#!/usr/bin/env python

def text_time_to_num_minutes(time_str):
    '''A helper function that converts a hour:minute string
    to an int representation of the number of minutes (since midnight).
    '''
    hour_str, minutes_str = time_str.split(':')
    return 60*int(hour_str) + int(minutes_str)

def convert_timed_obs_inp_to_waiting_time_outp(inp, outp):
    '''A function that an input representing timed observations
    of states, and writes to outp a series of waiting times
    between state changes.

    It iterates through inp. Each iteration is exected to yield
    a line of text with the syntax:
        hour:min\tstate\tidentifier\n
    Rows of inp must be in the correct sorted order (by identifier then time).

    When the state changes for observations associated with the same
    identifier, a waiting time record is written to outp file
    stream with the syntax:
        identifier\tnew state\twaiting time
    where the waiting time is the number of minutes spent in the previous
    state.
    '''
    current_bird = None
    for row in inp:
        # strip the newline character, separate the row based on
        #   tab characters, and unpack the row of data into its 3 parts
        time_str, state, bird = row.strip().split('\t')
        if current_bird is None:
            # The first bird in the whole data set as a special case
            current_bird = bird
            current_state = state
            prev_num_minutes = text_time_to_num_minutes(time_str)
        elif bird != current_bird or state != current_state:
            # We have a new bird or new state
            curr_num_minutes = text_time_to_num_minutes(time_str)
            if bird == current_bird:
                # We have a new state for the same bird
                wait_time = curr_num_minutes - prev_num_minutes
                while wait_time < 0:
                    # if we appeared to move back in time (negative wait_time),
                    #   then what really happened is we that times recorded
                    #   actually refer to the day after the previous measurements
                    #   e.g the clock went from 23:45 to 01:32
                    wait_time += 24*60
                    curr_num_minutes += 24*60
                # Write out a waiting time event to the output file
                outp.write('{b}\t{s}\t{w}\n'.format(b=current_bird,
                                                    s=current_state,
                                                    w=wait_time))
            current_bird = bird
            current_state = state
            prev_num_minutes = curr_num_minutes

# Now we can call the functions we have written for our data file
with open("hw3.birds.1.txt", 'rU') as data_file:
    # first just check that the header is what we expect it to be
    header_line = data_file.readline()
    assert header_line == 'Time\tHeight\tUnique ID\n'
    # creating the iterator and calling next "consumes" the 
    #   header line, so that our main parsing function just sees the
    #   data.
    with open("hw3.birds.2.txt", 'w') as outfile:
        convert_timed_obs_inp_to_waiting_time_outp(data_file, outfile)