namespace StellaOps.Notifier.Worker.Escalation;

/// <summary>
/// Service for managing on-call schedules.
/// </summary>
public interface IOnCallScheduleService
{
    /// <summary>
    /// Lists all on-call schedules for a tenant.
    /// </summary>
    Task<IReadOnlyList<OnCallSchedule>> ListSchedulesAsync(
        string tenantId,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Gets a specific on-call schedule.
    /// </summary>
    Task<OnCallSchedule?> GetScheduleAsync(
        string tenantId,
        string scheduleId,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Creates or updates an on-call schedule.
    /// </summary>
    Task<OnCallSchedule> UpsertScheduleAsync(
        OnCallSchedule schedule,
        string? actor,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Deletes an on-call schedule.
    /// </summary>
    Task<bool> DeleteScheduleAsync(
        string tenantId,
        string scheduleId,
        string? actor,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Gets the current on-call user(s) for a schedule.
    /// </summary>
    Task<IReadOnlyList<OnCallUser>> GetCurrentOnCallAsync(
        string tenantId,
        string scheduleId,
        DateTimeOffset? atTime = null,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Gets on-call coverage for a time range.
    /// </summary>
    Task<IReadOnlyList<OnCallShift>> GetCoverageAsync(
        string tenantId,
        string scheduleId,
        DateTimeOffset from,
        DateTimeOffset to,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Creates an override for a schedule.
    /// </summary>
    Task<OnCallOverride> CreateOverrideAsync(
        string tenantId,
        string scheduleId,
        OnCallOverride @override,
        string? actor,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Deletes an override.
    /// </summary>
    Task<bool> DeleteOverrideAsync(
        string tenantId,
        string scheduleId,
        string overrideId,
        string? actor,
        CancellationToken cancellationToken = default);
}

/// <summary>
/// An on-call schedule defining rotation coverage.
/// </summary>
public sealed record OnCallSchedule
{
    /// <summary>
    /// Unique schedule ID.
    /// </summary>
    public required string ScheduleId { get; init; }

    /// <summary>
    /// Tenant ID.
    /// </summary>
    public required string TenantId { get; init; }

    /// <summary>
    /// Display name.
    /// </summary>
    public required string Name { get; init; }

    /// <summary>
    /// Description.
    /// </summary>
    public string? Description { get; init; }

    /// <summary>
    /// Timezone for the schedule (IANA format).
    /// </summary>
    public required string Timezone { get; init; }

    /// <summary>
    /// Whether the schedule is enabled.
    /// </summary>
    public bool Enabled { get; init; } = true;

    /// <summary>
    /// Rotation layers (combined to determine on-call).
    /// </summary>
    public required IReadOnlyList<RotationLayer> Layers { get; init; }

    /// <summary>
    /// Active overrides.
    /// </summary>
    public IReadOnlyList<OnCallOverride>? Overrides { get; init; }

    /// <summary>
    /// When created.
    /// </summary>
    public DateTimeOffset CreatedAt { get; init; }

    /// <summary>
    /// Who created.
    /// </summary>
    public string? CreatedBy { get; init; }

    /// <summary>
    /// When last updated.
    /// </summary>
    public DateTimeOffset UpdatedAt { get; init; }

    /// <summary>
    /// Who last updated.
    /// </summary>
    public string? UpdatedBy { get; init; }
}

/// <summary>
/// A rotation layer in an on-call schedule.
/// </summary>
public sealed record RotationLayer
{
    /// <summary>
    /// Layer name.
    /// </summary>
    public required string Name { get; init; }

    /// <summary>
    /// Layer priority (lower = higher priority for conflicts).
    /// </summary>
    public int Priority { get; init; } = 100;

    /// <summary>
    /// Users in this rotation.
    /// </summary>
    public required IReadOnlyList<OnCallUser> Users { get; init; }

    /// <summary>
    /// Rotation type.
    /// </summary>
    public required RotationType Type { get; init; }

    /// <summary>
    /// Handoff time (when rotations change).
    /// </summary>
    public required TimeOnly HandoffTime { get; init; }

    /// <summary>
    /// Rotation interval.
    /// </summary>
    public required TimeSpan RotationInterval { get; init; }

    /// <summary>
    /// When this layer's rotation starts.
    /// </summary>
    public required DateTimeOffset RotationStart { get; init; }

    /// <summary>
    /// Days/times this layer is active (null = always).
    /// </summary>
    public IReadOnlyList<ScheduleRestriction>? Restrictions { get; init; }

    /// <summary>
    /// Whether this layer is enabled.
    /// </summary>
    public bool Enabled { get; init; } = true;
}

/// <summary>
/// Type of rotation.
/// </summary>
public enum RotationType
{
    /// <summary>Daily rotation.</summary>
    Daily,

    /// <summary>Weekly rotation.</summary>
    Weekly,

    /// <summary>Custom interval rotation.</summary>
    Custom
}

/// <summary>
/// A restriction on when a rotation layer is active.
/// </summary>
public sealed record ScheduleRestriction
{
    /// <summary>
    /// Type of restriction.
    /// </summary>
    public required RestrictionType Type { get; init; }

    /// <summary>
    /// Days of week (0=Sunday, 6=Saturday) for weekly restrictions.
    /// </summary>
    public IReadOnlyList<int>? DaysOfWeek { get; init; }

    /// <summary>
    /// Start time for the restriction.
    /// </summary>
    public TimeOnly? StartTime { get; init; }

    /// <summary>
    /// End time for the restriction.
    /// </summary>
    public TimeOnly? EndTime { get; init; }
}

/// <summary>
/// Type of schedule restriction.
/// </summary>
public enum RestrictionType
{
    /// <summary>Restrict to specific days of week.</summary>
    DaysOfWeek,

    /// <summary>Restrict to specific time range.</summary>
    TimeOfDay,

    /// <summary>Restrict to specific days and times.</summary>
    DaysAndTime
}

/// <summary>
/// A user in an on-call schedule.
/// </summary>
public sealed record OnCallUser
{
    /// <summary>
    /// User ID.
    /// </summary>
    public required string UserId { get; init; }

    /// <summary>
    /// Display name.
    /// </summary>
    public required string Name { get; init; }

    /// <summary>
    /// Email address.
    /// </summary>
    public string? Email { get; init; }

    /// <summary>
    /// Phone number.
    /// </summary>
    public string? Phone { get; init; }

    /// <summary>
    /// Preferred notification channel.
    /// </summary>
    public string? PreferredChannelId { get; init; }

    /// <summary>
    /// Position in rotation order.
    /// </summary>
    public int Order { get; init; }
}

/// <summary>
/// An override for an on-call schedule.
/// </summary>
public sealed record OnCallOverride
{
    /// <summary>
    /// Override ID.
    /// </summary>
    public required string OverrideId { get; init; }

    /// <summary>
    /// User taking over on-call.
    /// </summary>
    public required OnCallUser User { get; init; }

    /// <summary>
    /// When the override starts.
    /// </summary>
    public required DateTimeOffset StartsAt { get; init; }

    /// <summary>
    /// When the override ends.
    /// </summary>
    public required DateTimeOffset EndsAt { get; init; }

    /// <summary>
    /// Reason for the override.
    /// </summary>
    public string? Reason { get; init; }

    /// <summary>
    /// Who created the override.
    /// </summary>
    public string? CreatedBy { get; init; }

    /// <summary>
    /// When created.
    /// </summary>
    public DateTimeOffset CreatedAt { get; init; }
}

/// <summary>
/// A computed on-call shift.
/// </summary>
public sealed record OnCallShift
{
    /// <summary>
    /// User on call.
    /// </summary>
    public required OnCallUser User { get; init; }

    /// <summary>
    /// When the shift starts.
    /// </summary>
    public required DateTimeOffset StartsAt { get; init; }

    /// <summary>
    /// When the shift ends.
    /// </summary>
    public required DateTimeOffset EndsAt { get; init; }

    /// <summary>
    /// Layer this shift comes from.
    /// </summary>
    public required string LayerName { get; init; }

    /// <summary>
    /// Whether this is from an override.
    /// </summary>
    public bool IsOverride { get; init; }
}