/*
* Copyright (c) Meta Platforms, Inc. and affiliates.
* All rights reserved.
*
* This source code is licensed under both the BSD-style license (found in the
* LICENSE file in the root directory of this source tree) and the GPLv2 (found
* in the COPYING file in the root directory of this source tree).
* You may select, at your option, one of the above-listed licenses.
*/


#include <stdio.h>     // fprintf
#include <stdlib.h>    // free
#include <zstd.h>      // presumes zstd library is installed
#include "common.h"    // Helper functions, CHECK(), and CHECK_ZSTD()

static void decompressFile_orDie(const char* fname)
{
   FILE* const fin  = fopen_orDie(fname, "rb");
   size_t const buffInSize = ZSTD_DStreamInSize();
   void*  const buffIn  = malloc_orDie(buffInSize);
   FILE* const fout = stdout;
   size_t const buffOutSize = ZSTD_DStreamOutSize();  /* Guarantee to successfully flush at least one complete compressed block in all circumstances. */
   void*  const buffOut = malloc_orDie(buffOutSize);

   ZSTD_DCtx* const dctx = ZSTD_createDCtx();
   CHECK(dctx != NULL, "ZSTD_createDCtx() failed!");

   /* This loop assumes that the input file is one or more concatenated zstd
    * streams. This example won't work if there is trailing non-zstd data at
    * the end, but streaming decompression in general handles this case.
    * ZSTD_decompressStream() returns 0 exactly when the frame is completed,
    * and doesn't consume input after the frame.
    */
   size_t const toRead = buffInSize;
   size_t read;
   size_t lastRet = 0;
   int isEmpty = 1;
   while ( (read = fread_orDie(buffIn, toRead, fin)) ) {
       isEmpty = 0;
       ZSTD_inBuffer input = { buffIn, read, 0 };
       /* Given a valid frame, zstd won't consume the last byte of the frame
        * until it has flushed all of the decompressed data of the frame.
        * Therefore, instead of checking if the return code is 0, we can
        * decompress just check if input.pos < input.size.
        */
       while (input.pos < input.size) {
           ZSTD_outBuffer output = { buffOut, buffOutSize, 0 };
           /* The return code is zero if the frame is complete, but there may
            * be multiple frames concatenated together. Zstd will automatically
            * reset the context when a frame is complete. Still, calling
            * ZSTD_DCtx_reset() can be useful to reset the context to a clean
            * state, for instance if the last decompression call returned an
            * error.
            */
           size_t const ret = ZSTD_decompressStream(dctx, &output , &input);
           CHECK_ZSTD(ret);
           fwrite_orDie(buffOut, output.pos, fout);
           lastRet = ret;
       }
   }

   if (isEmpty) {
       fprintf(stderr, "input is empty\n");
       exit(1);
   }

   if (lastRet != 0) {
       /* The last return value from ZSTD_decompressStream did not end on a
        * frame, but we reached the end of the file! We assume this is an
        * error, and the input was truncated.
        */
       fprintf(stderr, "EOF before end of stream: %zu\n", lastRet);
       exit(1);
   }

   ZSTD_freeDCtx(dctx);
   fclose_orDie(fin);
   fclose_orDie(fout);
   free(buffIn);
   free(buffOut);
}


int main(int argc, const char** argv)
{
   const char* const exeName = argv[0];

   if (argc!=2) {
       fprintf(stderr, "wrong arguments\n");
       fprintf(stderr, "usage:\n");
       fprintf(stderr, "%s FILE\n", exeName);
       return 1;
   }

   const char* const inFilename = argv[1];

   decompressFile_orDie(inFilename);
   return 0;
}