/**
 * File: GIF Input
 *
 * Read GIF images.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
#include "gd.h"

/* Used only when debugging GIF compression code */
/* #define DEBUGGING_ENVARS */

#ifdef DEBUGGING_ENVARS

static int verbose_set = 0;
static int verbose;

#define VERBOSE (verbose_set ? verbose : set_verbose())

static int set_verbose(void)
{
	verbose = !!getenv("GIF_VERBOSE");
	verbose_set = 1;
	return(verbose);
}

#else

#define VERBOSE	0

#endif

#define MAXCOLORMAPSIZE	256

#define TRUE	1
#define FALSE	0

#define CM_RED		0
#define CM_GREEN	1
#define CM_BLUE		2

#define MAX_LWZ_BITS	12

#define INTERLACE		0x40
#define LOCALCOLORMAP	0x80

#define BitSet(byte, bit)	(((byte) & (bit)) == (bit))

#define ReadOK(file, buffer, len) (gdGetBuf(buffer, len, file) == len)

#define LM_to_uint(a, b)	(((b)<<8)|(a))

/* We may eventually want to use this information, but def it out for now */
#if 0
static struct {
	unsigned int    Width;
	unsigned int    Height;
	unsigned char   ColorMap[3][MAXCOLORMAPSIZE];
	unsigned int    BitPixel;
	unsigned int    ColorResolution;
	unsigned int    Background;
	unsigned int    AspectRatio;
} GifScreen;
#endif

#if 0
static struct {
	int     transparent;
	int     delayTime;
	int     inputFlag;
	int     disposal;
} Gif89 = { -1, -1, -1, 0 };
#endif

#define STACK_SIZE ((1<<(MAX_LWZ_BITS))*2)

#define CSD_BUF_SIZE 280

typedef struct {
	unsigned char buf[CSD_BUF_SIZE];
	int curbit;
	int lastbit;
	int done;
	int last_byte;
} CODE_STATIC_DATA;

typedef struct {
	int fresh;
	int code_size, set_code_size;
	int max_code, max_code_size;
	int firstcode, oldcode;
	int clear_code, end_code;
	int table[2][(1<< MAX_LWZ_BITS)];
	int stack[STACK_SIZE], *sp;
	CODE_STATIC_DATA scd;
} LZW_STATIC_DATA;

static int ReadColorMap (gdIOCtx *fd, int number, unsigned char (*buffer)[256]);
static int DoExtension (gdIOCtx *fd, int label, int *Transparent, int *ZeroDataBlockP);
static int GetDataBlock (gdIOCtx *fd, unsigned char *buf, int *ZeroDataBlockP);
static int GetCode (gdIOCtx *fd, CODE_STATIC_DATA *scd, int code_size, int flag, int *ZeroDataBlockP);
static int LWZReadByte (gdIOCtx *fd, LZW_STATIC_DATA *sd, char flag, int input_code_size, int *ZeroDataBlockP);

static void ReadImage (gdImagePtr im, gdIOCtx *fd, int len, int height, unsigned char (*cmap)[256], int interlace, int *ZeroDataBlockP); /*1.4//, int ignore); */

/*
  Function: gdImageCreateFromGif

    <gdImageCreateFromGif> is called to load images from GIF format
    files. Invoke <gdImageCreateFromGif> with an already opened
    pointer to a file containing the desired
    image.

    <gdImageCreateFromGif> returns a <gdImagePtr> to the new image, or
    NULL if unable to load the image (most often because the file is
    corrupt or does not contain a GIF image). <gdImageCreateFromGif>
    does not close the file. You can inspect the sx and sy members of
    the image to determine its size. The image must eventually be
    destroyed using <gdImageDestroy>.

  Variants:

    <gdImageCreateFromGifPtr> creates an image from GIF data (i.e. the
    contents of a GIF file) already in memory.

    <gdImageCreateFromGifCtx> reads in an image using the functions in
    a <gdIOCtx> struct.

  Parameters:

    infile - The input FILE pointer

  Returns:

    A pointer to the new image or NULL if an error occurred.

  Example:

    > gdImagePtr im;
    > ... inside a function ...
    > FILE *in;
    > in = fopen("mygif.gif", "rb");
    > im = gdImageCreateFromGif(in);
    > fclose(in);
    > // ... Use the image ...
    > gdImageDestroy(im);

*/
BGD_DECLARE(gdImagePtr) gdImageCreateFromGif(FILE *fdFile)
{
	gdIOCtx *fd = gdNewFileCtx(fdFile);
	gdImagePtr im;

	if (fd == NULL) return NULL;
	im = gdImageCreateFromGifCtx(fd);

	fd->gd_free(fd);

	return im;
}

/*
  Function: gdImageCreateFromGifPtr

  Parameters:

    size - size of GIF data in bytes.
    data - GIF data (i.e. contents of a GIF file).

  See <gdImageCreateFromGif>.
*/
BGD_DECLARE(gdImagePtr) gdImageCreateFromGifPtr (int size, void *data)
{
	gdImagePtr im;
	gdIOCtx *in = gdNewDynamicCtxEx(size, data, 0);
	if(!in) {
		return 0;
	}
	im = gdImageCreateFromGifCtx(in);
	in->gd_free(in);
	return im;
}

/*
  Function: gdImageCreateFromGifCtx

  See <gdImageCreateFromGif>.
*/
BGD_DECLARE(gdImagePtr) gdImageCreateFromGifCtx(gdIOCtxPtr fd)
{
	int BitPixel;
#if 0
	int ColorResolution;
	int Background;
	int AspectRatio;
#endif
	int Transparent = (-1);
	unsigned char buf[16];
	unsigned char c;
	unsigned char ColorMap[3][MAXCOLORMAPSIZE];
	unsigned char localColorMap[3][MAXCOLORMAPSIZE];
	int imw, imh, screen_width, screen_height;
	int useGlobalColormap;
	int bitPixel, i;
	/*1.4//int             imageCount = 0; */
	/* 2.0.28: threadsafe storage */
	int ZeroDataBlock = FALSE;
	int haveGlobalColormap;

	gdImagePtr im = 0;

	memset(ColorMap, 0, 3 * MAXCOLORMAPSIZE);
	memset(localColorMap, 0, 3 * MAXCOLORMAPSIZE);

	if(!ReadOK(fd, buf, 6)) {
		return 0;
	}

	if(strncmp((char *)buf, "GIF", 3) != 0) {
		return 0;
	}

	if(memcmp((char *)buf + 3, "87a", 3) == 0) {
		/* GIF87a */
	} else if(memcmp((char *)buf + 3, "89a", 3) == 0) {
		/* GIF89a */
	} else {
		return 0;
	}

	if(!ReadOK(fd, buf, 7)) {
		return 0;
	}

	BitPixel = 2 << (buf[4] & 0x07);
#if 0
	ColorResolution = (int) (((buf[4]&0x70)>>3)+1);
	Background = buf[5];
	AspectRatio = buf[6];
#endif
	screen_width = imw = LM_to_uint(buf[0], buf[1]);
	screen_height = imh = LM_to_uint(buf[2], buf[3]);

	haveGlobalColormap = BitSet(buf[4], LOCALCOLORMAP); /* Global Colormap */
	if(haveGlobalColormap) {
		if(ReadColorMap(fd, BitPixel, ColorMap)) {
			return 0;
		}
	}

	for (;;) {
		int top, left;
		int width, height;

		if(!ReadOK(fd, &c, 1)) {
			return 0;
		}

		if (c == ';') { /* GIF terminator */
			goto terminated;
		}

		if(c == '!') { /* Extension */
			if(!ReadOK(fd, &c, 1)) {
				return 0;
			}

			DoExtension(fd, c, &Transparent, &ZeroDataBlock);
			continue;
		}

		if(c != ',') { /* Not a valid start character */
			continue;
		}

		/*1.4//++imageCount; */

		if(!ReadOK(fd, buf, 9)) {
			return 0;
		}

		useGlobalColormap = !BitSet(buf[8], LOCALCOLORMAP);

		bitPixel = 1 << ((buf[8] & 0x07) + 1);
		left = LM_to_uint(buf[0], buf[1]);
		top = LM_to_uint(buf[2], buf[3]);
		width = LM_to_uint(buf[4], buf[5]);
		height = LM_to_uint(buf[6], buf[7]);

		if(((left + width) > screen_width) || ((top + height) > screen_height)) {
			if(VERBOSE) {
				printf("Frame is not confined to screen dimension.\n");
			}
			return 0;
		}

		if(!(im = gdImageCreate(width, height))) {
			return 0;
		}

		im->interlace = BitSet(buf[8], INTERLACE);
		if(!useGlobalColormap) {
			if(ReadColorMap(fd, bitPixel, localColorMap)) {
				gdImageDestroy(im);
				return 0;
			}

			ReadImage(im, fd, width, height, localColorMap, BitSet(buf[8], INTERLACE), &ZeroDataBlock);
		} else {
			if(!haveGlobalColormap) {
				// Still a valid gif, apply simple default palette as per spec
				ColorMap[CM_RED][1] = 0xff;
				ColorMap[CM_GREEN][1] = 0xff;
				ColorMap[CM_BLUE][1] = 0xff;
			}

			ReadImage(im, fd, width, height, ColorMap, BitSet(buf[8], INTERLACE), &ZeroDataBlock);
		}

		if(Transparent != (-1)) {
			gdImageColorTransparent(im, Transparent);
		}

		goto terminated;
	}

terminated:
	/* Terminator before any image was declared! */
	if(!im) {
		return 0;
	}

	/* Check for open colors at the end, so
	 * we can reduce colorsTotal and ultimately
	 * BitsPerPixel */
	for(i = im->colorsTotal - 1; i >= 0; i--) {
		if(im->open[i]) {
			im->colorsTotal--;
		} else {
			break;
		}
	}

	if(!im->colorsTotal) {
		gdImageDestroy(im);
		return 0;
	}

	return im;
}

static int
ReadColorMap(gdIOCtx *fd, int number, unsigned char (*buffer)[256])
{
	int i;
	unsigned char rgb[3];

	for(i = 0; i < number; ++i) {
		if(!ReadOK(fd, rgb, sizeof(rgb))) {
			return TRUE;
		}

		buffer[CM_RED][i] = rgb[0];
		buffer[CM_GREEN][i] = rgb[1];
		buffer[CM_BLUE][i] = rgb[2];
	}

	return FALSE;
}

static int
DoExtension(gdIOCtx *fd, int label, int *Transparent, int *ZeroDataBlockP)
{
	unsigned char buf[256];

	switch(label) {
	case 0xf9: /* Graphic Control Extension */
		memset(buf, 0, 4); /* initialize a few bytes in the case the next function fails */
		(void) GetDataBlock(fd, (unsigned char*) buf, ZeroDataBlockP);
#if 0
		Gif89.disposal  = (buf[0] >> 2) & 0x7;
		Gif89.inputFlag = (buf[0] >> 1) & 0x1;
		Gif89.delayTime = LM_to_uint(buf[1], buf[2]);
#endif
		if((buf[0] & 0x1) != 0) {
			*Transparent = buf[3];
		}

		while(GetDataBlock(fd, (unsigned char*) buf, ZeroDataBlockP) > 0);

		return FALSE;

	default:
		break;
	}

	while(GetDataBlock(fd, (unsigned char*) buf, ZeroDataBlockP) > 0);

	return FALSE;
}

static int
GetDataBlock_(gdIOCtx *fd, unsigned char *buf, int *ZeroDataBlockP)
{
	unsigned char count;

	if(!ReadOK(fd, &count, 1)) {
		return -1;
	}

	*ZeroDataBlockP = count == 0;

	if((count != 0) && (!ReadOK(fd, buf, count))) {
		return -1;
	}

	return count;
}

static int
GetDataBlock(gdIOCtx *fd, unsigned char *buf, int *ZeroDataBlockP)
{
	int rv, i;

	rv = GetDataBlock_(fd,buf, ZeroDataBlockP);

	if(VERBOSE) {
		printf("[GetDataBlock returning %d",rv);
		if(rv > 0) {
			printf(":");
			for(i = 0; i < rv; i++) {
				printf(" %02x",buf[i]);
			}
		}
		printf("]\n");
	}

	return rv;
}

static int
GetCode_(gdIOCtx *fd, CODE_STATIC_DATA *scd, int code_size, int flag, int *ZeroDataBlockP)
{
	int i, j, ret;
	int count;

	if(flag) {
		scd->curbit = 0;
		scd->lastbit = 0;
		scd->last_byte = 2;
		scd->done = FALSE;
		return 0;
	}

	if((scd->curbit + code_size) >= scd->lastbit) {
		if(scd->done) {
			if(scd->curbit >= scd->lastbit) {
				/* Oh well */
			}
			return -1;
		}

		scd->buf[0] = scd->buf[scd->last_byte - 2];
		scd->buf[1] = scd->buf[scd->last_byte - 1];

		if((count = GetDataBlock(fd, &scd->buf[2], ZeroDataBlockP)) <= 0) {
			scd->done = TRUE;
		}

		scd->last_byte = 2 + count;
		scd->curbit = (scd->curbit - scd->lastbit) + 16;
		scd->lastbit = (2 + count) * 8;
	}

	if ((scd->curbit + code_size - 1) >= (CSD_BUF_SIZE * 8)) {
		ret = -1;
	} else {
		ret = 0;
		for (i = scd->curbit, j = 0; j < code_size; ++i, ++j) {
			ret |= ((scd->buf[i / 8] & (1 << (i % 8))) != 0) << j;
		}
	}

	scd->curbit += code_size;

	return ret;
}

static int
GetCode(gdIOCtx *fd, CODE_STATIC_DATA *scd, int code_size, int flag, int *ZeroDataBlockP)
{
	int rv;

	rv = GetCode_(fd, scd, code_size,flag, ZeroDataBlockP);

	if(VERBOSE) {
		printf("[GetCode(,%d,%d) returning %d]\n",code_size,flag,rv);
	}

	return rv;
}

static int
LWZReadByte_(gdIOCtx *fd, LZW_STATIC_DATA *sd, char flag, int input_code_size, int *ZeroDataBlockP)
{
	int code, incode, i;

	if(flag) {
		sd->set_code_size = input_code_size;
		sd->code_size = sd->set_code_size + 1;
		sd->clear_code = 1 << sd->set_code_size;
		sd->end_code = sd->clear_code + 1;
		sd->max_code_size = 2 * sd->clear_code;
		sd->max_code = sd->clear_code + 2;

		GetCode(fd, &sd->scd, 0, TRUE, ZeroDataBlockP);

		sd->fresh = TRUE;

		for(i = 0; i < sd->clear_code; ++i) {
			sd->table[0][i] = 0;
			sd->table[1][i] = i;
		}

		for(; i < (1 << MAX_LWZ_BITS); ++i) {
			sd->table[0][i] = sd->table[1][0] = 0;
		}

		sd->sp = sd->stack;

		return 0;

	} else if(sd->fresh) {
		sd->fresh = FALSE;

		do {
			sd->firstcode = sd->oldcode =
			                    GetCode(fd, &sd->scd, sd->code_size, FALSE, ZeroDataBlockP);
		} while(sd->firstcode == sd->clear_code);

		return sd->firstcode;
	}

	if(sd->sp > sd->stack) {
		return *--sd->sp;
	}

	while((code = GetCode(fd, &sd->scd, sd->code_size, FALSE, ZeroDataBlockP)) >= 0) {
		if(code == sd->clear_code) {
			for(i = 0; i < sd->clear_code; ++i) {
				sd->table[0][i] = 0;
				sd->table[1][i] = i;
			}

			for (; i < (1 << MAX_LWZ_BITS); ++i) {
				sd->table[0][i] = sd->table[1][i] = 0;
			}

			sd->code_size = sd->set_code_size + 1;
			sd->max_code_size = 2 * sd->clear_code;
			sd->max_code = sd->clear_code + 2;
			sd->sp = sd->stack;
			sd->firstcode = sd->oldcode =
			                    GetCode(fd, &sd->scd, sd->code_size, FALSE, ZeroDataBlockP);

			return sd->firstcode;
		} else if(code == sd->end_code) {
			int count;
			unsigned char buf[260];

			if(*ZeroDataBlockP) {
				return -2;
			}

			while((count = GetDataBlock(fd, buf, ZeroDataBlockP)) > 0);

			if(count != 0) {
				return -2;
			}
		}

		incode = code;

		if(sd->sp == (sd->stack + STACK_SIZE)) {
			/* Bad compressed data stream */
			return -1;
		}

		if(code >= sd->max_code) {
			*sd->sp++ = sd->firstcode;
			code = sd->oldcode;
		}

		while(code >= sd->clear_code) {
			if(sd->sp == (sd->stack + STACK_SIZE)) {
				/* Bad compressed data stream */
				return -1;
			}
			if(code >= (1 << MAX_LWZ_BITS)) {
				/* Corrupted code */
				return -1;
			}

			*sd->sp++ = sd->table[1][code];

			if(code == sd->table[0][code]) {
				/* Oh well */
			}

			code = sd->table[0][code];
		}
		if(code >= (1 << MAX_LWZ_BITS)) {
			/* Corrupted code */
			return -1;
		}

		*sd->sp++ = sd->firstcode = sd->table[1][code];

		if((code = sd->max_code) < (1 << MAX_LWZ_BITS)) {
			sd->table[0][code] = sd->oldcode;
			sd->table[1][code] = sd->firstcode;
			++sd->max_code;

			if((sd->max_code >= sd->max_code_size) && (sd->max_code_size < (1<<MAX_LWZ_BITS))) {
				sd->max_code_size *= 2;
				++sd->code_size;
			}
		}

		sd->oldcode = incode;

		if(sd->sp > sd->stack) {
			return *--sd->sp;
		}
	}

	return code;
}

static int
LWZReadByte(gdIOCtx *fd, LZW_STATIC_DATA *sd, char flag, int input_code_size, int *ZeroDataBlockP)
{
	int rv;

	rv = LWZReadByte_(fd, sd, flag, input_code_size, ZeroDataBlockP);

	if(VERBOSE) {
		printf("[LWZReadByte(,%d,%d) returning %d]\n",flag,input_code_size,rv);
	}

	return rv;
}

static void
ReadImage(gdImagePtr im, gdIOCtx *fd, int len, int height, unsigned char (*cmap)[256], int interlace, int *ZeroDataBlockP) /*1.4//, int ignore) */
{
	unsigned char c;
	int xpos = 0, ypos = 0, pass = 0;
	int v, i;
	LZW_STATIC_DATA sd;

	/* Initialize the Compression routines */
	if(!ReadOK(fd, &c, 1)) {
		return;
	}

	if(c > MAX_LWZ_BITS) {
		return;
	}

	/* Stash the color map into the image */
	for(i=0; (i < gdMaxColors); i++) {
		im->red[i] = cmap[CM_RED][i];
		im->green[i] = cmap[CM_GREEN][i];
		im->blue[i] = cmap[CM_BLUE][i];
		im->open[i] = 1;
	}

	/* Many (perhaps most) of these colors will remain marked open. */
	im->colorsTotal = gdMaxColors;
	if(LWZReadByte(fd, &sd, TRUE, c, ZeroDataBlockP) < 0) {
		return;
	}

	/*
	**  If this is an "uninteresting picture" ignore it.
	**  REMOVED For 1.4
	*/
	/*if (ignore) { */
	/*        while (LWZReadByte(fd, &sd, FALSE, c) >= 0) */
	/*                ; */
	/*        return; */
	/*} */

	while((v = LWZReadByte(fd, &sd, FALSE, c, ZeroDataBlockP)) >= 0 ) {
		if(v >= gdMaxColors) {
			v = 0;
		}

		/* This how we recognize which colors are actually used. */
		if(im->open[v]) {
			im->open[v] = 0;
		}

		gdImageSetPixel(im, xpos, ypos, v);

		++xpos;
		if(xpos == len) {
			xpos = 0;
			if(interlace) {
				switch (pass) {
				case 0:
				case 1:
					ypos += 8;
					break;
				case 2:
					ypos += 4;
					break;
				case 3:
					ypos += 2;
					break;
				}

				if(ypos >= height) {
					++pass;
					switch (pass) {
					case 1:
						ypos = 4;
						break;
					case 2:
						ypos = 2;
						break;
					case 3:
						ypos = 1;
						break;
					default:
						goto fini;
					}
				}
			} else {
				++ypos;
			}
		}

		if(ypos >= height) {
			break;
		}
	}

fini:
	if(LWZReadByte(fd, &sd, FALSE, c, ZeroDataBlockP) >=0) {
		/* Ignore extra */
	}
}
