restored, these groups will be removed from the saved groups list
            // to prevent duplication.
            groupToSave.removeAfterRestore = true;
            groupsToSave.set(groupStateToSave.id, groupToSave);
          }
          groupToSave.tabs.push(
            lazy.SessionStore.formatTabStateForSavedGroup(tab)
          );
        }
        return tab;
      });
      groupsToSave.forEach(groupState => {
        const alreadySavedGroup = savedGroups.find(
          existingGroup => existingGroup.id == groupState.id
        );
        if (alreadySavedGroup) {
          alreadySavedGroup.removeAfterRestore = true;
        } else {
          savedGroups.push(groupState);
        }
      });
      win.selected = oldWin.selected;
      win._closedTabs = [];
      return win;
    });
    let url = "about:welcomeback";
    let formdata = { id: { sessionData: state }, url };
    let entry = {
      url,
      triggeringPrincipal_base64: lazy.E10SUtils.SERIALIZED_SYSTEMPRINCIPAL,
    };
    return {
      windows: [{ tabs: [{ entries: [entry], formdata }] }],
      savedGroups,
    };
  },
  /**
   * Asynchronously read session restore state (JSON) from a path
   */
  readState(aPath) {
    return IOUtils.readJSON(aPath, { decompress: true });
  },
  /**
   * Asynchronously write session restore state as JSON to a path
   */
  writeState(aPath, aState) {
    return IOUtils.writeJSON(aPath, aState, {
      compress: true,
      tmpPath: `${aPath}.tmp`,
    });
  },
};

export var SessionMigration = {
  /**
   * Migrate a limited set of session data from one path to another.
   */
  migrate(aFromPath, aToPath) {
    return (async function () {
      let inState = await SessionMigrationInternal.readState(aFromPath);
      let outState = SessionMigrationInternal.convertState(inState);
      // Unfortunately, we can't use SessionStore's own SessionFile to
      // write out the data because it has a dependency on the profile dir
      // being known. When the migration runs, there is no guarantee that
      // that's true.
      await SessionMigrationInternal.writeState(aToPath, outState);
    })();
  },
};
PK