@gmod/vcf/esm/parseMetaString.js

High performance streaming Variant Call Format (VCF) parser in pure JavaScript

// constructed with the assistance of claude AI
//
// I first prompted it with a regex that splits a comma separated string with
// awareness of quotation from this stackoverflow queston
// https://stackoverflow.com/a/18893443/2129219, and asked it to add support
// for square brackets
//
// it undid the regex into serial logic and the result was this function
function customSplit(str) {
    const result = [];
    let current = '';
    let inQuotes = false;
    let inBrackets = false;
    for (const char of str) {
        if (char === '"') {
            inQuotes = !inQuotes;
            current += char;
        }
        else if (char === '[') {
            inBrackets = true;
            current += char;
        }
        else if (char === ']') {
            inBrackets = false;
            current += char;
        }
        else if (char === ',' && !inQuotes && !inBrackets) {
            result.push(current.trim());
            current = '';
        }
        else {
            current += char;
        }
    }
    if (current) {
        result.push(current.trim());
    }
    return result;
}
function splitFirst(str, split) {
    const index = str.indexOf(split);
    return [str.slice(0, index), str.slice(index + 1)];
}
export function parseMetaString(metaString) {
    const inside = metaString.replace(/^<|>$/g, '');
    return Object.fromEntries(customSplit(inside).map(f => {
        const [key, val] = splitFirst(f, '=');
        if (val && val.startsWith('[') && val.endsWith(']')) {
            return [
                key,
                val
                    .slice(1, -1)
                    .split(',')
                    .map(f => f.trim()),
            ];
        }
        else if (val && val.startsWith('"') && val.endsWith('"')) {
            return [key, val.slice(1, -1)];
        }
        else {
            return [key, val?.replaceAll(/^"|"$/g, '')];
        }
    }));
}
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