//Module name: libbps
//Author: Alcaro
//Date: November 7, 2015
//Licence: GPL v3.0 or higher

#include "libbps.h"

#include <stdlib.h>//malloc, realloc, free
#include <string.h>//memcpy, memset
#include <stdint.h>//uint8_t, uint32_t
#include "crc32.h"//crc32

static uint32_t read32(uint8_t * ptr)
{
	uint32_t out;
	out =ptr[0];
	out|=ptr[1]<<8;
	out|=ptr[2]<<16;
	out|=ptr[3]<<24;
	return out;
}

enum { SourceRead, TargetRead, SourceCopy, TargetCopy };

static bool try_add(size_t& a, size_t b)
{
	if (SIZE_MAX-a < b) return false;
	a+=b;
	return true;
}

static bool try_shift(size_t& a, size_t b)
{
	if (SIZE_MAX>>b < a) return false;
	a<<=b;
	return true;
}

static bool decodenum(const uint8_t*& ptr, size_t& out)
{
	out=0;
	unsigned int shift=0;
	while (true)
	{
		uint8_t next=*ptr++;
		size_t addthis=(next&0x7F);
		if (shift) addthis++;
		if (!try_shift(addthis, shift)) return false;
		// unchecked because if it was shifted, the lowest bit is zero, and if not, it's <=0x7F.
		if (!try_add(out, addthis)) return false;
		if (next&0x80) return true;
		shift+=7;
	}
}

#define error(which) do { error=which; goto exit; } while(0)
#define assert_sum(a,b) do { if (SIZE_MAX-(a)<(b)) error(bps_too_big); } while(0)
#define assert_shift(a,b) do { if (SIZE_MAX>>(b)<(a)) error(bps_too_big); } while(0)
enum bpserror bps_apply(struct mem patch, struct mem in, struct mem * out, struct mem * metadata, bool accept_wrong_input)
{
	enum bpserror error = bps_ok;
	out->len=0;
	out->ptr=NULL;
	if (metadata)
	{
		metadata->len=0;
		metadata->ptr=NULL;
	}
	if (patch.len<4+3+12) return bps_broken;
	
	if (true)
	{
#define read8() (*(patchat++))
#define decodeto(var) \
				do { \
					if (!decodenum(patchat, var)) error(bps_too_big); \
				} while(false)
#define write8(byte) (*(outat++)=byte)
		
		const uint8_t * patchat=patch.ptr;
		const uint8_t * patchend=patch.ptr+patch.len-12;
		
		if (read8()!='B') error(bps_broken);
		if (read8()!='P') error(bps_broken);
		if (read8()!='S') error(bps_broken);
		if (read8()!='1') error(bps_broken);
		
		uint32_t crc_in_e = read32(patch.ptr+patch.len-12);
		uint32_t crc_out_e = read32(patch.ptr+patch.len-8);
		uint32_t crc_patch_e = read32(patch.ptr+patch.len-4);
		
		uint32_t crc_in_a = crc32(in.ptr, in.len);
		uint32_t crc_patch_a = crc32(patch.ptr, patch.len-4);
		
		if (crc_patch_a != crc_patch_e) error(bps_broken);
		
		size_t inlen;
		decodeto(inlen);
		
		size_t outlen;
		decodeto(outlen);
		
		if (inlen!=in.len || crc_in_a!=crc_in_e)
		{
			if (in.len==outlen && crc_in_a==crc_out_e) error=bps_to_output;
			else error=bps_not_this;
			if (!accept_wrong_input) goto exit;
		}
		
		out->len=outlen;
		out->ptr=(uint8_t*)malloc(outlen);
		
		const uint8_t * instart=in.ptr;
		const uint8_t * inreadat=in.ptr;
		const uint8_t * inend=in.ptr+in.len;
		
		uint8_t * outstart=out->ptr;
		uint8_t * outreadat=out->ptr;
		uint8_t * outat=out->ptr;
		uint8_t * outend=out->ptr+out->len;
		
		size_t metadatalen;
		decodeto(metadatalen);
		
		if (metadata && metadatalen)
		{
			metadata->len=metadatalen;
			metadata->ptr=(uint8_t*)malloc(metadatalen+1);
			for (size_t i=0;i<metadatalen;i++) metadata->ptr[i]=read8();
			metadata->ptr[metadatalen]='\0';//just to be on the safe side - that metadata is assumed to be text, might as well terminate it
		}
		else
		{
			for (size_t i=0;i<metadatalen;i++) (void)read8();
		}
		
		while (patchat<patchend)
		{
			size_t thisinstr;
			decodeto(thisinstr);
			size_t length=(thisinstr>>2)+1;
			int action=(thisinstr&3);
			if (outat+length>outend) error(bps_broken);
			
			switch (action)
			{
				case SourceRead:
				{
					if (outat-outstart+length > in.len) error(bps_broken);
					for (size_t i=0;i<length;i++)
					{
						size_t pos = outat-outstart; // don't inline, write8 changes outat
						write8(instart[pos]);
					}
				}
				break;
				case TargetRead:
				{
					if (patchat+length>patchend) error(bps_broken);
					for (size_t i=0;i<length;i++) write8(read8());
				}
				break;
				case SourceCopy:
				{
					size_t encodeddistance;
					decodeto(encodeddistance);
					size_t distance=encodeddistance>>1;
					if ((encodeddistance&1)==0) inreadat+=distance;
					else inreadat-=distance;
					
					if (inreadat<instart || inreadat+length>inend) error(bps_broken);
					for (size_t i=0;i<length;i++) write8(*inreadat++);
				}
				break;
				case TargetCopy:
				{
					size_t encodeddistance;
					decodeto(encodeddistance);
					size_t distance=encodeddistance>>1;
					if ((encodeddistance&1)==0) outreadat+=distance;
					else outreadat-=distance;
					
					if (outreadat<outstart || outreadat>=outat || outreadat+length>outend) error(bps_broken);
					for (size_t i=0;i<length;i++) write8(*outreadat++);
				}
				break;
			}
		}
		if (patchat!=patchend) error(bps_broken);
		if (outat!=outend) error(bps_broken);
		
		uint32_t crc_out_a = crc32(out->ptr, out->len);
		
		if (crc_out_a!=crc_out_e)
		{
			error=bps_not_this;
			if (!accept_wrong_input) goto exit;
		}
		return error;
#undef read8
#undef decodeto
#undef write8
	}
	
exit:
	free(out->ptr);
	out->len=0;
	out->ptr=NULL;
	if (metadata)
	{
		free(metadata->ptr);
		metadata->len=0;
		metadata->ptr=NULL;
	}
	return error;
}



#define write(val) \
			do { \
				out[outlen++]=(val); \
				if (outlen==outbuflen) \
				{ \
					outbuflen*=2; \
					uint8_t* newout=(uint8_t*)realloc(out, outbuflen); \
					if (!newout) { free(out); return bps_out_of_mem; } \
					out=newout; \
				} \
			} while(0)
#define write32(val) \
			do { \
				uint32_t tmp=(val); \
				write(tmp); \
				write(tmp>>8); \
				write(tmp>>16); \
				write(tmp>>24); \
			} while(0)
#define writenum(val) \
			do { \
				size_t tmpval=(val); \
				while (true) \
				{ \
					uint8_t tmpbyte=(tmpval&0x7F); \
					tmpval>>=7; \
					if (!tmpval) \
					{ \
						write(tmpbyte|0x80); \
						break; \
					} \
					write(tmpbyte); \
					tmpval--; \
				} \
			} while(0)

enum bpserror bps_create_linear(struct mem sourcemem, struct mem targetmem, struct mem metadata, struct mem * patchmem)
{
	if (sourcemem.len>=(SIZE_MAX>>2) - 16) return bps_too_big;//the 16 is just to be on the safe side, I don't think it's needed.
	if (targetmem.len>=(SIZE_MAX>>2) - 16) return bps_too_big;
	
	const uint8_t * source=sourcemem.ptr;
	const uint8_t * sourceend=sourcemem.ptr+sourcemem.len;
	if (sourcemem.len>targetmem.len) sourceend=sourcemem.ptr+targetmem.len;
	const uint8_t * targetbegin=targetmem.ptr;
	const uint8_t * target=targetmem.ptr;
	const uint8_t * targetend=targetmem.ptr+targetmem.len;
	
	const uint8_t * targetcopypos=targetbegin;
	
	size_t outbuflen=4096;
	uint8_t * out=(uint8_t*)malloc(outbuflen);
	if (!out) return bps_out_of_mem;
	size_t outlen=0;
	write('B');
	write('P');
	write('S');
	write('1');
	writenum(sourcemem.len);
	writenum(targetmem.len);
	writenum(metadata.len);
	for (size_t i=0;i<metadata.len;i++) write(metadata.ptr[i]);
	
	size_t mainContentPos=outlen;
	
	const uint8_t * lastknownchange=targetbegin;
	while (target<targetend)
	{
		size_t numunchanged=0;
		while (source+numunchanged<sourceend && source[numunchanged]==target[numunchanged]) numunchanged++;
		if (numunchanged>1 || numunchanged == (uintptr_t)(targetend-target))
		{
			//assert_shift((numunchanged-1), 2);
			writenum((numunchanged-1)<<2 | 0);//SourceRead
			source+=numunchanged;
			target+=numunchanged;
		}
		
		size_t numchanged=0;
		if (lastknownchange>target) numchanged=lastknownchange-target;
		while ((source+numchanged>=sourceend ||
		        source[numchanged]!=target[numchanged] ||
		        source[numchanged+1]!=target[numchanged+1] ||
		        source[numchanged+2]!=target[numchanged+2]) &&
		       target+numchanged<targetend)
		{
			numchanged++;
			if (source+numchanged>=sourceend) numchanged=targetend-target;
		}
		lastknownchange=target+numchanged;
		if (numchanged)
		{
			//assert_shift((numchanged-1), 2);
			size_t rle1start=(target==targetbegin);
			while (true)
			{
				if (
					target[rle1start-1]==target[rle1start+0] &&
					target[rle1start+0]==target[rle1start+1] &&
					target[rle1start+1]==target[rle1start+2] &&
					target[rle1start+2]==target[rle1start+3])
				{
					numchanged=rle1start;
					break;
				}
				if (
					target[rle1start-2]==target[rle1start+0] &&
					target[rle1start-1]==target[rle1start+1] &&
					target[rle1start+0]==target[rle1start+2] &&
					target[rle1start+1]==target[rle1start+3] &&
					target[rle1start+2]==target[rle1start+4])
				{
					numchanged=rle1start;
					break;
				}
				if (rle1start+3>=numchanged) break;
				rle1start++;
			}
			if (numchanged)
			{
				writenum((numchanged-1)<<2 | TargetRead);
				for (size_t i=0;i<numchanged;i++)
				{
					write(target[i]);
				}
				source+=numchanged;
				target+=numchanged;
			}
			if (target[-2]==target[0] && target[-1]==target[1] && target[0]==target[2])
			{
				//two-byte RLE
				size_t rlelen=0;
				while (target+rlelen<targetend && target[0]==target[rlelen+0] && target[1]==target[rlelen+1]) rlelen+=2;
				writenum((rlelen-1)<<2 | TargetCopy);
				writenum((target-targetcopypos-2)<<1);
				source+=rlelen;
				target+=rlelen;
				targetcopypos=target-2;
			}
			else if (target[-1]==target[0] && target[0]==target[1])
			{
				//one-byte RLE
				size_t rlelen=0;
				while (target+rlelen<targetend && target[0]==target[rlelen]) rlelen++;
				writenum((rlelen-1)<<2 | TargetCopy);
				writenum((target-targetcopypos-1)<<1);
				source+=rlelen;
				target+=rlelen;
				targetcopypos=target-1;
			}
		}
	}
	
	write32(crc32(sourcemem.ptr, sourcemem.len));
	write32(crc32(targetmem.ptr, targetmem.len));
	write32(crc32(out, outlen));
	
	patchmem->ptr=out;
	patchmem->len=outlen;
	
	//while this may look like it can be fooled by a patch containing exactly one of any other command, it
	//  can't, because the ones that aren't SourceRead requires an argument
	size_t i;
	for (i=mainContentPos;(out[i]&0x80)==0x00;i++) {}
	if (i==outlen-12-1) return bps_identical;
	
	return bps_ok;
}

#undef write_nocrc
#undef write
#undef writenum

void bps_free(struct mem mem)
{
	free(mem.ptr);
}
#undef error



struct bpsinfo bps_get_info(file* patch, bool changefrac)
{
#define error(why) do { ret.error=why; return ret; } while(0)
	struct bpsinfo ret;
	size_t len = patch->len();
	if (len<4+3+12) error(bps_broken);
	
	uint8_t top[256];
	if (!patch->read(top, 0, len>256 ? 256 : len)) error(bps_io);
	if (memcmp(top, "BPS1", 4)) error(bps_broken);
	
	const uint8_t* patchdat=top+4;
	if (!decodenum(patchdat, ret.size_in)) error(bps_too_big);
	if (!decodenum(patchdat, ret.size_out)) error(bps_too_big);
	
	if (!decodenum(patchdat, ret.meta_size)) error(bps_too_big);
	ret.meta_start = patchdat - top;
	
	uint8_t checksums[12];
	if (!patch->read(checksums, len-12, 12)) error(bps_io);
	ret.crc_in  = read32(checksums+0);
	ret.crc_out = read32(checksums+4);
	ret.crc_patch=read32(checksums+8);
	
	if (changefrac && ret.size_in>0)
	{
		//algorithm: each command adds its length to the numerator, unless it's above 32, in which case
		// it adds 32; or if it's SourceRead, in which case it adds 0
		//denominator is just input length
		uint8_t* patchbin=(uint8_t*)malloc(len);
		patch->read(patchbin, 0, len);
		size_t outpos=0; // position in the output file
		size_t changeamt=0; // change score
		const uint8_t* patchat=patchbin+(patchdat-top);
		
		size_t metasize;
		if (!decodenum(patchat, metasize)) error(bps_too_big);
		patchat+=metasize;
		
		const uint8_t* patchend=patchbin+len-12;
		
		while (patchat<patchend && outpos<ret.size_in)
		{
			size_t thisinstr;
			decodenum(patchat, thisinstr);
			size_t length=(thisinstr>>2)+1;
			int action=(thisinstr&3);
			int min_len_32 = (length<32 ? length : 32);
			
			switch (action)
			{
				case SourceRead:
				{
					changeamt+=0;
				}
				break;
				case TargetRead:
				{
					changeamt+=min_len_32;
					patchat+=length;
				}
				break;
				case SourceCopy:
				case TargetCopy:
				{
					changeamt+=min_len_32;
					size_t ignore;
					decodenum(patchat, ignore);
				}
				break;
			}
			outpos+=length;
		}
		if (patchat>patchend || outpos>ret.size_out) error(bps_broken);
		ret.change_num = (changeamt<ret.size_in ? changeamt : ret.size_in);
		ret.change_denom = ret.size_in;
		
		free(patchbin);
	}
	else
	{
		//this also happens if change fraction is not requested, but it's undefined behaviour anyways.
		ret.change_num=1;
		ret.change_denom=1;
	}
	
	ret.error=bps_ok;
	return ret;
}



#ifdef BPS_DEBUG
#warning Disable this in release versions.

#include <stdio.h>

//Congratulations, you found the undocumented features! They disassemble a patch, telling what it
// does; compare two equivalent BPS patches and tells where each one is more compact.
//They crash or give bogus answers on invalid patches, latter also misbehaves on non-equivalent ones.
//Have fun.
void bps_dump(struct mem patch)
{
#define read8() (*(patchat++))
#define decodeto(var) decodenum(patchat, var)
	const uint8_t * patchat=patch.ptr;
	const uint8_t * patchend=patch.ptr+patch.len-12;
	
	read8();
	read8();
	read8();
	read8();
	
	size_t inreadat = 0;
	size_t inlen;
	decodeto(inlen);
	
	size_t outat = 0;
	size_t outreadat = 0;
	size_t outlen;
	decodeto(outlen);
	
	size_t metadatalen;
	decodeto(metadatalen);
	
	patchat += metadatalen;
	
	while (patchat<patchend)
	{
		size_t thisinstr;
		decodeto(thisinstr);
		size_t length=(thisinstr>>2)+1;
		int action=(thisinstr&3);
		
		switch (action)
		{
			case SourceRead:
			{
				printf("SourceRead %zu from %zu to %zu (0)\n", length, outat, outat);
				outat += length;
			}
			break;
			case TargetRead:
			{
				printf("TargetRead %zu to %zu\n", length, outat);
				patchat += length;
				outat += length;
			}
			break;
			case SourceCopy:
			{
				size_t encodeddistance;
				decodeto(encodeddistance);
				size_t distance=encodeddistance>>1;
				if ((encodeddistance&1)==0) inreadat+=distance;
				else inreadat-=distance;
				
				printf("SourceCopy %zu from %zu to %zu (%+zi)\n", length, inreadat, outat, inreadat-outat);
				inreadat += length;
				outat += length;
			}
			break;
			case TargetCopy:
			{
				size_t encodeddistance;
				decodeto(encodeddistance);
				size_t distance=encodeddistance>>1;
				if ((encodeddistance&1)==0) outreadat+=distance;
				else outreadat-=distance;
				
				printf("TargetCopy %zu from %zu to %zu (%+zi)\n", length, outreadat, outat, outreadat-outat);
				outreadat += length;
				outat += length;
			}
			break;
		}
	}
	
	printf("sanity check: %zu=%zu (%+zi), ", patchat-patch.ptr, patchend-patch.ptr, patchat-patchend);
	printf("%zu=%zu (%+zi)", outat, outlen, outat-outlen);
#undef read8
#undef decodeto
}

void bps_compare(struct mem patch1mem, struct mem patch2mem)
{
	const uint8_t * patch[2]={patch1mem.ptr, patch2mem.ptr};
	size_t patchpos[2]={0,0};
	size_t patchlen[2]={patch1mem.len-12, patch2mem.len-12};
	size_t patchoutpos[2]={0,0};
	
	size_t patchcopypos[2][4]={0,0};//[0] and [1] are unused, but this is just debug code, it doesn't need to be neat.
	
#define read8(id) (patch[id][patchpos[id]++])
#define decodeto(id, var) \
				do { \
					var=0; \
					int shift=0; \
					while (true) \
					{ \
						uint8_t next=read8(id); \
						size_t addthis=(next&0x7F)<<shift; \
						var+=addthis; \
						if (next&0x80) break; \
						shift+=7; \
						var+=1<<shift; \
					} \
				} while(false)
	
	size_t lastmatch=0;
	size_t patchposatmatch[2]={0,0};
	
	size_t outlen;
	patch[0]+=4; patch[1]+=4;//BPS1
	size_t tempuint;
	decodeto(0, tempuint); decodeto(1, tempuint);//source-size
	decodeto(0, outlen); decodeto(1, outlen);//target-size
	decodeto(0, tempuint); patch[0]+=tempuint;//metadata
	decodeto(1, tempuint); patch[1]+=tempuint;//metadata
	
	bool show=false;
	while (patchpos[0]<patchlen[0] && patchpos[1]<patchlen[1])
	{
		bool step[2]={(patchoutpos[0]<=patchoutpos[1]), (patchoutpos[0]>=patchoutpos[1])};
		char describe[2][256];
		for (int i=0;i<2;i++)
		{
			if (step[i])
			{
				size_t patchposstart=patchpos[i];
				decodeto(i, tempuint);
				size_t len=(tempuint>>2)+1;
				patchoutpos[i]+=len;
				int action=(tempuint&3);
//enum { SourceRead, TargetRead, SourceCopy, TargetCopy };
				const char * actionnames[]={"SourceRead", "TargetRead", "SourceCopy", "TargetCopy"};
				if (action==TargetRead) patchpos[i]+=len;
				if (action==SourceCopy || action==TargetCopy)
				{
					decodeto(i, tempuint);
					int delta = tempuint>>1;
					if (tempuint&1) delta=-delta;
					patchcopypos[i][action]+=delta;
					sprintf(describe[i], "%s from %zu (%+i) for %zu in %zu",  actionnames[action], patchcopypos[i][action], delta, len, patchpos[i]-patchposstart);
					patchcopypos[i][action]+=len;
				}
				else sprintf(describe[i], "%s from %zu for %zu in %zu",  actionnames[action], patchoutpos[i], len, patchpos[i]-patchposstart);
				if (!step[i^1])
				{
					printf("%i: %s\n", i+1, describe[i]);
					show=true;
				}
			}
		}
		if (step[0] && step[1])
		{
			if (!strcmp(describe[0], describe[1])) /*printf("3: %s\n", describe[0])*/;
			else
			{
				printf("1: %s\n2: %s\n", describe[0], describe[1]);
				show=true;
			}
		}
		if (patchoutpos[0]==patchoutpos[1])
		{
			size_t used[2]={patchpos[0]-patchposatmatch[0], patchpos[1]-patchposatmatch[1]};
			char which='=';
			if (used[0]<used[1]) which='+';
			if (used[0]>used[1]) which='-';
			if (show)
			{
				printf("%c: %zu,%zu bytes since last match (%zu)\n", which, used[0], used[1], patchoutpos[0]);
				show=false;
			}
			patchposatmatch[0]=patchpos[0];
			patchposatmatch[1]=patchpos[1];
			lastmatch=patchoutpos[0];
		}
	}
#undef read8
#undef decodeto
}

static struct mem ReadWholeFile(const char * filename)
{
	struct mem null = {NULL, 0};
	
	FILE * file=fopen(filename, "rb");
	if (!file) return null;
	fseek(file, 0, SEEK_END);
	size_t len=ftell(file);
	fseek(file, 0, SEEK_SET);
	unsigned char * data=(unsigned char*)malloc(len);
	size_t truelen=fread(data, 1,len, file);
	fclose(file);
	if (len!=truelen)
	{
		free(data);
		return null;
	}
	
	struct mem ret = { (unsigned char*)data, len };
	return ret;
}

int main(int argc,char**argv)
{
	if (argc==1) puts("bad arguments");
	if (argc==2) bps_dump(ReadWholeFile(argv[1]));
	if (argc==3) bps_compare(ReadWholeFile(argv[1]),ReadWholeFile(argv[2]));
}
#endif