#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
MERRA-2 FTLE
============

Compute the FTLE field for atmospheric flow at time of Godzilla dust
storm using MERRA-2 data which is vertically averaged over pressure surfaces
ranging from 500hPa to 800hPa.
"""

# Author: ajarvis
# Data: MERRA-2 - Global Modeling and Assimilation Office - NASA

import numpy as np
from math import copysign
import matplotlib.pyplot as plt
from numbacs.flows import get_interp_arrays_2D, get_flow_2D
from numbacs.integration import flowmap_grid_2D
from numbacs.diagnostics import ftle_grid_2D
# %%
# Get flow data
# --------------
# Load in atmospheric velocity data, dates, and coordinates. Set domain for 
# FTLE computation and integration span. Create interpolant and retrieve flow.
# 
# .. note::
#    Pandas is a simpler option for storing and manipulating dates but we use
#    numpy here as Pandas is not a dependency.

# load in atmospheric data
dates = np.load('../data/merra_june2020/dates.npy')
dt = (dates[1] - dates[0]).astype('timedelta64[h]').astype(int)
t = np.arange(0,len(dates)*dt,dt,np.float64)
lon = np.load('../data/merra_june2020/lon.npy')
lat = np.load('../data/merra_june2020/lat.npy')

# NumbaCS uses 'ij' indexing, most geophysical data uses 'xy'
# indexing for the spatial coordintes. We need to switch axes and
# scale by 3.6 since velocity data is in m/s and we want km/hr.
u = np.moveaxis(np.load('../data/merra_june2020/u_500_800hPa.npy'),1,2)*3.6
v = np.moveaxis(np.load('../data/merra_june2020/v_500_800hPa.npy'),1,2)*3.6
nt,nx,ny = u.shape

# set domain on which ftle will be computed
dx = 0.15
dy = 0.15
lonf = np.arange(-100,35+dx,dx)
latf = np.arange(-5,45+dy,dy)

#%%
# set integration span and integration direction
day = 16
t0_date = np.datetime64("2020-06-{:02d}".format(day))
t0 = t[np.nonzero(dates == t0_date)[0][0]]
T = -72.0
params = np.array([copysign(1,T)])

# get interpolant arrays of velocity field
grid_vel, C_eval_u, C_eval_v = get_interp_arrays_2D(t, lon, lat, u, v)

# set integration direction and retrieve flow
# set spherical = 1 since flow is on spherical domain and lon is from [-180,180)
params = np.array([copysign(1,T)])
funcptr = get_flow_2D(grid_vel, C_eval_u, C_eval_v, spherical=1)

# %%
# Integrate
# ---------
# Integrate grid of particles and return final positions.
flowmap = flowmap_grid_2D(funcptr, t0, T, lonf, latf, params)

# %%
# FTLE
# ----
# Compute FTLE field from final particle positions.
ftle = ftle_grid_2D(flowmap,T,dx,dy)

# %%
# Plot
# ----
# Plot the results. Using the cartopy package for plotting geophysical data is
# advised but it is not a dependency so we simply use matplotlib.
coastlines = np.load('../data/merra_june2020/coastlines.npy')
fig,ax = plt.subplots(dpi=200)
ax.scatter(coastlines[:,0],coastlines[:,1],1,'k',marker='.',edgecolors=None,linewidths=0)
ax.contourf(lonf,latf,ftle.T,levels=80,zorder=0)
ax.set_xlim([lonf[0],lonf[-1]])
ax.set_ylim([latf[0],latf[-1]])
ax.set_aspect('equal')
plt.show()