# Problem 3: Rocket Recursion
from math import exp

# STAGE 1: surface to LEO = 9.4 km/s
# STAGE 2: LEO to moon capture = 3.26 km/s
# STAGE 3: moon capture to surface = 2.41 km/s

# Initialize the stages data
  # A list containing multiple dictionaries
stages = [{'d_v': 9.4, 'v_e': 2.3, 'sdm': 16000},
          {'d_v': 3.26, 'v_e': 2.3, 'sdm': 8000},
          {'d_v': 2.41, 'v_e': 2.3, 'sdm': 4500}]
# WHERE
  # d_v = delta velocity
  # v_e = exhaust velocity
  # sdm = dry mass of that specific stage


def wet_mass(stages):
    """Recursive solution for finding the wet mass
    of a series of stages
    Input: list of dictionaries with defined values:
    Example:
        stages = [{'d_v': 9.4, 'v_e': 2.3, 'sdm': 16000},
                  {'d_v': 3.26, 'v_e': 2.3, 'sdm': 8000},
                  {'d_v': 2.41, 'v_e': 2.3, 'sdm': 4500}]
    """
    # if there are no more stages, return 0
    if len(stages) == 0:
        return 0
    # otherwise, return the wet mass, and calculate
    # the next stage
    else:
        # index the first dictionary in the list
        workingdict = stages[0]
        d_v = workingdict.get('d_v')
        v_e = workingdict.get('v_e')
        sdm = workingdict.get('sdm')
        # m_o = m_f * exp(d_v/v_e)
        return (wet_mass(stages[1:])+sdm)*exp(d_v/v_e)
        # our above return statement indexes and passes the
        # rest of our dictionaries in the list
        # for the next recursion.


# Find the initial wet launch mass needed and print it.
launch_mass = wet_mass(stages)
print(f"Launch Mass: {launch_mass:.2f} kg")