// Versioned data contracts for the preview feature — design §12, schema v1.
//
// Plain frozen objects, framework-free, so the whole session core is
// unit-testable under node:test with no renderer. The reducer and manifest
// builders depend on THIS file's shapes, never on raw CatalogTrack rows.

export const MANIFEST_SCHEMA_VERSION = 1;

export const AVAILABILITY = Object.freeze({
    UNRESOLVED: "unresolved",
    AVAILABLE: "available",
    NOT_PROVIDED: "not_provided",
    UNRELEASED: "unreleased",
    REGION_UNAVAILABLE: "region_unavailable",
    TEMP_FAILED: "temporarily_failed",
});

const CONTEXT_KINDS = new Set(["artist", "album", "playlist", "search", "collection"]);
const PROVIDERS = new Set(["deezer", "apple", "local"]);
const CONFIDENCE = new Set(["native", "isrc", "strong_metadata"]);

/**
 * Stable provider identity for one source of a preview. Signed URLs are NOT
 * identity (Phase 0: every fetch mints a different URL); the provider track
 * id is. Apple rows keep their REAL provider id here — the backend's
 * synthetic-id flattening is a Phase 2 extension, and this contract is the
 * reason it can't silently regress.
 */
export function makeSourceRef({ provider, providerTrackId, isrc, matchConfidence = "native" }) {
    if (!PROVIDERS.has(provider)) throw new Error(`unknown provider ${provider}`);
    if (!CONFIDENCE.has(matchConfidence)) throw new Error(`unknown confidence ${matchConfidence}`);
    const id = String(providerTrackId ?? "");
    if (!id) throw new Error("providerTrackId required");
    return Object.freeze({ provider, providerTrackId: id, isrc, matchConfidence });
}

export function makeContext({ kind, contextKey, title, subtitle, artwork, sourceTrackCount }) {
    if (!CONTEXT_KINDS.has(kind)) throw new Error(`unknown context kind ${kind}`);
    if (!contextKey) throw new Error("contextKey required");
    return Object.freeze({
        kind,
        contextKey: String(contextKey),
        title: title ?? "",
        subtitle,
        artwork,
        sourceTrackCount: sourceTrackCount | 0,
    });
}

/**
 * One occurrence in a manifest. `sessionKey` is unique per occurrence (so
 * playlist duplicates stay distinct); `recordingKey` ties repeated
 * occurrences of the same recording together for shared action state.
 */
export function makeItem({
    sessionKey,
    sourceOrdinal,
    discNumber,
    trackNumber,
    recordingKey,
    title,
    artists,
    album,
    albumId,
    artwork,
    fullDurationMs,
    explicit,
    sources,
    initialAvailability,
    actions,
}) {
    if (!sessionKey) throw new Error("sessionKey required");
    if (!Number.isInteger(sourceOrdinal) || sourceOrdinal < 0) {
        throw new Error("sourceOrdinal must be a non-negative integer");
    }
    const avail = initialAvailability ?? AVAILABILITY.UNRESOLVED;
    if (!Object.values(AVAILABILITY).includes(avail)) {
        throw new Error(`unknown availability ${avail}`);
    }
    return Object.freeze({
        sessionKey: String(sessionKey),
        sourceOrdinal,
        discNumber,
        trackNumber,
        recordingKey,
        title: title ?? "",
        artists: Object.freeze(Array.isArray(artists) ? [...artists] : []),
        album,
        albumId: albumId != null ? String(albumId) : undefined,
        artwork,
        fullDurationMs,
        explicit,
        sources: Object.freeze((sources ?? []).map((s) => (Object.isFrozen(s) ? s : makeSourceRef(s)))),
        initialAvailability: avail,
        actions: Object.freeze(actions ?? { playFull: true, save: true, addToPlaylist: true, openAlbum: true }),
    });
}

/** Immutable, versioned manifest. `createdAtMs` is supplied by the caller so
 * everything here stays pure and replayable in tests. */
export function makeManifest({ context, items, createdAtMs }) {
    return Object.freeze({
        schemaVersion: MANIFEST_SCHEMA_VERSION,
        context,
        items: Object.freeze([...items]),
        createdAtMs,
    });
}

/** Sanity check used by tests and by the session boundary in dev builds. */
export function isValidManifest(m) {
    if (!m || m.schemaVersion !== MANIFEST_SCHEMA_VERSION) return false;
    if (!m.context || !CONTEXT_KINDS.has(m.context.kind)) return false;
    if (!Array.isArray(m.items)) return false;
    const keys = new Set();
    for (const it of m.items) {
        if (!it.sessionKey || keys.has(it.sessionKey)) return false; // dupes forbidden
        keys.add(it.sessionKey);
        // No signed URL may ride in a manifest — identity is provider ids.
        for (const s of it.sources ?? []) {
            if (typeof s.url === "string") return false;
        }
    }
    return true;
}