open Colitur_kernel

(** The EF lectionary resolution chain. All rubric knowledge about what a day
    with no proper falls back to lives here, not in the kernel.

    [lectionary] is caller-supplied, not loaded by this module -- the same
    reasoning rite_ef.mli's own [context] doc comment already gives for why
    the sanctoral {!Colitur_kernel.Layer.t} stays a separate argument rather
    than an embedded field: it lets a caller load data/ef/lectionary.sexp
    however suits it, and leaves room for a future diocesan/proper
    lectionary overlay to attach without this module changing at all.

    An eager filesystem read at module initialisation was tried first and
    reverted (fix round 1, coordinator review): [readings] used to close
    over a [lectionary] value loaded as a side effect of this module being
    LINKED, so `colitur easter <year>` -- which touches no lectionary data
    at all -- died at startup the moment data/ef/lectionary.sexp was
    missing from a bare `dune build`'s own default target (it was only
    present because test/dune's own deps happened to materialise it,
    masking the gap in every test run). See the task report for the
    reproduction.

    Steps 1-3 (Tasks 4-5): the observed celebration's own proper, else the
    day's own temporal slug in the lectionary, else -- for a weekday whose
    own slug has no entry -- the preceding Sunday's temporal slug (never its
    observed one; a Sunday is guarded out because it has no PRECEDING Sunday
    to resume, not because consulting itself would loop -- [readings] is not
    recursive, see its own implementation comment). A day matching none of
    the three gets [] for now -- the Commons (Task 6) are not built here. *)
val readings :
  lectionary:Lectionary.t ->
  observed:Vocab_ef.rank Celebration.t ->
  temporal:(Vocab_ef.season, Vocab_ef.rank) Temporal.t ->
  date:Date.t ->
  temporal_at:(Date.t -> (Vocab_ef.season, Vocab_ef.rank) Temporal.t) ->
  Citation.t list