"""
spack.vendor.altgraph.GraphStat - Functions providing various graph statistics
=================================================================
"""


def degree_dist(graph, limits=(0, 0), bin_num=10, mode="out"):
    """
    Computes the degree distribution for a graph.

    Returns a list of tuples where the first element of the tuple is the
    center of the bin representing a range of degrees and the second element
    of the tuple are the number of nodes with the degree falling in the range.

    Example::

        ....
    """

    deg = []
    if mode == "inc":
        get_deg = graph.inc_degree
    else:
        get_deg = graph.out_degree

    for node in graph:
        deg.append(get_deg(node))

    if not deg:
        return []

    results = _binning(values=deg, limits=limits, bin_num=bin_num)

    return results


_EPS = 1.0 / (2.0 ** 32)


def _binning(values, limits=(0, 0), bin_num=10):
    """
    Bins data that falls between certain limits, if the limits are (0, 0) the
    minimum and maximum values are used.

    Returns a list of tuples where the first element of the tuple is the
    center of the bin and the second element of the tuple are the counts.
    """
    if limits == (0, 0):
        min_val, max_val = min(values) - _EPS, max(values) + _EPS
    else:
        min_val, max_val = limits

    # get bin size
    bin_size = (max_val - min_val) / float(bin_num)
    bins = [0] * (bin_num)

    # will ignore these outliers for now
    for value in values:
        try:
            if (value - min_val) >= 0:
                index = int((value - min_val) / float(bin_size))
                bins[index] += 1
        except IndexError:
            pass

    # make it ready for an x,y plot
    result = []
    center = (bin_size / 2) + min_val
    for i, y in enumerate(bins):
        x = center + bin_size * i
        result.append((x, y))

    return result
