//  * jdtrans.c
//  *
//  * Copyright (C) 1995, Thomas G. Lane.
//  * This file is part of the Independent JPEG Group's software.
//  * For conditions of distribution and use, see the accompanying README file.
//  *
//  * This file contains library routines for transcoding decompression,
//  * that is, reading raw DCT coefficient arrays from an input JPEG file.
//  * The routines in jdapimin.c will also be needed by a transcoder.



#define JPEG_INTERNALS
#include "JINCLUDE.h"
#include "JPEGLIB.h"


// Forward declarations 
LOCAL void transdecode_master_selection JPP((j_decompress_ptr cinfo));


//  * Read the coefficient arrays from a JPEG file.
//  * jpeg_read_header must be completed before calling this.
//  *
//  * The entire image is read into a set of virtual coefficient-block arrays,
//  * one per component.  The return value is a pointer to the array of
//  * virtual-array descriptors.  These can be manipulated directly via the
//  * JPEG memory manager, or handed off to jpeg_write_coefficients().
//  * To release the memory occupied by the virtual arrays, call
//  * jpeg_finish_decompress() when done with the data.
//  *
//  * Returns NULL if suspended.  This case need be checked only if
//  * a suspending data source is used.

GLOBAL jvirt_barray_ptr *
jpeg_read_coefficients (j_decompress_ptr cinfo)
{
  if (cinfo->global_state == DSTATE_READY) {
    // First call: initialize active modules 
    transdecode_master_selection(cinfo);
    cinfo->global_state = DSTATE_RDCOEFS;
  } else if (cinfo->global_state != DSTATE_RDCOEFS)
    ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  // Absorb whole file into the coef buffer 
  for (;;) {
    int retcode;
    // Call progress monitor hook if present 
    if (cinfo->progress != NULL)
      (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
    // Absorb some more input 
    retcode = (*cinfo->inputctl->consume_input) (cinfo);
    if (retcode == JPEG_SUSPENDED)
      return NULL;
    if (retcode == JPEG_REACHED_EOI)
      break;
    // Advance progress counter if appropriate 
    if (cinfo->progress != NULL &&
	(retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
      if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
	// startup underestimated number of scans; ratchet up one scan 
	cinfo->progress->pass_limit += (LONG) cinfo->total_iMCU_rows;
      }
    }
  }
  // Set state so that jpeg_finish_decompress does the right thing 
  cinfo->global_state = DSTATE_STOPPING;
  return cinfo->coef->coef_arrays;
}


//  * Master selection of decompression modules for transcoding.
//  * This substitutes for jdmaster.c's initialization of the full decompressor.

LOCAL void
transdecode_master_selection (j_decompress_ptr cinfo)
{
  // Entropy decoding: either Huffman or arithmetic coding. 
  if (cinfo->arith_code) {
    ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
  } else {
    if (cinfo->progressive_mode) {
#ifdef D_PROGRESSIVE_SUPPORTED
      jinit_phuff_decoder(cinfo);
#else
      ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
    } else
      jinit_huff_decoder(cinfo);
  }

  // Always get a full-image coefficient buffer. 
  jinit_d_coef_controller(cinfo, TRUE);

  // We can now tell the memory manager to allocate virtual arrays. 
  (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);

  // Initialize input side of decompressor to consume first scan. 
  (*cinfo->inputctl->start_input_pass) (cinfo);

  // Initialize progress monitoring. 
  if (cinfo->progress != NULL) {
    int nscans;
    // Estimate number of scans to set pass_limit. 
    if (cinfo->progressive_mode) {
      // Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. 
      nscans = 2 + 3 * cinfo->num_components;
    } else if (cinfo->inputctl->has_multiple_scans) {
      // For a nonprogressive multiscan file, estimate 1 scan per component. 
      nscans = cinfo->num_components;
    } else {
      nscans = 1;
    }
    cinfo->progress->pass_counter = 0L;
    cinfo->progress->pass_limit = (LONG) cinfo->total_iMCU_rows * nscans;
    cinfo->progress->completed_passes = 0;
    cinfo->progress->total_passes = 1;
  }
}