#!/usr/bin/env python3

'''An alternative way to draw parallels and meridians with basemap.

Basemap is a toolkit of matplotlib used to plot geographic maps.

With this function you can:

* Draw the latitude/longitude grid easily in one line of code, specifying the
  lat/lon intervals.
* Use rcParams, so all your figures will look more consistent.
* Specify the label pad in points (instead of projection units).
* Place the labels indicating which margins will be used.

'''

import numpy as np


def latlon_grid(bmap, lon_int, lat_int, labels='lb', **kwargs):
    '''Draws a lat-lon grid in an easy way.

    Some default values are taken from rcParams instead of 'black' (color) and
    1.0 (linewidth) which is the default in Basemap.

    In Basemap, the label pad is computed in projection units. Now you can use
    the keyword argument 'labelpad' to control this separation in points. If
    not specified then this value is taken from rcParams.

    Arguments:

    bmap -- Basemap object.
    lon_int, lat_int -- Difference in degrees from one longitude or latitude to
                        the next.
    labels -- String specifying which margins will be used to write the labels.
              If None, no label will be shown.
              It is assummed that left/right margins (i.e. Y axes) correspond
              to latitudes and top/bottom (X axes) to longitudes. It is valid
              every combination of the characters 't' | 'b' | 'l' | 'r'
              (top|bottom|left|right).
              Ex: 'lrb' means that the longitude values will appear in bottom
              margin and latitudes in left and right.
    **kwargs -- Other arguments to drawparallels, drawmeridians and plt.text.
                labelpad has units of points.
    '''
    # Proccesses arguments and rcParams for defult values
    if 'color' not in kwargs:
        kwargs['color'] = plt.rcParams['grid.color']
    if 'linewidth' not in kwargs:
        kwargs['linewidth'] = plt.rcParams['grid.linewidth']
    if 'labelpad' in kwargs:
        padx = pady = kwargs['labelpad']
        del kwargs['labelpad']
    else:
        pady = plt.rcParams['xtick.major.pad']
        padx = plt.rcParams['ytick.major.pad']
    if 'size' in kwargs:
        xfontsize = yfontsize = kwargs['size']
        del kwargs['size']
    elif 'fontsize' in kwargs:
        xfontsize = yfontsize = kwargs['fontsize']
        del kwargs['fontsize']
    else:
        xfontsize = plt.rcParams['xtick.labelsize']
        yfontsize = plt.rcParams['ytick.labelsize']
    # Vectors of coordinates
    lon0 = bmap.lonmin // lon_int * lon_int
    lat0 = bmap.latmin // lat_int * lat_int
    lon1 = bmap.lonmax // lon_int * lon_int
    lat1 = bmap.latmax // lat_int * lat_int
    nlons = (lon1 - lon0) / lon_int + 1
    nlats = (lat1 - lat0) / lat_int + 1
    assert nlons / int(nlons) == 1, nlons
    assert nlats / int(nlats) == 1, nlats
    lons = np.linspace(lon0, lon1, int(nlons))
    lats = np.linspace(lat0, lat1, int(nlats))
    # If not specified then computes de label offset by 'labelpad'
    xos = yos = None
    if 'xoffset' in kwargs:
        xos = kwargs['xoffset']
    if 'yoffset' in kwargs:
        yos = kwargs['yoffset']
    if xos is None and yos is None:
        # Page size in inches and axes limits
        fig_w, fig_h = plt.gcf().get_size_inches()
        points = plt.gca().get_position().get_points()
        x1, y1 = tuple(points[0])
        x2, y2 = tuple(points[1])
        # Width and height of axes in points
        w = (x2 - x1) * fig_w * 72
        h = (y2 - y1) * fig_h * 72
        # If the aspect relation is fixed then compute the real values
        if bmap.fix_aspect:
            aspect = bmap.aspect * w / h
            if aspect > 1:
                w = h / bmap.aspect
            elif aspect < 1:
                h = w * bmap.aspect
        # Offset in projection units (meters or degrees)
        xos = padx * (bmap.urcrnrx - bmap.llcrnrx) / w
        yos = pady * (bmap.urcrnry - bmap.llcrnry) / h
    # Set the labels
    latlabels = [False] * 4
    lonlabels = [False] * 4
    if labels is not None:
        pst = {'l': 0, 'r': 1, 't': 2, 'b': 3}
        lst = {'l': latlabels, 'r': latlabels, 't': lonlabels, 'b': lonlabels}
        for i in labels.lower():
            lst[i][pst[i]] = True
    # Draws the grid
    bmap.drawparallels(lats, labels=latlabels, fontsize=yfontsize,
                       xoffset=xos, yoffset=yos, **kwargs)
    bmap.drawmeridians(lons, labels=lonlabels, fontsize=xfontsize,
                       xoffset=xos, yoffset=yos, **kwargs)


# TEST

if __name__ == '__main__':
    import matplotlib.pyplot as plt
    import mpl_toolkits.basemap as basemap
    # Some rcParams (example)
    plt.rc('grid', linewidth=0.5, color='g')
    plt.rcParams['xtick.major.pad'] = 6
    plt.rcParams['ytick.major.pad'] = 12
    plt.rcParams['xtick.labelsize'] = 'small'
    plt.rcParams['ytick.labelsize'] = 'x-small'
    # Basemap
    m = basemap.Basemap(projection='merc', llcrnrlon=-120, llcrnrlat=30,
                        urcrnrlon=120, urcrnrlat=70)
    # Plots a figure to compare
    plt.subplot(211)
    x = np.linspace(-10, 10, 10000)
    y = np.sin(x)
    plt.plot(x, y)
    plt.grid()
    plt.title('Example of figure using only rc values')
    # Draws the grid (using the function)
    plt.subplot(212)
    latlon_grid(m, 30, 10, labels='lb', dashes=[1, 3])
    m.drawcoastlines()
    plt.title('Using latlon_grid()')
    plt.show()