413 lines
17 KiB
Zig
413 lines
17 KiB
Zig
// From https://gist.github.com/WoodyAtHome/3ef50b17f0fa2860ac52b97af12f8d15
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// Translated from German. We don't need any local time for this use case, and conversion
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// really requires the TZ DB.
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const std = @import("std");
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const log = std.log.scoped(.date);
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pub const DateTime = struct { day: u8, month: u8, year: u16, hour: u8, minute: u8, second: u8 };
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const SECONDS_PER_DAY = 86400; //* 24* 60 * 60 */
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const DAYS_PER_YEAR = 365; //* Normal year (no leap year) */
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pub fn timestampToDateTime(timestamp: i64) DateTime {
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// aus https://de.wikipedia.org/wiki/Unixzeit
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const unixtime = @as(u64, @intCast(timestamp));
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const DAYS_IN_4_YEARS = 1461; //* 4*365 + 1 */
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const DAYS_IN_100_YEARS = 36524; //* 100*365 + 25 - 1 */
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const DAYS_IN_400_YEARS = 146097; //* 400*365 + 100 - 4 + 1 */
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const DAY_NUMBER_ADJUSTED_1970_01_01 = 719468; //* Day number relates to March 1st */
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var dayN: u64 = DAY_NUMBER_ADJUSTED_1970_01_01 + unixtime / SECONDS_PER_DAY;
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var seconds_since_midnight: u64 = unixtime % SECONDS_PER_DAY;
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var temp: u64 = 0;
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// Leap year rules for Gregorian Calendars
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// Any year divisible by 100 is not a leap year unless also divisible by 400
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temp = 4 * (dayN + DAYS_IN_100_YEARS + 1) / DAYS_IN_400_YEARS - 1;
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var year = @as(u16, @intCast(100 * temp));
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dayN -= DAYS_IN_100_YEARS * temp + temp / 4;
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// For Julian calendars, each year divisible by 4 is a leap year
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temp = 4 * (dayN + DAYS_PER_YEAR + 1) / DAYS_IN_4_YEARS - 1;
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year += @as(u16, @intCast(temp));
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dayN -= DAYS_PER_YEAR * temp + temp / 4;
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// dayN calculates the days of the year in relation to March 1
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var month = @as(u8, @intCast((5 * dayN + 2) / 153));
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var day = @as(u8, @intCast(dayN - (@as(u64, @intCast(month)) * 153 + 2) / 5 + 1));
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// 153 = 31+30+31+30+31 Days for the 5 months from March through July
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// 153 = 31+30+31+30+31 Days for the 5 months from August through December
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// 31+28 Days for January and February (see below)
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// +2: Rounding adjustment
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// +1: The first day in March is March 1st (not March 0)
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month += 3; // Convert from the day that starts on March 1st, to a human year */
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if (month > 12) { // months 13 and 14 become 1 (January) und 2 (February) of the next year
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month -= 12;
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year += 1;
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}
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var hours = @as(u8, @intCast(seconds_since_midnight / 3600));
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var minutes = @as(u8, @intCast(seconds_since_midnight % 3600 / 60));
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var seconds = @as(u8, @intCast(seconds_since_midnight % 60));
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return DateTime{ .day = day, .month = month, .year = year, .hour = hours, .minute = minutes, .second = seconds };
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}
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pub fn parseEnglishToTimestamp(data: []const u8) !i64 {
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return try dateTimeToTimestamp(try parseEnglishToDateTime(data));
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}
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const EnglishParsingState = enum { Start, Day, Month, Year, Hour, Minute, Second, End };
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/// Converts a string to a timestamp value. May not handle dates before the
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/// epoch. Dates should look like "Fri, 03 Jun 2022 18:12:36 GMT"
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pub fn parseEnglishToDateTime(data: []const u8) !DateTime {
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// Fri, 03 Jun 2022 18:12:36 GMT
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if (!std.mem.endsWith(u8, data, "GMT")) return error.InvalidFormat;
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var start: usize = 0;
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var state = EnglishParsingState.Start;
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// Anything not explicitly set by our string would be 0
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var rc = DateTime{ .year = 0, .month = 0, .day = 0, .hour = 0, .minute = 0, .second = 0 };
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for (data, 0..) |ch, i| {
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switch (ch) {
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',' => {},
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' ', ':' => {
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// State transition
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// We're going to coerce and this might not go well, but we
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// want the compiler to create checks, so we'll turn on
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// runtime safety for this block, forcing checks in ReleaseSafe
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// ReleaseFast modes.
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const next_state = try endEnglishState(state, &rc, data[start..i]);
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state = next_state;
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start = i + 1;
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},
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else => {}, // We need to be pretty trusting on this format...
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}
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}
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return rc;
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}
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fn endEnglishState(current_state: EnglishParsingState, date: *DateTime, prev_data: []const u8) !EnglishParsingState {
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var next_state: EnglishParsingState = undefined;
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log.debug("endEnglishState. Current state '{s}', data: {s}", .{ current_state, prev_data });
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// Using two switches is slightly less efficient, but more readable
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switch (current_state) {
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.End => return error.IllegalStateTransition,
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.Start => next_state = .Day,
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.Day => next_state = .Month,
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.Month => next_state = .Year,
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.Year => next_state = .Hour,
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.Hour => next_state = .Minute,
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.Minute => next_state = .Second,
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.Second => next_state = .End,
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}
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switch (current_state) {
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.Year => date.year = try std.fmt.parseUnsigned(u16, prev_data, 10),
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.Month => date.month = try parseEnglishMonth(prev_data),
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.Day => date.day = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Hour => date.hour = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Minute => date.minute = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Second => date.second = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Start => {},
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.End => return error.InvalidState,
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}
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return next_state;
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}
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fn parseEnglishMonth(data: []const u8) !u8 {
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if (std.ascii.startsWithIgnoreCase(data, "Jan")) return 1;
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if (std.ascii.startsWithIgnoreCase(data, "Feb")) return 2;
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if (std.ascii.startsWithIgnoreCase(data, "Mar")) return 3;
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if (std.ascii.startsWithIgnoreCase(data, "Apr")) return 4;
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if (std.ascii.startsWithIgnoreCase(data, "May")) return 5;
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if (std.ascii.startsWithIgnoreCase(data, "Jun")) return 6;
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if (std.ascii.startsWithIgnoreCase(data, "Jul")) return 7;
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if (std.ascii.startsWithIgnoreCase(data, "Aug")) return 8;
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if (std.ascii.startsWithIgnoreCase(data, "Sep")) return 9;
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if (std.ascii.startsWithIgnoreCase(data, "Oct")) return 10;
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if (std.ascii.startsWithIgnoreCase(data, "Nov")) return 11;
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if (std.ascii.startsWithIgnoreCase(data, "Dec")) return 12;
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return error.InvalidMonth;
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}
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pub fn parseIso8601ToTimestamp(data: []const u8) !i64 {
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return try dateTimeToTimestamp(try parseIso8601ToDateTime(data));
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}
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const IsoParsingState = enum { Start, Year, Month, Day, Hour, Minute, Second, Millisecond, End };
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/// Converts a string to a timestamp value. May not handle dates before the
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/// epoch
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pub fn parseIso8601ToDateTime(data: []const u8) !DateTime {
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// Basic format YYYYMMDDThhmmss
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if (data.len == "YYYYMMDDThhmmss".len and data[8] == 'T')
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return try parseIso8601BasicFormatToDateTime(data);
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var start: usize = 0;
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var state = IsoParsingState.Start;
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// Anything not explicitly set by our string would be 0
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var rc = DateTime{ .year = 0, .month = 0, .day = 0, .hour = 0, .minute = 0, .second = 0 };
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var zulu_time = false;
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for (data, 0..) |ch, i| {
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switch (ch) {
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'0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => {
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if (state == .Start) state = .Year;
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},
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'?', '~', '%' => {
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// These characters all specify the type of time (approximate, etc)
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// and we will ignore
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},
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'.', '-', ':', 'T' => {
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// State transition
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// We're going to coerce and this might not go well, but we
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// want the compiler to create checks, so we'll turn on
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// runtime safety for this block, forcing checks in ReleaseSafe
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// ReleaseFast modes.
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const next_state = try endIsoState(state, &rc, data[start..i]);
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state = next_state;
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start = i + 1;
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},
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'Z' => zulu_time = true,
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else => {
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log.err("Invalid character: {c}", .{ch});
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return error.InvalidCharacter;
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},
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}
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}
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if (!zulu_time) return error.LocalTimeNotSupported;
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// We know we have a Z at the end of this, so let's grab the last bit
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// of the string, minus the 'Z', and fly, eagles, fly!
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_ = try endIsoState(state, &rc, data[start .. data.len - 1]);
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return rc;
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}
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fn parseIso8601BasicFormatToDateTime(data: []const u8) !DateTime {
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return DateTime{
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.year = try std.fmt.parseUnsigned(u16, data[0..4], 10),
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.month = try std.fmt.parseUnsigned(u8, data[4..6], 10),
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.day = try std.fmt.parseUnsigned(u8, data[6..8], 10),
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.hour = try std.fmt.parseUnsigned(u8, data[9..11], 10),
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.minute = try std.fmt.parseUnsigned(u8, data[11..13], 10),
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.second = try std.fmt.parseUnsigned(u8, data[13..15], 10),
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};
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}
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fn endIsoState(current_state: IsoParsingState, date: *DateTime, prev_data: []const u8) !IsoParsingState {
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var next_state: IsoParsingState = undefined;
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log.debug("endIsoState. Current state '{s}', data: {s}", .{ current_state, prev_data });
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// Using two switches is slightly less efficient, but more readable
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switch (current_state) {
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.Start, .End => return error.IllegalStateTransition,
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.Year => next_state = .Month,
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.Month => next_state = .Day,
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.Day => next_state = .Hour,
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.Hour => next_state = .Minute,
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.Minute => next_state = .Second,
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.Second => next_state = .Millisecond,
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.Millisecond => next_state = .End,
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}
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// TODO: This won't handle signed, which Iso supports. For now, let's fail
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// explictly
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switch (current_state) {
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.Year => date.year = try std.fmt.parseUnsigned(u16, prev_data, 10),
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.Month => date.month = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Day => date.day = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Hour => date.hour = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Minute => date.minute = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Second => date.second = try std.fmt.parseUnsigned(u8, prev_data, 10),
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.Millisecond => {}, // We'll throw that away - our granularity is 1 second
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.Start, .End => return error.InvalidState,
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}
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return next_state;
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}
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fn dateTimeToTimestamp(datetime: DateTime) !i64 {
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const epoch = DateTime{
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.year = 1970,
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.month = 1,
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.day = 1,
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.hour = 0,
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.minute = 0,
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.second = 0,
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};
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return secondsBetween(epoch, datetime);
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}
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const DateTimeToTimestampError = error{
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DateTimeOutOfRange,
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};
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fn secondsBetween(start: DateTime, end: DateTime) DateTimeToTimestampError!i64 {
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try validateDatetime(start);
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try validateDatetime(end);
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if (end.year < start.year) return -1 * try secondsBetween(end, start);
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if (start.month != 1 or
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start.day != 1 or
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start.hour != 0 or
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start.minute != 0 or
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start.second != 0)
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{
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const seconds_into_start_year = secondsFromBeginningOfYear(
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start.year,
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start.month,
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start.day,
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start.hour,
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start.minute,
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start.second,
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);
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const new_start = DateTime{
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.year = start.year,
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.month = 1,
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.day = 1,
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.hour = 0,
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.minute = 0,
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.second = 0,
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};
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return (try secondsBetween(new_start, end)) - seconds_into_start_year;
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}
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const leap_years_between = leapYearsBetween(start.year, end.year);
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var add_days: u1 = 0;
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const years_diff = end.year - start.year;
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log.debug("Years from epoch: {d}, Leap years: {d}", .{ years_diff, leap_years_between });
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var days_diff: i32 = (years_diff * DAYS_PER_YEAR) + leap_years_between + add_days;
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log.debug("Days with leap year, without month: {d}", .{days_diff});
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const seconds_into_year = secondsFromBeginningOfYear(
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end.year,
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end.month,
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end.day,
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end.hour,
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end.minute,
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end.second,
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);
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return (days_diff * SECONDS_PER_DAY) + @as(i64, seconds_into_year);
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}
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fn validateDatetime(dt: DateTime) !void {
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if (dt.month > 12 or
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dt.day > 31 or
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dt.hour >= 24 or
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dt.minute >= 60 or
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dt.second >= 60) return error.DateTimeOutOfRange;
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}
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fn secondsFromBeginningOfYear(year: u16, month: u8, day: u8, hour: u8, minute: u8, second: u8) u32 {
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const current_year_is_leap_year = isLeapYear(year);
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const leap_year_days_per_month: [12]u5 = .{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
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const normal_days_per_month: [12]u5 = .{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
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const days_per_month = if (current_year_is_leap_year) leap_year_days_per_month else normal_days_per_month;
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var current_month: usize = 1;
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var end_month = month;
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var days_diff: u32 = 0;
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while (current_month != end_month) {
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days_diff += days_per_month[current_month - 1]; // months are 1-based vs array is 0-based
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current_month += 1;
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}
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log.debug("Days with month, without day: {d}. Day of month {d}, will add {d} days", .{
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days_diff,
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day,
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day - 1,
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});
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// We need -1 because we're not actually including the ending day (that's up to hour/minute)
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// In other words, days in the month are 1-based, while hours/minutes are zero based
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days_diff += day - 1;
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log.debug("Total days diff: {d}", .{days_diff});
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var seconds_diff: u32 = days_diff * SECONDS_PER_DAY;
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// From here out, we want to get everything into seconds
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seconds_diff += @as(u32, hour) * 60 * 60;
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seconds_diff += @as(u32, minute) * 60;
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seconds_diff += @as(u32, second);
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return seconds_diff;
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}
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fn isLeapYear(year: u16) bool {
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if (year % 4 != 0) return false;
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if (year % 400 == 0) return true;
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if (year % 100 == 0) return false;
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return true;
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}
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fn leapYearsBetween(start_year_inclusive: u16, end_year_exclusive: u16) u16 {
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const start = @min(start_year_inclusive, end_year_exclusive);
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const end = @max(start_year_inclusive, end_year_exclusive);
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var current = start;
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log.debug("Leap years starting from {d}, ending at {d}", .{ start, end });
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while (current % 4 != 0 and current < end) {
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current += 1;
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}
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if (current == end) return 0; // No leap years here. E.g. 1971-1973
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// We're on a potential leap year, and now we can step by 4
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var rc: u16 = 0;
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while (current < end) {
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if (current % 4 == 0) {
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if (current % 100 != 0) {
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log.debug("Year {d} is leap year", .{current});
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rc += 1;
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current += 4;
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continue;
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}
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// We're on a century, which is normally not a leap year, unless
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// it's divisible by 400
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if (current % 400 == 0) {
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log.debug("Year {d} is leap year", .{current});
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rc += 1;
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}
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}
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current += 4;
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}
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return rc;
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}
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fn printDateTime(dt: DateTime) void {
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log.debug("{:0>4}-{:0>2}-{:0>2}T{:0>2}:{:0>2}:{:0<2}Z", .{
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dt.year,
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dt.month,
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dt.day,
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dt.hour,
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dt.minute,
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dt.second,
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});
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}
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pub fn printNowUtc() void {
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printDateTime(timestampToDateTime(std.time.timestamp()));
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}
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test "Convert timestamp to datetime" {
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printDateTime(timestampToDateTime(std.time.timestamp()));
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try std.testing.expectEqual(DateTime{ .year = 2020, .month = 8, .day = 28, .hour = 9, .minute = 32, .second = 27 }, timestampToDateTime(1598607147));
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try std.testing.expectEqual(DateTime{ .year = 2020, .month = 11, .day = 1, .hour = 5, .minute = 6, .second = 7 }, timestampToDateTime(1604207167));
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// Get time for date: https://wtools.io/convert-date-time-to-unix-time
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try std.testing.expectEqual(DateTime{ .year = 2015, .month = 8, .day = 30, .hour = 12, .minute = 36, .second = 0 }, timestampToDateTime(1440938160));
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}
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test "Convert datetime to timestamp" {
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try std.testing.expectEqual(@as(i64, 1598607147), try dateTimeToTimestamp(DateTime{ .year = 2020, .month = 8, .day = 28, .hour = 9, .minute = 32, .second = 27 }));
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try std.testing.expectEqual(@as(i64, 1604207167), try dateTimeToTimestamp(DateTime{ .year = 2020, .month = 11, .day = 1, .hour = 5, .minute = 6, .second = 7 }));
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try std.testing.expectEqual(@as(i64, 1440938160), try dateTimeToTimestamp(DateTime{ .year = 2015, .month = 8, .day = 30, .hour = 12, .minute = 36, .second = 0 }));
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}
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test "Convert ISO8601 string to timestamp" {
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try std.testing.expectEqual(DateTime{ .year = 2020, .month = 8, .day = 28, .hour = 9, .minute = 32, .second = 27 }, try parseIso8601ToDateTime("20200828T093227"));
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try std.testing.expectEqual(DateTime{ .year = 2020, .month = 8, .day = 28, .hour = 9, .minute = 32, .second = 27 }, try parseIso8601ToDateTime("2020-08-28T9:32:27Z"));
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try std.testing.expectEqual(DateTime{ .year = 2020, .month = 11, .day = 1, .hour = 5, .minute = 6, .second = 7 }, try parseIso8601ToDateTime("2020-11-01T5:06:7Z"));
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try std.testing.expectEqual(DateTime{ .year = 2015, .month = 8, .day = 30, .hour = 12, .minute = 36, .second = 0 }, try parseIso8601ToDateTime("2015-08-30T12:36:00.000Z"));
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}
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test "Convert datetime to timestamp before 1970" {
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try std.testing.expectEqual(@as(i64, -449392815), try dateTimeToTimestamp(DateTime{ .year = 1955, .month = 10, .day = 5, .hour = 16, .minute = 39, .second = 45 }));
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}
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test "Convert whatever AWS is sending us to timestamp" {
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const string_date = "Fri, 03 Jun 2022 18:12:36 GMT";
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try std.testing.expectEqual(DateTime{ .year = 2022, .month = 6, .day = 3, .hour = 18, .minute = 12, .second = 36 }, try parseEnglishToDateTime(string_date));
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}
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