From efe922f835bafced06199c123be24033d071f466 Mon Sep 17 00:00:00 2001
From: falsycat <me@falsy.cat>
Date: Sat, 9 Sep 2023 09:21:17 +0900
Subject: [PATCH] add MetaEnv implementation

---
 core/CMakeLists.txt   |  2 +
 core/meta_env.hh      | 91 +++++++++++++++++++++++++++++++++++++++++++
 core/meta_env_test.cc | 74 +++++++++++++++++++++++++++++++++++
 3 files changed, 167 insertions(+)
 create mode 100644 core/meta_env.hh
 create mode 100644 core/meta_env_test.cc

diff --git a/core/CMakeLists.txt b/core/CMakeLists.txt
index fa3ef39..aab96e6 100644
--- a/core/CMakeLists.txt
+++ b/core/CMakeLists.txt
@@ -32,6 +32,7 @@ target_sources(nf7_core
     clock.hh
     dealer.hh
     logger.hh
+    meta_env.hh
     version.hh
 )
 
@@ -50,6 +51,7 @@ target_sources(nf7_core_test
     uv/file_test.cc
     uv/parallelism_test.cc
     clock_test.cc
+    meta_env_test.cc
 )
 target_link_libraries(nf7_core_test
   PRIVATE
diff --git a/core/meta_env.hh b/core/meta_env.hh
new file mode 100644
index 0000000..7f826f5
--- /dev/null
+++ b/core/meta_env.hh
@@ -0,0 +1,91 @@
+// No copyright
+#pragma once
+
+#include <algorithm>
+#include <cassert>
+#include <memory>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "iface/subsys/meta_env.hh"
+
+namespace nf7::core {
+
+class NullMetaEnv : public subsys::MetaEnv {
+ public:
+  static inline const auto kInstance = std::make_shared<NullMetaEnv>();
+
+ public:
+  NullMetaEnv() noexcept : subsys::MetaEnv("nf7::core::NullMetaEnv") { }
+
+ public:
+  Env* FindOr(std::string_view) const noexcept override { return nullptr; }
+  std::optional<Pair> FindOr(uint64_t) const noexcept override { return std::nullopt; }
+  std::vector<Pair> FetchAll() const override { return {}; }
+  std::shared_ptr<subsys::MetaEnv> parent() const noexcept override { return nullptr; }
+};
+
+class MetaEnv : public subsys::MetaEnv {
+ public:
+  using SharedPair = std::pair<std::string, std::shared_ptr<Env>>;
+
+ private:
+  static std::vector<SharedPair>&& Sort(std::vector<SharedPair>&& v) noexcept {
+    std::sort(v.begin(), v.end(),
+              [](const auto& a, const auto& b) { return a.first < b.first; });
+    return v;
+  }
+
+ public:
+  explicit MetaEnv(std::vector<SharedPair>&& children,
+                   const std::weak_ptr<subsys::MetaEnv>& parent = {}) noexcept
+      : subsys::MetaEnv("nf7::core::MetaEnv"),
+        children_(Sort(std::move(children))),
+        parent_(parent) {
+    assert(std::all_of(children_.begin(), children_.end(),
+                       [](auto& x) { return x.second; }));
+  }
+
+ public:
+  Env* FindOr(std::string_view name) const noexcept override {
+    const auto itr = std::lower_bound(
+        children_.cbegin(), children_.cend(), name,
+        [](const auto& a, const auto& b) { return a.first < b; });
+    if (children_.cend() == itr || itr->first != name) {
+      return nullptr;
+    }
+    return itr->second.get();
+  }
+  std::optional<Pair> FindOr(uint64_t index) const noexcept override {
+    if (index >= children_.size()) {
+      return std::nullopt;
+    }
+    const auto& child = children_[index];
+    return Pair {child.first, *child.second};
+  }
+
+  std::vector<Pair> FetchAll() const override
+  try {
+    std::vector<Pair> ret;
+    ret.reserve(children_.size());
+    for (const auto& child : children_) {
+      ret.emplace_back(child.first, *child.second);
+    }
+    return ret;
+  } catch (const std::bad_alloc&) {
+    throw MemoryException {};
+  }
+
+ public:
+  std::shared_ptr<subsys::MetaEnv> parent() const noexcept override {
+    return parent_.lock();
+  }
+
+ private:
+  const std::vector<SharedPair> children_;
+  const std::weak_ptr<subsys::MetaEnv> parent_;
+};
+
+}  // namespace nf7::core
diff --git a/core/meta_env_test.cc b/core/meta_env_test.cc
new file mode 100644
index 0000000..ba2254d
--- /dev/null
+++ b/core/meta_env_test.cc
@@ -0,0 +1,74 @@
+// No copyright
+#include "core/meta_env.hh"
+
+#include <gtest/gtest.h>
+
+#include "iface/env.hh"
+
+
+static inline std::shared_ptr<nf7::Env> MakeEmptyEnv() {
+  return std::make_shared<nf7::SimpleEnv>(nf7::SimpleEnv::FactoryMap {});
+}
+static inline bool MatchPair(const std::optional<nf7::subsys::MetaEnv::Pair>& a,
+                             const nf7::subsys::MetaEnv::Pair& b) {
+  return a && a->first == b.first && &a->second == &b.second;
+}
+
+TEST(MetaEnv, FindOrByName) {
+  const auto a = MakeEmptyEnv();
+  const auto b = MakeEmptyEnv();
+  const auto c = MakeEmptyEnv();
+
+  nf7::core::MetaEnv sut {
+    {
+      {"b", b},
+      {"c", c},
+      {"a", a},
+    },
+  };
+
+  EXPECT_EQ(sut.FindOr(""), nullptr);
+  EXPECT_EQ(sut.FindOr("a"), a.get());
+  EXPECT_EQ(sut.FindOr("b"), b.get());
+  EXPECT_EQ(sut.FindOr("c"), c.get());
+  EXPECT_EQ(sut.FindOr("d"), nullptr);
+}
+
+TEST(MetaEnv, FindOrByIndex) {
+  const auto a = MakeEmptyEnv();
+  const auto b = MakeEmptyEnv();
+  const auto c = MakeEmptyEnv();
+
+  nf7::core::MetaEnv sut {
+    {
+      {"b", b},
+      {"c", c},
+      {"a", a},
+    },
+  };
+
+  EXPECT_TRUE(MatchPair(sut.FindOr(0), {"a", *a}));
+  EXPECT_TRUE(MatchPair(sut.FindOr(1), {"b", *b}));
+  EXPECT_TRUE(MatchPair(sut.FindOr(2), {"c", *c}));
+  EXPECT_EQ(sut.FindOr(3), std::nullopt);
+}
+
+TEST(MetaEnv, FetchAll) {
+  const auto a = MakeEmptyEnv();
+  const auto b = MakeEmptyEnv();
+  const auto c = MakeEmptyEnv();
+
+  nf7::core::MetaEnv sut {
+    {
+      {"b", b},
+      {"c", c},
+      {"a", a},
+    },
+  };
+
+  const auto all = sut.FetchAll();
+  EXPECT_EQ(all.size(), 3);
+  EXPECT_TRUE(MatchPair(all[0], {"a", *a}));
+  EXPECT_TRUE(MatchPair(all[1], {"b", *b}));
+  EXPECT_TRUE(MatchPair(all[2], {"c", *c}));
+}