# Jay Summet
# CS 1301
# Released to the public domain, Oct 20th 2008
#
#
from random import randrange


#This function will load n-grams from a specified
#textfile of length N. It stores them in a dictionary and
#returns the dictioary.
def loadNgrams(fileName, N):

    nGrams = {}     #Start with an Empty Dictionary!
    f = open(fileName,"r")
    text = f.read()
    f.close()

    i = 0
    
    while(i < len(text) - N):
        nGram = text[i:i+N]
        nextLetter = text[i+N]
        #Append the next letter after this nGram
        #in the list associated with this nGram.
        #If the dictionary does not yet have a key
        #for this n-gram, the get() method will return
        #an empty list.
        lst = nGrams.get(nGram, [])
        lst = lst + [ nextLetter ]
        nGrams[nGram] = lst
        #Uncomment the following line for debugging text
        #print nGram, lst

        i = i+1
        
    return( nGrams)



#This function will generate text using a pre-loaded
#collection of n-Grams. You give it the dictionary of
#nGrams, the length of text you want it to generate,
#and an (optional) starting bit of text (that must be
#an nGram stored in the dictionry). If you don't pass
#in a starting nGram, the function will pick the first
#key in the dictionary and start with it.



def genText(Grams, length, nGram = None):
    #Do some error checking.
    if ( len(Grams) < 1):
        print "Error! nGrams is empty!"
        return
    
    if ( length < 0):
        print "Can not generate negative amounts of Text!"
        return
    
    #Handle our optional parameter. If the user does
    #not specify a starting nGram, we use the first
    #key in the dictionary.
    if (nGram == None):
        ourKeys = Grams.keys()
        nGram = ourKeys[0]

    text = ""
    done = 0
    while(done < length):
        #Get the next list for the current nGram!
        lst = Grams[nGram]
        #Pick a random letter from it.
        random = randrange(0,len(lst))
        #append the random letter to the text
        text = text + lst[random]
        #increment our done counter
        done = done + 1
        #Update our current nGram!
        nGram = nGram[1:] + lst[random]

    #When all finished, return the text!
    return(text)



    
Grams = loadNgrams("msnd.txt",5)

print genText(Grams,3000)