Add a chessboard field

Alright, here's my first (partial) code review.

+        $board = chessboard_parse_fen($item['fen']);
+        $item['value'] = implode('/', $board['board']);
+        $item = chessboard_process_chessboard_notation($item, $settings);
+        $items = array($item);
+        $element[$delta] = _chessboard_filter_formatter_view($items);

That last line introduces nasty chessboard_filter.module coupling.
And are we not parsing the piece placement, then undoing that parsing, then parsing it again but even more granular, then have it stuffed into a render array? Probably best to build that render array as quickly and directly as possible.

+/**
+ * Implements hook_field_is_empty().
+ */
+function chessboard_field_is_empty($item, $field) {
+  return empty($item['fen']);
+}

Probably better to implement it like this: link_field_is_empty().

In general, chessboard can learn from what link, email and text are doing with fields.

+  // Parse the board.
+  $rows = explode('/', $field[0]);
+  if (count($rows) != 8) {
+    return FALSE;
+  }
+  $rows = array_reverse($rows);

Why the reverse, what's happening here? Might need an inline comment.

At some point we'll have to add a test.

Last but not least:
I feel we really should add a caption. See also #101068: Caption option would be nice. Also, as the title indicates, we should investigate storing the chessboard in multiple columns instead of just string notation.

Alright, we'll go for the simplest feature set and implementation for now. I want a field in next mostly to help test and improve the overall architectural design. So, what I need is:

• just the piece placement
• just a standard 8x8 board (\Drupal\chessboard\PiecePlacement is in now.)
• a char(64) for storage
• an implementation of hook_field_load() for (cached) processing of the loaded value
• Let's not use _chessboard_filter_process_chessboard_notation() here. Instead we can inline the few lines that we need from that function body.

Also, I would like to not remove \Drupal\chessboard_filter\PiecePlacement.
Finally, I'm very, very happy to see Doxygen improvements, but I'd like to keep the unrelated changes outside of this patch and upcoming commit.

@kenneth.venken, do you still want to work on this? If you can do the above, I'll commit ASAP. (You can leave the test for me to do if you want.)

One more thing. Let's follow core's example and move the field code to an include file. We'll just do a require_once() at the top of the module file. This will also make it easier to keep 8.x-2.x and 7.x-2.x in sync. My plan is to commit this, then forward port to 8.x-2.x than port new classes back to 7.x-2.x.

an implementation of hook_field_load() for (cached) processing of the loaded value

My original intention was to build the pieces array or a PiecePlacement object in this hook, assuming that every field formatter is going to need that structure. But let's discuss wether it's worth the trouble.

a char(64) for storage

My idea is to store a string of length 64 with any empty square represented as '-', which makes everything so much simpler. (Which is also the way we have them when preparing for rendering). When building the widget we can use the #process property to reference a chessboard_form_process_piece_placement() callback function to process the data to normal FEN/ EPD piece placement syntax, no?

When building the widget we can use the #process property to reference a chessboard_form_process_piece_placement() callback function to process the data to normal FEN/ EPD piece placement syntax, no?

Hm, is there any use for a #process property if we're just computing the initial form element default value? I'll stop spamming the issue with ideas now. It's code that we need.

Re-rolled and cleaned up #11, temporarily re-introducing the dependency on _chessboard_filter_process_chessboard_notation(). (To fix that we can inline the few lines that we need from that function body.)

Implemented most of the changes mentioned earlier. Right now the widget only understands the '-'-syntax for empty squares.

Moved the code to chessboard.field.inc.

Now with include file loading.

Reroll for #1887698: Implement 8x8 board handling.

#22: chessboard-add-a-chessboard-field-1402020-22.patch queued for re-testing.

22: chessboard-add-a-chessboard-field-1402020-22.patch queued for re-testing.

EDIT: uploaded the wrong patch with the correct interdiff... (Regarding chessboard_field_schema().)
We're not storing FEN, so changed the patch to reflect this.

The default formatter is now the simple and direct piece placement format. E.g., rnbqkbnrpppppppp--------------------------------PPPPPPPPRNBQKBNR is formatted as

rnbqkbnr
pppppppp
--------
--------
--------
--------
PPPPPPPP
RNBQKBNR

With pre element tags we don't want nl2br()...

A little cleaning up.

Renamed widget and formatter to chessboard_default/ chessboard_simple plus some minor changes.

And a D8 patch.

Added Regex constraint. Changed Length constraint.

Core does not expose the Symfony Regex constraint (yet)...

Implemented isEmpty().

Pushed #36 to 8.x-2.x. Moving to 7.x-2.x.

Removed the index.

Pushed #38 to 7.x-2.x.

Time to start work on widgets and formatters!
Many thanks to @kenneth.venken for helping to drive this home.