Method floatIndexToTimestamp

src/Store.ts:1079–1129

* Converts a float data index to an interpolated timestamp. * This allows sub-bar precision for smooth freehand drawings. * Supports extrapolation beyond the data range (drawing in the "future"). * @param floatIndex - A floating point index (e.g., 42.75) * @returns An interpolated timest

(floatIndex: number)

   * @returns An interpolated timestamp between two bars
   */
  floatIndexToTimestamp (floatIndex: number): Nullable<number> {
    const length = this._dataList.length
    if (length === 0) {
      return null
    }

    const lastIndex = length - 1

    // Handle float index beyond the last bar (extrapolate into the future)
    if (floatIndex > lastIndex && length >= 2) {
      const lastTimestamp = this._dataList[lastIndex].timestamp
      const secondLastTimestamp = this._dataList[lastIndex - 1].timestamp
      const barDuration = lastTimestamp - secondLastTimestamp
      if (barDuration > 0) {
        const barsBeyondLast = floatIndex - lastIndex
        return Math.round(lastTimestamp + barsBeyondLast * barDuration)
      }
    }

    // Handle float index before the first bar (extrapolate into the past)
    if (floatIndex < 0 && length >= 2) {
      const firstTimestamp = this._dataList[0].timestamp
      const secondTimestamp = this._dataList[1].timestamp
      const barDuration = secondTimestamp - firstTimestamp
      if (barDuration > 0) {
        return Math.round(firstTimestamp + floatIndex * barDuration)
      }
    }

    // Normal case: interpolate between two bars within the data range
    const intIndex = Math.floor(floatIndex)
    const fraction = floatIndex - intIndex

    // Get timestamp at the integer index
    const timestampAtInt = this.dataIndexToTimestamp(intIndex)

    // If no fractional part, return the integer timestamp
    if (fraction === 0 || !isNumber(timestampAtInt)) {
      return timestampAtInt
    }

    // Get timestamp at the next index for interpolation
    const timestampAtNext = this.dataIndexToTimestamp(intIndex + 1)

    if (isNumber(timestampAtNext)) {
      // Linear interpolation between the two timestamps
      return Math.round(timestampAtInt + (timestampAtNext - timestampAtInt) * fraction)
    }

    return timestampAtInt
  }

  /**
   * Converts a precise timestamp to a float data index.