(** Formatting Git dates for display.

    Git records a commit date as a Unix timestamp plus the offset of the zone
    the author was in. Relative and short forms drop that offset and use the
    server's local zone, which is what a reader scanning a list wants; the
    detailed form preserves it, because on a single commit the author's own
    wall-clock time is the meaningful one. *)

let relative_time (date, _) =
  let seconds = Unix.time () -. Int64.to_float date |> int_of_float in
  let minutes = seconds / 60 in
  let hours = minutes / 60 in
  let days = hours / 24 in
  let months = days / 30 in
  let years = months / 12 in
  let quantity value singular =
    Printf.sprintf "%d %s%s ago" value singular (if value = 1 then "" else "s")
  in
  match seconds with
  | s when s < 60 -> "just now"
  | _ when minutes < 60 -> quantity minutes "minute"
  | _ when hours < 24 -> quantity hours "hour"
  | _ when days < 30 -> quantity days "day"
  | _ when months < 12 -> quantity months "month"
  | _ -> quantity years "year"

(** Minute precision, server-local, for dense listings. *)
let short_time (date, _) =
  let tm = date |> Int64.to_float |> Unix.localtime in
  Printf.sprintf "%04d-%02d-%02d %02d:%02d" (tm.tm_year + 1900) (tm.tm_mon + 1)
    tm.tm_mday tm.tm_hour tm.tm_min

(** Second precision in the recorded zone. Returns the machine-readable form for
    a [datetime] attribute alongside the human-readable form. *)
let exact_time (date, timezone) =
  let offset_seconds, suffix =
    match timezone with
    | None -> (0, "Z")
    | Some (offset : Git.User.tz_offset) ->
        let direction = match offset.sign with `Plus -> 1 | `Minus -> -1 in
        let seconds = direction * ((offset.hours * 60) + offset.minutes) * 60 in
        let sign = match offset.sign with `Plus -> "+" | `Minus -> "-" in
        (seconds, Printf.sprintf "%s%02d:%02d" sign offset.hours offset.minutes)
  in
  let adjusted = Int64.add date (Int64.of_int offset_seconds) in
  let tm = adjusted |> Int64.to_float |> Unix.gmtime in
  let day =
    Printf.sprintf "%04d-%02d-%02d" (tm.tm_year + 1900) (tm.tm_mon + 1)
      tm.tm_mday
  in
  let clock = Printf.sprintf "%02d:%02d:%02d" tm.tm_hour tm.tm_min tm.tm_sec in
  ( Printf.sprintf "%sT%s%s" day clock suffix,
    Printf.sprintf "%s %s %s" day clock suffix )