pub const Order = enum {
    /// Greater than (`>`)
    gt,

    /// Less than (`<`)
    lt,

    /// Equal (`==`)
    eq,

    pub fn invert(self: Order) Order {
        return switch (self) {
            .lt => .gt,
            .eq => .eq,
            .gt => .lt,
        };
    }

    test invert {
        try testing.expect(Order.invert(order(0, 0)) == .eq);
        try testing.expect(Order.invert(order(1, 0)) == .lt);
        try testing.expect(Order.invert(order(-1, 0)) == .gt);
    }

    pub fn differ(self: Order) ?Order {
        return if (self != .eq) self else null;
    }

    test differ {
        const neg: i32 = -1;
        const zero: i32 = 0;
        const pos: i32 = 1;
        try testing.expect(order(zero, neg).differ() orelse
            order(pos, zero) == .gt);
        try testing.expect(order(zero, zero).differ() orelse
            order(zero, zero) == .eq);
        try testing.expect(order(pos, pos).differ() orelse
            order(neg, zero) == .lt);
        try testing.expect(order(zero, zero).differ() orelse
            order(pos, neg).differ() orelse
            order(neg, zero) == .gt);
        try testing.expect(order(pos, pos).differ() orelse
            order(pos, pos).differ() orelse
            order(neg, neg) == .eq);
        try testing.expect(order(zero, pos).differ() orelse
            order(neg, pos).differ() orelse
            order(pos, neg) == .lt);
    }

    pub fn compare(self: Order, op: CompareOperator) bool {
        return switch (self) {
            .lt => switch (op) {
                .lt => true,
                .lte => true,
                .eq => false,
                .gte => false,
                .gt => false,
                .neq => true,
            },
            .eq => switch (op) {
                .lt => false,
                .lte => true,
                .eq => true,
                .gte => true,
                .gt => false,
                .neq => false,
            },
            .gt => switch (op) {
                .lt => false,
                .lte => false,
                .eq => false,
                .gte => true,
                .gt => true,
                .neq => true,
            },
        };
    }

    // https://github.com/ziglang/zig/issues/19295
    test "compare" {
        try testing.expect(order(-1, 0).compare(.lt));
        try testing.expect(order(-1, 0).compare(.lte));
        try testing.expect(order(0, 0).compare(.lte));
        try testing.expect(order(0, 0).compare(.eq));
        try testing.expect(order(0, 0).compare(.gte));
        try testing.expect(order(1, 0).compare(.gte));
        try testing.expect(order(1, 0).compare(.gt));
        try testing.expect(order(1, 0).compare(.neq));
    }
}