#pragma once

#include <limits>
#include <memory>
#include <utility>

#include "drake/common/drake_copyable.h"
#include "drake/common/eigen_types.h"
#include "drake/multibody/contact_solvers/sap/sap_constraint.h"

namespace drake {
namespace multibody {
namespace contact_solvers {
namespace internal {

/* Structure to store data needed for SapLimitConstraint computations.
 @tparam_nonsymbolic_scalar */
template <typename T>
class SapLimitConstraintData {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(SapLimitConstraintData);

  /* Constructs data for a SapLimitConstraint.
    Refer to SapLimitConstraint's documentation for further details.
    @param R Regularization parameters.
    @param v_hat Bias term. */
  SapLimitConstraintData(VectorX<T> R, VectorX<T> v_hat) {
    const int nk = R.size();
    parameters_.R_inv = R.cwiseInverse();
    parameters_.R = std::move(R);
    parameters_.v_hat = std::move(v_hat);
    vc_.resize(nk);
    y_.resize(nk);
    gamma_.resize(nk);
  }

  /* Regularization R. */
  const VectorX<T>& R() const { return parameters_.R; }

  /* Inverse of the regularization, R⁻¹. */
  const VectorX<T>& R_inv() const { return parameters_.R_inv; }

  /* Constraint bias. */
  const VectorX<T>& v_hat() const { return parameters_.v_hat; }

  /* Const access. */
  const VectorX<T>& vc() const { return vc_; }
  const VectorX<T>& y() const { return y_; }
  const VectorX<T>& gamma() const { return gamma_; }

  /* Mutable access. */
  VectorX<T>& mutable_vc() { return vc_; }
  VectorX<T>& mutable_y() { return y_; }
  VectorX<T>& mutable_gamma() { return gamma_; }

 private:
  // Values stored in this struct remain const after construction.
  struct ConstParameters {
    VectorX<T> R;  // Regularization R.
    VectorX<T> R_inv;
    VectorX<T> v_hat;  // Constraint velocity bias.
  };
  ConstParameters parameters_;

  VectorX<T> vc_;     // Constraint velocity.
  VectorX<T> y_;      // Un-projected impulse y = −R⁻¹⋅(vc−v̂).
  VectorX<T> gamma_;  // Projected impulse γ = P(y).
};

/* Implements limit constraints for the SAP solver, [Castro et al., 2021]. This
 constraint is used to impose a (compliant, see below) limit on the i-th degree
 of freedom (DOF) of a given clique in a SapContactModel. This constraint
 assumes that the rate of change of the i-th configuration exactly equals its
 corresponding generalized velocities, i.e. q̇ᵢ = vᵢ. This is specially true for
 1-DOF joints such as revolute and prismatic.

 Constraint kinematics:
  We consider the i-th DOF of a clique with m DOFs.
  We denote the configuration with qᵢ its lower limit with qₗ and its upper
  limit with qᵤ, where qₗ < qᵤ. The limit constraint defines a constraint
  function g(q) ∈ ℝ² as:
    g = |qᵢ - qₗ|   for the lower limit and,
        |qᵤ - qᵢ|   for the upper limit
  such that g(qᵢ) < 0 (componentwise) if the constraint is violated. The
  constraint velocity therefore is:
    ġ = | q̇ᵢ|
        |-q̇ᵢ|
  And therefore the constraint Jacobian is:
    J = | eᵢᵀ|
        |-eᵢᵀ|
  where eᵢ is the i-th element of the standard basis of ℝᵐ whose components are
  all zero, except for the i-th component that equals to 1.

  If one of the limits is infinite (qₗ = -∞ or qᵤ = +∞) then only one of the
  equations is considered (the one with finite bound) and g(q) ∈ ℝ i.e.
  num_constraint_equations() = 1.

 Compliant impulse:
  Limit constraints in the SAP formulation model a compliant impulse γ according
  to:
    y/dt = −k⋅g−d⋅ġ
    γ/δt = P(y)
    P(y) = (y)₊
  where δt is the time step used in the formulation, k is the constraint
  stiffness (in N/m), d is the dissipation (in N⋅s/m) and (x)₊ = max(0, x),
  componentwise. Dissipation is parameterized as d = tau_d⋅k, where tau_d is the
  "dissipation time scale". Notice that these impulses are positive when the
  constraint is active and zero otherwise.
  For this constraint the components of γ = [γₗ, γᵤ]ᵀ are constrained to live in
  ℝ⁺ and therefore the projection can trivially be computed analytically as
  P(y) = (y)₊, independent of the compliant regularization, see [Todorov, 2014].

 [Castro et al., 2021] Castro A., Permenter F. and Han X., 2021. An
   Unconstrained Convex Formulation of Compliant Contact. Available at
   https://arxiv.org/abs/2110.10107
 [Todorov, 2014] Todorov, E., 2014, May. Convex and analytically-invertible
   dynamics with contacts and constraints: Theory and implementation in mujoco.
   In 2014 IEEE International Conference on Robotics and Automation (ICRA) (pp.
   6054-6061). IEEE.

 @tparam_nonsymbolic_scalar */
template <typename T>
class SapLimitConstraint final : public SapConstraint<T> {
 public:
  /* We do not allow copy, move, or assignment generally to avoid slicing.
    Protected copy construction is enabled for sub-classes to use in their
    implementation of DoClone(). */
  //@{
  SapLimitConstraint& operator=(const SapLimitConstraint&) = delete;
  SapLimitConstraint(SapLimitConstraint&&) = delete;
  SapLimitConstraint& operator=(SapLimitConstraint&&) = delete;
  //@}

  /* Numerical parameters that define the constraint. Refer to this class's
   documentation for details. */
  class Parameters {
   public:
    DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Parameters);

    /* Constructs a valid set of parameters.
     @pre lower_limit < +∞
     @pre upper_limit > -∞
     @pre at least one of lower_limit and upper_limit is finite.
     @pre lower_limit <= upper_limit
     @pre stiffness > 0
     @pre dissipation_time_scale >= 0
     @pre beta > 0 */
    Parameters(const T& lower_limit, const T& upper_limit, const T& stiffness,
               const T& dissipation_time_scale, double beta = 0.1);

    const T& lower_limit() const { return lower_limit_; }
    const T& upper_limit() const { return upper_limit_; }
    const T& stiffness() const { return stiffness_; }
    const T& dissipation_time_scale() const { return dissipation_time_scale_; }
    double beta() const { return beta_; }

    bool operator==(const Parameters&) const = default;

   private:
    T lower_limit_;
    T upper_limit_;
    /* Contact stiffness k, in N/m. It must be strictly positive. */
    T stiffness_;
    /* Dissipation time scale tau_d, in seconds. It must be non-negative. */
    T dissipation_time_scale_;
    /* Rigid approximation constant: Rₙ = β²/(4π²)⋅w when the constraint
     frequency ωₙ is below the limit ωₙ⋅δt ≤ 2π. That is, the period is Tₙ =
     β⋅δt. w corresponds to a diagonal approximation of the Delassuss operator
     for each contact. See [Castro et al., 2021] for details. */
    double beta_{0.1};
  };

  /* Constructs a limit constraint for DOF with index `clique_dof` within clique
   with index `clique` in a given SapContactProblem. If one of the limits is
   infinite (qₗ = -∞ or qᵤ = +∞) then only one of the equations is considered
   (the one with finite bound) and g(q) ∈ ℝ i.e. num_constraint_equations() = 1.
   @param[in] clique The clique involved in the contact. Must be non-negative.
   @param[in] clique_dof DOF in `clique` to be constrained. It must be in [0,
   clique_nv).
   @param[in] clique_nv Number of generalized velocities for `clique`.
   @param[in] q0 Current configuration of the constraint.
   @param[in] parameters Parameters of the constraint. */
  SapLimitConstraint(int clique, int clique_dof, int clique_nv, const T& q0,
                     Parameters parameters);

  const Parameters& parameters() const { return parameters_; }

  /* Returns the degree of freedom, DOF, that this constraint limits. Provided
   at construction. */
  int clique_dof() const { return clique_dof_; }

  /* Returns the position provided at construction. */
  const T& position() const { return q0_; }

  /* Returns the value of the constraint function computed at construction. At
   construction, Parameters can specify limits that are infinite (-∞ for lower
   and ∞ for upper), indicating there is no limit. Therefore, this constraint
   will implement a constraint function that can have size two (both limits
   finite), size one (one of the limits is infinite) or even zero (both limits
   are infinite). Therefore the returned vector stores the value of the
   constraint function as:
     1. the first entry contains the value of the lower limit constraint
        function iff the lower limit is finite.
     2. The next entry contains the value of the upper limit constraint
        function iff the upper limit is finite.
   There is no information in the returned value on which limits were included.
   That information however is known to the client code that provided the
   initial constraint parameters. */
  const VectorX<T>& constraint_function() const { return g_; }

 private:
  /* Private copy construction is enabled to use in the implementation of
    DoClone(). */
  SapLimitConstraint(const SapLimitConstraint&) = default;

  /* Computes the constraint function g(q0) as a function of q0 for given lower
   limit ql and upper limit qu.
   @pre lower_limit < +∞
   @pre upper_limit > -∞ */
  static VectorX<T> CalcConstraintFunction(const T& q0, const T& ql,
                                           const T& qu);

  /* Computes the constraint Jacobian, independent of the configuration for this
   constraint. */
  static SapConstraintJacobian<T> CalcConstraintJacobian(
      int clique, int clique_dof, int clique_nv, const T& ql, const T& qu);

  /* Implementations of SapConstraint NVI functions. */
  std::unique_ptr<AbstractValue> DoMakeData(
      const T& time_step,
      const Eigen::Ref<const VectorX<T>>& delassus_estimation) const override;
  void DoCalcData(const Eigen::Ref<const VectorX<T>>& vc,
                  AbstractValue* abstract_data) const override;
  T DoCalcCost(const AbstractValue& abstract_data) const override;
  void DoCalcImpulse(const AbstractValue& abstract_data,
                     EigenPtr<VectorX<T>> gamma) const override;
  void DoCalcCostHessian(const AbstractValue& abstract_data,
                         MatrixX<T>* G) const override;
  std::unique_ptr<SapConstraint<T>> DoClone() const final {
    return std::unique_ptr<SapLimitConstraint<T>>(
        new SapLimitConstraint<T>(*this));
  }
  std::unique_ptr<SapConstraint<double>> DoToDouble() const final;
  void DoAccumulateGeneralizedImpulses(
      int c, const Eigen::Ref<const VectorX<T>>& gamma,
      EigenPtr<VectorX<T>> tau) const final;
  // no-op for this constraint.
  void DoAccumulateSpatialImpulses(int, const Eigen::Ref<const VectorX<T>>&,
                                   SpatialForce<T>*) const final{};

  Parameters parameters_;
  int clique_dof_{-1};  // Initialized to an invalid value.
  T q0_{};              // position at the configuration from construction.
  VectorX<T> g_;        // Constraint function g. See CalcConstraintFunction().
};

}  // namespace internal
}  // namespace contact_solvers
}  // namespace multibody
}  // namespace drake
