#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "wscm.h"

static O read(Lx *lex);

static void skipcomments(Lx *lex) {
  while (lex->kind == TOK_COMMENT) {
    if (!nexttoken(lex))
      break;
  }
}

static O makeobject(Lx *lex) {
  if (lex->kind == TOK_WORD) {
    char *tok = lex->buffer;
    char *end;
    long v = strtol(tok, &end, 10);
    if (end != tok && *end == '\0') {
      nexttoken(lex);
      return NUM((I)v);
    } else {
      S *s = intern(tok, (I)strlen(tok));
      O sym = BOX(TAG(s, TAG_SYM));
      nexttoken(lex);
      return sym;
    }
  } else if (lex->kind == TOK_STRING) {
    // TODO: string type
    char *tok = lex->buffer;
    S *s = intern(tok, (I)strlen(tok));
    O sym = BOX(TAG(s, TAG_SYM));
    nexttoken(lex);
    return sym;
  }
  return NIL;
}

static void lastcdr(O list, O cdr_val) {
  O curr = list;
  while (1) {
    C *c = uncons(curr);
    if (c->cdr == NIL) {
      c->cdr = cdr_val;
      return;
    }
    curr = c->cdr;
  }
}

static O readlist(Lx *lex) {
  nexttoken(lex);
  skipcomments(lex);

  if (lex->kind == TOK_RPAREN) {
    nexttoken(lex);
    return NIL;
  }

  O head = NIL;
  while (lex->kind != TOK_EOF) {
    skipcomments(lex);
    if (lex->kind == TOK_RPAREN) {
      nexttoken(lex);
      break;
    }

    if (lex->kind == TOK_DOT) {
      nexttoken(lex);
      skipcomments(lex);
      if (lex->kind == TOK_EOF) {
        fprintf(stderr, "reader error: unexpected EOF after '.'\n");
        abort();
      }
      O cdr_val = read(lex);
      skipcomments(lex);
      if (lex->kind != TOK_RPAREN) {
        fprintf(stderr, "reader error: expected ')' after dotted pair cdr\n");
        abort();
      }
      nexttoken(lex);
      O normal = listreverse(head);
      if (normal == NIL) {
        fprintf(stderr, "reader error: '.' with no preceding elements\n");
        abort();
      }
      lastcdr(normal, cdr_val);
      return normal;
    }
    O elem = read(lex);
    head = cons(elem, head);
    skipcomments(lex);
  }

  return listreverse(head);
}

static O readquote(Lx *lex) {
  nexttoken(lex);
  skipcomments(lex);
  O e = read(lex);
  O qsym = BOX(TAG(intern("quote", -1), TAG_SYM));
  return cons(qsym, cons(e, NIL));
}

static O read(Lx *lex) {
  skipcomments(lex);

  switch (lex->kind) {
  case TOK_EOF:
    return NIL;
  case TOK_LPAREN:
    return readlist(lex);
  case TOK_QUOTE:
    return readquote(lex);
  case TOK_WORD:
  case TOK_STRING:
    return makeobject(lex);
  case TOK_COMMENT:
    nexttoken(lex);
    return read(lex);
  default:
    nexttoken(lex);
    return NIL;
  }
}

O readfile(FILE *f) {
  if (!f)
    return NIL;

  Lx lex;
  lex.kind = TOK_EOF;
  lex.cursor = 0;
  lex.input = f;
  lex.buffer[0] = '\0';

  nexttoken(&lex);
  skipcomments(&lex);

  if (lex.kind == TOK_EOF)
    return NIL;
  return read(&lex);
}

O readstring(const char *s) {
  if (!s)
    return NIL;
  size_t len = strlen(s);
  FILE *f = fmemopen((void *)s, len, "r");
  O res = readfile(f);
  fclose(f);
  return res;
}