vibesonic/internal/metadataenrich/client.go

// Package metadataenrich looks up optional supplementary metadata for
// artists and albums that already carry a MusicBrainz ID from local
// tags — from MusicBrainz itself and the Cover Art Archive. It is never
// on any hot path and never required: VibeSonic must work completely
// offline, so every function here degrades to "no data" rather than an
// error when the network is unavailable, and nothing here ever
// fabricates a value the API didn't actually return.
package metadataenrich

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"time"
)

const userAgent = "VibeSonic/1.0 (+https://git.noroutes.net/NoRoutes/vibetunes)"

const (
	defaultMusicBrainzBaseURL     = "https://musicbrainz.org/ws/2"
	defaultCoverArtArchiveBaseURL = "https://coverartarchive.org"
)

// Client talks to the MusicBrainz and Cover Art Archive HTTP APIs. The
// zero value is usable and talks to the real public services;
// MusicBrainzBaseURL/CoverArtArchiveBaseURL exist so tests can point it
// at an httptest server instead.
type Client struct {
	HTTPClient             *http.Client
	MusicBrainzBaseURL     string
	CoverArtArchiveBaseURL string
}

func (c *Client) httpClient() *http.Client {
	if c.HTTPClient != nil {
		return c.HTTPClient
	}
	return &http.Client{Timeout: 10 * time.Second}
}

func (c *Client) musicBrainzBaseURL() string {
	if c.MusicBrainzBaseURL != "" {
		return c.MusicBrainzBaseURL
	}
	return defaultMusicBrainzBaseURL
}

func (c *Client) coverArtArchiveBaseURL() string {
	if c.CoverArtArchiveBaseURL != "" {
		return c.CoverArtArchiveBaseURL
	}
	return defaultCoverArtArchiveBaseURL
}

// ArtistData is the (small) subset of a MusicBrainz artist entity
// VibeSonic actually surfaces. Fields MusicBrainz didn't return are
// left as their zero value.
type ArtistData struct {
	Disambiguation string   `json:"disambiguation"`
	Genres         []string `json:"genres"`
}

type mbArtistResponse struct {
	Disambiguation string `json:"disambiguation"`
	Tags           []struct {
		Name string `json:"name"`
	} `json:"tags"`
}

// FetchArtist looks up a MusicBrainz artist entity by MBID. A network
// or lookup failure returns an error; there is no fallback value.
func (c *Client) FetchArtist(ctx context.Context, mbid string) (*ArtistData, error) {
	url := fmt.Sprintf("%s/artist/%s?fmt=json&inc=tags", c.musicBrainzBaseURL(), mbid)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("User-Agent", userAgent)
	req.Header.Set("Accept", "application/json")

	resp, err := c.httpClient().Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("musicbrainz: artist %s: HTTP %d", mbid, resp.StatusCode)
	}

	var raw mbArtistResponse
	if err := json.NewDecoder(resp.Body).Decode(&raw); err != nil {
		return nil, err
	}
	data := &ArtistData{Disambiguation: raw.Disambiguation}
	for _, t := range raw.Tags {
		data.Genres = append(data.Genres, t.Name)
	}
	return data, nil
}

// CoverArt is the image URLs the Cover Art Archive returned for a
// release's front cover, at three sizes. A blank field means the
// archive simply didn't provide that size, not that VibeSonic
// substituted anything.
type CoverArt struct {
	SmallURL  string
	MediumURL string
	LargeURL  string
}

type caaResponse struct {
	Images []struct {
		Front      bool              `json:"front"`
		Image      string            `json:"image"`
		Thumbnails map[string]string `json:"thumbnails"`
	} `json:"images"`
}

// FetchReleaseCoverArt looks up the Cover Art Archive entry for a
// release MBID and returns its front-cover image URLs. Returns
// (nil, nil) — not an error — when the release has no cover art
// registered, since that's a normal, common outcome, not a failure.
func (c *Client) FetchReleaseCoverArt(ctx context.Context, mbid string) (*CoverArt, error) {
	url := fmt.Sprintf("%s/release/%s", c.coverArtArchiveBaseURL(), mbid)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("User-Agent", userAgent)
	req.Header.Set("Accept", "application/json")

	resp, err := c.httpClient().Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode == http.StatusNotFound {
		return nil, nil
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("coverartarchive: release %s: HTTP %d", mbid, resp.StatusCode)
	}

	var raw caaResponse
	if err := json.NewDecoder(resp.Body).Decode(&raw); err != nil {
		return nil, err
	}
	for _, img := range raw.Images {
		if !img.Front {
			continue
		}
		return &CoverArt{
			SmallURL:  img.Thumbnails["small"],
			MediumURL: img.Thumbnails["large"],
			LargeURL:  img.Image,
		}, nil
	}
	return nil, nil
}