#include <ctype.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void usage(){
	fprintf(stderr,
		"Usage: c2bin [inputfile] [outputfile]\n"
		"\n"
		"Converts a C string to its parsed contents. The inverse of bin2c.\n"
		"Default values for the arguments are stdin and stdout; also '-' indicates the\n"
		"standard stream.\n");
}

int unhex(int c){
	if(c>='0'&&c<='9'){
		return c-'0';
	} else if(c>='a'&&c<='f'){
		return c-'a'+10;
	} else if(c>='A'&&c<='F'){
		return c-'A'+10;
	} else {
		return -1;
	}
}

void c2bin(FILE *input,FILE *output){
	bool stringmode=false;
	int c;
	while((c=fgetc(input))!=EOF){
		if(c=='"'){
			stringmode=!stringmode;
		} else if(!stringmode){
			if(!isspace(c)){
				fprintf(stderr,"Characters outside string\n");
				exit(1);
			}
		} else if(c=='\n'){
			fprintf(stderr,"Invalid newline in string\n");
			exit(1);
		} else if(c!='\\'){
			fputc(c,output);
		} else {
			c=fgetc(input);
			if(c==EOF){
				fprintf(stderr,"Invalid backslash at end of input\n");
				exit(1);
			} else if(c=='\n'){
				continue;
			} else if(c!='x'&&!isdigit(c)){
				switch(c){
					case 'a': fputc('\a',output); break;
					case 'b': fputc('\b',output); break;
					case 'f': fputc('\f',output); break;
					case 'n': fputc('\n',output); break;
					case 'r': fputc('\r',output); break;
					case 't': fputc('\t',output); break;
					case 'v': fputc('\v',output); break;
					default: fputc(c,output); break;
				}
			} else if(c=='x'){
				int c1=fgetc(input);
				int c2=fgetc(input);
				if(c1==-1||c2==-1){
					fprintf(stderr,"Invalid end of input\n");
					exit(1);
				}
				c1=unhex(c1);
				c2=unhex(c2);
				if(c1==-1){
					fprintf(stderr,"Invalid hexadecimal escape\n");
					exit(1);
				}
				if(c2==-1){
					fputc(c1,output);
				} else {
					c=fgetc(input);
					if(c==-1){
						fprintf(stderr,"Invalid end of input\n");
						exit(1);
					}
					if(unhex(c)!=-1){
						fprintf(stderr,"Invalid wide hexadecimal escape\n");
						exit(1);
					}
					ungetc(c,input);

					fputc(16*c1+c2,output);
				}
			} else {
				ungetc(c,input);
				int res=0,i;
				for(i=0;i<3;i++){
					c=fgetc(input);
					if(c==EOF){
						fprintf(stderr,"Invalid end of input\n");
						exit(1);
					}
					if(c<'0'||c>='8'){
						ungetc(c,input);
						break;
					}
					res=8*res+c-'0';
				}
				if(i==0){
					fprintf(stderr,"Invalid octal escape\n");
					exit(1);
				}
				fputc(res,output);
			}
		}
		fflush(output);
	}
}

int main(int argc,char **argv){
	if(argc==1){
		c2bin(stdin,stdout);
	} else if(argc==2){
		if(strcmp(argv[1],"-h")==0||strcmp(argv[1],"--help")==0){
			usage();
		} else if(strcmp(argv[1],"-")==0){
			c2bin(stdin,stdout);
		} else {
			FILE *f=fopen(argv[1],"rb");
			if(!f){
				fprintf(stderr,"Could not open file '%s'\n",argv[1]);
				return 1;
			}
			c2bin(f,stdout);
			fclose(f);
		}
	} else if(argc==3){
		FILE *fin,*fout;
		if(strcmp(argv[1],"-")==0){
			fin=stdin;
		} else {
			fin=fopen(argv[1],"rb");
			if(!fin){
				fprintf(stderr,"Could not open file '%s'\n",argv[1]);
				return 1;
			}
		}

		if(strcmp(argv[2],"-")==0){
			fout=stdout;
		} else {
			fout=fopen(argv[2],"wb");
			if(!fout){
				fprintf(stderr,"Could not open file '%s'\n",argv[2]);
				return 1;
			}
		}

		c2bin(fin,fout);

		fclose(fin);
		fclose(fout);
	} else {
		usage();
		return 1;
	}
}