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/Replica.cpp

@@ -0,0 +1,162 @@
+////////////////////////////////////////////////////////////////////////////////
+//
+// Copyright 2022, Dustin J. Mitchell
+//
+// 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
+//
+////////////////////////////////////////////////////////////////////////////////
+
+#include <cmake.h>
+#include <format.h>
+#include "tc/Replica.h"
+#include "tc/Task.h"
+#include "tc/WorkingSet.h"
+#include "tc/util.h"
+
+using namespace tc::ffi;
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Replica::Replica ()
+{
+  inner = unique_tcreplica_ptr (
+      tc_replica_new_in_memory (),
+      [](TCReplica* rep) { tc_replica_free (rep); });
+}
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Replica::Replica (Replica &&other) noexcept
+{
+  // move inner from other
+  inner = unique_tcreplica_ptr (
+      other.inner.release (),
+      [](TCReplica* rep) { tc_replica_free (rep); });
+}
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Replica& tc::Replica::operator= (Replica &&other) noexcept
+{
+  if (this != &other) {
+    // move inner from other
+    inner = unique_tcreplica_ptr (
+        other.inner.release (),
+        [](TCReplica* rep) { tc_replica_free (rep); });
+  }
+  return *this;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Replica::Replica (const std::string& dir)
+{
+  TCString path = tc_string_borrow (dir.c_str ());
+  TCString error;
+  auto tcreplica = tc_replica_new_on_disk (path, &error);
+  if (!tcreplica) {
+    auto errmsg = format ("Could not create replica at {1}: {2}", dir, tc_string_content (&error));
+    tc_string_free (&error);
+    throw errmsg;
+  }
+  inner = unique_tcreplica_ptr (
+      tcreplica,
+      [](TCReplica* rep) { tc_replica_free (rep); });
+}
+
+////////////////////////////////////////////////////////////////////////////////
+tc::WorkingSet tc::Replica::working_set ()
+{
+  TCWorkingSet *tcws = tc_replica_working_set (&*inner);
+  if (!tcws) {
+    throw replica_error ();
+  }
+  return WorkingSet {tcws};
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::optional<tc::Task> tc::Replica::get_task (const std::string &uuid)
+{
+  TCTask *tctask = tc_replica_get_task (&*inner, uuid2tc (uuid));
+  if (!tctask) {
+    auto error = tc_replica_error (&*inner);
+    if (error.ptr) {
+      throw replica_error (error);
+    } else {
+      return std::nullopt;
+    }
+  }
+  return std::make_optional (Task (tctask));
+}
+
+////////////////////////////////////////////////////////////////////////////////
+tc::Task tc::Replica::new_task (tc::Status status, const std::string &description)
+{
+  TCTask *tctask = tc_replica_new_task (&*inner, (tc::ffi::TCStatus)status, string2tc (description));
+  if (!tctask) {
+    throw replica_error ();
+  }
+  return Task (tctask);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::vector<tc::Task> tc::Replica::all_tasks ()
+{
+  TCTaskList tasks = tc_replica_all_tasks (&*inner);
+  if (!tasks.items) {
+    throw replica_error ();
+  }
+
+  std::vector <Task> all;
+  all.reserve (tasks.len);
+  for (size_t i = 0; i < tasks.len; i++) {
+    auto tctask = tc_task_list_take (&tasks, i);
+    if (tctask) {
+      all.push_back (Task (tctask));
+    }
+  }
+
+  return all;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+void tc::Replica::rebuild_working_set ()
+{
+  auto res = tc_replica_rebuild_working_set (&*inner, true);
+  if (res != TC_RESULT_OK) {
+    throw replica_error ();
+  }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::string tc::Replica::replica_error () {
+  return replica_error (tc_replica_error (&*inner));
+}
+
+////////////////////////////////////////////////////////////////////////////////
+std::string tc::Replica::replica_error (TCString error) {
+  std::string errmsg;
+  if (!error.ptr) {
+    errmsg = std::string ("Unknown TaskChampion error");
+  } else {
+    errmsg = std::string (tc_string_content (&error));
+  }
+  tc_string_free (&error);
+  return errmsg;
+}
+
+////////////////////////////////////////////////////////////////////////////////