"""
Test to analyze file.seek positional errors.
Feel free to play with different file formats, just pass it as a file object to the functions.
"""


# Pass in file object from external file
def seekread(file):
    f = open(file, 'rb')
    # Read entire file
    f.read()
    # You can seek within the limit. Negative results will fail!
    print '--Result of read--'
    pos1 = f.tell()
    print 'File position:', pos1, '<-- read limit'
    # Seek backwards
    seek_back = 4096
    f.seek(-seek_back, 1)
    pos2 = f.tell()
    print 'New position: ', pos2
    if pos2 == pos1 - seek_back:
        print 'Correct position!'
    else:
        print 'Wrong position'
    f.close()


def seekreadline(file):
    # Now for processing readline()
    f = open(file, 'rb')
    # readline() produces incorrect file position!
    # Change to readlines() and it will pass!
    f.readline()
    print '--- Result of readline() ---'
    pos1 = f.tell()
    print 'File position:        ', pos1, '<--current position'
    seek_back = 0
    f.seek(-seek_back, 1)
    pos2 = f.tell()
    print 'New position in file: ', pos2
    if pos2 == pos1 - seek_back:
        print 'Correct position'
    else:
        print 'Wrong position'
    f.close()


def seekboth(file):
    # Now for processing readline()
    f = open(file, 'rb')
    f.read()
    posread = f.tell()
    f.readline()
    print '--- Result of both() ---'
    pos1 = f.tell()
    print 'File position from read():     ', posread
    print 'File position from readline(): ', pos1
    seek_back = 4100
    f.seek(-seek_back, 1)
    pos2 = f.tell()
    print 'New position in file: ', pos2
    if pos2 == pos1 - seek_back:
        print 'Correct position'
    else:
        print 'Wrong position'
    f.close()


# generate file
file = open("test.log", "wb")
file.write("."*100 + "\n" + "."*4100 + "\n" + "."*100)
file.close()

# Run tests
seekread('test.log')        # pass
seekreadline('test.log')    # Fail
seekboth('test.log')        # Pass