# -*- coding: utf-8 -*-
"""Created on Fri Apr  8 08:32:48 2016.

@author: RCGlade
"""

import numpy as np

from landlab import Component, LinkStatus


class DepthDependentDiffuser(Component):

    """This component implements a depth and slope dependent linear diffusion
    rule in the style of Johnstone and Hilley (2014).

    Hillslope sediment flux uses depth dependent component inspired by
    Johnstone and Hilley (2014). The flux :math:`q_s` is given as:

    .. math::

        q_s = - D S H^* (1.0 - exp( - H / H^*)

    where :math:`D` is is the diffusivity, :math:`S` is the slope (defined as
    negative downward), :math:`H` is the soil depth on links, and :math:`H^*`
    is the soil transport decay depth.

    This component will ignore soil thickness located at non-core nodes.

    Examples
    --------
    >>> import numpy as np
    >>> from landlab import RasterModelGrid
    >>> from landlab.components import ExponentialWeatherer
    >>> from landlab.components import DepthDependentDiffuser
    >>> mg = RasterModelGrid((5, 5))
    >>> soilTh = mg.add_zeros("soil__depth", at="node")
    >>> z = mg.add_zeros("topographic__elevation", at="node")
    >>> BRz = mg.add_zeros("bedrock__elevation", at="node")
    >>> expweath = ExponentialWeatherer(mg)
    >>> DDdiff = DepthDependentDiffuser(mg)
    >>> expweath.calc_soil_prod_rate()
    >>> np.allclose(mg.at_node['soil_production__rate'][mg.core_nodes], 1.)
    True
    >>> DDdiff.run_one_step(2.)
    >>> np.allclose(mg.at_node['topographic__elevation'][mg.core_nodes], 0.)
    True
    >>> np.allclose(mg.at_node['bedrock__elevation'][mg.core_nodes], -2.)
    True
    >>> np.allclose(mg.at_node['soil__depth'][mg.core_nodes], 2.)
    True

    Now with a slope:

    >>> mg = RasterModelGrid((3, 5))
    >>> soilTh = mg.add_zeros("soil__depth", at="node")
    >>> z = mg.add_zeros("topographic__elevation", at="node")
    >>> BRz = mg.add_zeros("bedrock__elevation", at="node")
    >>> z += mg.node_x.copy()
    >>> BRz += mg.node_x/2.
    >>> soilTh[:] = z - BRz
    >>> expweath = ExponentialWeatherer(mg)
    >>> DDdiff = DepthDependentDiffuser(mg)
    >>> expweath.calc_soil_prod_rate()
    >>> np.allclose(
    ...     mg.at_node['soil_production__rate'][mg.core_nodes],
    ...     np.array([ 0.60653066,  0.36787944,  0.22313016]))
    True
    >>> DDdiff.run_one_step(2.)
    >>> np.allclose(
    ...     mg.at_node['topographic__elevation'][mg.core_nodes],
    ...     np.array([ 1.47730244,  2.28949856,  3.17558975]))
    True
    >>> np.allclose(mg.at_node['bedrock__elevation'][mg.core_nodes],
    ...     np.array([-0.71306132,  0.26424112,  1.05373968]))
    True
    >>> np.allclose(mg.at_node['soil__depth'], z - BRz)
    True

    Now, we'll test that changing the transport decay depth behaves as expected.

    >>> mg = RasterModelGrid((3, 5))
    >>> soilTh = mg.add_zeros("soil__depth", at="node")
    >>> z = mg.add_zeros("topographic__elevation", at="node")
    >>> BRz = mg.add_zeros("bedrock__elevation", at="node")
    >>> z += mg.node_x.copy()**0.5
    >>> BRz = z.copy() - 1.0
    >>> soilTh[:] = z - BRz
    >>> expweath = ExponentialWeatherer(mg)
    >>> DDdiff = DepthDependentDiffuser(mg, soil_transport_decay_depth = 0.1)
    >>> DDdiff.run_one_step(1)
    >>> soil_decay_depth_point1 = mg.at_node['topographic__elevation'][mg.core_nodes]
    >>> z[:] = 0
    >>> z += mg.node_x.copy()**0.5
    >>> BRz = z.copy() - 1.0
    >>> soilTh[:] = z - BRz
    >>> DDdiff = DepthDependentDiffuser(mg, soil_transport_decay_depth = 1.0)
    >>> DDdiff.run_one_step(1)
    >>> soil_decay_depth_1 = mg.at_node['topographic__elevation'][mg.core_nodes]
    >>> np.greater(soil_decay_depth_1[1], soil_decay_depth_point1[1])
    False

    References
    ----------
    **Required Software Citation(s) Specific to this Component**

    Barnhart, K., Glade, R., Shobe, C., Tucker, G. (2019). Terrainbento 1.0: a
    Python package for multi-model analysis in long-term drainage basin
    evolution. Geoscientific Model Development  12(4), 1267--1297.
    https://dx.doi.org/10.5194/gmd-12-1267-2019

    **Additional References**

    Johnstone, S., Hilley, G. (2015). Lithologic control on the form of
    soil-mantled hillslopes Geology  43(1), 83-86.
    https://dx.doi.org/10.1130/g36052.1

    """

    _name = "DepthDependentDiffuser"

    _unit_agnostic = True

    _cite_as = """
    @article{barnhart2019terrain,
      author = {Barnhart, Katherine R and Glade, Rachel C and Shobe, Charles M and Tucker, Gregory E},
      title = {{Terrainbento 1.0: a Python package for multi-model analysis in long-term drainage basin evolution}},
      doi = {10.5194/gmd-12-1267-2019},
      pages = {1267---1297},
      number = {4},
      volume = {12},
      journal = {Geoscientific Model Development},
      year = {2019},
    }
    """

    _info = {
        "bedrock__elevation": {
            "dtype": float,
            "intent": "out",
            "optional": False,
            "units": "m",
            "mapping": "node",
            "doc": "elevation of the bedrock surface",
        },
        "soil__depth": {
            "dtype": float,
            "intent": "inout",
            "optional": False,
            "units": "m",
            "mapping": "node",
            "doc": "Depth of soil or weathered bedrock",
        },
        "soil__flux": {
            "dtype": float,
            "intent": "out",
            "optional": False,
            "units": "m^2/yr",
            "mapping": "link",
            "doc": "flux of soil in direction of link",
        },
        "soil_production__rate": {
            "dtype": float,
            "intent": "in",
            "optional": False,
            "units": "m/yr",
            "mapping": "node",
            "doc": "rate of soil production at nodes",
        },
        "topographic__elevation": {
            "dtype": float,
            "intent": "inout",
            "optional": False,
            "units": "m",
            "mapping": "node",
            "doc": "Land surface topographic elevation",
        },
        "topographic__slope": {
            "dtype": float,
            "intent": "out",
            "optional": False,
            "units": "m/m",
            "mapping": "link",
            "doc": "gradient of the ground surface",
        },
    }

    def __init__(self, grid, linear_diffusivity=1.0, soil_transport_decay_depth=1.0):
        """
        Parameters
        ----------
        grid: ModelGrid
            Landlab ModelGrid object
        linear_diffusivity: float
            Hillslope diffusivity, m**2/yr
        soil_transport_decay_depth: float
            Characteristic transport soil depth, m
        """
        super().__init__(grid)
        # Store grid and parameters

        self._K = linear_diffusivity
        self._soil_transport_decay_depth = soil_transport_decay_depth

        # get reference to inputs
        self._elev = self._grid.at_node["topographic__elevation"]
        self._soil_prod_rate = self._grid.at_node["soil_production__rate"]
        self._depth = self._grid.at_node["soil__depth"]

        # create outputs if necessary and get reference.
        self.initialize_output_fields()
        self._slope = self._grid.at_link["topographic__slope"]
        self._flux = self._grid.at_link["soil__flux"]
        self._bedrock = self._grid.at_node["bedrock__elevation"]

    def soilflux(self, dt):
        """Calculate soil flux for a time period 'dt'.

        Parameters
        ----------

        dt: float (time)
            The imposed timestep.
        """

        # update soil thickness
        self._grid.at_node["soil__depth"][:] = (
            self._grid.at_node["topographic__elevation"]
            - self._grid.at_node["bedrock__elevation"]
        )

        # Calculate soil depth at links.
        H_link = self._grid.map_value_at_max_node_to_link(
            "topographic__elevation", "soil__depth"
        )

        # Calculate gradients
        slope = self._grid.calc_grad_at_link(self._elev)
        slope[self._grid.status_at_link == LinkStatus.INACTIVE] = 0.0

        # Calculate flux
        self._flux[:] = (
            -self._K
            * slope
            * self._soil_transport_decay_depth
            * (1.0 - np.exp(-H_link / self._soil_transport_decay_depth))
        )

        # Calculate flux divergence
        dqdx = self._grid.calc_flux_div_at_node(self._flux)

        # Calculate change in soil depth
        dhdt = self._soil_prod_rate - dqdx

        # Calculate soil depth at nodes
        self._depth[self._grid.core_nodes] += dhdt[self._grid.core_nodes] * dt

        # prevent negative soil thickness
        self._depth[self._depth < 0.0] = 0.0

        # Calculate bedrock elevation
        self._bedrock[self._grid.core_nodes] -= (
            self._soil_prod_rate[self._grid.core_nodes] * dt
        )

        # Update topography
        self._elev[self._grid.core_nodes] = (
            self._depth[self._grid.core_nodes] + self._bedrock[self._grid.core_nodes]
        )

    def run_one_step(self, dt):
        """

        Parameters
        ----------
        dt: float (time)
            The imposed timestep.
        """

        self.soilflux(dt)
