/*===================== begin_copyright_notice ==================================

Copyright (c) 2017 Intel Corporation

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======================= end_copyright_notice ==================================*/


#pragma once

#include <cinttypes>
#include <vector>

#include "cif/common/cif.h"

namespace CIF {

constexpr Version_t CompatibilityEncoderVersion = 1;
using CompatibilityDataHandle = const void*;

namespace Helpers {

template<typename EncodingBaseType>
struct EncInterface{
    static constexpr size_t GetDescriptorSizeInEncodingBaseType(){
        return 3;
    }
    static constexpr size_t GetDescriptorSizeInBytes(){
        return GetDescriptorSizeInEncodingBaseType() * sizeof(EncodingBaseType);
    }

    static constexpr size_t GetInterfaceIdIdx(){
        return 0;
    }

    static constexpr size_t GetVersionIdx(){
        return 1;
    }

    static constexpr size_t GetChildrenCountIdx(){
        return 2;
    }

    static void Encode(EncodingBaseType * out,
                       InterfaceId_t interfaceId, Version_t version, EncodingBaseType childrenCount){
        out[GetInterfaceIdIdx()] = interfaceId;
        out[GetVersionIdx()] = version;
        out[GetChildrenCountIdx()] = childrenCount;
    }

    static void Decode(const EncodingBaseType * in,
                       InterfaceId_t &interfaceIdRet, Version_t &versionRet, EncodingBaseType &childrenCountRet){
        interfaceIdRet = in[GetInterfaceIdIdx()];
        versionRet = in[GetVersionIdx()];
        childrenCountRet = in[GetChildrenCountIdx()];
    }
};

template<typename EncodingBaseType>
struct EncHeader{
    static constexpr size_t GetHeaderSizeInEncodingBaseType(){
        return 3;
    }

    static constexpr size_t GetHeaderSizeInBytes(){
        return GetHeaderSizeInEncodingBaseType() * sizeof(EncodingBaseType);
    }

    static constexpr size_t GetMagicIdx(){
        return 0;
    }

    static constexpr size_t GetVersionIdx(){
        return 1;
    }

    static constexpr size_t GetSizeIdx(){
        return 2;
    }

    static void Encode(EncodingBaseType * out, EncodingBaseType magic, 
                       EncodingBaseType version, EncodingBaseType encodedInterfacesNum){
        auto * header = out;
        header[GetMagicIdx()] = magic;
        header[GetVersionIdx()] = version;
        header[GetSizeIdx()] = GetHeaderSizeInBytes() +
                               encodedInterfacesNum * EncInterface<EncodingBaseType>::GetDescriptorSizeInBytes();
    }

    static const EncodingBaseType *Decode(CompatibilityDataHandle handle, EncodingBaseType magic, EncodingBaseType version, 
                                          EncodingBaseType & encodedInterfacesNumRet, EncodingBaseType & encodedEncoderVersionRet){
        uint64_t invalidHeader[GetHeaderSizeInEncodingBaseType()];
        invalidHeader[GetMagicIdx()] = InvalidInterface;
        invalidHeader[GetVersionIdx()] = InvalidVersion;
        invalidHeader[GetSizeIdx()] = 0;

        auto * header = reinterpret_cast<const EncodingBaseType*>(handle);
        if((header == nullptr) || (header[GetMagicIdx()] != magic)){
            header = invalidHeader;
        }

        encodedEncoderVersionRet = header[GetVersionIdx()];
        encodedInterfacesNumRet = (header[GetSizeIdx()] - GetHeaderSizeInBytes());
        encodedInterfacesNumRet /= EncInterface<EncodingBaseType>::GetDescriptorSizeInBytes();

        if(header[GetVersionIdx()] != version){
            // incompatible encoder/decoders
            // we require strict compatibility (no backwards compatibility), 
            // but this encoder should not change very often (hardly ever)
            return nullptr;
        }

        return header + GetHeaderSizeInEncodingBaseType();
    }
};

/// Node class that compatibility tree is made of
struct CompatibilityNode{
    /// Id of this interface
    InterfaceId_t InterfaceId = InvalidInterface;

    /// Version requested by the client
    Version_t RequestedVersion = InvalidVersion;

    /// Next child of parent node
    CompatibilityNode * NextSibling = nullptr;

    /// First child of this node
    CompatibilityNode * FirstChild = nullptr;

    /// Minimum version supported by server
    Version_t MinSupportedVersion = InvalidVersion;

    /// Maximum version supported by server
    Version_t MaxSupportedVersion = InvalidVersion;

    /// Adds a child node to this node (will update current children's nextSibling members)
    void AddChild(CompatibilityNode & nd){
        if(FirstChild == nullptr){
            FirstChild = &nd;
            return;
        }

        CompatibilityNode * currNd = FirstChild;
        while(currNd->NextSibling != nullptr){
            currNd = currNd->NextSibling;
        }

        currNd->NextSibling = &nd;
    }

    /// Looks for child node with requested interfaceId
    CompatibilityNode * FindChild(InterfaceId_t interfaceId){
        CompatibilityNode * currNd = FirstChild;
        while((currNd != nullptr)&&(currNd->InterfaceId != interfaceId)){
            currNd = currNd->NextSibling;
        }
        return currNd;
    }

    /// Decodes the compatibility data into a tree of nodes
    /// First node in the returned vector is the root node 
    template<typename EncodingBaseType, template <Version_t> class EntryPointInterface>
    static std::vector<CompatibilityNode> BuildTree(const EncodingBaseType* enc, uint64_t encWordsCount){
        if((enc == nullptr) || (encWordsCount%EncInterface<EncodingBaseType>::GetDescriptorSizeInEncodingBaseType() != 0)){
            assert(0);
            return std::vector<CompatibilityNode>{};
        }
        std::vector<CompatibilityNode> allNodes;
        CompatibilityNode dummyRootNode;
        allNodes.reserve(static_cast<size_t>(encWordsCount / EncInterface<EncodingBaseType>::GetDescriptorSizeInEncodingBaseType()));
        uint64_t currOffset = 0;
        BuildTreeImpl<EncodingBaseType>(enc, encWordsCount, currOffset, dummyRootNode, allNodes);
        PatchSupportedVersionFwd::Call<EntryPointInterface>(dummyRootNode);
        return allNodes;
    }

    template <typename InterfacesTree>
    static void PatchSupportedVersion(CompatibilityNode & parentNode){
        InterfacesTree::template forwardToAll<PatchSupportedVersionFwd>(parentNode);
    }

protected:
    /// Helper forwarder struct - see PatchSupportedVersionFwd::Call for details
   struct PatchSupportedVersionFwd
    {
        /// Recursive worker for patching compatibility tree with data 
        /// of interface versions supported by server
        template<template <Version_t> class Interface>
        static void Call(CompatibilityNode & parentNode){
            CompatibilityNode * matchingNd = parentNode.FindChild(Interface<CIF::BaseVersion>::GetInterfaceId());
            if(matchingNd == nullptr){
                return;
            }

            auto minVer = Interface<CIF::TraitsSpecialVersion>::GetOldestSupportedVersion();
            auto maxVer = Interface<CIF::TraitsSpecialVersion>::GetOldestSupportedVersion();
            matchingNd->MinSupportedVersion = minVer;
            matchingNd->MaxSupportedVersion = maxVer;

            Interface<CIF::TraitsSpecialVersion>::AllUsedInterfaces::template forwardToAll<PatchSupportedVersionFwd>(*matchingNd);
        }
    };

   /// Recursive worker for decoding compatibility data into a tree
   template<typename EncodingBaseType>
    static void BuildTreeImpl(const EncodingBaseType* enc, uint64_t encWordsCount, uint64_t &currOffset,
                         CompatibilityNode & parent, std::vector<CompatibilityNode> &nodesAllocator){
        if(currOffset >= encWordsCount){
            return; // no more data to decode
        }

        nodesAllocator.push_back(CompatibilityNode{});
        CompatibilityNode * nd = &*(--nodesAllocator.end());
        parent.AddChild(*nd);

        EncodingBaseType numChildren = 0;
        EncInterface<EncodingBaseType>::Decode(enc + currOffset, nd->InterfaceId, nd->RequestedVersion, numChildren);
        currOffset += EncInterface<EncodingBaseType>::GetDescriptorSizeInEncodingBaseType();
        for(EncodingBaseType childIt = 0; childIt < numChildren; ++childIt){
            BuildTreeImpl(enc, encWordsCount, currOffset, *nd, nodesAllocator);
        }
    }
};

} // end namespace Helpers

/// Compatibility data is encoded in units of uint64_t
/// First value is InterfaceId of CompatibilityEncoder
/// Second value is version of CompatibilityEncoder that was used for encoding the data.
/// Third value is the size (in bytes) of the whole encoding (including id, version and this size).
/// Next, are encoded requirements of all interfaces that were used for encoding. 
/// Encoding is based on DFS and has following layout:
///   | uint64_t CurrentInterfaceId | uint64_t VersionOfCurrentInterface | uint64_t NumChildInterfacesOfCurrent | ENCODING OF CHILD INTERFACES | uint64_t NextInterfaceId ...
struct CompatibilityEncoder {
    using EncodingBaseType = uint64_t;
    using BackingStorage = std::vector<EncodingBaseType>;

    struct IncompatibilityData{
        InterfaceId_t Interface;
        Version_t     RequestedVersion;
        Version_t     MinVersionSupported;
        Version_t     MaxVersionSupported;
    };

    CompatibilityEncoder(){
    }

    static constexpr InterfaceId_t GetIntefaceId(){
        return CIF::InterfaceIdCoder::Enc("CIF_COMP_ENC");
    }

    template <template <Version_t> class EntryPointInterface>
    CompatibilityDataHandle Encode(){
        const size_t sizeToReserve = Helpers::EncHeader<EncodingBaseType>::GetHeaderSizeInEncodingBaseType()
                                     +
                                     (Helpers::EncInterface<EncodingBaseType>::GetDescriptorSizeInEncodingBaseType()
                                      * 2); // *2 - potential overestimate
        
        encodedData.clear();
        encodedData.reserve(sizeToReserve);

        // reserve space for header
        for(EncodingBaseType i = 0; i < Helpers::EncHeader<EncodingBaseType>::GetHeaderSizeInEncodingBaseType(); ++i){
            encodedData.push_back(0);
        }

        // encode compatibility descriptors
        EncodeFwd::Call<EntryPointInterface>(encodedData);
        //EncodeAll<CIF::InterfacesList<Interfaces...>>(encodedData);

        // encode header
        const size_t encodedInterfacesNum = (encodedData.size() - Helpers::EncHeader<EncodingBaseType>::GetHeaderSizeInEncodingBaseType()) 
                                                        / Helpers::EncInterface<EncodingBaseType>::GetDescriptorSizeInEncodingBaseType();
        Helpers::EncHeader<EncodingBaseType>::Encode(encodedData.data(), GetIntefaceId(), CompatibilityEncoderVersion, 
                                                     encodedInterfacesNum);
        return encodedData.data();
    }

    template <template <Version_t> class EntryPointInterface>
    static bool GetFirstIncompatible(CompatibilityDataHandle externalEncoding, IncompatibilityData & ret){
        uint64_t encodedInterfacesNum = 0;
        uint64_t encodedEncoderVersion = InvalidVersion;
        const EncodingBaseType* encodedInterfaces = 
                            Helpers::EncHeader<EncodingBaseType>::Decode(externalEncoding, GetIntefaceId(), CompatibilityEncoderVersion,
                                                                encodedInterfacesNum, encodedEncoderVersion);

        if(encodedInterfaces == nullptr){
            // incompatible encoder/decoders
            // we require strict compatibility, but this encoder should not change very often
            ret.Interface = GetIntefaceId();
            ret.RequestedVersion = encodedEncoderVersion;
            ret.MinVersionSupported = ret.MaxVersionSupported = CompatibilityEncoderVersion;
            return true;
        }

        {
            // TODO : Verify if this is actually better performant then full comparison
            // TODO : Maybe hash encodings in compile time instead?
            CompatibilityEncoder enc;
            auto thisSideEncoding = enc.Encode<EntryPointInterface>();
            auto sizeInBytes = encodedInterfacesNum * Helpers::EncInterface<EncodingBaseType>::GetDescriptorSizeInBytes()
                               + Helpers::EncInterface<EncodingBaseType>::GetDescriptorSizeInBytes();
            if(0 == std::memcmp(externalEncoding, thisSideEncoding, static_cast<uint32_t>(sizeInBytes))){
                // fast path - exactly the same versions of interfaces
                return false;
            }
        }

        auto incomp = GetAllIncompatibleImpl<EntryPointInterface>(encodedInterfaces, encodedInterfacesNum *
                                                                  Helpers::EncInterface<EncodingBaseType>::GetDescriptorSizeInEncodingBaseType());
        if(incomp.size() == 0){
            return false;
        }

        ret = *incomp.begin();
        return true;
    }
    
    static bool AreIdentical(CompatibilityDataHandle a, CompatibilityDataHandle b){
        if(a == b){
            return true;
        }

        if((a == nullptr) || (b == nullptr)){
            return false;
        }

        uint64_t encodedInterfacesNum = 0;
        uint64_t encodedEncoderVersion = InvalidVersion;

        Helpers::EncHeader<EncodingBaseType>::Decode(a, GetIntefaceId(), CompatibilityEncoderVersion,
                                                     encodedInterfacesNum, encodedEncoderVersion);

        auto sizeInBytes = encodedInterfacesNum * Helpers::EncInterface<EncodingBaseType>::GetDescriptorSizeInBytes()
                            + Helpers::EncInterface<EncodingBaseType>::GetDescriptorSizeInBytes();
        return 0 == std::memcmp(a, b, static_cast<size_t>(sizeInBytes));
    }

protected:
    struct EncodeFwd
    {
        template<template <Version_t> class Interface>
        static void Call(BackingStorage & storage){
            auto offset = storage.size();
            for(EncodingBaseType i = 0; i < Helpers::EncInterface<EncodingBaseType>::GetDescriptorSizeInEncodingBaseType(); ++i){
                storage.push_back(0);
            }

            Helpers::EncInterface<EncodingBaseType>::Encode(storage.data() + offset,
                                                            Interface<CIF::BaseVersion>::GetInterfaceId(),
                                                            Interface<CIF::TraitsSpecialVersion>::GetLatestSupportedVersion(),
                                                            Interface<CIF::TraitsSpecialVersion>::AllUsedInterfaces::GetNumInterfaces());

            Interface<CIF::TraitsSpecialVersion>::AllUsedInterfaces::template forwardToAll<EncodeFwd>(storage);
        }
    };

    template <template <Version_t> class EntryPointInterface>
    static std::vector<IncompatibilityData> GetAllIncompatibleImpl(const EncodingBaseType* enc, uint64_t encWordsCount){
        std::vector<Helpers::CompatibilityNode> allNodes;
        allNodes = Helpers::CompatibilityNode::BuildTree<EncodingBaseType, EntryPointInterface>(enc, encWordsCount);

        std::vector<IncompatibilityData> ret;
        for(auto & nd : allNodes){
            bool supported = (nd.RequestedVersion >= nd.MinSupportedVersion) & (nd.RequestedVersion <= nd.MaxSupportedVersion);
            if(supported){
                continue;
            }
            IncompatibilityData id;
            id.Interface = nd.InterfaceId;
            id.RequestedVersion = nd.RequestedVersion;
            id.MaxVersionSupported = nd.MaxSupportedVersion;
            id.MinVersionSupported = nd.MinSupportedVersion;
            ret.push_back(std::move(id));
        }
        
        return ret;
    }

    BackingStorage encodedData;
};

}
