Add fromTimestamp and improved testing coverage and feedback

src/main.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const debug = std.debug;
 const testing = std.testing;
 
 pub const SECONDS_PER_MINUTE = 60;
@@ -9,18 +10,18 @@ pub const YearTag = enum(u1) {
     normal,
     leap,
 
-    fn new(year: u31) YearTag {
+    fn new(year: i32) YearTag {
-        return if (year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)) .leap else .normal;
+        return if (@rem(year, 4) == 0 and (@rem(year, 100) != 0 or @rem(year, 400) == 0)) .leap else .normal;
     }
 };
 
 pub const Year = union(YearTag) {
-    normal: u31,
+    normal: i32,
-    leap: u31,
+    leap: i32,
 
     const Self = @This();
 
-    pub fn new(year: u31) Self {
+    pub fn new(year: i32) Self {
         return switch (YearTag.new(year)) {
             .normal => Self{ .normal = year },
             .leap => Self{ .leap = year },
@@ -38,7 +39,7 @@ pub const Year = union(YearTag) {
         return @as(i64, self.days()) * SECONDS_PER_DAY;
     }
 
-    pub fn get(self: Self) u31 {
+    pub fn get(self: Self) i32 {
         return switch (self) {
             .normal => |year| year,
             .leap => |year| year,
@@ -57,19 +58,23 @@ pub const Year = union(YearTag) {
 test "new year" {
     try testing.expectEqual(Year.new(2023), Year{ .normal = 2023 });
     try testing.expectEqual(Year.new(2024), Year{ .leap = 2024 });
+    debug.print("Passed\n", .{});
 }
 
 test "get year" {
     try testing.expectEqual(Year.new(2023).get(), 2023);
     try testing.expectEqual(Year.new(2024).get(), 2024);
+    debug.print("Passed\n", .{});
 }
 
 test "next year" {
     try testing.expectEqual(Year.new(2023).next(), Year{ .leap = 2024 });
+    debug.print("Passed\n", .{});
 }
 
 test "last year" {
     try testing.expectEqual(Year.new(2024).previous(), Year{ .normal = 2023 });
+    debug.print("Passed\n", .{});
 }
 
 pub const Month = enum(u4) {
@@ -118,16 +123,19 @@ test "get days in month" {
     const year = Year.new(2023);
     const month = Month.february;
     try testing.expectEqual(month.days(year), 28);
+    debug.print("Passed\n", .{});
 }
 
 test "next month" {
     try testing.expectEqual(Month.june.next(), .july);
     try testing.expectEqual(Month.december.next(), null);
+    debug.print("Passed\n", .{});
 }
 
 test "last month" {
     try testing.expectEqual(Month.june.previous(), .may);
     try testing.expectEqual(Month.january.previous(), null);
+    debug.print("Passed\n", .{});
 }
 
 pub const TimeZoneTag = enum(u1) {
@@ -186,11 +194,13 @@ pub const Offset = union(Sign) {
 test "new offsets" {
     try testing.expectEqual(Offset.new(-5, null), Offset{ .negative = .{ .hours = 5, .minutes = null } });
     try testing.expectEqual(Offset.new(3, null), Offset{ .positive = .{ .hours = 3, .minutes = null } });
+    debug.print("Passed\n", .{});
 }
 
 test "as seconds" {
     try testing.expectEqual(Offset.new(-4, 30).?.asSeconds(), -16200);
     try testing.expectEqual(Offset.new(3, null).?.asSeconds(), 10800);
+    debug.print("Passed\n", .{});
 }
 
 pub const TimeZone = union(TimeZoneTag) {
@@ -219,6 +229,7 @@ test "new timezone" {
         .offset => |ofs| try testing.expectEqual(ofs, Offset{ .negative = .{ .hours = 5, .minutes = null } }),
         else => unreachable,
     }
+    debug.print("Passed\n", .{});
 }
 
 test "new timezone utc" {
@@ -226,6 +237,7 @@ test "new timezone utc" {
     const tz1 = TimeZone.new(0, null).?;
     try testing.expectEqual(@as(TimeZoneTag, tz0), .utc);
     try testing.expectEqual(@as(TimeZoneTag, tz1), .utc);
+    debug.print("Passed\n", .{});
 }
 
 pub const WeekDay = enum(u3) {
@@ -255,7 +267,7 @@ pub const DateTime = struct {
 
     const Self = @This();
 
-    pub fn getYear(self: Self) u32 {
+    pub fn getYear(self: Self) i32 {
         return self.year.get();
     }
 
@@ -302,6 +314,87 @@ pub const DateTime = struct {
         return seconds;
     }
 
+    pub fn fromTimestamp(ts: i64) Self {
+        if (ts < 0) {
+            var seconds: i64 = 0;
+            var year = Year.new(-1);
+            while (seconds > -year.seconds()) {
+                seconds -= year.seconds();
+                year = year.previous();
+            }
+            var month: ?Month = Month.december;
+            while (month != null) {
+                if (month) |m| {
+                    if (seconds > m.seconds(year)) break;
+                    seconds -= m.seconds(year);
+                    month = m.previous();
+                }
+            }
+            var day = month.?.days(year);
+            while (day > 0 and seconds < -SECONDS_PER_DAY) {
+                seconds -= SECONDS_PER_DAY;
+                day -= 1;
+            }
+            var hours: u5 = 23;
+            while (hours >= 0 and seconds < -SECONDS_PER_HOUR) {
+                seconds -= SECONDS_PER_HOUR;
+                hours -= 1;
+            }
+            var minutes: u6 = 60;
+            while (minutes >= 0 and seconds < -60) {
+                seconds -= 60;
+                minutes -= 1;
+            }
+            const second = @intCast(u6, seconds + 60);
+            return Self{
+                .year = year,
+                .month = month.?,
+                .day = day,
+                .hour = hours,
+                .minute = minutes,
+                .second = @as(u6, second),
+                .tz = .utc,
+            };
+        } else if (ts > 0) {
+            var seconds = ts;
+            var year = Year.new(1970);
+            while (year.seconds() < seconds) {
+                seconds -= year.seconds();
+                year = year.next();
+            }
+            var month = Month.january;
+            while (month.seconds(year) < seconds) {
+                seconds -= month.seconds(year);
+                month = month.next().?;
+            }
+            const day = @divTrunc(seconds, SECONDS_PER_DAY) + 1;
+            seconds = @rem(seconds, SECONDS_PER_DAY);
+            const hour = @divTrunc(seconds, SECONDS_PER_HOUR);
+            seconds = @rem(seconds, SECONDS_PER_HOUR);
+            const minute = @divTrunc(seconds, 60);
+            seconds = @rem(seconds, 60);
+            return Self{
+                .year = year,
+                .month = month,
+                .day = @intCast(u8, day),
+                .hour = @intCast(u5, hour),
+                .minute = @intCast(u6, minute),
+                .second = @intCast(u6, seconds),
+                .tz = .utc,
+            };
+        } else {
+            return Self{
+                .year = Year.new(0),
+                .month = .january,
+                .day = 1,
+                .hour = 0,
+                .minute = 0,
+                .second = 0,
+                .tz = .utc,
+            };
+        }
+    }
+
     pub fn weekday(self: Self) WeekDay {
         const ts = self.toTimestamp();
         const days = @divTrunc(ts, SECONDS_PER_DAY);
@@ -326,6 +419,7 @@ test "get year" {
         .tz = TimeZone.new(-5, null).?,
     };
     try testing.expectEqual(dt.getYear(), 2023);
+    debug.print("Passed\n", .{});
 }
 
 test "get offset" {
@@ -339,6 +433,7 @@ test "get offset" {
         .tz = TimeZone.new(-5, null).?,
     };
     try testing.expectEqual(dt.getOffset().?, Offset{ .negative = .{ .hours = 5, .minutes = null } });
+    debug.print("Passed\n", .{});
 }
 
 test "to timestamp utc" {
@@ -352,6 +447,7 @@ test "to timestamp utc" {
         .tz = .utc,
     };
     try testing.expectEqual(dt.toTimestamp(), 1686633682);
+    debug.print("Passed\n", .{});
 }
 
 test "to timestamp negative offset" {
@@ -365,6 +461,14 @@ test "to timestamp negative offset" {
         .tz = TimeZone.new(-5, null).?,
     };
     try testing.expectEqual(dt.toTimestamp(), 1686633682);
+    debug.print("Passed\n", .{});
+}
+
+test "conversions" {
+    const ts = std.time.timestamp();
+    const dt = DateTime.fromTimestamp(ts);
+    try testing.expectEqual(dt.toTimestamp(), ts);
+    debug.print("Passed\n", .{});
 }
 
 test "get weekday" {
@@ -378,6 +482,7 @@ test "get weekday" {
         .tz = .utc,
     };
     try testing.expectEqual(dt.weekday(), .tuesday);
+    debug.print("Passed\n", .{});
 }
 
 test "get weekday 2" {
@@ -391,6 +496,7 @@ test "get weekday 2" {
         .tz = .utc,
     };
     try testing.expectEqual(dt.weekday(), .saturday);
+    debug.print("Passed\n", .{});
 }
 
 test "ordering lt" {
@@ -413,6 +519,7 @@ test "ordering lt" {
         .tz = .utc,
     };
     try testing.expectEqual(a.compare(b), .lt);
+    debug.print("Passed\n", .{});
 }
 
 test "ordering gt" {
@@ -435,4 +542,5 @@ test "ordering gt" {
         .tz = TimeZone.new(1, null).?,
     };
     try testing.expectEqual(a.compare(b), .gt);
+    debug.print("Passed\n", .{});
 }