StoneX Group wants to display Fibonacci retracement levels for a price series in a market-analysis surface. Given chronological prices and a trend direction, identify the largest valid directional swing, then calculate the standard retracement levels for that swing.
For an uptrend, the swing low must occur before the swing high. Select the pair with the greatest increase. For a downtrend, the swing high must occur before the swing low. Select the pair with the greatest decrease.
Use the ratios [0.0, 0.236, 0.382, 0.5, 0.618, 0.786, 1.0]. For an uptrend, calculate each level as high - (high - low) * ratio. For a downtrend, calculate it as low + (high - low) * ratio. Round every returned numeric value to six decimal places.
Implement fibonacci_retracement(prices, direction). Return a dictionary containing swing_low, swing_high, and levels, where levels is an array ordered by the ratios above. Assume prices contain valid positive numbers and the direction is either "uptrend" or "downtrend".
def fibonacci_retracement(prices, direction):