ADD: Two level sort function

This commit add the first interesting difference from freitass original
version. It provides a two level sort function which allow the user to sort
the todo by project (or context) then by priority.

TODO: Maybe think about three level sort (project, context, priority) in any
order.

plugin/todo-txt.vim

@@ -0,0 +1,78 @@
+" File:        todo.txt.vim
+" Description: Todo.txt sorting plugin
+" Author:      Leandro Freitas <david@beniamine.net>
+" Licence:     Vim licence
+" Website:     http://github.com/dbeniamine/todo.txt.vim
+" Version:     0.3
+
+" These two variables are parameters for the first and second call to the vim
+" sort function
+"   '' means no flags
+"   '! i' means reverse and ignore case
+"   for more information on flags, see :help sort
+if (! exists("g:Todo_txt_first_level_sort_mode"))
+    let g:Todo_txt_first_level_sort_mode="i"
+endif
+if (! exists("g:Todo_txt_second_level_sort_mode"))
+    let g:Todo_txt_second_level_sort_mode="i"
+endif
+
+" Sort todo by (first) context
+noremap <leader>sc :call Todo_txt_TwoLevelsSort('@')<CR>
+" Sort todo by (first) project
+noremap <leader>sp :call Todo_txt_TwoLevelsSort('+')<CR>
+
+" This is a two level sort designed for todo.txt todo lists
+" At the first level, lines are sorted by the word right after the first
+" occurence of a:symbol, there must be no space between the symbol and the
+" word. Therefore, according to todo.txt syntaxt, if
+"   a:symbol is a '+' it sort by the first project
+"   a:symbol is an '@' it sort by the first context
+" The second level of sort is done direcetly on the line, so according to
+" todo.txt syntax, it means sort by priority
+function! Todo_txt_TwoLevelsSort(symbol)
+    "if the sort modes doesn't start by '!' it must start with a space
+    let l:sortmode=Todo_txt_InsertSpaceIfNeeded(g:Todo_txt_first_level_sort_mode)
+    let l:sortmode2=Todo_txt_InsertSpaceIfNeeded(g:Todo_txt_second_level_sort_mode)
+
+    " Count the number of lines
+    let l:position= getpos(".")
+    execute "silent normal g\<c-g>"
+    if v:statusmsg =~ '--No lines in buffer--'
+        "Empty buffer do nothing
+        return
+    endif
+    let l:linecount=str2nr(split(v:statusmsg)[7])
+
+    " Get all the groups names
+    let l:curline=0
+    let l:groups=[]
+    while l:curline <= l:linecount
+        let l:curproj=strpart(matchstr(getline(l:curline),a:symbol.'\a*'),1)
+        if l:curproj != "" && index(l:groups,l:curproj) == -1
+            let l:groups=add(l:groups , l:curproj)
+        endif
+        let l:curline += 1
+    endwhile
+
+    " Sort by groups
+    execute 'sort'.l:sortmode.' /.\{-}\ze'.a:symbol.'/'
+    for l:p in l:groups
+        execute '/^.\{-}'.a:symbol.l:p.'.*$'
+        normal ma
+        normal G
+        execute '?^.\{-}'.a:symbol.l:p.'.*$'
+        normal mb
+        execute "'a,'b sort".l:sortmode2
+    endfor
+    " Restore the cursor position
+    call setpos('.', position)
+endfunction
+
+function! Todo_txt_InsertSpaceIfNeeded(str)
+    let l:c=strpart(a:str,1,1)
+    if( l:c != '!' && l:c !=' ')
+        return " ".a:str
+    endif
+    retur a:str
+endfunction