Dawn/src/dawn/asset/AssetDataLoader.hpp

// Copyright (c) 2023 Dominic Masters
// 
// This software is released under the MIT License.
// https://opensource.org/licenses/MIT

#pragma once
#include "dawnlibs.hpp"

extern "C" {
  #include <archive.h>
  #include <archive_entry.h>
}

#define ASSET_LOADER_BUFFER_SIZE 32768

/**
 * Method invoked by the libarchive internals to read bytes from the archive
 * file pointer.
 * 
 * @param archive Archive requesting the read. 
 * @param data Data pointer passed to the archive.
 * @param buffer Pointer to where the buffer pointer should be stored.
 * @return Count of bytes read.
 */
ssize_t assetDataLoaderArchiveRead(
  struct archive *archive,
  void *data,
  const void **buffer
);

/**
 * Method invoked by the libarchive internals to seek the archive file pointer.
 * 
 * @param archive Archive requesting the seek.
 * @param data Data pointer passed to the archive.
 * @param offset Offset to seek to.
 * @param whence Whence to seek from.
 * @return The new offset.
 */
int64_t assetDataLoaderArchiveSeek(
  struct archive *archive,
  void *data,
  int64_t offset,
  int32_t whence
);

/**
 * Method invoked by the libarchive internals to open the archive file pointer.
 * 
 * @param archive Archive requesting the open.
 * @param data Data pointer passed to the archive.
 * @return 0 if success, otherwise for failure.
 */
int32_t assetDataLoaderArchiveOpen(struct archive *a, void *data);

/**
 * Method invoked by the libarchive internals to close the archive file pointer.
 * 
 * @param archive Archive requesting the close.
 * @param data Data pointer passed to the archive.
 * @return 0 if success, otherwise for failure.
 */
int32_t assetDataLoaderArchiveClose(struct archive *a, void *data);

namespace Dawn {
  class AssetDataLoader {
    protected:
      struct archive *assetArchive = nullptr;
      struct archive_entry *assetArchiveEntry = nullptr;
      size_t position;
      std::string fileName;

    public:
      uint8_t buffer[ASSET_LOADER_BUFFER_SIZE];
      FILE *assetArchiveFile = nullptr;

      /**
       * Unimplemented method intended to be implemented by the platform that
       * will be used to request a File pointer to the asset.
       * 
       * @return Pointer to the opened asset archive.
       */
      FILE * openAssetArchiveFile();
      
      /**
       * Create a new asset loader. Asset Loaders can be used to load data from
       * a file in a myriad of ways.
       * 
       * @param fileName File name of the asset that is to be loaded.
       */
      AssetDataLoader(std::string filename);

      /**
       * Platform-centric method to open a file buffer to an asset.
       */
      void open();

      /**
       * Closes the previously ppened asset.
       * @return 0 if successful, otherwise false.
       */
      int32_t close();

      /**
       * Read bytes from buffer.
       * @param buffer Pointer to a ubyte array to buffer data into.
       * @param size Length of the data buffer (How many bytes to read).
       * @return The count of bytes read.
       */
      size_t read(uint8_t *buffer, size_t size);

      /**
       * Reads bytes from the buffer until a given delimiter is found. Returned
       * position will be the index of the delimiter within the buffer.
       * 
       * @param buffer Buffer to read into.
       * @param maxSize Maximum size of the buffer.
       * @param delimiter Delimiter to read until.
       * @return The count of bytes read (including null terminator)
       */
      size_t readUntil(
        uint8_t *buffer,
        const size_t maxSize,
        const char_t delimiter
      );
      
      /**
       * Get the size of the asset.
       * @return The size of the asset in bytes.
       */
      size_t getSize();

      /**
       * Skips the read head forward to a given position.
       * 
       * @param n Count of bytes to progress the read head by.
       * @return Count of bytes progressed.
       */
      size_t skip(size_t n);

      /**
       * Rewind the read head to the beginning of the file.
       */
      void rewind();

      /**
       * Sets the absolute position of the read head within the buffer of the
       * file.
       * 
       * @param absolutePosition Absolute position to set the read head to.
       */
      size_t setPosition(const size_t absolutePosition);

      /**
       * Returns the current position of the read head.
       * 
       * @return The current read head position.
       */
      size_t getPosition();

      /**
       * Cleanup the asset loader.
       */
      virtual ~AssetDataLoader();
  };
}