namespace FundLab.Domain

open System

module CapitalPolicy =
    let cashMaximum = 999999999999999999.99m

    let validateDeposit (amount: decimal) : Result<unit, string> =
        if amount <= 0m then
            Error "deposit amount must be positive"
        elif Decimal.Round(amount, 2) <> amount then
            Error "deposit amount exceeds cash precision"
        elif amount > cashMaximum then
            Error "deposit amount exceeds database precision"
        else
            Ok ()

    let settle (availableCash: decimal) (amount: decimal) : Result<decimal, string> =
        match validateDeposit amount with
        | Error message -> Error message
        | Ok() ->
            let updated = availableCash + amount

            if updated > cashMaximum then
                Error "available cash exceeds database precision"
            else
                Ok updated