feat: media duplicate purge, part 1 of 3: persisted purge settings and the purge API

internal/domain/purge/purgeDomain.go

@@ -0,0 +1,48 @@
+package purge
+
+import (
+	"errors"
+	"time"
+)
+
+var ErrInvalidPurgeInterval = errors.New("invalid purge interval")
+var ErrPurgeConflict = errors.New("the library changed since the fingerprint")
+var ErrPurgeBusy = errors.New("a purge is already running")
+
+const (
+	DefaultIntervalDays = 30
+	MinIntervalDays     = 1
+	MaxIntervalDays     = 365
+)
+
+type Settings struct {
+	AutoPurgeEnabled         bool       `json:"auto_purge_enabled"`
+	AutoPurgeIntervalDays    int        `json:"auto_purge_interval_days"`
+	LastPurgeAt              *time.Time `json:"last_purge_at"`
+	LastPurgeMerged          int        `json:"last_purge_merged"`
+	LastPurgeArticlesUpdated int        `json:"last_purge_articles_updated"`
+	EnabledAt                *time.Time `json:"enabled_at"`
+}
+
+func DefaultSettings() Settings {
+	return Settings{AutoPurgeIntervalDays: DefaultIntervalDays}
+}
+
+func ValidateIntervalDays(days int) error {
+	if days < MinIntervalDays || days > MaxIntervalDays {
+		return ErrInvalidPurgeInterval
+	}
+	return nil
+}
+
+func (s Settings) NextPurgeAt() *time.Time {
+	if !s.AutoPurgeEnabled || s.EnabledAt == nil {
+		return nil
+	}
+	base := *s.EnabledAt
+	if s.LastPurgeAt != nil && s.LastPurgeAt.After(base) {
+		base = *s.LastPurgeAt
+	}
+	next := base.AddDate(0, 0, s.AutoPurgeIntervalDays)
+	return &next
+}