namespace BigRegister.Domain.Intake;

/// <summary>
/// Config value (ADR-0001's "config value" shape). Below this many NL work-hours the
/// scholing question is required. The frontend receives this value
/// (<c>GET /intake/policy</c>) and applies it for instant UX feedback
/// (<c>intake.machine.ts</c>'s <c>lageUren</c>); <see cref="RejectIncompleteScholing"/> is the
/// backend re-validating it as the authority on submit (WP-69) —
/// <c>POST /aanvragen/{id}/submit</c> (intake-typed aanvragen only) calls it before
/// writing anything, and a violation 400s (<c>ProblemDetails</c>), never silently accepts
/// an incomplete answer.
/// </summary>
public static class IntakePolicy
{
  public const int ScholingThreshold = 1000;

  /// <summary>
  /// Completeness rule for the scholing question (WP-69) — not merit: below
  /// <see cref="ScholingThreshold"/> an answer must be present, but "nee" is a legal answer
  /// that still submits (turning "few uren + no scholing" into a rejection is out of scope,
  /// see the WP). Three-valued, so two parameters (uren, punten) couldn't express it:
  /// <list type="bullet">
  /// <item>below threshold and no answer at all ⇒ incomplete;</item>
  /// <item>answered <c>true</c> (scholing gevolgd) ⇒ punten required and non-negative
  /// (mirrors <c>parseUren</c>);</item>
  /// <item>answered anything but <c>true</c> ⇒ punten must be absent (a stale answer left
  /// behind by raising <c>uren</c> is not a legal payload).</item>
  /// </list>
  /// Returns the Dutch detail message for a <c>400 ProblemDetails</c>, or null when complete.
  /// Boundary is <c>&lt;</c>, not <c>&lt;=</c> — mirrors <c>lageUren</c>.
  /// </summary>
  public static string? RejectIncompleteScholing(int uren, bool? aanvullendeScholing, int? scholingPunten)
  {
    if (uren < ScholingThreshold && aanvullendeScholing is null)
      return $"Beantwoord de vraag over aanvullende scholing: bij minder dan {ScholingThreshold} gewerkte uren is dit verplicht.";
    if (aanvullendeScholing == true && (scholingPunten is null || scholingPunten < 0))
      return "Vul het aantal behaalde nascholingspunten in.";
    if (aanvullendeScholing != true && scholingPunten is not null)
      return "Nascholingspunten horen alleen bij een gevolgde aanvullende scholing.";
    return null;
  }
}