/* Copyright 2026, UCAR/Unidata.

   See the COPYRIGHT file for more information. */

/**

 * @file

 * @internal This file contains functions for loading UDF plugins from RC files.

 *

 * @author Ed Hartnett

 * @date 2/2/26

 */

#include "config.h"

#include <stdlib.h>

#include <string.h>

#include <stdio.h>

#include "netcdf.h"

#include "netcdf_dispatch.h"

#include "nclog.h"

#include "ncrc.h"

#include "ncudfplugins.h"

/* Platform-specific dynamic loading headers */

#ifdef _WIN32

#include <windows.h>

#else

#include <dlfcn.h>

#endif

/**

 * Load a dynamic library (platform-specific).

 *

 * @param path Full path to the library file.

 * @return Handle to the loaded library, or NULL on failure.

 *

 * @author Edward Hartnett

 * @date 2/2/26

 */

static void*

load_library(const char* path)

{

    void* handle = NULL;

#ifdef _WIN32

    handle = (void*)LoadLibraryA(path);

    if (!handle) {

        DWORD err = GetLastError();

        nclog(NCLOGERR, "LoadLibrary failed for %s: error %lu", path, err);

    }

#else

    handle = dlopen(path, RTLD_NOW | RTLD_LOCAL);

    if (!handle) {

        nclog(NCLOGERR, "dlopen failed for %s: %s", path, dlerror());

    }

#endif

    return handle;

}

/**

 * Get a symbol from a loaded library (platform-specific).

 *

 * @param handle Handle to the loaded library.

 * @param symbol Name of the symbol to retrieve.

 * @return Pointer to the symbol, or NULL on failure.

 *

 * @author Edward Hartnett

 * @date 2/2/26

 */

static void*

get_symbol(void* handle, const char* symbol)

{

    void* sym = NULL;

#ifdef _WIN32

    sym = (void*)GetProcAddress((HMODULE)handle, symbol);

    if (!sym) {

        DWORD err = GetLastError();

        nclog(NCLOGERR, "GetProcAddress failed for %s: error %lu", symbol, err);

    }

#else

    sym = dlsym(handle, symbol);

    if (!sym) {

        nclog(NCLOGERR, "dlsym failed for %s: %s", symbol, dlerror());

    }

#endif

    return sym;

}

/**

 * Load a single UDF plugin library and call its initialization function.

 *

 * @param udf_number UDF slot number (0-9).

 * @param library_path Full path to the plugin library.

 * @param init_func Name of the initialization function.

 * @param magic Optional magic number string (can be NULL).

 * @return NC_NOERR on success, error code on failure.

 *

 * @author Edward Hartnett

 * @date 2/2/26

 */

static int

load_udf_plugin(int udf_number, const char* library_path,

                const char* init_func, const char* magic)

{

    int stat = NC_NOERR;

    void* handle = NULL;

    int mode_flag;

#ifndef HAVE_NETCDF_UDF_SELF_REGISTRATION

    NC_Dispatch* dispatch_table = NULL;

    char magic_check[NC_MAX_MAGIC_NUMBER_LEN + 1];

#endif

    /* Determine mode flag from UDF number.

     * Use explicit array to avoid bit-collision bugs from shifting. */

    {

        int udf_flags[NC_MAX_UDF_FORMATS] = {

            NC_UDF0, NC_UDF1, NC_UDF2, NC_UDF3, NC_UDF4,

            NC_UDF5, NC_UDF6, NC_UDF7, NC_UDF8, NC_UDF9

        };

        mode_flag = udf_flags[udf_number];

    }

    /* Load the library */

    handle = load_library(library_path);

    if (!handle) {

        stat = NC_ENOTNC;

        goto done;

    }

#ifdef HAVE_NETCDF_UDF_SELF_REGISTRATION

    /* Self-registration mode: init function returns NC_Dispatch* */

    {

        NC_Dispatch* (*init_function)(void) = NULL;

        NC_Dispatch* table = NULL;

        /* Get the initialization function */

        init_function = (NC_Dispatch* (*)(void))get_symbol(handle, init_func);

        if (!init_function) {

            stat = NC_ENOTNC;

            goto done;

        }

        /* Call the initialization function to get the dispatch table */

        table = init_function();

        if (!table) {

            nclog(NCLOGERR, "Plugin init function %s returned NULL", init_func);

            stat = NC_ENOTNC;

            goto done;

        }

        /* Verify dispatch ABI version */

        if (table->dispatch_version != NC_DISPATCH_VERSION) {

            nclog(NCLOGERR, "Plugin dispatch ABI mismatch for UDF%d: expected %d, got %d",

                  udf_number, NC_DISPATCH_VERSION, table->dispatch_version);

            stat = NC_EINVAL;

            goto done;

        }

        /* Register the dispatch table returned by the plugin */

        if ((stat = nc_def_user_format(mode_flag, table, (char*)magic))) {

            nclog(NCLOGERR, "Failed to register dispatch table for UDF%d: %d",

                  udf_number, stat);

            goto done;

        }

    }

#else

    /* Legacy mode: init function returns int and registers itself */

    {

        int (*init_function)(void) = NULL;

        /* Get the initialization function */

        init_function = (int (*)(void))get_symbol(handle, init_func);

        if (!init_function) {

            stat = NC_ENOTNC;

            goto done;

        }

        /* Call the initialization function */

        if ((stat = init_function())) {

            nclog(NCLOGERR, "Plugin init function %s failed: %d", init_func, stat);

            goto done;

        }

        /* Verify the dispatch table was registered */

        memset(magic_check, 0, sizeof(magic_check));

        if ((stat = nc_inq_user_format(mode_flag, &dispatch_table, magic_check))) {

            nclog(NCLOGERR, "Plugin did not register dispatch table for UDF%d", udf_number);

            goto done;

        }

        if (dispatch_table == NULL) {

            nclog(NCLOGERR, "Plugin registered NULL dispatch table for UDF%d", udf_number);

            stat = NC_EINVAL;

            goto done;

        }

        /* Verify dispatch ABI version */

        if (dispatch_table->dispatch_version != NC_DISPATCH_VERSION) {

            nclog(NCLOGERR, "Plugin dispatch ABI mismatch for UDF%d: expected %d, got %d",

                  udf_number, NC_DISPATCH_VERSION, dispatch_table->dispatch_version);

            stat = NC_EINVAL;

            goto done;

        }

        /* Optionally verify magic number matches */

        if (magic != NULL && strlen(magic_check) > 0) {

            if (strcmp(magic, magic_check) != 0) {

                nclog(NCLOGWARN, "Plugin magic number mismatch for UDF%d: expected %s, got %s",

                      udf_number, magic, magic_check);

            }

        }

    }

#endif

    nclog(NCLOGNOTE, "Successfully loaded UDF%d plugin from %s", 

          udf_number, library_path);

done:

    /* Handles are intentionally not closed; the OS will reclaim at process exit.

     * The dispatch table and its functions must remain accessible. */

    return stat;

}

/**

 * Load and initialize all UDF plugins from RC file configuration.

 *

 * This function loops through all 10 UDF slots (0-9) and checks for

 * corresponding RC file entries. If both LIBRARY and INIT keys are

 * present for a slot, it attempts to load that plugin.

 *

 * @return NC_NOERR (always succeeds, even if plugins fail to load).

 *

 * @author Edward Hartnett

 * @date 2/2/26

 */

int

NC_udf_load_plugins(void)

{

    int stat = NC_NOERR;

    /* Loop through all 10 UDF slots */

    for (int i = 0; i < NC_MAX_UDF_FORMATS; i++) {

        char key_lib[64], key_init[64], key_magic[64];

        const char* lib = NULL;

        const char* init = NULL;

        const char* magic = NULL;

        /* Build RC key names for this UDF slot */

        snprintf(key_lib, sizeof(key_lib), "NETCDF.UDF%d.LIBRARY", i);

        snprintf(key_init, sizeof(key_init), "NETCDF.UDF%d.INIT", i);

        snprintf(key_magic, sizeof(key_magic), "NETCDF.UDF%d.MAGIC", i);

        /* Look up RC values */

        lib = NC_rclookup(key_lib, NULL, NULL);

        init = NC_rclookup(key_init, NULL, NULL);

        magic = NC_rclookup(key_magic, NULL, NULL);

        /* If both LIBRARY and INIT are present, try to load the plugin */

        if (lib && init) {

            if ((stat = load_udf_plugin(i, lib, init, magic))) {

                nclog(NCLOGWARN, "Failed to load UDF%d plugin from %s: %d", i, lib, stat);

            }

        } else if (lib || init) {

            /* Warn about partial configuration */

            nclog(NCLOGWARN, "Ignoring partial UDF%d configuration "

                  "(both NETCDF.UDF%d.LIBRARY and NETCDF.UDF%d.INIT are required)",

                  i, i, i);

        }

    }

    /* Always return success - plugin loading failures are not fatal */

    return NC_NOERR;

}