Implement BFT fork choice rules

[2snEM6]

What was the problem?

New fork choice rules needed to be implemented to comply with the new BFT consensus protocol

How did I fix it?

Implementing Fork Choice Rules according to LIP-0014

How to test it?

Run unit tests for blocks/process.js

Review checklist

• The PR resolves Implement the fork choice rules described in "Introduce BFT consensus protocol" LIP #3559
• All new code is covered with unit tests
• All new code was formatted with Prettier
• Linting passes
• Tests pass
• Commit messages follow the commit guidelines
• Documentation has been added/updated

[nazarhussain]

@limiaspasdaniel A suggestion to make this logic look more readable.

// Case 2
const isValidBlock = (last, current) =>
	last.height + 1 === current.height && last.id === current.previousBlock;

// Case 1
const isIdenticalBlock = (last, current) => last.id === current.id;

const isDuplicateBlock = (last, current) =>
	last.height === current.height &&
	last.heightPrevoted === current.heightPrevoted &&
	last.previousBlock === current.previousBlock;

// Case 3
const isDoubleForging = (last, current) =>
	isDuplicateBlock(last, current) &&
	last.generatorPublicKey === current.generatorPublicKey;

// Case 4
const isTieBlocks = (last, current) =>
	isDuplicateBlock(last, current) &&
	slots.getSlotNumber(last.timestamp) <
		slots.getSlotNumber(current.timestamp) &&
	!this._receivedInSlot(last, modules.blocks.lastReceipt.get()) &&
	this._receivedInSlot(current, current.timestamp);

// Case 5
const isDifferentChain = (last, current) =>
	last.heightPrevoted < current.heightPrevoted ||
	(last.height < current.height &&
		last.heightPrevoted === current.heightPrevoted);

if(isIdenticalBlock(last, current)){
	return this._handleSameBlockReceived(current);
} else if(isValidBlock(last, current)) {
	return this._handleGoodBlock(current);
} else if(isDoubleForging(last, current)) {
	return this._handleDoubleForging(current);
} else if(isTieBlocks(last, current)) {
	return this._handleDoubleForgingTieBreak(current);
}else if(isDifferentChain(last, current)) {
	return this._handleMovingToDifferentChain(current);
} else {
	return this._handleDiscardedBlock(current);
}

[2snEM6]

@nazarhussain, regarding your suggestion to make the logic more readable:

I like the format and it definitely reads better and clearer, however, I wouldn't nest functions inside functions, this complicates testing. What I can do instead is move those functions as private functions with the following format this._functionName as we are not using _private anymore. This way we can still apply your

[shuse2]

Also. logs take first argument as metadata object and second parameter is the string

[michielmulders]

Some small feedback. Looks good overall.

[shuse2]

Overall LGTM

[michielmulders]

Thanks for making the changes!