+/*
+ * validate_fen() is taken from chess.js, which has this license:
+ *
+ * Copyright (c) 2017, Jeff Hlywa (jhlywa@gmail.com)
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ *----------------------------------------------------------------------------*/
+function validate_fen(fen) {
+ var errors = {
+ 0: 'No errors.',
+ 1: 'FEN string must contain six space-delimited fields.',
+ 2: '6th field (move number) must be a positive integer.',
+ 3: '5th field (half move counter) must be a non-negative integer.',
+ 4: '4th field (en-passant square) is invalid.',
+ 5: '3rd field (castling availability) is invalid.',
+ 6: '2nd field (side to move) is invalid.',
+ 7: '1st field (piece positions) does not contain 8 \'/\'-delimited rows.',
+ 8: '1st field (piece positions) is invalid [consecutive numbers].',
+ 9: '1st field (piece positions) is invalid [invalid piece].',
+ 10: '1st field (piece positions) is invalid [row too large].',
+ 11: 'Illegal en-passant square',
+ };
+
+ /* 1st criterion: 6 space-seperated fields? */
+ var tokens = fen.split(/\s+/);
+ if (tokens.length !== 6) {
+ return {valid: false, error_number: 1, error: errors[1]};
+ }
+
+ /* 2nd criterion: move number field is a integer value > 0? */
+ if (isNaN(tokens[5]) || (parseInt(tokens[5], 10) <= 0)) {
+ return {valid: false, error_number: 2, error: errors[2]};
+ }
+
+ /* 3rd criterion: half move counter is an integer >= 0? */
+ if (isNaN(tokens[4]) || (parseInt(tokens[4], 10) < 0)) {
+ return {valid: false, error_number: 3, error: errors[3]};
+ }
+
+ /* 4th criterion: 4th field is a valid e.p.-string? */
+ if (!/^(-|[abcdefgh][36])$/.test(tokens[3])) {
+ return {valid: false, error_number: 4, error: errors[4]};
+ }
+
+ /* 5th criterion: 3th field is a valid castle-string? */
+ if( !/^[C-HK]?[A-FQ]?[c-hk]?[a-fq]?$/.test(tokens[2]) &&
+ tokens[2] !== '-') {
+ return {valid: false, error_number: 5, error: errors[5]};
+ }
+
+ /* 6th criterion: 2nd field is "w" (white) or "b" (black)? */
+ if (!/^(w|b)$/.test(tokens[1])) {
+ return {valid: false, error_number: 6, error: errors[6]};
+ }
+
+ /* 7th criterion: 1st field contains 8 rows? */
+ var rows = tokens[0].split('/');
+ if (rows.length !== 8) {
+ return {valid: false, error_number: 7, error: errors[7]};
+ }
+
+ /* 8th criterion: every row is valid? */
+ for (var i = 0; i < rows.length; i++) {
+ /* check for right sum of fields AND not two numbers in succession */
+ var sum_fields = 0;
+ var previous_was_number = false;
+
+ for (var k = 0; k < rows[i].length; k++) {
+ if (!isNaN(rows[i][k])) {
+ if (previous_was_number) {
+ return {valid: false, error_number: 8, error: errors[8]};
+ }
+ sum_fields += parseInt(rows[i][k], 10);
+ previous_was_number = true;
+ } else {
+ if (!/^[prnbqkPRNBQK]$/.test(rows[i][k])) {
+ return {valid: false, error_number: 9, error: errors[9]};
+ }
+ sum_fields += 1;
+ previous_was_number = false;
+ }
+ }
+ if (sum_fields !== 8) {
+ return {valid: false, error_number: 10, error: errors[10]};
+ }
+ }
+
+ if ((tokens[3][1] == '3' && tokens[1] == 'w') ||
+ (tokens[3][1] == '6' && tokens[1] == 'b')) {
+ return {valid: false, error_number: 11, error: errors[11]};
+ }
+
+ /* everything's okay! */
+ return {valid: true, error_number: 0, error: errors[0]};
+}