Elder Ray Index (ERI)

/**
 * Calculates the Elder-Ray Index.
 * Measures buying and selling pressure.
 * Components:
 * 1. EMA(Close, period)
 * 2. Bull Power = High - EMA
 * 3. Bear Power = Low - EMA
 *
 * @param {array} data - The input range. Must include at least 5 columns: Date, Open, High, Low, Close.
 * @param {number} [period=13] - The EMA period (default 13).
 * @returns {array} A multi-column array with headers "Date", "Bull Power", "Bear Power", "EMA".
 * @customfunction
 */
function ERI(data, period = 13) {
    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", `Bull Power (${period})`, `Bear Power (${period})`, `EMA (${period})`]];

    // Logic: Calculate EMA, then subtract from High/Low.
    // We use self-contained EMA calculation loop.

    let ema = 0;
    const k = 2 / (period + 1);
    const buffer = []; // buffer for initial SMA
    let sum = 0;

    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];

        let bullPower = "";
        let bearPower = "";
        let currentEma = "";

        // EMA State Machine
        if (buffer.length < period) {
            buffer.push(close);
            sum += close;

            if (buffer.length === period) {
                // Initialize EMA with SMA
                ema = sum / period;
                currentEma = ema;
                bullPower = high - ema;
                bearPower = low - ema;
            }
        } else {
            // Calculate EMA
            ema = (close * k) + (ema * (1 - k));
            currentEma = ema;
            bullPower = high - ema;
            bearPower = low - ema;
        }

        if (currentEma === "") {
            results.push([date, "", "", ""]);
        } else {
            results.push([date, bullPower, bearPower, currentEma]);
        }
    }

    // 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]];
    }
}