tic-tac-toe.ts

/**
 * Tic-Tac-Toe extension - demonstrates executionMode: "sequential" on tools.
 *
 * The user plays via /tic-tac-toe (arrow keys + Enter).
 * The agent plays via a single tool `tic_tac_toe` that takes ONE atomic action
 * per call. To play at (r, c) from its cursor (r0, c0) the agent must emit the
 * required move_* and a final `play` as SEPARATE tool_use blocks inside ONE
 * assistant response.
 *
 * Move actions share the agent cursor and have a 300ms delay. Under the
 * default parallel tool-execution mode this races: `play` can resolve before
 * the earlier `move_*` calls finish and O lands on the wrong cell. With
 * `executionMode: "sequential"` the runner serializes the sibling calls and O
 * lands on the intended cell.
 *
 * The user cursor (TUI-only) and the agent cursor (tool-only) are stored in
 * separate variables. Only the agent cursor is ever exposed to the agent.
 */

import { StringEnum } from "@earendil-works/pi-ai";
import type { ExtensionAPI, ExtensionContext, Theme, ToolExecutionMode } from "@earendil-works/pi-coding-agent";
import { type Component, matchesKey, Text, truncateToWidth, visibleWidth } from "@earendil-works/pi-tui";
import { Type } from "typebox";

// Thrown from the tool on illegal actions. The agent runtime surfaces thrown
// errors as tool errors (isError=true) without resetting any of our state.
class TicTacToeError extends Error {
	constructor(message: string) {
		super(message);
		this.name = "TicTacToeError";
	}
}

// ---------------------------------------------------------------------------
// Types
// ---------------------------------------------------------------------------

type Cell = " " | "X" | "O";
type GameStatus = "playing" | "win_X" | "win_O" | "draw";

interface GameState {
	board: Cell[][];
	// User cursor (TUI-only, never exposed to the agent).
	userCursorRow: number;
	userCursorCol: number;
	// Agent cursor (manipulated by the tool, shown in the TUI during O's turn).
	agentCursorRow: number;
	agentCursorCol: number;
	status: GameStatus;
	userMark: Cell;
	agentMark: Cell;
	currentTurn: Cell;
}

// Persisted with each toolResult for state reconstruction AND sent to the
// agent as `details`. Only the agent cursor is included: the user cursor is
// private to the TUI.
interface BoardDetails {
	board: Cell[][];
	agentCursorRow: number;
	agentCursorCol: number;
	status: GameStatus;
	currentTurn: Cell;
}

// ---------------------------------------------------------------------------
// Game logic
// ---------------------------------------------------------------------------

// Agent cursor home: where the cursor is reset to after a SUCCESSFUL play.
// Pinned at (0,0) so every non-origin play requires at least one move, which
// guarantees multiple tool calls per turn and makes the parallel-vs-sequential
// behavior observable in the demo. The cursor is NOT reset when the user plays
// nor on a failed `play` (cell taken), so the agent can retry without
// starting over.
const AGENT_CURSOR_HOME_ROW = 0;
const AGENT_CURSOR_HOME_COL = 0;

function createInitialState(): GameState {
	return {
		board: [
			[" ", " ", " "],
			[" ", " ", " "],
			[" ", " ", " "],
		],
		userCursorRow: 1,
		userCursorCol: 1,
		agentCursorRow: AGENT_CURSOR_HOME_ROW,
		agentCursorCol: AGENT_CURSOR_HOME_COL,
		status: "playing",
		userMark: "X",
		agentMark: "O",
		currentTurn: "X",
	};
}

function getWinLine(board: Cell[][]): [number, number][] | null {
	const lines: [number, number][][] = [
		[
			[0, 0],
			[0, 1],
			[0, 2],
		],
		[
			[1, 0],
			[1, 1],
			[1, 2],
		],
		[
			[2, 0],
			[2, 1],
			[2, 2],
		],
		[
			[0, 0],
			[1, 0],
			[2, 0],
		],
		[
			[0, 1],
			[1, 1],
			[2, 1],
		],
		[
			[0, 2],
			[1, 2],
			[2, 2],
		],
		[
			[0, 0],
			[1, 1],
			[2, 2],
		],
		[
			[0, 2],
			[1, 1],
			[2, 0],
		],
	];
	for (const line of lines) {
		const vals = line.map(([r, c]) => board[r][c]);
		if (vals[0] !== " " && vals[0] === vals[1] && vals[1] === vals[2]) {
			return line;
		}
	}
	return null;
}

function checkWin(board: Cell[][]): GameStatus {
	const winLine = getWinLine(board);
	if (winLine) {
		const [r, c] = winLine[0];
		return board[r][c] === "X" ? "win_X" : "win_O";
	}
	if (board.every((row) => row.every((c) => c !== " "))) {
		return "draw";
	}
	return "playing";
}

function boardToAscii(board: Cell[][], agentCursorRow: number, agentCursorCol: number): string {
	// Plain grid with coordinates for empty cells, marking the agent cursor
	// position with angle brackets. The user cursor is NEVER included: it is a
	// TUI-only concept and must not leak to the agent.
	const rows = board.map((row, r) =>
		row
			.map((c, cIdx) => {
				const onCursor = r === agentCursorRow && cIdx === agentCursorCol;
				if (c === " ") return onCursor ? `<[${r},${cIdx}]>` : ` [${r},${cIdx}] `;
				return onCursor ? `   <${c}>   ` : `    ${c}    `;
			})
			.join("|"),
	);
	const separator = "---------+---------+---------";
	return rows.join(`\n${separator}\n`);
}

// ---------------------------------------------------------------------------
// Visual board rendering (ANSI).
// - Cells have NO background fill. Only the centered glyph is drawn.
// - Played cells color their glyph AND their surrounding borders in the
//   player's color, so each mark reads as a colored boxed region.
// - Cursor is indicated with colored borders around the cursor cell.
// ---------------------------------------------------------------------------

const CELL_WIDTH = 7;
const CELL_HEIGHT = 3;

// Player colors (SGR fg codes). Also used for the borders of played cells.
const FG_CODE_X = "34"; // blue
const FG_CODE_O = "33"; // yellow
const FG_CODE_WIN = "32"; // green (overrides on the winning line)

// Single-character glyphs, picked for maximum visual size without emoji.
// - \u2573 (BOX DRAWINGS LIGHT DIAGONAL CROSS) for X
// - \u25ef (LARGE CIRCLE) for O
const GLYPH_X = "\u2573";
const GLYPH_O = "\u25ef";

const DIM = (s: string) => `\x1b[2m${s}\x1b[22m`;
const RESET = "\x1b[0m";

function centerPad(content: string, width: number): string {
	const contentLen = visibleWidth(content);
	if (contentLen >= width) return truncateToWidth(content, width);
	const pad = width - contentLen;
	const left = Math.floor(pad / 2);
	return " ".repeat(left) + content + " ".repeat(pad - left);
}

// Fg color for a played cell's glyph and its surrounding borders. Undefined
// for empty cells.
function cellFgCode(cell: Cell, isWin: boolean): string | undefined {
	if (cell === " ") return undefined;
	if (isWin) return FG_CODE_WIN;
	return cell === "X" ? FG_CODE_X : FG_CODE_O;
}

function buildCellContent(mark: Cell, lineIdx: number, isWin: boolean): string {
	const empty = " ".repeat(CELL_WIDTH);
	if (mark === " ") return empty;

	const isMidLine = lineIdx === Math.floor(CELL_HEIGHT / 2);
	if (!isMidLine) return empty;

	const glyph = mark === "X" ? GLYPH_X : GLYPH_O;
	const fg = cellFgCode(mark, isWin) as string;
	const padLen = CELL_WIDTH - visibleWidth(glyph);
	const leftPad = Math.floor(padLen / 2);
	const rightPad = padLen - leftPad;
	return `${" ".repeat(leftPad)}\x1b[${fg};1m${glyph}${RESET}${" ".repeat(rightPad)}`;
}

// Fg color for a border char based on its adjacent cells. Undefined when no
// adjacent cell is played or when adjacent plays disagree (border stays dim
// to show the separation).
function borderFgCode(adjacent: ReadonlyArray<{ cell: Cell; isWin: boolean }>): string | undefined {
	const fgs = adjacent.map((a) => cellFgCode(a.cell, a.isWin)).filter((f): f is string => !!f);
	if (fgs.length === 0) return undefined;
	const first = fgs[0];
	return fgs.every((f) => f === first) ? first : undefined;
}

interface BoardRenderOpts {
	board: Cell[][];
	maxWidth: number;
	// Optional cursor overlay. Omit to render a static snapshot (used in tool
	// results, move messages, and the game-over banner).
	cursor?: { row: number; col: number; owner: "user" | "agent" };
}

function renderBoard(opts: BoardRenderOpts): string[] {
	const { board, maxWidth, cursor } = opts;
	const showCursor = !!cursor;
	const cr = cursor?.row ?? -1;
	const cc = cursor?.col ?? -1;

	// Green for user cursor, yellow for agent cursor.
	const cursorSgr = cursor?.owner === "agent" ? "\x1b[33;1m" : "\x1b[32;1m";

	const winLine = getWinLine(board);
	const winCells = new Set((winLine ?? []).map(([r, c]) => `${r},${c}`));
	const cellAt = (r: number, c: number) => ({ cell: board[r][c], isWin: winCells.has(`${r},${c}`) });

	const isCursorCorner = (gridR: number, gridC: number): boolean =>
		showCursor && (gridR === cr || gridR === cr + 1) && (gridC === cc || gridC === cc + 1);
	const isCursorHSegment = (gridR: number, c: number): boolean =>
		showCursor && c === cc && (gridR === cr || gridR === cr + 1);
	const isCursorVBorder = (r: number, gridC: number): boolean =>
		showCursor && r === cr && (gridC === cc || gridC === cc + 1);

	const paintBorder = (ch: string, highlighted: boolean, fgCode: string | undefined): string => {
		if (highlighted) return `${cursorSgr}${ch}${RESET}`;
		if (fgCode) return `\x1b[${fgCode};1m${ch}${RESET}`;
		return DIM(ch);
	};

	const cornerChar = (gridR: number, gridC: number): string => {
		if (gridR === 0 && gridC === 0) return "\u250c";
		if (gridR === 0 && gridC === 3) return "\u2510";
		if (gridR === 3 && gridC === 0) return "\u2514";
		if (gridR === 3 && gridC === 3) return "\u2518";
		if (gridR === 0) return "\u252c";
		if (gridR === 3) return "\u2534";
		if (gridC === 0) return "\u251c";
		if (gridC === 3) return "\u2524";
		return "\u253c";
	};

	const cornerAdjacent = (gridR: number, gridC: number) => {
		const out: { cell: Cell; isWin: boolean }[] = [];
		for (const [dr, dc] of [
			[-1, -1],
			[-1, 0],
			[0, -1],
			[0, 0],
		]) {
			const r = gridR + dr;
			const c = gridC + dc;
			if (r >= 0 && r < 3 && c >= 0 && c < 3) out.push(cellAt(r, c));
		}
		return out;
	};

	const lines: string[] = [];

	for (let gridR = 0; gridR <= 3; gridR++) {
		// Horizontal border row.
		let row = "";
		for (let gridC = 0; gridC <= 3; gridC++) {
			const cornerColor = borderFgCode(cornerAdjacent(gridR, gridC));
			row += paintBorder(cornerChar(gridR, gridC), isCursorCorner(gridR, gridC), cornerColor);
			if (gridC < 3) {
				const adj: { cell: Cell; isWin: boolean }[] = [];
				if (gridR > 0) adj.push(cellAt(gridR - 1, gridC));
				if (gridR < 3) adj.push(cellAt(gridR, gridC));
				const segColor = borderFgCode(adj);
				row += paintBorder("\u2500".repeat(CELL_WIDTH), isCursorHSegment(gridR, gridC), segColor);
			}
		}
		lines.push(centerPad(row, maxWidth));

		if (gridR === 3) break;

		for (let lineIdx = 0; lineIdx < CELL_HEIGHT; lineIdx++) {
			let contentRow = "";
			for (let gridC = 0; gridC <= 3; gridC++) {
				const adj: { cell: Cell; isWin: boolean }[] = [];
				if (gridC > 0) adj.push(cellAt(gridR, gridC - 1));
				if (gridC < 3) adj.push(cellAt(gridR, gridC));
				const vColor = borderFgCode(adj);
				contentRow += paintBorder("\u2502", isCursorVBorder(gridR, gridC), vColor);
				if (gridC < 3) {
					contentRow += buildCellContent(board[gridR][gridC], lineIdx, winCells.has(`${gridR},${gridC}`));
				}
			}
			lines.push(centerPad(contentRow, maxWidth));
		}
	}

	return lines;
}

// Full TUI board with the right cursor overlayed for the current turn.
function renderVisualBoard(state: GameState, maxWidth: number): string[] {
	const isUserTurn = state.currentTurn === state.userMark;
	const cursor =
		state.status !== "playing"
			? undefined
			: {
					row: isUserTurn ? state.userCursorRow : state.agentCursorRow,
					col: isUserTurn ? state.userCursorCol : state.agentCursorCol,
					owner: (isUserTurn ? "user" : "agent") as "user" | "agent",
				};
	return renderBoard({ board: state.board, maxWidth, cursor });
}

/** Static snapshot used inside tool results and custom messages. */
function renderBoardSnapshot(board: Cell[][], maxWidth: number): string[] {
	return renderBoard({ board, maxWidth });
}

// ---------------------------------------------------------------------------
// TUI component
// ---------------------------------------------------------------------------

class TicTacToeComponent implements Component {
	private state: GameState;
	private onClose: () => void;
	private onUserPlay: (row: number, col: number) => void;
	private tui: { requestRender: () => void };
	private cachedLines: string[] = [];
	private cachedWidth = 0;
	private version = 0;
	private cachedVersion = -1;

	constructor(
		tui: { requestRender: () => void },
		onClose: () => void,
		onUserPlay: (row: number, col: number) => void,
		state: GameState,
	) {
		this.tui = tui;
		this.onClose = onClose;
		this.onUserPlay = onUserPlay;
		this.state = state;
	}

	updateState(state: GameState): void {
		this.state = state;
		this.version++;
		this.tui.requestRender();
	}

	handleInput(data: string): boolean {
		if (matchesKey(data, "escape") || data === "q" || data === "Q") {
			this.onClose();
			return true;
		}
		if (this.state.status !== "playing") {
			if (data === "r" || data === "R") {
				this.onClose();
				return true;
			}
			return true;
		}
		if (this.state.currentTurn !== this.state.userMark) return true;

		if (matchesKey(data, "up") && this.state.userCursorRow > 0) {
			this.state.userCursorRow--;
			this.version++;
			this.tui.requestRender();
		} else if (matchesKey(data, "down") && this.state.userCursorRow < 2) {
			this.state.userCursorRow++;
			this.version++;
			this.tui.requestRender();
		} else if (matchesKey(data, "left") && this.state.userCursorCol > 0) {
			this.state.userCursorCol--;
			this.version++;
			this.tui.requestRender();
		} else if (matchesKey(data, "right") && this.state.userCursorCol < 2) {
			this.state.userCursorCol++;
			this.version++;
			this.tui.requestRender();
		} else if (matchesKey(data, "return") || data === " ") {
			const { userCursorRow, userCursorCol } = this.state;
			if (this.state.board[userCursorRow][userCursorCol] === " ") {
				this.onUserPlay(userCursorRow, userCursorCol);
			}
		}
		return true;
	}

	invalidate(): void {
		this.cachedWidth = 0;
	}

	render(width: number): string[] {
		if (width === this.cachedWidth && this.cachedVersion === this.version) {
			return this.cachedLines;
		}

		const ESC = "\x1b[";
		const reset = `${ESC}0m`;
		const bold = (s: string) => `${ESC}1m${s}${reset}`;
		const dim = (s: string) => `${ESC}2m${s}${reset}`;
		const blue = (s: string) => `${ESC}34m${s}${reset}`;
		const yellow = (s: string) => `${ESC}33m${s}${reset}`;
		const green = (s: string) => `${ESC}32m${s}${reset}`;

		const lines: string[] = [];

		// Top title banner, full width.
		const titleText = " Tic-Tac-Toe ";
		const titleLen = visibleWidth(titleText);
		const borderLen = Math.max(0, width - titleLen);
		const leftBorder = Math.floor(borderLen / 2);
		const rightBorder = borderLen - leftBorder;
		lines.push(dim("\u2500".repeat(leftBorder)) + bold(blue(titleText)) + dim("\u2500".repeat(rightBorder)));

		lines.push("");

		// Status line.
		if (this.state.status !== "playing") {
			const statusText =
				this.state.status === "draw"
					? bold(yellow("Draw!"))
					: this.state.status === "win_X"
						? bold(green("X wins!"))
						: bold(yellow("O wins!"));
			lines.push(centerPad(statusText, width));
		} else if (this.state.currentTurn === "X") {
			lines.push(centerPad(`Turn: ${bold(blue("X"))} (You)  ${dim("|")}  ${bold(yellow("O"))} (Agent)`, width));
		} else {
			lines.push(centerPad(`${blue("X")} (You)  ${dim("|")}  Turn: ${bold(yellow("O"))} (Agent)`, width));
		}

		lines.push("");
		lines.push("");

		lines.push(...renderVisualBoard(this.state, width));

		lines.push("");
		lines.push("");

		// Footer.
		let footer: string;
		if (this.state.status !== "playing") {
			footer = `${bold("R")} restart  ${dim("|")}  ${bold("Q")}/${bold("ESC")} quit`;
		} else if (this.state.currentTurn !== this.state.userMark) {
			footer = dim("Agent is thinking...");
		} else {
			footer = `${bold("\u2190\u2191\u2193\u2192")} move  ${dim("|")}  ${bold("ENTER")} play  ${dim("|")}  ${bold("ESC")} quit`;
		}
		lines.push(centerPad(footer, width));

		// Bottom separator between the component and the editor below.
		lines.push("");
		lines.push(dim("\u2500".repeat(width)));

		this.cachedLines = lines;
		this.cachedWidth = width;
		this.cachedVersion = this.version;
		return lines;
	}
}

// ---------------------------------------------------------------------------
// Move-message renderer (full width banner)
// ---------------------------------------------------------------------------

// Full-width banner message with an optional board snapshot underneath.
class BannerMessageComponent implements Component {
	private readonly title: string;
	private readonly details: BoardDetails | undefined;
	private readonly expanded: boolean;
	private readonly theme: Theme;

	constructor(title: string, details: BoardDetails | undefined, expanded: boolean, theme: Theme) {
		this.title = title;
		this.details = details;
		this.expanded = expanded;
		this.theme = theme;
	}

	invalidate(): void {}

	render(width: number): string[] {
		const dim = (s: string) => this.theme.fg("dim", s);
		const lines: string[] = [];
		const titleLen = visibleWidth(this.title);
		const fillLen = Math.max(0, width - titleLen - 2);
		const leftFill = Math.floor(fillLen / 2);
		const rightFill = fillLen - leftFill;
		lines.push(`${dim("\u2500".repeat(leftFill))} ${this.title} ${dim("\u2500".repeat(rightFill))}`);

		if (this.expanded && this.details) {
			lines.push("");
			lines.push(...renderBoardSnapshot(this.details.board, width));
		}

		return lines;
	}
}

// End-of-game banner: two dim hrs, a big colored title line, and the final
// board with the winning line highlighted.
class GameOverMessageComponent implements Component {
	private readonly status: GameStatus;
	private readonly details: BoardDetails | undefined;
	private readonly theme: Theme;

	constructor(status: GameStatus, details: BoardDetails | undefined, theme: Theme) {
		this.status = status;
		this.details = details;
		this.theme = theme;
	}

	invalidate(): void {}

	render(width: number): string[] {
		const dim = (s: string) => this.theme.fg("dim", s);
		const bold = (s: string) => this.theme.bold(s);

		const hr = dim("\u2500".repeat(width));
		const lines: string[] = [];
		lines.push(hr);
		lines.push("");

		let title: string;
		let sub: string;
		switch (this.status) {
			case "win_X":
				title = bold(this.theme.fg("accent", "\u2605 Player X wins \u2605"));
				sub = "You beat the agent.";
				break;
			case "win_O":
				title = bold(this.theme.fg("warning", "\u2605 Player O wins \u2605"));
				sub = "The agent beat you.";
				break;
			case "draw":
				title = bold(this.theme.fg("muted", "\u2014 Draw \u2014"));
				sub = "No winner.";
				break;
			default:
				title = bold("Game over");
				sub = "";
				break;
		}

		for (const line of [title, dim(sub)]) {
			const pad = Math.max(0, width - visibleWidth(line));
			lines.push(`${" ".repeat(Math.floor(pad / 2))}${line}`);
		}

		lines.push("");
		if (this.details) {
			lines.push(...renderBoardSnapshot(this.details.board, width));
			lines.push("");
		}
		lines.push(hr);

		return lines;
	}
}

// ---------------------------------------------------------------------------
// Delay helper
// ---------------------------------------------------------------------------

function delay(ms: number): Promise<void> {
	return new Promise((resolve) => setTimeout(resolve, ms));
}

// ---------------------------------------------------------------------------
// Extension
// ---------------------------------------------------------------------------

const SAVE_TYPE = "tic-tac-toe-save";
const MOVE_MESSAGE_TYPE = "tic-tac-toe-move";
const GAME_OVER_MESSAGE_TYPE = "tic-tac-toe-game-over";

let gameState: GameState = createInitialState();
let component: TicTacToeComponent | null = null;
let gameActive = false;

function reconstructState(ctx: ExtensionContext): void {
	gameState = createInitialState();
	gameActive = false;

	for (const entry of ctx.sessionManager.getBranch()) {
		if (entry.type !== "message") continue;
		const msg = entry.message;
		if (msg.role !== "toolResult") continue;
		if (msg.toolName !== "tic_tac_toe" && msg.toolName !== "tic_tac_toe_see_board") continue;

		const details = msg.details as BoardDetails | undefined;
		if (details) {
			gameState.board = details.board.map((row) => [...row]);
			gameState.agentCursorRow = details.agentCursorRow;
			gameState.agentCursorCol = details.agentCursorCol;
			gameState.status = details.status;
			gameState.currentTurn = details.currentTurn;
		}
	}
}

function getBoardDetails(): BoardDetails {
	return {
		board: gameState.board.map((row) => [...row]),
		agentCursorRow: gameState.agentCursorRow,
		agentCursorCol: gameState.agentCursorCol,
		status: gameState.status,
		currentTurn: gameState.currentTurn,
	};
}

export default function (pi: ExtensionAPI) {
	pi.on("session_start", async (_event, ctx) => reconstructState(ctx));
	pi.on("session_tree", async (_event, ctx) => reconstructState(ctx));

	// Sent once per game at end-of-game. The custom renderer paints the banner;
	// `content` is a plain-text fallback for any non-TUI consumer and for the
	// LLM (in case the message ends up in future context).
	const emitGameOverMessage = (): void => {
		const label =
			gameState.status === "win_X"
				? "Player X (human) wins"
				: gameState.status === "win_O"
					? "Player O (agent) wins"
					: gameState.status === "draw"
						? "Draw"
						: "Game over";
		pi.sendMessage({
			customType: GAME_OVER_MESSAGE_TYPE,
			content: `Game over: ${label}.`,
			display: true,
			details: getBoardDetails(),
		});
	};

	// -----------------------------------------------------------------------
	// Custom message renderer for user move messages
	// -----------------------------------------------------------------------
	pi.registerMessageRenderer(MOVE_MESSAGE_TYPE, (message, { expanded }, theme) => {
		const details = message.details as BoardDetails | undefined;
		const turnLabel =
			details?.currentTurn === "O"
				? `${theme.fg("warning", theme.bold("O"))} (Agent)`
				: `${theme.fg("accent", theme.bold("X"))} (You)`;
		const title = `${theme.fg("accent", theme.bold("Player X played"))}  ${theme.fg("dim", "\u2192")}  next: ${turnLabel}`;
		return new BannerMessageComponent(title, details, expanded, theme);
	});

	// -----------------------------------------------------------------------
	// Custom message renderer for game-over messages
	// -----------------------------------------------------------------------
	pi.registerMessageRenderer(GAME_OVER_MESSAGE_TYPE, (message, _options, theme) => {
		const details = message.details as BoardDetails | undefined;
		const status = (details?.status ?? "draw") as GameStatus;
		return new GameOverMessageComponent(status, details, theme);
	});

	// -----------------------------------------------------------------------
	// before_agent_start - inject game instructions each turn
	// -----------------------------------------------------------------------
	pi.on("before_agent_start", async (event) => {
		if (!gameActive) return undefined;

		const instructions = `

## Tic-Tac-Toe (you are Player O)

A tic-tac-toe game is in progress. The human is Player X. You are Player O.
The human plays through a TUI; you play through the \`tic_tac_toe\` tool.

### Turn protocol

When the human plays, you receive a message that contains the cell X marked,
the full board, and YOUR cursor position (Player O's cursor). The message is
the source of truth for the board.

Player O's cursor persists between O turns. It is reset to (row=${AGENT_CURSOR_HOME_ROW}, col=${AGENT_CURSOR_HOME_COL})
only after a successful \`play\`. If a \`play\` fails (cell already taken), the
cursor stays where it was, so you can move and retry.

You may also call \`tic_tac_toe_see_board\` if you want the current board and
your cursor position restated at any point. The user's cursor is private and
is never shown to you.

### The tool

\`tic_tac_toe\` takes ONE action per call:
- \`move_up\` / \`move_down\` / \`move_left\` / \`move_right\`: move YOUR cursor one cell (clamped at edges)
- \`play\`: place O on the cell under YOUR cursor. Errors if the cell is not empty.

There is no batched form. One call = one action.

### CRITICAL: emit the whole turn in a single response

To play at (r, c) from your cursor (r0, c0) emit, in order:
- \`move_down\` (r - r0) times (or \`move_up\` (r0 - r) times if r < r0)
- \`move_right\` (c - c0) times (or \`move_left\` (c0 - c) times if c < c0)
- one call of \`play\`

All of these tool calls MUST be emitted in the SAME assistant response, as
separate tool_use blocks, before you stop. Do not:
- split the sequence across multiple assistant responses,
- wait for a move result before emitting the next move or \`play\`,
- write any explanation or text between the tool calls,
- call any other tool during your turn (except \`tic_tac_toe_see_board\` when you
  explicitly need the state restated).

Decide the target cell first, then dump every action for the turn in one go.

### Examples (cursor starts at (${AGENT_CURSOR_HOME_ROW}, ${AGENT_CURSOR_HOME_COL}))

- Target (0,0): one call, \`play\`.
- Target (0,2): \`move_right\`, \`move_right\`, \`play\`. Three calls, one response.
- Target (1,1): \`move_down\`, \`move_right\`, \`play\`. Three calls, one response.
- Target (2,2): \`move_down\`, \`move_down\`, \`move_right\`, \`move_right\`, \`play\`. Five calls, one response.

### Strategy

1. If you have two O's in a line with the third cell empty, win by playing there.
2. Otherwise, if X has two in a line with the third cell empty, block there.
3. Otherwise, prefer center, then corners, then edges.
`;

		return {
			systemPrompt: event.systemPrompt + instructions,
		};
	});

	// -----------------------------------------------------------------------
	// /tic-tac-toe command
	// -----------------------------------------------------------------------
	pi.registerCommand("tic-tac-toe", {
		description: "Play tic-tac-toe against the agent",

		handler: async (_args, ctx) => {
			if (!ctx.hasUI) {
				ctx.ui.notify("Tic-tac-toe requires interactive mode", "error");
				return;
			}

			reconstructState(ctx);
			if (gameState.status !== "playing") {
				gameState = createInitialState();
			}
			gameActive = true;
			pi.setSessionName("Tic-Tac-Toe");

			await ctx.ui.custom<void>((tui, _theme, _kb, done) => {
				component = new TicTacToeComponent(
					tui,
					() => {
						component = null;
						gameActive = false;
						done(undefined);
					},
					(row, col) => {
						gameState.board[row][col] = gameState.userMark;
						gameState.status = checkWin(gameState.board);
						if (gameState.status === "playing") {
							gameState.currentTurn = gameState.agentMark;
						}
						component?.updateState(gameState);
						pi.appendEntry(SAVE_TYPE, getBoardDetails());

						if (gameState.status === "playing") {
							// IMPORTANT: user play does NOT touch the agent cursor.
							// The agent cursor is only reset after a successful agent play.
							const boardAscii = boardToAscii(
								gameState.board,
								gameState.agentCursorRow,
								gameState.agentCursorCol,
							);
							pi.sendMessage(
								{
									customType: MOVE_MESSAGE_TYPE,
									content:
										`Player X played at (row=${row}, col=${col}). It is now Player O's turn.\n\n` +
										`Board (your cursor marked with <>):\n${boardAscii}\n\n` +
										`Your cursor is at (row=${gameState.agentCursorRow}, col=${gameState.agentCursorCol}). ` +
										`Decide your target cell, then emit every move_* and the final play ` +
										`as separate tic_tac_toe tool calls in THIS response.`,
									display: true,
									details: getBoardDetails(),
								},
								{ triggerTurn: true },
							);
						} else {
							emitGameOverMessage();
							gameActive = false;
						}
					},
					gameState,
				);
				return component;
			});
		},
	});

	// -----------------------------------------------------------------------
	// tic_tac_toe tool - one action per call.
	// -----------------------------------------------------------------------

	type Action = "move_up" | "move_down" | "move_left" | "move_right" | "play";

	const ACTION_DELAYS: Record<Action, number> = {
		move_up: 300,
		move_down: 300,
		move_left: 300,
		move_right: 300,
		play: 0,
	};

	pi.registerTool({
		name: "tic_tac_toe",
		label: "Tic-Tac-Toe",
		description:
			"Execute ONE tic-tac-toe action as Player O. `action` is exactly one of: move_up, move_down, move_left, move_right (move YOUR cursor one cell, clamped at edges), or play (place O under YOUR cursor; errors if the cell is not empty). There is no batched form. To play at (r, c) from your current cursor (r0, c0), emit the required move_down/move_up and move_right/move_left calls, then play, all as separate tool_use blocks in the SAME assistant response. Do not split the sequence across responses and do not wait for a result before emitting the next call. Your cursor position persists between turns and is reset to (0,0) only after a successful play.",
		promptSnippet: "Play a tic-tac-toe action (move_up/down/left/right or play) as Player O",
		promptGuidelines: [
			"When it is your tic-tac-toe turn, decide the target cell first, then emit every move_* plus the final play as separate tic_tac_toe tool calls in a SINGLE assistant response. Never split them across responses or wait for intermediate results.",
			"Never ask the user for the board. The board and your cursor position are included in the user's move message; use tic_tac_toe_see_board if you need them restated.",
		],
		parameters: Type.Object({
			action: StringEnum(["move_up", "move_down", "move_left", "move_right", "play"] as const, {
				description:
					"The single action to perform this call. Emit multiple tic_tac_toe calls in one response to string actions together.",
			}),
		}),
		executionMode: "sequential" as ToolExecutionMode,

		async execute(_toolCallId, params, _signal, _onUpdate, _ctx) {
			const actionDelay = ACTION_DELAYS[params.action];
			if (actionDelay > 0) await delay(actionDelay);

			let result: string;

			switch (params.action) {
				case "move_up":
					if (gameState.agentCursorRow > 0) gameState.agentCursorRow--;
					result = `Moved up. Cursor: (${gameState.agentCursorRow}, ${gameState.agentCursorCol})`;
					break;
				case "move_down":
					if (gameState.agentCursorRow < 2) gameState.agentCursorRow++;
					result = `Moved down. Cursor: (${gameState.agentCursorRow}, ${gameState.agentCursorCol})`;
					break;
				case "move_left":
					if (gameState.agentCursorCol > 0) gameState.agentCursorCol--;
					result = `Moved left. Cursor: (${gameState.agentCursorRow}, ${gameState.agentCursorCol})`;
					break;
				case "move_right":
					if (gameState.agentCursorCol < 2) gameState.agentCursorCol++;
					result = `Moved right. Cursor: (${gameState.agentCursorRow}, ${gameState.agentCursorCol})`;
					break;
				case "play": {
					if (gameState.status !== "playing") {
						throw new TicTacToeError(`Game is over (${gameState.status}).`);
					}
					if (gameState.currentTurn !== gameState.agentMark) {
						throw new TicTacToeError("It is not your turn.");
					}
					const r = gameState.agentCursorRow;
					const c = gameState.agentCursorCol;
					if (gameState.board[r][c] !== " ") {
						// Do NOT reset the cursor on failure. The agent can retry
						// from the cursor's current position.
						component?.updateState(gameState);
						pi.appendEntry(SAVE_TYPE, getBoardDetails());
						throw new TicTacToeError(
							`Cell (${r},${c}) is already ${gameState.board[r][c]}. Your cursor is still at (${r},${c}). Move to an empty cell and retry play.`,
						);
					}
					gameState.board[r][c] = gameState.agentMark;
					gameState.status = checkWin(gameState.board);
					// Reset agent cursor to home ONLY on successful play.
					gameState.agentCursorRow = AGENT_CURSOR_HOME_ROW;
					gameState.agentCursorCol = AGENT_CURSOR_HOME_COL;
					if (gameState.status === "playing") {
						gameState.currentTurn = gameState.userMark;
						result = `Placed O at (${r},${c}). Cursor reset to (${AGENT_CURSOR_HOME_ROW},${AGENT_CURSOR_HOME_COL}). Your turn, X!`;
					} else if (gameState.status === "win_O") {
						result = `Placed O at (${r},${c}). Player O wins!`;
						gameActive = false;
						emitGameOverMessage();
					} else if (gameState.status === "draw") {
						result = `Placed O at (${r},${c}). It's a draw!`;
						gameActive = false;
						emitGameOverMessage();
					} else {
						result = `Placed O at (${r},${c}).`;
					}
					break;
				}
			}

			component?.updateState(gameState);
			pi.appendEntry(SAVE_TYPE, getBoardDetails());

			return {
				content: [{ type: "text", text: result }],
				details: getBoardDetails(),
			};
		},

		renderCall(args, theme) {
			const action = typeof args.action === "string" ? args.action : "";
			return new Text(theme.fg("toolTitle", theme.bold("tic_tac_toe ")) + theme.fg("muted", action), 0, 0);
		},

		renderResult(result, { expanded }, theme, context) {
			const details = result.details as BoardDetails | undefined;
			const text = result.content[0];
			const msg = text?.type === "text" ? text.text : "";
			const prefix = context?.isError ? theme.fg("error", "\u2717 ") : theme.fg("success", "\u2713 ");
			const summary = prefix + theme.fg("muted", msg);

			if (expanded && details) {
				return new BannerMessageComponent(summary, details, true, theme);
			}
			return new Text(summary, 0, 0);
		},
	});

	// -----------------------------------------------------------------------
	// tic_tac_toe_see_board tool - inspect board + agent cursor.
	// -----------------------------------------------------------------------
	pi.registerTool({
		name: "tic_tac_toe_see_board",
		label: "See Board",
		description:
			"Return the current tic-tac-toe board state and YOUR cursor position (Player O). Takes no arguments. Use this if you need the current state restated mid-turn (for example after a failed play). The user's cursor is never exposed.",
		promptSnippet: "Inspect the tic-tac-toe board and your cursor",
		parameters: Type.Object({}),

		async execute(_toolCallId, _params, _signal, _onUpdate, _ctx) {
			const boardAscii = boardToAscii(gameState.board, gameState.agentCursorRow, gameState.agentCursorCol);
			const text =
				`Board (your cursor marked with <>):\n${boardAscii}\n\n` +
				`Your cursor: (row=${gameState.agentCursorRow}, col=${gameState.agentCursorCol})\n` +
				`Status: ${gameState.status}\n` +
				`Turn: ${gameState.currentTurn === gameState.agentMark ? "Player O (you)" : "Player X"}`;
			return {
				content: [{ type: "text", text }],
				details: getBoardDetails(),
			};
		},

		renderCall(_args, theme) {
			return new Text(theme.fg("toolTitle", theme.bold("tic_tac_toe_see_board")), 0, 0);
		},

		renderResult(result, { expanded }, theme) {
			const details = result.details as BoardDetails | undefined;
			const summary =
				theme.fg("success", "\u2713 ") +
				theme.fg("muted", `cursor (${details?.agentCursorRow ?? 0},${details?.agentCursorCol ?? 0})`);
			if (expanded && details) {
				return new BannerMessageComponent(summary, details, true, theme);
			}
			return new Text(summary, 0, 0);
		},
	});
}