+/* Copyright (c) 2007-2023. The SimGrid Team. All rights reserved. */
+
+/* This program is free software; you can redistribute it and/or modify it
+ * under the terms of the license (GNU LGPL) which comes with this package. */
+
+#ifndef SIMGRID_MC_ODPOR_WAKEUP_TREE_HPP
+#define SIMGRID_MC_ODPOR_WAKEUP_TREE_HPP
+
+#include "src/mc/explo/odpor/WakeupTreeIterator.hpp"
+#include "src/mc/explo/odpor/odpor_forward.hpp"
+#include "src/mc/transition/Transition.hpp"
+
+#include <memory>
+#include <optional>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+namespace simgrid::mc::odpor {
+
+/**
+ * @brief A single node in a wakeup tree
+ *
+ * Each node in a wakeup tree represents a single step
+ * taken in an extension of the execution represented
+ * by the tree within which the node is contained. That is,
+ * a node in the tree is one step on a "pre-defined"
+ * path forward for some execution sequence. The partial
+ * execution that is implicitly represented by the node
+ * is that formed by taking each step on the (unique)
+ * path in the tree from the root node to this node.
+ * Thus, the tree itself contains all of the paths
+ * that "should be" searched, while each node is
+ * simply a step on each path.
+ */
+class WakeupTreeNode {
+private:
+ WakeupTreeNode* parent_ = nullptr;
+
+ /** An ordered list of children of for this node in the tree */
+ std::list<WakeupTreeNode*> children_;
+
+ /** @brief The contents of the node */
+ std::shared_ptr<Transition> action_;
+
+ /** @brief Removes the node as a child from the parent */
+ void detatch_from_parent();
+
+ /** Allows the owning tree to insert directly into the child */
+ friend WakeupTree;
+ friend WakeupTreeIterator;
+
+public:
+ explicit WakeupTreeNode(std::shared_ptr<Transition> u) : action_(u) {}
+
+ WakeupTreeNode() = default;
+ ~WakeupTreeNode() = default;
+ WakeupTreeNode(const WakeupTreeNode&) = delete;
+ WakeupTreeNode(WakeupTreeNode&&) = default;
+ WakeupTreeNode& operator=(const WakeupTreeNode&) = delete;
+ WakeupTreeNode& operator=(WakeupTreeNode&&) = default;
+
+ auto begin() const { return this->children_.begin(); }
+ auto end() const { return this->children_.end(); }
+ auto rbegin() const { return this->children_.rbegin(); }
+ auto rend() const { return this->children_.rend(); }
+
+ bool is_leaf() const { return children_.empty(); }
+ bool is_root() const { return parent_ == nullptr; }
+ aid_t get_actor() const { return action_->aid_; }
+ PartialExecution get_sequence() const;
+ std::shared_ptr<Transition> get_action() const { return action_; }
+ const std::list<WakeupTreeNode*>& get_ordered_children() const { return children_; }
+
+ std::string string_of_whole_tree(int indentation_level) const;
+
+ /** Insert a node `node` as a new child of this node */
+ void add_child(WakeupTreeNode* node);
+};
+
+/**
+ * @brief The structure used by ODPOR to maintains paths of execution
+ * that should be followed in the future
+ *
+ * The wakeup tree data structure is formally defined in the Abdulla et al.
+ * 2017 ODPOR paper. Conceptually, the tree consists of nodes which are
+ * mapped to actions. Each node represents a partial extension of an execution,
+ * the complete extension being the transitions taken in sequence from
+ * the root of the tree to the node itself. Leaf nodes in the tree conceptually,
+ * then, represent paths that are guaranteed to explore different parts
+ * of the search space.
+ *
+ * Iteration over a wakeup tree occurs as a post-order traversal of its nodes
+ *
+ * @note A wakeup tree is defined relative to some execution `E`. The
+ * structure itself does not hold onto a reference of the execution with
+ * respect to which it is a wakeup tree.
+ *
+ * @todo: If the idea of execution "views" is ever added -- viz. being able
+ * to share the contents of a single execution -- then a wakeup tree could
+ * contain a reference to such a view which would then be maintained by the
+ * manipulator of the tree
+ */
+class WakeupTree {
+private:
+ WakeupTreeNode* root_;
+
+ /**
+ * @brief All of the nodes that are currently are a part of the tree
+ *
+ * @invariant Each node event maps itself to the owner of that node,
+ * i.e. the unique pointer that manages the data at the address. The tree owns all
+ * of the addresses that are referenced by the nodes WakeupTreeNode.
+ * ODPOR guarantees that nodes are persisted as long as needed.
+ */
+ std::unordered_map<WakeupTreeNode*, std::unique_ptr<WakeupTreeNode>> nodes_;
+
+ void insert_node(std::unique_ptr<WakeupTreeNode> node);
+ void insert_sequence_after(WakeupTreeNode* node, const PartialExecution& w);
+ void remove_node(WakeupTreeNode* node);
+ bool contains(const WakeupTreeNode* node) const;
+
+ /**
+ * @brief Removes the node `root` and all of its descendants from
+ * this wakeup tree
+ *
+ * @throws: If the node `root` is not contained in this tree, an
+ * exception is raised
+ */
+ void remove_subtree_rooted_at(WakeupTreeNode* root);
+
+ /**
+ * @brief Adds a new node to the tree, disconnected from
+ * any other, which represents the partial execution
+ * "fragment" `u`
+ */
+ WakeupTreeNode* make_node(std::shared_ptr<Transition> u);
+
+ /* Allow the iterator to access the contents of the tree */
+ friend WakeupTreeIterator;
+
+public:
+ WakeupTree();
+ explicit WakeupTree(std::unique_ptr<WakeupTreeNode> root);
+
+ /**
+ * @brief Creates a copy of the subtree whose root is the node
+ * `root` in this tree
+ */
+ static WakeupTree make_subtree_rooted_at(WakeupTreeNode* root);
+
+ auto begin() const { return WakeupTreeIterator(*this); }
+ auto end() const { return WakeupTreeIterator(); }
+
+ std::vector<std::string> get_single_process_texts() const;
+
+ std::string string_of_whole_tree() const;
+
+ /**
+ * @brief Remove the subtree of the smallest (with respect
+ * to the tree's "<" relation) single-process node.
+ *
+ * A "single-process" node is one whose execution represents
+ * taking a single action (i.e. those of the root node). The
+ * smallest under "<" is that which is continuously selected and
+ * removed by ODPOR.
+ *
+ * If the tree is empty, this method has no effect.
+ */
+ void remove_min_single_process_subtree();
+
+ void remove_subtree_at_aid(aid_t proc);
+
+ /**
+ * @brief Whether or not this tree is considered empty
+ *
+ * @note Unlike other collection types, a wakeup tree is
+ * considered "empty" if it only contains the root node;
+ * that is, if it is "uninteresting". In such a case,
+ */
+ bool empty() const { return nodes_.size() == static_cast<size_t>(1); }
+
+ /**
+ * @brief Returns the number of *non-empty* entries in the tree, viz. the
+ * number of nodes in the tree that have an action mapped to them
+ */
+ size_t get_num_entries() const { return not empty() ? (nodes_.size() - 1) : static_cast<size_t>(0); }
+
+ /**
+ * @brief Returns the number of nodes in the tree, including the root node
+ */
+ size_t get_num_nodes() const { return nodes_.size(); }
+
+ /**
+ * @brief Gets the actor of the node that is the "smallest" (with respect
+ * to the tree's "<" relation) single-process node.
+ *
+ * If the tree is empty, returns std::nullopt
+ */
+ std::optional<aid_t> get_min_single_process_actor() const;
+
+ /**
+ * @brief Gets the node itself that is the "smallest" (with respect
+ * to the tree's "<" relation) single-process node.
+ *
+ * If the tree is empty, returns std::nullopt
+ */
+ std::optional<WakeupTreeNode*> get_min_single_process_node() const;
+
+ /** @brief Describes how a tree insertion was carried out */
+ enum class InsertionResult { leaf, interior_node, root };
+
+ /**
+ * @brief Inserts an sequence `seq` of processes into the tree
+ * such that that this tree is a wakeup tree relative to the
+ * given execution
+ *
+ * A key component of managing wakeup trees in ODPOR is
+ * determining what should be inserted into a wakeup tree.
+ * The procedure for implementing the insertion is outlined in section 6.2
+ * of Abdulla et al. 2017 as follows:
+ *
+ * | Let `v` be the smallest (w.r.t to "<") sequence in [the tree] B
+ * | such that `v ~_[E] w`. If `v` is a leaf node, the tree can be left
+ * | unmodified.
+ * |
+ * | Otherwise let `w'` be the shortest sequence such that `w [=_[E] v.w'`
+ * | and add `v.w'` as a new leaf, ordered after all already existing nodes
+ * | of the form `v.w''`
+ *
+ * This method performs the post-order search of part one and the insertion of
+ * `v.w'` of part two of the above procedure. Note that the execution will
+ * provide `v.w'` (see `Execution::get_shortest_odpor_sq_subset_insertion()`).
+ *
+ * @invariant: It is assumed that this tree is a wakeup tree
+ * with respect to the given execution `E`
+ *
+ * @return Whether a sequence equivalent to `seq` is already contained
+ * as a leaf node in the tree
+ */
+ InsertionResult insert(const Execution& E, const PartialExecution& seq);
+};
+
+} // namespace simgrid::mc::odpor
+#endif