vapore 0.5.0

Vangaurd portfolio rebalancing algorithm
Documentation 
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use anyhow::{ensure, Result};

use crate::{
    arguments::Args,
    asset::{Allocations, SubAllocations},
    holdings::{
        AccountHoldings, HoldingType, ShareValues, StockSymbol, VanguardHoldings, VanguardRebalance,
    },
};

const HIGH_TO_LOW_RISK: [StockSymbol; 8] = [
    StockSymbol::VWO,
    StockSymbol::VXUS,
    StockSymbol::VB,
    StockSymbol::VO,
    StockSymbol::VV,
    StockSymbol::BNDX,
    StockSymbol::VTC,
    StockSymbol::VTIP,
];

/// to_buy calculates how much of each stock and bond should be bought and sold to rebalance the
/// portfolio.
pub fn to_buy(vanguard_holdings: VanguardHoldings, args: Args) -> Result<VanguardRebalance> {
    let mut rebalance = VanguardRebalance::new();
    let (traditional_ira_account_option, roth_ira_account_option, target_overall_retirement_option) =
        retirement_calc(&vanguard_holdings, args.clone())?;
    if let Some(traditional_account) = traditional_ira_account_option {
        rebalance.add_account_holdings(traditional_account, HoldingType::TraditionalIra)
    }
    if let Some(roth_account) = roth_ira_account_option {
        rebalance.add_account_holdings(roth_account, HoldingType::RothIra)
    }
    if let Some(brokerage_holdings) = vanguard_holdings.brokerage_holdings() {
        rebalance.add_account_holdings(
            brokerage_calc(vanguard_holdings.stock_quotes(), brokerage_holdings, args)?,
            HoldingType::Brokerage,
        )
    }
    if let Some(target_overall_retirement) = target_overall_retirement_option {
        rebalance.add_retirement_target(target_overall_retirement);
    }
    Ok(rebalance)
}

/// brokerage_calc calculates the amount of stocks and bonds that should be bought/sold within the
/// brokerage account in order to rebalance
fn brokerage_calc(
    quotes: ShareValues,
    mut brokerage: ShareValues,
    args: Args,
) -> Result<AccountHoldings> {
    brokerage.add_stock_value(
        StockSymbol::VMFXX,
        brokerage.stock_value(StockSymbol::VMFXX) + args.brokerage_cash_add,
    );
    brokerage.add_outside_stock_value(args.brokerage_us_stock_add + args.brokerage_int_stock_add);
    brokerage.add_outside_bond_value(args.brokerage_us_bond_add + args.brokerage_int_bond_add);
    let asset_allocations = Allocations::custom(
        args.percent_stock_brokerage,
        args.percent_bond_brokerage,
        0.0,
    )?;
    let sub_allocations = SubAllocations::new_custom(asset_allocations)?;
    let target_holdings = ShareValues::new_target(
        sub_allocations,
        brokerage.total_value(),
        args.brokerage_us_stock_add,
        args.brokerage_us_bond_add,
        args.brokerage_int_stock_add,
        args.brokerage_int_bond_add,
    );
    let difference = target_holdings - brokerage;
    let stock_purchase = difference / quotes;
    Ok(AccountHoldings::new(
        brokerage,
        target_holdings,
        stock_purchase,
    ))
}

type TraditionalIraAccount = AccountHoldings;
type RothIraAccount = AccountHoldings;
type TargetOverallRetirement = ShareValues;

/// retirement_calc calculates the amount of stocks and bonds that should be bought/sold within the
/// retirement account in order to rebalance.  If there are both a roth and traditional IRA
/// account, the riskiest assets are shifted towards the roth account while the less risky assets
/// are within the tradiitonal account.  This is to keep the largest growth within the account that
/// is not taxed after withdrawals
fn retirement_calc(
    vanguard_holdings: &VanguardHoldings,
    args: Args,
) -> Result<(
    Option<TraditionalIraAccount>,
    Option<RothIraAccount>,
    Option<TargetOverallRetirement>,
)> {
    let mut traditional_ira_account_option = None;
    let mut roth_ira_account_option = None;
    let mut target_overall_retirement_option = None;

    let mut allocations = Allocations::new();

    if let Some(retirement_year) = args.retirement_year_option {
        allocations = Allocations::retirement(retirement_year)?;
    }
    if let Some(stock_percent) = args.percent_stock_retirement_option {
        let bond_percent;
        if let Some(input_bond_percent) = args.percent_bond_retirement_option {
            bond_percent = input_bond_percent;
        } else {
            bond_percent = 100.0 - stock_percent;
        }
        allocations = Allocations::custom(stock_percent, bond_percent, 0.0)?;
    } else if let Some(bond_percent) = args.percent_bond_retirement_option {
        let stock_percent = 100.0 - bond_percent;
        allocations = Allocations::custom(stock_percent, bond_percent, 0.0)?;
    };

    let sub_allocations = SubAllocations::new_custom(allocations)?;

    if let Some(mut roth_holdings) = vanguard_holdings.roth_ira_holdings() {
        roth_holdings.add_stock_value(
            StockSymbol::VMFXX,
            roth_holdings.stock_value(StockSymbol::VMFXX) + args.roth_cash_add,
        );
        // If there are both Roth and Traditional accounts, shift the risky assets to the roth
        // account
        if let Some(mut traditional_holdings) = vanguard_holdings.traditional_ira_holdings() {
            traditional_holdings.add_stock_value(
                StockSymbol::VMFXX,
                traditional_holdings.stock_value(StockSymbol::VMFXX) + args.traditional_cash_add,
            );
            let target_overall_retirement = ShareValues::new_target(
                sub_allocations,
                roth_holdings.total_value() + traditional_holdings.total_value(),
                args.traditional_us_stock_add + args.roth_us_stock_add,
                args.traditional_us_bond_add + args.roth_us_bond_add,
                args.traditional_int_stock_add + args.roth_int_stock_add,
                args.traditional_int_bond_add + args.roth_int_bond_add,
            );

            target_overall_retirement_option = Some(target_overall_retirement);
            let mut roth_total = roth_holdings.total_value();
            let mut roth_target = ShareValues::new();
            for stock_symbol in HIGH_TO_LOW_RISK {
                let value = target_overall_retirement
                    .stock_value(stock_symbol.clone())
                    .min(roth_total);
                roth_total -= value;
                roth_target.add_stock_value(stock_symbol.clone(), value);
                if roth_total <= 0.0 {
                    break;
                }
            }
            ensure!(roth_total == 0.0, "Unexpected leftover roth cash");
            ensure!(
                roth_target.total_value() > (0.99 * roth_holdings.total_value())
                    && roth_target.total_value() < (1.01 * roth_holdings.total_value()),
                "Roth target and total do not match\n\nRoth target:\n{}\n\nRoth:\n{}",
                roth_target,
                roth_holdings
            );
            let roth_difference = roth_target - roth_holdings;
            let roth_purchase = roth_difference / vanguard_holdings.stock_quotes();
            let roth_account = AccountHoldings::new(roth_holdings, roth_target, roth_purchase);
            let traditional_target = target_overall_retirement - roth_target;
            let traditional_difference = traditional_target - traditional_holdings;
            let traditional_purchase = traditional_difference / vanguard_holdings.stock_quotes();
            let traditional_account = AccountHoldings::new(
                traditional_holdings,
                traditional_target,
                traditional_purchase,
            );
            roth_ira_account_option = Some(roth_account);
            traditional_ira_account_option = Some(traditional_account);
        } else {
            let roth_target = ShareValues::new_target(
                sub_allocations,
                roth_holdings.total_value(),
                args.roth_us_stock_add,
                args.roth_us_bond_add,
                args.roth_int_stock_add,
                args.roth_int_bond_add,
            );
            let roth_difference = roth_target - roth_holdings;
            let roth_purchase = roth_difference / vanguard_holdings.stock_quotes();
            let roth_account = AccountHoldings::new(roth_holdings, roth_target, roth_purchase);
            roth_ira_account_option = Some(roth_account);
        }
    } else if let Some(mut traditional_holdings) = vanguard_holdings.traditional_ira_holdings() {
        traditional_holdings.add_stock_value(
            StockSymbol::VMFXX,
            traditional_holdings.stock_value(StockSymbol::VMFXX) + args.traditional_cash_add,
        );
        let traditional_target = ShareValues::new_target(
            sub_allocations,
            traditional_holdings.total_value(),
            args.traditional_us_stock_add,
            args.traditional_us_bond_add,
            args.traditional_int_stock_add,
            args.traditional_int_bond_add,
        );
        let traditional_difference = traditional_target - traditional_holdings;
        let traditional_purchase = traditional_difference / vanguard_holdings.stock_quotes();
        let traditional_account = AccountHoldings::new(
            traditional_holdings,
            traditional_target,
            traditional_purchase,
        );
        traditional_ira_account_option = Some(traditional_account)
    }
    Ok((
        traditional_ira_account_option,
        roth_ira_account_option,
        target_overall_retirement_option,
    ))
}