1 files changed, 150 insertions, 0 deletions
diff --git a/subprojects/exess/src/timezone.c b/subprojects/exess/src/timezone.c
new file mode 100644
index 00000000..717f0d08
--- /dev/null
+++ b/subprojects/exess/src/timezone.c
@@ -0,0 +1,150 @@
+/*
+  Copyright 2019-2021 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "timezone.h"
+#include "date_utils.h"
+#include "read_utils.h"
+#include "string_utils.h"
+#include "write_utils.h"
+
+#include "exess/exess.h"
+
+#include <stdint.h>
+#include <stdlib.h>
+
+ExessResult
+exess_read_timezone(ExessTimezone* const out, const char* const str)
+{
+  out->quarter_hours = INT8_MAX;
+
+  // Start at the beginning (no whitespace skipping here)
+  size_t i = 0;
+
+  // Handle UTC special case
+  if (str[i] == 'Z') {
+    out->quarter_hours = 0;
+    return result(EXESS_SUCCESS, i + 1);
+  }
+
+  // Read leading sign (required)
+  int sign = 1;
+  switch (str[i]) {
+  case '+':
+    ++i;
+    break;
+  case '-':
+    sign = -1;
+    ++i;
+    break;
+  default:
+    return result(EXESS_EXPECTED_SIGN, i);
+  }
+
+  const char h0 = str[i];
+  if (!is_digit(h0)) {
+    return result(EXESS_EXPECTED_DIGIT, i);
+  }
+
+  const char h1 = str[++i];
+  if (!is_digit(h1)) {
+    return result(EXESS_EXPECTED_DIGIT, i);
+  }
+
+  ++i;
+
+  const int8_t hour = (int8_t)(sign * (10 * (h0 - '0') + (h1 - '0')));
+  if (hour > 14 || hour < -14) {
+    return result(EXESS_OUT_OF_RANGE, i);
+  }
+
+  if (str[i] != ':') {
+    return result(EXESS_EXPECTED_COLON, i);
+  }
+
+  const char m0 = str[++i];
+  if (!is_digit(m0)) {
+    return result(EXESS_EXPECTED_DIGIT, i);
+  }
+
+  const char m1 = str[++i];
+  if (!is_digit(m1)) {
+    return result(EXESS_EXPECTED_DIGIT, i);
+  }
+
+  const int8_t minute = (int8_t)(sign * (10 * (m0 - '0') + (m1 - '0')));
+
+  ++i;
+
+  if (minute % 15) {
+    return result(EXESS_UNSUPPORTED, i);
+  }
+
+  if (minute > 59 || minute < -59) {
+    return result(EXESS_OUT_OF_RANGE, i);
+  }
+
+  const int8_t quarters = (int8_t)(4 * hour + minute / 15);
+  if (quarters < -56 || quarters > 56) {
+    return result(EXESS_OUT_OF_RANGE, i);
+  }
+
+  out->quarter_hours = quarters;
+
+  return result(EXESS_SUCCESS, i);
+}
+
+size_t
+exess_timezone_string_length(const ExessTimezone value)
+{
+  return value.quarter_hours != EXESS_LOCAL ? (value.quarter_hours == 0) ? 1 : 6
+                                            : 0;
+}
+
+ExessResult
+write_timezone(const ExessTimezone value,
+               const size_t        buf_size,
+               char* const         buf,
+               size_t              o)
+{
+  if (value.quarter_hours == EXESS_LOCAL) {
+    return result(EXESS_SUCCESS, 0);
+  }
+
+  if (value.quarter_hours < -56 || value.quarter_hours > 56) {
+    return result(EXESS_BAD_VALUE, 0);
+  }
+
+  if (!buf) {
+    return result(EXESS_SUCCESS, exess_timezone_string_length(value));
+  }
+
+  if (value.quarter_hours == 0) {
+    write_char('Z', buf_size, buf, o);
+    return result(EXESS_SUCCESS, 1);
+  }
+
+  const uint8_t abs_quarters = (uint8_t)abs(value.quarter_hours);
+  const uint8_t abs_hour     = abs_quarters / 4;
+  const uint8_t abs_minute   = (uint8_t)(15u * (abs_quarters % 4u));
+
+  size_t n = 0;
+  n += write_char(value.quarter_hours < 0 ? '-' : '+', buf_size, buf, o + n);
+  n += write_two_digit_number(abs_hour, buf_size, buf, o + n);
+  n += write_char(':', buf_size, buf, o + n);
+  n += write_two_digit_number(abs_minute, buf_size, buf, o + n);
+
+  return result(EXESS_SUCCESS, n);
+}