Add PGN export and a Copy PGN button for finished games

- Record moves in standard algebraic notation (GameState.SanHistory), built at
  move time in ChessService (captures, disambiguation, castling, promotion,
  en passant, and the check/mate suffix)
- Add PgnExporter.ToPgn (seven-tag header + movetext + result) and a
  GET /api/chess/{gameId}/pgn endpoint
- Show a Copy PGN button when a game ends on both the play and watch pages,
  prefetching the PGN so it works during the post-game cleanup window

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

JoshHeaps.Net/wwwroot/js/ChessScripts/ChessAPI.js

@@ -14,6 +14,12 @@ const ChessAPI = {
         return await response.json();
     },
 
+    async getPgn(gameId) {
+        const response = await fetch(`/api/chess/${gameId}/pgn`);
+        if (!response.ok) throw new Error("PGN unavailable");
+        return await response.text();
+    },
+
     async forfeit(gameId, playerId) {
         await fetch("/api/chess/forfeit", {
             method: "POST",
@@ -115,6 +121,7 @@ const ChessAPI = {
             }
 
             if (gameOver) {
+                showCopyPgn(GameState.currentGameId);
                 await ChessSignalR.leaveGame();
             }
         }, 500);

JoshHeaps.Net/wwwroot/js/ChessScripts/ChessSignalR.js

@@ -46,6 +46,7 @@ const ChessSignalR = {
         if (reason === "forfeit")
             alert(youWon ? "🏳️ Your opponent forfeited — you win!" : "🏳️ You forfeited this game.");
 
+        showCopyPgn(gameId);
         await this.leaveGame();
     },
 

JoshHeaps.Net/wwwroot/js/ChessScripts/Spectate.js

@@ -1,6 +1,7 @@
 const Spectate = {
     connection: null,
     games: new Map(),   // gameId -> { isVsComputer, isComputerVsComputer, result }
+    pgns: new Map(),    // gameId -> PGN text (prefetched when a game finishes)
 
     pieceTypeNames: ["Pawn", "Rook", "Knight", "Bishop", "Queen", "King"],
 
@@ -106,6 +107,7 @@ const Spectate = {
 
     async removeGame(gameId) {
         this.games.delete(gameId);
+        this.pgns.delete(gameId);
         document.getElementById(`card-${gameId}`)?.remove();
         await this.connection.invoke("LeaveWebsocketGroup", gameId).catch(() => { });
     },
@@ -207,6 +209,7 @@ const Spectate = {
 
         if (!text) {
             banner?.remove();
+            card.querySelector(".copyPgnBtn")?.remove();
             card.classList.remove("over");
             return;
         }
@@ -219,6 +222,47 @@ const Spectate = {
 
         banner.textContent = text;
         card.classList.add("over");
+        this.addCopyPgn(gameId, card);
+    },
+
+    addCopyPgn(gameId, card) {
+        if (card.querySelector(".copyPgnBtn")) return;
+
+        const btn = document.createElement("button");
+        btn.className = "copyPgnBtn";
+        btn.textContent = "Copy PGN";
+        btn.onclick = (event) => { event.stopPropagation(); this.copyPgn(gameId); };
+        card.appendChild(btn);
+
+        // Prefetch now (while the game is still in memory) so copy works during the
+        // brief window before the finished game is cleaned up.
+        fetch(`/api/chess/${gameId}/pgn`)
+            .then(r => r.ok ? r.text() : null)
+            .then(t => { if (t) this.pgns.set(gameId, t); })
+            .catch(() => { });
+    },
+
+    async copyPgn(gameId) {
+        let pgn = this.pgns.get(gameId);
+
+        if (!pgn) {
+            try {
+                const r = await fetch(`/api/chess/${gameId}/pgn`);
+                if (r.ok) pgn = await r.text();
+            } catch { /* ignore */ }
+        }
+
+        if (!pgn) {
+            alert("PGN is no longer available for this game.");
+            return;
+        }
+
+        try {
+            await navigator.clipboard.writeText(pgn);
+            alert("📋 PGN copied to clipboard!");
+        } catch {
+            alert("Couldn't access the clipboard. Here's the PGN:\n\n" + pgn);
+        }
     },
 
     enterFullscreen(gameId) {

JoshHeaps.Net/wwwroot/js/ChessScripts/chessMain.js

@@ -1,3 +1,35 @@
+let lastPgn = null;
+
+async function showCopyPgn(gameId) {
+    try {
+        lastPgn = await ChessAPI.getPgn(gameId);
+        const btn = document.getElementById("copyPgnBtn");
+        if (btn) btn.style.display = "";
+    } catch (err) {
+        console.warn("Could not load PGN.", err);
+    }
+}
+
+async function copyPgn() {
+    if (!lastPgn) return;
+
+    try {
+        await navigator.clipboard.writeText(lastPgn);
+        alert("📋 PGN copied to clipboard!");
+    } catch {
+        alert("Couldn't access the clipboard. Here's the PGN:\n\n" + lastPgn);
+    }
+}
+
+function resetCopyPgn() {
+    lastPgn = null;
+    const btn = document.getElementById("copyPgnBtn");
+    if (btn) btn.style.display = "none";
+}
+
+window.copyPgn = copyPgn;
+window.showCopyPgn = showCopyPgn;
+
 async function forfeitCurrentGame() {
     const gameId = ChessUtils.getCookie("chessGameId");
     const playerId = ChessUtils.getCookie("chessPlayerId");
@@ -14,6 +46,7 @@ async function forfeitCurrentGame() {
 async function startNewGame() {
     await ChessSignalR.stopConnection();
     await forfeitCurrentGame();
+    resetCopyPgn();
 
     try {
         const gameData = await ChessAPI.joinGame();
@@ -40,6 +73,7 @@ async function startNewGame() {
 async function startCPUGame() {
     await ChessSignalR.stopConnection();
     await forfeitCurrentGame();
+    resetCopyPgn();
 
     try {
         const difficulty = await ChessModals.promptDifficulty();