from __future__ import division, print_function, absolute_import
import numpy as np
import scipy.sparse as sps
from ._numdiff import approx_derivative, group_columns
from ._hessian_update_strategy import HessianUpdateStrategy
from scipy.sparse.linalg import LinearOperator


FD_METHODS = ('2-point', '3-point', 'cs')


class ScalarFunction(object):
    """Scalar function and its derivatives.

    This class defines a scalar function F: R^n->R and methods for
    computing or approximating its first and second derivatives.

    Notes
    -----
    This class implements a memoization logic. There are methods `fun`,
    `grad`, hess` and corresponding attributes `f`, `g` and `H`. The following
    things should be considered:

        1. Use only public methods `fun`, `grad` and `hess`.
        2. After one of the methods is called, the corresponding attribute
           will be set. However, a subsequent call with a different argument
           of *any* of the methods may overwrite the attribute.
    """
    def __init__(self, fun, x0, args, grad, hess, finite_diff_rel_step,
                 finite_diff_bounds):
        if not callable(grad) and grad not in FD_METHODS:
            raise ValueError("`grad` must be either callable or one of {}."
                             .format(FD_METHODS))

        if not (callable(hess) or hess in FD_METHODS
                or isinstance(hess, HessianUpdateStrategy)):
            raise ValueError("`hess` must be either callable,"
                             "HessianUpdateStrategy or one of {}."
                             .format(FD_METHODS))

        if grad in FD_METHODS and hess in FD_METHODS:
            raise ValueError("Whenever the gradient is estimated via "
                             "finite-differences, we require the Hessian "
                             "to be estimated using one of the "
                             "quasi-Newton strategies.")

        self.x = np.atleast_1d(x0).astype(float)
        self.n = self.x.size
        self.nfev = 0
        self.ngev = 0
        self.nhev = 0
        self.f_updated = False
        self.g_updated = False
        self.H_updated = False

        finite_diff_options = {}
        if grad in FD_METHODS:
            finite_diff_options["method"] = grad
            finite_diff_options["rel_step"] = finite_diff_rel_step
            finite_diff_options["bounds"] = finite_diff_bounds
        if hess in FD_METHODS:
            finite_diff_options["method"] = hess
            finite_diff_options["rel_step"] = finite_diff_rel_step
            finite_diff_options["as_linear_operator"] = True

        # Function evaluation
        def fun_wrapped(x):
            self.nfev += 1
            return fun(x, *args)

        def update_fun():
            self.f = fun_wrapped(self.x)

        self._update_fun_impl = update_fun
        self._update_fun()

        # Gradient evaluation
        if callable(grad):
            def grad_wrapped(x):
                self.ngev += 1
                return np.atleast_1d(grad(x, *args))

            def update_grad():
                self.g = grad_wrapped(self.x)

        elif grad in FD_METHODS:
            def update_grad():
                self._update_fun()
                self.g = approx_derivative(fun_wrapped, self.x, f0=self.f,
                                           **finite_diff_options)

        self._update_grad_impl = update_grad
        self._update_grad()

        # Hessian Evaluation
        if callable(hess):
            self.H = hess(x0, *args)
            self.H_updated = True
            self.nhev += 1

            if sps.issparse(self.H):
                def hess_wrapped(x):
                    self.nhev += 1
                    return sps.csr_matrix(hess(x, *args))
                self.H = sps.csr_matrix(self.H)

            elif isinstance(self.H, LinearOperator):
                def hess_wrapped(x):
                    self.nhev += 1
                    return hess(x, *args)

            else:
                def hess_wrapped(x):
                    self.nhev += 1
                    return np.atleast_2d(np.asarray(hess(x, *args)))
                self.H = np.atleast_2d(np.asarray(self.H))

            def update_hess():
                self.H = hess_wrapped(self.x)

        elif hess in FD_METHODS:
            def update_hess():
                self._update_grad()
                self.H = approx_derivative(grad_wrapped, self.x, f0=self.g,
                                           **finite_diff_options)
                return self.H

            update_hess()
            self.H_updated = True
        elif isinstance(hess, HessianUpdateStrategy):
            self.H = hess
            self.H.initialize(self.n, 'hess')
            self.H_updated = True
            self.x_prev = None
            self.g_prev = None

            def update_hess():
                self._update_grad()
                self.H.update(self.x - self.x_prev, self.g - self.g_prev)

        self._update_hess_impl = update_hess

        if isinstance(hess, HessianUpdateStrategy):
            def update_x(x):
                self._update_grad()
                self.x_prev = self.x
                self.g_prev = self.g

                self.x = np.atleast_1d(x).astype(float)
                self.f_updated = False
                self.g_updated = False
                self.H_updated = False
                self._update_hess()
        else:
            def update_x(x):
                self.x = np.atleast_1d(x).astype(float)
                self.f_updated = False
                self.g_updated = False
                self.H_updated = False
        self._update_x_impl = update_x

    def _update_fun(self):
        if not self.f_updated:
            self._update_fun_impl()
            self.f_updated = True

    def _update_grad(self):
        if not self.g_updated:
            self._update_grad_impl()
            self.g_updated = True

    def _update_hess(self):
        if not self.H_updated:
            self._update_hess_impl()
            self.H_updated = True

    def fun(self, x):
        if not np.array_equal(x, self.x):
            self._update_x_impl(x)
        self._update_fun()
        return self.f

    def grad(self, x):
        if not np.array_equal(x, self.x):
            self._update_x_impl(x)
        self._update_grad()
        return self.g

    def hess(self, x):
        if not np.array_equal(x, self.x):
            self._update_x_impl(x)
        self._update_hess()
        return self.H


class VectorFunction(object):
    """Vector function and its derivatives.

    This class defines a vector function F: R^n->R^m and methods for
    computing or approximating its first and second derivatives.

    Notes
    -----
    This class implements a memoization logic. There are methods `fun`,
    `jac`, hess` and corresponding attributes `f`, `J` and `H`. The following
    things should be considered:

        1. Use only public methods `fun`, `jac` and `hess`.
        2. After one of the methods is called, the corresponding attribute
           will be set. However, a subsequent call with a different argument
           of *any* of the methods may overwrite the attribute.
    """
    def __init__(self, fun, x0, jac, hess,
                 finite_diff_rel_step, finite_diff_jac_sparsity,
                 finite_diff_bounds, sparse_jacobian):
        if not callable(jac) and jac not in FD_METHODS:
            raise ValueError("`jac` must be either callable or one of {}."
                             .format(FD_METHODS))

        if not (callable(hess) or hess in FD_METHODS
                or isinstance(hess, HessianUpdateStrategy)):
            raise ValueError("`hess` must be either callable,"
                             "HessianUpdateStrategy or one of {}."
                             .format(FD_METHODS))

        if jac in FD_METHODS and hess in FD_METHODS:
            raise ValueError("Whenever the Jacobian is estimated via "
                             "finite-differences, we require the Hessian to "
                             "be estimated using one of the quasi-Newton "
                             "strategies.")

        self.x = np.atleast_1d(x0).astype(float)
        self.n = self.x.size
        self.nfev = 0
        self.njev = 0
        self.nhev = 0
        self.f_updated = False
        self.J_updated = False
        self.H_updated = False

        finite_diff_options = {}
        if jac in FD_METHODS:
            finite_diff_options["method"] = jac
            finite_diff_options["rel_step"] = finite_diff_rel_step
            if finite_diff_jac_sparsity is not None:
                sparsity_groups = group_columns(finite_diff_jac_sparsity)
                finite_diff_options["sparsity"] = (finite_diff_jac_sparsity,
                                                   sparsity_groups)
            finite_diff_options["bounds"] = finite_diff_bounds
            self.x_diff = np.copy(self.x)
        if hess in FD_METHODS:
            finite_diff_options["method"] = hess
            finite_diff_options["rel_step"] = finite_diff_rel_step
            finite_diff_options["as_linear_operator"] = True
            self.x_diff = np.copy(self.x)
        if jac in FD_METHODS and hess in FD_METHODS:
            raise ValueError("Whenever the Jacobian is estimated via "
                             "finite-differences, we require the Hessian to "
                             "be estimated using one of the quasi-Newton "
                             "strategies.")

        # Function evaluation
        def fun_wrapped(x):
            self.nfev += 1
            return np.atleast_1d(fun(x))

        def update_fun():
            self.f = fun_wrapped(self.x)

        self._update_fun_impl = update_fun
        update_fun()

        self.v = np.zeros_like(self.f)
        self.m = self.v.size

        # Jacobian Evaluation
        if callable(jac):
            self.J = jac(self.x)
            self.J_updated = True
            self.njev += 1

            if (sparse_jacobian or
                    sparse_jacobian is None and sps.issparse(self.J)):
                def jac_wrapped(x):
                    self.njev += 1
                    return sps.csr_matrix(jac(x))
                self.J = sps.csr_matrix(self.J)
                self.sparse_jacobian = True

            elif sps.issparse(self.J):
                def jac_wrapped(x):
                    self.njev += 1
                    return jac(x).toarray()
                self.J = self.J.toarray()
                self.sparse_jacobian = False

            else:
                def jac_wrapped(x):
                    self.njev += 1
                    return np.atleast_2d(jac(x))
                self.J = np.atleast_2d(self.J)
                self.sparse_jacobian = False

            def update_jac():
                self.J = jac_wrapped(self.x)

        elif jac in FD_METHODS:
            self.J = approx_derivative(fun_wrapped, self.x, f0=self.f,
                                       **finite_diff_options)
            self.J_updated = True

            if (sparse_jacobian or
                    sparse_jacobian is None and sps.issparse(self.J)):
                def update_jac():
                    self._update_fun()
                    self.J = sps.csr_matrix(
                        approx_derivative(fun_wrapped, self.x, f0=self.f,
                                          **finite_diff_options))
                self.J = sps.csr_matrix(self.J)
                self.sparse_jacobian = True

            elif sps.issparse(self.J):
                def update_jac():
                    self._update_fun()
                    self.J = approx_derivative(fun_wrapped, self.x, f0=self.f,
                                               **finite_diff_options).toarray()
                self.J = self.J.toarray()
                self.sparse_jacobian = False

            else:
                def update_jac():
                    self._update_fun()
                    self.J = np.atleast_2d(
                        approx_derivative(fun_wrapped, self.x, f0=self.f,
                                          **finite_diff_options))
                self.J = np.atleast_2d(self.J)
                self.sparse_jacobian = False

        self._update_jac_impl = update_jac

        # Define Hessian
        if callable(hess):
            self.H = hess(self.x, self.v)
            self.H_updated = True
            self.nhev += 1