Add structured logging and better error handling

internal/jobs/record.go

@@ -2,7 +2,7 @@ package jobs
 
 import (
 	"encoding/json"
-	"log"
+	"log/slog"
 	"os"
 	"path/filepath"
 	"time"
@@ -69,23 +69,28 @@ func phaseFor(status Status, downloaded bool) string {
 func (job *Job) saveRecord() {
 	data, err := json.MarshalIndent(job.record(), "", "  ")
 	if err != nil {
-		log.Printf("could not encode download %s: %v", job.id, err)
+		job.logger().Error("could not encode download state", "error", err)
 		return
 	}
 	job.recordMutex.Lock()
 	defer job.recordMutex.Unlock()
 	if err := files.WriteAtomically(filepath.Join(job.directory, files.JobFileName), data); err != nil && !os.IsNotExist(err) {
-		log.Printf("could not save download %s: %v", job.id, err)
+		job.logger().Error("could not save download state", "error", err)
 	}
 }
 
 func readRecord(directory string) (jobRecord, bool) {
-	data, err := os.ReadFile(filepath.Join(directory, files.JobFileName))
+	recordPath := filepath.Join(directory, files.JobFileName)
+	data, err := os.ReadFile(recordPath)
 	if err != nil {
+		if !os.IsNotExist(err) {
+			slog.Warn("could not read saved download state", "path", recordPath, "error", err)
+		}
 		return jobRecord{}, false
 	}
 	var record jobRecord
 	if err := json.Unmarshal(data, &record); err != nil {
+		slog.Warn("saved download state is damaged, treating the download as finished", "path", recordPath, "error", err)
 		return jobRecord{}, false
 	}
 	return record, true