sub(fp, 1, c1 - 1);
    ii = 1;
    while true do
      -- Search for last "/" before found "/../"
      c2 = string.find(fd, geany.dirsep, ii, true);
      if (c2 == nil) then
        if (ii == 1) then
          return nil; -- Bad path
        else
          break;
        end
      end
      ii = c2 + 1;
    end
    fd = string.sub(fd, 1, ii - 2);
    td = string.sub(fp, c1 + 4, -1);
    fp = string.gsub(fd .. geany.dirsep .. td, geany.dirsep .. geany.dirsep, geany.dirsep);
  end
  return fp;
end

local wc = geany.wordchars
local sel = geany.selection()
local ai, fn, pn, tm

if (sel == nil) then return end;
if (sel == '') then
  if (geany.dirsep == '\\') then
    geany.wordchars = wc .. './-\\:'; --Win
  elseif (geany.dirsep == '/') then
    geany.wordchars = wc .. './-'; --Unix
  else
    geany.message('Where are you?');
    return;
  end
  sel = geany.word();
  if (string.len(sel) == 0) then return end;
end
if path_is_absolute(sel) then
  fn = sel;
else
  -- Relative filename, add the path of the current file
  tm = geany.filename();
  if (tm ~= nil) then
    pn = geany.dirname(tm);
  else
    pn = geany.wkdir();
  end
  fn = pn .. geany.dirsep .. sel;
  if not file_is_exists(fn) then
    -- Try the project's base path
    ai = geany.appinfo();
    if (ai.project ~= nil) then
      if path_is_absolute(ai.project.base) then
        pn = ai.project.base;
      else
        -- Build path out of project file name's dir and base path
        tm = geany.dirname(ai.project.file);
        if (ai.project.base == './') or (ai.project.base == '.\\') then
          pn = tm;
        else
          pn = tm .. geany.dirsep .. ai.project.base;
        end
      end
      fn = pn .. geany.dirsep .. sel;
      if (geany.dirsep == '/') then
        if not file_is_exists(fn) then fn = '/usr/local/include/' .. sel end;
        if not file_is_exists(fn) then fn = '/usr/include/' .. sel end;
      end
    end
  end
end
fn = tidy_path(fn);
if (fn ~= nil) and (file_is_exists(fn)) then
  geany.message('File:\n"' .. fn .. '"');
  return;
end
geany.message('File not found!\n"' .. fn .. '"');