/* eslint-disable no-param-reassign */
export function parseImageSize(str: string, pos: number, max: number) {
    const result = {
        ok: false,
        pos: 0,
        width: '',
        height: '',
    };

    if (pos >= max) {
        return result;
    }

    let code = str.charCodeAt(pos);

    if (code !== 0x3d /* = */) {
        return result;
    }

    pos++;

    // size must follow = without any white spaces as follows
    // (1) =300x200
    // (2) =300x
    // (3) =x200
    code = str.charCodeAt(pos);
    if (code !== 0x78 /* x */ && (code < 0x30 || code > 0x39) /* [0-9] */) {
        return result;
    }

    // parse width
    const resultW = parseNextNumber(str, pos, max);
    pos = resultW.pos;

    // next charactor must be 'x'
    code = str.charCodeAt(pos);
    if (code !== 0x78 /* x */) {
        return result;
    }

    pos++;

    // parse height
    const resultH = parseNextNumber(str, pos, max);
    pos = resultH.pos;

    result.width = resultW.value;
    result.height = resultH.value;
    result.pos = pos;
    result.ok = true;

    return result;
}

function parseNextNumber(str: string, pos: number, max: number) {
    let code;
    const start = pos;
    const result = {
        pos,
        ok: false,
        value: '',
    };

    code = str.charCodeAt(pos);

    while ((pos < max && code >= 0x30 /* 0 */ && code <= 0x39) /* 9 */ || code === 0x25 /* % */) {
        code = str.charCodeAt(++pos);
    }

    result.ok = true;
    result.pos = pos;
    result.value = str.slice(start, pos);

    return result;
}