from __future__ import print_function, division, absolute_import
import unittest

import numpy as np

import openmdao.api as om
from openmdao.utils.assert_utils import assert_rel_error


class Resistor(om.ExplicitComponent):
    """Computes current across a resistor using Ohm's law."""

    def initialize(self):
        self.options.declare('R', default=1., desc='Resistance in Ohms')

    def setup(self):
        self.add_input('V_in', units='V')
        self.add_input('V_out', units='V')
        self.add_output('I', units='A')

        self.declare_partials('I', 'V_in', method='fd')
        self.declare_partials('I', 'V_out', method='fd')

    def compute(self, inputs, outputs):
        deltaV = inputs['V_in'] - inputs['V_out']
        outputs['I'] = deltaV / self.options['R']


class Diode(om.ExplicitComponent):
    """Computes current across a diode using the Shockley diode equation."""

    def initialize(self):
        self.options.declare('Is', default=1e-15, desc='Saturation current in Amps')
        self.options.declare('Vt', default=.025875, desc='Thermal voltage in Volts')

    def setup(self):
        self.add_input('V_in', units='V')
        self.add_input('V_out', units='V')
        self.add_output('I', units='A')

        self.declare_partials('I', 'V_in', method='fd')
        self.declare_partials('I', 'V_out', method='fd')

    def compute(self, inputs, outputs):
        deltaV = inputs['V_in'] - inputs['V_out']
        Is = self.options['Is']
        Vt = self.options['Vt']
        outputs['I'] = Is * (np.exp(deltaV / Vt) - 1)


class Node(om.ImplicitComponent):
    """Computes voltage residual across a node based on incoming and outgoing current."""

    def initialize(self):
        self.options.declare('n_in', default=1, types=int, desc='number of connections with + assumed in')
        self.options.declare('n_out', default=1, types=int, desc='number of current connections + assumed out')

    def setup(self):
        self.add_output('V', val=5., units='V')

        for i in range(self.options['n_in']):
            i_name = 'I_in:{}'.format(i)
            self.add_input(i_name, units='A')

        for i in range(self.options['n_out']):
            i_name = 'I_out:{}'.format(i)
            self.add_input(i_name, units='A')

        #note: we don't declare any partials wrt `V` here,
        #      because the residual doesn't directly depend on it
        self.declare_partials('V', 'I*', method='fd')

    def apply_nonlinear(self, inputs, outputs, residuals):
        residuals['V'] = 0.
        for i_conn in range(self.options['n_in']):
            residuals['V'] += inputs['I_in:{}'.format(i_conn)]
        for i_conn in range(self.options['n_out']):
            residuals['V'] -= inputs['I_out:{}'.format(i_conn)]


# note: This is defined twice in the file. Once so you can import it, and once inside a test that gets included in the docs.
class Circuit(om.Group):

    def setup(self):
        self.add_subsystem('n1', Node(n_in=1, n_out=2), promotes_inputs=[('I_in:0', 'I_in')])
        self.add_subsystem('n2', Node())  # leaving defaults

        self.add_subsystem('R1', Resistor(R=100.), promotes_inputs=[('V_out', 'Vg')])
        self.add_subsystem('R2', Resistor(R=10000.))
        self.add_subsystem('D1', Diode(), promotes_inputs=[('V_out', 'Vg')])

        self.connect('n1.V', ['R1.V_in', 'R2.V_in'])
        self.connect('R1.I', 'n1.I_out:0')
        self.connect('R2.I', 'n1.I_out:1')

        self.connect('n2.V', ['R2.V_out', 'D1.V_in'])
        self.connect('R2.I', 'n2.I_in:0')
        self.connect('D1.I', 'n2.I_out:0')

        self.nonlinear_solver = om.NewtonSolver()
        self.nonlinear_solver.options['iprint'] = 2
        self.nonlinear_solver.options['maxiter'] = 20
        self.linear_solver = om.DirectSolver()


if __name__ == "__main__":
    import openmdao.api as om

    p = om.Problem()
    model = p.model

    model.add_subsystem('ground', om.IndepVarComp('V', 0., units='V'))

    # replacing the fixed current source with a BalanceComp to represent a fixed Voltage source
    # model.add_subsystem('source', IndepVarComp('I', 0.1, units='A'))
    model.add_subsystem('batt', om.IndepVarComp('V', 1.5, units='V'))
    bal = model.add_subsystem('batt_balance', om.BalanceComp())
    bal.add_balance('I', units='A', eq_units='V')

    model.add_subsystem('circuit', Circuit())
    model.add_subsystem('batt_deltaV', om.ExecComp('dV = V1 - V2', V1={'units':'V'},
                                                   V2={'units':'V'}, dV={'units':'V'}))

    # current into the circuit is now the output state from the batt_balance comp
    model.connect('batt_balance.I', 'circuit.I_in')
    model.connect('ground.V', ['circuit.Vg','batt_deltaV.V2'])
    model.connect('circuit.n1.V', 'batt_deltaV.V1')

    # set the lhs and rhs for the battery residual
    model.connect('batt.V', 'batt_balance.rhs:I')
    model.connect('batt_deltaV.dV', 'batt_balance.lhs:I')

    p.setup()

    ###################
    # Solver Setup
    ###################

    # change the circuit solver to RunOnce because we're
    # going to converge at the top level of the model with newton instead
    p.model.circuit.nonlinear_solver = om.NonlinearRunOnce()
    p.model.circuit.linear_solver = om.LinearRunOnce()

    # Put Newton at the top so it can also converge the new BalanceComp residual
    newton = p.model.nonlinear_solver = om.NewtonSolver()
    p.model.linear_solver = om.DirectSolver()
    newton.options['iprint'] = 2
    newton.options['maxiter'] = 20
    newton.options['solve_subsystems'] = True
    newton.linesearch = om.ArmijoGoldsteinLS()
    newton.linesearch.options['maxiter'] = 10
    newton.linesearch.options['iprint'] = 2

    # set initial guesses from the current source problem
    p['circuit.n1.V'] = 9.8
    p['circuit.n2.V'] = .7

    p.run_model()
