#include "runtime.h"

box_t cons(box_t car, box_t cdr) {
  cons_t* kons = alloc();
  kons->car = car;
  kons->cdr = cdr;
  box_t box;
  box.type = CONS;
  box.cons = kons;
  return box;
}

void chomp_ws() {
  char c = getchar();
  for(;;) {
    if (c == ' ' || c == '\t' || c == '\n' || c == '\r') {
      c = getchar();
    } else {
      ungetchar(c);
      break;
    }
  }
}

box_t read_integer() {
  char buf[256];
  size_t i = 0;
  char next = getchar();
  while(isdigit(next)) {
    buf[i] = next;
    next = getchar();
    i++;
  }
  ungetchar(next);
  buf[i] = 0;
  box_t res;
  res.type = INTEGER;
  res.integer = atoi(buf);
  chomp_ws();
  return res;
}

box_t read_symbol() {
  char buf[256];
  size_t i = 0;
  char next = getchar();
  while (isalpha(next)) { // Totally insufficent but we'll look into it later
    buf[i] = next;
    next = getchar();
    i++;
  }
  ungetchar(next);
  buf[i] = 0;
  box_t res;
  char *str = strndup(buf, i);
  res.type = SYMBOL;
  res.symbol = str;
  chomp_ws(); // Clean up whitespace afterwards
  return res;
}

box_t read_list() {
  char c = getchar();
  box_t val;
  if (c == ')') {
    chomp_ws();
    val.type = CONS;
    val.cons = the_empty_list;
    return val;
  } else {
    ungetchar(c);
    box_t car = read();
    box_t cdr = read_list();
    return cons(car, cdr);
  }
}
    
box_t read() {
  chomp_ws();
  char next = getchar();
  if (next == '(') {
    chomp_ws();
    return read_list();
  } else if (isdigit(next)) {
    ungetchar(next);
    return read_integer();
  } else if (isalpha(next) || ispunct(next)) {
    ungetchar(next);
    return read_symbol();
  } else if (next == EOF) {
    box_t bye;
    bye.type = BYE;
    return bye;
  } else {
    fprintf(stderr, "Bad input");
    exit(1);
  }
}

void scm_print_cons(box_t exp) {
  printf("(");
  while(exp.type = CONS && exp.cons != the_empty_list) {
    scm_print(exp.cons->car);
    if (exp.cons->cdr.cons != the_empty_list) {
      printf(" ");
    }
    exp = exp.cons->cdr;
  }
  if (exp.cons == the_empty_list) {
    printf(")");
  } else {
    printf(". ");
    scm_print(exp);
    printf(")");
  }
}

void scm_print(box_t exp) {
  switch (exp.type) {
  case INTEGER:
    printf("%d", exp.integer);
    break;
  case SYMBOL:
    printf("%s", exp.symbol);
    break;
  case CONS:
    scm_print_cons(exp);
    break;
  }
}
    

box_t eval(box_t exp) {
  return exp;
}