# Functions go here


# function that consists of all the instructions
def instructions():
    print()
    print("******** Instructions ********")
    print()
    print("This handy program compares one item to another, it can convert between grams to kilograms and millilitres to litres. \n"
          "It also tells you what item is the best value for your money! Imagine that!.")

    print()
    print("The program will ask for your budget. \n"
          "All you need to do is put in how much you have on hand. \n"
          "Leave the rest to the program.")

    print()
    print("The program also asks for the type of item you are comparing. \n"
          "This is relatively straight forward. But here is an explanation if you are still confused: \n"
          "if you are comparing Kit-Kat with Snickers than the type of item you are comparing is Chocolates.")
    print()
    print("Then the computer will ask you for the item name. \n"
          "Going back about to the example of chocolates above, the item name will be Kit-Kat.")
    print()
    print("The program will then ask you about the weight of your item.\n"
          "e.g Kit-Kat weighs 55 grams so you put in 55. \n"
          "Then the program will ask you the unit, so you can enter grams or gm (use any abbreviation you like).")
    print()
    print("Lastly, you would be asked for the cost of the item. \n"
          "If for example Kit-Kat 55 grams costs 1.50, then you put in 1.50 \n"
          "Yup, it's as simple as that.")
    print()
    print("This process is repeated unit you put in 'xxx'. This tells the program that you have entered all the items \n"
          "you want to compare.")
    print()
    print("Then as if it were magic, the program will sort out all your items and give you a recommendation on what to buy.")
    print("**********")
    print()


# Check user input is either yes or no
def yes_no_check(question):
    error = "Please enter 'yes' or 'no'"

    valid = False
    while not valid:
        response = input(question).lower()

        if response == "y" or response == "yes":
            return ("yes")
        elif response == "n" or response == "no":
            return ("no")
        else:
            print(error)


# unit checker function checks the unit is gm,kg,ml and sees the abbreviations for them
def unit_checker():
    unit = not_blank("What is the unit of measurement for this item?: ",
                     "",
                     "no")
    unit_tocheck = unit.lower()

    # Abbreviations lists
    gram = ["grams", "g", "gms", "gm", "gram", "grm", "grms"]
    kilogram = ["kilograms", "kg", "kgs", "kilogram", "k"]
    litre = ["litre",  "ltr","liter", "l", "litres","ltrs", "liters", "lit"]
    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 if something 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)


# function that checks if there are numbers in the input or not
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
        # response can't be blank
        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

# ***** Welcome / Instructions ********
print("******** Welcome to the Great Comparison Calculator ********")
print()

get_instructions = yes_no_check("Welcome.  Is it your first time using this "
                                "program? ")

if get_instructions.lower() == "yes":
    instructions()
else:
    print()


budget = ""
minimum_amount = False
while not minimum_amount:
    budget = num_check("What is your budget?: $")
    budget_too_small = "Please enter a number that is more than or equal to 10."
    if budget < 10:  # budget must be at least $10
        print(budget_too_small)
        continue
    else:
        break

item_type = not_blank("What type of item do you want to compare? (e.g. Chocolates): ",
                      "",  # rather than having a generic error like "Blanks and numbers are not allowed"
                      "no")  # I wanted to tell the user exactly what is wrong in their code.


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

# Set up empty items list
items = []
avg_unit_price = []
# just declaring some locally assigned variables
unit = ""
item_cost = ""
display_unit = ""
item_weight = ""

# loop to ask users to enter item details

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
        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: $")
        # user may want to enter non-compareble items
        while user_keeps == "":
            # item cost needs to be smaller than the budget
            if budget < item_cost:
                print("Your item cost is greater than your budget, it won't be included in the recommendation")
                user_keeps = "True"
                break
            # item cost needs to be greater than 10 cents
            if item_cost < 0.10:
                print("Please enter a number that is more than or equal to 0.1.")
                continue
            else:
                break
        break

    if user_keeps != "":
        print()
        continue

# this print() makes a space and this tells the user to put the next item.
    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
    # add to list
    item.append(item_cost)
    cost_per = item[2] / item[1]
    item.append(cost_per)  # find cost per gram and add to item

    # I want the first unit to be displayed as grams or millilitres
    # second unit to be displayed as kilograms or litres
    if unit.startswith("k", 0, 1):
        unit = unit.replace(unit, "grams")
        display_unit = "kilograms"
    elif unit.startswith("l", 0, 1):
        unit = unit.replace(unit, "millilitres")
        display_unit = "litres"
    elif unit.startswith("g", 0, 1):
        display_unit = "kilograms"
        unit = unit.replace(unit, "grams")
    elif unit.startswith("m", 0, 1):
        display_unit = "litres"
        unit = unit.replace(unit, "millilitres")

    # add it to the list
    item.append(unit)
    item.append(display_unit)
    item.append(cost_per * 1000)

    items.append(item)
# looks better with a space
print()
print("***** Comparison Time! *****")
print()
# if budget has a decimal value - then show the decimal value, if not then don't
if budget % 1 == 0:
    print("Budget is ${:.0f}".format(budget))
else:
    print("Budget is ${:.2f}".format(budget))

print()  # spaces things out -> easier to see

# 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 ${:.2f} per {}".format(items[x][0], items[x][1], items[x][4], items[x][6],
                                                     # take away the 's' e.g cost per grams should be cost per gram.
                                                     items[x][5].replace('s', '')))
    avg_unit_price.append(items[x][6])

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

print()
print("The average unit price is ${:.2f} in {}s".format(avg_unit_price, items[0][5].replace('s', '')))
print()

# Recommend
print("**** Recommendations ****")

print("The cheapest item is {} {} for ${:.2f} and the most expensive item is {} {} for ${:.2f}"
      .format(items[0][0], item_type.replace('s', ''), items[0][2] ,items[-1][0], item_type.replace('s', ''), items[-1][2]))

print("When comparing {}, I recommend buying {} as it costs you the least and is the best value for your money."
      .format(item_type, items[0][0]))