Coverage Summary for Class: ExchangeRateTable (com.georgeci.moneysurfer.domain.model)

 package com.georgeci.moneysurfer.domain.model
 
 import com.georgeci.moneysurfer.domain.primitives.CurrencyCode
 import com.georgeci.moneysurfer.domain.primitives.Money
 import kotlin.math.abs
 import kotlin.math.roundToLong
 import kotlin.time.Instant
 
 /**
  * One FX quote table, all rates expressed against a single [baseCurrency].
  *
  * [rates] holds *units of the quoted currency per one unit of [baseCurrency]* — the shape every
  * mainstream provider publishes (`base=USD` → `{"EUR": 0.92}` means 1 USD buys 0.92 EUR). Turning
  * a foreign balance into the base therefore divides rather than multiplies; see [convertToBase].
  *
  * [asOf] is the provider's own publication moment, not when the app fetched it — ECB-style feeds
  * only publish on business days, so a table fetched this morning can legitimately be two days old
  * and the UI has to be able to say so.
  */
 data class ExchangeRateTable(
     val baseCurrency: CurrencyCode,
     val rates: Map<CurrencyCode, Double>,
     val asOf: Instant,
 ) {
 
     /**
      * Quote for [currency], or `null` when this table cannot price it.
      *
      * The base currency always quotes at 1 even when the provider omits it from its own payload
      * (most do), and non-positive or non-finite quotes are treated as absent rather than trusted
      * into a division — a zero rate from a malformed payload would otherwise produce an infinite
      * balance.
      */
     fun rateFor(currency: CurrencyCode): Double? {
         if (currency == baseCurrency) return 1.0
         val rate = rates[currency] ?: return null
         return rate.takeIf { it.isFinite() && it > 0.0 }
     }
 
     /**
      * [money], denominated in [currency], expressed in [baseCurrency]; `null` when no rate covers
      * [currency] and the caller has to surface the amount separately instead of dropping it.
      *
      * Rounds to the nearest minor unit (half away from zero). Money stays integral `Long` minor
      * units — the `Double` only ever appears inside this one division, and balances are capped at
      * [Money.MAX_MINOR], four orders of magnitude below the point where a `Double` stops
      * representing whole minor units exactly.
      *
      * A quote small enough to push the quotient past [Long] also counts as "cannot price it":
      * `roundToLong` saturates rather than throwing, so an absurd rate from a malformed payload
      * would otherwise turn into a silently clamped balance and then blow up the overflow-checked
      * sum. Reporting it as unconverted keeps that amount visible and the total honest.
      */
     fun convertToBase(money: Money, currency: CurrencyCode): Money? {
         val rate = rateFor(currency) ?: return null
         if (rate == 1.0) return money
         return (money.minor / rate)
             .takeIf { it.isFinite() && abs(it) <= Money.MAX_MINOR }
             ?.let { Money(it.roundToLong()) }
     }
 }
 
 /** The base currency in force plus the newest rates cached for it, if any have been cached yet. */
 data class ExchangeRateSnapshot(
     val baseCurrency: CurrencyCode,
     val rates: ExchangeRateTable?,
 )