PainterCore/lib/downloader.js

const SAVED_FILES_KEY = 'savedFiles';
const KEY_TOTAL_SIZE = 'totalSize';
const KEY_PATH = 'path';
const KEY_TIME = 'time';
const KEY_SIZE = 'size';

// 可存储总共为 6M，目前小程序可允许的最大本地存储为 10M
const MAX_SPACE_IN_B = 6 * 1024 * 1024;
let savedFiles = {};

export default class Dowloader {
  constructor() {
    wx.getStorage({
      key: SAVED_FILES_KEY,
      success: function (res) {
        if (res.data) {
          savedFiles = res.data;
        }
      },
    });
  }

  /**
   * 下载文件，会用 lru 方式来缓存文件到本地
   * @param {String} url 文件的 url
   */
  download(url) {
    return new Promise((resolve, reject) => {
      if (!(url && url.startsWith('http'))) {
        resolve(url);
        return;
      }
      const file = getFile(url);
      if (file) {
        resolve(file[KEY_PATH]);
        return;
      }
      wx.downloadFile({
        url: url,
        success: function (res) {
          if (res.statusCode !== 200) {
            console.error(`downloadFile ${url} failed res.statusCode is not 200`);
            reject();
            return;
          }
          const { tempFilePath } = res;
          wx.getFileInfo({
            filePath: tempFilePath,
            success: (tmpRes) => {
              const newFileSize = tmpRes.size;
              doLru(newFileSize).then(() => {
                saveFile(url, newFileSize, tempFilePath).then((filePath) => {
                  resolve(filePath);
                });
              }, () => {
                resolve(tempFilePath);
              });
            },
            fail: (error) => {
              // 文件大小信息获取失败，则此文件也不要进行存储
              console.error(`getFileInfo ${res.tempFilePath} failed, ${JSON.stringify(error)}`);
              resolve(res.tempFilePath);
            },
          });
        },
        fail: function (error) {
          console.error(`downloadFile failed, ${JSON.stringify(error)} `);
          reject();
        },
      });
    });
  }
}

function saveFile(key, newFileSize, tempFilePath) {
  return new Promise((resolve, reject) => {
    wx.saveFile({
      tempFilePath: tempFilePath,
      success: (fileRes) => {
        const totalSize = savedFiles[KEY_TOTAL_SIZE] ? savedFiles[KEY_TOTAL_SIZE] : 0;
        savedFiles[key] = {};
        savedFiles[key][KEY_PATH] = fileRes.savedFilePath;
        savedFiles[key][KEY_TIME] = new Date().getTime();
        savedFiles[key][KEY_SIZE] = newFileSize;
        savedFiles['totalSize'] = newFileSize + totalSize;
        wx.setStorage({
          key: SAVED_FILES_KEY,
          data: savedFiles,
        });
        resolve(fileRes.savedFilePath);
      },
      fail: (error) => {
        console.error(`saveFile ${key} failed, then we delete all files, ${JSON.stringify(error)}`);
        // 由于 saveFile 成功后，res.tempFilePath 处的文件会被移除，所以在存储未成功时，我们还是继续使用临时文件
        resolve(tempFilePath);
        // 如果出现错误，就直接情况本地的所有文件，因为你不知道是不是因为哪次lru的某个文件未删除成功
        reset();
      },
    });
  });
}

/**
 * 清空所有下载相关内容
 */
function reset() {
  wx.removeStorage({
    key: SAVED_FILES_KEY,
    success: () => {
      wx.getSavedFileList({
        success: (listRes) => {
          removeFiles(listRes.fileList);
        },
        fail: (getError) => {
          console.error(`getSavedFileList failed, ${JSON.stringify(getError)}`);
        },
      });
    },
  });
}

function doLru(size) {
  return new Promise((resolve, reject) => {
    let totalSize = savedFiles[KEY_TOTAL_SIZE] ? savedFiles[KEY_TOTAL_SIZE] : 0;

    if (size + totalSize <= MAX_SPACE_IN_B) {
      resolve();
      return;
    }
    // 如果加上新文件后大小超过最大限制，则进行 lru
    const pathsShouldDelete = [];
    // 按照最后一次的访问时间，从小到大排序
    const allFiles = JSON.parse(JSON.stringify(savedFiles));
    delete allFiles[KEY_TOTAL_SIZE];
    const sortedKeys = Object.keys(allFiles).sort((a, b) => {
      return allFiles[a][KEY_TIME] - allFiles[b][KEY_TIME];
    });

    for (const sortedKey of sortedKeys) {
      totalSize -= savedFiles[sortedKey].size;
      pathsShouldDelete.push(savedFiles[sortedKey][KEY_PATH]);
      delete savedFiles[sortedKey];
      if (totalSize + size < MAX_SPACE_IN_B) {
        break;
      }
    }

    savedFiles['totalSize'] = totalSize;

    wx.setStorage({
      key: SAVED_FILES_KEY,
      data: savedFiles,
      success: () => {
      // 保证 storage 中不会存在不存在的文件数据
        if (pathsShouldDelete.length > 0) {
          removeFiles(pathsShouldDelete);
        }
        resolve();
      },
      fail: (error) => {
        console.error(`doLru setStorage failed, ${JSON.stringify(error)}`);
        reject();
      },
    });
  });
}

function removeFiles(pathsShouldDelete) {
  for (const pathDel of pathsShouldDelete) {
    let delPath = pathDel;
    if (typeof pathDel === 'object') {
      delPath = pathDel.filePath;
    }
    wx.removeSavedFile({
      filePath: delPath,
      fail: (error) => {
        console.error(`removeSavedFile ${pathDel} failed, ${JSON.stringify(error)}`);
      },
    });
  }
}

function getFile(key) {
  if (!savedFiles[key]) {
    return;
  }
  savedFiles[key]['time'] = new Date().getTime();
  wx.setStorage({
    key: SAVED_FILES_KEY,
    data: savedFiles,
  });
  return savedFiles[key];
}