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namespace FundLab.Domain
open System
module RedemptionPolicy =
let unitsMaximum = 99999999999999999999.99999999m
let cashMaximum = 999999999999999999.99m
let roundDown (scale: int) (value: decimal) : decimal =
let factor = decimal (pown 10 scale)
Decimal.Truncate(value * factor) / factor
let validateRequest
(availableUnits: decimal)
(requestedUnits: decimal)
(feeAmount: decimal)
: Result<unit, string> =
if requestedUnits <= 0m then
Error "redemption units must be positive"
elif requestedUnits > unitsMaximum then
Error "redemption units exceed supported precision"
elif requestedUnits > availableUnits then
Error "requested units exceed available holdings"
elif feeAmount < 0m then
Error "redemption fee cannot be negative"
elif feeAmount > cashMaximum then
Error "redemption fee exceeds supported precision"
else
Ok ()
type RedemptionComputation =
{
GrossCash: decimal
Fee: decimal
Proceeds: decimal
RedeemedCost: decimal
}
let compute
(requestedUnits: decimal)
(unitNav: decimal)
(feeAmount: decimal)
(positionCost: decimal)
(positionUnits: decimal)
: Result<RedemptionComputation, string> =
if unitNav <= 0m then
Error "unit nav must be positive"
elif unitNav < 0.00000001m then
Error "unit nav is below database precision"
elif requestedUnits <= 0m then
Error "redemption units must be positive"
elif positionUnits <= 0m then
Error "position units must be positive"
elif requestedUnits > positionUnits then
Error "redemption units exceed position units"
elif feeAmount < 0m then
Error "redemption fee cannot be negative"
else
let gross = requestedUnits * unitNav
let grossRounded = roundDown 2 gross
if grossRounded <= 0m then
Error "redemption cash rounds to zero"
elif feeAmount > grossRounded then
Error "redemption fee exceeds redemption value"
else
let proceeds = grossRounded - feeAmount
if proceeds <= 0m then
Error "redemption proceeds rounds to zero"
else
let redeemedCost =
if requestedUnits = positionUnits then
positionCost
else
roundDown 2 (positionCost * requestedUnits / positionUnits)
Ok
{
GrossCash = grossRounded
Fee = feeAmount
Proceeds = proceeds
RedeemedCost = redeemedCost
}
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