+
+define('DB_ORD_MAX', 2000000000);
+
+function db_reposition_respace($table, $field) {
+ $ids = db_get_column($table, 'id', "where $field != 0 order by $field");
+ $c = count($ids);
+ if(!$c) {
+ # should never happen
+ return;
+ }
+ $inc = floor(DB_ORD_MAX / ($c + 1));
+ $cur = $inc;
+ foreach($ids as $id) {
+ db_update($table, $field, $cur, 'where id=%i', $id);
+ $cur += $inc;
+ }
+}
+
+# this function facilitates letting the user manually sort records (with (int) $field != 0)
+#
+# When editing a particular row, give the user a pulldown, with 0 -> first, 1 -> second, etc, and pass this integer to db_reposition (3rd parameter). The value "ignored" can be passed, and the row will be given a sort value of 0 and ignored for all sorting.
+#
+# $pretty is used in error messages to refer to the row, it defaults to whatever you pass for $table.
+
+function db_reposition($table, $row_id, $new_pos, $field = 'ord', $pretty = 'same as $table', $renumbered_already = false) {
+ if($pretty == 'same as $table') {
+ $pretty = $table;
+ }
+
+ if($new_pos === 'ignored') {
+ # not sorted
+ return '0';
+ }
+
+ # strategy: calculate $prev_ord and $next_ord. If there's no space between, renumber and recurse
+ if($new_pos == '0') {
+ $row = db_get_row($table, "id,$field", "where $field != 0 order by $field limit 1");
+ if($row) {
+ list($first_row_id, $first_row_ord) = $row;
+ if($first_row_id == $row_id) {
+ # already first
+ return $first_row_ord;
+ }
+ $next_ord = $first_row_ord;
+ } else {
+ # this is the only row, put it in the middle
+ return '' + floor(DB_ORD_MAX / 2);
+ }
+
+ $prev_ord = 0;
+ } else {
+ $new_pos = format_int_0($new_pos);
+ $rows = db_get_rows($table, "id,$field", "where $field != 0 order by $field limit %i,2", $new_pos - 1);
+ if(!$rows) {
+ message("Sorry, couldn't find the $pretty you asked to put this $pretty after. Putting it first instead.");
+ return db_reposition($table, $row_id, '0', $field, $pretty);
+ } else {
+ list($prev_id, $prev_ord) = $rows[0];
+ if($prev_id == $row_id) {
+ # after self? this shouldn't happen
+ return $prev_ord;
+ }
+ if(count($rows) == 1) {
+ # we should be last
+ $next_ord = DB_ORD_MAX;
+ } else {
+ list($next_id, $next_ord) = $rows[1];
+ if($next_id == $row_id) {
+ # after prev (already there)
+ return $next_ord;
+ }
+ }
+ }
+ }
+ if($prev_ord + 1 == $next_ord || $prev_ord == $next_ord) { # the latter should never happen
+ if($renumbered_already) {
+ message("Programmer error in $pretty ordering code. Please tell your website administrator.");
+ return '' . rand(2, DB_ORD_MAX - 2); # reasonably unlikely to be the same as some other ord
+ }
+ db_reposition_respace($table, $field);
+ return db_reposition($table, $row_id, $new_pos, $field, $pretty, $renumbered_already = true);
+ } else {
+ return $prev_ord + round(($next_ord - $prev_ord) / 2);
+ }
+}