export async function blobToBase64(data: Blob): Promise<string> {
    return new Promise<string>((resolve, reject) => {
        var fileReader = new FileReader();
        fileReader.onloadend = () => {
            resolve(fileReader.result as string);
        };
        fileReader.onerror = () => {
            reject();
        };
        fileReader.readAsDataURL(data);
    });
}

/** returns true of the string is a data: with base64 content */
export function isBase64ImageData(str: string): boolean {
    return str.startsWith("data") && str.indexOf("base64") > 0;
}

const alphabet = [
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
    'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
    'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
    'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
    'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
    'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
    'w', 'x', 'y', 'z', '0', '1', '2', '3',
    '4', '5', '6', '7', '8', '9', '+', '/'
];

const values = {};
for (let i = 0; i < alphabet.length; ++i) {
    values[alphabet[i]] = i;
}

function encode(bytes: ArrayBuffer): string {
    const array = new Uint8Array(bytes);
    const base64 = [];
    let index = 0;
    let quantum;
    let value;

    // Grab as many sets of 3 bytes as we can, that form 24 bits.
    while (index + 2 < array.byteLength) {
        quantum = (array[index] << 16) | (array[index + 1] << 8) | array[index + 2];
        // 24 bits will become 4 base64 chars.
        value = (quantum >> 18) & 0x3f;
        base64.push(alphabet[value]);
        value = (quantum >> 12) & 0x3f;
        base64.push(alphabet[value]);
        value = (quantum >> 6) & 0x3f;
        base64.push(alphabet[value]);
        value = quantum & 0x3f;
        base64.push(alphabet[value]);
        index += 3;
    }
    // At this point, there are 0, 1 or 2 bytes left.
    if (index + 1 === array.byteLength) {
        // 8 bits; shift by 4 to pad on the right with 0s to make 12 bits total.
        quantum = array[index] << 4;
        value = (quantum >> 6) & 0x3f;
        base64.push(alphabet[value]);
        value = quantum & 0x3f;
        base64.push(alphabet[value]);
        base64.push('==');
    } else if (index + 2 === array.byteLength) {
        // 16 bits; shift by 2 to pad on the right with 0s to make 18 bits total.
        quantum = (array[index] << 10) | (array[index + 1] << 2);
        value = (quantum >> 12) & 0x3f;
        base64.push(alphabet[value]);
        value = (quantum >> 6) & 0x3f;
        base64.push(alphabet[value]);
        value = quantum & 0x3f;
        base64.push(alphabet[value]);
        base64.push('=');
    }
    return base64.join('');
}

function decode(string: string): Uint8Array {
    let size = string.length;
    if (size === 0) {
        return new Uint8Array(new ArrayBuffer(0));
    }
    if (size % 4 !== 0) {
        throw new Error('Bad length: ' + size);
    }
    if (!string.match(/^[a-zA-Z0-9+/]+={0,2}$/)) {
        throw new Error('Invalid base64 encoded value');
    }
    // Every 4 base64 chars = 24 bits = 3 bytes. But, we also need to figure out
    // padding, if any.
    let bytes = 3 * (size / 4);
    let numPad = 0;
    if (string.charAt(size - 1) === '=') {
        numPad++;
        bytes--;
    }
    if (string.charAt(size - 2) === '=') {
        numPad++;
        bytes--;
    }
    const buffer = new Uint8Array(new ArrayBuffer(bytes));
    let index = 0;
    let bufferIndex = 0;
    let quantum;
    if (numPad > 0) {
        size -= 4; // handle the last one specially
    }

    while (index < size) {
        quantum = 0;
        for (let i = 0; i < 4; ++i) {
            quantum = (quantum << 6) | values[string.charAt(index + i)];
        }
        // quantum is now a 24-bit value.
        buffer[bufferIndex++] = (quantum >> 16) & 0xff;
        buffer[bufferIndex++] = (quantum >> 8) & 0xff;
        buffer[bufferIndex++] = quantum & 0xff;
        index += 4;
    }
    if (numPad > 0) {
        // if numPad === 1, there is one =, and we have 18 bits with 2 0s at end.
        // if numPad === 2, there is two ==, and we have 12 bits with 4 0s at end.
        // First, grab my quantum.
        quantum = 0;
        for (let i = 0; i < 4 - numPad; ++i) {
            quantum = (quantum << 6) | values[string.charAt(index + i)];
        }
        if (numPad === 1) {
            // quantum is 18 bits, but really represents two bytes.
            quantum = quantum >> 2;
            buffer[bufferIndex++] = (quantum >> 8) & 0xff;
            buffer[bufferIndex++] = quantum & 0xff;
        } else {
            // quantum is 12 bits, but really represents only one byte.
            quantum = quantum >> 4;
            buffer[bufferIndex++] = quantum & 0xff;
        }
    }
    return buffer;
}

export function toArrayBuffer(base64: string): ArrayBuffer {
    var uint8Array = decode(base64);
    return uint8Array.buffer;
}

export function toUint8Array(base64: string): Uint8Array {
    return decode(base64);
}

export function fromArrayBuffer(arraybuffer: ArrayBuffer) {
    return encode(arraybuffer);
}

export function fromUint8Array(uint8Array: Uint8Array) {
    return encode(uint8Array.buffer);
}

export function dataURLtoFile(dataurl, filename): File {

    var arr = dataurl.split(','),
        mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]),
        n = bstr.length,
        u8arr = new Uint8Array(n);

    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }

    return new File([u8arr], filename, { type: mime });
}