using System;
using System.Runtime.InteropServices;
using SQLite;

namespace Touchin.SQLiteExtensions
{
    public static partial class SQLite3Extensions
    {
		private static void CreateFunction (this SQLiteConnection connection, string functionName, int paramCount, Action<IntPtr, int, IntPtr> functionBody)
        {
			var result = CreateFunction (connection.Handle, functionName, paramCount, TextEncoding.UTF8, IntPtr.Zero, functionBody, null, null);
            if (result != SQLite3.Result.OK)
            {
                throw SQLiteException.New (result, "Can not create function");
            }
        }

        private static IntPtr [] ExtractArgs (int argc, IntPtr argv)
        {
            IntPtr [] args = new IntPtr [argc];
            Marshal.Copy (argv, args, 0, argc);
            return args;
        }

        // SQLITE_API int sqlite3_create_function(
        //     sqlite3 *db,
        //     const char *zFunctionName,
        //     int nArg,
        //     int eTextRep,
        //     void *pApp,
        //     void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
        //     void (*xStep)(sqlite3_context*,int,sqlite3_value**),
        //     void (*xFinal)(sqlite3_context*)
        // );
        [DllImport("sqlite3", CallingConvention = CallingConvention.Cdecl, EntryPoint = "sqlite3_create_function")]
        private static extern SQLite3.Result CreateFunction (
            IntPtr db,
            string zFunctionName,
            int nArg,
            TextEncoding eTextRep,
            IntPtr pApp,
            Action<IntPtr, int, IntPtr> xFunc,
            Action<IntPtr, int, IntPtr> xStep,
            Action<IntPtr, int, IntPtr> xFinal
        );

        #region sqlite3_value
     
        // SQLITE_API int sqlite3_value_type(sqlite3_value*);
        [DllImport("sqlite3", CallingConvention = CallingConvention.Cdecl, EntryPoint = "sqlite3_value_type")]
        private static extern SQLite3.ColType ValueType (IntPtr value);
     
        // SQLITE_API double sqlite3_value_double(sqlite3_value*);
        [DllImport("sqlite3", CallingConvention = CallingConvention.Cdecl, EntryPoint = "sqlite3_value_double")]
        private static extern double ValueDouble (IntPtr value);

        #endregion

        #region sqlite3_context
     
        // SQLITE_API void sqlite3_result_null(sqlite3_context*);
        [DllImport("sqlite3", CallingConvention = CallingConvention.Cdecl, EntryPoint = "sqlite3_result_null")]
        private static extern void ResultNull (IntPtr ctx);
     
        // SQLITE_API void sqlite3_result_double(sqlite3_context*, double);
        [DllImport("sqlite3", CallingConvention = CallingConvention.Cdecl, EntryPoint = "sqlite3_result_double")]
        private static extern void ResultDouble (IntPtr ctx, double value);

        #endregion
     
        // These constant define integer codes that represent the various text encodings supported by SQLite.
        private enum TextEncoding
        {
            UTF8         = 1,
            UTF16LE      = 2,
            UTF16BE      = 3,
            UTF16        = 4, /* Use native byte order */
            Any          = 5, /* sqlite3_create_function only */
            UTF16Aligned = 8, /* sqlite3_create_collation only */
        }
    }
}