module database.mysql.packet;

import std.algorithm;
import std.traits;

import database.mysql.exception;

struct InputPacket
{
    @disable this();

    this(ubyte[]* buffer)
    {
        buffer_ = buffer;
        in_ = *buffer_;
    }

    T peek(T)() if (!isArray!T)
    {
        assert(T.sizeof <= in_.length);
        return *(cast(T*)in_.ptr);
    }

    T eat(T)() if (!isArray!T)
    {
        assert(T.sizeof <= in_.length);
        auto ptr = cast(T*)in_.ptr;
        in_ = in_[T.sizeof..$];
        return *ptr;
    }

    T peek(T)(size_t count) if (isArray!T)
    {
        alias ValueType = typeof(Type.init[0]);

        assert(ValueType.sizeof * count <= in_.length);
        auto ptr = cast(ValueType*)in_.ptr;
        return ptr[0..count];
    }

    T eat(T)(size_t count) if (isArray!T)
    {
        alias ValueType = typeof(T.init[0]);

        assert(ValueType.sizeof * count <= in_.length);
        auto ptr = cast(ValueType*)in_.ptr;
        in_ = in_[ValueType.sizeof * count..$];
        return ptr[0..count];
    }

    void expect(T)(T x)
    {
        if (x != eat!T)
            throw new MySQLProtocolException("Bad packet format");
    }

    void skip(size_t count)
    {
        if (in_.length == 0) return;
        assert(count <= in_.length);
        in_ = in_[count..$];
    }

    auto countUntil(ubyte x, bool expect)
    {
        auto index = in_.countUntil(x);

        if (expect)
        {
            if ((index < 0) || (in_[index] != x))
                throw new MySQLProtocolException("Bad packet format");
        }

        return index;
    }

    void skipLenEnc()
    {
        auto header = eat!ubyte;
        if (header >= 0xfb)
        {
            switch(header)
            {
                case 0xfb:
                    return;
                case 0xfc:
                    skip(2);
                    return;
                case 0xfd:
                    skip(3);
                    return;
                case 0xfe:
                    skip(8);
                    return;
                default:
                    throw new MySQLProtocolException("Bad packet format");
            }
        }
    }

    ulong eatLenEnc()
    {
        auto header = eat!ubyte;
        if (header < 0xfb)
            return header;

        ulong lo;
        ulong hi;

        switch(header)
        {
            case 0xfb:
                return 0;
            case 0xfc:
                return eat!ushort;
            case 0xfd:
                lo = eat!ubyte;
                hi = eat!ushort;
                return lo | (hi << 8);
            case 0xfe:
                lo = eat!uint;
                hi = eat!uint;
                return lo | (hi << 32);
            default:
                throw new MySQLProtocolException("Bad packet format");
        }
    }

    auto remaining() const
    {
        return in_.length;
    }

    bool empty() const
    {
        return in_.length == 0;
    }

protected:

    ubyte[]* buffer_;
    ubyte[] in_;
}

struct OutputPacket
{
    @disable this();

    this(ubyte[]* buffer)
    {
        buffer_ = buffer;
        out_ = buffer_.ptr + 4;
    }

    pragma(inline, true) void put(T)(T x)
    {
        put(offset_, x);
    }

    void put(T)(size_t offset, T x) if (!isArray!T)
    {
        grow(offset, T.sizeof);

        *(cast(T*)(out_ + offset)) = x;
        offset_ = max(offset + T.sizeof, offset_);
    }

    void put(T)(size_t offset, T x) if (isArray!T)
    {
        alias ValueType = Unqual!(typeof(T.init[0]));

        grow(offset, ValueType.sizeof * x.length);

        (cast(ValueType*)(out_ + offset))[0..x.length] = x;
        offset_ = max(offset + (ValueType.sizeof * x.length), offset_);
    }

    void putLenEnc(ulong x)
    {
        if (x < 0xfb)
        {
            put!ubyte(cast(ubyte)x);
        }
        else if (x <= ushort.max)
        {
            put!ubyte(0xfc);
            put!ushort(cast(ushort)x);
        }
        else if (x <= (uint.max >> 8))
        {
            put!ubyte(0xfd);
            put!ubyte(cast(ubyte)(x));
            put!ushort(cast(ushort)(x >> 8));
        }
        else
        {
            put!ubyte(0xfe);
            put!uint(cast(uint)x);
            put!uint(cast(uint)(x >> 32));
        }
    }

    size_t marker(T)() if (!isArray!T)
    {
        grow(offset_, T.sizeof);

        auto place = offset_;
        offset_ += T.sizeof;
        return place;
    }

    size_t marker(T)(size_t count) if (isArray!T)
    {
        alias ValueType = Unqual!(typeof(T.init[0]));
        grow(offset_, ValueType.sizeof * x.length);

        auto place = offset_;
        offset_ += (ValueType.sizeof * x.length);
        return place;
    }

    void finalize(ubyte seq)
    {
        if (offset_ >=  0xffffff)
            throw new MySQLConnectionException("Packet size exceeds 2^24");
        uint length = cast(uint)offset_;
        uint header = cast(uint)((offset_ & 0xffffff) | (seq << 24));
        *(cast(uint*)buffer_.ptr) = header;
    }

    void finalize(ubyte seq, size_t extra)
    {
        if (offset_ + extra >= 0xffffff)
            throw new MySQLConnectionException("Packet size exceeds 2^24");
        uint length = cast(uint)(offset_ + extra);
        uint header = cast(uint)((length & 0xffffff) | (seq << 24));
        *(cast(uint*)buffer_.ptr) = header;
    }

    void reset()
    {
        offset_ = 0;
    }

    void reserve(size_t size)
    {
        (*buffer_).length = max((*buffer_).length, 4 + size);
        out_ = buffer_.ptr + 4;
    }

    void fill(ubyte x, size_t size)
    {
        grow(offset_, size);
        out_[offset_..offset_ + size] = 0;
        offset_ += size;
    }

    size_t length() const
    {
        return offset_;
    }

    bool empty() const
    {
        return offset_ == 0;
    }

    const(ubyte)[] get() const
    {
        return (*buffer_)[0..4 + offset_];
    }

protected:

    void grow(size_t offset, size_t size)
    {
        auto requested = 4 + offset + size;

        if (requested > buffer_.length)
        {
            auto capacity = max(128, (*buffer_).capacity);
            while (capacity < requested)
            {
                capacity <<= 1;
            }

            buffer_.length = capacity;
            out_ = buffer_.ptr + 4;
        }
    }

    ubyte[]* buffer_;
    ubyte* out_;
    size_t offset_;
}