Commodity Channel Index (CCI)

/**
 * Calculates the Commodity Channel Index (CCI).
 * CCI = (Typical Price - SMA(Typical Price)) / (0.015 * Mean Deviation)
 * Mean Deviation = SMA(abs(Typical Price - SMA(TP)))
 *
 * @param {array} data - The input range. Must include at least 5 columns: Date, Open, High, Low, Close.
 * @param {number} [period=20] - The lookback period (default 20).
 * @returns {array} A two-column array with headers "Date" and "CCI".
 * @customfunction
 */
function CCI(data, period = 20) {
    checkPremium();

    // Argument validation
    if (arguments.length < 1 || arguments.length > 2) {
        throw new Error(`Wrong number of arguments. Expected 1 or 2, but got ${arguments.length}.`);
    }
    if (period !== undefined) {
        if (typeof period !== 'number' || period <= 0 || !Number.isInteger(period)) {
            throw new Error(`Invalid period. The period must be a positive integer. Got: ${period}`);
        }
    }

    const processedData = getData(data);

    // --- Validate Data Structure ---
    const columnCount = processedData[0].length;
    if (columnCount < 5) {
        throw new Error(`Invalid data structure. Expected at least 5 columns (Date, O, H, L, C), but got ${columnCount}.`);
    }

    const dataRows = processedData.slice(1);
    const results = [["Date", `CCI (${period})`]];

    // We need a sliding window of Typical Prices (TP)
    // TP = (H + L + C) / 3
    const tpBuffer = [];

    for (let i = 0; i < dataRows.length; i++) {
        const row = dataRows[i];
        const date = row[0];
        const high = row[2];
        const low = row[3];
        const close = row[4];

        const tp = (high + low + close) / 3;
        tpBuffer.push(tp);

        if (tpBuffer.length > period) {
            tpBuffer.shift();
        }

        if (tpBuffer.length < period) {
            results.push([date, ""]);
            continue;
        }

        // Calculate SMA of TP
        let sumTP = 0;
        for (let j = 0; j < tpBuffer.length; j++) {
            sumTP += tpBuffer[j];
        }
        const smaTP = sumTP / period;

        // Calculate Mean Deviation
        // MeanDev = Sum(Abs(TP - SMA)) / period
        let sumDev = 0;
        for (let j = 0; j < tpBuffer.length; j++) {
            sumDev += Math.abs(tpBuffer[j] - smaTP);
        }
        const meanDev = sumDev / period;

        // Calculate CCI
        // 0.015 is the standard Lambert constant.
        // Handle div by zero if meanDev is 0 (price perfectly flat)
        let cci = 0;
        if (meanDev === 0) {
            cci = 0;
        } else {
            cci = (tp - smaTP) / (0.015 * meanDev);
        }

        results.push([date, cci]);
    }

    // Trim Output
    let firstValidIndex = -1;
    for (let i = 1; i < results.length; i++) {
        if (results[i][1] !== "" && results[i][1] !== null) {
            firstValidIndex = i;
            break;
        }
    }

    if (firstValidIndex !== -1) {
        return [results[0], ...results.slice(firstValidIndex)];
    } else {
        return [results[0]];
    }
}