typia/lib/internal/_notationSnake.mjs

Superfast runtime validators with only one line

const _notationSnake = (str) => {
    if (str.length === 0)
        return str;
    // PREFIX
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    let prefix = "";
    for (let i = 0; i < str.length; i++) {
        if (str[i] === "_")
            prefix += "_";
        else
            break;
    }
    if (prefix.length !== 0)
        str = str.substring(prefix.length);
    const out = (s) => `${prefix}${s}`;
    // SNAKE CASE
    const items = str.split("_");
    if (items.length > 1)
        return out(items.map((s) => s.toLowerCase()).join("_"));
    // CAMEL OR PASCAL CASE
    const indexes = [];
    for (let i = 0; i < str.length; i++) {
        const code = str.charCodeAt(i);
        if (65 <= code && code <= 90)
            indexes.push(i);
    }
    for (let i = indexes.length - 1; i > 0; --i) {
        const now = indexes[i];
        const prev = indexes[i - 1];
        if (now - prev === 1)
            indexes.splice(i, 1);
    }
    if (indexes.length !== 0 && indexes[0] === 0)
        indexes.splice(0, 1);
    if (indexes.length === 0)
        return str.toLowerCase();
    let ret = "";
    for (let i = 0; i < indexes.length; i++) {
        const first = i === 0 ? 0 : indexes[i - 1];
        const last = indexes[i];
        ret += str.substring(first, last).toLowerCase();
        ret += "_";
    }
    ret += str.substring(indexes[indexes.length - 1]).toLowerCase();
    return out(ret);
};

export { _notationSnake };
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