/*!@file
  \brief   lexical analyzer implementation for APC
  \details The lexer manages two FIFO stacks.  One for maintaining tokens, the
           other for maintaining a list of files to be scanned.  During
           execution, the lexer will return a token from its token queue if any
           are present.  If not, the lexer will will pop an element from its
           file queue to 'scanner' to be tokenized.  If the file queue is empty,
           the lexer will instead call 'parsedir' to traverse the directory tree
           and tokenize the results.  If 'parsedir' does not generate any new
           tokens, we are done.
  \author  Jordan Lavatai
  \date    Aug 2016
  ----------------------------------------------------------------------------*/
/* Standard */
#include <stdio.h>
#include <string.h>
#include <errno.h>
/* Posix */
#include <unistd.h>
#include <stdlib.h>
#include <dirent.h>
/* Local */
#include "parser.tab.h"
#ifndef DE_STACKSIZE
#define DE_STACKSIZE 1024
#endif
#ifndef TK_STACKSIZE
#define TK_STACKSIZE 1024
#endif
/* Public */
int  lexer_init(void);
int  lexer(void);
void lexer_pushtok(int, YYSTYPE);
extern //lexer_lex.rl
int lexer_lex(const char*);
struct dirent* lexer_direntpa[DE_STACKSIZE], **lexer_direntpp;
/* Private */
extern //scanner.c
int scanner_init(void);
extern //scanner.c
int scanner(void);
static inline
int dredge_current_depth(void);
extern //bison
YYSTYPE yylval;
static
struct tok
{ YYSTYPE lval;  //token val
  int     tok_t; //token type
} token_stack[TK_STACKSIZE];
static
union tokp
{ int*        tpt; //token pointer type
  struct tok* tok;
  YYSTYPE*    tvp; //token value pointer
} tks, tkx;

/* Directory Entity Array/Stack
   Simple array for keeping track of dirents yet to be processed by the scanner.
   If this list is empty and there are no tokens, the lexer is done.
   This array is populated by the scanner as an array, and popped locally by the
   lexer as a stack.
*/
#define DE_STACK    (lexer_direntpa)
#define DE_STACKP   (lexer_direntpp)
#define DE_LEN()    (DE_STACKP - DE_STACK)
#define DE_INIT()   (DE_STACKP = DE_STACK)
#define DE_POP()    (*--DE_STACKP)

/* Token Stack
   This is a FIFO stack whose pointers are a union of either a pointer to an
   integer, or a pointer to two integers (a struct tok).  This way, integers may
   be added or removed from the stack either singularly (IPUSH/IPOP), or as a
   full token of two integers (PUSH/POP).
   An alignment error will occur if IPOP or IPUSH are used a non-even number of
   times in a sequence!
*/
#define TK_STACK     (token_stack)
#define TK_STACKP    (tks.tok)
#define TK_STACKPI   (tks.tpt)
#define TK_STACKPL   (tks.tvp)
#define TK_STACKX    (tkx.tok)
#define TK_STACKXI   (tkx.tpt)
#define TK_LEN()     (TK_STACKX - TK_STACKP)
#define TK_INIT()    (TK_STACKP = TK_STACKX = TK_STACK)
#define TK_POP()     (*TK_STACKP++)
#define TK_POPI()    (*TK_STACKPI++);
#define TK_POPL()    (*TK_STACKPL++);
#define TK_PUSH(T,L) (*TK_STACKX++ = (struct tok){L,T})

/* Initializer
   The initializer returns boolean true if an error occurs, which may be handled   with standard errno.
*/
int lexer_init
()
{ TK_INIT();
  DE_INIT();
  return scanner_init();
}

/* Lexer
   If the token buffer is empty, 'lexer' will initialize the token buffer and
   call 'lexer_scandir'.  If SCAN_ERROR is returned, an error is printed
   before sending a null return to bison.  If 0 tokens are generated, the error
   printing is skipped.  In all other cases, 'yylval' is set, and the token's
   integer representation is returned.
*/
int lexer
#define $($)#$
#define SCAN_ERROR -1
#define TK_EMPTY   (TK_STACKP == TK_STACKX)
#define FAIL(...)				\
  do {						\
    fprintf(stderr,__VA_ARGS__);		\
    goto done;					\
  } while (0)
()
{start:
  while (DE_LEN() > 0)    //lex any directory entries in our stack
    if (lexer_lex(DE_POP()->d_name) == 0) //fail if it generates no tokens
      FAIL("Lexer failed to tokenize [%s]\n",(*DE_STACKP)->d_name);
  if (TK_EMPTY)           //if there are no tokens,
    { TK_INIT();            //initialize the token stack back to 0
      switch (scanner())
        { case SCAN_ERROR:    //if an error occurred,
	    FAIL("Scanner error\n");
	  case 0:             //if the the scanner finds no dirents,
	    goto done;        //then we are done
          default:            //if we found some elements to scan,
	    goto start;       //start over and lex them
        }
    }
  yylval = TK_POPL();
  return TK_POPI();
 done:
  yylval.val = 0;
  return 0;
}


/* Token Receiver
   This receiver takes a struct tok and pushes it to the FIFO stack.
*/
void lexer_pushtok
#define $($)#$ //stringifier
#define ERR_TK "Fatal: Generated over " $(TK_STACKSIZE) " tokens in one pass."
( int tok, YYSTYPE lval )
{ if (TK_LEN() >= TK_STACKSIZE)
    { fprintf(stderr, ERR_TK);
      exit(EXIT_FAILURE);
    }
  TK_PUSH(tok, lval);
  printf("Pushed Token  %i | %i\n", TK_STACK[TK_LEN() - 1].tok_t, TK_STACK[TK_LEN() - 1].lval.val);
}