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conversion from DateTime structure to timestamp (partial)

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This only handles dates after 1970. The code
is getting ugly and I think it is the wrong approach.
Will clean up in the next commit
This commit is contained in:
Emil Lerch 2022-02-15 14:21:17 -08:00
parent 0706dd5e6f
commit 49f3f48aa8
Signed by: lobo
GPG Key ID: A7B62D657EF764F8
1 changed files with 153 additions and 5 deletions
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158
src/date.zig
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@ -6,12 +6,13 @@ const std = @import("std");
pub const DateTime = struct { day: u8, month: u8, year: u16, hour: u8, minute: u8, second: u8 };
const SECONDS_PER_DAY = 86400; //* 24* 60 * 60 */
const DAYS_PER_YEAR = 365; //* Normal year (no leap year) */
pub fn timestampToDateTime(timestamp: i64) DateTime {
// aus https://de.wikipedia.org/wiki/Unixzeit
const unixtime = @intCast(u64, timestamp);
const SECONDS_PER_DAY = 86400; //* 24* 60 * 60 */
const DAYS_PER_YEAR = 365; //* Normal year (no leap year) */
const DAYS_IN_4_YEARS = 1461; //* 4*365 + 1 */
const DAYS_IN_100_YEARS = 36524; //* 100*365 + 25 - 1 */
const DAYS_IN_400_YEARS = 146097; //* 400*365 + 100 - 4 + 1 */
@ -54,6 +55,127 @@ pub fn timestampToDateTime(timestamp: i64) DateTime {
return DateTime{ .day = day, .month = month, .year = year, .hour = hours, .minute = minutes, .second = seconds };
}
/// Converts a string to a timestamp value. May not handle dates before the
/// epoch
pub fn parseIso8601Timestamp(data: []const u8) !i64 {
_ = data;
return error.NotImplemented;
// TODO: Use a parsing for loop with a state machine implementation
// to tell us where we are in the string
// if (data.len < 4) return error.NotEnoughData;
// var year = try std.fmt.parseInt(u8, data[0..4], 10);
//
// var month:u4 = 0;
// if (data.len > 5) {
// if (data[5] != '-') return error.InvalidCharacter;
// var next_dash = std.mem.indexOf(u8, data[6..], "-");
// if (next_dash == null)
// next_dash = data.len - 6;
// month = std.fmt.parseInt(u8, data[6..next_dash + 6], 10);
// }
// var day:u5 = 0;
// var hours: u5 = 0;
// var minutes: u6 = 0;
// var seconds: u6 = 0;
// var milliseconds: u9 = 0;
// ISO 8601 is complicated. We're going
}
fn dateTimeToTimestamp(datetime: DateTime) !i64 {
if (datetime.month > 12 or
datetime.day > 31 or
datetime.hour >= 24 or
datetime.minute >= 60 or
datetime.second >= 60) return error.DateTimeOutOfRange;
const epoch_year = 1970;
if (datetime.year < epoch_year) return error.DatesBeforeEpochNotImplemented;
const leap_years_between = leapYearsBetween(epoch_year, datetime.year);
var add_days: u1 = 0;
const years_diff = std.math.absCast(@as(i17, datetime.year) - @as(i17, epoch_year));
std.log.debug("Years from epoch: {d}, Leap years: {d}", .{ years_diff, leap_years_between });
var days_diff: i32 = (years_diff * DAYS_PER_YEAR) + leap_years_between + add_days;
std.log.debug("Days with leap year, without month: {d}", .{days_diff});
const seconds_into_year = secondsFromBeginningOfYear(
datetime.year,
datetime.month,
datetime.day,
datetime.hour,
datetime.minute,
datetime.second,
);
return (days_diff * SECONDS_PER_DAY) + @as(i64, seconds_into_year);
}
fn secondsFromBeginningOfYear(year: u16, month: u8, day: u8, hour: u8, minute: u8, second: u8) u32 {
const current_year_is_leap_year = isLeapYear(year);
const leap_year_days_per_month: [12]u5 = .{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
const normal_days_per_month: [12]u5 = .{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
const days_per_month = if (current_year_is_leap_year) leap_year_days_per_month else normal_days_per_month;
var current_month: usize = 1;
var end_month = month;
var days_diff: u32 = 0;
while (current_month != end_month) {
days_diff += days_per_month[current_month - 1]; // months are 1-based vs array is 0-based
current_month += 1;
}
std.log.debug("Days with month, without day: {d}. Day of month {d}, will add {d} days", .{
days_diff,
day,
day - 1,
});
// We need -1 because we're not actually including the ending day (that's up to hour/minute)
// In other words, days in the month are 1-based, while hours/minutes are zero based
days_diff += day - 1;
std.log.debug("Total days diff: {d}", .{days_diff});
var seconds_diff: u32 = days_diff * SECONDS_PER_DAY;
// From here out, we want to get everything into seconds
seconds_diff += @as(u32, hour) * 60 * 60;
seconds_diff += @as(u32, minute) * 60;
seconds_diff += @as(u32, second);
return seconds_diff;
}
fn isLeapYear(year: u16) bool {
if (year % 4 != 0) return false;
if (year % 400 == 0) return true;
if (year % 100 == 0) return false;
return true;
}
fn leapYearsBetween(start_year_inclusive: u16, end_year_exclusive: u16) u16 {
const start = std.math.min(start_year_inclusive, end_year_exclusive);
const end = std.math.max(start_year_inclusive, end_year_exclusive);
var current = start;
std.log.debug("Leap years starting from {d}, ending at {d}", .{ start, end });
while (current % 4 != 0 and current < end) {
current += 1;
}
if (current == end) return 0; // No leap years here. E.g. 1971-1973
// We're on a potential leap year, and now we can step by 4
var rc: u16 = 0;
while (current < end) {
if (current % 4 == 0) {
if (current % 100 != 0) {
std.log.debug("Year {d} is leap year", .{current});
rc += 1;
current += 4;
continue;
}
// We're on a century, which is normally not a leap year, unless
// it's divisible by 400
if (current % 400 == 0) {
std.log.debug("Year {d} is leap year", .{current});
rc += 1;
}
}
current += 4;
}
return rc;
}
fn printDateTime(dt: DateTime) void {
std.log.debug("{:0>4}-{:0>2}-{:0>2}T{:0>2}:{:0>2}:{:0<2}Z", .{
dt.year,
@ -69,9 +191,7 @@ pub fn printNowUtc() void {
printDateTime(timestampToDateTime(std.time.timestamp()));
}
test "GMT and localtime" {
std.testing.log_level = .debug;
std.log.debug("\n", .{});
test "Convert timestamp to datetime" {
printDateTime(timestampToDateTime(std.time.timestamp()));
try std.testing.expectEqual(DateTime{ .year = 2020, .month = 8, .day = 28, .hour = 9, .minute = 32, .second = 27 }, timestampToDateTime(1598607147));
@ -79,3 +199,31 @@ test "GMT and localtime" {
// Get time for date: https://wtools.io/convert-date-time-to-unix-time
try std.testing.expectEqual(DateTime{ .year = 2015, .month = 08, .day = 30, .hour = 12, .minute = 36, .second = 00 }, timestampToDateTime(1440938160));
}
test "Convert datetime to timestamp" {
std.testing.log_level = .debug;
std.log.debug("\n", .{});
try std.testing.expectEqual(@as(i64, 1598607147), try dateTimeToTimestamp(DateTime{ .year = 2020, .month = 8, .day = 28, .hour = 9, .minute = 32, .second = 27 }));
try std.testing.expectEqual(@as(i64, 1604207167), try dateTimeToTimestamp(DateTime{ .year = 2020, .month = 11, .day = 1, .hour = 5, .minute = 6, .second = 7 }));
try std.testing.expectEqual(@as(i64, 1440938160), try dateTimeToTimestamp(DateTime{ .year = 2015, .month = 08, .day = 30, .hour = 12, .minute = 36, .second = 00 }));
}
test "Convert ISO8601 string to timestamp" {
try std.testing.expectEqual(@as(i64, 1598607147), try dateTimeToTimestamp(DateTime{ .year = 2020, .month = 8, .day = 28, .hour = 9, .minute = 32, .second = 27 }));
try std.testing.expectEqual(@as(i64, 1604207167), try dateTimeToTimestamp(DateTime{ .year = 2020, .month = 11, .day = 1, .hour = 5, .minute = 6, .second = 7 }));
try std.testing.expectEqual(@as(i64, 1440938160), try dateTimeToTimestamp(DateTime{ .year = 2015, .month = 08, .day = 30, .hour = 12, .minute = 36, .second = 00 }));
}
// TODO: I think before epoch, the best approach is to flip the epoch and the
// input date, calculate the answer, then flip signs. However, this requires
// re-designing the algorithm to start from something other than midnight
// January 1st. This will require an overhaul, so for now, we'll leave
// this unimplemented.
//
// test "Convert datetime to timestamp before 1970" {
// std.testing.log_level = .debug;
// std.log.debug("\n", .{});
// try std.testing.expectEqual(@as(i64, -449392815000), try dateTimeToTimestamp(DateTime{ .year = 1955, .month = 10, .day = 05, .hour = 16, .minute = 39, .second = 45 }));
//
//
// 1955.1 - .1 + x = 1970
// }