maps-offline-test/app/functions.js

import { db } from "./database/db";
import * as FileSystem from 'expo-file-system';

export async function downloadTile(url, z, x, y) {
  try {
    const fileUri = FileSystem.cacheDirectory + `tiles/${z}/${x}/${y}.png`;
    if (!FileSystem.getInfoAsync(FileSystem.cacheDirectory + `tiles/${z}/${x}`).exists) {
      await FileSystem.makeDirectoryAsync(FileSystem.cacheDirectory + `tiles/${z}/${x}`, { intermediates: true });
    }
    if (FileSystem.getInfoAsync(FileSystem.cacheDirectory + `tiles/${z}/${x}/${y}.png`).exists) {
      console.log('File already exists');
    } else {
      const downloadResult = await FileSystem.downloadAsync(url, fileUri);

      if (downloadResult.status !== 200) {
        throw new Error('Failed to download the tile');
      }
    }
  } catch (error) {
    console.error("Error downloading tile:", error);
  }
}

export async function loadGeoJSONData(region) {
  const selectQuery = `SELECT data FROM regions WHERE region_id = ${region};`;

  return new Promise((resolve, reject) => {
    db.transaction(tx => {
      tx.executeSql(
        selectQuery,
        [],
        (_, { rows }) => {
          if (rows.length > 0) {
            resolve(JSON.parse(rows._array[0].data));
          } else {
            resolve(null);
          }
        },
        (_, error) => {
          reject(error);
        }
      );
    });
  });
}

export async function loadMarkersData() {
  const selectQuery = `SELECT marker_id, l, g, i, n, d FROM markers;`;

  return new Promise((resolve, reject) => {
    db.transaction(tx => {
      tx.executeSql(
        selectQuery,
        [],
        (_, { rows }) => {
          if (rows.length > 0) {
            resolve(rows._array.slice(0, 20));
          } else {
            resolve(null);
          }
        },
        (_, error) => {
          reject(error);
        }
      );
    });
  });
}