Completes removal of callbacks from the setState calls in App.js - replaces PR 206

[evgenyfadeev]

Replaces PR #206

• adds App.shouldUpdateLessonsProgress(state)

• moves update of lessonsProgress from applyStopLessonSideEffects to getFutureStateToStopLesson

• stopLesson():

  • factored out applyStopLessonSideEffects()
  • factored out getFutureStateToStopLesson()

• isFinished takes state as an argument, instead of using this.state

• processBuffer():

  • consists of getNewStateAndSideEffectsForBuffer(), application of side-effects and a single setState() call

• getNewStateAndSideEffectsForBuffer():

  • contains the logic of the past processBuffer function, but does not use the global this.state, instead takes the previous value as an argument and returns the updated value, which is then applied in the setState() call
  • if the lesson is finished, applies the stop lesson side effects and returns the state for the stopped lesson
  • getNewStateAndSideEffectsForBuffer is intended to be a pure function
  • returns a tuple of [newState, sideEffects]

[evgenyfadeev]

@didoesdigital I've created this new PR by applying a diff of #206 (excluding the submodule) as a single commit on top of the master. If it's easier to view what was done previously commit-by commit, you might have a look at the commits in #206.

Otherwise (excluding that this is a single commit and no submodule merge conflict), this PR is identical to 206.

I've closed the #206 for clarity.

[didoesdigital]

@evgenyfadeev Great work on this. Thanks for fixing up the submodule by opening a new PR.

There's a bug in this PR that I can't quite track down. When visiting progress revision lessons such as Your words, Your memorised words, or Your revision words via the links at the top of the Progress page, it doesn't correctly update the lesson. To reproduce an example of the issue:

• Start on the Progress page
• Visit a regular lesson like Introduction
• Visit the Progress page via primary nav
• Visit the memorised words progress revision lesson:
  • Expected: Shows "Your memorised words" as the lesson title
  • Actual: Continues to show "Introduction" as the lesson title
• If that doesn't consistently reproduce it, then continue: Visit Progress page again
• Visit the seen words progress revision lesson:
  • Expected: Shows the lesson title that matches the URL
  • Actual: Continues to show the previous lesson's title

I haven't been able to pin down the exact cause. It might be related to changing user settings triggering a late setupLesson() call with no arguments, or maybe a race condition from setupLesson being called with the old state from handle lesson after setUpProgressRevisionLesson calls it with the correct state, or something else. Would you please investigate this further?

[didoesdigital]

Probably no need to check for /setup here because there's no stop button on the lessons/custom/setup page to trigger the stop lesson code that usually updates lesson progress info.

[didoesdigital]

We should pass in a copy of the state instead of the current state so that we don't mutate state directly with assignments like state.timer = 0; instead of using setState to make changes.

[didoesdigital]

We could add const state = Object.assign({}, this.state); here and pass in state instead of this.state below (see next comment for details)

[evgenyfadeev]

@didoesdigital I'll investigate, thanks for the details.