namespace SeaHaven.Services.Implementation
{
    /// <summary>
    /// Server-owned uplift state machine (SH-101). Canonical states are
    /// Pending, Approved, Rejected, ChangesRequested, Withdrawn, Expired.
    /// Legacy stored values "Denied" (-> Rejected) and "Cancelled" (-> Withdrawn)
    /// are read as their canonical equivalents but never (re)written.
    /// </summary>
    public static class UpliftStatus
    {
        public const string Pending = "Pending";
        public const string Approved = "Approved";
        public const string Rejected = "Rejected";
        public const string ChangesRequested = "ChangesRequested";
        public const string Withdrawn = "Withdrawn";
        public const string Expired = "Expired";
        public const string NoApprovalRequired = "NoApprovalRequired";
        public const string Revoked = "Revoked";

        // Legacy aliases retained only for reads; never written by new code.
        public const string LegacyDenied = "Denied";
        public const string LegacyCancelled = "Cancelled";

        private static readonly HashSet<string> TerminalStates =
            new(StringComparer.Ordinal) { Approved, Rejected, Withdrawn, Expired, Revoked, NoApprovalRequired };

        private static readonly HashSet<string> ActiveStates =
            new(StringComparer.Ordinal) { Pending, ChangesRequested };

        /// <summary>
        /// Maps a stored status to its canonical DTO value. Legacy "Denied" is
        /// read as "Rejected" and "Cancelled" as "Withdrawn".
        /// </summary>
        public static string ToCanonical(string? status) => status switch
        {
            LegacyDenied => Rejected,
            LegacyCancelled => Withdrawn,
            _ => status ?? Pending
        };

        /// <summary>True for terminal (immutable) states, including legacy aliases.</summary>
        public static bool IsTerminal(string? status) =>
            TerminalStates.Contains(ToCanonical(status));

        /// <summary>True for actionable states that block a new active request.</summary>
        public static bool IsActive(string? status) =>
            ActiveStates.Contains(ToCanonical(status));

        /// <summary>
        /// Validates a server-owned transition. Only legal transitions return true.
        /// Terminal states (incl. legacy aliases) never transition out.
        /// </summary>
        public static bool CanTransition(string? from, string to)
        {
            var canonicalFrom = ToCanonical(from);

            if (TerminalStates.Contains(canonicalFrom))
                return false;

            return canonicalFrom switch
            {
                Pending => to is Approved or Rejected or ChangesRequested or Withdrawn or Expired,
                ChangesRequested => to is Pending or Withdrawn or Expired,
                _ => false
            };
        }

        /// <summary>Snapshot-readable active states, used by data-service filters.</summary>
        public static IReadOnlyCollection<string> ActiveStatuses => ActiveStates;
    }

    /// <summary>
    /// Notification pipeline status (separate from the workflow <see cref="UpliftStatus"/>).
    /// A notification failure never destroys an actionable request.
    /// </summary>
    public static class UpliftNotificationStatus
    {
        public const string Pending = "Pending";
        public const string Sent = "Sent";
        public const string Error = "Error";
    }

    /// <summary>
    /// Vendor completion document purposes (SH-101). Completion is the legacy/default
    /// behavior; UpliftEvidence is immutable supporting evidence for an uplift request.
    /// </summary>
    public static class VendorDocumentPurpose
    {
        public const string Completion = "Completion";
        public const string UpliftEvidence = "UpliftEvidence";

        public static bool IsValid(string? purpose) =>
            purpose is Completion or UpliftEvidence;
    }
}