"""
Formats nose output into format easily parsable by machine.
It is intended to be use to integrate nose with your IDE such as Vim.
"""

import os
import traceback
from nose.plugins import Plugin


class DummyStream:

    def write(self, *arg):
        pass

    def writeln(self, *arg):
        pass

    def flush(self):
        pass


class NoseMachineReadableOutput(Plugin):
    """
    Output errors and failures in a machine-readable way.
    """

    name = 'machineout'

    def __init__(self):
        super(NoseMachineReadableOutput, self).__init__()
        self.basepath = os.getcwd()

    def addError(self, test, err):
        self.add_formatted('error', err)

    def addFailure(self, test, err):
        self.add_formatted('fail', err)

    def setOutputStream(self, stream):
        self.stream = stream
        return DummyStream()

    def _calcScore(self, frame):
        """Calculates a score for this stack frame, so that can be used as a
        quality indicator to compare to other stack frames in selecting the
        most developer-friendly one to show in one-line output.

        """
        fname, _, funname, _ = frame
        score = 0.0
        max_score = 7.0  # update this when new conditions are added

        # Being in the project directory means it's one of our own files
        if fname.startswith(self.basepath):
            score += 4

        # Being one of our tests means it's a better match
        if os.path.basename(fname).find('test') >= 0:
            score += 2

        # The check for the `assert' prefix allows the user to extend
        # unittest.TestCase with custom assert-methods, while
        # machineout still returns the most useful error line number.
        if not funname.startswith('assert'):
            score += 1
        return score / max_score

    def _selectBestStackFrame(self, traceback):
        best_score = 0
        best = traceback[-1]   # fallback value
        for frame in traceback:
            curr_score = self._calcScore(frame)
            if curr_score > best_score:
                best = frame
                best_score = curr_score

                # Terminate the walk as soon as possible
                if best_score >= 1:
                    break
        return best

    def add_formatted(self, etype, err):
        exctype, value, tb = err
        fulltb = traceback.extract_tb(tb)
        fname, lineno, funname, msg = self._selectBestStackFrame(fulltb)

        lines = traceback.format_exception_only(exctype, value)
        lines = [line.strip('\n') for line in lines]
        msg = lines[0]

        fname = self._format_testfname(fname)
        prefix = "%s:%d" % (fname, lineno)
        self.stream.writeln("%s: %s: %s" % (prefix, etype, msg))

        if len(lines) > 1:
            pad = ' ' * (len(etype) + 1)
            for line in lines[1:]:
                self.stream.writeln("%s: %s %s" % (prefix, pad, line))

    def _format_testfname(self, fname):
        if fname.startswith(self.basepath):
            return fname[len(self.basepath) + 1:]

        return fname