add more precise disambiguation of pieces in history

js/chess.js

@@ -79,6 +79,24 @@ function boardPut(board, where, side, piece){
    board[side][row] = prefix + piece + suffix;
 }
 
+function movedFrom(board){
+   if (!board || !board.move || !board.move.from) {
+      return null;
+   } else if (board.move.from === 'phantom') {
+      return board.prior.phantom.from;
+   } else {
+      return board.move.from;
+   }
+}
+
+function movedTo(board){
+   if (!board || !board.move || !board.move.to) {
+      return null;
+   } else {
+      return board.move.to;
+   }
+}
+
 function countMoves(board) {
    let n = 0;
    while (board && board.prior) {
@@ -145,6 +163,7 @@ function hasMoved(board, side, where){
 
 function legalMoves(board, side, type, from, canCapture){
    if (board.move && board.move.took === 'k') {
+      /* checkmate, the game is over */
       return [];
    }
 
@@ -236,11 +255,8 @@ function legalMoves(board, side, type, from, canCapture){
                   if (otherBoard && otherBoard.move) {
                      const move = otherBoard.move;
                      if (move.side[0] !== side[0] && move.type === 'p') {
-                        const from =
+                        const from = movedFrom(otherBoard);
-                           (move.from === 'phantom') ?
+                        if (from && from[0] === there[0] && from[1] === forward2[1]) {
-                              otherBoard.prior.phantom.from :
-                              move.from;
-                        if (from[0] === there[0] && from[1] === forward2[1]) {
                            /* en passant */
                            legals.push(there);
                         }
@@ -324,7 +340,7 @@ function movePiece(priorBoard, side, from, to){
       if (otherBoard && otherBoard.move) {
          const move = otherBoard.move;
          if (move.type === 'p' && move.to[0] === to[0] && move.to[1] === actuallyFrom[1]) {
-            const moveFrom = (move.from === 'phantom') ? otherBoard.prior.phantom.from : move.from;
+            const moveFrom = movedFrom(otherBoard);
             if (move.side[0] === other[0] && moveFrom[1] != to[1]) {
                board.move.en_passant = true;
                board.move.took = 'p';
@@ -372,14 +388,21 @@ function movePiece(priorBoard, side, from, to){
    return board;
 }
 
-function findPieces(board, side, type){
+function findPieces(board, side, type, alongside){
    let pieces = [];
+   const other = otherSide(side);
+
+   if (board.phantom && board.phantom.type === type + side[0]) {
+      pieces.push(board.phantom.from);
+   }
 
    for (const row of "12345678") {
       for (const column of "abcdefgh") {
          const here = column + row;
          if (boardGet(board, here, side) === type) {
-            pieces.push(here);
+            if (!alongside || boardGet(board, here, other) === alongside) {
+               pieces.push(here);
+            }
          }
       }
    }
@@ -437,8 +460,10 @@ function renderHistory(currentBoard) {
             piece = move.type === 'p' ? '' : move.type.toUpperCase();
          }
 
-         if (move.from !== 'phantom') {
+         const from = movedFrom(board);
-            const sameKind = findPieces(board.prior, move.side, move.type);
+
+         if (move.from !== 'phantom' || from !== movedTo(board.prior)) {
+            const sameKind = findPieces(board.prior, move.side, move.type, move.alongside || ' ');
             const legalFrom = [];
             let sameFile = 0;  /* column / letter */
             let sameRank = 0;  /* row / number */
@@ -447,24 +472,24 @@ function renderHistory(currentBoard) {
                if (legalMoves(board.prior, move.side, move.type, where, true).includes(move.to)) {
                   legalFrom.push(where);
 
-                  if (where[0] === move.from[0]) {
+                  if (where[0] === from[0]) {
                      sameFile += 1;
                   }
 
-                  if (where[1] === move.from[1]) {
+                  if (where[1] === from[1]) {
                      sameRank += 1;
                   }
                }
             }
 
-            if (legalFrom.length !== 1) {
+            if (legalFrom.length !== 1 || move.en_passant || (move.type === 'p' && move.took)) {
                /* append file, rank, or both to disambiguate */
                if (sameFile === 1) {
-                  piece += move.from[0];
+                  piece += from[0];
                } else if (sameRank === 1) {
-                  piece += move.from[1];
+                  piece += from[1];
                } else {
-                  piece += move.from;
+                  piece += from;
                }
             }
          }