import sys
from datetime import datetime, timedelta
from cStringIO import StringIO

locked = False
timestamp = None
err_stream = None
nest = 0

EPSILON = timedelta(seconds=.05)
INSPECTING = False
if INSPECTING:
    import inspect

class benchmarking(object):
    # Pass offset to include the caller (offset stack frames up) in the msg
    def __init__(self, desc, offset=None):
        self.desc = desc
        self.offset = offset
    def __enter__(self):
        global timestamp, nest
        if not locked: return
        if timestamp is not None:
            newts = datetime.now()
            delta = newts - timestamp
            if delta > EPSILON:
                print >>err_stream, '  '*nest, '# Time elapsed:', delta
            desc = self.desc
            if self.offset is not None and INSPECTING:
                caller = inspect.stack()[1 + self.offset][1:4]
                caller = (caller[0].rsplit('/', 1)[-1],) + caller[1:]
                desc += ' for %s' % (caller,)
            print >>err_stream, '  '*nest, 'Start', desc
            nest += 1
            timestamp = newts
            self.starttime = newts
    def __exit__(self, exc_type, exc_val, exc_tb):
        global timestamp, nest
        if not locked: return
        if timestamp is not None:
            newts = datetime.now()
            delta = newts - timestamp
            if delta > EPSILON:
                print >>err_stream, '  '*nest, '# Time elapsed:', delta
            nest -= 1
            print >>err_stream, '  '*nest, 'End', self.desc, '(took %s)' % (newts - self.starttime)
            timestamp = newts

    @staticmethod
    def info(msg):
        if locked:
            print >>err_stream, '  '*nest, msg

    @staticmethod
    def start(err=sys.stderr, prevent_override=False):
        global timestamp, err_stream, locked
        if not locked:
            timestamp = datetime.now()
            err_stream = err
        if prevent_override:
            locked = True