// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Text;
using System;
using System.Runtime.InteropServices;

namespace System.Text
{
    // An Encoder is used to encode a sequence of blocks of characters into
    // a sequence of blocks of bytes. Following instantiation of an encoder,
    // sequential blocks of characters are converted into blocks of bytes through
    // calls to the GetBytes method. The encoder maintains state between the
    // conversions, allowing it to correctly encode character sequences that span
    // adjacent blocks.
    //
    // Instances of specific implementations of the Encoder abstract base
    // class are typically obtained through calls to the GetEncoder method
    // of Encoding objects.
    //

    internal class EncoderNLS : Encoder
    {
        // Need a place for the last left over character, most of our encodings use this
        internal char _charLeftOver;
        private Encoding _encoding;
        private bool _mustFlush;
        internal bool _throwOnOverflow;
        internal int _charsUsed;

        internal EncoderNLS(Encoding encoding)
        {
            _encoding = encoding;
            _fallback = _encoding.EncoderFallback;
            this.Reset();
        }

        internal EncoderNLS()
        {
            _encoding = null;
            this.Reset();
        }

        public override void Reset()
        {
            _charLeftOver = (char)0;
            if (_fallbackBuffer != null)
                _fallbackBuffer.Reset();
        }

        public override unsafe int GetByteCount(char[] chars, int index, int count, bool flush)
        {
            // Validate input parameters
            if (chars == null)
                throw new ArgumentNullException(nameof(chars),
                      SR.ArgumentNull_Array);

            if (index < 0 || count < 0)
                throw new ArgumentOutOfRangeException((index < 0 ? nameof(index) : nameof(count)),
                      SR.ArgumentOutOfRange_NeedNonNegNum);

            if (chars.Length - index < count)
                throw new ArgumentOutOfRangeException(nameof(chars),
                      SR.ArgumentOutOfRange_IndexCountBuffer);

            // Just call the pointer version
            int result = -1;
            fixed (char* pChars = &MemoryMarshal.GetReference((Span<char>)chars))
            {
                result = GetByteCount(pChars + index, count, flush);
            }
            return result;
        }

        public unsafe override int GetByteCount(char* chars, int count, bool flush)
        {
            // Validate input parameters
            if (chars == null)
                throw new ArgumentNullException(nameof(chars),
                      SR.ArgumentNull_Array);

            if (count < 0)
                throw new ArgumentOutOfRangeException(nameof(count),
                      SR.ArgumentOutOfRange_NeedNonNegNum);

            _mustFlush = flush;
            _throwOnOverflow = true;
            return _encoding.GetByteCount(chars, count, this);
        }

        public override unsafe int GetBytes(char[] chars, int charIndex, int charCount,
                                              byte[] bytes, int byteIndex, bool flush)
        {
            // Validate parameters
            if (chars == null || bytes == null)
                throw new ArgumentNullException((chars == null ? nameof(chars) : nameof(bytes)),
                      SR.ArgumentNull_Array);

            if (charIndex < 0 || charCount < 0)
                throw new ArgumentOutOfRangeException((charIndex < 0 ? nameof(charIndex) : nameof(charCount)),
                      SR.ArgumentOutOfRange_NeedNonNegNum);

            if (chars.Length - charIndex < charCount)
                throw new ArgumentOutOfRangeException(nameof(chars),
                      SR.ArgumentOutOfRange_IndexCountBuffer);

            if (byteIndex < 0 || byteIndex > bytes.Length)
                throw new ArgumentOutOfRangeException(nameof(byteIndex),
                     SR.ArgumentOutOfRange_Index);

            int byteCount = bytes.Length - byteIndex;

            // Just call pointer version
            fixed (char* pChars = &MemoryMarshal.GetReference((Span<char>)chars))
            fixed (byte* pBytes = &MemoryMarshal.GetReference((Span<byte>)bytes))

                // Remember that charCount is # to decode, not size of array.
                return GetBytes(pChars + charIndex, charCount,
                                pBytes + byteIndex, byteCount, flush);
        }

        public unsafe override int GetBytes(char* chars, int charCount, byte* bytes, int byteCount, bool flush)
        {
            // Validate parameters
            if (chars == null || bytes == null)
                throw new ArgumentNullException((chars == null ? nameof(chars) : nameof(bytes)),
                      SR.ArgumentNull_Array);

            if (byteCount < 0 || charCount < 0)
                throw new ArgumentOutOfRangeException((byteCount < 0 ? nameof(byteCount) : nameof(charCount)),
                      SR.ArgumentOutOfRange_NeedNonNegNum);

            _mustFlush = flush;
            _throwOnOverflow = true;
            return _encoding.GetBytes(chars, charCount, bytes, byteCount, this);
        }

        // This method is used when your output buffer might not be large enough for the entire result.
        // Just call the pointer version.  (This gets bytes)
        public override unsafe void Convert(char[] chars, int charIndex, int charCount,
                                              byte[] bytes, int byteIndex, int byteCount, bool flush,
                                              out int charsUsed, out int bytesUsed, out bool completed)
        {
            // Validate parameters
            if (chars == null || bytes == null)
                throw new ArgumentNullException((chars == null ? nameof(chars) : nameof(bytes)),
                      SR.ArgumentNull_Array);

            if (charIndex < 0 || charCount < 0)
                throw new ArgumentOutOfRangeException((charIndex < 0 ? nameof(charIndex) : nameof(charCount)),
                      SR.ArgumentOutOfRange_NeedNonNegNum);

            if (byteIndex < 0 || byteCount < 0)
                throw new ArgumentOutOfRangeException((byteIndex < 0 ? nameof(byteIndex) : nameof(byteCount)),
                      SR.ArgumentOutOfRange_NeedNonNegNum);

            if (chars.Length - charIndex < charCount)
                throw new ArgumentOutOfRangeException(nameof(chars),
                      SR.ArgumentOutOfRange_IndexCountBuffer);

            if (bytes.Length - byteIndex < byteCount)
                throw new ArgumentOutOfRangeException(nameof(bytes),
                      SR.ArgumentOutOfRange_IndexCountBuffer);

            // Just call the pointer version (can't do this for non-msft encoders)
            fixed (char* pChars = &MemoryMarshal.GetReference((Span<char>)chars))
            {
                fixed (byte* pBytes = &MemoryMarshal.GetReference((Span<byte>)bytes))
                {
                    Convert(pChars + charIndex, charCount, pBytes + byteIndex, byteCount, flush,
                        out charsUsed, out bytesUsed, out completed);
                }
            }
        }

        // This is the version that uses pointers.  We call the base encoding worker function
        // after setting our appropriate internal variables.  This is getting bytes
        public override unsafe void Convert(char* chars, int charCount,
                                              byte* bytes, int byteCount, bool flush,
                                              out int charsUsed, out int bytesUsed, out bool completed)
        {
            // Validate input parameters
            if (bytes == null || chars == null)
                throw new ArgumentNullException(bytes == null ? nameof(bytes) : nameof(chars),
                    SR.ArgumentNull_Array);
            if (charCount < 0 || byteCount < 0)
                throw new ArgumentOutOfRangeException((charCount < 0 ? nameof(charCount) : nameof(byteCount)),
                    SR.ArgumentOutOfRange_NeedNonNegNum);

            // We don't want to throw
            _mustFlush = flush;
            _throwOnOverflow = false;
            _charsUsed = 0;

            // Do conversion
            bytesUsed = _encoding.GetBytes(chars, charCount, bytes, byteCount, this);
            charsUsed = _charsUsed;

            // Its completed if they've used what they wanted AND if they didn't want flush or if we are flushed
            completed = (charsUsed == charCount) && (!flush || !this.HasState) &&
                (_fallbackBuffer == null || _fallbackBuffer.Remaining == 0);

            // Our data thingys are now full, we can return
        }

        public Encoding Encoding
        {
            get
            {
                return _encoding;
            }
        }

        public bool MustFlush
        {
            get
            {
                return _mustFlush;
            }
        }


        // Anything left in our encoder?
        internal virtual bool HasState
        {
            get
            {
                return (_charLeftOver != (char)0);
            }
        }

        // Allow encoding to clear our must flush instead of throwing (in ThrowBytesOverflow)
        internal void ClearMustFlush()
        {
            _mustFlush = false;
        }
    }
}