Implement parsing for tree objects (#40)

* Add documentation for tree objects

* Implement parsing of tree objects

* Remove redundant newline for cat-file

Author: C-likethis123

doc/commits.md

@@ -1,7 +1,7 @@
 # Commits
 
 ## Structure of a commit
-tree - tree commit
+[tree](tree.md) - tree commit
 parent - reference to its parents
 author - author name
 committer - committer name

doc/tree.md

@@ -0,0 +1,36 @@
+# tree
+
+## What's in a tree?
+
+A tree describes the content of the current folder by associating blobs to paths.
+It's a table with 3 columns: file mode, file path, SHA-1.
+Each subfolder will be represented by its own tree object.
+
+## Tree format
+
+A tree is a concatenation of records of the format:
+```
+[mode] space [path] 0x00 [sha-1]
+```
+
+## How does Git store version history in the worktree?
+
+1. Each branch is associated with one worktree object
+2. Current versions of the worktree is associated with a blob object
+
+## How to parse a tree object?
+
+1. Not sure if there's a format header
+2. Follow the tree format.
+3. It can be parsed into:
+- a mapping of a path to a file mode, and a SHA-1 hash
+- when needed, the SHA-1 hash could be read
+
+# What do we do with trees?
+1. Every commit object stores a reference to the tree, which represents the working object.
+2. Need to modify the paths in the working tree.
+3. Need to add to the working tree.
+4. Delete from the working tree
+5. Show the mode, sha1, object type, from a given file path
+
+Since I'm using `git add`, `git rm` in terms of file paths, I will use the file path as a key and represent it in an unordered_map.

include/tree.h

@@ -0,0 +1,27 @@
+#ifndef TREE_H
+#define TREE_H
+
+#include <string>
+#include <unordered_map>
+
+#include "object.h"
+
+class GitTree : public GitObject {
+public:
+  GitTree(const std::string &data = std::string(""));
+
+  void deserialise(
+      const std::string &data) override; // convert string format to data object
+  std::string
+  serialise(GitRepository &repo) override; // convert this to a string format
+  std::string print_matching_files(
+      const std::string &filePathPattern); // print tree entries that
+                                           // match the given file path
+  void init();
+
+protected:
+  std::vector<std::string> pathNames;
+  std::unordered_map<std::string, std::tuple<int, std::string>> fileEntries;
+};
+
+#endif // TREE_H

include/util.h

@@ -8,5 +8,6 @@ namespace fs = boost::filesystem;
 std::string read_file(const fs::path &filePath);
 bool create_file(const fs::path &filePath, const std::string &content = "");
 std::string sha1_hexdigest(const std::string &data);
-
+std::string binaryToHex(const std::string &binary);
+std::string hexToBinary(const std::string &hexString);
 #endif // UTIL_H

src/CMakeLists.txt

@@ -15,7 +15,7 @@ target_link_libraries(repository PRIVATE inih util boost_libraries)
 target_include_directories(repository PUBLIC ../include)
 target_compile_features(repository PUBLIC cxx_std_17)
 
-add_library(object object.cpp blob.cpp commit.cpp)
+add_library(object object.cpp blob.cpp commit.cpp tree.cpp)
 target_link_libraries(object PRIVATE repository boost_libraries)
 target_include_directories(object PUBLIC ../include)
 target_compile_features(object PUBLIC cxx_std_17)

src/cat-file.cpp

@@ -27,7 +27,7 @@ void catfile(std::vector<std::string> &args) {
     if (repo) {
       GitObject *obj =
           GitObject::read(*repo, GitObject::find(*repo, hash, type));
-      std::cout << obj->serialise(*repo) << "\n";
+      std::cout << obj->serialise(*repo);
     }
   } catch (std::runtime_error &err) {
     std::cerr << err.what() << "\n";

src/tree.cpp

@@ -0,0 +1,49 @@
+#include "tree.h"
+#include "repository.h"
+#include "util.h"
+#include <iostream>
+#include <sstream>
+
+GitTree::GitTree(const std::string &data) : GitObject() {
+  this->deserialise(data);
+};
+
+std::string GitTree::serialise(GitRepository &repo) {
+  std::stringstream ss;
+  for (const auto &path : this->pathNames) {
+    auto &[mode, sha] = this->fileEntries[path];
+    ss << mode << " " << path << '\0' << hexToBinary(sha);
+  }
+  return ss.str();
+}
+
+void GitTree::deserialise(const std::string &data) {
+  int curr = 0;
+  while (curr < data.size()) {
+    int space = data.find(' ', curr);
+    int mode = std::stoi(data.substr(curr, space - curr));
+    curr = space + 1;
+    space = data.find('\0', curr);
+    std::string path = data.substr(curr, space - curr);
+    curr = space + 1;
+    std::string sha = binaryToHex(data.substr(curr, 20));
+    curr += 20;
+    this->fileEntries[path] = {mode, sha};
+    pathNames.push_back(path);
+  }
+  // maintain sort order via path names to ensure
+  // consistent tree objects are generated each time
+  std::sort(pathNames.begin(), pathNames.end());
+}
+
+std::string GitTree::print_matching_files(const std::string &filePath) {
+  std::stringstream ss;
+  for (const auto &path : this->pathNames) {
+    // TODO: implement better file path matching
+    if (filePath.empty() || path == filePath) {
+      auto &[mode, sha] = this->fileEntries[path];
+      ss << mode << " " << sha << " " << path << "\n";
+    }
+  }
+  return ss.str();
+}

src/util.cpp

@@ -1,69 +1,93 @@
-#include <iostream>
-#include <iomanip>
-#include <string>
-#include <fstream>
-#include <sstream>
 #include <boost/filesystem.hpp>
 #include <boost/uuid/detail/sha1.hpp>
+#include <fstream>
+#include <iomanip>
+#include <iostream>
+#include <sstream>
+#include <string>
 
 namespace fs = boost::filesystem;
 
 std::string read_file(const fs::path &filePath) {
-    try {
-        // Open the file
-        std::ifstream fileStream(filePath.string());
+  try {
+    // Open the file
+    std::ifstream fileStream(filePath.string());
 
-        // Check if the file is successfully opened
-        if (fileStream.is_open()) {
-            // Read the content of the file
-            std::stringstream buffer;
-            buffer << fileStream.rdbuf();
-            return buffer.str();
-        } else {
-            std::cerr << "Error opening the file for reading: " << filePath << std::endl;
-            return "";
-        }
-    } catch (const std::exception& e) {
-        std::cerr << "Exception: " << e.what() << std::endl;
-        return "";
+    // Check if the file is successfully opened
+    if (fileStream.is_open()) {
+      // Read the content of the file
+      std::stringstream buffer;
+      buffer << fileStream.rdbuf();
+      return buffer.str();
+    } else {
+      std::cerr << "Error opening the file for reading: " << filePath
+                << std::endl;
+      return "";
     }
+  } catch (const std::exception &e) {
+    std::cerr << "Exception: " << e.what() << std::endl;
+    return "";
+  }
 }
 
-bool create_file(const fs::path &filePath, const std::string& content = "") {
-    try {
-        // Create the file
-        std::ofstream fileStream(filePath.string());
+bool create_file(const fs::path &filePath, const std::string &content = "") {
+  try {
+    // Create the file
+    std::ofstream fileStream(filePath.string());
 
-        // Check if the file is successfully opened
-        if (fileStream.is_open()) {
-            // Write content to the file if provided
-            if (!content.empty()) {
-                fileStream << content;
-            }
+    // Check if the file is successfully opened
+    if (fileStream.is_open()) {
+      // Write content to the file if provided
+      if (!content.empty()) {
+        fileStream << content;
+      }
 
-            std::cout << "File created successfully: " << filePath << std::endl;
-            return true;
-        } else {
-            std::cerr << "Error opening the file for writing: " << filePath << std::endl;
-            return false;
-        }
-    } catch (const std::exception& e) {
-        std::cerr << "Exception: " << e.what() << std::endl;
-        return false;
+      std::cout << "File created successfully: " << filePath << std::endl;
+      return true;
+    } else {
+      std::cerr << "Error opening the file for writing: " << filePath
+                << std::endl;
+      return false;
     }
+  } catch (const std::exception &e) {
+    std::cerr << "Exception: " << e.what() << std::endl;
+    return false;
+  }
 }
 
-std::string sha1_hexdigest(const std::string& data) {
-    boost::uuids::detail::sha1 sha1;
-    sha1.process_bytes(data.data(), data.size());
+std::string sha1_hexdigest(const std::string &data) {
+  boost::uuids::detail::sha1 sha1;
+  sha1.process_bytes(data.data(), data.size());
 
-    unsigned int digest[5];
-    sha1.get_digest(digest);
+  unsigned int digest[5];
+  sha1.get_digest(digest);
 
-    std::stringstream ss;
-    ss << std::hex << std::setfill('0');
-    for (unsigned int i : digest) {
-        ss << std::setw(8) << i;
-    }
-    return ss.str();
+  std::stringstream ss;
+  ss << std::hex << std::setfill('0');
+  for (unsigned int i : digest) {
+    ss << std::setw(8) << i;
+  }
+  return ss.str();
 }
+
+std::string binaryToHex(const std::string &binaryData) {
+  std::ostringstream hexStream;
+  for (unsigned char byte : binaryData) {
+    hexStream << std::setw(2) << std::setfill('0') << std::hex
+              << static_cast<int>(byte);
+  }
+  return hexStream.str();
+}
+
+std::string hexToBinary(const std::string &hexString) {
+  std::string binaryData;
+  for (size_t i = 0; i < hexString.size(); i += 2) {
+    // Take two hex characters at a time
+    std::string byteStr = hexString.substr(i, 2);
+
+    // Convert hex pair to a single byte (char)
+    char byte = static_cast<char>(std::stoi(byteStr, nullptr, 16));
+    binaryData.push_back(byte);
+  }
+  return binaryData;
+}