/**
 * Prompt Customizer Extension
 *
 * Demonstrates using systemPromptOptions to make informed, context-aware
 * modifications to the system prompt without re-discovering resources.
 *
 * This extension adds tool-specific guidance based on what tools and skills
 * are currently active, respecting whatever the user has configured.
 *
 * Usage:
 * 1. Copy this file to ~/.atomic/agent/extensions/ or your project's .atomic/extensions/ (legacy .pi/extensions/ also works)
 * 2. Use the extension — it automatically adapts to your active tools and skills
 */

import type { BuildSystemPromptOptions, ExtensionAPI } from "@bastani/atomic";

/**
 * Adds tool-specific guidance that adapts to the active tool set.
 * Mutate recorded `promptGuidelines` so the change is a chronological
 * transcript patch rather than an unrecorded forced prompt.
 */
function addToolGuidance(options: BuildSystemPromptOptions): string[] {
	const hasTool = (name: string) => options.selectedTools?.includes(name) ?? false;
	const parts: string[] = [];
	if (hasTool("read")) {
		parts.push(
			"Use the `read` tool for file contents (supports text and images). For large files, use `offset` and `limit` to read in chunks.",
		);
	}
	if (hasTool("bash")) {
		parts.push("Execute commands with the `bash` tool. Use it for file operations like `ls`, `find`, `grep`.");
	}
	if (hasTool("edit")) {
		parts.push(
			"Use the `edit` tool for precise text replacements in files. Match exact content including whitespace.",
		);
	}
	if (hasTool("write")) {
		parts.push("Use the `write` tool to create new files or overwrite existing ones completely.");
	}
	if (options.skills && options.skills.length > 0) {
		parts.push(
			`Available skills: ${options.skills.map((s) => s.name).join(", ")}. Use skill documentation for best practices on specific tools.`,
		);
	}
	return parts;
}

/**
 * Merges extension instructions with user-provided append prompts.
 * This respects whatever the user configured via --append-system-prompt
 * flags or files, rather than duplicating that work.
 */
function mergeWithUserAppend(options: BuildSystemPromptOptions): string {
	const userAppend = options.appendSystemPrompt;
	const extensionSpecific = `
## Extension-Added Context

This prompt includes tool guidance and skill information loaded dynamically.
If you have additional requirements, configure them via --append-system-prompt or project context files.
`;
	if (userAppend) {
		return `${userAppend}\n\n${extensionSpecific}`;
	}
	return extensionSpecific;
}

export default function promptCustomizer(pi: ExtensionAPI) {
	pi.on("before_agent_start", async (event) => {
		const { systemPromptOptions } = event;
		const guidance = addToolGuidance(systemPromptOptions);
		if (guidance.length > 0) {
			systemPromptOptions.promptGuidelines = [...(systemPromptOptions.promptGuidelines ?? []), ...guidance];
		}
		systemPromptOptions.appendSystemPrompt = mergeWithUserAppend(systemPromptOptions);
	});
}