oh-my-pi/packages/coding-agent/src/session/artifacts.ts

/**
 * Session-scoped artifact storage for truncated tool outputs.
 *
 * Artifacts are stored in a directory alongside the session file,
 * accessible via artifact:// URLs.
 */
import * as fs from "node:fs/promises";
import * as path from "node:path";

/**
 * Manages artifact storage for a session.
 *
 * Artifacts are stored with sequential IDs in the session's artifact directory.
 * The directory is created lazily on first write.
 *
 * Subagents do not own their own `ArtifactManager`. The parent's instance is
 * adopted via `SessionManager.adoptArtifactManager`, so the whole parent +
 * subagent tree shares one ID space and one directory.
 */
export class ArtifactManager {
	#nextId = 0;
	readonly #dir: string;
	#dirCreated = false;
	#initialized = false;

	/**
	 * @param dir Directory that will hold artifact files. Created lazily on first save.
	 */
	constructor(dir: string) {
		this.#dir = dir;
	}

	/**
	 * Artifact directory path.
	 * Directory may not exist until first artifact is saved.
	 */
	get dir(): string {
		return this.#dir;
	}

	async #ensureDir(): Promise<void> {
		if (!this.#dirCreated) {
			await fs.mkdir(this.#dir, { recursive: true });
			this.#dirCreated = true;
		}
		if (!this.#initialized) {
			await this.#scanExistingIds();
			this.#initialized = true;
		}
	}

	/**
	 * Scan existing artifact files to find the next available ID.
	 * This ensures we don't overwrite artifacts when resuming a session.
	 */
	async #scanExistingIds(): Promise<void> {
		const files = await this.listFiles();
		let maxId = -1;
		for (const file of files) {
			// Files are named: {id}.{toolType}.log
			const match = file.match(/^(\d+)\..*\.log$/);
			if (match) {
				const id = parseInt(match[1], 10);
				if (id > maxId) maxId = id;
			}
		}
		this.#nextId = maxId + 1;
	}

	/**
	 * Atomically allocate next artifact ID.
	 * IDs are sequential within the session.
	 */
	allocateId(): number {
		return this.#nextId++;
	}

	/**
	 * Allocate a new artifact path and ID without writing content.
	 *
	 * @param toolType Tool name for file extension (e.g., "bash", "read")
	 */
	async allocatePath(toolType: string): Promise<{ id: string; path: string }> {
		await this.#ensureDir();
		const id = String(this.allocateId());
		const filename = `${id}.${toolType}.log`;
		return { id, path: path.join(this.#dir, filename) };
	}

	/**
	 * Save content as an artifact and return the artifact ID.
	 *
	 * @param content Full content to save
	 * @param toolType Tool name for file extension (e.g., "bash", "read")
	 * @returns Artifact ID (numeric string)
	 */
	async save(content: string, toolType: string): Promise<string> {
		const { id, path } = await this.allocatePath(toolType);
		await Bun.write(path, content);
		return id;
	}

	/**
	 * Check if an artifact exists.
	 * @param id Artifact ID (numeric string)
	 */
	async exists(id: string): Promise<boolean> {
		const files = await this.listFiles();
		return files.some(f => f.startsWith(`${id}.`));
	}

	/**
	 * List all artifact files in the directory.
	 * Returns empty array if directory doesn't exist.
	 */
	async listFiles(): Promise<string[]> {
		try {
			return await fs.readdir(this.#dir);
		} catch {
			return [];
		}
	}

	/**
	 * Get the full path to an artifact file.
	 * Returns null if artifact doesn't exist.
	 *
	 * @param id Artifact ID (numeric string)
	 */
	async getPath(id: string): Promise<string | null> {
		const files = await this.listFiles();
		const match = files.find(f => f.startsWith(`${id}.`));
		return match ? path.join(this.#dir, match) : null;
	}
}