// What one chart read carries for the original view it is rendered in: the view header, and a binder that receives the
// exact answer so a server receipt can be checked against the bytes it names. Passed per call, never set globally.

/** One served answer as it arrived: its own response headers and the exact body text before parsing. */
export interface ServedAnswer {
    header: (name: string) => string | null;
    text: string;
}

export interface ReadOptions {
    headers?: Record<string, string>;
    /** Called once with the answer of a successful read; anything it throws is kept from the read. */
    onResponse?: (answer: ServedAnswer) => void | Promise<void>;
}

const headersOf = (headers: unknown): Record<string, string> => {
    if (!headers) return {};
    if (headers instanceof Headers) return Object.fromEntries(headers.entries());
    if (Array.isArray(headers)) return Object.fromEntries(headers as Array<[string, string]>);
    return headers as Record<string, string>;
};

/** Joins a read's own request options with the view's, keeping both sets of headers. */
export function withRead<O extends object>(base: O, read?: ReadOptions): O & ReadOptions {
    if (!read) return base as O & ReadOptions;
    const own = headersOf((base as { headers?: unknown }).headers);
    return { ...base, headers: { ...own, ...(read.headers ?? {}) }, ...(read.onResponse ? { onResponse: read.onResponse } : {}) } as O & ReadOptions;
}