// This file is part of OpenCV project.
// It is subject to the license terms in the LICENSE file found in the top-level directory
// of this distribution and at http://opencv.org/license.html.
//
// Copyright (C) 2018-2021 Intel Corporation


#ifndef OPENCV_GAPI_GISLANDMODEL_HPP
#define OPENCV_GAPI_GISLANDMODEL_HPP

#include <unordered_set> // unordered_map
#include <memory>        // shared_ptr
#include <exception>     // exception_ptr
#include <string>        // string
#include <cstddef>       // size_t

#include <ade/graph.hpp>
#include <ade/typed_graph.hpp>
#include <ade/passes/topological_sort.hpp>

#include <opencv2/gapi/util/optional.hpp>
#include <opencv2/gapi/gkernel.hpp>

#include "compiler/gobjref.hpp"

namespace cv { namespace gimpl {

// FIXME: GAPI_EXPORTS only because of tests!
class GAPI_EXPORTS GIsland
{
public:
    using node_set = std::unordered_set
         < ade::NodeHandle
         , ade::HandleHasher<ade::Node>
         >;

    // Initial constructor (constructs a single-op Island)
    GIsland(const gapi::GBackend &bknd,
            ade::NodeHandle op,
            util::optional<std::string>&& user_tag);

    // Merged constructor
    GIsland(const gapi::GBackend &bknd,
            node_set &&all,
            node_set &&in_ops,
            node_set &&out_ops,
            util::optional<std::string>&& user_tag);

    const node_set& contents() const;
    const node_set& in_ops() const;
    const node_set& out_ops() const;

    std::string name() const;
    gapi::GBackend backend() const;

    /**
     * Returns all GModel operation node handles which are _reading_
     * from a GModel data object associated (wrapped in) the given
     * Slot object.
     *
     * @param g an ade::Graph with GIslandModel information inside
     * @param slot_nh Slot object node handle of interest
     * @return a set of GModel operation node handles
     */
    node_set consumers(const ade::Graph &g,
                       const ade::NodeHandle &slot_nh) const;

    /**
     * Returns a GModel operation node handle which is _writing_
     * to a GModel data object associated (wrapped in) the given
     * Slot object.
     *
     * @param g an ade::Graph with GIslandModel information inside
     * @param slot_nh Slot object node handle of interest
     * @return a node handle of original GModel
     */
    ade::NodeHandle producer(const ade::Graph &g,
                             const ade::NodeHandle &slot_nh) const;

    void debug() const;
    bool is_user_specified() const;

protected:
    gapi::GBackend m_backend; // backend which handles this Island execution

    node_set m_all;     // everything (data + operations) within an island
    node_set m_in_ops;  // operations island begins with
    node_set m_out_ops; // operations island ends with

    // has island name IF specified by user. Empty for internal (inferred) islands
    util::optional<std::string> m_user_tag;
};

// GIslandExecutable - a backend-specific thing which executes
// contents of an Island
// * Is instantiated by the last step of the Islands fusion procedure;
// * Is orchestrated by a GExecutor instance.
//
// GAPI_EXPORTS is here since this class comes with the default
// implementation to some methods and it needs to be exported to allow
// it to use in the external (extra) backends.
class GAPI_EXPORTS GIslandExecutable
{
public:
    using InObj  = std::pair<RcDesc, cv::GRunArg>;
    using OutObj = std::pair<RcDesc, cv::GRunArgP>;

    class  IODesc;
    struct IInput;
    struct IOutput;

    // FIXME: now run() requires full input vector to be available.
    // actually, parts of subgraph may execute even if there's no all data
    // slots in place.
    // TODO: Add partial execution capabilities
    // TODO: This method is now obsolette and is here for backwards
    //       compatibility only.  Use (implement) the new run instead.
    virtual void run(std::vector<InObj>  &&input_objs,
                     std::vector<OutObj> &&output_objs) = 0;

    // Let the island execute. I/O data is obtained from/submitted to
    // in/out objects.
    virtual void run(IInput &in, IOutput &out);

    virtual bool canReshape() const = 0;
    virtual void reshape(ade::Graph& g, const GCompileArgs& args) = 0;
    virtual bool allocatesOutputs() const { return false; }
    virtual cv::RMat allocate(const cv::GMatDesc&) const { GAPI_Error("should never be called"); }

    // This method is called when the GStreamingCompiled gets a new
    // input source to process. Normally this method is called once
    // per stream execution.
    //
    // The idea of this method is to reset backend's stream-associated
    // internal state, if there is any.
    //
    // The regular GCompiled invocation doesn't call this, there may
    // be reset() introduced there but it is completely unnecessary at
    // this moment.
    //
    // FIXME: The design on this and so-called "stateful" kernels is not
    // closed yet.
    // FIXME: This thing will likely break stuff once we introduce
    // "multi-source streaming", a better design needs to be proposed
    // at that stage.
    virtual void handleNewStream() {} // do nothing here by default

    // This method is called for every IslandExecutable when
    // the stream-based execution is stopped.
    // All processing is guaranteed to be stopped by this moment,
    // with no pending or running 'run()' processes ran in background.
    // FIXME: This method is tightly bound to the GStreamingExecutor
    // now.
    virtual void handleStopStream() {} // do nothing here by default

    virtual ~GIslandExecutable() = default;
};

class GIslandExecutable::IODesc {
    std::vector<cv::gimpl::RcDesc> d;
public:
    void set(std::vector<cv::gimpl::RcDesc> &&newd)      { d = std::move(newd); }
    void set(const std::vector<cv::gimpl::RcDesc> &newd) { d = newd; }
    const std::vector<cv::gimpl::RcDesc> &desc() const   { return d; }
};
struct EndOfStream {};

struct Exception {
    std::exception_ptr eptr;
};

using StreamMsg = cv::util::variant<EndOfStream, cv::GRunArgs, Exception>;
struct GIslandExecutable::IInput: public GIslandExecutable::IODesc {
    virtual ~IInput() = default;
    virtual StreamMsg get() = 0;     // Get a new input vector (blocking)
    virtual StreamMsg try_get() = 0; // Get a new input vector (non-blocking)
};
struct GIslandExecutable::IOutput: public GIslandExecutable::IODesc {
    virtual ~IOutput() = default;
    virtual GRunArgP get(int idx) = 0;                                 // Allocate (wrap) a new data object for output idx
    virtual void post(GRunArgP&&, const std::exception_ptr& = {}) = 0; // Release the object back to the framework (mark available)
    virtual void post(EndOfStream&&) = 0;                              // Post end-of-stream marker back to the framework
    virtual void post(Exception&&) = 0;


    // Assign accumulated metadata to the given output object.
    // This method can only be called after get() and before post().
    virtual void meta(const GRunArgP&, const GRunArg::Meta &) = 0;
};

// GIslandEmitter - a backend-specific thing which feeds data into
// the pipeline. This one is just an interface, implementations are executor-defined.
class GIslandEmitter
{
public:
    // Obtain next value from the emitter
    virtual bool pull(GRunArg &) = 0;
    virtual void halt() = 0;
    virtual ~GIslandEmitter() = default;
};

// Couldn't reuse NodeType here - FIXME unify (move meta to a shared place)
struct NodeKind
{
    static const char *name() { return "NodeKind"; }
    enum { ISLAND, SLOT, EMIT, SINK} k;
};

// FIXME: Rename to Island (as soon as current GModel::Island is renamed
// to IslandTag).
struct FusedIsland
{
    static const char *name() { return "FusedIsland"; }
    std::shared_ptr<GIsland> object;
};

struct DataSlot
{
    static const char *name() { return "DataSlot"; }
    ade::NodeHandle original_data_node; // direct link to GModel
};

struct IslandExec
{
    static const char *name() { return "IslandExecutable"; }
    std::shared_ptr<GIslandExecutable> object;
};

struct Emitter
{
    static const char *name() { return "Emitter"; }
    std::size_t proto_index;
    std::shared_ptr<GIslandEmitter> object;
};

struct Sink
{
    static const char *name() { return "Sink"; }
    std::size_t proto_index;
};

// This flag is set in graph's own metadata if compileIsland was successful
struct IslandsCompiled
{
    static const char *name() { return "IslandsCompiled"; }
};

// This flag marks an edge in an GIslandModel as "desynchronized"
// i.e. it starts a new desynchronized subgraph
struct DesyncIslEdge
{
    static const char *name() { return "DesynchronizedIslandEdge"; }

    // Projection from GModel/DesyncEdge.index
    int index;
};

namespace GIslandModel
{

    using Graph = ade::TypedGraph
        < NodeKind
        , FusedIsland
        , DataSlot
        , IslandExec
        , Emitter
        , Sink
        , IslandsCompiled
        , DesyncIslEdge
        , ade::passes::TopologicalSortData
        >;

    // FIXME: derive from TypedGraph
    using ConstGraph = ade::ConstTypedGraph
        < NodeKind
        , FusedIsland
        , DataSlot
        , IslandExec
        , Emitter
        , Sink
        , IslandsCompiled
        , DesyncIslEdge
        , ade::passes::TopologicalSortData
        >;

    // Top-level function
    void generateInitial(Graph &g, const ade::Graph &src_g);
    // "Building blocks"
    ade::NodeHandle mkSlotNode(Graph &g, const ade::NodeHandle &data_nh);
    ade::NodeHandle mkIslandNode(Graph &g, const gapi::GBackend &bknd, const ade::NodeHandle &op_nh, const ade::Graph &orig_g);
    ade::NodeHandle mkIslandNode(Graph &g, std::shared_ptr<GIsland>&& isl);
    ade::NodeHandle mkEmitNode(Graph &g, std::size_t in_idx); // streaming-related
    ade::NodeHandle mkSinkNode(Graph &g, std::size_t out_idx); // streaming-related

    // GIslandModel API
    void syncIslandTags(Graph &g, ade::Graph &orig_g);
    void compileIslands(Graph &g, const ade::Graph &orig_g, const GCompileArgs &args);

    // Debug routines
    // producerOf - returns an Island handle which produces given data object
    //     from the original model (! don't mix with DataSlot)
    // FIXME: GAPI_EXPORTS because of tests only!
    ade::NodeHandle GAPI_EXPORTS producerOf(const ConstGraph &g, ade::NodeHandle &data_nh);
    // traceIslandName - returns pretty island name for passed island node.
    //     Function uses RTTI to assembly name.
    //     In case if name of backend implementation class doesn't fit *G[Name]BackendImpl* pattern,
    //     raw mangled name of class will be used.
    std::string traceIslandName(const ade::NodeHandle& op_nh, const Graph& g);
} // namespace GIslandModel

}} // namespace cv::gimpl

#endif // OPENCV_GAPI_GISLANDMODEL_HPP
