Got conversion to timestamp working and passing tests

src/main.zig

@@ -35,7 +35,7 @@ pub const Year = union(YearTag) {
     }
 
     pub fn seconds(self: Self) i64 {
-        return self.days * SECONDS_PER_DAY;
+        return @as(i64, self.days()) * SECONDS_PER_DAY;
     }
 
     pub fn get(self: Self) u31 {
@@ -99,8 +99,8 @@ pub const Month = enum(u4) {
         };
     }
 
-    pub fn seconds(self: Self) u32 {
-        return self.days() * SECONDS_PER_DAY;
+    pub fn seconds(self: Self, year: Year) u32 {
+        return @as(u32, self.days(year)) * SECONDS_PER_DAY;
     }
 
     pub fn next(self: Self) ?Self {
@@ -252,35 +252,39 @@ pub const DateTime = struct {
     }
 
     pub fn toTimestamp(self: Self) i64 {
-        var seconds = 0;
+        var seconds: i64 = 0;
         if (self.year.get() < 1970) {
             var year = Year.new(1970);
-            while (year != self.year) {
+            while (year.get() != self.year.get()) {
                 year = year.previous();
                 seconds -= year.seconds();
             }
         } else if (self.year.get() > 1970) {
             var year = Year.new(1970);
-            while (year != self.year) {
+            while (year.get() != self.year.get()) {
                 seconds += year.seconds();
                 year = year.next();
             }
         }
         var month = Month.january;
         while (month != self.month) {
-            seconds += month.seconds();
+            seconds += month.seconds(self.year);
             month = month.next().?;
         }
-        seconds += (self.day - 1) * SECONDS_PER_DAY;
-        if (self.hours) |h| {
-            seconds += h * 3600;
+        seconds += @as(i64, self.day - 1) * SECONDS_PER_DAY;
+        if (self.hour) |h| {
+            seconds += @as(i64, h - 1) * 3600;
         }
-        if (self.minutes) |m| {
-            seconds += m * 60;
+        if (self.minute) |m| {
+            seconds += @as(i64, m) * 60;
         }
-        if (self.seconds) |s| {
+        if (self.second) |s| {
             seconds += s;
         }
+        switch (self.tz) {
+            .utc => {},
+            .offset => |ofs| seconds -= ofs.asSeconds(),
+        }
         return seconds;
     }
 };
@@ -312,3 +316,31 @@ test "get offset" {
     };
     try testing.expectEqual(dt.getOffset().?, Offset{ .negative = .{ .hours = 5, .minutes = null } });
 }
+
+test "to timestamp utc" {
+    const dt = DateTime{
+        .year = Year.new(2023),
+        .month = .june,
+        .day = 13,
+        .hour = 6,
+        .minute = 21,
+        .second = 22,
+        .nanos = null,
+        .tz = .utc,
+    };
+    try testing.expectEqual(dt.toTimestamp(), 1686633682);
+}
+
+test "to timestamp negative offset" {
+    const dt = DateTime{
+        .year = Year.new(2023),
+        .month = .june,
+        .day = 13,
+        .hour = 1,
+        .minute = 21,
+        .second = 22,
+        .nanos = null,
+        .tz = TimeZone.new(-5, null).?,
+    };
+    try testing.expectEqual(dt.toTimestamp(), 1686633682);
+}