const REPEAT_COUNT = 7;
const MAX_PATTERN_TOKENS = 256;
const MAX_BUFFER_CHARS = 32768;

function tokenize(text) {
    return String(text ?? "").match(/<[^>\s]+>|[\p{L}\p{M}\p{N}_]+|[^\s\p{L}\p{M}\p{N}_]+/gu) || [];
}

function sameBlock(tokens, aStart, bStart, length) {
    for (let i = 0; i < length; i++) {
        if (tokens[aStart + i] !== tokens[bStart + i]) return false;
    }
    return true;
}

function findRepeatedTail(tokens, options = {}) {
    const repeatCount = options.repeatCount ?? REPEAT_COUNT;
    const maxPatternTokens = options.maxPatternTokens ?? MAX_PATTERN_TOKENS;
    if (repeatCount < 2) throw new Error("repeatCount must be at least 2");

    const maxPeriod = Math.min(maxPatternTokens, Math.floor(tokens.length / repeatCount));
    for (let periodTokens = 1; periodTokens <= maxPeriod; periodTokens++) {
        const tailStart = tokens.length - (periodTokens * repeatCount);
        const referenceStart = tokens.length - periodTokens;
        let repeated = true;

        for (let repeat = 0; repeat < repeatCount - 1; repeat++) {
            const candidateStart = tailStart + (repeat * periodTokens);
            if (!sameBlock(tokens, candidateStart, referenceStart, periodTokens)) {
                repeated = false;
                break;
            }
        }

        if (!repeated) continue;
        const pattern = tokens.slice(referenceStart);
        return {
            repeatCount,
            periodTokens,
            pattern,
            sample: pattern.join(" ").slice(0, 240)
        };
    }

    return null;
}

function createDetector(options = {}) {
    const maxBufferChars = options.maxBufferChars ?? MAX_BUFFER_CHARS;
    let buffer = "";

    return {
        push(text) {
            buffer += String(text ?? "");
            if (buffer.length > maxBufferChars) buffer = buffer.slice(-maxBufferChars);
            return findRepeatedTail(tokenize(buffer), options);
        },
        reset() {
            buffer = "";
        }
    };
}

module.exports = {
    REPEAT_COUNT,
    MAX_PATTERN_TOKENS,
    tokenize,
    findRepeatedTail,
    createDetector
};