From 0de3a787ff7fcf247600fbd26e7d8fa80bcc7750 Mon Sep 17 00:00:00 2001
From: Homing So <i@homing.so>
Date: Thu, 23 May 2024 16:34:55 +0800
Subject: [PATCH] feat: add concept for WriteStream

Signed-off-by: Homing So <i@homing.so>
---
 example/struct.cc        |  6 ++--
 include/bencode/writer.h | 67 +++++++++++++++++++++++++++++++---------
 2 files changed, 55 insertions(+), 18 deletions(-)

diff --git a/example/struct.cc b/example/struct.cc
index 2e0ef54..0281813 100644
--- a/example/struct.cc
+++ b/example/struct.cc
@@ -77,7 +77,7 @@ struct TorrentFile {
   }
 };
 
-int main(int argc, char *argv[]) {
+int main(const int argc, char *argv[]) {
   (void)argc;
   (void)argv;
 
@@ -89,10 +89,10 @@ int main(int argc, char *argv[]) {
   }
 
   // 2. Bind DOM to struct.
-  auto torrent_file = TorrentFile(doc);
+  const auto torrent_file = TorrentFile(doc);
 
   // 3. Convert struct to Bencode and output
-  auto value = torrent_file.toBencode();
+  const auto value = torrent_file.toBencode();
   char writeBuffer[65536];
   bencode::FileWriteStream out(stdout, writeBuffer);
   bencode::Writer writer(out);
diff --git a/include/bencode/writer.h b/include/bencode/writer.h
index 66ef0e3..2a16058 100644
--- a/include/bencode/writer.h
+++ b/include/bencode/writer.h
@@ -44,7 +44,35 @@ BENCODE_DIAG_OFF(effc++)
 
 namespace bencode {
 
-template <typename WriteStream> class Writer : NonCopyable {
+namespace required::write_stream {
+namespace details {
+
+template <typename WriteStream>
+concept HasPut = requires(WriteStream os, char ch) {
+  { os.put(ch) } -> std::same_as<void>;
+};
+
+template <typename WriteStream>
+concept HasPuts =
+    requires(WriteStream os, const char *str, std::size_t length) {
+      { os.puts(str, length) } -> std::same_as<void>;
+    };
+
+template <typename WriteStream>
+concept HasFlush = requires(WriteStream os) {
+  { os.flush() } -> std::same_as<void>;
+};
+
+} // namespace details
+
+template <typename T>
+concept HasAllRequiredFunctions =
+    details::HasPut<T> && details::HasPuts<T> && details::HasFlush<T>;
+
+} // namespace required::write_stream
+
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+class Writer : NonCopyable {
 protected:
   uint64_t stack_;
   WriteStream &os_;
@@ -54,11 +82,15 @@ template <typename WriteStream> class Writer : NonCopyable {
   virtual ~Writer() = default;
 
   virtual bool Null() { return true; }
-  virtual bool Integer(int64_t i64) { return EndValue(WriteInteger(i64)); }
-  virtual bool String(std::string_view str) {
+  virtual bool Integer(const int64_t i64) {
+    return EndValue(WriteInteger(i64));
+  }
+  virtual bool String(const std::string_view str) {
     return EndValue(WriteString(str));
   }
-  virtual bool Key(std::string_view str) { return EndValue(WriteKey(str)); }
+  virtual bool Key(const std::string_view str) {
+    return EndValue(WriteKey(str));
+  }
   virtual bool StartList() {
     ++stack_;
     return EndValue(WriteStartList());
@@ -88,8 +120,8 @@ template <typename WriteStream> class Writer : NonCopyable {
   void Flush() { os_.flush(); }
 };
 
-template <typename WriteStream>
-bool Writer<WriteStream>::WriteInteger(int64_t i64) {
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+bool Writer<WriteStream>::WriteInteger(const int64_t i64) {
   char buf[32]{};
   auto size = static_cast<std::size_t>(internal::i64toa(i64, buf) - buf);
   os_.put('i');
@@ -98,8 +130,8 @@ bool Writer<WriteStream>::WriteInteger(int64_t i64) {
   return true;
 }
 
-template <typename WriteStream>
-bool Writer<WriteStream>::WriteString(std::string_view str) {
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+bool Writer<WriteStream>::WriteString(const std::string_view str) {
   char buf[32]{};
   auto size =
       static_cast<std::size_t>(internal::u64toa(str.length(), buf) - buf);
@@ -109,33 +141,38 @@ bool Writer<WriteStream>::WriteString(std::string_view str) {
   return true;
 }
 
-template <typename WriteStream>
-bool Writer<WriteStream>::WriteKey(std::string_view str) {
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+bool Writer<WriteStream>::WriteKey(const std::string_view str) {
   WriteString(str);
   return true;
 }
 
-template <typename WriteStream> bool Writer<WriteStream>::WriteStartList() {
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+bool Writer<WriteStream>::WriteStartList() {
   os_.put('l');
   return true;
 }
 
-template <typename WriteStream> bool Writer<WriteStream>::WriteEndList() {
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+bool Writer<WriteStream>::WriteEndList() {
   os_.put('e');
   return true;
 }
 
-template <typename WriteStream> bool Writer<WriteStream>::WriteStartDict() {
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+bool Writer<WriteStream>::WriteStartDict() {
   os_.put('d');
   return true;
 }
 
-template <typename WriteStream> bool Writer<WriteStream>::WriteEndDict() {
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+bool Writer<WriteStream>::WriteEndDict() {
   os_.put('e');
   return true;
 }
 
-template <typename WriteStream> bool Writer<WriteStream>::EndValue(bool ret) {
+template <required::write_stream::HasAllRequiredFunctions WriteStream>
+bool Writer<WriteStream>::EndValue(const bool ret) {
   // end of bencode text
   if (stack_ == 0) {
     Flush();