__all__ = ()

import reprlib

from . import format_helpers

# States for Future.
_PENDING = 'PENDING'
_CANCELLED = 'CANCELLED'
_FINISHED = 'FINISHED'


def isfuture(obj):
 """Check for a Future.

 This returns True when obj is a Future instance or is advertising
 itself as duck-type compatible by setting _asyncio_future_blocking.
 See comment in Future for more details.
 """
 return (hasattr(obj.__class__, '_asyncio_future_blocking') and
 obj._asyncio_future_blocking is not None)


def _format_callbacks(cb):
 """helper function for Future.__repr__"""
 size = len(cb)
 if not size:
 cb = ''

 def format_cb(callback):
 return format_helpers._format_callback_source(callback, ())

 if size == 1:
 cb = format_cb(cb[0][0])
 elif size == 2:
 cb = '{}, {}'.format(format_cb(cb[0][0]), format_cb(cb[1][0]))
 elif size > 2:
 cb = '{}, <{} more>, {}'.format(format_cb(cb[0][0]),
 size - 2,
 format_cb(cb[-1][0]))
 return f'cb=[{cb}]'


def _future_repr_info(future):
 # (Future) -> str
 """helper function for Future.__repr__"""
 info = [future._state.lower()]
 if future._state == _FINISHED:
 if future._exception is not None:
 info.append(f'exception={future._exception!r}')
 else:
 # use reprlib to limit the length of the output, especially
 # for very long strings
 result = reprlib.repr(future._result)
 info.append(f'result={result}')
 if future._callbacks:
 info.append(_format_callbacks(future._callbacks))
 if future._source_traceback:
 frame = future._source_traceback[-1]
 info.append(f'created at {frame[0]}:{frame[1]}')
 return info