New options --build-cache and --dry-run

Closes #11

3 files changed, 38 insertions, 16 deletions

diff --git a/internal/feed/cache.go b/internal/feed/cache.go
index df7559b..0b2f905 100644
--- a/internal/feed/cache.go
+++ b/internal/feed/cache.go
@@ -70,12 +70,16 @@ func storeCache(cache Cache, fileName string) error {
 	return nil
 }
 
+func newCache() (Cache, error) {
+	return cacheForVersion(currentVersion)
+}
+
 func loadCache(fileName string) (Cache, error) {
 	f, err := os.Open(fileName)
 	if err != nil {
 		if errors.Is(err, os.ErrNotExist) {
 			// no cache there yet -- make new
-			return cacheForVersion(currentVersion)
+			return newCache()
 		}
 		return nil, fmt.Errorf("opening cache at '%s': %w", fileName, err)
 	}
diff --git a/internal/feed/state.go b/internal/feed/state.go
index 154fafd..a060a77 100644
--- a/internal/feed/state.go
+++ b/internal/feed/state.go
@@ -34,8 +34,18 @@ func (state *State) ForeachGo(goFunc func(*Feed)) {
 	wg.Wait()
 }
 
-func (state *State) LoadCache(fileName string) error {
-	cache, err := loadCache(fileName)
+func (state *State) LoadCache(fileName string, forceNew bool) error {
+	var (
+		cache Cache
+		err   error
+	)
+
+	if forceNew {
+		cache, err = newCache()
+	} else {
+		cache, err = loadCache(fileName)
+	}
+
 	if err != nil {
 		return err
 	}
diff --git a/main.go b/main.go
index 08640d1..24cb0a4 100644
--- a/main.go
+++ b/main.go
@@ -16,15 +16,17 @@ var cfgFile = flag.String("f", "config.yml", "configuration file")
 var cacheFile = flag.String("c", "feed.cache", "cache file")
 var verbose = flag.Bool("v", false, "enable verbose output")
 var debug = flag.Bool("d", false, "enable debug output")
+var dryRun = flag.Bool("dry-run", false, "do everything short of uploading and writing the cache")
+var buildCache = flag.Bool("build-cache", false, "only (re)build the cache; useful after migration or when the cache is lost or corrupted")
 
-func processFeed(feed *feed.Feed, cfg *config.Config, client *imap.Client) {
+func processFeed(feed *feed.Feed, cfg *config.Config, client *imap.Client, dryRun bool) {
 	mails, err := feed.ToMails(cfg)
 	if err != nil {
 		log.Errorf("Processing items of feed %s: %s", feed.Name, err)
 		return
 	}
 
-	if len(mails) == 0 {
+	if dryRun || len(mails) == 0 {
 		feed.MarkSuccess()
 		return
 	}
@@ -66,7 +68,7 @@ func run() error {
 
 	state := feed.NewState(cfg)
 
-	err = state.LoadCache(*cacheFile)
+	err = state.LoadCache(*cacheFile, *buildCache)
 	if err != nil {
 		return err
 	}
@@ -89,19 +91,25 @@ func run() error {
 		return fmt.Errorf("parsing 'target': %w", err)
 	}
 
-	c, err := imap.Connect(imapUrl)
-	if err != nil {
-		return err
-	}
+	var c *imap.Client
+	if !*dryRun && !*buildCache {
+		if c, err = imap.Connect(imapUrl); err != nil {
+			return err
+		}
 
-	defer c.Disconnect()
+		defer c.Disconnect()
+	}
 
-	state.ForeachGo(func(f *feed.Feed) {
-		processFeed(f, cfg, c)
-	})
+	if !*buildCache {
+		state.ForeachGo(func(f *feed.Feed) {
+			processFeed(f, cfg, c, *dryRun)
+		})
+	}
 
-	if err = state.StoreCache(*cacheFile); err != nil {
-		return err
+	if !*dryRun {
+		if err = state.StoreCache(*cacheFile); err != nil {
+			return err
+		}
 	}
 
 	return nil