safe-ios/Multisig/UI/Transaction/ExecuteTransaction/OwnerKeySelectionPolicy.swift

//
//  OwnerKeySelectionPolicy.swift
//  Multisig
//
//  Created by Dmitry Bespalov on 13.01.22.
//  Copyright © 2022 Gnosis Ltd. All rights reserved.
//

import Foundation
import Solidity

class OwnerKeySelectionPolicy {

    struct KeyCandidate: Equatable {
        var key: KeyInfo
        var balance: Sol.UInt256 = 0
        var isOwner: Bool = false
    }

    /// Searches for the default key matching required amount on their balance.
    /// - Parameters:
    ///   - keys: list of keys with balances and owner status. If balance is unknown, it should be set to 0.
    ///   - requiredAmount: if the required balance is known, it should be passed. Default is 0.
    /// - Returns:
    ///     - Prefers owner to non-owners with enough balance
    ///     - Prefers higher-balance keys
    ///     - If none of the keys have enough balance or required amount is not specified, prefers owner key with the highest balance
    func defaultExecutionKey(in candidates: [KeyCandidate], requiredAmount: Sol.UInt256 = 0) -> KeyCandidate? {
        if candidates.isEmpty {
            return nil
        }

        if candidates.count == 1 {
            return candidates.first
        }

        let byBalanceDescending = { (lhs: KeyCandidate, rhs: KeyCandidate) -> Bool in
            lhs.balance > rhs.balance
        }
        let sortedOwners = candidates.filter { $0.isOwner }.sorted(by: byBalanceDescending)

        if let firstOwner = sortedOwners.first, firstOwner.balance >= requiredAmount {
            return firstOwner
        }

        // now we know that owners don't have enough balance.

        let sortedNonOwners = candidates.filter { !$0.isOwner }.sorted(by: byBalanceDescending)

        if let firstNonOwner = sortedNonOwners.first, firstNonOwner.balance >= requiredAmount {
            return firstNonOwner
        }

        // now we know that non-owners also don't have enough balance.
        // return any owner or non-owner with the highest balance.
        let result = sortedOwners.first ?? sortedNonOwners.first
        return result
    }
}