#include "cst_util.h"

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

static int buf_reserve(cst_buf_t *b, size_t extra) {
  if (b->len + extra + 1 <= b->cap)
    return 0;
  size_t nc = b->cap ? b->cap : 256;
  while (nc < b->len + extra + 1)
    nc *= 2;
  char *nb = realloc(b->buf, nc);
  if (!nb)
    return -1;
  b->buf = nb;
  b->cap = nc;
  return 0;
}

int cst_buf_append(cst_buf_t *b, const char *s, size_t n) {
  if (!b)
    return -1;
  if (buf_reserve(b, n) != 0)
    return -1;
  if (n)
    memcpy(b->buf + b->len, s, n);
  b->len += n;
  b->buf[b->len] = 0;
  return 0;
}

int cst_buf_puts(cst_buf_t *b, const char *s) {
  return cst_buf_append(b, s ? s : "", s ? strlen(s) : 0);
}

int cst_buf_printf(cst_buf_t *b, const char *fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  va_list ap2;
  va_copy(ap2, ap);
  int n = vsnprintf(NULL, 0, fmt, ap);
  va_end(ap);
  if (n < 0 || buf_reserve(b, (size_t)n) != 0) {
    va_end(ap2);
    return -1;
  }
  vsnprintf(b->buf + b->len, (size_t)n + 1, fmt, ap2);
  va_end(ap2);
  b->len += (size_t)n;
  return 0;
}

void cst_buf_free(cst_buf_t *b) {
  if (!b)
    return;
  free(b->buf);
  b->buf = NULL;
  b->len = b->cap = 0;
}

char *cst_buf_steal(cst_buf_t *b) {
  if (buf_reserve(b, 0) != 0)
    return NULL;
  char *s = b->buf;
  b->buf = NULL;
  b->len = b->cap = 0;
  return s;
}

size_t cst_utf8_floor(const char *s, size_t n) {
  if (!s || n == 0)
    return 0;
  size_t i = n;
  /* walk back over at most 3 continuation bytes to the lead byte */
  size_t back = 0;
  while (i > 0 && back < 3 && ((unsigned char)s[i - 1] & 0xC0) == 0x80) {
    i--;
    back++;
  }
  if (i == 0)
    return n;
  unsigned char lead = (unsigned char)s[i - 1];
  size_t need = 1;
  if (lead >= 0xF0)
    need = 4;
  else if (lead >= 0xE0)
    need = 3;
  else if (lead >= 0xC0)
    need = 2;
  if (need == 1)
    return n; /* ASCII lead; any continuation bytes after it are invalid
                 anyway and get sanitized later */
  if (back + 1 >= need)
    return n;
  return i - 1; /* sequence incomplete: cut before lead byte */
}

static size_t utf8_seq_ok(const unsigned char *p, size_t left) {
  unsigned char c = p[0];
  size_t need;
  unsigned cp;
  if (c < 0x80)
    return 1;
  if ((c & 0xE0) == 0xC0) {
    need = 2;
    cp = c & 0x1F;
  } else if ((c & 0xF0) == 0xE0) {
    need = 3;
    cp = c & 0x0F;
  } else if ((c & 0xF8) == 0xF0) {
    need = 4;
    cp = c & 0x07;
  } else {
    return 0;
  }
  if (left < need)
    return 0;
  for (size_t i = 1; i < need; i++) {
    if ((p[i] & 0xC0) != 0x80)
      return 0;
    cp = (cp << 6) | (p[i] & 0x3F);
  }
  if ((need == 2 && cp < 0x80) || (need == 3 && cp < 0x800) ||
      (need == 4 && (cp < 0x10000 || cp > 0x10FFFF)) ||
      (cp >= 0xD800 && cp <= 0xDFFF))
    return 0;
  return need;
}

char *cst_utf8_sanitize(const char *s, size_t n, size_t *out_len) {
  char *out = malloc(n + 1);
  if (!out)
    return NULL;
  size_t o = 0;
  const unsigned char *p = (const unsigned char *)(s ? s : "");
  size_t i = 0;
  while (i < n) {
    size_t k = utf8_seq_ok(p + i, n - i);
    if (k == 0) {
      out[o++] = '?';
      i++;
      continue;
    }
    memcpy(out + o, p + i, k);
    o += k;
    i += k;
  }
  out[o] = 0;
  if (out_len)
    *out_len = o;
  return out;
}

uint64_t cst_fnv1a64(uint64_t h, const void *data, size_t n) {
  const unsigned char *p = data;
  for (size_t i = 0; i < n; i++) {
    h ^= p[i];
    h *= 1099511628211ULL;
  }
  return h;
}