from tkinter import*

country=[]                  #empty list of countries
populations=[]              #empty list of populations.

def function1(chosenLetter,shownCountries):         #function accepts parameters
    counter=0                                         #starts counter from 0
    for line in shownCountries:                   #loops through the characters of each lines
        if((line[0]== chosenLetter)):                 #matches contents of converted file with letter inputted by user
            splitCountry=line.split("\t-\t")    #splits each line with "    -    "
            country.append(splitCountry[0])             #split by countries
            populations.append(int(splitCountry[1]))    #split by their correspoding populations
    for countryname in country:
        counter+=1
        print(countryname)
    print("Countries with the letter inputted by user: ",chosenLetter, "number of coutries ",counter)



def function2(country,populations):
    for x in  range(0,len(populations)):
        if (max(populations) == populations[x]):
            print("country with highest population is ",country[x], "- ", populations[x])

def btnPress():
            if userName.get()=="admin" and password.get()=="secret":
                messagebox.showinfo("info", "Valid")
                root.destroy()
                while(True):
                    chosenLetter=input("Enter only the first letter: ").upper() #allows user to type in whatever case he wants
                    if chosenLetter.isalpha()==True and len(chosenLetter) == 1:     #if chosenletter is alpha (alphabet) and is only 1 letter
                        shownCountries=open("Countries.txt", "r")   #read access from text file
                        function1(chosenLetter,shownCountries)    #executes function
                        function2(country,populations)   #executes function
                    else:
                        print("numbers are not allowed")
            else:
                messagebox.showinfo("info", "Invalid")

root=Tk()
root.minsize(width=350, height=300)
root.wm_title("Countries Generation")

lblMessage1 = Label(root,text="Username:", fg="black")
lblMessage1.pack()

userName=StringVar()
Entry(root, textvariable=userName).pack()

lblMessage2 = Label(root,text="Password:", fg="black")
lblMessage2.pack()

password=StringVar()
Entry(root, textvariable=password).pack()

btnLoginName=Button(root, text="Check Login..", command=btnPress)
btnLoginName.pack()

root.mainloop()