(ns calendar
  "Erlang :calendar module — date and time calculations.

   In CljElixir: (calendar/local-time), (calendar/universal-time), etc.
   Works with Erlang date/time tuples: {Year Month Day} and {Hour Min Sec}.")

(defn local-time
  "Returns the current local datetime as {{Y M D} {H M S}}.
   (calendar/local-time) ;=> {{2024 3 9} {12 30 0}}"
  [])

(defn universal-time
  "Returns the current UTC datetime as {{Y M D} {H M S}}.
   (calendar/universal-time) ;=> {{2024 3 9} {12 30 0}}"
  [])

(defn local-time-to-universal-time-dst
  "Converts local time to UTC, handling DST. Returns list of possible results."
  [datetime])

(defn universal-time-to-local-time
  "Converts UTC to local time."
  [datetime])

(defn now-to-datetime
  "Converts erlang:now/0 tuple to datetime tuple."
  [now])

(defn now-to-local-time
  "Converts erlang:now/0 to local datetime."
  [now])

(defn now-to-universal-time
  "Converts erlang:now/0 to UTC datetime."
  [now])

(defn datetime-to-gregorian-seconds
  "Converts {{Y M D} {H M S}} to Gregorian seconds (since year 0).
   (calendar/datetime-to-gregorian-seconds {{2024 1 1} {0 0 0}}) ;=> 63871..."
  [datetime])

(defn gregorian-seconds-to-datetime
  "Converts Gregorian seconds back to {{Y M D} {H M S}}.
   (calendar/gregorian-seconds-to-datetime 63871...)"
  [seconds])

(defn date-to-gregorian-days
  "Converts {Year Month Day} to Gregorian day count.
   (calendar/date-to-gregorian-days {2024 1 1})"
  ([date])
  ([year month day]))

(defn gregorian-days-to-date
  "Converts Gregorian day count to {Year Month Day}."
  [days])

(defn day-of-the-week
  "Returns day of week (1=Monday, 7=Sunday).
   (calendar/day-of-the-week {2024 3 9}) ;=> 6"
  ([date])
  ([year month day]))

(defn is-leap-year
  "Returns true if year is a leap year.
   (calendar/is-leap-year 2024) ;=> true"
  [year])

(defn last-day-of-the-month
  "Returns the last day of the month.
   (calendar/last-day-of-the-month 2024 2) ;=> 29"
  [year month])

(defn valid-date
  "Returns true if the date is valid.
   (calendar/valid-date {2024 2 29}) ;=> true"
  ([date])
  ([year month day]))

(defn iso-week-number
  "Returns {year week} for a date.
   (calendar/iso-week-number {2024 3 9}) ;=> {2024 10}"
  ([date])
  ([year month day]))

(defn time-difference
  "Returns the time difference between two datetimes.
   (calendar/time-difference dt1 dt2) ;=> {days {hours mins secs}}"
  [datetime1 datetime2])

(defn seconds-to-daystime
  "Converts seconds to {days {hours minutes seconds}}.
   (calendar/seconds-to-daystime 90061) ;=> {1 {1 1 1}}"
  [seconds])

(defn seconds-to-time
  "Converts seconds to {hours minutes seconds}.
   (calendar/seconds-to-time 3661) ;=> {1 1 1}"
  [seconds])

(defn time-to-seconds
  "Converts {hours minutes seconds} to seconds.
   (calendar/time-to-seconds {1 1 1}) ;=> 3661"
  [time])

(defn system-time-to-local-time
  "Converts system time to local datetime."
  [time unit])

(defn system-time-to-universal-time
  "Converts system time to UTC datetime."
  [time unit])

(defn rfc3339-to-system-time
  "Parses RFC 3339 timestamp to system time.
   (calendar/rfc3339-to-system-time \"2024-03-09T12:00:00Z\") ;=> integer"
  ([string])
  ([string opts]))

(defn system-time-to-rfc3339
  "Converts system time to RFC 3339 string.
   (calendar/system-time-to-rfc3339 time) ;=> \"2024-03-09T12:00:00Z\""
  ([time])
  ([time opts]))