//===--- DependencyGraph.h - Track intra-module dependencies ----*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#ifndef SWIFT_DRIVER_DEPENDENCYGRAPH_H
#define SWIFT_DRIVER_DEPENDENCYGRAPH_H

#include "swift/Basic/LLVM.h"
#include "swift/Basic/OptionSet.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/PointerLikeTypeTraits.h"
#include <string>
#include <vector>

namespace llvm {
  class MemoryBuffer;
}

namespace swift {

/// The non-templated implementation of DependencyGraph.
///
/// \see DependencyGraph
class DependencyGraphImpl {
public:
  /// Possible dependency kinds.
  ///
  /// Clients of DependencyGraph should have no reason to use this type.
  /// It is only used in the implementation.
  enum class DependencyKind : uint8_t;

  /// Describes the result of loading a dependency file for a particular node.
  enum class LoadResult {
    /// There was an error loading the file; the entire graph should be
    /// considered suspect.
    HadError,

    /// The file was loaded successfully; with current information the node
    /// does not need to be rebuilt.
    UpToDate,

    /// The file was loaded successfully; anything that depends on the node
    /// should be considered out of date.
    AffectsDownstream
  };

private:
  enum class DependencyFlags : uint8_t;
  using DependencyMaskTy = OptionSet<DependencyKind>;
  using DependencyFlagsTy = OptionSet<DependencyFlags>;

  struct DependencyEntryTy {
    const void *node;
    DependencyMaskTy kindMask;
    DependencyFlagsTy flags;
  };
  static_assert(std::is_move_constructible<DependencyEntryTy>::value, "");

  struct ProvidesEntryTy {
    std::string name;
    DependencyMaskTy kindMask;
  };
  static_assert(std::is_move_constructible<ProvidesEntryTy>::value, "");

  /// The "outgoing" edge map. This lists all outgoing (kind, string) edges
  /// representing satisified dependencies from a particular node.
  ///
  /// For multiple outgoing edges with the same string, the kinds are combined
  /// into one field.
  ///
  /// \sa DependencyMaskTy
  llvm::DenseMap<const void *, std::vector<ProvidesEntryTy>> Provides;

  /// The "incoming" edge map. Semantically this maps incoming (kind, string)
  /// edges representing dependencies to the nodes that depend on them, as
  /// well as a flag marking whether that (kind, string) pair has been marked
  /// dirty.
  ///
  /// The representation is a map from strings to kind mask / node pairs, plus
  /// a mask of kinds that have been marked dirty. This is because it is
  /// unusual (though not impossible) for dependencies of different kinds to
  /// have the same strings. In the case of multiple incoming edges with the
  /// same string, the kinds are combined into the one field.
  ///
  /// \sa DependencyMaskTy
  llvm::StringMap<std::pair<std::vector<DependencyEntryTy>, DependencyMaskTy>> Dependencies;

  /// The set of marked nodes.
  llvm::SmallPtrSet<const void *, 16> Marked;

  LoadResult loadFromBuffer(const void *node, llvm::MemoryBuffer &buffer);

protected:
  LoadResult loadFromString(const void *node, StringRef data);
  LoadResult loadFromPath(const void *node, StringRef path);
  void markTransitive(SmallVectorImpl<const void *> &visited,
                      const void *node);
  bool markIntransitive(const void *node) {
    assert(Provides.count(node) && "node is not in the graph");
    return Marked.insert(node).second;
  }

  bool isMarked(const void *node) const {
    assert(Provides.count(node) && "node is not in the graph");
    return Marked.count(node);
  }
};

/// Tracks dependencies between opaque nodes.
///
/// This is implemented in terms of separate "depends" and "provides" sets
/// that together represent edges between nodes. Abstractly, each edge is
/// labeled with a (kind, string) pair, where the "kind" distinguishes
/// different kinds of dependencies. A node's "provides" set is matched up
/// with other nodes' "depends" sets to form a traversable directed graph.
/// Information on a particular node can be updated at any time, which will
/// affect any following operations. The "depends" entries can be "cascading"
/// or "non-cascading", which describes whether or not downstream nodes should
/// be traversed after following a particular dependency edge.
///
/// The graph also supports a "mark" operation, which is intended to track
/// nodes that have been not just visited but transitively marked through.
template <typename T>
class DependencyGraph : public DependencyGraphImpl {
  using Traits = llvm::PointerLikeTypeTraits<T>;
  static_assert(Traits::NumLowBitsAvailable >= 0, "not a pointer-like type");
public:
  /// Load "depends" and "provides" data for \p node from the file at the given
  /// path.
  ///
  /// If \p node is already in the graph, outgoing edges ("provides") are
  /// cleared and replaced with the newly loaded data. Incoming edges
  /// ("depends") are not cleared; new dependencies are considered additive.
  ///
  /// If \p node has already been marked, only its outgoing edges are updated.
  LoadResult loadFromPath(T node, StringRef path) {
    return DependencyGraphImpl::loadFromPath(Traits::getAsVoidPointer(node),
                                             path);
  }

  /// Load "depends" and "provides" data for \p node from a plain string.
  ///
  /// This is only intended for testing purposes.
  ///
  /// \sa loadFromPath
  LoadResult loadFromString(T node, StringRef data) {
    return DependencyGraphImpl::loadFromString(Traits::getAsVoidPointer(node),
                                               data);
  }

  /// Marks \p node and all nodes that depend on \p node, and places any nodes
  /// that get transitively marked into \p visited.
  ///
  /// Nodes that have been previously marked are not included in \p newlyMarked,
  /// nor are their successors traversed, <em>even if their "provides" set has
  /// been updated since it was marked.</em> (However, nodes that depend on the
  /// given \p node are always traversed.)
  ///
  /// Nodes that are only reachable through "non-cascading" edges are added to
  /// the \p visited set, but are \em not added to the graph's marked set.
  template <unsigned N>
  void markTransitive(SmallVector<T, N> &visited, T node) {
    SmallVector<const void *, N> rawMarked;
    DependencyGraphImpl::markTransitive(rawMarked,
                                        Traits::getAsVoidPointer(node));

    // FIXME: How can we avoid this copy?
    visited.reserve(visited.size() + rawMarked.size());
    for (const void *constRawNode : rawMarked) {
      void *rawNode = const_cast<void *>(constRawNode);
      visited.push_back(Traits::getFromVoidPointer(rawNode));
    }
  }

  /// Marks \p node without marking any dependencies.
  ///
  /// \returns true if the node is newly marked, false if not.
  ///
  /// \sa #markTransitive
  bool markIntransitive(T node) {
    return
        DependencyGraphImpl::markIntransitive(Traits::getAsVoidPointer(node));
  }

  /// Returns true if \p node has been marked (directly or transitively).
  bool isMarked(T node) const {
    return DependencyGraphImpl::isMarked(Traits::getAsVoidPointer(node));
  }
};

} // end namespace swift

#endif