#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Mon Mar 30 21:55:38 2020

@author: Ciaran Beggan (British Geological Survey)
 
Based on code from : chaosmagpy, Clemens Kloss (DTU Space)
                   : spherical harmonic code from David Kerridge (BGS)
                   
Functions for computing main field, the non-linear coefficients of the field,
    loading in coefficients files, format checking and coordinate rotation from
    geodetic to geocentric frame

"""

import os
import numpy as np
from numpy import degrees, radians
from math import pi
import warnings

r2d = np.rad2deg
d2r = np.deg2rad


class igrf_utils:  # A simple class to put the igrf file values into
    def __init__(self, time, coeffs, parameters):
        self.time = time
        self.coeffs = coeffs
        self.parameters = parameters

    def check_int(self, s):
        """Convert to integer."""
        try:
            return int(s)
        except ValueError:
            raise ValueError(f"Could not convert {s} to integer.")

    def check_float(self, s):
        """Convert to float."""
        try:
            return float(s)
        except ValueError:
            raise ValueError(f"Could not convert {s} to float.")

    def load_shcfile(self, filepath, leap_year=None):
        """
        Load shc-file and return coefficient arrays.

        Parameters
        ----------
        filepath : str
            File path to spherical harmonic coefficient shc-file.
        leap_year : {True, False}, optional
            Take leap year in time conversion into account (default). Otherwise,
            use conversion factor of 365.25 days per year.

        Returns
        -------
        time : ndarray, shape (N,)
            Array containing `N` times for each model snapshot in modified
            Julian dates with origin January 1, 2000 0:00 UTC.
        coeffs : ndarray, shape (nmax(nmax+2), N)
            Coefficients of model snapshots. Each column is a snapshot up to
            spherical degree and order `nmax`.
        parameters : dict, {'SHC', 'nmin', 'nmax', 'N', 'order', 'step'}
            Dictionary containing parameters of the model snapshots and the
            following keys: ``'SHC'`` shc-file name, `nmin` minimum degree,
            ``'nmax'`` maximum degree, ``'N'`` number of snapshot models,
            ``'order'`` piecewise polynomial order and ``'step'`` number of
            snapshots until next break point. Extract break points of the
            piecewise polynomial with ``breaks = time[::step]``.

        """
        leap_year = True if leap_year is None else leap_year

        read_values_flag = False

        with open(filepath, "r") as f:

            data = np.array([])
            for line in f.readlines():

                if line[0] == "#":
                    continue

                read_line = np.fromstring(line, sep=" ")
                if (read_line.size == 7) and not (read_values_flag):
                    name = os.path.split(filepath)[1]  # file name string
                    values = [name] + read_line.astype(int).tolist()
                    read_values_flag = True
                else:
                    data = np.append(data, read_line)

            # unpack parameter line
            keys = [
                "SHC",
                "nmin",
                "nmax",
                "N",
                "order",
                "step",
                "start_year",
                "end_year",
            ]
            parameters = dict(zip(keys, values))

            time = data[: parameters["N"]]
            coeffs = data[parameters["N"] :].reshape((-1, parameters["N"] + 2))
            coeffs = np.squeeze(coeffs[:, 2:])  # discard columns with n and m

        return igrf_utils(time, coeffs, parameters)

    def check_lat_lon_bounds(self, latd, latm, lond, lonm):
        """Check the bounds of the given lat, long are within -90 to +90 and -180
        to +180 degrees

        Paramters
        ---------
        latd, latm, lond, lonm : int or float

        Returns
        -------
        latd, latm, lond, lonm : bounded to -90:90 and -180:180 and converted to
        decimal degrees

        Otherwise, an exception is raised

        """

        if latd < -90 or latd > 90 or latm < -60 or latm > 60:
            raise ValueError(f"Latitude {latd} or {latm} out of bounds.")
        if lond < -360 or lond > 360 or lonm < -60 or lonm > 60:
            raise ValueError(f"Longitude {lond} or {lonm} out of bounds.")
        if latm < 0 and lond != 0:
            raise ValueError(f"Lat mins {latm} and {lond} out of bounds.")
        if lonm < 0 and lond != 0:
            raise ValueError(f"Longitude mins {lonm} and {lond} out of bounds.")

        # Convert to decimal degrees
        if latd < 0:
            latm = -latm
        lat = latd + latm / 60.0

        if lond < 0:
            lonm = -lonm
        lon = lond + lonm / 60.0

        return lat, lon

    def gg_to_geo(self, h, gdcolat):
        """
        Compute geocentric colatitude and radius from geodetic colatitude and
        height.

        Parameters
        ----------
        h : ndarray, shape (...)
            Altitude in kilometers.
        gdcolat : ndarray, shape (...)
            Geodetic colatitude

        Returns
        -------
        radius : ndarray, shape (...)
            Geocentric radius in kilometers.
        theta : ndarray, shape (...)
            Geocentric colatitude in degrees.

        sd : ndarray shape (...)
            rotate B_X to gd_lat
        cd :  ndarray shape (...)
            rotate B_Z to gd_lat

        References
        ----------
        Equations (51)-(53) from "The main field" (chapter 4) by Langel, R. A. in:
        "Geomagnetism", Volume 1, Jacobs, J. A., Academic Press, 1987.

        Malin, S.R.C. and Barraclough, D.R., 1981. An algorithm for synthesizing
        the geomagnetic field. Computers & Geosciences, 7(4), pp.401-405.

        """
        # Use WGS-84 ellipsoid parameters

        eqrad = 6378.137  # equatorial radius
        flat = 1 / 298.257223563
        plrad = eqrad * (1 - flat)  # polar radius
        ctgd = np.cos(np.deg2rad(gdcolat))
        stgd = np.sin(np.deg2rad(gdcolat))
        a2 = eqrad * eqrad
        a4 = a2 * a2
        b2 = plrad * plrad
        b4 = b2 * b2
        c2 = ctgd * ctgd
        s2 = 1 - c2
        rho = np.sqrt(a2 * s2 + b2 * c2)

        rad = np.sqrt(h * (h + 2 * rho) + (a4 * s2 + b4 * c2) / rho**2)

        cd = (h + rho) / rad
        sd = (a2 - b2) * ctgd * stgd / (rho * rad)

        cthc = ctgd * cd - stgd * sd  # Also: sthc = stgd*cd + ctgd*sd
        thc = np.rad2deg(np.arccos(cthc))  # arccos returns values in [0, pi]

        return rad, thc, sd, cd

    def geo_to_gg(self, radius, theta):
        """
        Compute geodetic colatitude and vertical height above the ellipsoid from
        geocentric radius and colatitude.

        Parameters
        ----------
        radius : ndarray, shape (...)
            Geocentric radius in kilometers.
        theta : ndarray, shape (...)
            Geocentric colatitude in degrees.

        Returns
        -------
        height : ndarray, shape (...)
            Altitude in kilometers.
        beta : ndarray, shape (...)
            Geodetic colatitude

        Notes
        -----
        Round-off errors might lead to a failure of the algorithm especially but
        not exclusively for points close to the geographic poles. Corresponding
        geodetic coordinates are returned as NaN.

        References
        ----------
        Function uses Heikkinen's algorithm taken from:

        Zhu, J., "Conversion of Earth-centered Earth-fixed coordinates to geodetic
        coordinates", IEEE Transactions on Aerospace and Electronic Systems}, 1994,
        vol. 30, num. 3, pp. 957-961

        """

        # Use WGS-84 ellipsoid parameters
        a = 6378.137  # equatorial radius
        b = 6356.752  # polar radius

        a2 = a**2
        b2 = b**2

        e2 = (a2 - b2) / a2  # squared eccentricity
        e4 = e2 * e2
        ep2 = (a2 - b2) / b2  # squared primed eccentricity

        r = radius * np.sin(radians(theta))
        z = radius * np.cos(radians(theta))

        r2 = r**2
        z2 = z**2

        F = 54 * b2 * z2

        G = r2 + (1.0 - e2) * z2 - e2 * (a2 - b2)

        c = e4 * F * r2 / G**3

        s = (1.0 + c + np.sqrt(c**2 + 2 * c)) ** (1.0 / 3)

        P = F / (3 * (s + 1.0 / s + 1.0) ** 2 * G**2)

        Q = np.sqrt(1.0 + 2 * e4 * P)

        r0 = -P * e2 * r / (1.0 + Q) + np.sqrt(
            0.5 * a2 * (1.0 + 1.0 / Q)
            - P * (1.0 - e2) * z2 / (Q * (1.0 + Q))
            - 0.5 * P * r2
        )

        U = np.sqrt((r - e2 * r0) ** 2 + z2)

        V = np.sqrt((r - e2 * r0) ** 2 + (1.0 - e2) * z2)

        z0 = b2 * z / (a * V)

        height = U * (1.0 - b2 / (a * V))

        beta = 90.0 - degrees(np.arctan2(z + ep2 * z0, r))

        return height, beta

    def synth_values(self, coeffs, radius, theta, phi, nmax=None, nmin=None, grid=None):
        """
        Based on chaosmagpy from Clemens Kloss (DTU Space, Copenhagen)
        Computes radial, colatitude and azimuthal field components from the
        magnetic potential field in terms of spherical harmonic coefficients.
        A reduced version of the DTU synth_values chaosmagpy code

        Parameters
        ----------

        coeffs : ndarray, shape (..., N)
            Coefficients of the spherical harmonic expansion. The last dimension is
            equal to the number of coefficients, `N` at the grid points.
        radius : float or ndarray, shape (...)
            Array containing the radius in kilometers.
        theta : float or ndarray, shape (...)
            Array containing the colatitude in degrees
            :math:`[0^\\circ,180^\\circ]`.
        phi : float or ndarray, shape (...)
            Array containing the longitude in degrees.
        nmax : int, positive, optional
            Maximum degree up to which expansion is to be used (default is given by
            the ``coeffs``, but can also be smaller if specified
            :math:`N` :math:`\\geq` ``nmax`` (``nmax`` + 2)
        nmin : int, positive, optional
            Minimum degree from which expansion is to be used (defaults to 1).
            Note that it will just skip the degrees smaller than ``nmin``, the
            whole sequence of coefficients 1 through ``nmax`` must still be given
            in ``coeffs``.
            Magnetic field source (default is an internal source).
        grid : bool, optional
            If ``True``, field components are computed on a regular grid. Arrays
            ``theta`` and ``phi`` must have one dimension less than the output grid
            since the grid will be created as their outer product (defaults to
            ``False``).

        Returns
        -------
        B_radius, B_theta, B_phi : ndarray, shape (...)
            Radial, colatitude and azimuthal field components.

        Notes
        -----
        The function can work with different grid shapes, but the inputs have to
        satisfy NumPy's `broadcasting rules \\
        <https://docs.scipy.org/doc/numpy-1.15.0/user/basics.broadcasting.html>`_
        (``grid=False``, default). This also applies to the dimension of the
        coefficients ``coeffs`` excluding the last dimension.

        The optional parameter ``grid`` is for convenience. If set to ``True``,
        a singleton dimension is appended (prepended) to ``theta`` (``phi``)
        for broadcasting to a regular grid. The other inputs ``radius`` and
        ``coeffs`` must then be broadcastable as before but now with the resulting
        regular grid.

        Examples
        --------
        The most straight forward computation uses a fully specified grid. For
        example, compute the magnetic field at :math:`N=50` grid points on the
        surface.

        .. code-block:: python

        import igrf_utils as iut
        import numpy as np

        N = 13
        coeffs = np.ones((3,))  # degree 1 coefficients for all points
        radius = 6371.2 * np.ones((N,))  # radius of 50 points in km
        phi = np.linspace(-180., 180., num=N)  # azimuth of 50 points in deg.
        theta = np.linspace(0., 180., num=N)  # colatitude of 50 points in deg.

        B = iut.synth_values(coeffs, radius, theta, phi)
        print([B[num].shape for num in range(3)])  # (N,) shaped output

        Instead of `N` points, compute the field on a regular
        :math:`N\\times N`-grid in azimuth and colatitude (slow).

        .. code-block:: python

        radius_grid = 6371.2 * np.ones((N, N))
        phi_grid, theta_grid = np.meshgrid(phi, theta)  # regular NxN grid

        B = iut.synth_values(coeffs, radius_grid, theta_grid, phi_grid)
        print([B[num].shape for num in range(3)])  # NxN output

        But this is slow since some computations on the grid are executed several
        times. The preferred method is to use NumPy's broadcasting rules (fast).

        .. code-block:: python

        radius_grid = 6371.2  # float, () or (1,)-shaped array broadcasted to NxN
        phi_grid = phi[None, ...]  # prepend singleton: 1xN
        theta_grid = theta[..., None]  # append singleton: Nx1

        B = iut.synth_values(coeffs, radius_grid, theta_grid, phi_grid)
        print([B[num].shape for num in range(3)])  # NxN output

        For convenience, you can do the same by using ``grid=True`` option.

        .. code-block:: python

        B = iut.synth_values(coeffs, radius_grid, theta, phi, grid=True)
        print([B[num].shape for num in range(3)])  # NxN output

        Remember that ``grid=False`` (or left out completely) will result in
        (N,)-shaped outputs as in the first example.

        """
        radius = 6371.2
        # ensure ndarray inputs
        coeffs = np.array(coeffs, dtype=float)
        radius = np.array(radius, dtype=float) / 6371.2  # Earth's average radius
        theta = np.array(theta, dtype=float)
        phi = np.array(phi, dtype=float)

        if np.amin(theta) <= 0.0 or np.amax(theta) >= 180.0:
            if np.amin(theta) == 0.0 or np.amax(theta) == 180.0:
                warnings.warn("The geographic poles are included.")
            else:
                raise ValueError("Colatitude outside bounds [0, 180].")

        if nmin is None:
            nmin = 1
        else:
            if nmin <= 0:
                raise ValueError("Only positive nmin allowed.")

        # handle optional argument: nmax
        nmax_coeffs = int(np.sqrt(coeffs.shape[-1] + 1) - 1)  # degree
        if nmax is None:
            nmax = nmax_coeffs
        else:
            if nmax <= 0:
                raise ValueError("Only positive nmax allowed.")

        if nmax > nmax_coeffs:
            warnings.warn(
                "Supplied nmax = {0} and nmin = {1} is "
                "incompatible with number of model coefficients. "
                "Using nmax = {2} instead.".format(nmax, nmin, nmax_coeffs)
            )
            nmax = nmax_coeffs

        if nmax < nmin:
            raise ValueError(f"Nothing to compute: nmax < nmin ({nmax} < {nmin}.)")

        # handle grid option
        grid = False if grid is None else grid

        # manually broadcast input grid on surface
        if grid:
            theta = theta[..., None]  # first dimension is theta
            phi = phi[None, ...]  # second dimension is phi

        # get shape of broadcasted result
        try:
            b = np.broadcast(radius, theta, phi, np.broadcast_to(0, coeffs.shape[:-1]))
        except ValueError:
            print("Cannot broadcast grid shapes (excl. last dimension of coeffs):")
            print(f"radius: {radius.shape}")
            print(f"theta:  {theta.shape}")
            print(f"phi:    {phi.shape}")
            print(f"coeffs: {coeffs.shape[:-1]}")
            raise

        grid_shape = b.shape

        # initialize radial dependence given the source
        r_n = radius ** (-(nmin + 2))

        # compute associated Legendre polynomials as (n, m, theta-points)-array
        Pnm = self.legendre_poly(nmax, theta)

        # save sinth for fast access
        sinth = Pnm[1, 1]

        # calculate cos(m*phi) and sin(m*phi) as (m, phi-points)-array
        phi = radians(phi)
        cmp = np.cos(np.multiply.outer(np.arange(nmax + 1), phi))
        smp = np.sin(np.multiply.outer(np.arange(nmax + 1), phi))

        # allocate arrays in memory
        B_radius = np.zeros(grid_shape)
        B_theta = np.zeros(grid_shape)
        B_phi = np.zeros(grid_shape)

        num = nmin**2 - 1
        for n in range(nmin, nmax + 1):
            B_radius += (n + 1) * Pnm[n, 0] * r_n * coeffs[..., num]

            B_theta += -Pnm[0, n + 1] * r_n * coeffs[..., num]

            num += 1

            for m in range(1, n + 1):
                B_radius += (
                    (n + 1)
                    * Pnm[n, m]
                    * r_n
                    * (coeffs[..., num] * cmp[m] + coeffs[..., num + 1] * smp[m])
                )

                B_theta += (
                    -Pnm[m, n + 1]
                    * r_n
                    * (coeffs[..., num] * cmp[m] + coeffs[..., num + 1] * smp[m])
                )

                with np.errstate(divide="ignore", invalid="ignore"):
                    # handle poles using L'Hopital's rule
                    div_Pnm = np.where(theta == 0.0, Pnm[m, n + 1], Pnm[n, m] / sinth)
                    div_Pnm = np.where(theta == degrees(pi), -Pnm[m, n + 1], div_Pnm)

                B_phi += (
                    m
                    * div_Pnm
                    * r_n
                    * (coeffs[..., num] * smp[m] - coeffs[..., num + 1] * cmp[m])
                )

                num += 2

            r_n = r_n / radius  # equivalent to r_n = radius**(-(n+2))

        return B_radius, B_theta, B_phi

    def legendre_poly(self, nmax, theta):
        """
        Returns associated Legendre polynomials `P(n,m)` (Schmidt quasi-normalized)
        and the derivative :math:`dP(n,m)/d\\theta` evaluated at :math:`\\theta`.

        Parameters
        ----------
        nmax : int, positive
            Maximum degree of the spherical expansion.
        theta : ndarray, shape (...)
            Colatitude in degrees :math:`[0^\\circ, 180^\\circ]`
            of arbitrary shape.

        Returns
        -------
        Pnm : ndarray, shape (n, m, ...)
            Evaluated values and derivatives, grid shape is appended as trailing
            dimensions. `P(n,m)` := ``Pnm[n, m, ...]`` and `dP(n,m)` :=
            ``Pnm[m, n+1, ...]``

        """

        costh = np.cos(radians(theta))
        sinth = np.sqrt(1 - costh**2)

        Pnm = np.zeros((nmax + 1, nmax + 2) + costh.shape)
        Pnm[0, 0] = 1  # is copied into trailing dimenions
        Pnm[1, 1] = sinth  # write theta into trailing dimenions via broadcasting

        rootn = np.sqrt(np.arange(2 * nmax**2 + 1))

        # Recursion relations after Langel "The Main Field" (1987),
        # eq. (27) and Table 2 (p. 256)
        for m in range(nmax):
            Pnm_tmp = rootn[m + m + 1] * Pnm[m, m]
            Pnm[m + 1, m] = costh * Pnm_tmp

            if m > 0:
                Pnm[m + 1, m + 1] = sinth * Pnm_tmp / rootn[m + m + 2]

            for n in np.arange(m + 2, nmax + 1):
                d = n * n - m * m
                e = n + n - 1
                Pnm[n, m] = (
                    e * costh * Pnm[n - 1, m] - rootn[d - e] * Pnm[n - 2, m]
                ) / rootn[d]

        # dP(n,m) = Pnm(m,n+1) is the derivative of P(n,m) vrt. theta
        Pnm[0, 2] = -Pnm[1, 1]
        Pnm[1, 2] = Pnm[1, 0]
        for n in range(2, nmax + 1):
            Pnm[0, n + 1] = -np.sqrt((n * n + n) / 2) * Pnm[n, 1]
            Pnm[1, n + 1] = (
                np.sqrt(2 * (n * n + n)) * Pnm[n, 0]
                - np.sqrt((n * n + n - 2)) * Pnm[n, 2]
            ) / 2

            for m in np.arange(2, n):
                Pnm[m, n + 1] = 0.5 * (
                    np.sqrt((n + m) * (n - m + 1)) * Pnm[n, m - 1]
                    - np.sqrt((n + m + 1) * (n - m)) * Pnm[n, m + 1]
                )

            Pnm[n, n + 1] = np.sqrt(2 * n) * Pnm[n, n - 1] / 2

        return Pnm

    def xyz2dhif(self, x, y, z):
        """Calculate D, H, I and F from (X, Y, Z)

        Based on code from D. Kerridge, 2019

        Parameters
        ---------------
        X: north component (nT) : float
        Y: east component (nT) : float
        Z: vertical component (nT) : float

        Returns
        ------
        A tuple: (D, H, I, F) : float
        D: declination (degrees) : float
        H: horizontal intensity (nT) : float
        I: inclination (degrees) : float
        F: total intensity (nT) : float



        """
        hsq = x * x + y * y
        hoz = np.sqrt(hsq)
        eff = np.sqrt(hsq + z * z)
        dec = np.arctan2(y, x)
        inc = np.arctan2(z, hoz)

        return r2d(dec), hoz, r2d(inc), eff

    def xyz2dhif_sv(self, x, y, z, xdot, ydot, zdot):
        """Calculate secular variation in D, H, I and F from (X, Y, Z) and
        (Xdot, Ydot, Zdot)

        Based on code from D. Kerridge, 2019

        Parameters
        ---------------
        X: north component (nT) : float
        Y: east component (nT) : float
        Z: vertical component (nT) : float
        Xdot=dX/dt : rate of change of X : float
        Ydot=dY/dt : rate of change of Y : float
        Zdot=dZ/dt : rate of change of Z : float

        Returns
        ------
        A tuple: (Ddot, Hdot, Idot, Fdot)
        Ddot: rate of change of declination (degrees/year)
        Hdot: rate of change of horizontal intensity (nT/year)
        Idot: rate of change of inclination (degrees/year)
        Fdot: rate of change of total intensity (nT/year)



        """
        h2 = x * x + y * y
        h = np.sqrt(h2)
        f2 = h2 + z * z
        hdot = (x * xdot + y * ydot) / h
        fdot = (x * xdot + y * ydot + z * zdot) / np.sqrt(f2)
        ddot = r2d((ydot * x - xdot * y) / h2) * 60
        idot = r2d((h * zdot - hdot * z) / f2) * 60

        return ddot, hdot, idot, fdot
