feat(ui): Board component — rotated grid, coloured pieces, highlights, ghosts

src/lib/Board.svelte

@@ -0,0 +1,112 @@
+<script lang="ts">
+  import type { BoardId, Player, Square } from '../engine/types';
+  import type { SelectionHighlight } from '../engine/legality';
+  import { BOARD_ROTATION, BOARD_PLAYERS } from '../engine/boards';
+
+  interface Props {
+    id: BoardId;
+    fen: string;
+    /** Player colours, e.g. { N:'#4a90d9', ... }. */
+    colors: Record<Player, string>;
+    ghosts: Square[];
+    /** Highlight for this board, or null if no piece is grabbed / not active. */
+    highlight: { playable: Square[]; local: Square[]; selected: Square | null } | null;
+    active: boolean;
+    onSquare: (square: Square) => void;
+  }
+
+  let { id, fen, colors, ghosts, highlight, active, onSquare }: Props = $props();
+
+  const FILES = 'abcdefgh';
+  const GLYPH: Record<string, string> = {
+    k: '♚', q: '♛', r: '♜', b: '♝', n: '♞', p: '♟',
+  };
+
+  interface Cell { square: Square; piece: { glyph: string; color: string } | null; }
+
+  let cells = $derived.by<Cell[]>(() => {
+    const placement = fen.split(' ')[0];
+    const white = colors[BOARD_PLAYERS[id].w];
+    const black = colors[BOARD_PLAYERS[id].b];
+    const map: Record<string, { glyph: string; color: string }> = {};
+    placement.split('/').forEach((row, ri) => {
+      const rank = 8 - ri;
+      let file = 0;
+      for (const ch of row) {
+        if (/\d/.test(ch)) { file += Number(ch); continue; }
+        const isWhite = ch === ch.toUpperCase();
+        map[`${FILES[file]}${rank}`] = {
+          glyph: GLYPH[ch.toLowerCase()],
+          color: isWhite ? white : black,
+        };
+        file += 1;
+      }
+    });
+    const out: Cell[] = [];
+    for (let rank = 8; rank >= 1; rank--) {
+      for (let f = 0; f < 8; f++) {
+        const square = `${FILES[f]}${rank}`;
+        out.push({ square, piece: map[square] ?? null });
+      }
+    }
+    return out;
+  });
+
+  function classes(cell: Cell, index: number): string {
+    const dark = (index + Math.floor(index / 8)) % 2 === 1;
+    const hl = highlight;
+    const list = ['sq', dark ? 'dark' : 'light'];
+    if (ghosts.includes(cell.square)) list.push('ghost-sq');
+    if (hl?.playable.includes(cell.square)) list.push(cell.piece ? 'play occ' : 'play');
+    if (hl?.local.includes(cell.square)) list.push('local');
+    if (hl?.selected === cell.square) list.push('selected');
+    return list.join(' ');
+  }
+</script>
+
+<div class="board" class:active style="--rot:{BOARD_ROTATION[id]}deg">
+  {#each cells as cell, i (cell.square)}
+    <button class={classes(cell, i)} onclick={() => onSquare(cell.square)} aria-label={cell.square}>
+      {#if cell.piece}
+        <span class="pc" class:ghost={ghosts.includes(cell.square)}
+              style="color:{cell.piece.color}">{cell.piece.glyph}</span>
+      {/if}
+    </button>
+  {/each}
+</div>
+
+<style>
+  .board {
+    display: grid;
+    grid-template-columns: repeat(8, var(--sq, 34px));
+    grid-template-rows: repeat(8, var(--sq, 34px));
+    transform: rotate(var(--rot));
+    border: 1px solid #20232b;
+    border-radius: 3px;
+  }
+  .board.active { box-shadow: 0 0 0 3px var(--glow, #4a90d9), 0 0 20px 2px var(--glow, #4a90d9); }
+  .sq {
+    position: relative; padding: 0; border: 0; cursor: pointer;
+    display: flex; align-items: center; justify-content: center;
+  }
+  .sq.light { background: #cabf9f; }
+  .sq.dark { background: #7d6f55; }
+  .pc {
+    font-size: calc(var(--sq, 34px) * 0.76); line-height: 1;
+    text-shadow: -1px -1px 0 #15171c, 1px -1px 0 #15171c,
+                 -1px 1px 0 #15171c, 1px 1px 0 #15171c;
+  }
+  .pc.ghost { opacity: 0.42; }
+  .ghost-sq { outline: 2px dashed #888; outline-offset: -2px; }
+  .sq.play::after, .sq.local::after {
+    content: ''; position: absolute; border-radius: 50%;
+    width: 32%; height: 32%;
+  }
+  .sq.play::after { background: #46c24f; box-shadow: 0 0 7px #46c24f; }
+  .sq.play.occ::after {
+    width: 84%; height: 84%; background: transparent;
+    border: 3px solid #46c24f; box-shadow: 0 0 7px #46c24f;
+  }
+  .sq.local::after { background: transparent; border: 2px dashed #9aa0aa; }
+  .sq.selected { outline: 3px solid #3fd9d9; outline-offset: -3px; }
+</style>