commit 2029bf3778841788c2888dd3f87632ea01308dad
Author: Nathan Fisher <nfisher.sr@gmail.com>
Date:   Mon Jun 12 22:59:12 2023 -0400

    Initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a50a769
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+zig-out/
+zig-cache/
+tags
+tags.temp
+tags.lock
diff --git a/build.zig b/build.zig
new file mode 100644
index 0000000..70d52ce
--- /dev/null
+++ b/build.zig
@@ -0,0 +1,17 @@
+const std = @import("std");
+
+pub fn build(b: *std.build.Builder) void {
+    // Standard release options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
+    const mode = b.standardReleaseOptions();
+
+    const lib = b.addStaticLibrary("zigDateTime", "src/main.zig");
+    lib.setBuildMode(mode);
+    lib.install();
+
+    const main_tests = b.addTest("src/main.zig");
+    main_tests.setBuildMode(mode);
+
+    const test_step = b.step("test", "Run library tests");
+    test_step.dependOn(&main_tests.step);
+}
diff --git a/src/main.zig b/src/main.zig
new file mode 100644
index 0000000..387e9aa
--- /dev/null
+++ b/src/main.zig
@@ -0,0 +1,223 @@
+const std = @import("std");
+const testing = std.testing;
+
+pub const SECONDS_PER_MINUTE = 60;
+pub const SECONDS_PER_HOUR = 60 * 60;
+pub const SECONDS_PER_DAY = SECONDS_PER_HOUR * 24;
+
+pub const YearTag = enum(u1) {
+    normal,
+    leap,
+
+    fn new(year: u31) YearTag {
+        return if (year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)) .leap else .normal;
+    }
+};
+
+pub const Year = union(YearTag) {
+    normal: u31,
+    leap: u31,
+
+    const Self = @This();
+
+    pub fn new(year: u31) Self {
+        return switch (YearTag.new(year)) {
+            .normal => Self{ .normal = year },
+            .leap => Self{ .leap = year },
+        };
+    }
+
+    pub fn days(self: Self) u16 {
+        return switch (self) {
+            .normal => 365,
+            .leap => 366,
+        };
+    }
+
+    pub fn seconds(self: Self) i64 {
+        return self.days * SECONDS_PER_DAY;
+    }
+
+    pub fn get(self: Self) u31 {
+        return switch (self) {
+            .normal => |year| year,
+            .leap => |year| year,
+        };
+    }
+
+    pub fn next(self: Self) Self {
+        return Self.new(self.get() + 1);
+    }
+
+    pub fn previous(self: Self) Self {
+        return Self.new(self.get() - 1);
+    }
+};
+
+test "new year" {
+    try testing.expectEqual(Year.new(2023), Year{ .normal = 2023 });
+    try testing.expectEqual(Year.new(2024), Year{ .leap = 2024 });
+}
+
+test "get year" {
+    try testing.expectEqual(Year.new(2023).get(), 2023);
+    try testing.expectEqual(Year.new(2024).get(), 2024);
+}
+
+test "next year" {
+    try testing.expectEqual(Year.new(2023).next(), Year{ .leap = 2024 });
+}
+
+test "last year" {
+    try testing.expectEqual(Year.new(2024).previous(), Year{ .normal = 2023 });
+}
+
+pub const Month = enum(u4) {
+    january = 1,
+    february = 2,
+    march = 3,
+    april = 4,
+    may = 5,
+    june = 6,
+    july = 7,
+    august = 8,
+    september = 9,
+    october = 10,
+    november = 11,
+    december = 12,
+
+    const Self = @This();
+
+    pub fn days(self: Self, year: Year) u5 {
+        return switch (@enumToInt(self)) {
+            1, 3, 5, 7, 8, 10, 12 => 31,
+            2 => switch (year) {
+                .normal => 28,
+                .leap => 29,
+            },
+            else => 30,
+        };
+    }
+
+    pub fn seconds(self: Self) u32 {
+        return self.days() * SECONDS_PER_DAY;
+    }
+
+    pub fn next(self: Self) ?Self {
+        const num = @enumToInt(self);
+        return if (num < 12) @intToEnum(Self, num + 1) else null;
+    }
+
+    pub fn previous(self: Self) ?Self {
+        const num = @enumToInt(self);
+        return if (num > 1) @intToEnum(Self, num - 1) else null;
+    }
+};
+
+test "get days in month" {
+    const year = Year.new(2023);
+    const month = Month.february;
+    try testing.expectEqual(month.days(year), 28);
+}
+
+test "next month" {
+    try testing.expectEqual(Month.june.next(), .july);
+    try testing.expectEqual(Month.december.next(), null);
+}
+
+test "last month" {
+    try testing.expectEqual(Month.june.previous(), .may);
+    try testing.expectEqual(Month.january.previous(), null);
+}
+
+pub const TimeZoneTag = enum(u1) {
+    utc,
+    offset,
+};
+
+pub const TimeZone = union(TimeZoneTag) {
+    utc: void,
+    offset: i8,
+
+    const Self = @This();
+
+    pub fn new(offset: ?i8) ?Self {
+        return if (offset) |ofs| blk: {
+            if (ofs < -12 or ofs > 12) {
+                break :blk null;
+            } else if (ofs == 0) {
+                break :blk .utc;
+            } else {
+                break :blk Self{ .offset = ofs };
+            }
+        } else .utc;
+    }
+};
+
+test "new timezone" {
+    const tz = TimeZone.new(-5).?;
+    try testing.expectEqual(@as(TimeZoneTag, tz), .offset);
+    switch (tz) {
+        .offset => |ofs| try testing.expectEqual(ofs, -5),
+        else => unreachable,
+    }
+}
+
+test "new timezone utc" {
+    const tz0 = TimeZone.new(null).?;
+    const tz1 = TimeZone.new(0).?;
+    try testing.expectEqual(@as(TimeZoneTag, tz0), .utc);
+    try testing.expectEqual(@as(TimeZoneTag, tz1), .utc);
+}
+
+pub const DateTime = struct {
+    year: Year,
+    month: Month,
+    day: u8,
+    hour: ?u5,
+    minute: ?u6,
+    second: ?u6,
+    nanos: ?u32,
+    tz: TimeZone,
+
+    const Self = @This();
+
+    pub fn getYear(self: Self) u32 {
+        return self.year.get();
+    }
+
+    pub fn getOffset(self: Self) ?i8 {
+        return switch (self.tz) {
+            .utc => null,
+            .offset => |ofs| ofs,
+        };
+    }
+};
+
+test "get year" {
+    const dt = DateTime{
+        .year = Year.new(2023),
+        .month = .june,
+        .day = 12,
+        .hour = 1,
+        .minute = 5,
+        .second = 14,
+        .nanos = null,
+        .tz = TimeZone.new(-5).?,
+    };
+    try testing.expectEqual(dt.getYear(), 2023);
+}
+
+test "get offset" {
+    const dt = DateTime{
+        .year = Year.new(2023),
+        .month = .june,
+        .day = 12,
+        .hour = 1,
+        .minute = 5,
+        .second = 14,
+        .nanos = null,
+        .tz = TimeZone.new(-5).?,
+    };
+    try testing.expectEqual(dt.getOffset().?, -5);
+}