Pagination problem

I can't work out the algorithm for a pager I want to use. I've been struggling with this for a few days now and need some help, I don't even have a good strategy.


There are two groups, start and end. I want to represent missing pages with ... and to supply the minimum no of adjacent pages there should always be (where possible).

the first two and last two pages should always be shown
[n] = current page
... is attached to end, should only appear when there are missing pages

The best way to describe it is by showing expected output


total_pages = 6
adjacent_pages = 1
[1] 2 ... 5 6
1 [2] 3 ... 5 6
1 2 [3] 4 5 6
1 2 3 [4] 5 6
1 2 ... 4 [5] 6
1 2 ... 5 [6]

total_pages = 6
adjacent_pages = 2
[1] 2 3 ... 5 6
1 [2] 3 4 5 6
1 2 [3] 4 5 6
1 2 3 [4] 5 6
1 2 3 4 [5] 6
1 2 ... 4 5 [6]

total_pages = 7
adjacent_pages = 2
[1] 2 3 ... 6 7
1 [2] 3 4 ... 6 7
1 2 [3] 4 5 6 7
1 2 3 [4] 5 6 7
1 2 3 4 [5] 6 7
1 2 ... 4 5 [6] 7
1 2 ... 5 6 [7]


Ideally I would also like to have a middle section as well eg

total_pages = 9
adjacent_pages = 1
1 2 3 [4] 5 ... 8 9 (... attached to end group)
1 2 ... 4 [5] 6 ... 8 9 (first ... attached to middle group)
1 2 ... 5 [6] 7 8 9 (... attached to end group)

I can try to give you some pointers.
Basically, you should iterate over all pages, and for each page, reach a decision whether you should show it's number or not.
If you decided that you shouldn't show a certain page x, then remember that you might decide not to show page x+1 as well - in that case '...' will stand for both pages (or for some k following pages).
Pseudo code should be something like:

Code:

---

PROCEDURE PRINT_PAGINATION(input N = total number of pages, n = current page)
    FOR i <-- 1 to N, DO
      IF SHOULD_SHOW( i ), THEN
          PRINT( i )
          PRINT( " " ) //print 'space'     
      ELSE //we shouldn't show page i - now, when should we print "... " ?!?
          IF NOT SHOULD_SHOW( i-1 ), THEN
              PRINT( "... ")
          END IF
      END IF
    END FOR
END PROCEDURE

---

Please try to understand why the pseudo code above will work.
You should still figure out by yourself how to write the SHOULD_SHOW function.

Regards,
Zachm