kernel(layer): sanctoral layer with canonical order and date index

Entries sort by slug so equal layers serialise identically. The by-date index
is built once per layer rather than per year, since fixed dates are
year-independent; a full-domain sweep would otherwise rescan every entry for
every day. load turns parse and validation failures into result.

1 files changed, 25 insertions, 0 deletions

diff --git a/lib/kernel/layer.mli b/lib/kernel/layer.mli
new file mode 100644
index 0000000..3092353
--- /dev/null
+++ b/lib/kernel/layer.mli
@@ -0,0 +1,25 @@
+(** One calendar layer: a rite's base sanctoral, or a data file of the same
+    shape. Entries are canonically sorted by slug. *)
+type 'r entry = { date : Date_spec.t; cel : 'r Celebration.t } [@@deriving sexp]
+type 'r t = { id : string; name : string; entries : 'r entry list } [@@deriving sexp]
+
+val empty : id:string -> name:string -> 'r t
+val of_entries : id:string -> name:string -> 'r entry list -> 'r t
+val find : 'r t -> Slug.t -> 'r entry option
+val mem : 'r t -> Slug.t -> bool
+
+(** Replaces any entry with the same slug. *)
+val set : 'r t -> 'r entry -> 'r t
+
+val remove : 'r t -> Slug.t -> 'r t
+
+(** Date index. Built once per layer, not per year: [Date_spec] dates are
+    year-independent. *)
+type 'r by_date
+
+val index_by_date : 'r t -> 'r by_date
+val on_date : 'r by_date -> month:int -> day:int -> 'r entry list
+
+(** Loads a layer from a sexp file. Parse and validation failures come back as
+    [Error], never as an exception. *)
+val load : (Sexplib0.Sexp.t -> 'r) -> string -> ('r t, string) result