/* Generic SSE client wrapper for novel-app streams.
 *
 * 后端事件契约:
 *   token:         {text:string}
 *   section_start: {section:string}   (拆书)
 *   section_end:   {section:string, content:string}
 *   context:       {summary:string}   (写章节)
 *   done:          {content:string, word_count:number}
 *   error:         {error:string}
 *
 * handlers 全部可选:
 *   {onToken, onSectionStart, onSectionEnd, onContext, onDone, onError}
 * 返回句柄 {close()}, close() 幂等. done / error 帧后自动 close.
 */

const EVENTS = ["token", "section_start", "section_end", "context", "done", "error"];

export function createSSEStream(url, handlers = {}) {
    let closed = false;
    const es = new EventSource(url);

    function close() {
        if (closed) return;
        closed = true;
        es.close();
    }

    function parse(e) {
        try {
            return JSON.parse(e.data);
        } catch (err) {
            return null;
        }
    }

    es.addEventListener("token", (e) => {
        const d = parse(e);
        if (d && handlers.onToken) handlers.onToken(d.text || "");
    });

    es.addEventListener("section_start", (e) => {
        const d = parse(e);
        if (d && handlers.onSectionStart) handlers.onSectionStart(d.section);
    });

    es.addEventListener("section_end", (e) => {
        const d = parse(e);
        if (d && handlers.onSectionEnd) handlers.onSectionEnd(d.section, d.content || "");
        close();
    });

    es.addEventListener("context", (e) => {
        const d = parse(e);
        if (d && handlers.onContext) handlers.onContext(d.summary || "");
    });

    es.addEventListener("done", (e) => {
        const d = parse(e);
        if (d && handlers.onDone) handlers.onDone(d.content || "", d.word_count || 0);
        close();
    });

    es.addEventListener("error", (e) => {
        const d = parse(e);
        if (handlers.onError) handlers.onError(d && d.error ? d.error : "未知错误", "server");
        close();
    });

    es.onerror = () => {
        if (!closed) {
            if (handlers.onError) handlers.onError("连接错误, 请检查后端日志", "connection");
            close();
        }
    };

    return { close };
}