import BigNumber from "bignumber.js";

export interface SimpleInterestContractTerms {
    principalTokenIndex: number;
    principalAmount: number;
    interestRateFixedPoint: number;
    amortizationUnitType: number;
    termLengthUnits: number;
}

export interface CollateralizedContractTerms {
    collateralTokenIndex: number;
    collateralAmount: number;
    gracePeriodInDays: number;
}

class TermsContractParameters {
    public static bitShiftLeft(target: number, numPlaces: number): BigNumber {
        const binaryTargetString = new BigNumber(target).toString(2);
        const binaryTargetStringShifted = binaryTargetString + "0".repeat(numPlaces);

        return new BigNumber(binaryTargetStringShifted, 2);
    }
}

export class SimpleInterestParameters extends TermsContractParameters {
    public static pack(terms: SimpleInterestContractTerms): string {
        const principalTokenIndexShifted = TermsContractParameters.bitShiftLeft(terms.principalTokenIndex, 248);

        const principalAmountShifted = TermsContractParameters.bitShiftLeft(terms.principalAmount, 152);

        const interestRateShifted = TermsContractParameters.bitShiftLeft(terms.interestRateFixedPoint, 128);

        const amortizationUnitTypeShifted = TermsContractParameters.bitShiftLeft(terms.amortizationUnitType, 124);
        const termLengthShifted = TermsContractParameters.bitShiftLeft(terms.termLengthUnits, 108);

        const baseTenParameters = principalTokenIndexShifted
            .plus(principalAmountShifted)
            .plus(interestRateShifted)
            .plus(amortizationUnitTypeShifted)
            .plus(termLengthShifted);

        return `0x${baseTenParameters.toString(16).padStart(64, "0")}`;
    }
}

export class CollateralizedSimpleInterestTermsParameters extends TermsContractParameters {
    public static pack(
        collateralTerms: CollateralizedContractTerms,
        // Optionally, get the full contract terms parameters string by providing the contract terms.
        contractTerms?: SimpleInterestContractTerms
    ): string {
        const encodedCollateralToken = collateralTerms.collateralTokenIndex.toString(16).padStart(2, "0");
        const encodedCollateralAmount = collateralTerms.collateralAmount.toString(16).padStart(23, "0");
        const encodedGracePeriodInDays = collateralTerms.gracePeriodInDays.toString(16).padStart(2, "0");

        const packedCollateralParameters = encodedCollateralToken + encodedCollateralAmount + encodedGracePeriodInDays;

        if (contractTerms) {
            const packedTermsParameters = SimpleInterestParameters.pack(contractTerms);
            return `${packedTermsParameters.substr(0, 39)}${packedCollateralParameters.padStart(27, "0")}`;
        } else {
            return `0x${packedCollateralParameters.padStart(64, "0")}`;
        }
    }
}