identify-media/src/lib/makeHash.ts

Analyse file path and content to make search criteria for media APIs

const initBlock = (size: number): number[] => {
    let temp = size;
    const longs: number[] = [];

    for (let i = 0; i < 8; i++) {
        longs[i] = temp & 255;
        temp = temp >> 8;
    }

    return longs;
}

const processChunk = (chunk: string, init: number[]): number[] => {
    return chunk.split('').reduce((result, current, index): number[] => {
        const idx = (index + 8) % 8;
        return result.slice(0, idx).concat(result[idx] + current.charCodeAt(0)).concat(result.slice(idx+1));
    }, init);
}

interface Normalized {
    normalized: number[];
    overflow: number;
}

const longsToBin = (longs: number[]): number[] => {
    return longs.reduce((result, current): Normalized => {
        const sum = current + result.overflow;
        const overflow = sum >> 8;
        return {
            normalized: result.normalized.concat(sum & 255),
            overflow
        }
    }, {normalized: [], overflow: 0} as Normalized).normalized;
}

const bin2hex = (longs: number[]): string => {
    const hexString = '0123456789abcdef';
    return longsToBin(longs).reverse().reduce((result, current): string => {
        return result + hexString.charAt(current >> 4 & 15) + hexString.charAt(current & 15);
    }, '');
}

export const makeHash = (size: number, firstChunk: Promise<string>, secondChunk: Promise<string>): Promise<string> => {
    return firstChunk
        .then((chunk) => processChunk(chunk, initBlock(size)))
        .then((longs) => secondChunk.then((chunk) => processChunk(chunk, longs)))
        .then(bin2hex);
}