Parses a variety of date formats into a Date struct.

Supported inputs

• "" or "0" – returns nil
• A Date struct – returns the date itself
• Excel serial date string (e.g. "40135") – returns the corresponding Date
• ISO-ish strings (e.g. "2023-1-5", "2023-01-05") – returns the parsed Date
• Strings with leading/trailing whitespace are trimmed
• Invalid or malformed strings return nil

Examples

iex> to_date("40135") ~D[2009-11-18]

iex> to_date("2024-1-9") ~D[2024-01-09]

iex> to_date("") nil

iex> to_date(%Date{year: 2020, month: 5, day: 10}) ~D[2020-05-10]

iex> to_date("not a date") nil