import type { AdSensePushCommand } from "./types.js";

const SCRIPT_MARKER = "adsbygoogle.js";

let scriptPromise: Promise<void> | null = null;
let scriptClient: string | null = null;

function findExistingScript(adClient: string): HTMLScriptElement | null {
    for (const el of Array.from(document.scripts)) {
        if (el.src.includes(SCRIPT_MARKER) && el.src.includes(adClient)) {
            return el;
        }
    }
    return null;
}

/**
 * 加载 Google AdSense 官方脚本（幂等）。
 * - 仅浏览器环境生效，SSR 中为 no-op
 * - 同一 adClient 复用同一 Promise；已在页面中的脚本会被识别并跳过
 */
export function loadAdSense(adClient: string): Promise<void> {
    if (typeof document === "undefined") {
        return Promise.resolve();
    }
    if (scriptPromise) {
        if (scriptClient === adClient) {
            return scriptPromise;
        }
        return Promise.reject(
            new Error(
                `[adsense] 脚本已按 client=${scriptClient} 加载，不支持同时加载多个发布商 ID`,
            ),
        );
    }

    const existing = findExistingScript(adClient);
    if (existing) {
        scriptClient = adClient;
        scriptPromise = Promise.resolve();
        return scriptPromise;
    }

    scriptClient = adClient;
    scriptPromise = new Promise<void>((resolve, reject) => {
        const script = document.createElement("script");
        script.async = true;
        script.crossOrigin = "anonymous";
        script.src = `https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=${encodeURIComponent(adClient)}`;
        script.onload = () => resolve();
        script.onerror = () => {
            // 失败必须重置状态，否则后续调用会一直复用 rejected Promise 无法重试
            scriptPromise = null;
            scriptClient = null;
            script.remove();
            reject(new Error("[adsense] AdSense 脚本加载失败"));
        };
        document.head.appendChild(script);
    });
    return scriptPromise;
}

/** 向队列 push 一条命令，触发对已挂载 <ins class="adsbygoogle"> 的渲染。 */
export function pushAdSense(command: AdSensePushCommand = {}): void {
    if (typeof window === "undefined") {
        return;
    }
    window.adsbygoogle ??= [];
    window.adsbygoogle.push(command);
}