Start on interest rate implementation

[Kay-Zee]

Description

Implementation of insurance fund

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the standards mentioned here.
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[turbolent]

No need to static cast, the type is already inferred

Suggested change

	if self.totalCreditBalance == 0.0 as UFix128 {
	if self.totalCreditBalance == 0.0 {

[turbolent]

Type annotations are not needed, types can get inferred.
Also, FlowCreditMarketMath.toUFix128 is not needed, just call the UFix128 conversion function directly

Suggested change

	let secondsPerYear: UFix64 = 365.25 * 24.0 * 60.0 * 60.0
	let yearsElapsed = timeElapsed / secondsPerYear
	let insuranceRate: UFix128 = FlowCreditMarketMath.toUFix128(self.insuranceRate)
	// Insurance amount is a percentage of total credit balance per year
	let insuranceAmount: UFix128 = self.totalCreditBalance * insuranceRate * FlowCreditMarketMath.toUFix128(yearsElapsed)
	let insuranceAmountUFix64 = FlowCreditMarketMath.toUFix64RoundDown(insuranceAmount)
	let secondsPerYear = 365.25 * 24.0 * 60.0 * 60.0
	let yearsElapsed = timeElapsed / secondsPerYear
	let insuranceRate = UFix128(self.insuranceRate)
	// Insurance amount is a percentage of total credit balance per year
	let insuranceAmount = self.totalCreditBalance * insuranceRate * FlowCreditMarketMath.toUFix128(yearsElapsed)
	let insuranceAmountUFix64 = FlowCreditMarketMath.toUFix64RoundDown(insuranceAmount)

[turbolent]

Avoid force unwrapping, repeatedly:

Suggested change

	// Validate swapper output type (input type is already validated when swapper is set)
	assert(self.insuranceSwapper!.outType() == Type<@MOET.Vault>(), message: "Insurance swapper must output MOET")
	// Get quote and perform swap
	let quote = self.insuranceSwapper!.quoteOut(forProvided: amountToCollect, reverse: false)
	var moetVault <- self.insuranceSwapper!.swap(quote: quote, inVault: <-insuranceVault)
	let insuranceSwapper = self.insuranceSwapper ?? panic("missing insurance swapper")
	// Validate swapper output type (input type is already validated when swapper is set)
	assert(insuranceSwapper.outType() == Type<@MOET.Vault>(), message: "Insurance swapper must output MOET")
	// Get quote and perform swap
	let quote = insuranceSwapper.quoteOut(forProvided: amountToCollect, reverse: false)
	var moetVault <- insuranceSwapper.swap(quote: quote, inVault: <-insuranceVault)

[turbolent]

Here and below: Remove unnecessary parentheses

Suggested change

	let fundRef = (&self.insuranceFund as &MOET.Vault)
	let fundRef = &self.insuranceFund as &MOET.Vault

[turbolent]

Avoid force unwrapping, use if-let instead:

Suggested change

	if swapper != nil {
	// Validate swapper types match
	assert(swapper!.inType() == tokenType, message: "Swapper input type must match token type")
	assert(swapper!.outType() == Type<@MOET.Vault>(), message: "Swapper output type must be MOET")
	}
	if let swapper = swapper {
	// Validate swapper types match
	assert(swapper.inType() == tokenType, message: "Swapper input type must match token type")
	assert(swapper.outType() == Type<@MOET.Vault>(), message: "Swapper output type must be MOET")
	}