/*
   l_io.c - Input and output routines for L.
   Samuel A. Rebelsky
   Version 0.1 of 3 March 2007
 */

#include <stdio.h>
#include <string.h>
#include "l.h"

/* Predeclarations for simplicity. */
pair _l_parse();
pair _l_parsetail();

/* The following two variables are used to keep track of our position in the parse. */
static int pos;
static char *parseme;

int
is_letter(char ch)
{
  return (('a' <= ch) && (ch <= 'z'))
         || (('A' <= ch) && (ch <= 'Z'));
} /* is_letter(char) */

int 
is_digit(char ch)
{
  return ('0' <= ch) && (ch <= '9');
} /* is_digit(char) */

int
is_whitespace(char ch)
{
  return (' ' == ch)
         || ('\n' == ch)
         || ('\t' == ch);
} /* is_whitespace(char) */

void
skip_whitespace()
{
  while (is_whitespace(parseme[pos])) {
    pos++;
  }
} /* skip_whitespace() */

/* Parse the tail of a list. Assumes we've read the first value. */
pair
_l_parsetail()
{
  skip_whitespace();
  /* Special case: Out of input.  Crash. */
  if (!parseme[pos]) {
    fprintf(stderr, "Parse error: Early end of input in '%s'.\n", parseme);
    return L_ERROR;
  }
  /* Special case: End of list.  Return NIL. */
  else if (parseme[pos] == ')') {
    pos++;
    return L_NIL;
  }
  /* Special case: Dotted end of list.  Return the next thing. */
  else if (parseme[pos] == '.') {
    pos++;
    pair right = _l_parse();
    skip_whitespace();
    if (parseme[pos] != ')') {
      fprintf(stderr, "Parse error: Expected ')', found '%c' at position %d of '%s'\n", parseme[pos], pos, parseme);
      return L_ERROR;
    }
    pos++;
    return right;
  }
  /* Regular case: Normal position in the list. */
  else {
    pair left = _l_parse();
    pair right = _l_parsetail();
    return allocate_pair(left, right);
  }
} /* _l_parsetail() */

/*
 * Parse the substring of parseme starting at pos, advancing pos to immediately
 * beyond what we just parsed.  Returned the parsed value.
 */
pair
_l_parse()
{
  char ch;
  int newpos;
  pair tmp;

  skip_whitespace();
  /* Check for end of stuff. */
  if (!parseme[pos]) {
    fprintf(stderr, "Parse error: Early end of input in '%s'.\n", parseme);
    return L_ERROR;
  } /* whoops! ran out of string */

  if (is_digit(parseme[pos])) {
    /* Assumption: ASCII ordering. */
    int result = 0;
    while (is_digit(parseme[pos])) {
      result = result*10 + (parseme[pos] - '0');
      pos++;
    } /* while */
    return make_int(result);
  } /* is_digit() */
  else if (parseme[pos] == '"') {
    newpos = pos;
    while (parseme[++newpos] != '"')
      ;
    parseme[newpos] = '\0';
    tmp = make_string(parseme + pos + 1);
    parseme[newpos] = '"';
    pos = newpos + 1;
    return tmp;
  }
  else if (is_letter(parseme[pos])) {
    newpos = pos + 1;
    while (is_digit(parseme[newpos]) || (is_letter(parseme[newpos]))) {
      newpos++;
    }
    ch = parseme[newpos];
    parseme[newpos] = '\0';
    tmp = make_symbol(parseme + pos);
    parseme[newpos] = ch;
    pos = newpos;
    return tmp;
  } /* is_letter */
  else if (parseme[pos] == '(') {
    pos++;
    pair left = _l_parse();
    pair right = _l_parsetail();
    return allocate_pair(left, right);
  }
  else {
    fprintf(stderr, "Parse error in position %d of '%s'\n", pos, parseme);
    return L_ERROR;
  }
} /* _l_parse(char *) */

pair
l_parse(char *str)
{
  pos = 0;
  parseme = str;
  return _l_parse(); 
} /* l_parse(char *) */

void
l_print(FILE *stream, pair root)
{
  if (is_symbol(root)) {
    fprintf(stream, "%s", CDR(root));
  }
  else if (is_int(root)) {
    fprintf(stream, "%d", CDR(root));
  }
  else if (is_string(root)) {
    fprintf(stream, "\"%s\"", CDR(root));
  }
  else if (is_pair(root)) {
    fprintf(stream, "(");
    l_print(stream, CAR(root));
    fprintf(stream, " . ");
    l_print(stream, CDR(root));
    fprintf(stream, ")");
  }
  else {
    fprintf(stream, "<unknown(%d,%d)>", CAR(root), CDR(root));
  }
} /* l_print(pair) */