Amphlify/Packages/AmphlifyKit/Sources/SourceSubsonic/SubsonicCrawl.swift

import Domain
import Foundation

struct SubsonicMemory: Sendable {
    var seen: [EntityKind: Set<String>] = [:]
    var formats: [String: AudioFormat] = [:]
}

struct SubsonicCrawl {
    static let pageSize = 500

    let client: SubsonicClient
    let mapper: SubsonicMapper
    let emit: (Change) -> Void
    private var memory = SubsonicMemory()
    private var bestByAlbum: [String: AudioFormat] = [:]
    private var annotations: [Change] = []

    init(client: SubsonicClient, mapper: SubsonicMapper, emit: @escaping (Change) -> Void) {
        self.client = client
        self.mapper = mapper
        self.emit = emit
    }

    mutating func run(previous: [EntityKind: Set<String>]) async throws -> SubsonicMemory {
        try await crawlArtists()
        try await crawlTracks()
        try await crawlAlbums()
        try await crawlPlaylists()
        try await crawlStations()
        try await crawlStarred()
        annotations.forEach(emit)
        emitRemovals(previous: previous)
        return memory
    }

    private mutating func upsert(_ entity: Entity, kind: EntityKind, remote: String) {
        memory.seen[kind, default: []].insert(remote)
        emit(.upsert(entity))
    }

    private mutating func crawlArtists() async throws {
        let payload = try await client.call("getArtists", as: ArtistsPayload.self)
        for index in payload.artists.index ?? [] {
            for artist in index.artist ?? [] {
                upsert(.artist(mapper.artist(artist)), kind: .artist, remote: artist.id)
            }
        }
    }

    private mutating func crawlTracks() async throws {
        var offset = 0
        while true {
            try Task.checkCancellation()
            let params = [
                "query": "\"\"",
                "songCount": String(Self.pageSize),
                "songOffset": String(offset),
                "artistCount": "0",
                "albumCount": "0",
            ]
            let songs = try await client.call("search3", params, as: SearchPayload.self).searchResult3.song ?? []
            songs.forEach { consume($0) }
            offset += songs.count
            if songs.count < Self.pageSize {
                return
            }
        }
    }

    private mutating func consume(_ song: SongJSON) {
        let track = mapper.track(song)
        upsert(.track(track), kind: .track, remote: song.id)
        if let format = track.formats.first {
            memory.formats[song.id] = format
            if let albumId = song.albumId, format.isBetter(than: bestByAlbum[albumId]) {
                bestByAlbum[albumId] = format
            }
        }
        if let annotation = mapper.annotation(song) {
            annotations.append(.annotate(track.id, annotation))
        }
    }

    private mutating func crawlAlbums() async throws {
        var offset = 0
        while true {
            try Task.checkCancellation()
            let params = ["type": "alphabeticalByName", "size": String(Self.pageSize), "offset": String(offset)]
            let albums = try await client.call("getAlbumList2", params, as: AlbumListPayload.self).albumList2.album ?? []
            for album in albums {
                upsert(.album(mapper.album(album, bestFormat: bestByAlbum[album.id])), kind: .album, remote: album.id)
            }
            offset += albums.count
            if albums.count < Self.pageSize {
                return
            }
        }
    }

    private mutating func crawlPlaylists() async throws {
        let playlists = try await client.call("getPlaylists", as: PlaylistsPayload.self).playlists.playlist ?? []
        for summary in playlists {
            try Task.checkCancellation()
            let detail = try await client.call("getPlaylist", ["id": summary.id], as: PlaylistPayload.self).playlist
            let (playlist, entries) = mapper.playlist(detail)
            upsert(.playlist(playlist, entries: entries), kind: .playlist, remote: detail.id)
        }
    }

    private mutating func crawlStations() async throws {
        let stations = try await client.call("getInternetRadioStations", as: StationsPayload.self).internetRadioStations
        for json in stations.internetRadioStation ?? [] {
            if let station = mapper.station(json) {
                upsert(.station(station), kind: .station, remote: json.id)
            }
        }
    }

    private mutating func crawlStarred() async throws {
        let starred = try await client.call("getStarred2", as: StarredPayload.self).starred2
        for artist in starred.artist ?? [] {
            annotations.append(.annotate(mapper.id(artist.id), Annotation(favoritedAt: SubsonicDate.parse(artist.starred) ?? .now)))
        }
        for album in starred.album ?? [] {
            annotations.append(.annotate(mapper.id(album.id), Annotation(favoritedAt: SubsonicDate.parse(album.starred) ?? .now)))
        }
    }

    private func emitRemovals(previous: [EntityKind: Set<String>]) {
        for (kind, remotes) in previous {
            for remote in remotes.subtracting(memory.seen[kind] ?? []).sorted() {
                emit(.remove(kind, mapper.id(remote)))
            }
        }
    }
}