# functions go here


def unit_checker():
    unit = not_blank("What is the unit of measurement for these items?: ",
                             "",
                             "no")
    unit_tocheck = unit.lower()

    # Abbreviations lists
    gram = ["grams", "g", "gms", "gm", "gram"]
    kilogram = ["kilograms", "kg", "kgs", "kilogram"]
    litre = ["litre",  "ltr","liter", "l", "litres","ltrs", "liters"]
    millilitre = ["ml", "millilitre", "milliliter", "mls", "millilitres", "milliliters"]
    valid = False
    while not valid:
        if unit_tocheck in gram:
            return "gram"
        elif unit_tocheck in kilogram:
            return "kilogram"
        elif unit_tocheck in litre:
            return "litre"
        elif unit_tocheck in millilitre:
            return "millilitre"
        else:
            global not_right_unit
            not_right_unit = "False"
            break


# checks input is a number
def num_check(question):

    error = "Please enter a number."

    valid = False
    while not valid:
        try:
            response = float(input(question))
            return response
        except ValueError:
            print(error)


# Not blank function
def not_blank(question, error_msg, num_ok):
    error = error_msg

    valid = False
    while not valid:
        response = input(question)
        has_errors = ""

        if num_ok != "yes":
            # look at each character in string and if it's a number, complain
            for letter in response:
                if letter.isdigit() == True:
                    has_errors = "yes"
                    error = "Please try again - numbers are not allowed in this field"
                    break

        if response == "" or response == " ":
            error = "Please type something (this can't be left blank)"
            print(error)
            continue
        elif has_errors != "":
            print(error)
            continue
        else:
            return response


# Main routine...

# setting up conversion dictionary
unit_central = {
    "litre": 1000,
    "millilitre": 1,
    "gram": 1,
    "kilogram": 1000
}

# Set up empty items list
items = []
is_unit_same = []
avg_unit_price = []

# just declaring some locally assigned variables
unit = ""
item_weight = ""
item_cost = ""

# loop to ask users to enter an item

stop = ""
while stop != "xxx":
    item = []
    user_keeps = ""
    # Ask user for item (via not blank function)
    item_name = not_blank("Please type in the item name (type 'xxx' to stop): ",
                                "",
                                "yes")
    # Stop looping if exit code is typed and there are more
    # than 2 items
    if item_name.lower() == "xxx" and len(items) > 1:
        break

    elif item_name.lower() == "xxx" and len(items) < 2:
        print("You need at least two items in the list. "
              "Please add more items")
        continue
    is_item_weight_too_small = ""
    while is_item_weight_too_small == "":
        item_weight = num_check("Please type in the item weight/volume: ")
        # item weight needs to be greater than 0.1 because users might be comparing lutetium
        # with other elements and I want them to be able to do that
        if item_weight < 0.1:
            print("Please enter a number that is more than (or equal to) 0.1.")
            continue
        else:
            break

    # unit should only be gms, kgs, mls and litres
    is_unit_false = ""
    while is_unit_false == "":
        not_right_unit = ""
        unit = unit_checker()
        if not_right_unit == "False":
            print("Only Gms, Kgs, Mls and Litres are allowed")
        else:
            break
    # check if item cost is below $10
    is_item_cost_too_small = ""
    while is_item_cost_too_small == "":
        item_cost = num_check("Please type in the item cost: $")
        if item_cost < 0.10:
            print("Please enter a number that is more than or equal to 0.1.")
            continue
        else:
            break

    print()

# add item to list
    item.append(item_name)
    item.append(item_weight)

# turning everything to gram or mls
    make_all_units_one = False
    while not make_all_units_one:
        if unit in unit_central:
            multiply_by = unit_central.get(unit)
            item[1] = item[1] * multiply_by
            break

# display unit as grams or millilitres
    if unit.startswith("k", 0, 1):
        unit = unit.replace(unit, "grams")
    elif unit.startswith("l", 0, 1):
        unit = unit.replace(unit, "millilitres")

# add to list
    item.append(item_cost)
    item.append(item[2] / item[1])  # find cost per gram and add to item

    item.append(unit)
    items.append(item)

print()

# sorts by least expensive to most expensive
items.sort(key=lambda x: x[3],)
print("**** Items by Cost <Least Expensive to Most Expensive> ****")
# Every item in items gets gets formatted and printed.
for x in range(len(items)):
    print("{} {:.0f} {} costs ${:.4f} per {}".format(items[x][0], items[x][1], items[x][4], items[x][3], items[x][4].replace('s', ''))) # take away the 's' e.g cost per grams should be cost per gram.
    avg_unit_price.append(items[x][3])
    is_unit_same.append(items[x][4].replace('s', ''))

is_unit_same = list(dict.fromkeys(is_unit_same))

# if the measuring items are not of the same unit
if len(is_unit_same) != 1:
    print()
    print("Note: to get accurate results please compare items with the same unit")

# Calculate Average Unit Price
avg_unit_price = sum(avg_unit_price) / len(avg_unit_price)

print()
# Print Avg Unit Price
print("The average unit price is ${:.4f} in {}s".format(avg_unit_price, items[0][4].replace('s', '')))