consider negative relative delta

FObersteiner · Nov 7, 2024 · 8c71cf1 · 8c71cf1
1 parent 7fec00a
commit 8c71cf1
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Showing 2 changed files with 31 additions and 10 deletions.
diff --git a/lib/Datetime.zig b/lib/Datetime.zig
@@ -626,17 +626,20 @@ pub fn addRelative(dt: *const Datetime, rel_delta: Duration.RelativeDelta) !Date
     });
     var result: Datetime = try dt.add(abs_delta);
 
-    // TODO : account for negative rel_delta
-    const new_month: u8 = @truncate((rel_delta.months + @as(u32, dt.month)) % 12);
-    result.year += @truncate(rel_delta.years + (rel_delta.months + @as(u32, dt.month)) / 12);
-    result.month = new_month;
+    var m_off: i32 = @intCast(rel_delta.months + rel_delta.years * 12);
+    if (rel_delta.negative) m_off *= -1;
+    m_off += result.month;
+
+    result.year = @intCast(@as(i32, result.year) + @divFloor(m_off, 12));
+    const new_month: u8 = @intCast(@mod(m_off, 12));
+    if (new_month <= 0) {
+        result.month = new_month + 12;
+        result.year -= 1;
+    } else result.month = new_month;
 
     const days_in_month = cal.daysInMonth(result.month, cal.isLeapYear(result.year));
     if (result.day > days_in_month) result.day = days_in_month;
 
-    const opts: ?tz_options = if (dt.tz) |tz_ptr| .{ .tz = tz_ptr } else null;
-
-    // TODO : 'normalizeTOFields'
     return try Datetime.fromFields(.{
         .year = result.year,
         .month = result.month,
@@ -646,7 +649,7 @@ pub fn addRelative(dt: *const Datetime, rel_delta: Duration.RelativeDelta) !Date
         .second = result.second,
         .nanosecond = result.nanosecond,
         .dst_fold = result.dst_fold,
-        .tz_options = opts,
+        .tz_options = if (dt.tz) |tz_ptr| .{ .tz = tz_ptr } else null,
     });
 }
 

diff --git a/tests/test_duration.zig b/tests/test_duration.zig
@@ -414,12 +414,30 @@ test "add relative delta to datetime" {
             .datetime_b = try Datetime.fromFields(.{ .year = 1971, .month = 2 }),
             .rel_delta = .{ .years = 1, .months = 1 },
         },
+        .{
+            .datetime_a = try Datetime.fromFields(.{ .year = 1970 }),
+            .datetime_b = try Datetime.fromFields(.{ .year = 1969, .month = 11 }),
+            .rel_delta = .{ .months = 2, .negative = true },
+        },
+        .{
+            .datetime_a = try Datetime.fromFields(.{ .year = 1970, .day = 31 }),
+            .datetime_b = try Datetime.fromFields(.{ .year = 1970, .month = 2, .day = 28 }),
+            .rel_delta = .{ .months = 1 },
+        },
+        .{
+            .datetime_a = try Datetime.fromFields(.{ .year = 1970, .month = 1, .day = 31 }),
+            .datetime_b = try Datetime.fromFields(.{ .year = 1968, .month = 12, .day = 31 }),
+            .rel_delta = .{ .months = 13, .negative = true },
+        },
+        .{
+            .datetime_a = try Datetime.fromFields(.{ .year = 1970, .month = 1, .day = 31 }),
+            .datetime_b = try Datetime.fromFields(.{ .year = 1965, .month = 11, .day = 30 }),
+            .rel_delta = .{ .years = 3, .months = 14, .negative = true },
+        },
     };
 
     for (cases) |case| {
         const dt_new = try case.datetime_a.addRelative(case.rel_delta);
-        log.warn("old: {s}, want {s}", .{ case.datetime_a, case.datetime_b });
-        log.warn("new: {s}", .{dt_new});
         try testing.expectEqual(case.datetime_b, dt_new);
     }
 }