NimbleParsec grammar for Chronix expressions.

This module compiles into the core parsers used by Chronix.Time, Chronix.Duration, and Chronix.Parser. Each of those modules is a thin façade that invokes a defparsec defined here and post-processes the AST for its own public contract via Chronix.Evaluator.

The public API remains on the façade modules; nothing here is intended for direct use by callers of Chronix.

AST shapes

Time (:time):

• :noon, :midnight
• {:time_12h, keyword_list} — e.g. [hour: 3, minute: 15, meridiem: :pm]
• {:time_24h, keyword_list} — e.g. [hour: 15, minute: 30, second: 45]

Duration (:duration):

• {:future_shift, [number, {base_unit, multiplier}]}
• {:past_shift, [number, {base_unit, multiplier}]}

• {:next_period, [:week | :month | :year]}

• {:last_period, [:week | :month | :year]}

• {:next_weekday, [atom | {:unknown_weekday, str}]}

• {:last_weekday, [atom | {:unknown_weekday, str}]}

• {:upcoming_weekday, [atom | {:unknown_weekday, str}]} — this/on

• :in_ago_error
• Inside shifts, unknown numbers/units: {:unknown_number, str}, {:unknown_unit, str}

Expression (:expression):

• :now — now
• {:day_offset, n} — today (0)/tomorrow/yesterday/day-after/day-before

• {:this_period, :week | :month | :year}

• :tonight, :last_night
• {:this_tod, %Time{}}, {:tomorrow_tod, %Time{}}, {:yesterday_tod, %Time{}}
• {:at_time, [time_ast]}
• {:year_first_date, [year, month, day]}
• {:year_last_date, [a, b, year]}
• {:beginning_of, [duration_ast]}, {:end_of, [duration_ast]}
• Duration and Time AST shapes (passed through)

Custom errors from post_traverse are wrapped as {:chronix_error, reason} to distinguish them from generic grammar-mismatch failures.