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

#include "ltm/common.h"
#include "ltm/template.h"
#include "ltm/template_internal.h"

static bool ltm_template_next_placeholder(ltm_placeholder *ph, const char *s,
                                          size_t len) {
  if (len == 0) {
    return false;
  }

  ph->start = memchr(s, '{', len - 1);

  if ((ph->start == NULL) || (ph->start[1] != '{')) {
    return false;
  }

  size_t new_len = len - (ph->start - s);

  // A template can never be valid without at least 5 characters
  if (new_len < 5) {
    ph->type = ltm_placeholder_type_invalid;

    return true;
  }

  ph->end = memchr(ph->start + 2, '}', new_len - 3);

  // Non-terminated placeholders aren't valid
  if ((ph->end == NULL) || (ph->end[1] != '}')) {
    ph->type = ltm_placeholder_type_invalid;

    return true;
  }

  // End should point to final character
  ph->end++;

  // Parse the words
  ph->name.s = ph->start + 2;

  while ((*ph->name.s == ' ') && (ph->name.s != ph->end - 1)) {
    ph->name.s++;
  }

  // Placeholder is empty
  if (ph->name.s == ph->end - 1) {
    ph->type = ltm_placeholder_type_invalid;

    return true;
  }

  const char *ident = ph->name.s;

  while ((*ident != ' ') && (ident != ph->end - 1)) {
    ident++;
  }

  ph->name.len = ident - ph->name.s;

  // Skip whitespace over to next word
  while ((*ident == ' ') && (ident != ph->end - 1)) {
    ident++;
  }

  if (ident == ph->end - 1) {
    ph->type = ltm_placeholder_type_var;
  } else {
    // Further parse the identifier
    const char *temp = ident;

    while ((*temp != ' ') && (temp != ph->end - 1)) {
      temp++;
    }

    size_t ident_len = temp - ident;

    if (strncmp("start", ident, ident_len) == 0) {
      ph->type = ltm_placeholder_type_nested_start;
    } else if (strncmp("end", ident, ident_len) == 0) {
      ph->type = ltm_placeholder_type_nested_end;
    } else {
      ph->type = ltm_placeholder_type_invalid;
    }
  }

  return true;
}

ltm_err ltm_template_compile_n(ltm_template **out, const char *s, size_t len) {
  ltm_template *template;
  LTM_RES(ltm_template_init(&template));

  ltm_placeholder ph;
  bool in_nested = false;
  const char *nested_start = NULL, *nested_name = NULL;
  size_t nested_depth = 0, nested_name_len = 0;

  size_t cur_nested_depth = 0;

  while (ltm_template_next_placeholder(&ph, s, len)) {
    // Add part before placeholder as literal
    if (!in_nested && (ph.start != s)) {
      LTM_RES2(ltm_template_block_append(template,
                                         ltm_template_block_type_literal,
                                         (void *)s, ph.start - s),
               ltm_template_free(template));
    }

    switch (ph.type) {
    // Invalid placeholders can be detected as early as possible
    case ltm_placeholder_type_invalid:
      ltm_template_free(template);

      return ltm_err_invalid_template;
    case ltm_placeholder_type_var:
      if (!in_nested) {
        LTM_RES2(ltm_template_block_append(
                     template, ltm_template_block_type_var, NULL, 0),
                 ltm_template_free(template));
        LTM_RES2(ltm_template_name_append(template, ph.name.s, ph.name.len,
                                          template->blocks.len - 1),
                 ltm_template_free(template));
      }
      break;
    case ltm_placeholder_type_nested_start:
      if (!in_nested) {
        nested_start = ph.end + 1;
        nested_depth = cur_nested_depth;
        nested_name = ph.name.s;
        nested_name_len = ph.name.len;
        in_nested = true;
      }
      cur_nested_depth++;
      break;
    case ltm_placeholder_type_nested_end:
      // This means there's more nested end placeholders than nested starts
      if (cur_nested_depth == 0) {
        ltm_template_free(template);

        return ltm_err_invalid_template;
      }

      cur_nested_depth--;

      if (in_nested && (cur_nested_depth == nested_depth)) {
        size_t nested_len = ph.start - nested_start;
        ltm_template *nested_template;
        LTM_RES2(
            ltm_template_compile_n(&nested_template, nested_start, nested_len),
            ltm_template_free(template));
        LTM_RES(ltm_template_block_append(
            template, ltm_template_block_type_nested, nested_template, 0));
        LTM_RES2(ltm_template_name_append(template, nested_name,
                                          nested_name_len,
                                          template->blocks.len - 1),
                 ltm_template_free(template));

        in_nested = false;
      }
      // We encountered a nested end without a start
      else if (!in_nested) {
        ltm_template_free(template);

        return ltm_err_invalid_template;
      }
      break;
    }

    len -= ph.end + 1 - s;
    s = ph.end + 1;
  }

  // Unfinished nested
  if (in_nested) {
    ltm_template_free(template);

    return ltm_err_invalid_template;
  }

  // Add remaining trailing literal
  if (len > 0) {
    LTM_RES2(ltm_template_block_append(
                 template, ltm_template_block_type_literal, (void *)s, len),
             ltm_template_free(template));
  }

  *out = template;

  return ltm_err_ok;
}

ltm_err ltm_template_compile(ltm_template **out, const char *template) {
  return ltm_template_compile_n(out, template, strlen(template));
}