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#ifndef ECP_INTEGRAL_DERIVATIVE_COMPUTE_API_H
#define ECP_INTEGRAL_DERIVATIVE_COMPUTE_API_H

#include <stddef.h>

#include "../macros.h"
#include "../types/cuest_types.h"
#include "../types/cuest_parameter_types.h"
#include "../types/workspace_api.h"

#ifdef __cplusplus
extern "C" {
#endif

/**
 * @brief Compute the electronic gradient (derivative) of the effective core potential integral matrix
 * using the provided plan and density matrix.
 * @ingroup ECPCompute
 *
 * Both the input density matrix and the output gradient must be preallocated. The density 
 * matrix must be an (nao x nao) array and the output gradient must have space for (natom x 3) 
 * elements, where nao is the number of atomic orbitals and natom the number of atoms in the system.
 * All required temporary workspace must be allocated by the user prior to calling this function
 * using size returned by \c cuestECPDerivativeComputeWorkspaceQuery.
 *
 * @param[in]      handle                       cuEST handle. Must not be NULL.
 * @param[in]      plan                         ECP integral computation plan (opaque handle).
 * @param[in]      parameters                   Handle to \c cuestECPDerivativeComputeParameters_t. Must not be NULL.
 * @param[in]      variableBufferSize           User-provided descriptor for the amount of memory used to evaluate the ECP integrals.
 *                                                  2 GB is a good default buffer size for device memory. If an insufficient amount
 *                                                  of memory is provided, the cuestECPDerivativeCompute call will return CUEST_STATUS_EXCEPTION. 
 *                                                  If this occurs, increase the variableBufferSize and make the WorkspaceQuery and Compute calls
 *                                                  again. This value MUST remain unchanged between the WorkspaceQuery call and the Compute call.
 *                                                  Host memory is currently unused. Must not be NULL.
 * @param[in]      temporaryWorkspace           Temporary workspace buffers for computation (preallocated).
 * @param[in]      densityMatrix                Pointer to input density matrix (size: nao × nao) on the GPU. Must not be NULL.
 * @param[out]     outGradient                  Output buffer for computed ECP gradient (size: natom × 3) on the GPU. Must not be NULL.
 *                                                  Elements of this array are overwritten by the calculation results.
 *
 * @return
 *   - \c CUEST_STATUS_SUCCESS on success;
 *   - \c CUEST_STATUS_INVALID_HANDLE if the cuEST handle is NULL;
 *   - \c CUEST_STATUS_NULL_POINTER if any required pointer is NULL;
 *   - \c CUEST_STATUS_INVALID_TYPE if opaque handles are not the correct type.
 *   - \c CUEST_STATUS_EXCEPTION or \c CUEST_STATUS_UNKNOWN_ERROR otherwise.
 *   - \c CUEST_STATUS_EXCEPTION often indicates variableBufferSize is too small.
 */
CUEST_API
cuestStatus_t cuestECPDerivativeCompute(
    cuestHandle_t handle,
    const cuestECPIntPlan_t plan,
    const cuestECPDerivativeComputeParameters_t parameters,
    const cuestWorkspaceDescriptor_t* variableBufferSize,
    cuestWorkspace_t* temporaryWorkspace,
    const double* densityMatrix,
    double* outGradient);

/**
 * @brief Query the temporary workspace required (in bytes) for electronic gradient (derivative) of the
 * effective core potential matrix using the supplied integral plan and density matrix.
 * @ingroup ECPCompute
 *
 * This function computes the workspace requirements for a requested ECP gradient calculation. Fill the 
 * provided workspace descriptor with host and device buffer sizes required. The \c outGradient pointer may be NULL.
 *
 * @param[in]      handle                        cuEST handle. Must not be NULL.
 * @param[in]      plan                          ECP integral computation plan (opaque handle).
 * @param[in]      parameters                    Handle to \c cuestECPDerivativeComputeParameters_t. Must not be NULL.
 * @param[in]      variableBufferSize            User-provided descriptor for the amount of memory used to evaluate the ECP integrals.
 *                                                   2 GB is a good default buffer size for device memory. If an insufficient amount
 *                                                   of memory is provided, the cuestECPDerivativeCompute call will return CUEST_STATUS_EXCEPTION. 
 *                                                   If this occurs, increase the variableBufferSize and make the WorkspaceQuery and Compute calls
 *                                                   again. This value MUST remain unchanged between the WorkspaceQuery call and the Compute call.
 *                                                   Host memory is currently unused. Must not be NULL.
 * @param[out]     temporaryWorkspaceDescriptor  Output descriptor for temporary workspace sizes. Must not be NULL.
 * @param[in]      densityMatrix                 Pointer to input density matrix. May be NULL.
 * @param[in]      outGradient                   User buffer. May be NULL.
 *
 * @return
 *   - \c CUEST_STATUS_SUCCESS on success;
 *   - \c CUEST_STATUS_INVALID_HANDLE if the cuEST handle is NULL;
 *   - \c CUEST_STATUS_NULL_POINTER if any required pointer is NULL;
 *   - \c CUEST_STATUS_INVALID_TYPE if opaque handles are not the correct type.
 *   - \c CUEST_STATUS_EXCEPTION or \c CUEST_STATUS_UNKNOWN_ERROR otherwise.
 */
CUEST_API
cuestStatus_t cuestECPDerivativeComputeWorkspaceQuery(
    cuestHandle_t handle,
    const cuestECPIntPlan_t plan,
    const cuestECPDerivativeComputeParameters_t parameters,
    const cuestWorkspaceDescriptor_t* variableBufferSize,
    cuestWorkspaceDescriptor_t* temporaryWorkspaceDescriptor,
    const double* densityMatrix,
    double* outGradient);

#ifdef __cplusplus
}
#endif

#endif /* ECP_INTEGRAL_DERIVATIVE_COMPUTE_API_H */
