feat: initial commit — unarr CLI

Search, inspect, stream, and download torrents from the terminal.
Replaces the entire *arr stack with a single binary.

internal/engine/resolve.go

@@ -0,0 +1,75 @@
+package engine
+
+import (
+	"context"
+	"fmt"
+	"log"
+)
+
+// resolveMethod determines which download method to use for a task.
+// For "auto": tries available methods in priority order (torrent > debrid > usenet).
+// For specific method: uses only that method.
+func resolveMethod(ctx context.Context, task *Task, downloaders map[DownloadMethod]Downloader) (DownloadMethod, error) {
+	var order []DownloadMethod
+	switch task.PreferredMethod {
+	case "torrent":
+		order = []DownloadMethod{MethodTorrent}
+	case "debrid":
+		order = []DownloadMethod{MethodDebrid}
+	case "usenet":
+		order = []DownloadMethod{MethodUsenet}
+	default: // "auto"
+		order = []DownloadMethod{MethodTorrent, MethodDebrid, MethodUsenet}
+	}
+
+	for _, method := range order {
+		// Skip already-tried methods
+		tried := false
+		for _, tm := range task.TriedMethods {
+			if tm == method {
+				tried = true
+				break
+			}
+		}
+		if tried {
+			continue
+		}
+
+		dl, ok := downloaders[method]
+		if !ok {
+			continue // downloader not registered
+		}
+
+		available, err := dl.Available(ctx, task)
+		if err != nil {
+			taskID := task.ID
+			if len(taskID) > 8 {
+				taskID = taskID[:8]
+			}
+			log.Printf("[%s] %s availability check failed: %v", taskID, method, err)
+			continue
+		}
+		if available {
+			return method, nil
+		}
+	}
+
+	return "", fmt.Errorf("no download method available (tried: %v)", task.TriedMethods)
+}
+
+// tryFallback attempts to fall back to the next untried download method.
+// Returns true if fallback was initiated, false if no more methods.
+func tryFallback(task *Task, downloaders map[DownloadMethod]Downloader) bool {
+	if task.PreferredMethod != "auto" {
+		return false // specific method requested, no fallback
+	}
+
+	task.TriedMethods = append(task.TriedMethods, task.ResolvedMethod)
+
+	available := make([]DownloadMethod, 0, len(downloaders))
+	for m := range downloaders {
+		available = append(available, m)
+	}
+
+	return task.HasUntried(available)
+}