Implemented the compare method, but the sorting is not working

Todo.txt

@@ -4,7 +4,7 @@
 (C) 2011-06-01 Improve syntax file @syntax
 2011-05-30 Map commands to add, rm, ls, pri, depri etc @ftplugin
 2011-05-30 Contact main project for reference
-X 2011-05-31 Stop breaking lines automatically @ftplugin
 X 2011-05-30 Implement filetype detection @ftdetect
 X 2011-05-30 Implement colorized priorities @syntax
 X 2011-05-31 Highlight date, project and context of tasks with no priority @syntax
+X 2011-05-31 Stop breaking lines automatically @ftplugin

ftplugin/todo.vim

@@ -1,57 +1,82 @@
-" Vim Todo.txt plugin
-" Last Change:	2011 Jun 01
-" Maintainer:	Leandro Freitas <freitass@gmail.com>
-" License:	This file is placed in the public domain.
+" File:        todo.txt.vim
+" Description: Todo.txt filetype detection
+" Author:      Leandro Freitas <freitass@gmail.com>
+" Licence:     Vim licence
+" Website:     http://github.com/freitass/todo.txt.vim
+" Version:     0.2
 
-if exists("g:loaded_todo")
-  finish
-endif
+" TODO uncomment
+"if exists("g:loaded_todo")
+"    finish
+"endif
+"let g:loaded_todo = 1
+
+let s:save_cpo = &cpo
+set cpo&vim
 
-" Stop breaking lines automatically
 setlocal textwidth=0
 setlocal wrapmargin=0
 
-"" Vim global plugin for correcting typing mistakes
-"" Last Change:	2000 Oct 15
-"" Maintainer:	Bram Moolenaar <Bram@vim.org>
-"" License:	This file is placed in the public domain.
-"
-"if exists("g:loaded_typecorr")
-"  finish
-"endif
-"let g:loaded_typecorr = 1
-"
-"let s:save_cpo = &cpo
-"set cpo&vim
-"
-"iabbrev teh the
-"iabbrev otehr other
-"iabbrev wnat want
-"iabbrev synchronisation
-"	\ synchronization
-"let s:count = 4
-"
-"if !hasmapto('<Plug>TypecorrAdd')
-"  map <unique> <Leader>a  <Plug>TypecorrAdd
-"endif
-"noremap <unique> <script> <Plug>TypecorrAdd  <SID>Add
-"
-"noremenu <script> Plugin.Add\ Correction      <SID>Add
-"
-"noremap <SID>Add  :call <SID>Add(expand("<cword>"), 1)<CR>
-"
-"function s:Add(from, correct)
-"  let to = input("type the correction for " . a:from . ": ")
-"  exe ":iabbrev " . a:from . " " . to
-"  if a:correct | exe "normal viws\<C-R>\" \b\e" | endif
-"  let s:count = s:count + 1
-"  echo s:count . " corrections now"
-"endfunction
-"
-"if !exists(":Correct")
-"  command -nargs=1  Correct  :call s:Add(<q-args>, 0)
-"endif
-"
-"let &cpo = s:save_cpo
+if !hasmapto('<Plug>TodoSortlines')
+    map <unique> <leader>s <Plug>TodoSortlines
+endif
 
-let g:loaded_todo = 1
+"TODO replace
+"noremap <unique> <script> <Plug>TodoSortlines <SID>SortLines
+noremap <script> <Plug>TodoSortlines <SID>SortLines
+
+noremap <SID>SortLines :call <SID>SortLines()<CR>
+
+function! s:Compare(line1,line2)
+    " Matches a line starting with 'X '.
+    let done_pattern = '\m^X\s\+.*'
+    " Matches a line starting with '(\a) ' where \a is a letter.
+    let priority_pattern = '\m^(\a)\s\+.*'
+    " Matches date YYYY-MM-DD
+    let date_pattern = '\m\d\{4\}-\d\{2\}-\d\{2\}'
+    " Check PRIORITY first.
+    let done_1 = match(a:line1,done_pattern)
+    let done_2 = match(a:line2,done_pattern)
+    if done_1 != done_2
+        " Swap if only the first has been done.
+        return -done_2
+    endif
+    let pri_set_1 = match(a:line1,priority_pattern)
+    let pri_set_2 = match(a:line2,priority_pattern)
+    if pri_set_1 != pri_set_2
+        " Swap if only the second has priority set.
+        return -pri_set_1
+    elseif pri_set_1 >= 0
+        " Swap if the second has higher proprity.
+        return a:line2[1] <? a:line1[1]
+    endif
+    " If the execution reached this code, both tasks have the same priority.
+    " Go for the date, sorting older tasks first.
+    let x1 = match(a:line1,date_pattern)
+    let x2 = match(a:line2,date_pattern)
+    if x1 != x2
+        " Swap if only the second has creation date.
+        return -x1
+    endif
+    if x2 == -1
+        " If none has date, keep the order.
+        return 0
+    endif
+    " Calculate which date should come first
+    let date_1 = a:line1[(x1):(x1+9)]
+    let date_1 = substitute(date_1,"-","","g")
+    let date_2 = a:line2[(x2):(x2+9)]
+    let date_2 = substitute(date_2,"-","","g")
+    return date_1 > date_2
+endfunction
+
+function! s:SortLines()
+    let list_of_lines = getline(0,'$')
+    let sorted_list = sort(copy(list_of_lines),'s:Compare')
+    "%delete
+    for line in sorted_list
+        echo line
+    endfor
+endfunction
+
+let &cpo = s:save_cpo