/*
 * QUANTCONNECT.COM - Democratizing Finance, Empowering Individuals.
 * Lean Algorithmic Trading Engine v2.0. Copyright 2014 QuantConnect Corporation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
*/

using QuantConnect.Orders;
using QuantConnect.Orders.Fees;
using QuantConnect.Util;
using System;
using System.Collections.Generic;
using System.Linq;
using static QuantConnect.StringExtensions;

namespace QuantConnect.Securities.Positions
{
    /// <summary>
    /// Provides a base class for implementations of <see cref="IPositionGroupBuyingPowerModel"/>
    /// </summary>
    public abstract class PositionGroupBuyingPowerModel : IPositionGroupBuyingPowerModel
    {
        /// <summary>
        /// Gets the percentage of portfolio buying power to leave as a buffer
        /// </summary>
        protected decimal RequiredFreeBuyingPowerPercent { get; }

        /// <summary>
        /// Initializes a new instance of the <see cref="PositionGroupBuyingPowerModel"/> class
        /// </summary>
        /// <param name="requiredFreeBuyingPowerPercent">The percentage of portfolio buying power to leave as a buffer</param>
        protected PositionGroupBuyingPowerModel(decimal requiredFreeBuyingPowerPercent = 0m)
        {
            RequiredFreeBuyingPowerPercent = requiredFreeBuyingPowerPercent;
        }

        /// <summary>
        /// Gets the margin currently allocated to the specified holding
        /// </summary>
        /// <param name="parameters">An object containing the security</param>
        /// <returns>The maintenance margin required for the </returns>
        public abstract MaintenanceMargin GetMaintenanceMargin(PositionGroupMaintenanceMarginParameters parameters);

        /// <summary>
        /// The margin that must be held in order to increase the position by the provided quantity
        /// </summary>
        /// <param name="parameters">An object containing the security and quantity</param>
        public abstract InitialMargin GetInitialMarginRequirement(PositionGroupInitialMarginParameters parameters);

        /// <summary>
        /// Gets the total margin required to execute the specified order in units of the account currency including fees
        /// </summary>
        /// <param name="parameters">An object containing the portfolio, the security and the order</param>
        /// <returns>The total margin in terms of the currency quoted in the order</returns>
        public abstract InitialMargin GetInitialMarginRequiredForOrder(PositionGroupInitialMarginForOrderParameters parameters);

        /// <summary>
        /// Computes the impact on the portfolio's buying power from adding the position group to the portfolio. This is
        /// a 'what if' analysis to determine what the state of the portfolio would be if these changes were applied. The
        /// delta (before - after) is the margin requirement for adding the positions and if the margin used after the changes
        /// are applied is less than the total portfolio value, this indicates sufficient capital.
        /// </summary>
        /// <param name="parameters">An object containing the portfolio and a position group containing the contemplated
        /// changes to the portfolio</param>
        /// <returns>Returns the portfolio's total portfolio value and margin used before and after the position changes are applied</returns>
        public virtual ReservedBuyingPowerImpact GetReservedBuyingPowerImpact(ReservedBuyingPowerImpactParameters parameters)
        {
            // This process aims to avoid having to compute buying power on the entire portfolio and instead determines
            // the set of groups that can be impacted by the changes being contemplated. The only real way to determine
            // the change in maintenance margin is to determine what groups we'll have after the changes and compute the
            // margin based on that.
            //   1. Determine impacted groups (depends on IPositionGroupResolver.GetImpactedGroups)
            //   2. Compute the currently reserved buying power of impacted groups
            //   3. Create position collection using impacted groups and apply contemplated changes
            //   4. Resolve new position groups using position collection with applied contemplated changes
            //   5. Compute the contemplated reserved buying power on these newly resolved groups

            // 1. Determine impacted groups
            var positionManager = parameters.Portfolio.Positions;

            // 2. Compute current reserved buying power
            var current = 0m;
            var impactedGroups = new List<IPositionGroup>();

            // 3. Determine set of impacted positions to be grouped
            var positions = parameters.Orders.Select(o => o.CreatePositions(parameters.Portfolio.Securities)).SelectMany(p => p).ToList();

            var impactedPositions = positions.ToDictionary(p => p.Symbol);

            foreach (var impactedGroup in positionManager.GetImpactedGroups(positions))
            {
                impactedGroups.Add(impactedGroup);
                current += impactedGroup.BuyingPowerModel.GetReservedBuyingPowerForPositionGroup(
                    parameters.Portfolio, impactedGroup
                );

                foreach (var position in impactedGroup)
                {
                    IPosition existing;
                    if (impactedPositions.TryGetValue(position.Symbol, out existing))
                    {
                        // if it already exists then combine it with the existing
                        impactedPositions[position.Symbol] = existing.Combine(position);
                    }
                    else
                    {
                        impactedPositions[position.Symbol] = position;
                    }
                }
            }

            // 4. Resolve new position groups
            var contemplatedGroups = positionManager.ResolvePositionGroups(new PositionCollection(impactedPositions.Values));

            // 5. Compute contemplated margin
            var contemplated = GetContemplatedGroupsInitialMargin(parameters.Portfolio, contemplatedGroups, positions);

            return new ReservedBuyingPowerImpact(current, contemplated, impactedGroups, parameters.ContemplatedChanges, contemplatedGroups);
        }

        /// <summary>
        /// Gets the initial margin required for the specified contemplated position group.
        /// Used by <see cref="GetReservedBuyingPowerImpact"/> to get the contemplated groups margin.
        /// </summary>
        protected virtual decimal GetContemplatedGroupsInitialMargin(SecurityPortfolioManager portfolio, PositionGroupCollection contemplatedGroups,
            List<IPosition> ordersPositions)
        {
            var contemplatedMargin = 0m;
            foreach (var contemplatedGroup in contemplatedGroups)
            {
                // We use the initial margin requirement as the contemplated groups margin in order to ensure
                // the available buying power is enough to execute the order.
                contemplatedMargin += contemplatedGroup.BuyingPowerModel.GetInitialMarginRequirement(portfolio, contemplatedGroup);
            }

            return contemplatedMargin;
        }

        /// <summary>
        /// Check if there is sufficient buying power for the position group to execute this order.
        /// </summary>
        /// <param name="parameters">An object containing the portfolio, the position group and the order</param>
        /// <returns>Returns buying power information for an order against a position group</returns>
        public virtual HasSufficientBuyingPowerForOrderResult HasSufficientBuyingPowerForOrder(
            HasSufficientPositionGroupBuyingPowerForOrderParameters parameters
            )
        {
            // The addition of position groups requires that we not only check initial margin requirements, but also
            // that we confirm that after the changes have been applied and the new groups resolved our maintenance
            // margin is still in a valid range (less than TPV). For this model, we use the security's sufficient buying
            // power impl to confirm initial margin requirements and lean heavily on GetReservedBuyingPowerImpact for
            // help with confirming that our expected maintenance margin is still less than TPV.
            //   1. Confirm we have sufficient buying power to execute the trade using security's BP model
            //   2. Confirm we pass position group specific checks
            //   3. Confirm we haven't exceeded maintenance margin limits via GetReservedBuyingPowerImpact's delta

            // 1. Confirm we meet initial margin requirements, accounting for buffer
            var deltaBuyingPowerArgs = new ReservedBuyingPowerImpactParameters(parameters.Portfolio, parameters.PositionGroup, parameters.Orders);
            var deltaBuyingPower = GetReservedBuyingPowerImpact(deltaBuyingPowerArgs).Delta;

            // When order only reduces or closes a security position, capital is always sufficient
            if (deltaBuyingPower < 0)
            {
                return parameters.Sufficient();
            }

            var availableBuyingPower = parameters.Portfolio.MarginRemaining;

            // 2. Confirm we pass position group specific checks
            var result = PassesPositionGroupSpecificBuyingPowerForOrderChecks(parameters, availableBuyingPower);
            if (result?.IsSufficient == false)
            {
                return result;
            }

            // 3. Confirm that the new groupings arising from the change doesn't make maintenance margin exceed TPV
            // We can just compare the delta to the available buying power because the delta how much the maintenance margin will increase by
            // if the order is executed, so it needs to stay below the available buying power
            if (deltaBuyingPower <= availableBuyingPower)
            {
                return parameters.Sufficient();
            }

            return parameters.Insufficient(Invariant($@"Id: {string.Join(",", parameters.Orders.Select(o => o.Id))}, Maintenance Margin Delta: {
                deltaBuyingPower.Normalize()}, Free Margin: {availableBuyingPower.Normalize()}"
            ));
        }

        /// <summary>
        /// Provides a mechanism for derived types to add their own buying power for order checks without needing to
        /// recompute the available buying power. Implementations should return null if all checks pass and should
        /// return an instance of <see cref="HasSufficientBuyingPowerForOrderResult"/> with IsSufficient=false if it
        /// fails.
        /// </summary>
        protected virtual HasSufficientBuyingPowerForOrderResult PassesPositionGroupSpecificBuyingPowerForOrderChecks(
            HasSufficientPositionGroupBuyingPowerForOrderParameters parameters,
            decimal availableBuyingPower
            )
        {
            return null;
        }

        /// <summary>
        /// Computes the amount of buying power reserved by the provided position group
        /// </summary>
        public virtual ReservedBuyingPowerForPositionGroup GetReservedBuyingPowerForPositionGroup(
            ReservedBuyingPowerForPositionGroupParameters parameters
            )
        {
            return this.GetMaintenanceMargin(parameters.Portfolio, parameters.PositionGroup);
        }

        /// <summary>
        /// Get the maximum position group order quantity to obtain a position with a given buying power
        /// percentage. Will not take into account free buying power.
        /// </summary>
        /// <param name="parameters">An object containing the portfolio, the position group and the target
        ///     signed buying power percentage</param>
        /// <returns>
        /// Returns the maximum allowed market order quantity and if zero, also the reason.
        ///
        /// Since there is no sense of "short" or "long" on position groups with multiple positions,
        /// the sign of the returned quantity will indicate the direction of the order regarding the
        /// reference position group passed in the parameters:
        ///     - quantity &gt; 0: the order should be placed in the same direction as the reference position group to increase it,
        ///                        without changing the positions' signs.
        ///     - quantity &lt; 0: the order should be placed in the opposite direction as the reference position group to reduce it,
        ///                        using each position's opposite sign.
        /// </returns>
        public virtual GetMaximumLotsResult GetMaximumLotsForTargetBuyingPower(
            GetMaximumLotsForTargetBuyingPowerParameters parameters
            )
        {
            // In order to determine maximum order quantity for a particular amount of buying power, we must resolve
            // the group's 'unit' as this will be the quantity step size. If we don't step according to these units
            // then we could be left with a different type of group with vastly different margin requirements, so we
            // must keep the ratios between all of the position quantities the same. First we'll determine the target
            // buying power, taking into account RequiredFreeBuyingPowerPercent to ensure a buffer. Then we'll evaluate
            // the initial margin requirement using the provided position group position quantities. From this value,
            // we can determine if we need to add more quantity or remove quantity by looking at the delta from the target
            // to the computed initial margin requirement. We can also compute, assuming linearity, the change in initial
            // margin requirements for each 'unit' of the position group added. The final value we need before starting to
            // iterate to solve for quantity is the minimum quantities. This is the 'unit' of the position group, and any
            // quantities less than the unit's quantity would yield an entirely different group w/ different margin calcs.
            // Now that we've resolved our target, our group unit and the unit's initial margin requirement, we can iterate
            // increasing/decreasing quantities in multiples of the unit's quantities until we're within a unit's amount of
            // initial margin to the target buying power.
            // NOTE: The first estimate MUST be greater than the target and iteration will successively decrease quantity estimates.
            //   1. Determine current holdings of position group
            //   2. Determine target buying power, taking into account RequiredFreeBuyingPowerPercent
            //  2a. If targeting zero, simply return the negative of the quantity
            //   3. Determine current used margin [we're using initial here to match BuyingPowerModel]
            //   4. Check that the change of margin is above our models minimum percentage change
            //   5. Resolve the group's 'unit' quantities, this is our step size
            //  5a. Compute the initial margin requirement for a single unit
            //   6. Begin iterating until the allocated holdings margin (after order fees are applied) less or equal to the expected target margin
            //  6a. Calculate the amount to order to get the target margin
            //  6b. Apply order fees to the allocated holdings margin and compare to the target margin to end loop.

            var portfolio = parameters.Portfolio;

            // 1. Determine current holdings of position group
            var currentPositionGroup = portfolio.Positions[parameters.PositionGroup.Key];

            var inverted = false;
            var targetBuyingPower = parameters.TargetBuyingPower;
            // The reference position group is not necessarily in the same side as the position group in the portfolio, it could be the inverted.
            // So the consumer needs the result relative to that position group instead of the one being held.
            if (parameters.PositionGroup.IsInvertedOf(currentPositionGroup))
            {
                inverted = true;
                targetBuyingPower = -targetBuyingPower;
            }

            // 2. Determine target buying power, taking into account RequiredFreeBuyingPowerPercent
            var bufferFactor = 1 - RequiredFreeBuyingPowerPercent;
            var targetBufferFactor = bufferFactor * targetBuyingPower;
            var totalPortfolioValue = portfolio.TotalPortfolioValue;
            var targetFinalMargin = targetBufferFactor * totalPortfolioValue;

            // 2a. If targeting zero, simply return the negative of the quantity
            if (targetFinalMargin == 0)
            {
                var quantity = -Math.Abs(currentPositionGroup.Quantity);
                return parameters.Result(inverted ? -quantity : quantity);
            }

            // 3. Determine initial margin requirement for current holdings
            var currentUsedMargin = 0m;
            if (currentPositionGroup.Quantity != 0)
            {
                currentUsedMargin = Math.Abs(currentPositionGroup.BuyingPowerModel.GetInitialMarginRequirement(portfolio, currentPositionGroup));
            }

            // 4. Check that the change of margin is above our models minimum percentage change
            var absDifferenceOfMargin = Math.Abs(targetFinalMargin - currentUsedMargin);
            if (!BuyingPowerModelExtensions.AboveMinimumOrderMarginPortfolioPercentage(parameters.Portfolio,
                parameters.MinimumOrderMarginPortfolioPercentage, absDifferenceOfMargin))
            {
                string reason = null;
                if (!parameters.SilenceNonErrorReasons)
                {
                    var minimumValue = totalPortfolioValue * parameters.MinimumOrderMarginPortfolioPercentage;
                    reason = Messages.BuyingPowerModel.TargetOrderMarginNotAboveMinimum(absDifferenceOfMargin, minimumValue);
                }
                return new GetMaximumLotsResult(0, reason, false);
            }

            // 5. Resolve 'unit' group -- this is our step size
            var groupUnit = currentPositionGroup.CreateUnitGroup(parameters.Portfolio.Positions);

            // 5a. Compute initial margin requirement for a single unit
            var unitMargin = Math.Abs(groupUnit.BuyingPowerModel.GetInitialMarginRequirement(portfolio, groupUnit));
            if (unitMargin == 0m)
            {
                // likely due to missing price data
                var zeroPricedPosition = parameters.PositionGroup.FirstOrDefault(
                    p => portfolio.Securities.GetValueOrDefault(p.Symbol)?.Price == 0m
                );
                return parameters.Error(zeroPricedPosition?.Symbol.GetZeroPriceMessage()
                    ?? Messages.PositionGroupBuyingPowerModel.ComputedZeroInitialMargin(parameters.PositionGroup));
            }

            // 6. Begin iterating
            var lastPositionGroupOrderQuantity = 0m;    // For safety check
            decimal orderFees;
            decimal targetHoldingsMargin;
            decimal positionGroupQuantity;
            do
            {
                // 6a.Calculate the amount to order to get the target margin
                positionGroupQuantity = GetPositionGroupOrderQuantity(portfolio, currentPositionGroup, currentUsedMargin, targetFinalMargin,
                    groupUnit, unitMargin, out targetHoldingsMargin);
                if (positionGroupQuantity == 0)
                {
                    string reason = null;
                    if (!parameters.SilenceNonErrorReasons)
                    {
                        reason = Messages.PositionGroupBuyingPowerModel.PositionGroupQuantityRoundedToZero(targetFinalMargin - currentUsedMargin);
                    }

                    return new GetMaximumLotsResult(0, reason, false);
                }

                // 6b.Apply order fees to the allocated holdings margin
                orderFees = GetOrderFeeInAccountCurrency(portfolio, currentPositionGroup.WithQuantity(positionGroupQuantity, portfolio.Positions));

                // Update our target portfolio margin allocated when considering fees, then calculate the new FinalOrderMargin
                targetFinalMargin = (totalPortfolioValue - orderFees) * targetBufferFactor;

                // Start safe check after first loop, stops endless recursion
                if (lastPositionGroupOrderQuantity == positionGroupQuantity)
                {
                    throw new ArgumentException(Messages.PositionGroupBuyingPowerModel.FailedToConvergeOnTargetMargin(targetFinalMargin,
                        positionGroupQuantity, orderFees, parameters));
                }

                lastPositionGroupOrderQuantity = positionGroupQuantity;

            }
            // Ensure that our target holdings margin will be less than or equal to our target allocated margin
            while (Math.Abs(targetHoldingsMargin) > Math.Abs(targetFinalMargin));

            return parameters.Result(inverted ? -positionGroupQuantity : positionGroupQuantity);
        }

        /// <summary>
        /// Get the maximum market position group order quantity to obtain a delta in the buying power used by a position group.
        /// The deltas sign defines the position side to apply it to, positive long, negative short.
        /// </summary>
        /// <param name="parameters">An object containing the portfolio, the position group and the delta buying power</param>
        /// <returns>Returns the maximum allowed market order quantity and if zero, also the reason</returns>
        /// <remarks>Used by the margin call model to reduce the position by a delta percent.</remarks>
        public virtual GetMaximumLotsResult GetMaximumLotsForDeltaBuyingPower(
            GetMaximumLotsForDeltaBuyingPowerParameters parameters
            )
        {
            // we convert this delta request into a target buying power request through projection
            // by determining the currently used (reserved) buying power and adding the delta to
            // arrive at a target buying power percentage

            var currentPositionGroup = parameters.Portfolio.Positions[parameters.PositionGroup.Key];
            var usedBuyingPower = parameters.PositionGroup.BuyingPowerModel.GetReservedBuyingPowerForPositionGroup(
                parameters.Portfolio, currentPositionGroup
            );

            var targetBuyingPower = usedBuyingPower + parameters.DeltaBuyingPower;
            // The reference position group is not necessarily in the same side as the position group in the portfolio, it could be the inverted.
            // So the consumer needs the result relative to that position group instead of the one being held.
            if (parameters.PositionGroup.IsInvertedOf(currentPositionGroup))
            {
                targetBuyingPower = parameters.DeltaBuyingPower - usedBuyingPower;
            }

            var targetBuyingPowerPercent = parameters.Portfolio.TotalPortfolioValue != 0
                ? targetBuyingPower / parameters.Portfolio.TotalPortfolioValue
                : 0;

            return GetMaximumLotsForTargetBuyingPower(new GetMaximumLotsForTargetBuyingPowerParameters(
                parameters.Portfolio, parameters.PositionGroup, targetBuyingPowerPercent, parameters.MinimumOrderMarginPortfolioPercentage
            ));
        }

        /// <summary>
        /// Gets the buying power available for a position group trade
        /// </summary>
        /// <param name="parameters">A parameters object containing the algorithm's portfolio, security, and order direction</param>
        /// <returns>The buying power available for the trade</returns>
        public PositionGroupBuyingPower GetPositionGroupBuyingPower(PositionGroupBuyingPowerParameters parameters)
        {
            // SecurityPositionGroupBuyingPowerModel models buying power the same as non-grouped, so we can simply delegate
            // to the security's model. For posterity, however, I'll lay out the process for computing the available buying
            // power for a position group trade. There's two separate cases, one where we're increasing the position and one
            // where we're decreasing the position and potentially crossing over zero. When decreasing the position we have
            // to account for the reserved buying power that the position currently holds and add that to any free buying power
            // in the portfolio.
            //   1. Get portfolio's MarginRemaining (free buying power)
            //   2. Determine if closing position
            //   2a. Add reserved buying power freed up by closing the position
            //   2b. Rebate initial buying power required for current position [to match current behavior, might not be possible]

            // 1. Get MarginRemaining
            var buyingPower = parameters.Portfolio.MarginRemaining;

            // 2. Determine if closing position
            IPositionGroup existing;
            if (parameters.Portfolio.Positions.Groups.TryGetGroup(parameters.PositionGroup.Key, out existing))
            {
                var isInverted = parameters.PositionGroup.IsInvertedOf(existing);
                if (isInverted && parameters.Direction == OrderDirection.Buy || !isInverted && parameters.Direction == OrderDirection.Sell)
                {
                    // 2a. Add reserved buying power of current position
                    // Using the existing position group's buying power model to compute its reserved buying power and initial margin requirement.
                    // This is necessary because the margin calculations depend on the option strategy underneath the position group's BPM.
                    buyingPower += existing.Key.BuyingPowerModel.GetReservedBuyingPowerForPositionGroup(parameters.Portfolio, existing);

                    // 2b. Rebate the initial margin equivalent of current position
                    // this interface doesn't have a concept of initial margin as it's an impl detail of the BuyingPowerModel base class
                    buyingPower += Math.Abs(existing.Key.BuyingPowerModel.GetInitialMarginRequirement(parameters.Portfolio, existing));
                }
            }

            return buyingPower;
        }

        /// <summary>
        /// Helper function to convert a <see cref="CashAmount"/> to the account currency
        /// </summary>
        protected virtual decimal ToAccountCurrency(SecurityPortfolioManager portfolio, CashAmount cash)
        {
            return portfolio.CashBook.ConvertToAccountCurrency(cash).Amount;
        }

        /// <summary>
        /// Helper function to compute the order fees associated with executing market orders for the specified <paramref name="positionGroup"/>
        /// </summary>
        protected virtual decimal GetOrderFeeInAccountCurrency(SecurityPortfolioManager portfolio, IPositionGroup positionGroup)
        {
            // TODO : Add Order parameter to support Combo order type, pulling the orders per position

            var orderFee = 0m;
            var utcTime = portfolio.Securities.UtcTime;

            foreach (var position in positionGroup)
            {
                var security = portfolio.Securities[position.Symbol];
                var order = new MarketOrder(position.Symbol, position.Quantity, utcTime);
                var positionOrderFee = security.FeeModel.GetOrderFee(new OrderFeeParameters(security, order)).Value;
                orderFee += ToAccountCurrency(portfolio, positionOrderFee);
            }

            return orderFee;
        }

        /// <summary>
        /// Checks if the margin difference is not growing in final margin calculation, just making sure we don't end up in an infinite loop.
        /// This function was split out to support derived types using the same error message as well as removing the added noise of the check
        /// and message creation.
        /// </summary>
        protected static bool UnableToConverge(decimal currentMarginDifference, decimal lastMarginDifference, IPositionGroup groupUnit,
            SecurityPortfolioManager portfolio, decimal positionGroupQuantity, decimal targetMargin, decimal currentMargin,
            decimal absUnitMargin, out ArgumentException error)
        {
            // determine if we're unable to converge by seeing if quantity estimate hasn't changed
            if (Math.Abs(currentMarginDifference) > Math.Abs(lastMarginDifference) &&
                Math.Sign(currentMarginDifference) == Math.Sign(lastMarginDifference)
                || currentMarginDifference == lastMarginDifference)
            {
                string message;
                if (groupUnit.Count == 1)
                {
                    // single security group
                    var security = portfolio.Securities[groupUnit.Single().Symbol];
                    message = "GetMaximumPositionGroupOrderQuantityForTargetBuyingPower failed to converge to target margin " +
                        Invariant($"{targetMargin}. Current margin is {currentMargin}. Position group quantity {positionGroupQuantity}. ") +
                        Invariant($"Lot size is {security.SymbolProperties.LotSize}.Security symbol ") +
                        Invariant($"{security.Symbol}. Margin unit {absUnitMargin}.");
                }
                else
                {
                    message = "GetMaximumPositionGroupOrderQuantityForTargetBuyingPower failed to converge to target margin " +
                        Invariant($"{targetMargin}. Current margin is {currentMargin}. Position group quantity {positionGroupQuantity}. ") +
                        Invariant($"Position Group Unit is {groupUnit.Key}. Position Group Name ") +
                        Invariant($"{groupUnit.GetUserFriendlyName()}. Margin unit {absUnitMargin}.");
                }

                error = new ArgumentException(message);
                return true;
            }

            error = null;
            return false;
        }

        /// <summary>Indicates whether the current object is equal to another object of the same type.</summary>
        /// <param name="other">An object to compare with this object.</param>
        /// <returns>true if the current object is equal to the <paramref name="other" /> parameter; otherwise, false.</returns>
        public virtual bool Equals(IPositionGroupBuyingPowerModel other)
        {
            if (ReferenceEquals(null, other))
            {
                return false;
            }

            if (ReferenceEquals(this, other))
            {
                return true;
            }

            return GetType() == other.GetType();
        }

        /// <summary>Determines whether the specified object is equal to the current object.</summary>
        /// <param name="obj">The object to compare with the current object. </param>
        /// <returns>true if the specified object  is equal to the current object; otherwise, false.</returns>
        public override bool Equals(object obj)
        {
            if (ReferenceEquals(null, obj))
            {
                return false;
            }

            if (ReferenceEquals(this, obj))
            {
                return true;
            }

            if (obj.GetType() != GetType())
            {
                return false;
            }

            return Equals((IPositionGroupBuyingPowerModel) obj);
        }

        /// <summary>Serves as the default hash function. </summary>
        /// <returns>A hash code for the current object.</returns>
        public override int GetHashCode()
        {
            return GetType().GetHashCode();
        }

        /// <summary>
        /// Helper method that determines the amount to order to get to a given target safely.
        /// Meaning it will either be at or just below target always.
        /// </summary>
        /// <param name="portfolio">Current portfolio</param>
        /// <param name="currentPositionGroup">Current position group</param>
        /// <param name="currentUsedMargin">Current margin reserved for the position</param>
        /// <param name="targetFinalMargin">The target margin</param>
        /// <param name="groupUnit">Unit position group corresponding to the <paramref name="currentPositionGroup"/></param>
        /// <param name="unitMargin">Margin required for the <paramref name="groupUnit"/></param>
        /// <param name="finalMargin">Output the final margin allocated for the position group</param>
        /// <returns>The size of the order to get safely to our target</returns>
        public decimal GetPositionGroupOrderQuantity(SecurityPortfolioManager portfolio, IPositionGroup currentPositionGroup,
            decimal currentUsedMargin, decimal targetFinalMargin, IPositionGroup groupUnit, decimal unitMargin,
            out decimal finalMargin)
        {
            // Determine the direction to go towards when updating the estimate: +1 to increase, -1 to decrease.
            var quantityStep = targetFinalMargin > currentUsedMargin ? +1 : -1;

            // Compute initial position group quantity estimate -- group quantities are whole numbers [number of lots/unit quantities].
            //   - If going to the opposite side (target margin < 0), move towards said side from 0 since we need to completely close the position.
            //   - Else, just start with a unit step towards the determined direction.
            var currentGroupAbsQuantity = Math.Abs(currentPositionGroup.Quantity);
            var positionGroupQuantity = targetFinalMargin < 0 ? -currentGroupAbsQuantity + quantityStep : quantityStep;

            // Calculate the initial value for the wanted final margin after the delta is applied.
            var finalPositionGroup = currentPositionGroup.WithQuantity(currentGroupAbsQuantity + positionGroupQuantity, portfolio.Positions);
            finalMargin = Math.Abs(finalPositionGroup.BuyingPowerModel.GetInitialMarginRequirement(portfolio, finalPositionGroup));

            // Keep the previous calculated final margin we would get after the delta is applied.
            // This is useful for the cases were the final group gets us with final margin greater than the target.
            var prevFinalMargin = finalMargin;

            // Begin iterating until the final margin is equal or greater than the target margin.
            var absTargetFinalMargin = Math.Abs(targetFinalMargin);
            var getMarginDifference = (decimal currentFinalMargin) =>
                targetFinalMargin < 0 ? absTargetFinalMargin - currentFinalMargin : currentFinalMargin - absTargetFinalMargin;

            var marginDifference = getMarginDifference(finalMargin);
            while ((quantityStep < 0 && marginDifference > 0) || (quantityStep > 0 && marginDifference < 0))
            {
                positionGroupQuantity += quantityStep;
                finalPositionGroup = currentPositionGroup.WithQuantity(currentGroupAbsQuantity + positionGroupQuantity, portfolio.Positions);
                finalMargin = Math.Abs(finalPositionGroup.BuyingPowerModel.GetInitialMarginRequirement(portfolio, finalPositionGroup));

                var newMarginDifference = getMarginDifference(finalMargin);
                if (UnableToConverge(newMarginDifference, marginDifference, groupUnit, portfolio, positionGroupQuantity,
                    targetFinalMargin, currentUsedMargin, unitMargin, out var error))
                {
                    throw error;
                }

                marginDifference = newMarginDifference;
            }

            // If the final margin is greater than the target, the result is the previous quantity,
            // which is the maximum allowed to be within the target margin.
            if (finalMargin > absTargetFinalMargin)
            {
                finalMargin = prevFinalMargin;
                return positionGroupQuantity - quantityStep;
            }

            return positionGroupQuantity;
        }
    }
}