Add a C++ wrapper around TC FFI

This uses CMake to build a simple Rust library (in `src/tc/rust`) that
just re-exports everything from the `taskchampion-lib` crate.

The C++ wrappers then wrap this into C++ objects with proper lifecycle
maintenance, in the `tc` namespace.

The C++ wrappers are incomplete, and missing methods are tagged with
"TODO".  These will be added as needed.

src/tc/Task.h

@@ -0,0 +1,119 @@
+////////////////////////////////////////////////////////////////////////////////
+//
+// Copyright 2022, Dustin J. Mitchell, Tomas Babej, Paul Beckingham, Federico Hernandez.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// https://www.opensource.org/licenses/mit-license.php
+//
+////////////////////////////////////////////////////////////////////////////////
+
+#ifndef INCLUDED_TC_TASK
+#define INCLUDED_TC_TASK
+
+#include <string>
+#include <functional>
+#include <memory>
+#include <map>
+#include "tc/ffi.h"
+
+namespace tc {
+  class Replica;
+
+  enum Status {
+    Pending = tc::ffi::TC_STATUS_PENDING,
+    Completed = tc::ffi::TC_STATUS_COMPLETED,
+    Deleted = tc::ffi::TC_STATUS_DELETED,
+    Unknown = tc::ffi::TC_STATUS_UNKNOWN,
+  };
+
+  // a unique_ptr to a TCReplica which will automatically free the value when
+  // it goes out of scope.
+  using unique_tctask_ptr = std::unique_ptr<
+    tc::ffi::TCTask,
+    std::function<void(tc::ffi::TCTask*)>>;
+
+
+  // Task wraps the TCTask type, managing its memory, errors, and so on.
+  //
+  // Except as noted, method names match the suffix to `tc_task_..`.
+  class Task
+  {
+  protected:
+    // Tasks may only be created by tc::Replica
+    friend class tc::Replica;
+    explicit Task (tc::ffi::TCTask *);
+
+  public:
+    // This object "owns" inner, so copy is not allowed.
+    Task (const Task &) = delete;
+    Task &operator=(const Task &) = delete;
+
+    // Explicit move constructor and assignment
+    Task (Task &&) noexcept;
+    Task &operator=(Task &&) noexcept;
+
+// TODO: void tc_task_to_mut(struct TCTask *task, struct TCReplica *tcreplica);
+// TODO: void tc_task_to_immut(struct TCTask *task);
+    std::string get_uuid () const;
+    Status get_status () const;
+    std::map <std::string, std::string> get_taskmap() const;
+    std::string get_description() const;
+// TODO: time_t tc_task_get_entry(struct TCTask *task);
+// TODO: time_t tc_task_get_wait(struct TCTask *task);
+// TODO: time_t tc_task_get_modified(struct TCTask *task);
+// TODO: bool tc_task_is_waiting(struct TCTask *task);
+// TODO: bool tc_task_is_active(struct TCTask *task);
+// TODO: bool tc_task_has_tag(struct TCTask *task, struct TCString tag);
+// TODO: struct TCStringList tc_task_get_tags(struct TCTask *task);
+// TODO: struct TCAnnotationList tc_task_get_annotations(struct TCTask *task);
+// TODO: struct TCString tc_task_get_uda(struct TCTask *task, struct TCString ns, struct TCString key);
+// TODO: struct TCString tc_task_get_legacy_uda(struct TCTask *task, struct TCString key);
+// TODO: struct TCUdaList tc_task_get_udas(struct TCTask *task);
+// TODO: struct TCUdaList tc_task_get_legacy_udas(struct TCTask *task);
+// TODO: TCResult tc_task_set_status(struct TCTask *task, enum TCStatus status);
+// TODO: TCResult tc_task_set_description(struct TCTask *task, struct TCString description);
+// TODO: TCResult tc_task_set_entry(struct TCTask *task, time_t entry);
+// TODO: TCResult tc_task_set_wait(struct TCTask *task, time_t wait);
+// TODO: TCResult tc_task_set_modified(struct TCTask *task, time_t modified);
+// TODO: TCResult tc_task_start(struct TCTask *task);
+// TODO: TCResult tc_task_stop(struct TCTask *task);
+// TODO: TCResult tc_task_done(struct TCTask *task);
+// TODO: TCResult tc_task_delete(struct TCTask *task);
+// TODO: TCResult tc_task_add_tag(struct TCTask *task, struct TCString tag);
+// TODO: TCResult tc_task_remove_tag(struct TCTask *task, struct TCString tag);
+// TODO: TCResult tc_task_add_annotation(struct TCTask *task, struct TCAnnotation *annotation);
+// TODO: TCResult tc_task_remove_annotation(struct TCTask *task, int64_t entry);
+// TODO: TCResult tc_task_set_uda(struct TCTask *task,
+// TODO: TCResult tc_task_remove_uda(struct TCTask *task, struct TCString ns, struct TCString key);
+// TODO: TCResult tc_task_set_legacy_uda(struct TCTask *task, struct TCString key, struct TCString value);
+// TODO: TCResult tc_task_remove_legacy_uda(struct TCTask *task, struct TCString key);
+
+  private:
+    unique_tctask_ptr inner;
+
+    std::string task_error () const; // tc_task_error
+  };
+}
+
+// TODO: struct TCTask *tc_task_list_take(struct TCTaskList *tasks, size_t index);
+// TODO: void tc_task_list_free(struct TCTaskList *tasks);
+
+#endif
+////////////////////////////////////////////////////////////////////////////////