import { OfflineManager, type OfflinePackStatus } from '@maplibre/maplibre-react-native';

type LngLatBounds = [number, number, number, number]; // [west, south, east, north]

// Vector style URL — only vector styles support offline packs
export const OFFLINE_STYLE_URL = 'https://tiles.openfreemap.org/styles/liberty';

// Zoom levels: 6 (region overview) → 16 (street detail, good for cycling)
const MIN_ZOOM = 6;
const MAX_ZOOM = 16;

export interface OfflineRegion {
  id: string;
  name: string;
  bounds: LngLatBounds;
  createdAt: string;
  completedTiles: number;
  totalSizeBytes: number;
  state: 'active' | 'inactive' | 'complete';
  percentage: number;
}

// ── Download ──────────────────────────────────────────────────────────────────

/**
 * Download a region and return a Promise that resolves only when the pack
 * reaches state 'complete'. Transient tile-fetch errors (e.g. "stream was
 * reset: CANCEL") are silently ignored — MapLibre retries them internally
 * and they do not indicate a failed download.
 */
export function downloadRegion(
  name: string,
  bounds: LngLatBounds,
  onProgress: (pct: number, tilesDown: number, sizeBytes: number) => void,
): Promise<string> {
  OfflineManager.setProgressEventThrottle(500);

  return new Promise((resolve, reject) => {
    let packId: string;

    OfflineManager.createPack(
      {
        mapStyle: OFFLINE_STYLE_URL,
        bounds,
        minZoom: MIN_ZOOM,
        maxZoom: MAX_ZOOM,
        metadata: { name, createdAt: new Date().toISOString() },
      },
      (pack, status: OfflinePackStatus) => {
        packId = pack.id;
        onProgress(status.percentage, status.completedTileCount, status.completedTileSize);
        if (status.state === 'complete') {
          resolve(packId);
        }
      },
      (_pack, _error) => {
        // Transient tile-level errors — MapLibre retries these automatically.
        // Do not reject: the overall download is still in progress.
      },
    ).catch(reject); // only rejects on createPack failure (e.g. bad style URL)
  });
}

// ── List ──────────────────────────────────────────────────────────────────────

export async function listRegions(): Promise<OfflineRegion[]> {
  const packs = await OfflineManager.getPacks();
  const regions: OfflineRegion[] = [];

  for (const pack of packs) {
    const status = await pack.status();
    const meta = pack.metadata as { name?: string; createdAt?: string };
    regions.push({
      id: pack.id,
      name: meta.name ?? 'Unnamed region',
      bounds: pack.bounds,
      createdAt: meta.createdAt ?? '',
      completedTiles: status.completedTileCount,
      totalSizeBytes: status.completedTileSize,
      state: status.state,
      percentage: status.percentage,
    });
  }

  return regions;
}

// ── Delete ────────────────────────────────────────────────────────────────────

export async function deleteRegion(id: string): Promise<void> {
  await OfflineManager.deletePack(id);
}

// ── Helpers ───────────────────────────────────────────────────────────────────

export function formatBytes(bytes: number): string {
  if (bytes < 1024) return `${bytes} B`;
  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
}

/** Expand a [w,s,e,n] bounds by `km` kilometres in every direction. */
export function expandBounds(bounds: LngLatBounds, km: number): LngLatBounds {
  const latDelta = km / 111;
  const lonDelta = km / (111 * Math.cos((bounds[1] + bounds[3]) / 2 * Math.PI / 180));
  return [
    bounds[0] - lonDelta,
    bounds[1] - latDelta,
    bounds[2] + lonDelta,
    bounds[3] + latDelta,
  ];
}