#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>

/* forward reference for the C compiler */
int getchunk(char *chunkname);

char *chunkbegin = "<pre id=\"";     int chunkbeginlen = 9;
char *chunkend = "</pre>";           int chunkendlen = 6;
char *chunkget = "<getchunk id=\"";  int chunkgetlen = 14;

/* a memory mapped buffer copy of the file */
char *buffer;
int bufsize;

/* return the length of the next line */
int nextline(int i) {
  int j;
  if (i >= bufsize) return(-1);
  for (j=0; ((i+j < bufsize) && (buffer[i+j] != '\n')); j++);
  return(j);
}

/* output the line we need */
int printline(int i, int length) {
  int j; 
  for (j=0; j<length; j++) { putchar(buffer[i+j]); }
  printf("\n");
}

/* handle <pre id="chunkname">            */
/* is this chunk name we are looking for? */
int foundchunk(int i, char *chunkname) {
  if ((strncmp(&buffer[i],chunkbegin,chunkbeginlen) == 0) &&
      (strncmp(&buffer[i+9],chunkname,strlen(chunkname)) == 0) &&
      (buffer[i+chunkbeginlen+strlen(chunkname)] == '"') &&
      (buffer[i+chunkbeginlen+strlen(chunkname)+1] == '>')) return(1);
  return(0);
}

/* handle </pre>   */
/* is it really an end? */
int foundEnd(int i) {
  if (strncmp(&buffer[i],chunkend,chunkendlen) == 0) {
    return(1); 
  }
  return(0);
}

/* handle <getchunk id="chunkname"/> */
/* is this line a getchunk?          */
int foundGetchunk(int i, int linelen) {
  int len;
  if (strncmp(&buffer[i],chunkget,chunkgetlen) == 0) {
   for(len=1; ((len < linelen) && (buffer[i+chunkgetlen+len] != '\"')); len++);
   return(len);
  }
  return(0);
}

/* Somebody did a getchunk and we need a copy of the name */
/* malloc string storage for a copy of the getchunk name  */
char *getChunkname(int k, int getlen) {
  char *result = (char *)malloc(getlen+1);
  strncpy(result,&buffer[k+chunkgetlen],getlen);
  result[getlen]='\0';
  return(result);
}

/* print lines in this chunk, possibly recursing into getchunk */
int printchunk(int i, int chunklinelen, char *chunkname) {
  int j;
  int k;
  int linelen;
  char *getname;
  int getlen = 0;
  for (k=i+chunklinelen+1; ((linelen=nextline(k)) != -1); ) {
    if ((getlen=foundGetchunk(k,linelen)) > 0) {
       getname = getChunkname(k,getlen);
       getchunk(getname);
       free(getname);
       k=k+getlen+17;
    } else {
    if ((linelen >= chunkendlen) && (foundEnd(k) == 1)) {
      return(k+chunkbeginlen);
    } else {
      printline(k,linelen);
      k=k+linelen+1;
    }
  }}
  return(k);
}

/* find the named chunk and call printchunk on it */
int getchunk(char *chunkname) {
  int i;
  int j;
  int linelen;
  int chunklen = strlen(chunkname);
  for (i=0; ((linelen=nextline(i)) != -1); ) {
    if ((linelen >= chunklen+11) && (foundchunk(i,chunkname) == 1)) {
      i=printchunk(i,linelen,chunkname);
    } else {
      i=i+linelen+1;
    }
  }
  return(i);
}

void fixHTMLcode() {
  int point = 0;
  int mark = 0;
  int i=0;
  for(point = 0; point < bufsize;) {
    if ((buffer[point] == '&') &&
        (strncmp(&buffer[point+1],"lt;",3) == 0)) {
      buffer[mark++] = 60;
      point = point + 4;  
    } else
    if ((buffer[point] == '&') &&
        (strncmp(&buffer[point+1],"gt;",3) == 0)) {
      buffer[mark++] = 62;
      point = point + 4;  
    } else
      buffer[mark++] = buffer[point++]; 
  }
  bufsize = mark;
}

/* memory map the input file into the global buffer and get the chunk */
int main(int argc, char *argv[]) {
  int fd;
  struct stat filestat;
  if ((argc < 2) || (argc > 3)) { 
    perror("Usage: tangle filename chunkname");
    exit(-1);
  }
  fd = open(argv[1], O_RDONLY);
  if (fd == -1) {
    perror("Error opening file for reading");
    exit(-2);
  }
  if (fstat(fd,&filestat) < 0) {
    perror("Error getting input file size");
    exit(-3);
  }
  bufsize = (int)filestat.st_size;
  buffer = (char *)malloc(bufsize);
  read(fd,buffer,bufsize);
  fixHTMLcode(); 
  getchunk(argv[2]);
  close(fd);
  return(0);
}