Weighted Moving Average (WMA)

**
 * Calculates the Weighted Moving Average (WMA) for a given dataset and period.
 *
 * @param {array} data - A range containing date and close prices.
 * @param {number} period - The number of periods for the WMA.
 * @returns {array} - A 2D array with headers: Date, WMA.
 * @customfunction
 */

function WMA(data, period) {
  const processedData = getData(data);
  const dates = processedData.slice(1).map(row => row[0]); // Extract dates
  const closePrices = processedData[0].length === 2
    ? processedData.slice(1).map(row => row[1]) // For 2-column arrays, use the second column
    : processedData.slice(1).map(row => row[4]); // Default: use index 4 for close price

  // Check if the period is greater than the length of the data
  if (period > closePrices.length) {
    throw new Error("Error: The specified period exceeds the length of the data.");
  }

  // Initialize an array to store WMA values with corresponding dates
  let results = [["Date", `WMA(${period})`]]; // Include headers

  // Calculate weights
  const weights = Array.from({ length: period }, (_, i) => period - i); // [n, n-1, ..., 1]
  const totalWeight = weights.reduce((sum, weight) => sum + weight, 0); // Sum of weights

  // Calculate WMA for the given period
  for (let i = period - 1; i < closePrices.length; i++) {
    let weightedSum = 0;

    // Calculate weighted sum for the current period
    for (let j = 0; j < period; j++) {
      weightedSum += closePrices[i - j] * weights[j];
    }

    const wma = weightedSum / totalWeight; // Calculate WMA

    // Append the current date and WMA to the results array
    results.push([dates[i], wma]);
  }

  return results;
}

/**
 *
 * @param {Array<Array>} data - A 2D array of cell values to process. The first row should contain headers.
 * @returns {Array<Array>} - A 2D array where the first row contains headers and subsequent rows contain processed data.
 *
 * @customfunction
 * 
 */

function getData(data) {
  if (!data || data.length === 0) {
    throw new Error("Input data is empty or invalid.");
  }

  // Check if the first row contains headers
  const headers = Array.isArray(data[0]) && data[0].every(item => typeof item === "string")
    ? data[0]
    : null;

  if (!headers) {
    // If no headers, assume the first column is the date column and process data
    return data.map(row => row.map((value, index) => {
      return index === 0 ? new Date(value) : parseFloat(value);
    }));
  }

  // Process rows with headers
  return [headers, ...data.slice(1).map(row => headers.map((header, index) => {
    const key = header.toLowerCase();
    return key === "date" ? new Date(row[index]) : parseFloat(row[index]) || row[index];
  }))];
}