import csv

def readData():
    fields = ("name", "city", "miles", "gallons")
    f = open("travel.txt", "r")
    travels = []    # create empty list

    dReader = csv.DictReader(f, fieldnames=fields, delimiter="\t")  # read file f, using fields by tab

    for row in dReader: # each row is converted to a dictionary
        travels.append(row) # append dictionary to list

    f.close()
    return travels  # return list of dictionaries

def displayData(trips):     # trips is the list of dictionaries
    fs = "%-8s %-16s %7s %s"    # create format string
    print(fs % ("Name", "City", "Miles", "Gallons"))    # print header
    print()
    for t in trips:                 # t is a dictionary
        fs = "%-8s %-16s %6s %5s"   # makes format string
        print(fs % (t['name'].title(), t['city'].title(), t['miles'], t['gallons']))

def calculateData(trips):
    totalM = []
    totalG = []
    print()
    userName = input("Enter user's first name: ").lower()
    print()
    for row in trips:
        if row.get('name') == userName:
            totalM.append(float(row.get('miles')))
            totalG.append(float(row.get('gallons')))
            totalMiles = sum(totalM)
            totalGallons = sum(totalG)
    mpg = totalMiles / totalGallons
    cost = totalMiles * 0.75
    print('Name: ', userName.title())
    print("Total miles: ", "%.2f" % totalMiles)
    print("Total gallons: ", "%.2f" % totalGallons)
    print("mpg = ", "%.2f" % mpg)
    print("Owed: $", "%.2f" % cost, "at 75 cents per mile")

def addTrip(trips):
    nom = input("Enter your first name: ")
    city = input("Enter destination city: ")
    mi = input("Enter miles traveled: ")    # get user input, create dictionary, add to list
    gal = input( "Enter gallons used: ")    # all the data are strings
    record = {'name' : nom, 'city' : city, 'miles' : mi, 'gallons' : gal}   # create the dictionary
    trips.append(record)                    # append dictionary to list
    return trips

def storeData(trips):
    fields = ("name", "city", "miles", "gallons")
    f = open("travel.txt", "w")
    dWriter = csv.DictWriter(f, fieldnames=fields, delimiter="\t", lineterminator="\n") # get file ready
    dWriter.writerows(trips)    # write the whole list of dictionaries to tab separated text file

    f.close()

def main():
    travel_log = readData()   # read file, convert records to a list of dictionaries
    while True:
        print("""
Menu options. Choose 1, 2, 3, or 4
1. Display all trip data
2. Calculate user data
3. Add a trip
4. Save and exit
""")
        opt = input("   Enter your choice, 1, 2, 3 or 4: ")
        if opt == "1":
            print()         #prints a blank line
            displayData(travel_log)
        elif opt == "2":
            calculateData(travel_log)
        elif opt == "3":
            travel_log = addTrip(travel_log)
        elif opt == "4":
            storeData(travel_log)
            print("Goodbye")
            print()
            break     #exit loop
        else:
            print("Invalid entry, please re-enter your choice")
            print()

main() # Call main(), execute the program