/**
 * Runtime promotion for pi-ast-grep.
 *
 * A bounded guidance block appended to the system prompt (via
 * `before_agent_start`) so models reach for the ast-grep tools at the right
 * moments. Toggleable through `.pi/ast-grep.json`:
 *
 *   { "promotion": { "enabled": false } }
 *
 * The default is enabled. The block is only appended when at least one
 * ast-grep tool is active in the session, so it never advertises tools the
 * model cannot call.
 */

import { readFileSync } from "node:fs";
import { join } from "node:path";
import { CONFIG_DIR_NAME } from "@earendil-works/pi-coding-agent";
import { TOOL_NAMES } from "./tools.ts";

export const PROMOTION_DEFAULT_ENABLED = true;
export const MAX_CONFIG_CHARS = 16 * 1024;

/** The bounded guidance block; keep it a few lines and pointer-only. */
export function promotionBlock(): string {
	return [
		"[pi-ast-grep] Structural code tools are active:",
		"- ast_grep_outline: map a file or directory (items/view/match) before reading it.",
		"- ast_grep_run: structural search (pattern/kind) instead of text grep when shape matters.",
		"- ast_grep_scan: relational/composite rules (inside, has, any, not; stopBy: end) or project rules.",
		"- ast_grep_debug_query: when a pattern fails to match, dump node kinds first.",
		"- ast_grep_rewrite: preview with apply=false, then apply=true for the same arguments.",
		"- ast_grep_languages: check supported language aliases before run/rewrite/scan.",
	].join("\n");
}

/**
 * Parses the `promotion.enabled` flag from a raw config value. Non-object
 * shapes, wrong types, and unknown keys fall back to the default rather than
 * failing the extension load; a strictly invalid structure is treated as
 * "not configured" so a malformed file cannot disable promotion silently.
 */
export function parsePromotionEnabled(value: unknown): boolean {
	if (value === null || typeof value !== "object" || Array.isArray(value)) {
		return PROMOTION_DEFAULT_ENABLED;
	}
	const promotion = (value as Record<string, unknown>).promotion;
	if (promotion === null || typeof promotion !== "object" || Array.isArray(promotion)) {
		return PROMOTION_DEFAULT_ENABLED;
	}
	const enabled = (promotion as Record<string, unknown>).enabled;
	return typeof enabled === "boolean" ? enabled : PROMOTION_DEFAULT_ENABLED;
}

function readConfigText(cwd: string): string | undefined {
	const path = join(cwd, CONFIG_DIR_NAME, "ast-grep.json");
	try {
		return readFileSync(path, "utf8");
	} catch (error) {
		if ((error as NodeJS.ErrnoException).code !== "ENOENT") {
			throw error;
		}
	}
}

/**
 * Loads the promotion toggle for the session. Reads `.pi/ast-grep.json` from
 * the working directory; untrusted projects and missing/invalid files use the
 * default (enabled).
 */
export function loadPromotionEnabled(cwd: string, projectTrusted: boolean): boolean {
	if (!projectTrusted) {
		return PROMOTION_DEFAULT_ENABLED;
	}
	const text = readConfigText(cwd);
	if (text === undefined) {
		return PROMOTION_DEFAULT_ENABLED;
	}
	if (text.length > MAX_CONFIG_CHARS) {
		return PROMOTION_DEFAULT_ENABLED;
	}
	try {
		return parsePromotionEnabled(JSON.parse(text));
	} catch {
		return PROMOTION_DEFAULT_ENABLED;
	}
}

/** True when at least one ast-grep tool is among the active tool names. */
export function hasActiveAstGrepTools(activeTools: readonly string[] | undefined): boolean {
	if (activeTools === undefined) {
		return false;
	}
	const active = new Set(activeTools);
	return TOOL_NAMES.some((name) => active.has(name));
}