From a0ac08df866d66661bbe2e86e7f18db0db92cb82 Mon Sep 17 00:00:00 2001
From: Green Sky <green@g-s.xyz>
Date: Sat, 19 Aug 2023 21:39:12 +0200
Subject: [PATCH] detect and reuse existing data

---
 src/sha1_ngcft1.cpp | 53 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 41 insertions(+), 12 deletions(-)

diff --git a/src/sha1_ngcft1.cpp b/src/sha1_ngcft1.cpp
index 85ffb35..c55579b 100644
--- a/src/sha1_ngcft1.cpp
+++ b/src/sha1_ngcft1.cpp
@@ -519,32 +519,61 @@ bool SHA1_NGCFT1::onEvent(const Message::Events::MessageUpdated& e) {
 
 	ce.emplace<Message::Components::Transfer::FileInfoLocal>(std::vector{full_file_path});
 
-	// HACK truncate
-	auto file_impl = std::make_unique<FileRWFile>(full_file_path, info.file_size, true);
+	std::unique_ptr<FileRWFile> file_impl;
+	const bool file_exists = std::filesystem::exists(full_file_path);
+
+	{
+		const bool truncate = !file_exists;
+		file_impl = std::make_unique<FileRWFile>(full_file_path, info.file_size, truncate);
+	}
+
 	if (!file_impl->isGood()) {
 		std::cerr << "SHA1_NGCFT1 error: failed opening file '" << full_file_path << "'!\n";
 		//e.e.remove<Message::Components::Transfer::ActionAccept>(); // stop
 		return false;
 	}
-	ce.emplace<Message::Components::Transfer::File>(std::move(file_impl));
 
-	// next, create chuck cache and check for existing data
-	// TODO: check existing and dont truncate
-	{
+	{ // next, create chuck cache and check for existing data
 		auto& cc = ce.emplace<Components::FT1ChunkSHA1Cache>();
 		cc.have_all = false;
 		cc.have_count = 0;
 
 		cc.chunk_hash_to_index.clear(); // if copy pasta
-		for (size_t i = 0; i < info.chunks.size(); i++) {
-			cc.have_chunk.push_back(false);
-			_chunks[info.chunks[i]] = ce;
-			cc.chunk_hash_to_index[info.chunks[i]].push_back(i);
+
+		if (file_exists) {
+			// iterate existing file
+			for (size_t i = 0; i < info.chunks.size(); i++) {
+				auto existing_data = file_impl->read(i*info.chunk_size, info.chunkSize(i));
+				// TODO: avoid copy
+				cc.have_chunk.push_back(
+					SHA1Digest{hash_sha1(existing_data.data(), existing_data.size())} == info.chunks.at(i)
+				);
+				if (cc.have_chunk.back()) {
+					cc.have_count += 1;
+				}
+
+				_chunks[info.chunks[i]] = ce;
+				cc.chunk_hash_to_index[info.chunks[i]].push_back(i);
+			}
+
+			if (cc.have_count == info.chunks.size()) {
+				cc.have_all = true;
+			}
+		} else {
+			for (size_t i = 0; i < info.chunks.size(); i++) {
+				cc.have_chunk.push_back(false);
+				_chunks[info.chunks[i]] = ce;
+				cc.chunk_hash_to_index[info.chunks[i]].push_back(i);
+			}
+		}
+
+		if (!cc.have_all) {
+			// now, enque
+			_queue_content_want_chunk.push_back(ce);
 		}
 	}
 
-	// now, enque
-	_queue_content_want_chunk.push_back(ce);
+	ce.emplace<Message::Components::Transfer::File>(std::move(file_impl));
 
 	ce.remove<Message::Components::Transfer::TagPaused>();