import sys
import traceback

from qgis.PyQt import QtCore


class WorkerSignals(QtCore.QObject):
    """
    Defines the signals available from a running worker thread.

    Supported signals are:

    finished
        No data

    error
        tuple (exctype, value, traceback.format_exc() )

    result
        object data returned from processing, anything

    progress
        int indicating % progress

    """

    finished = QtCore.pyqtSignal()
    error = QtCore.pyqtSignal(tuple)
    result = QtCore.pyqtSignal(object)
    progress = QtCore.pyqtSignal(object)


class Worker(QtCore.QRunnable):
    """
    Worker thread

    Inherits from QRunnable to handler worker thread setup, signals and wrap-up.

    :param callback: The function callback to run on this worker thread. Supplied args
                     and kwargs will be passed through to the runner.
    :type callback: function
    :param args: Arguments to pass to the callback function
    :param kwargs: Keywords to pass to the callback function

    """

    def __init__(self, fn, *args, **kwargs):
        super().__init__()

        # Store constructor arguments (re-used for processing)
        self.fn = fn
        self.args = args
        self.kwargs = kwargs
        self.signals = WorkerSignals()

        # Add the callback to our kwargs
        self.kwargs["progress_callback"] = self.signals.progress

    @QtCore.pyqtSlot()
    def run(self):
        """
        Initialise the runner function with passed args, kwargs.
        """

        try:
            result = self.fn(*self.args, **self.kwargs)
        except Exception:
            traceback.print_exc()
            exctype, value = sys.exc_info()[:2]
            self.signals.error.emit((exctype, value, traceback.format_exc()))
        else:
            self.signals.result.emit(result)
        finally:
            self.signals.finished.emit()
