import { refreshStoredToken } from "./auth.js";
import { loadToken, tokenNeedsRefresh } from "./token-store.js";
import type { SpotifyPlaylist, SpotifyToken, SpotifyTrack } from "./types.js";

type FetchLike = typeof fetch;

export interface SpotifyUser {
  id: string;
  display_name?: string | null;
}

export interface SpotifyApiClientOptions {
  fetchImpl?: FetchLike;
  loadToken?: () => Promise<SpotifyToken | undefined>;
  refreshToken?: () => Promise<SpotifyToken>;
  sleep?: (ms: number) => Promise<void>;
  now?: () => number;
  baseUrl?: string;
}

export interface CreatePlaylistOptions {
  description?: string;
  public?: boolean;
}

export interface PlaylistMutationResult {
  snapshot_id?: string;
}

const DEFAULT_BASE_URL = "https://api.spotify.com/v1";

function chunk<T>(items: T[], size: number): T[][] {
  const chunks: T[][] = [];
  for (let index = 0; index < items.length; index += size) {
    chunks.push(items.slice(index, index + size));
  }
  return chunks;
}

async function noSleep(): Promise<void> {
  return undefined;
}

export class SpotifyApiClient {
  private readonly fetchImpl: FetchLike;
  private readonly loadStoredToken: () => Promise<SpotifyToken | undefined>;
  private readonly refreshStoredToken: () => Promise<SpotifyToken>;
  private readonly sleep: (ms: number) => Promise<void>;
  private readonly now: () => number;
  private readonly baseUrl: string;

  constructor(options: SpotifyApiClientOptions = {}) {
    this.fetchImpl = options.fetchImpl ?? fetch;
    this.loadStoredToken = options.loadToken ?? (() => loadToken());
    this.refreshStoredToken = options.refreshToken ?? (() => refreshStoredToken());
    this.sleep = options.sleep ?? noSleep;
    this.now = options.now ?? Date.now;
    this.baseUrl = options.baseUrl ?? DEFAULT_BASE_URL;
  }

  async getCurrentUser(): Promise<SpotifyUser> {
    return this.request<SpotifyUser>("GET", "/me");
  }

  async searchTracks(query: string, limit: number): Promise<SpotifyTrack[]> {
    const params = new URLSearchParams({ type: "track", q: query, limit: String(limit) });
    const response = await this.request<{ tracks: { items: SpotifyTrack[] } }>("GET", `/search?${params.toString()}`);
    return response.tracks.items;
  }

  async listPlaylists(limit: number, offset: number): Promise<SpotifyPlaylist[]> {
    const params = new URLSearchParams({ limit: String(limit), offset: String(offset) });
    const response = await this.request<{ items: SpotifyPlaylist[] }>("GET", `/me/playlists?${params.toString()}`);
    return response.items;
  }

  async createPlaylist(name: string, options: CreatePlaylistOptions = {}): Promise<SpotifyPlaylist> {
    return this.request<SpotifyPlaylist>("POST", "/me/playlists", {
      name,
      description: options.description,
      public: Boolean(options.public)
    });
  }

  async addItemsToPlaylist(playlistId: string, uris: string[]): Promise<PlaylistMutationResult[]> {
    const results: PlaylistMutationResult[] = [];
    for (const batch of chunk(uris, 100)) {
      results.push(await this.request<PlaylistMutationResult>("POST", `/playlists/${encodeURIComponent(playlistId)}/items`, { uris: batch }));
    }
    return results;
  }

  async removeItemsFromPlaylist(playlistId: string, uris: string[]): Promise<PlaylistMutationResult[]> {
    const results: PlaylistMutationResult[] = [];
    for (const batch of chunk(uris, 100)) {
      results.push(await this.request<PlaylistMutationResult>("DELETE", `/playlists/${encodeURIComponent(playlistId)}/items`, {
        tracks: batch.map((uri) => ({ uri }))
      }));
    }
    return results;
  }

  private async getAccessToken(): Promise<SpotifyToken> {
    const token = await this.loadStoredToken();
    if (!token) {
      throw new Error("Spotify auth token not found. Run `scripts/spotify auth` first.");
    }
    if (tokenNeedsRefresh(token, this.now())) {
      return this.refreshAccessTokenSafely();
    }
    return token;
  }

  private async request<T>(method: string, path: string, body?: unknown, authRetried = false): Promise<T> {
    const token = await this.getAccessToken();
    const response = await this.fetchWithTransientRetries(method, path, token.accessToken, body);
    if (response.status === 401 && !authRetried) {
      const refreshed = await this.refreshAccessTokenSafely();
      const retryResponse = await this.fetchWithTransientRetries(method, path, refreshed.accessToken, body);
      return this.parseResponse<T>(retryResponse);
    }
    return this.parseResponse<T>(response);
  }

  private async fetchWithTransientRetries(method: string, path: string, accessToken: string, body: unknown): Promise<Response> {
    let retried429 = false;
    let serverRetries = 0;
    while (true) {
      const response = await this.fetchImpl(`${this.baseUrl}${path}`, {
        method,
        headers: {
          authorization: `Bearer ${accessToken}`,
          ...(body === undefined ? {} : { "content-type": "application/json" })
        },
        body: body === undefined ? undefined : JSON.stringify(body)
      });

      if (response.status === 429 && !retried429) {
        retried429 = true;
        const retryAfter = Number(response.headers.get("retry-after") ?? "1");
        await this.sleep(Number.isFinite(retryAfter) ? retryAfter * 1000 : 1000);
        continue;
      }
      if (response.status >= 500 && response.status < 600 && serverRetries < 2) {
        serverRetries += 1;
        await this.sleep(100 * serverRetries);
        continue;
      }
      return response;
    }
  }

  private async refreshAccessTokenSafely(): Promise<SpotifyToken> {
    try {
      return await this.refreshStoredToken();
    } catch {
      throw new Error("Spotify token refresh failed. Run `scripts/spotify auth` again.");
    }
  }

  private async parseResponse<T>(response: Response): Promise<T> {
    if (!response.ok) {
      throw new Error(`Spotify API request failed with status ${response.status}.`);
    }
    if (response.status === 204) {
      return undefined as T;
    }
    return response.json() as Promise<T>;
  }
}

export function createSpotifyApiClient(options: SpotifyApiClientOptions = {}): SpotifyApiClient {
  return new SpotifyApiClient(options);
}