import {leading} from "@http4t/core/uri";

/**
 * Function which, given a path with leading slashes removed, tells me which index to consume until.
 *
 * Returning -1 if nothing can be consumed (e.g. path is empty, not long enough, etc.)
 */
export type PathConsumer = (pathNoLeadingSlashes: string) => number;

export type Consumed = {
    captured: string,
    consumed: string
    remaining: string
};

/**
 * 1. consume leading slashes from path
 * 2. use consumer to capture some substring of what's left, e.g. everything until the index of the first '/'
 */
export function consume(path: string, consumer: PathConsumer): Consumed | undefined {
    const prefix = path.match(leading)?.[0] || "";

    const leadingStripped = path.substring(prefix.length);

    const index = consumer(leadingStripped);
    if (index < 0) return undefined;
    if (index > leadingStripped.length) throw new Error(`cannot consume ${index} characters from ${leadingStripped.length} character path '${leadingStripped}'`);

    const captured = leadingStripped.substring(0, index);

    const consumed = prefix + captured;
    return {
        captured,
        consumed,
        remaining: path.substring(consumed.length)
    }
}

export function upToChars(count: number) {
    return (path: string): number => {
        return Math.min(count, path.length);
    }
}

export function exactlyChars(count: number) {
    return (path: string): number => {
        return path.length < count ? -1 : count;
    }
}

export function upToSegments(count: number) {
    return (path: string): number => {
        const segments = path.split('/', count);
        return segments.reduce((acc, s) => acc + 1 + s.length, -1);
    }
}

export function exactlySegments(count: number) {
    return (path: string): number => {
        const segments = path.split('/', count);
        return segments.length !== count ? -1 : segments.reduce((acc, s) => acc + 1 + s.length, -1);
    }
}

export function nextSlashOrEnd(path: string): number {
    const i = path.indexOf('/');
    return i > 0
        ? i
        : path !== ""
            ? path.length
            : -1;
}

export function endOfPath(path: string): number {
    return path === "" ? -1 : path.length;
}