feat: allow overriding the output directory via GODEEZ_OUTPUT_DIR

The output directory used to be fixed at ~/Music/GoDeez. config.Load
now honours GODEEZ_OUTPUT_DIR when set, with a leading ~ expanded by
hand since the shell only does that for unquoted arguments, not for
values read out of the environment. Falls back to the previous default
when unset.

.github/copilot-instructions.md

@@ -0,0 +1,87 @@
+# GoDeez
+
+GoDeez is a Go CLI that downloads music (tracks, albums, playlists, artist top
+tracks) from Deezer in MP3 or lossless FLAC/WAV, embeds metadata tags, and
+tracks what has already been downloaded so repeat runs can skip it.
+
+## Build, test, lint
+
+Mirror what CI (`.github/workflows/ci.yml`) runs:
+
+```bash
+gofmt -l .        # must print nothing; CI fails on unformatted files
+go vet ./...
+go test ./...
+go build ./...
+```
+
+Run a single test:
+
+```bash
+go test ./internal/download/ -run TestHashFile
+go test ./internal/download/ -run TestHashFile -v
+```
+
+Release packaging is validated with `goreleaser check` (config in
+`.goreleaser.yaml`); releases are cut by pushing a `v*` tag, which requires a
+matching section in `CHANGELOG.md` (`.github/scripts/release-notes.sh`
+extracts it and fails the release otherwise).
+
+## Architecture
+
+The flow is `cmd` → `download.Downloader` → `deezer` client → `store`/`tag`/`audio`:
+
+- **`cmd`** is a thin cobra layer (`download`, `login`, `logout`, `update`,
+  `version`). It parses flags and delegates; it does not contain download
+  logic. `cmd.Execute` also kicks off an async update check
+  (`internal/update.StartCheck`) before running the command and prints the
+  result after, so the network round trip overlaps with the command instead
+  of adding to startup time.
+- **`internal/deezer`** is the API client. `Kind` (`album`/`playlist`/
+  `artist`/`track`) is the single source of truth mapping a resource type to
+  its gw-light page method, request id field, and `Resource` implementation
+  (`Album`/`Playlist`/`Artist`/`Single`). Adding a new resource kind means
+  extending every switch in `kind.go`. `Resource`'s `decode` method is
+  unexported to seal the interface to this package.
+- **`internal/download`** (package `download`) drives the per-track pipeline
+  via `Downloader.Run`: fetch resource → for each track, resolve a media
+  source → decide skip/hash-dedupe → stream and decrypt → optionally convert
+  FLAC to WAV → write tags → record in the store. Tracks are processed
+  sequentially, one at a time. Most per-track failures (bad cover, failed BPM
+  lookup, etc.) are collected as warnings rather than aborting the whole run;
+  only `context.Canceled` stops the loop early.
+- **`internal/store`** is a bbolt-backed ledger (`.tracks.db`) written as a
+  hidden file inside the output directory, so it travels with the music
+  library it describes. Losing it is harmless — the only cost is
+  re-downloading.
+- **`internal/tag`** writes metadata per container format (ID3v2 for MP3,
+  Vorbis comments for FLAC, ID3 chunk + RIFF LIST/INFO for WAV), dispatching
+  on file extension. Taggers write through a temp file so a mid-write failure
+  can't corrupt existing audio.
+- **`internal/config`** has no config file — the output directory
+  (`~/Music/GoDeez`) is fixed, and the only setting is the `DEEZER_ARL`
+  env var, which is optional (falls back to keyring-stored credentials from
+  `godeez login`).
+- **`internal/buildinfo`** holds the version/commit/date injected by
+  goreleaser via `-ldflags`; unreleased builds report `dev`, which disables
+  update-related behavior (`IsDev()`).
+- **`internal/update`** implements self-update: checks GitHub releases,
+  verifies the downloaded binary's SHA256 against the published
+  `checksums.txt`, and replaces the running binary in place.
+
+## Conventions
+
+- Package- and function-level doc comments consistently explain *why*, not
+  just what — e.g. why a check happens where it does, or why an error is
+  handled a particular way. Preserve this style when touching existing code
+  or adding new exported functions.
+- Most per-track errors during a download are non-fatal and surfaced as
+  warnings in the run summary; only cancellation (`context.Canceled`) should
+  abort the loop. Keep new failure modes inside this pattern unless they are
+  truly unrecoverable for the whole run.
+- `Kind` in `internal/deezer/kind.go` is deliberately exhaustive with no
+  default case that silently returns a zero value in the id/method switches —
+  follow the same pattern (explicit cases, empty/error fallback) if extending
+  it.
+- Credentials: `DEEZER_ARL` always takes precedence over keyring-stored
+  login credentials when both are present.

README.md

@@ -147,6 +147,14 @@ export DEEZER_MOBILE_GW_KEY="your_gateway_key"   # exactly 16 characters
 
 Downloaded files are saved to `~/Music/GoDeez`. The download database (`.tracks.db`) is stored in the same directory as your music.
 
+To use a different location, set `GODEEZ_OUTPUT_DIR`:
+
+```bash
+export GODEEZ_OUTPUT_DIR="/path/to/your/music"
+```
+
+A leading `~` is expanded to your home directory.
+
 > **Upgrading from v1.3.0?** The `~/.godeez` directory and `config.toml` are no longer used. Set the `DEEZER_ARL` environment variable instead. Your existing database will be migrated automatically on first run.
 
 ## Usage

internal/config/config.go

@@ -1,6 +1,7 @@
 // Package config resolves where godeez reads its session from and writes its
-// downloads to. There is no config file: the output directory is fixed and
-// the only setting is the DEEZER_ARL environment variable, which exists as an
+// downloads to. There is no config file: the output directory defaults to
+// ~/Music/GoDeez but can be overridden with GODEEZ_OUTPUT_DIR, and the only
+// other setting is the DEEZER_ARL environment variable, which exists as an
 // escape hatch for users who would rather not store credentials in the system
 // keyring.
 package config
@@ -9,6 +10,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/mathismqn/godeez/internal/fsutil"
 )
@@ -27,12 +29,11 @@ type Config struct {
 func Load() (*Config, error) {
 	arl := os.Getenv("DEEZER_ARL")
 
-	homeDir, err := os.UserHomeDir()
+	outputDir, err := resolveOutputDir()
 	if err != nil {
-		return nil, fmt.Errorf("failed to get home directory: %w", err)
+		return nil, err
 	}
 
-	outputDir := filepath.Join(homeDir, "Music", "GoDeez")
 	if err := fsutil.EnsureDir(outputDir); err != nil {
 		return nil, fmt.Errorf("failed to create output directory: %w", err)
 	}
@@ -42,3 +43,29 @@ func Load() (*Config, error) {
 		OutputDir: outputDir,
 	}, nil
 }
+
+// resolveOutputDir honours GODEEZ_OUTPUT_DIR when set, falling back to
+// ~/Music/GoDeez otherwise.
+//
+// A leading "~" is expanded by hand because the shell only does that for
+// unquoted arguments, not for values read out of the environment, so users
+// setting this in a profile file would otherwise end up with a literal "~"
+// directory.
+func resolveOutputDir() (string, error) {
+	homeDir, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("failed to get home directory: %w", err)
+	}
+
+	if dir := strings.TrimSpace(os.Getenv("GODEEZ_OUTPUT_DIR")); dir != "" {
+		if dir == "~" {
+			return homeDir, nil
+		}
+		if rest, ok := strings.CutPrefix(dir, "~/"); ok {
+			return filepath.Join(homeDir, rest), nil
+		}
+		return dir, nil
+	}
+
+	return filepath.Join(homeDir, "Music", "GoDeez"), nil
+}

internal/download/download.go

@@ -134,6 +134,8 @@ func (d *Downloader) downloadAllTracks(ctx context.Context, resource deezer.Reso
 
 	progress := newProgressTracker(len(tracks), d.kind)
 
+	var m3uEntries []m3uEntry
+
 	for i, track := range tracks {
 		if ctx.Err() != nil {
 			return ctx.Err()
@@ -148,6 +150,19 @@ func (d *Downloader) downloadAllTracks(ctx context.Context, resource deezer.Reso
 		}
 
 		progress.handleResult(i, track, result)
+
+		if d.kind == deezer.KindPlaylist && result.err == nil {
+			m3uEntries = append(m3uEntries, m3uEntry{track: track, path: result.path})
+		}
+	}
+
+	// Written after the loop, not per track, so a run that fails partway
+	// through still produces a playlist covering whatever did make it to
+	// disk instead of no playlist at all.
+	if d.kind == deezer.KindPlaylist {
+		if err := writeM3U(outputDir, m3uEntries); err != nil {
+			fmt.Printf("\nWarning: failed to write m3u playlist: %v\n", err)
+		}
 	}
 
 	progress.printSummary(outputDir, time.Since(startTime))

internal/download/m3u.go

@@ -0,0 +1,60 @@
+package download
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"github.com/mathismqn/godeez/internal/deezer"
+)
+
+// m3uEntry pairs a playlist track with the file it ended up at, so the m3u
+// can be written after the fact without re-deriving the path.
+type m3uEntry struct {
+	track *deezer.Track
+	path  string
+}
+
+// writeM3U records a playlist's tracks in their original order as an
+// extended M3U file next to the downloaded audio.
+//
+// This exists because the on-disk file names carry no ordering for
+// playlists (unlike albums, which get a zero padded track number prefix):
+// without an m3u, the sequence the user curated on Deezer is lost the moment
+// the tracks land in a directory that any player will list alphabetically.
+//
+// Skipped tracks are included: they are already on disk from a previous run
+// and belong at their playlist position just as much as one downloaded this
+// run. Failed tracks are left out since there is nothing on disk to point
+// at, and a broken entry would only confuse the player.
+//
+// Paths are written relative to outputDir so the m3u keeps working if the
+// whole playlist folder is moved or copied elsewhere.
+func writeM3U(outputDir string, entries []m3uEntry) error {
+	if len(entries) == 0 {
+		return nil
+	}
+
+	m3uPath := filepath.Join(outputDir, filepath.Base(outputDir)+".m3u")
+
+	var b strings.Builder
+	b.WriteString("#EXTM3U\n")
+
+	for _, e := range entries {
+		duration, err := strconv.Atoi(e.track.Duration)
+		if err != nil {
+			duration = 0
+		}
+
+		rel, err := filepath.Rel(outputDir, e.path)
+		if err != nil {
+			rel = e.path
+		}
+
+		fmt.Fprintf(&b, "#EXTINF:%d,%s - %s\n%s\n", duration, e.track.Artist, e.track.FullTitle(), rel)
+	}
+
+	return os.WriteFile(m3uPath, []byte(b.String()), 0644)
+}

internal/download/track.go

@@ -107,7 +107,7 @@ func (d *Downloader) downloadTrack(ctx context.Context, resource deezer.Resource
 	warnings = append(warnings, metadata.warnings...)
 	warnings = append(warnings, d.finalizeDownload(resource, track, outputPath, outputFormat, metadata.genre, cover, metadata.bpmKey)...)
 
-	return downloadResult{warnings: warnings}
+	return downloadResult{path: outputPath, warnings: warnings}
 }
 
 // uniqueOutputPath avoids clobbering an unrelated file by appending " (2)",