Attempt to clarify installation instructions a little

[vchess.git] / client / src / variants / Xiangqi.js

import { ChessRules } from "@/base_rules";

export class XiangqiRules extends ChessRules {

  static get Options() {
    return null;
  }

  // NOTE (TODO?) scanKings() could be more efficient (in Jangqi too)

  static get Monochrome() {
    return true;
  }

  static get Notoodark() {
    return true;
  }

  static get Lines() {
    let lines = [];
    // Draw all inter-squares lines, shifted:
    for (let i = 0; i < V.size.x; i++)
      lines.push([[i+0.5, 0.5], [i+0.5, V.size.y-0.5]]);
    for (let j = 0; j < V.size.y; j++)
      lines.push([[0.5, j+0.5], [V.size.x-0.5, j+0.5]]);
    // Add palaces:
    lines.push([[0.5, 3.5], [2.5, 5.5]]);
    lines.push([[0.5, 5.5], [2.5, 3.5]]);
    lines.push([[9.5, 3.5], [7.5, 5.5]]);
    lines.push([[9.5, 5.5], [7.5, 3.5]]);
    // Show river:
    lines.push([[4.5, 0.5], [5.5, 8.5]]);
    lines.push([[5.5, 0.5], [4.5, 8.5]]);
    return lines;
  }

  static get HasFlags() {
    return false;
  }

  static get HasEnpassant() {
    return false;
  }

  static get LoseOnRepetition() {
    return true;
  }

  static get ELEPHANT() {
    return "e";
  }

  static get CANNON() {
    return "c";
  }

  static get ADVISOR() {
    return "a";
  }

  static get PIECES() {
    return [V.PAWN, V.ROOK, V.KNIGHT, V.ELEPHANT, V.ADVISOR, V.KING, V.CANNON];
  }

  getPpath(b) {
    return "Xiangqi/" + b;
  }

  static get size() {
    return { x: 10, y: 9};
  }

  getPotentialMovesFrom(sq) {
    let moves = [];
    const piece = this.getPiece(sq[0], sq[1]);
    switch (piece) {
      case V.PAWN:
        moves = this.getPotentialPawnMoves(sq);
        break;
      case V.ROOK:
        moves = super.getPotentialRookMoves(sq);
        break;
      case V.KNIGHT:
        moves = this.getPotentialKnightMoves(sq);
        break;
      case V.ELEPHANT:
        moves = this.getPotentialElephantMoves(sq);
        break;
      case V.ADVISOR:
        moves = this.getPotentialAdvisorMoves(sq);
        break;
      case V.KING:
        moves = this.getPotentialKingMoves(sq);
        break;
      case V.CANNON:
        moves = this.getPotentialCannonMoves(sq);
        break;
    }
    if (piece != V.KING && this.kingPos['w'][1] != this.kingPos['b'][1])
      return moves;
    if (this.kingPos['w'][1] == this.kingPos['b'][1]) {
      const colKing = this.kingPos['w'][1];
      let intercept = 0; //count intercepting pieces
      for (let i = this.kingPos['b'][0] + 1; i < this.kingPos['w'][0]; i++) {
        if (this.board[i][colKing] != V.EMPTY) intercept++;
      }
      if (intercept >= 2) return moves;
      // intercept == 1 (0 is impossible):
      // Any move not removing intercept is OK
      return moves.filter(m => {
        return (
          // From another column?
          m.start.y != colKing ||
          // From behind a king? (including kings themselves!)
          m.start.x <= this.kingPos['b'][0] ||
          m.start.x >= this.kingPos['w'][0] ||
          // Intercept piece moving: must remain in-between
          (
            m.end.y == colKing &&
            m.end.x > this.kingPos['b'][0] &&
            m.end.x < this.kingPos['w'][0]
          )
        );
      });
    }
    // piece == king: check only if move.end.y == enemy king column
    const color = this.getColor(sq[0], sq[1]);
    const oppCol = V.GetOppCol(color);
    // colCheck == -1 if unchecked, 1 if checked and occupied,
    //              0 if checked and clear
    let colCheck = -1;
    return moves.filter(m => {
      if (m.end.y != this.kingPos[oppCol][1]) return true;
      if (colCheck < 0) {
        // Do the check:
        colCheck = 0;
        for (let i = this.kingPos['b'][0] + 1; i < this.kingPos['w'][0]; i++) {
          if (this.board[i][m.end.y] != V.EMPTY) {
            colCheck++;
            break;
          }
        }
        return colCheck == 1;
      }
      // Check already done:
      return colCheck == 1;
    });
  }

  getPotentialPawnMoves([x, y]) {
    const c = this.getColor(x, y);
    const shiftX = (c == 'w' ? -1 : 1);
    const crossedRiver = (c == 'w' && x <= 4 || c == 'b' && x >= 5);
    const lastRank = (c == 'w' && x == 0 || c == 'b' && x == 9);
    let steps = [];
    if (!lastRank) steps.push([shiftX, 0]);
    if (crossedRiver) {
      if (y > 0) steps.push([0, -1]);
      if (y < 9) steps.push([0, 1]);
    }
    return super.getSlideNJumpMoves([x, y], steps, 1);
  }

  knightStepsFromRookStep(step) {
    if (step[0] == 0) return [ [1, 2*step[1]], [-1, 2*step[1]] ];
    return [ [2*step[0], 1], [2*step[0], -1] ];
  }

  getPotentialKnightMoves([x, y]) {
    let steps = [];
    for (let rookStep of ChessRules.steps[V.ROOK]) {
      const [i, j] = [x + rookStep[0], y + rookStep[1]];
      if (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
        Array.prototype.push.apply(steps,
          // These moves might be impossible, but need to be checked:
          this.knightStepsFromRookStep(rookStep));
      }
    }
    return super.getSlideNJumpMoves([x, y], steps, 1);
  }

  getPotentialElephantMoves([x, y]) {
    let steps = [];
    const c = this.getColor(x, y);
    for (let bishopStep of ChessRules.steps[V.BISHOP]) {
      const [i, j] = [x + bishopStep[0], y + bishopStep[1]];
      if (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
        const [newX, newY] = [x + 2*bishopStep[0], y + 2*bishopStep[1]];
        if ((c == 'w' && newX >= 5) || (c == 'b' && newX <= 4))
          // A priori valid (elephant don't cross the river)
          steps.push(bishopStep.map(s => 2*s));
          // "out of board" checks delayed to next method
      }
    }
    return super.getSlideNJumpMoves([x, y], steps, 1);
  }

  getPotentialAdvisorMoves([x, y]) {
    // Diagonal steps inside palace
    const c = this.getColor(x, y);
    if (
      y != 4 ||
      (c == 'w' && x != V.size.x - 2) ||
      (c == 'b' && x != 1)
    ) {
      // In a corner: only one step available
      let step = null;
      const direction = (c == 'w' ? -1 : 1);
      if ((c == 'w' && x == V.size.x - 1) || (c == 'b' && x == 0)) {
        // On first line
        if (y == 3) step = [direction, 1];
        else step = [direction, -1];
      }
      else {
        // On third line
        if (y == 3) step = [-direction, 1];
        else step = [-direction, -1];
      }
      return super.getSlideNJumpMoves([x, y], [step], 1);
    }
    // In the middle of the palace:
    return (
      super.getSlideNJumpMoves([x, y], ChessRules.steps[V.BISHOP], 1)
    );
  }

  getPotentialKingMoves([x, y]) {
    // Orthogonal steps inside palace
    const c = this.getColor(x, y);
    if (
      y != 4 ||
      (c == 'w' && x != V.size.x - 2) ||
      (c == 'b' && x != 1)
    ) {
      // On the edge: only two steps available
      let steps = [];
      if (x < (c == 'w' ? V.size.x - 1 : 2)) steps.push([1, 0]);
      if (x > (c == 'w' ? V.size.x - 3 : 0)) steps.push([-1, 0]);
      if (y > 3) steps.push([0, -1]);
      if (y < 5) steps.push([0, 1]);
      return super.getSlideNJumpMoves([x, y], steps, 1);
    }
    // In the middle of the palace:
    return (
      super.getSlideNJumpMoves([x, y], ChessRules.steps[V.ROOK], 1)
    );
  }

  // NOTE: duplicated from Shako (TODO?)
  getPotentialCannonMoves([x, y]) {
    const oppCol = V.GetOppCol(this.turn);
    let moves = [];
    // Look in every direction until an obstacle (to jump) is met
    for (const step of V.steps[V.ROOK]) {
      let i = x + step[0];
      let j = y + step[1];
      while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
        moves.push(this.getBasicMove([x, y], [i, j]));
        i += step[0];
        j += step[1];
      }
      // Then, search for an enemy
      i += step[0];
      j += step[1];
      while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
        i += step[0];
        j += step[1];
      }
      if (V.OnBoard(i, j) && this.getColor(i, j) == oppCol)
        moves.push(this.getBasicMove([x, y], [i, j]));
    }
    return moves;
  }

  // (King) Never attacked by advisor, since it stays in the palace
  // Also, never attacked by elephants since they don't cross the river.
  isAttacked(sq, color) {
    return (
      this.isAttackedByPawn(sq, color) ||
      super.isAttackedByRook(sq, color) ||
      this.isAttackedByKnight(sq, color) ||
      this.isAttackedByCannon(sq, color)
    );
  }

  isAttackedByPawn([x, y], color) {
    // The pawn necessarily crossed the river (attack on king)
    const shiftX = (color == 'w' ? 1 : -1); //shift from king
    return super.isAttackedBySlideNJump(
      [x, y], color, V.PAWN, [[shiftX, 0], [0, 1], [0, -1]], 1);
  }

  knightStepsFromBishopStep(step) {
    return [ [2*step[0], step[1]], [step[0], 2*step[1]] ];
  }

  isAttackedByKnight([x, y], color) {
    // Check bishop steps: if empty, look continuation knight step
    let steps = [];
    for (let s of ChessRules.steps[V.BISHOP]) {
      const [i, j] = [x + s[0], y + s[1]];
      if (
        V.OnBoard(i, j) &&
        this.board[i][j] == V.EMPTY
      ) {
        Array.prototype.push.apply(steps, this.knightStepsFromBishopStep(s));
      }
    }
    return (
      super.isAttackedBySlideNJump([x, y], color, V.KNIGHT, steps, 1)
    );
  }

  // NOTE: duplicated from Shako (TODO?)
  isAttackedByCannon([x, y], color) {
    // Reversed process: is there an obstacle in line,
    // and a cannon next in the same line?
    for (const step of V.steps[V.ROOK]) {
      let [i, j] = [x+step[0], y+step[1]];
      while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
        i += step[0];
        j += step[1];
      }
      if (V.OnBoard(i, j)) {
        // Keep looking in this direction
        i += step[0];
        j += step[1];
        while (V.OnBoard(i, j) && this.board[i][j] == V.EMPTY) {
          i += step[0];
          j += step[1];
        }
        if (
          V.OnBoard(i, j) &&
          this.getPiece(i, j) == V.CANNON &&
          this.getColor(i, j) == color
        ) {
          return true;
        }
      }
    }
    return false;
  }

  getCurrentScore() {
    if (this.atLeastOneMove()) return "*";
    // Game over
    const color = this.turn;
    // No valid move: I lose!
    return (color == "w" ? "0-1" : "1-0");
  }

  static get VALUES() {
    return {
      p: 1,
      r: 9,
      n: 4,
      e: 2.5,
      a: 2,
      c: 4.5,
      k: 1000
    };
  }

  evalPosition() {
    let evaluation = 0;
    for (let i = 0; i < V.size.x; i++) {
      for (let j = 0; j < V.size.y; j++) {
        if (this.board[i][j] != V.EMPTY) {
          const c = this.getColor(i, j);
          const sign = (c == 'w' ? 1 : -1);
          const piece = this.getPiece(i, j);
          let pieceEval = V.VALUES[this.getPiece(i, j)];
          if (
            piece == V.PAWN &&
            (
              (c == 'w' && i <= 4) ||
              (c == 'b' && i >= 5)
            )
          ) {
            // Pawn crossed the river: higher value
            pieceEval++;
          }
          evaluation += sign * pieceEval;
        }
      }
    }
    return evaluation;
  }

  static get SEARCH_DEPTH() {
    return 2;
  }

  static GenRandInitFen() {
    // No randomization here (TODO?)
    return "rneakaenr/9/1c5c1/p1p1p1p1p/9/9/P1P1P1P1P/1C5C1/9/RNEAKAENR w 0";
  }

  getNotation(move) {
    let notation = super.getNotation(move);
    if (move.vanish.length == 2 && move.vanish[0].p == V.PAWN)
      notation = "P" + notation.substr(1);
    return notation;
  }

};