add level table JSON format

src/CommonFileFormats.hh

@@ -197,3 +197,79 @@ size_t get_rel_array_count(const std::set<uint32_t>& offsets, size_t start_offse
   }
   return (*it - start_offset) / sizeof(T);
 }
+
+template <bool BE>
+class RELFileWriter {
+public:
+  RELFileWriter() = default;
+  ~RELFileWriter() = default;
+
+  template <typename T>
+  uint32_t put(const T& obj) {
+    uint32_t ret = this->w.size();
+    this->w.put<T>(obj);
+    return ret;
+  }
+
+  uint32_t write(const void* data, size_t size) {
+    uint32_t ret = this->w.size();
+    this->w.write(data, size);
+    return ret;
+  }
+
+  uint32_t write(const std::string& data) {
+    uint32_t ret = this->w.size();
+    this->w.write(data);
+    return ret;
+  }
+
+  uint32_t write_offset(uint32_t value) {
+    uint32_t ret = this->w.size();
+    this->relocations.emplace(ret);
+    this->w.put<U32T<BE>>(value);
+    return ret;
+  }
+
+  uint32_t write_ref(const ArrayRefT<BE>& ref) {
+    uint32_t ret = this->w.size();
+    this->w.put<ArrayRefT<BE>>(ref);
+    this->relocations.emplace(ret + offsetof(ArrayRefT<BE>, offset));
+    return ret;
+  }
+
+  void align(size_t alignment) {
+    while (this->w.size() & (alignment - 1)) {
+      this->w.put_u8(0);
+    }
+  }
+
+  std::string finalize(uint32_t root_offset) {
+    RELFileFooterT<BE> footer;
+    footer.root_offset = root_offset;
+
+    this->align(0x20);
+    footer.relocations_offset = this->w.size();
+    footer.num_relocations = this->relocations.size();
+    footer.unused1[0] = 1;
+    uint32_t last_offset = 0;
+    for (uint32_t reloc_offset : this->relocations) {
+      if (reloc_offset & 3) {
+        throw std::logic_error("Relocation is not 4-byte aligned");
+      }
+      size_t reloc_value = (reloc_offset - last_offset) >> 2;
+      if (reloc_value > 0xFFFF) {
+        throw std::runtime_error("Relocation offset is too far away from previous");
+      }
+      this->w.put<U16T<BE>>(reloc_value);
+      last_offset = reloc_offset;
+    }
+
+    align(0x20);
+    this->w.put<RELFileFooterT<BE>>(footer);
+
+    return std::move(this->w.str());
+  }
+
+  phosg::StringWriter w;
+  std::set<uint32_t> relocations;
+};