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module ExhangeRatesAPI.Service | |
open ExhangeRatesAPI.Types | |
open ExhangeRatesAPI.Common | |
type Rate = | |
{ Left: Symbol | |
Right: Symbol | |
Value: decimal } | |
module Rate = | |
let right rate = rate.Right | |
let left rate = rate.Left | |
let flipRate rate = | |
{ Left = rate.Right | |
Right = rate.Left | |
Value = 1m / rate.Value } | |
let calculateRates (src: Symbol) (dst: Symbol list) (rates: Rate list) : Rate list = | |
let all = | |
rates |> List.append (rates |> List.map flipRate) | |
let getLeft src = | |
all |> List.filter (fun x -> x.Left = src) | |
let getRight dst = | |
all |> List.filter (fun x -> x.Right = dst) | |
let tryGetDirect dst = | |
all | |
|> List.tryFind (fun x -> x.Left = src && x.Right = dst) | |
let tryGetWithJoin dst = | |
optional { | |
// nested loops method | |
let left = getLeft src | |
let right = getRight dst | |
let innerJoin left = | |
right | |
|> Seq.filter (fun right -> left.Right = right.Left) | |
|> Seq.map (fun right -> left, right) | |
let! result = | |
left | |
|> Seq.map innerJoin | |
|> Seq.concat | |
|> Seq.tryHead | |
let left = fst result | |
let right = snd result | |
return | |
{ Left = left.Left | |
Right = right.Right | |
Value = left.Value * right.Value } | |
} | |
let getRate dst = | |
tryGetDirect dst | |
|> Option.orElseWith (fun _ -> tryGetWithJoin dst) | |
dst | |
|> Seq.map getRate | |
|> Seq.map Option.get | |
|> Seq.toList |
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