/* Copyright (C) 2025 Aryadev Chavali

 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License Version 2 for
 * details.

 * You may distribute and modify this code under the terms of the GNU General
 * Public License Version 2, which you should have received a copy of along with
 * this program.  If not, please go to <https://www.gnu.org/licenses/>.

 * Created: 2025-04-16
 * Description: Implementation of parser
 */

#include <lisp/reader.h>

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

bool is_digit(char c)
{
  return isdigit(c);
}

bool is_alpha(char c)
{
  return isalpha(c);
}

bool is_space(char c)
{
  return isspace(c);
}

bool is_skip(char c)
{
  return is_space(c) || c == ';';
}

bool is_sym(char c)
{
  return strchr(SYM_CHARS, c) != NULL;
}

void input_from_sv(context_t *ctx, input_t *inp, const char *name, sv_t sv)
{
  inp->name = name;
  inp->str  = sv_copy(&ctx->read, sv);
}

void input_from_fp(context_t *ctx, input_t *input, const char *name, FILE *fp)
{
  input->name = name;
  // TODO: Choose a best fit (i.e. maximal capacity, unused) page
  page_t *page = page_create(INPUT_CHUNK_SIZE);
  // chunk should be in scratch space so we can reset it later.
  char *chunk = context_salloc(ctx, INPUT_CHUNK_SIZE);

  u64 total_size = 0, size_read = 0;
  while (!feof(fp))
  {
    size_read = fread(chunk, 1, INPUT_CHUNK_SIZE, fp);
    if (size_read > 0)
    {
      page_rappend(&page, chunk, size_read);
      total_size += size_read;
    }
  }

  input->str = SV((char *)page->data, total_size);

  // Memory cleanup
  context_reset_scratch(ctx);
  arena_attach(&ctx->read, page);
}

bool input_eof(input_t *input)
{
  return !input || (input->offset >= input->str.size) ||
         (input->str.data[input->offset] == '\0');
}

char input_peek(input_t *input, u64 offset)
{
  if (input_eof(input) || input->offset + offset >= input->str.size)
    return '\0';
  return input->str.data[input->offset + offset];
}

char input_next(input_t *input, u64 offset)
{
  if (input_eof(input) || input->offset + offset >= input->str.size)
    return '\0';
  input->offset += offset;
  return input->str.data[input->offset];
}

void input_skip(input_t *inp)
{
  while (!input_eof(inp))
  {
    sv_t current = sv_cut(inp->str, inp->offset);
    // Skip any whitespace
    inp->offset += sv_while(current, is_space);
    current = sv_cut(inp->str, inp->offset);
    // Is there a comment to skip?
    if (current.size && current.data[0] == ';')
    {
      // Skip till newline
      i64 newline = sv_find_subcstr(current, "\n", 1);
      if (newline < 0)
        inp->offset = inp->str.size;
      else
        inp->offset += newline + 1;
      // Then skip any whitespace
    }
    // Multiline comment to skip?
    else if (current.size > 2 && strncmp(current.data, "#|", 2) == 0)
    {
      i64 offset = sv_find_subcstr(current, "|#", 2);
      if (offset < 0)
        inp->offset = inp->str.size;
      else
        inp->offset += offset + 2;
      // Then skip any whitespace
    }
    // Nothing to skip, stop.
    else
      break;
  }
  return;
}

perr_t parse_int(context_t *ctx, input_t *inp, lisp_t **ret)
{
  debug("parse_int[%lu] => ", inp->offset);

  // TODO: Parse arbitrary sized integers
  (void)ctx;

  bool negative = (input_peek(inp, 0) == '-');
  sv_t current  = sv_cut(inp->str, inp->offset + (negative ? 1 : 0));
  sv_t digits   = sv_chop(current, sv_while(current, is_digit));

  debug("`" PR_SV "` => ", SV_FMT(digits));
  i64 x = (negative ? -1L : 1L) * strtol(digits.data, NULL, 10);
  debug("%ld\n", x);

  input_next(inp, digits.size + (negative ? 1 : 0));

  *ret = make_int(x);
  return PERR_OK;
}

perr_t parse_sym(context_t *ctx, input_t *inp, lisp_t **ret)
{
  debug("parse_sym[%lu] => ", inp->offset);

  sv_t current = sv_cut(inp->str, inp->offset);
  sv_t sym     = sv_chop(current, sv_while(current, is_sym));
  debug("`" PR_SV "` => ", SV_FMT(sym));

  if (sym.size == 3)
  {
    // NOTE: We can't mutate sym directly because it's on `read` space.

    // TODO: Make this beautiful please.
    char buf[3];
    for (u64 i = 0; i < 3; ++i)
      buf[i] = toupper(sym.data[i]);

    // NOTE: NIL symbol to actual NIL
    if (strncmp(buf, "NIL", 3) == 0)
    {
      input_next(inp, 3);
      *ret = NIL;
      return PERR_OK;
    }
  }

  *ret = make_sym(ctx, sym.data, sym.size);
  debug("%#16lx\n", *ret);
  input_next(inp, sym.size);

  return PERR_OK;
}

perr_t parse_bool(context_t *ctx, input_t *inp, lisp_t **ret)
{
  (void)ctx;
  debug("parse_bool[%lu] => ", inp->offset);
  char c = input_peek(inp, 1);
  bool b = -1;
  if (c == 't')
    b = true;
  else if (c == 'f')
    b = false;
  else
    return PERR_EXPECTED_BOOLEAN;
  *ret = tag_bool(b);
  input_next(inp, 2);
  return PERR_OK;
}

perr_t parse_cons(context_t *ctx, input_t *inp, lisp_t **ret)
{
  // TODO: Put this in a symbol table
  lisp_t *lisp_dot = make_sym(ctx, ".", 1);
  debug("parse_cons[%lu] => (\n", inp->offset);
  inp->offset += 1;

  lisp_t *root = NIL;
  lisp_t **cur = NIL;
  bool dotted  = false;

  while (!input_eof(inp) && input_peek(inp, 0) != ')')
  {
    lisp_t *lisp = NIL;
    perr_t res   = parse(ctx, inp, &lisp);
    if (res)
      return res;

    // This is cheap to do
    if (lisp == lisp_dot)
    {
      dotted = true;
      continue;
    }

    if (!root)
    {
      root = make_cons(ctx, lisp, NIL);
      cur  = &root;
    }
    else if (!dotted)
      *cur = make_cons(ctx, lisp, NIL);
    else
      *cur = lisp;

    if (cur && !dotted)
      cur = &as_cons(*cur)->cdr;

    input_skip(inp);
  }

  if (input_peek(inp, 0) != ')')
    return PERR_EXPECTED_CLOSE_BRACKET;

  input_next(inp, 1);

  debug(")\n");
  *ret = root;
  return PERR_OK;
}

perr_t parse_vec(context_t *ctx, input_t *inp, lisp_t **ret)
{
  debug("parse_vec[%lu] => [\n", inp->offset);
  input_next(inp, 2);

  lisp_t *lvec = make_vec(ctx, 0);
  vec_t *vec   = as_vec(lvec);

  while (!input_eof(inp) && input_peek(inp, 0) != ')')
  {
    lisp_t *lisp = NIL;
    perr_t res   = parse(ctx, inp, &lisp);
    if (res)
      return res;

    vec_append(&ctx->memory, vec, &lisp, sizeof(lisp));
    input_skip(inp);
  }

  if (input_peek(inp, 0) != ')')
    return PERR_EXPECTED_CLOSE_BRACKET;

  input_next(inp, 1);

  debug("]\n");
  *ret = lvec;
  return PERR_OK;
}

perr_t parse_str(context_t *ctx, input_t *inp, lisp_t **ret)
{
  debug("parse_str[%lu] => ", inp->offset);
  input_next(inp, 1); // 1 for the first speechmark
  sv_t sv  = sv_cut(inp->str, inp->offset);
  i64 size = sv_find_subcstr(sv, "\"", 1);
  if (size < 0)
    return PERR_EXPECTED_SPEECH_MARK;

  input_next(inp, size + 1); // 1 for that last speechmark
  sv_t str_content = sv_chop(sv, size);
  debug("\"" PR_SV "\" => ", SV_FMT(str_content));
  *ret = make_str(ctx, str_content.data, str_content.size);
  debug("%#16lx\n", *ret);
  return PERR_OK;
}

perr_t parse_quote(context_t *ctx, input_t *inp, lisp_t **ret)
{
  char c = input_peek(inp, 0);
  if (!(c == '\'' || c == '`'))
    return PERR_UNEXPECTED_CHAR;
  input_next(inp, 1);
  sv_t prefix = {0};
  if (c == '\'')
    prefix = SV("quote", 5);
  else if (c == '`')
    prefix = SV("quasiquote", 10);
  lisp_t *root = make_cons(ctx, make_sym(ctx, prefix.data, prefix.size), NIL);
  lisp_t *rest = NIL;
  perr_t perr  = parse(ctx, inp, &rest);
  if (perr)
    return perr;
  CDR(root) = make_cons(ctx, rest, NIL);
  *ret      = root;
  return PERR_OK;
}

// TODO: Make this interactable with user once we have evaluation
perr_t parse_reader_macro(context_t *ctx, input_t *inp, lisp_t **ret)
{
  char c = input_peek(inp, 1);
  if (c == '\\')
  {
    // character or weird base integer
    TODO("Not implemented reader macro for characters or weird bases");
  }
  else if (c == '(')
    return parse_vec(ctx, inp, ret);
  else if (c == 't' || c == 'f')
    return parse_bool(ctx, inp, ret);
  else if (c == 'e')
  {
    // Scientific notation for floats
  }
  return PERR_UNEXPECTED_READER_MACRO_SYMBOL;
}

static_assert(NUM_TAGS == 9);
perr_t parse(context_t *ctx, input_t *inp, lisp_t **ret)
{
  debug("parse => ");
  input_skip(inp);
  if (input_eof(inp))
    return PERR_EOF;

  char c = input_peek(inp, 0);

  if (is_digit(c) || (c == '-' && is_digit(input_peek(inp, 1))))
    return parse_int(ctx, inp, ret);
  else if (c == '#')
    return parse_reader_macro(ctx, inp, ret);
  else if (is_sym(c))
    return parse_sym(ctx, inp, ret);
  else if (c == '(')
    return parse_cons(ctx, inp, ret);
  else if (c == '\'' || c == '`')
    return parse_quote(ctx, inp, ret);
  else if (c == '\"')
    return parse_str(ctx, inp, ret);
  else
    return PERR_UNEXPECTED_CHAR;
}

perr_t parse_all(context_t *ctx, input_t *inp, vec_t *vec)
{
  while (!input_eof(inp))
  {
    lisp_t *member = NIL;
    perr_t err     = parse(ctx, inp, &member);

    if (err)
      return err;
    else
      vec_append(&ctx->scratch, vec, &member, sizeof(member));

    input_skip(inp);
  }
  return PERR_OK;
}

int print_perror(FILE *fp, input_t *inp, perr_t error)
{
  pos_t pos = input_offset_to_pos(inp);
  fprintf(fp, "%s:%lu:%lu: %s", inp->name, pos.line, pos.col,
          perr_to_cstr(error));
  switch (error)
  {
  case PERR_UNEXPECTED_CHAR:
    fprintf(fp, "(`%c`)", input_peek(inp, 0));
    break;
  case PERR_OK:
  case PERR_EOF:
  case PERR_EXPECTED_BOOLEAN:
  case PERR_UNEXPECTED_READER_MACRO_SYMBOL:
  case PERR_EXPECTED_CLOSE_BRACKET:
  case PERR_EXPECTED_SPEECH_MARK:
  default:
    break;
  }
  fprintf(stderr, "\n");

  return error;
}

pos_t input_offset_to_pos(input_t *inp)
{
  pos_t pos = {.col = 1, .line = 1};
  for (u64 i = 0; i < inp->offset && i < inp->str.size; ++i)
  {
    char c = (inp->str.data[i]);
    if (c == '\n')
    {
      ++pos.line;
      pos.col = 1;
    }
    else
    {
      ++pos.col;
    }
  }
  return pos;
}