# Coordinate reference systems and functions.
#
# PROJ.4 is the law of this land: http://proj.osgeo.org/. But whereas PROJ.4
# coordinate reference systems are described by strings of parameters such as
#
#   +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs
#
# here we use mappings:
#
#   {'proj': 'longlat', 'ellps': 'WGS84', 'datum': 'WGS84', 'no_defs': True}
#

from six import string_types

def to_string(crs):
    """Turn a parameter mapping into a more conventional PROJ.4 string.

    Mapping keys are tested against the ``all_proj_keys`` list. Values of
    ``True`` are omitted, leaving the key bare: {'no_defs': True} -> "+no_defs"
    and items where the value is otherwise not a str, int, or float are
    omitted.
    """
    items = []
    for k, v in sorted(filter(
            lambda x: x[0] in all_proj_keys and x[1] is not False and (
                isinstance(x[1], (bool, int, float)) or 
                isinstance(x[1], string_types)),
            crs.items() )):
        items.append(
            "+" + "=".join(
                map(str, filter(
                    lambda y: (y or y == 0) and y is not True, (k, v)))) )
    return " ".join(items)

def from_string(prjs):
    """Turn a PROJ.4 string into a mapping of parameters.

    Bare parameters like "+no_defs" are given a value of ``True``. All keys
    are checked against the ``all_proj_keys`` list.
    """
    parts = [o.lstrip('+') for o in prjs.strip().split()]
    def parse(v):
        try:
            return int(v)
        except ValueError:
            pass
        try:
            return float(v)
        except ValueError:
            return v
    items = map(
        lambda kv: len(kv) == 2 and (kv[0], parse(kv[1])) or (kv[0], True),
        (p.split('=') for p in parts) )
    return dict((k,v) for k, v in items if k in all_proj_keys)

def from_epsg(code):
    """Given an integer code, returns an EPSG-like mapping.

    Note: the input code is not validated against an EPSG database.
    """
    if int(code) <= 0:
        raise ValueError("EPSG codes are positive integers")
    return {'init': "epsg:%s" % code, 'no_defs': True}


# Below is the big list of PROJ4 parameters from
# http://trac.osgeo.org/proj/wiki/GenParms.
# It is parsed into a list of paramter keys ``all_proj_keys``.

_param_data = """
+a         Semimajor radius of the ellipsoid axis
+alpha     ? Used with Oblique Mercator and possibly a few others
+axis      Axis orientation (new in 4.8.0)
+b         Semiminor radius of the ellipsoid axis
+datum     Datum name (see `proj -ld`)
+ellps     Ellipsoid name (see `proj -le`)
+init      Initialize from a named CRS
+k         Scaling factor (old name)
+k_0       Scaling factor (new name)
+lat_0     Latitude of origin
+lat_1     Latitude of first standard parallel
+lat_2     Latitude of second standard parallel
+lat_ts    Latitude of true scale
+lon_0     Central meridian
+lonc      ? Longitude used with Oblique Mercator and possibly a few others
+lon_wrap  Center longitude to use for wrapping (see below)
+nadgrids  Filename of NTv2 grid file to use for datum transforms (see below)
+no_defs   Don't use the /usr/share/proj/proj_def.dat defaults file
+over      Allow longitude output outside -180 to 180 range, disables wrapping (see below)
+pm        Alternate prime meridian (typically a city name, see below)
+proj      Projection name (see `proj -l`)
+south     Denotes southern hemisphere UTM zone
+to_meter  Multiplier to convert map units to 1.0m
+towgs84   3 or 7 term datum transform parameters (see below)
+units     meters, US survey feet, etc.
+vto_meter vertical conversion to meters.
+vunits    vertical units.
+x_0       False easting
+y_0       False northing
+zone      UTM zone
+a         Semimajor radius of the ellipsoid axis
+alpha     ? Used with Oblique Mercator and possibly a few others
+azi
+b         Semiminor radius of the ellipsoid axis
+belgium
+beta
+czech
+e         Eccentricity of the ellipsoid = sqrt(1 - b^2/a^2) = sqrt( f*(2-f) )
+ellps     Ellipsoid name (see `proj -le`)
+es        Eccentricity of the ellipsoid squared
+f         Flattening of the ellipsoid (often presented as an inverse, e.g. 1/298)
+gamma
+geoc
+guam
+h
+k         Scaling factor (old name)
+K
+k_0       Scaling factor (new name)
+lat_0     Latitude of origin
+lat_1     Latitude of first standard parallel
+lat_2     Latitude of second standard parallel
+lat_b
+lat_t
+lat_ts    Latitude of true scale
+lon_0     Central meridian
+lon_1
+lon_2
+lonc      ? Longitude used with Oblique Mercator and possibly a few others
+lsat
+m
+M
+n
+no_cut
+no_off
+no_rot
+ns
+o_alpha
+o_lat_1
+o_lat_2
+o_lat_c
+o_lat_p
+o_lon_1
+o_lon_2
+o_lon_c
+o_lon_p
+o_proj
+over
+p
+path
+proj      Projection name (see `proj -l`)
+q
+R
+R_a
+R_A       Compute radius such that the area of the sphere is the same as the area of the ellipsoid
+rf        Reciprocal of the ellipsoid flattening term (e.g. 298)
+R_g
+R_h
+R_lat_a
+R_lat_g
+rot
+R_V
+s
+south     Denotes southern hemisphere UTM zone
+sym
+t
+theta
+tilt
+to_meter  Multiplier to convert map units to 1.0m
+units     meters, US survey feet, etc.
+vopt
+W
+westo
+x_0       False easting
+y_0       False northing
+zone      UTM zone
"""

_lines = filter(lambda x: len(x) > 1, _param_data.split("\n"))
all_proj_keys = list(
    set(line.split()[0].lstrip("+").strip() for line in _lines) 
    ) + ['no_mayo']

