feat(calfeed): shared day builder + reusable reading resolver

4 files changed, 149 insertions, 20 deletions

diff --git a/internal/caldata/readings.go b/internal/caldata/readings.go
new file mode 100644
index 0000000..a11235d
--- /dev/null
+++ b/internal/caldata/readings.go
@@ -0,0 +1,31 @@
+package caldata
+
+import (
+	"time"
+
+	"github.com/lukaszkasprzak/lectio/internal/calendar"
+)
+
+// Readings resolves a day's Mass readings: the observed celebration's inline
+// propers, else the temporal lectionary for its slug, else -- for an EF
+// weekday with no proper Mass -- the preceding Sunday's Mass (the 1962 rule
+// that green-season ferias repeat the Sunday). Shared by the CLI (cli.dayReadings
+// delegates here) and calfeed.Build (injected as its readings func).
+func Readings(sel calendar.Selection, layers []calendar.Layer, date time.Time, day calendar.LiturgicalDay) []calendar.Reading {
+	var rs []calendar.Reading
+	for _, m := range day.Observed.Masses {
+		rs = append(rs, m.Readings...)
+	}
+	if len(rs) > 0 {
+		return rs
+	}
+	if r := TemporalReadings(sel.Form, day.Observed.Slug); len(r) > 0 {
+		return r
+	}
+	if sel.Form == "old" && day.Observed.Layer == "temporal" && date.Weekday() != time.Sunday {
+		sun := date.AddDate(0, 0, -int(date.Weekday())) // preceding Sunday (Sunday = 0)
+		sd := calendar.Compute(sun, sel, layers)
+		return TemporalReadings(sel.Form, sd.Observed.Slug)
+	}
+	return nil
+}
diff --git a/internal/calfeed/build.go b/internal/calfeed/build.go
new file mode 100644
index 0000000..d3962aa
--- /dev/null
+++ b/internal/calfeed/build.go
@@ -0,0 +1,68 @@
+package calfeed
+
+import (
+	"strings"
+	"time"
+
+	"github.com/lukaszkasprzak/lectio/internal/calendar"
+)
+
+// Build computes the day list from..to inclusive (calendar.Compute per date)
+// and maps it to the wire model. readings is injected -- the caller passes
+// caldata.Readings -- so calfeed never imports internal/caldata.
+func Build(from, to time.Time, uiLang string, sel calendar.Selection, layers []calendar.Layer, readings func(date time.Time, day calendar.LiturgicalDay) []calendar.Reading) []DayView {
+	var days []DayView
+	for d := from; !d.After(to); d = d.AddDate(0, 0, 1) {
+		day := calendar.Compute(d, sel, layers)
+
+		others := make([]CelView, 0, len(day.Others))
+		for _, o := range day.Others {
+			others = append(others, celView(uiLang, o))
+		}
+
+		var rs []ReadingView
+		for _, r := range readings(d, day) {
+			rs = append(rs, ReadingView{Part: r.Part, Citation: r.Citation})
+		}
+
+		days = append(days, DayView{
+			Date:     d.Format("2006-01-02"),
+			Season:   string(day.Season),
+			Week:     day.Week,
+			Weekday:  day.Weekday.String(),
+			Colour:   string(day.Colour),
+			Observed: celView(uiLang, day.Observed),
+			Others:   others,
+			Cycles:   Cycles{Sunday: day.SundayCycle, Weekday: day.WeekdayCycle},
+			Readings: rs,
+		})
+	}
+	return days
+}
+
+// celView maps a calendar.Celebration to its wire view.
+func celView(uiLang string, c calendar.Celebration) CelView {
+	return CelView{
+		Slug:  c.Slug,
+		Name:  celebrationName(uiLang, c),
+		Rank:  string(c.Rank),
+		Class: int(c.Class),
+	}
+}
+
+// celebrationName resolves c's name in uiLang, falling back to English, then
+// a humanized slug (with the "ef-" prefix stripped and dashes turned to
+// spaces), then "(feria)" for an unnamed temporal day. Mirrors
+// cli.celebrationName.
+func celebrationName(uiLang string, c calendar.Celebration) string {
+	if n := c.Name[uiLang]; n != "" {
+		return n
+	}
+	if n := c.Name["en"]; n != "" {
+		return n
+	}
+	if c.Slug == "" {
+		return "(feria)"
+	}
+	return strings.ReplaceAll(strings.TrimPrefix(c.Slug, "ef-"), "-", " ")
+}
diff --git a/internal/calfeed/build_test.go b/internal/calfeed/build_test.go
new file mode 100644
index 0000000..333a51b
--- /dev/null
+++ b/internal/calfeed/build_test.go
@@ -0,0 +1,46 @@
+package calfeed
+
+import (
+	"testing"
+	"time"
+
+	"github.com/lukaszkasprzak/lectio/internal/caldata"
+	"github.com/lukaszkasprzak/lectio/internal/calendar"
+)
+
+func TestBuildThreeDayRange(t *testing.T) {
+	sel := calendar.DefaultSelection()
+	sel.Form = "old"
+	layers := []calendar.Layer{caldata.Tridentine()}
+
+	from := time.Date(2026, 1, 5, 0, 0, 0, 0, time.UTC)
+	to := time.Date(2026, 1, 7, 0, 0, 0, 0, time.UTC)
+	days := Build(from, to, "en", sel, layers, func(date time.Time, day calendar.LiturgicalDay) []calendar.Reading {
+		return caldata.Readings(sel, layers, date, day)
+	})
+
+	if len(days) != 3 {
+		t.Fatalf("len(days) = %d, want 3", len(days))
+	}
+
+	wantDates := []string{"2026-01-05", "2026-01-06", "2026-01-07"}
+	seenWeekday := false
+	feastFound := false
+	for i, d := range days {
+		if d.Date != wantDates[i] {
+			t.Errorf("day %d: date = %q, want %q", i, d.Date, wantDates[i])
+		}
+		if d.Weekday != "" {
+			seenWeekday = true
+		}
+		if d.Date == "2026-01-06" && d.Observed.Name != "" {
+			feastFound = true
+		}
+	}
+	if !seenWeekday {
+		t.Errorf("expected weekday strings to be set: %+v", days)
+	}
+	if !feastFound {
+		t.Errorf("expected Epiphany (2026-01-06) to have a non-empty Observed.Name: %+v", days)
+	}
+}
diff --git a/internal/cli/liturgy.go b/internal/cli/liturgy.go
index ced23ae..5b6036e 100644
--- a/internal/cli/liturgy.go
+++ b/internal/cli/liturgy.go
@@ -38,27 +38,11 @@ func runLiturgy(cfg config.Config, date string, stdout, stderr io.Writer) int {
 	return 0
 }
 
-// dayReadings resolves the day's Mass readings: the observed celebration's
-// inline propers, else the temporal lectionary for its slug, else -- for an EF
-// weekday with no proper Mass -- the preceding Sunday's Mass (the 1962 rule
-// that green-season ferias repeat the Sunday).
+// dayReadings resolves the day's Mass readings; the logic lives in
+// caldata.Readings (shared with calfeed.Build) so it stays reusable outside
+// the CLI.
 func dayReadings(sel calendar.Selection, layers []calendar.Layer, date time.Time, day calendar.LiturgicalDay) []calendar.Reading {
-	var rs []calendar.Reading
-	for _, m := range day.Observed.Masses {
-		rs = append(rs, m.Readings...)
-	}
-	if len(rs) > 0 {
-		return rs
-	}
-	if r := caldata.TemporalReadings(sel.Form, day.Observed.Slug); len(r) > 0 {
-		return r
-	}
-	if sel.Form == "old" && day.Observed.Layer == "temporal" && date.Weekday() != time.Sunday {
-		sun := date.AddDate(0, 0, -int(date.Weekday())) // preceding Sunday (Sunday = 0)
-		sd := calendar.Compute(sun, sel, layers)
-		return caldata.TemporalReadings(sel.Form, sd.Observed.Slug)
-	}
-	return nil
+	return caldata.Readings(sel, layers, date, day)
 }
 
 // vernacularVersion is the corpus that renders reading text: the config's