/** Reusable Server-Sent Events parser for browser and test environments. */
export class SseParseError extends Error {
    constructor(message, details = {}) {
        super(message);
        this.name = "SseParseError";
        Object.assign(this, details);
    }
}

function parseEvent(block, {onComment, onRetry} = {}) {
    if (!block) return null;
    let event = "message";
    const data = [];
    let id;
    let retry;
    for (const line of block.split(/\r?\n/)) {
        if (line.startsWith(":")) { onComment?.(line.slice(1).trimStart()); continue; }
        const separator = line.indexOf(":");
        const field = separator < 0 ? line : line.slice(0, separator);
        const value = separator < 0 ? "" : line.slice(separator + 1).replace(/^ /, "");
        if (field === "event") event = value;
        else if (field === "data") data.push(value);
        else if (field === "id" && !value.includes("\u0000")) id = value;
        else if (field === "retry" && /^\d+$/.test(value)) { retry = Number(value); onRetry?.(retry); }
    }
    if (!data.length) return null;
    return {event, data: data.join("\n"), ...(id !== undefined ? {id} : {}), ...(retry !== undefined ? {retry} : {})};
}

export function createSseParser(options = {}) {
    let buffer = "";
    return {
        push(text) {
            buffer += text;
            const blocks = buffer.split(/\r?\n\r?\n/);
            buffer = blocks.pop() || "";
            return blocks.map(block => parseEvent(block, options)).filter(Boolean);
        },
        finish() {
            const event = parseEvent(buffer, options);
            buffer = "";
            return event ? [event] : [];
        }
    };
}

export function parseSseData(event) {
    try { return JSON.parse(event.data); }
    catch (error) { throw new SseParseError("Malformed SSE JSON payload.", {cause: error, event}); }
}