//-----------------------------------------------------------------------------
// FileIO.c
// Finds the unique tokens contained in infile. Tokens are defined as the 
// maximal substrings of a line not containing any character in delim[]. 
// Unique tokens are printed to outfile in the order of first appearance in 
// infile. Upper and lower case chars are not distinguished. To distinguish 
// upper from lower, comment out the call to function lower()
//
// compile:       gcc -std=c17 -Wall -o FileIO FileIO.c
//
//     run:       FileIO file1 file2
//
// This program illustrates File input-output operations in C like fgets()
// and fprintf(). It also illustrates string handling functions in C, such 
// as strlen(), strcmp(), strcat() and strtok(), all in string.h, and also 
// heap memory operations such as malloc(), calloc(), realloc() and free()
// in stdlib.h.  
//-----------------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <ctype.h>

// findWord()
// Returns true if char array buf contains word, false otherwise. Array buf 
// must consist of consecutive strings separated by the null '\0' character.
bool find(char* word, char* buf, int n){
   char* next = buf;
   int i;
   for( i=0; i<n; i++ ){
      if( strcmp(word, next)==0 ){
         return true;
      }
      next += (strlen(next)+1);
   }
   return false;
}

// lower()
// Converts all chars in word to lower case.
void lower(char* word){
   int i;
   for ( i=0; word[i] != '\0'; i++) {
      word[i] = tolower( (unsigned char)word[i] );
   }
}

int main(int argc, char * argv[]){

   FILE *infile, *outfile;

   const size_t lineBufferSize = 5000;
   const size_t tokenBufferSizeIncrement = 1000;
   char lineBuffer[lineBufferSize];
   char* token;                       // a single token in lineBuffer
   char* tokenBuffer;                 // concatenation of all tokens, separated by \0
   size_t tokenBufferSize;            // current physical size of tokenBuffer
   int tokenBufferNext;               // index of next open element in tokenBuffer
   int tokenCount;
   int i;
   char delim[] = " \t\n\r\\\"\',<.>/?;:[{]}|`~!@#$%^&*()-_=+0123456789";
   

   // check command line for correct number of arguments
   if( argc != 3 ){
      fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
      exit(EXIT_FAILURE);
   }

   // open files for reading and writing 
   infile  = fopen(argv[1], "r");
   outfile = fopen(argv[2], "w");
   if( infile==NULL ){
      fprintf(stderr, "Unable to open file %s for reading\n", argv[1]);
      exit(EXIT_FAILURE);
   }
   if( outfile==NULL ){
      fprintf(stderr, "Unable to open file %s for writing\n", argv[2]);
      exit(EXIT_FAILURE);
   }

   // read each line of infile, parse tokens, add unique tokens to tokenBuffer
   tokenCount = 0;
   tokenBufferSize = tokenBufferSizeIncrement;
   tokenBuffer = calloc(tokenBufferSize, sizeof(char));
   tokenBufferNext = 0;
   while( fgets(lineBuffer, lineBufferSize, infile) != NULL ) {

      // get first token in lineBuffer
      token = strtok(lineBuffer, delim);

      while( token!=NULL ){ // a token exists
         
         // check if new
         lower(token);  // don't distinguish upper and lower case
         if( find(token, tokenBuffer, tokenCount) ){  // already have it
            token = strtok(NULL, delim);              //    try another
            continue;
         }

         // expand tokenBuffer if necessary
         if( strlen(token)+2 > tokenBufferSize-tokenBufferNext ){  // #bytes needed > #bytes available
            tokenBufferSize += tokenBufferSizeIncrement;
            tokenBuffer = realloc(tokenBuffer, tokenBufferSize*sizeof(char));
         }

         // append token to tokenBuffer
         strcat(&tokenBuffer[tokenBufferNext], token);
         tokenBufferNext += strlen(token)+1;
         tokenBuffer[tokenBufferNext] = '\0';
         tokenCount++;

         // get next token in lineBuffer
         token = strtok(NULL, delim);        
      }
   }

   // print tokens to outfile
   token = tokenBuffer;
   for( i=0; i<tokenCount; i++ ){
      fprintf(outfile, "%s\n", token);
      token += (strlen(token)+1);
   }

   // free memory
   free(tokenBuffer);

   // close files 
   fclose(infile);
   fclose(outfile);

   return(0);
}