import { File, Directory, Paths } from 'expo-file-system';
import { TrackPoint } from '../types';

function recordingsDir(): Directory {
  return new Directory(Paths.document, 'recordings');
}

export function ensureRecordingsDir(): void {
  const dir = recordingsDir();
  if (!dir.exists) dir.create();
}

export function saveGpx(trackPoints: TrackPoint[], title: string): string {
  ensureRecordingsDir();
  const filename = `${sanitizeFilename(title)}_${Date.now()}.gpx`;
  const file = new File(recordingsDir(), filename);
  file.write(buildGpx(trackPoints, title));
  return file.uri;
}

export function buildGpx(trackPoints: TrackPoint[], title: string): string {
  const trkpts = trackPoints.map(buildTrkpt).join('\n');
  return `<?xml version="1.0" encoding="UTF-8"?>
<gpx version="1.1" creator="bincio-rec"
  xmlns="http://www.topografix.com/GPX/1/1"
  xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1">
  <metadata><name>${escapeXml(title)}</name></metadata>
  <trk>
    <name>${escapeXml(title)}</name>
    <trkseg>
${trkpts}
    </trkseg>
  </trk>
</gpx>`;
}

function buildTrkpt(pt: TrackPoint): string {
  const ext = buildExtensions(pt);
  return `      <trkpt lat="${pt.lat}" lon="${pt.lon}">
        <ele>${pt.ele.toFixed(1)}</ele>
        <time>${pt.time.toISOString()}</time>${ext}
      </trkpt>`;
}

function buildExtensions(pt: TrackPoint): string {
  if (pt.hr == null && pt.power == null && pt.cad == null) return '';
  const hr = pt.hr != null ? `<gpxtpx:hr>${pt.hr}</gpxtpx:hr>` : '';
  const power = pt.power != null ? `<gpxtpx:power>${pt.power}</gpxtpx:power>` : '';
  const cad = pt.cad != null ? `<gpxtpx:cad>${pt.cad}</gpxtpx:cad>` : '';
  return `
        <extensions>
          <gpxtpx:TrackPointExtension>
            ${hr}${power}${cad}
          </gpxtpx:TrackPointExtension>
        </extensions>`;
}

export async function parseGpxFile(fileUri: string): Promise<TrackPoint[]> {
  const content = await new File(fileUri).text();
  const points: TrackPoint[] = [];
  const re = /<trkpt\s+lat="([^"]+)"\s+lon="([^"]+)">([\s\S]*?)<\/trkpt>/g;
  let m;
  while ((m = re.exec(content)) !== null) {
    const lat = parseFloat(m[1]);
    const lon = parseFloat(m[2]);
    const inner = m[3];
    const ele     = parseFloat(inner.match(/<ele>([\d.-]+)<\/ele>/)?.[1] ?? '0');
    const timeStr = inner.match(/<time>([^<]+)<\/time>/)?.[1] ?? '';
    const hr      = parseInt(inner.match(/<gpxtpx:hr>(\d+)<\/gpxtpx:hr>/)?.[1] ?? '') || undefined;
    const power   = parseInt(inner.match(/<gpxtpx:power>(\d+)<\/gpxtpx:power>/)?.[1] ?? '') || undefined;
    const cad     = parseInt(inner.match(/<gpxtpx:cad>(\d+)<\/gpxtpx:cad>/)?.[1] ?? '') || undefined;
    if (!isNaN(lat) && !isNaN(lon)) {
      points.push({ lat, lon, ele, time: new Date(timeStr), hr, power, cad });
    }
  }
  return points;
}

function escapeXml(s: string): string {
  return s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;');
}

function sanitizeFilename(s: string): string {
  return s.replace(/[^a-zA-Z0-9_-]/g, '_').slice(0, 64);
}