import sys
import string
import numpy


_codes =  {
    1  : ('x', float),
    2  : ('y', float),
    3  : ('y_domain_lower_bound', float),
    4  : ('x_domain_lower_bound', float),
    5  : ('y_domain_upper_bound', float),
    6  : ('x_domain_upper_bound', float),
    7  : ('z_domain_lower_bound', float),
    8  : ('x_domain_upper_bound', float),
    10 : ('title', str),
    11 : ('domain_title', str),
    12 : ('x_lower_bound', float),
    13 : ('x_upper_bound', float),
    14 : ('y_lower_bound', float),
    15 : ('y_upper_bound', float),
    }


class ExtraData(dict):
    """
    Extends dictionary class with a comparison method between extra 
    data for different records.
    """

    _key_to_type = dict([(key, typ) for key, typ in _codes.values()])

    def sorted_keys(self):
        k = self.keys()
        k.sort()
        return k

    _tolerances = {numpy.dtype(numpy.float32): 1e-5,
                   numpy.dtype(numpy.float64): 1e-13}

    def _cmp_floats(self, a, b, tolerance):
        if a == b:
            return 0
        delta = abs(b * tolerance)
        if a < b - delta: return -1
        if a > b + delta: return 1
        return 0    

    def _cmp_float_arrays(self, avals, bvals):
        n = len(avals)
        c = cmp(n, len(bvals))
        if c != 0:
            return c
        tolerance = self._tolerances[avals.dtype]
        for i in range(n):
            c = self._cmp_floats(avals[i], bvals[i], tolerance)
            if c != 0:
                return c
        return 0

    def __cmp__(self, other):
        """
        Compare two extra data dictionaries returned by unpacker
        """
        if other == None:
            return 1
        ka = self.sorted_keys()
        kb = other.sorted_keys()
        c = cmp(ka, kb)
        if c != 0:
            return c
        for key in ka:
            valsa = self[key]
            valsb = other[key]
            typ = self._key_to_type[key]
            if typ == float:
                c = self._cmp_float_arrays(valsa, valsb)
            elif type == str:
                c = cmp(valsa, valsb)
            else:
                assert(False)
            if c != 0:
                return c
        return 0
        

class ExtraDataUnpacker:

    _int_types = {4: numpy.int32, 8: numpy.int64}
    _float_types = {4: numpy.float32, 8: numpy.float64}

    def __init__(self, raw_extra_data, word_size, byte_ordering):
        self.rdata = raw_extra_data
        self.ws = word_size
        self.itype = self._int_types[word_size]
        self.ftype = self._float_types[word_size]
        # byte_ordering is 'little_endian' or 'big_endian'
        # sys.byteorder is 'little' or 'big'
        self.is_swapped = not byte_ordering.startswith(sys.byteorder)

    def next_words(self, n):
        """
        return next n words as raw data string, and pop them off the 
        front of the string
        """
        pos = n * self.ws
        rv = self.rdata[:pos]
        assert(len(rv) == pos)
        self.rdata = self.rdata[pos:]
        return rv

    def tweak_string(self, st):
        """
        undo byte-swapping of string and remove trailing NULs
        """
        if self.is_swapped:
            # concatenate backwards substrings
            st = string.join([st[pos : pos + self.ws][::-1]
                              for pos in range(0, len(st), self.ws)], "")
        while st.endswith("\x00"):
            st = st[:-1]
        return st

    def get_data(self):
        """
        get list of (key, value) for extra data
        """
        d = {}
        while self.rdata:
            i = numpy.fromstring(self.next_words(1), self.itype)[0]
            if i == 0:
                break
            ia, ib = (i / 1000, i % 1000)
            key, type = _codes[ib]
            rawvals = self.next_words(ia)
            if type == float:
                vals = numpy.fromstring(rawvals, self.ftype)
            elif type == str:
                vals = self.tweak_string(rawvals)
            d[key] = vals
        return ExtraData(d)
