import pandas as pd       # reading in data for location information from text file
import numpy as np        # working with arrays, vectors, cross/dot products, and radians

from pyproj import Geod   # working with the Earth as an ellipsod (WGS-84)
import geopy.distance     # working with the Earth as an ellipsod

import matplotlib.pyplot as plt                        # plotting a graph
from cartopy import crs as ccrs, feature as cfeature   # plotting a world map

# Get all Coordinates for Locations
location_df = pd.read_csv("../location_full_coords.txt")
location_df = location_df.rename(columns=lambda x: x.strip()) # strip excess white space from column names and values
location_df.head()

location_df.index = location_df["name"]

# Generate Latitude Coordinates based on Longitude Coordinates
def generate_latitude_along_gc(start_point=None, end_point=None, number_of_lon_pts=360):
    lon1 = np.deg2rad(location_df.loc[start_point, "longitude"])
    lat1 = np.deg2rad(location_df.loc[start_point, "latitude"])
    lon2 = np.deg2rad(location_df.loc[end_point, "longitude"])
    lat2 = np.deg2rad(location_df.loc[end_point, "latitude"])

    # Verify not meridian (longitude passes through the poles)
    if np.sin(lon1 - lon2) == 0:
        print("Invalid inputs: start/end points are meridians")
        # plotting meridians at 0 longitude through all latitudes
        meridian_lat = np.arange(-90, 90, 180/len(longitude_lst)) # split in n number
        meridians = []
        for lat in meridian_lat:
            meridians.append((lat, 0))
        return meridians

    # verify not anitpodal (diametrically opposite, points)
    if lat1 + lat2 == 0 and abs(lon1-lon2) == np.pi:
        print("Invalid inputs: start/end points are antipodal")
        return []

    # note: can be expanded to handle input of np arrays by filter out antipodal/merdiain points

    # generate n total number of longitude points along the great circle
    # https://github.com/rspatial/geosphere/blob/master/R/greatCircle.R#L18C3-L18C7
    gc_lon_lst = []
    for lon in range(1, number_of_lon_pts+1):
        new_lon = (lon  * (360/number_of_lon_pts) - 180)
        gc_lon_lst.append(np.deg2rad(new_lon))

    # Intermediate points on a great circle: https://edwilliams.org/avform147.htm"
    gc_lat_lon = []
    for gc_lon in gc_lon_lst:
        num = np.sin(lat1)*np.cos(lat2)*np.sin(gc_lon-lon2)-np.sin(lat2)*np.cos(lat1)*np.sin(gc_lon-lon1)
        den = np.cos(lat1)*np.cos(lat2)*np.sin(lon1-lon2)
        new_lat = np.arctan(num/den)
        gc_lat_lon.append((np.rad2deg(new_lat), np.rad2deg(gc_lon)))
    return gc_lat_lon

lat_lon_pts = generate_latitude_along_gc("boulder", "boston", 360)

def intersection_of_gc(start_gc1=None, end_gc1=None,
                      start_gc2=None, end_gc2=None):
    # get normal of planes containing great circles

    # cross product of vectors
    normal_one = np.cross([location_df.loc[start_gc1, "cart_x"],
                           location_df.loc[start_gc1, "cart_y"],
                           location_df.loc[start_gc1, "cart_z"]],
                          [location_df.loc[end_gc1, "cart_x"],
                           location_df.loc[end_gc1, "cart_y"],
                           location_df.loc[end_gc1, "cart_z"]])
    normal_two = np.cross([location_df.loc[start_gc2, "cart_x"],
                           location_df.loc[start_gc2, "cart_y"],
                           location_df.loc[start_gc2, "cart_z"]],
                          [location_df.loc[end_gc2, "cart_x"],
                           location_df.loc[end_gc2, "cart_y"],
                           location_df.loc[end_gc2, "cart_z"]])
    # intersection of planes, normal to the poles of each plane
    line_of_intersection = np.cross(normal_one, normal_two)
    # intersection points (one on each side of the earth)
    x1 = line_of_intersection /  np.sqrt(line_of_intersection[0]**2 + line_of_intersection[1]**2 + line_of_intersection[2]**2) 
    x2 = -x1
    lat1 = np.rad2deg(np.arctan2(x1[2], np.sqrt(pow(x1[0],2)+pow(x1[1],2))))
    lon1 = np.rad2deg(np.arctan2(x1[1], x1[0]))
    lat2 = np.rad2deg(np.arctan2(x2[2], np.sqrt(pow(x2[0],2)+pow(x2[1],2))))
    lon2 = np.rad2deg(np.arctan2(x2[1], x2[0]))
    return [(lat1, lon1), (lat2, lon2)]

intersect_pts = intersection_of_gc("boulder", "boston", "greenwich", "cairo")
intersect_pts

def interpolate_points_along_gc(start_point=None, end_point=None,
                                distance_between_points_meter=0): 
    geodesic = Geod(ellps="WGS84")
    
    lat_start = location_df.loc[start_point, "latitude"]
    lon_start = location_df.loc[start_point, "longitude"]
    lat_end = location_df.loc[end_point, "latitude"]
    lon_end = location_df.loc[end_point, "longitude"]

    lat_lon_points = [(lat_start, lon_start)]
    
    # move to next point when distance between points is less than the equal distance
    move_to_next_point = True
    while(move_to_next_point):
        forward_bearing, _, distance_meters = geodesic.inv(lon_start,
                                                            lat_start, 
                                                            lon_end,
                                                            lat_end)
        if distance_meters < distance_between_points_meter:
            # ends before overshooting
            move_to_next_point = False
        else:
            start_point = geopy.Point(lat_start, lon_start)
            distance_to_move = geopy.distance.distance(
                            kilometers=distance_between_points_meter /
                            1000)  # distance to move towards the next point
            final_position = distance_to_move.destination(
                            start_point, bearing=forward_bearing)
            lat_lon_points.append((final_position.latitude, final_position.longitude))
            # new starting position is newly found end position
            lon_start, lat_start = final_position.longitude, final_position.latitude
    lat_lon_points.append((lat_end, lon_end))
    return lat_lon_points

def arc_points(start_point=None, end_point=None,
               n_total_points=10):
    start_lat = location_df.loc[start_point, "latitude"]
    start_lon = location_df.loc[start_point, "longitude"]
    end_lat = location_df.loc[end_point, "latitude"]
    end_lon = location_df.loc[end_point, "longitude"]

    geodesic = Geod(ellps="WGS84")

    _, _, distance_meter =  geodesic.inv(start_lon,
                                        start_lat,
                                        end_lon,
                                        end_lat)
        
    distance_between_points_meter = distance_meter / (n_total_points + 1)

    
    points_along_arc = interpolate_points_along_gc(start_point, end_point,
                                              distance_between_points_meter)
    return points_along_arc

def plot_gc_with_intersection(start_gc1=None, end_gc1=None,
                             start_gc2=None, end_gc2=None,
                             lon_west=-180, lon_east=180,
                             lat_south=-90, lat_north=90):
    # Set up world map plot
    fig = plt.subplots(figsize=(15, 10))
    projection_map = ccrs.PlateCarree()
    ax = plt.axes(projection=projection_map)
    ax.set_extent([lon_west, lon_east, lat_south, lat_north], crs=projection_map)
    ax.coastlines(color="black")
    ax.add_feature(cfeature.STATES, edgecolor="black")

    # Plot Great Circle Path
    gc_one_lat_pts = generate_latitude_along_gc(start_gc1, end_gc1)
    longitudes = [x[1] for x in gc_one_lat_pts] # longitude
    latitudes = [x[0] for x in gc_one_lat_pts] # latitude
    plt.plot(longitudes, latitudes)
    gc_two_lat_pts = generate_latitude_along_gc(start_gc2, end_gc2)
    longitudes = [x[1] for x in gc_two_lat_pts] # longitude
    latitudes = [x[0] for x in gc_two_lat_pts] # latitude
    plt.plot(longitudes, latitudes)

    # Plot intersection point
    intersection_point = intersection_of_gc(start_gc1, end_gc1,
                                            start_gc2, end_gc2)
    longitudes = [x[1] for x in intersection_point] # longitude
    latitudes = [x[0] for x in intersection_point] # latitude
    plt.scatter(longitudes, latitudes, s=200, c="purple", label="intersection")

    # Plot Great Circle Arc
    gc_one_arc_pts = arc_points(start_gc1, end_gc1)
    longitudes = [x[1] for x in gc_one_arc_pts] # longitude
    latitudes = [x[0] for x in gc_one_arc_pts] # latitude
    plt.plot(longitudes, latitudes, c="pink", label="GC 1")
    plt.scatter(longitudes[0], latitudes[0], s=100, c="green", label="Arc Start")
    plt.scatter(longitudes[-1], latitudes[-1],s=100, c="red", label="Arc End")

    gc_two_arc_pts = arc_points(start_gc2, end_gc2)
    longitudes = [x[1] for x in gc_two_arc_pts] # longitude
    latitudes = [x[0] for x in gc_two_arc_pts] # latitude
    plt.plot(longitudes, latitudes, c="cyan", label="GC 2")
    plt.scatter(longitudes[0], latitudes[0],s=100, c="green")
    plt.scatter(longitudes[-1], latitudes[-1],s=100, c="red")

    plt.legend(loc="lower left")
    plt.title(f"Intersection Point = {intersection_point}")
    plt.show()

plot_gc_with_intersection("boulder", "boston", "greenwich", "cairo")

plot_gc_with_intersection("arecibo", "zambezi", "johannesburg", "reykjavík")