minstrel/internal/config/config.go

package config

import (
	"crypto/rand"
	"encoding/base64"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"gopkg.in/yaml.v3"
)

type Config struct {
	Server         ServerConfig         `yaml:"server"`
	Storage        StorageConfig        `yaml:"storage"`
	Database       DatabaseConfig       `yaml:"database"`
	Log            LogConfig            `yaml:"log"`
	Library        LibraryConfig        `yaml:"library"`
	Subsonic       SubsonicConfig       `yaml:"subsonic"`
	Events         EventsConfig         `yaml:"events"`
	Recommendation RecommendationConfig `yaml:"recommendation"`
	Branding       BrandingConfig       `yaml:"branding"`
	// StreamSecret is the base64-decoded HMAC key used to sign UPnP /
	// Sonos stream URLs (see internal/api/stream_token.go and
	// docs/superpowers/specs/2026-06-03-android-output-picker-upnp-design.md).
	// Sourced from MINSTREL_STREAM_SECRET (base64-encoded), with a
	// per-machine fallback persisted at <Storage.DataDir>/stream_secret.
	// Not serialized to YAML — operator-machine-scoped runtime state, not
	// a user-facing setting. Never log the contents.
	StreamSecret []byte `yaml:"-"`
}

type ServerConfig struct {
	Address string `yaml:"address"`
}

// StorageConfig points at on-disk locations the server uses for cached
// runtime artifacts. Currently:
//   - DataDir hosts <DataDir>/playlist_covers/{playlist_id}.jpg (M7 #352).
//
// More entries may grow here (e.g., transcode cache) without breaking
// existing layouts.
type StorageConfig struct {
	// DataDir is the root for cached artifacts. Default: "./data" (relative
	// to the working directory). Operators in production should set an
	// absolute path persistent across restarts.
	DataDir string `yaml:"data_dir"`
}

// BrandingConfig drives per-instance UI labelling: the app name shown
// in the header / tab title and the description used in OG share-preview
// metadata. Both default to sensible values when unset.
type BrandingConfig struct {
	AppName     string `yaml:"app_name"`
	Description string `yaml:"description"`
}

type DatabaseConfig struct {
	URL string `yaml:"url"`
}

type LogConfig struct {
	Level  string `yaml:"level"`
	Format string `yaml:"format"`
}

type LibraryConfig struct {
	ScanPaths         []string `yaml:"scan_paths"`
	ScanOnStartup     bool     `yaml:"scan_on_startup"`
	CoverArtFromMBCAA bool     `yaml:"coverart_from_mbcaa"` // default true
	ContactEmail      string   `yaml:"contact_email"`       // optional override for MBCAA UA
}

// SubsonicConfig controls wire-format concessions on the /rest/* surface.
// AllowPlaintextPassword gates the `p=` parameter; the recommended posture is
// to leave it disabled and require apiKey (OpenSubsonic) or t+s.
type SubsonicConfig struct {
	AllowPlaintextPassword bool `yaml:"allow_plaintext_password"`
}

// EventsConfig governs play-event ingestion: session window, skip rule.
type EventsConfig struct {
	SessionTimeoutMinutes   int     `yaml:"session_timeout_minutes"`
	SkipMaxCompletionRatio  float64 `yaml:"skip_max_completion_ratio"`
	SkipMaxDurationPlayedMs int     `yaml:"skip_max_duration_played_ms"`
}

// RecommendationConfig governs the M3 weighted-shuffle scoring (spec §6).
// All weights are operator-tunable; defaults match the spec recommendations.
type RecommendationConfig struct {
	BaseWeight          float64 `yaml:"base_weight"`
	LikeBoost           float64 `yaml:"like_boost"`
	RecencyWeight       float64 `yaml:"recency_weight"`
	SkipPenalty         float64 `yaml:"skip_penalty"`
	JitterMagnitude     float64 `yaml:"jitter_magnitude"`
	ContextWeight       float64 `yaml:"context_weight"`
	SimilarityWeight    float64 `yaml:"similarity_weight"`
	RecentlyPlayedHours int     `yaml:"recently_played_hours"`
	RadioSize           int     `yaml:"radio_size"`
	RadioSizeMax        int     `yaml:"radio_size_max"`
}

func Default() Config {
	return Config{
		Server:   ServerConfig{Address: ":4533"},
		Storage:  StorageConfig{DataDir: "./data"},
		Database: DatabaseConfig{URL: ""},
		Log:      LogConfig{Level: "info", Format: "text"},
		Branding: BrandingConfig{
			AppName:     "Minstrel",
			Description: "Self-hosted music server with Subsonic compatibility, smart shuffle, and Lidarr integration.",
		},
		Events: EventsConfig{
			SessionTimeoutMinutes:   30,
			SkipMaxCompletionRatio:  0.5,
			SkipMaxDurationPlayedMs: 30000,
		},
		Recommendation: RecommendationConfig{
			BaseWeight:          1.0,
			LikeBoost:           2.0,
			RecencyWeight:       1.0,
			SkipPenalty:         1.0,
			JitterMagnitude:     0.1,
			ContextWeight:       2.0,
			SimilarityWeight:    2.0,
			RecentlyPlayedHours: 1,
			RadioSize:           50,
			RadioSizeMax:        200,
		},
		Library: LibraryConfig{
			CoverArtFromMBCAA: true,
		},
	}
}

func Load(path string) (Config, error) {
	cfg := Default()
	if path != "" {
		data, err := os.ReadFile(path)
		if err != nil {
			if !os.IsNotExist(err) {
				return cfg, fmt.Errorf("read config %q: %w", path, err)
			}
		} else if err := yaml.Unmarshal(data, &cfg); err != nil {
			return cfg, fmt.Errorf("parse config %q: %w", path, err)
		}
	}
	applyEnv(&cfg)
	if err := resolveStreamSecret(&cfg); err != nil {
		return cfg, err
	}
	return cfg, nil
}

// streamSecretBytes is the raw HMAC-key length; 64 bytes gives 512 bits
// of entropy, more than enough for HMAC-SHA256, and lands at a 86-char
// base64-url-no-padding string that fits cleanly in a single .env line.
const streamSecretBytes = 64

// streamSecretFile is the basename for the per-machine persisted fallback
// under <Storage.DataDir>. Kept as a constant so tests assert against the
// exact path and operators can find it during backup planning.
const streamSecretFile = "stream_secret"

// resolveStreamSecret populates cfg.StreamSecret using, in order:
//  1. MINSTREL_STREAM_SECRET env var (operator-supplied, base64-url
//     encoded — accepts either padded or raw form).
//  2. <Storage.DataDir>/stream_secret if present (auto-generated on a
//     previous boot; survives restarts so signed URLs stay valid).
//  3. Auto-generate streamSecretBytes random bytes, persist them to that
//     file at 0600, then use them.
//
// Logs (only) when an auto-generation happens so the operator can spot
// it during first-boot. Never logs the contents.
//
// The loader runs before slog is initialized in cmd/minstrel/main.go;
// log.Printf is the project's pre-logger convention.
func resolveStreamSecret(cfg *Config) error {
	if raw := strings.TrimSpace(os.Getenv("MINSTREL_STREAM_SECRET")); raw != "" {
		decoded, err := decodeBase64Secret(raw)
		if err != nil {
			return fmt.Errorf("decode MINSTREL_STREAM_SECRET: %w", err)
		}
		cfg.StreamSecret = decoded
		return nil
	}
	if cfg.Storage.DataDir == "" {
		return fmt.Errorf("stream secret: empty storage.data_dir; " +
			"set MINSTREL_STREAM_SECRET or storage.data_dir")
	}
	path := filepath.Join(cfg.Storage.DataDir, streamSecretFile)
	if buf, err := os.ReadFile(path); err == nil && len(buf) > 0 {
		decoded, err := decodeBase64Secret(strings.TrimSpace(string(buf)))
		if err != nil {
			return fmt.Errorf("decode %s: %w", path, err)
		}
		cfg.StreamSecret = decoded
		return nil
	}
	raw := make([]byte, streamSecretBytes)
	if _, err := rand.Read(raw); err != nil {
		return fmt.Errorf("auto-gen stream secret: %w", err)
	}
	encoded := base64.RawURLEncoding.EncodeToString(raw)
	if err := os.MkdirAll(cfg.Storage.DataDir, 0o755); err != nil {
		return fmt.Errorf("ensure data_dir for stream secret: %w", err)
	}
	if err := os.WriteFile(path, []byte(encoded), 0o600); err != nil {
		return fmt.Errorf("persist stream secret: %w", err)
	}
	log.Printf("config: auto-generated MINSTREL_STREAM_SECRET (persisted to %s)", path)
	cfg.StreamSecret = raw
	return nil
}

// decodeBase64Secret accepts base64-url with OR without padding; the
// stream-secret bytes are opaque so callers shouldn't have to know which
// encoder produced their string. Returns an error on any other shape.
func decodeBase64Secret(s string) ([]byte, error) {
	if buf, err := base64.RawURLEncoding.DecodeString(s); err == nil {
		return buf, nil
	}
	return base64.URLEncoding.DecodeString(s)
}

func applyEnv(cfg *Config) {
	if v, ok := os.LookupEnv("MINSTREL_SERVER_ADDRESS"); ok {
		cfg.Server.Address = v
	}
	if v, ok := os.LookupEnv("MINSTREL_STORAGE_DATA_DIR"); ok {
		cfg.Storage.DataDir = v
	}
	if v, ok := os.LookupEnv("MINSTREL_DATABASE_URL"); ok {
		cfg.Database.URL = v
	}
	if v, ok := os.LookupEnv("MINSTREL_LOG_LEVEL"); ok {
		cfg.Log.Level = strings.ToLower(v)
	}
	if v, ok := os.LookupEnv("MINSTREL_LOG_FORMAT"); ok {
		cfg.Log.Format = strings.ToLower(v)
	}
	if v, ok := os.LookupEnv("MINSTREL_BRANDING_APP_NAME"); ok && v != "" {
		cfg.Branding.AppName = v
	}
	if v, ok := os.LookupEnv("MINSTREL_BRANDING_DESCRIPTION"); ok && v != "" {
		cfg.Branding.Description = v
	}
	if v, ok := os.LookupEnv("MINSTREL_LIBRARY_SCAN_PATHS"); ok {
		cfg.Library.ScanPaths = splitPaths(v)
	}
	if v, ok := os.LookupEnv("MINSTREL_LIBRARY_SCAN_ON_STARTUP"); ok {
		if b, err := strconv.ParseBool(v); err == nil {
			cfg.Library.ScanOnStartup = b
		}
	}
	if v, ok := os.LookupEnv("MINSTREL_LIBRARY_COVERART_FROM_MBCAA"); ok {
		if b, err := strconv.ParseBool(v); err == nil {
			cfg.Library.CoverArtFromMBCAA = b
		}
	}
	if v, ok := os.LookupEnv("MINSTREL_CONTACT_EMAIL"); ok {
		cfg.Library.ContactEmail = v
	}
	if v, ok := os.LookupEnv("MINSTREL_SUBSONIC_ALLOW_PLAINTEXT_PASSWORD"); ok {
		if b, err := strconv.ParseBool(v); err == nil {
			cfg.Subsonic.AllowPlaintextPassword = b
		}
	}
}

// splitPaths splits a colon-separated path list, dropping empty entries.
// Colon matches PATH-style Unix conventions; Minstrel ships Linux-only.
func splitPaths(s string) []string {
	parts := strings.Split(s, ":")
	out := parts[:0]
	for _, p := range parts {
		if p != "" {
			out = append(out, p)
		}
	}
	return out
}