/* expr.c - Don Yang (uguu.org)

   03/13/04
                                                                           */
/*@ -usedef @*/

#include<assert.h>
#include<ctype.h>
#include<stdio.h>
#include<string.h>


static int GetN(char **p);
static int SetMarker(char *str, int size,
                     int dir, int *pos1, int *pos2, char *expr);

int main(int argc, char **argv)
{
   int size, left, right, i;

   if( argc < 4 )
      return printf("%s <left expr> <right expr> <string>\n", *argv);

   size = (int)strlen(argv[3]);
   left = 0;
   right = size - 1;
   printf("execute ^%s -> %d\n", argv[1],
      SetMarker(argv[3], size, 1, &left, &right, argv[1]));
   printf("execute $%s -> %d\n", argv[2],
      SetMarker(argv[3], size, -1, &right, &left, argv[2]));
   printf("cursor: %d / %d\n", left, right);

   (void)puts(argv[3]);
   for(i = 0; i < size; i++)
   {
      if( i == left )         (void)putchar(left == right ? '^' : '[');
      else if( i == right )   (void)putchar(']');
      else                    (void)putchar(' ');
   }
   (void)putchar('\n');
   return 0;
}


static int GetN(char **p)
{
   int n;

   for(n = (int)*((*p)++) - (int)'0'; isdigit(**p); ++*p)
      n = n * 10 + (int)**p - (int)'0';
   --*p;
   return n;
}

static int SetMarker(char *str, int size,
                     int dir, int *pos1, int *pos2, char *expr)
{
   #define MAX_NEST  8
   char *paren[MAX_NEST], *p, *q;
   int repeat[MAX_NEST + 1], cursor, lastsearch, nest;

   cursor = *pos1;
   lastsearch = nest = 0;
   repeat[0] = 0;
   for(p = expr; *p != '\0'; p++)
   {
      switch( *p )
      {
         /* Set current cursor position / direction */
         case '^':   cursor = 0;          /*@fallthrough@*/
         case '+':   dir = 1;             break;

         case '$':   cursor = size - 1;   /*@fallthrough@*/
         case '-':   dir = -1;            break;

         /* Set other marker position */
         case '@':   *pos2 = cursor;      break;

         /* Repeat expression */
         case '(':
            if( nest >= MAX_NEST )
               return 5;            /* Error5: Nest level too deep */
            paren[nest++] = p;
            repeat[nest] = 0;
            break;
         case ')':
            if( nest == 0 )
               return 6;            /* Error6: Unmatched parentheses */
            nest--;
            if( repeat[nest] > 1 )
            {
               /* Repeat */
               assert(paren[nest] != NULL);
               p = paren[nest];
               repeat[nest]--;
               nest++;
            }
            else if( repeat[nest] == 1 )
            {
               /* End last iteration */
               assert(isdigit(*(p + 1)));
               p++;
               (void)GetN(&p);
               repeat[nest]--;
            }
            else
            {
               /* Start repeat */
               q = p + 1;
               if( !isdigit(*q) )
                  return 4;         /* Error4: No repeat count */
               if( (repeat[nest] = GetN(&q)) < 2 )
               {
                  p = q;
                  repeat[nest] = 0;
               }
               else
               {
                  p--;
                  nest++;
               }
            }
            break;

         /* Move cursor */
         case '0': case '1': case '2': case '3': case '4':
         case '5': case '6': case '7': case '8': case '9':
            cursor += GetN(&p) * dir;
            if( cursor < 0 || cursor >= size )
               return 3;            /* Error3: Cursor moved out of range */
            lastsearch = 0;
            break;

         /* Character search */
         default:
            if( strchr("asdiASDI", *p) != NULL )
            {
               /* Character class */
               if( lastsearch == -(int)*p )
                  cursor += dir;
               switch( *p )
               {
                  #define CHARSEARCH(chartest) \
                     for(; cursor >= 0 && cursor < size; cursor += dir)    \
                     {                                                     \
                        if( chartest(str[cursor]) )                        \
                           break;                                          \
                     }                                                     \
                     if( cursor < 0 || cursor >= size ) return 1;
                  case 'a':   CHARSEARCH(isalpha); break;
                  case 's':   CHARSEARCH(isspace); break;
                  case 'd':   CHARSEARCH(isdigit); break;
                  case 'i':   CHARSEARCH(isalnum); break;
                  #undef CHARSEARCH

                  #define CHARSEARCH(chartest) \
                     for(; cursor >= 0 && cursor < size; cursor += dir)    \
                     {                                                     \
                        if( !chartest(str[cursor]) )                       \
                           break;                                          \
                     }                                                     \
                     if( cursor < 0 || cursor >= size ) return 1;
                  case 'A':   CHARSEARCH(isalpha); break;
                  case 'S':   CHARSEARCH(isspace); break;
                  case 'D':   CHARSEARCH(isdigit); break;
                  case 'I':   CHARSEARCH(isalnum); break;
                  #undef CHARSEARCH

                  default: assert(0); break;
               }
               lastsearch = -(int)*p;
            }
            else
            {
               /* Single character */
               if( *p == '/' )
               {
                  if( *++p == '\0' )
                     return 2;         /* Error2: "/" not followed by char */
               }
               if( lastsearch == (int)*p )
                  cursor += dir;
               for(; cursor >= 0 && cursor < size; cursor += dir)
               {
                  if( str[cursor] == *p )
                     break;
               }
               if( cursor < 0 || cursor >= size )
                  return 1;            /* Error1: Search character not found */

               lastsearch = (int)*p;
            }
            break;
      }
   }

   *pos1 = cursor;
   return 0;
}