1 files changed, 64 insertions, 6 deletions

diff --git a/internal/tradlit/tradlit.go b/internal/tradlit/tradlit.go
index edb9ce0..a7b53bc 100644
--- a/internal/tradlit/tradlit.go
+++ b/internal/tradlit/tradlit.go
@@ -9,6 +9,8 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"os"
+	"path/filepath"
 	"regexp"
 	"strings"
 
@@ -86,11 +88,57 @@ func Parse(jsonBody []byte) ([]liturgy.Section, error) {
 	return out, nil
 }
 
-// Load fetches a day's traditional propers from the missalemeum API
-// (https://www.missalemeum.com/{lang}/api/v5/proper/{date}) and parses
-// them. On HTTP 404 (no propers published for that date) it returns a
-// clear error rather than attempting to parse.
-func Load(date, lang string) ([]liturgy.Section, error) {
+// cachePath returns where Load caches a (date, lang) day's raw API response:
+// <CacheDir>/<date>.trad.<lang>.json -- date-prefixed (like the modern
+// lectionary's own cache files) so liturgy.CleanCache can prune it by date.
+func cachePath(date, lang string) string {
+	return filepath.Join(liturgy.CacheDir(), date+".trad."+lang+".json")
+}
+
+// Load returns a day's traditional propers for lang, either read from the
+// on-disk cache (offline) or fetched live from missalemeum and cached for
+// next time (online). Both paths share Parse, so cached and live results
+// are identical.
+//
+//   - offline: reads the cache file written by a prior online Load (see
+//     cachePath); if it doesn't exist, returns a clear error telling the
+//     caller to go online or run 'lectio update' first.
+//   - online: fetches https://www.missalemeum.com/{lang}/api/v5/proper/{date}
+//     as before. On a successful 200, the raw response body is written to
+//     the cache path (best-effort -- a cache-write failure never fails the
+//     request) before being parsed. On HTTP 404 (no propers published for
+//     that date) it returns a clear error and writes nothing to the cache.
+func Load(date, lang string, offline bool) ([]liturgy.Section, error) {
+	if offline {
+		return loadCached(date, lang)
+	}
+	return loadLive(date, lang)
+}
+
+// loadCached implements Load's offline path.
+func loadCached(date, lang string) ([]liturgy.Section, error) {
+	body, err := os.ReadFile(cachePath(date, lang))
+	if err != nil {
+		return nil, fmt.Errorf("tradlit: no cached traditional propers for %s (%s); view it online or run 'lectio update' first", date, lang)
+	}
+	return Parse(body)
+}
+
+// loadLive implements Load's online path: fetch, best-effort cache the raw
+// body, then parse.
+func loadLive(date, lang string) ([]liturgy.Section, error) {
+	body, err := fetch(date, lang)
+	if err != nil {
+		return nil, err
+	}
+	writeCache(date, lang, body)
+	return Parse(body)
+}
+
+// fetch GETs the day's proper-of-the-day JSON from missalemeum and returns
+// the raw response body. On HTTP 404 (no propers published for that date)
+// it returns a clear error rather than the raw 404 body.
+func fetch(date, lang string) ([]byte, error) {
 	url := fmt.Sprintf(baseURL, lang, date)
 
 	req, err := http.NewRequest(http.MethodGet, url, nil)
@@ -116,6 +164,16 @@ func Load(date, lang string) ([]liturgy.Section, error) {
 	if err != nil {
 		return nil, fmt.Errorf("tradlit: load %s: %w", date, err)
 	}
+	return body, nil
+}
 
-	return Parse(body)
+// writeCache best-effort writes a day's raw API response body to its cache
+// path; a failure to cache (e.g. an unwritable cache dir) must never fail
+// the live request that produced body.
+func writeCache(date, lang string, body []byte) {
+	path := cachePath(date, lang)
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return
+	}
+	_ = os.WriteFile(path, body, 0o644)
 }