#include <cstdio>

#include <sqlite3ext.h>

#include <unistd.h>

/**

 * This is just an example – use official documentation: https://www.sqlite.org/loadext.html

 */

#define C_API extern "C"

#define SQL_FN(functionName) C_API void functionName (sqlite3_context* ctx, int valueCount, sqlite3_value** values)

SQLITE_EXTENSION_INIT1

/**

 * Returns number of values passed to the SQL function.

 */

SQL_FN(valueCount) {

	sqlite3_result_int(ctx, valueCount);

}

/**

 * Returns current PID (process id).

 */

SQL_FN(getPID) {

	sqlite3_result_int(ctx, getpid());

}

/**

 * Returns multiplication of all arguments or zero, if there are no arguments.

 */

SQL_FN(multiply) {

	sqlite3_int64 result = valueCount == 0 ? 0 : 1;

	for (int i = 0; i < valueCount; i++) result *= sqlite3_value_int64(values[i]);

	sqlite3_result_int64(ctx, result);

}

/**

 * Function name should match the library file name: libdemo.so → sqlite3_demo_init.

 * Or we can specify different entry point when loading the module.

 */

C_API int sqlite3_demo_init(sqlite3* db, char** error, const sqlite3_api_routines* api) {

	SQLITE_EXTENSION_INIT2(api);

	sqlite3_create_function(db, "value_count", -1, SQLITE_UTF8, nullptr, valueCount, nullptr, nullptr);

	sqlite3_create_function(db, "get_pid", 0, SQLITE_UTF8, nullptr, getPID, nullptr, nullptr);

	sqlite3_create_function(db, "multiply", -1, SQLITE_UTF8, nullptr, multiply, nullptr, nullptr);

	// -1 = function accepts arbitrary number of arguments

	return SQLITE_OK;

}