namespace StellaOps.Notifier.Worker.Escalations;

/// <summary>
/// Manages on-call schedules and determines who is currently on-call.
/// </summary>
public interface IOnCallScheduleService
{
    /// <summary>
    /// Gets a schedule by ID.
    /// </summary>
    Task<OnCallSchedule?> GetAsync(string tenantId, string scheduleId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Lists all schedules for a tenant.
    /// </summary>
    Task<IReadOnlyList<OnCallSchedule>> ListAsync(string tenantId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Creates or updates a schedule.
    /// </summary>
    Task<OnCallSchedule> UpsertAsync(OnCallSchedule schedule, CancellationToken cancellationToken = default);

    /// <summary>
    /// Deletes a schedule.
    /// </summary>
    Task<bool> DeleteAsync(string tenantId, string scheduleId, CancellationToken cancellationToken = default);

    /// <summary>
    /// Gets who is currently on-call for a schedule.
    /// </summary>
    Task<OnCallResolution> GetCurrentOnCallAsync(
        string tenantId,
        string scheduleId,
        DateTimeOffset? asOf = null,
        CancellationToken cancellationToken = default);

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

    /// <summary>
    /// Adds an override to a schedule.
    /// </summary>
    Task<OnCallOverride> AddOverrideAsync(
        string tenantId,
        string scheduleId,
        OnCallOverride @override,
        CancellationToken cancellationToken = default);

    /// <summary>
    /// Removes an override from a schedule.
    /// </summary>
    Task<bool> RemoveOverrideAsync(
        string tenantId,
        string scheduleId,
        string overrideId,
        CancellationToken cancellationToken = default);
}

/// <summary>
/// On-call schedule defining rotation of responders.
/// </summary>
public sealed record OnCallSchedule
{
    /// <summary>
    /// Unique schedule identifier.
    /// </summary>
    public required string ScheduleId { get; init; }

    /// <summary>
    /// Tenant this schedule belongs to.
    /// </summary>
    public required string TenantId { get; init; }

    /// <summary>
    /// Human-readable name.
    /// </summary>
    public required string Name { get; init; }

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

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

    /// <summary>
    /// Rotation layers (evaluated in order, first match wins).
    /// </summary>
    public required IReadOnlyList<RotationLayer> Layers { get; init; }

    /// <summary>
    /// Current overrides to the schedule.
    /// </summary>
    public IReadOnlyList<OnCallOverride> Overrides { get; init; } = [];

    /// <summary>
    /// Fallback user if no one is on-call.
    /// </summary>
    public string? FallbackUserId { get; init; }

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

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

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

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

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

    /// <summary>
    /// Users in the rotation (in order).
    /// </summary>
    public required IReadOnlyList<OnCallUser> Users { get; init; }

    /// <summary>
    /// When this rotation starts.
    /// </summary>
    public required DateTimeOffset StartTime { get; init; }

    /// <summary>
    /// Rotation interval (e.g., 1 week for weekly rotation).
    /// </summary>
    public required TimeSpan RotationInterval { get; init; }

    /// <summary>
    /// Handoff time of day (in schedule timezone).
    /// </summary>
    public TimeOnly HandoffTime { get; init; } = new(9, 0);

    /// <summary>
    /// Days of week this layer is active (empty = all days).
    /// </summary>
    public IReadOnlyList<DayOfWeek>? ActiveDays { get; init; }

    /// <summary>
    /// Time restrictions (e.g., only active 9am-5pm).
    /// </summary>
    public OnCallTimeRestriction? TimeRestriction { get; init; }

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

/// <summary>
/// Type of rotation.
/// </summary>
public enum RotationType
{
    /// <summary>
    /// Users rotate on a regular interval.
    /// </summary>
    Daily,

    /// <summary>
    /// Users rotate weekly.
    /// </summary>
    Weekly,

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

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

    /// <summary>
    /// Display name.
    /// </summary>
    public string? DisplayName { get; init; }

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

    /// <summary>
    /// Preferred notification channels.
    /// </summary>
    public IReadOnlyList<string> PreferredChannels { get; init; } = [];

    /// <summary>
    /// Contact methods in priority order.
    /// </summary>
    public IReadOnlyList<ContactMethod> ContactMethods { get; init; } = [];
}

/// <summary>
/// Contact method for a user.
/// </summary>
public sealed record ContactMethod
{
    /// <summary>
    /// Contact type (email, sms, phone, slack, etc.).
    /// </summary>
    public required string Type { get; init; }

    /// <summary>
    /// Contact address/number.
    /// </summary>
    public required string Address { get; init; }

    /// <summary>
    /// Label for this contact method.
    /// </summary>
    public string? Label { get; init; }

    /// <summary>
    /// Whether this is verified.
    /// </summary>
    public bool Verified { get; init; }
}

/// <summary>
/// Time restriction for a rotation layer.
/// </summary>
public sealed record OnCallTimeRestriction
{
    /// <summary>
    /// Start time of active period.
    /// </summary>
    public required TimeOnly StartTime { get; init; }

    /// <summary>
    /// End time of active period.
    /// </summary>
    public required TimeOnly EndTime { get; init; }

    /// <summary>
    /// Whether the restriction spans midnight (e.g., 10pm-6am).
    /// </summary>
    public bool SpansMidnight => EndTime < StartTime;
}

/// <summary>
/// Override to the normal on-call schedule.
/// </summary>
public sealed record OnCallOverride
{
    /// <summary>
    /// Override identifier.
    /// </summary>
    public required string OverrideId { get; init; }

    /// <summary>
    /// User who will be on-call during this override.
    /// </summary>
    public required string UserId { get; init; }

    /// <summary>
    /// Display name of the override user.
    /// </summary>
    public string? UserDisplayName { get; init; }

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

    /// <summary>
    /// When the override ends.
    /// </summary>
    public required DateTimeOffset EndTime { 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 the override was created.
    /// </summary>
    public DateTimeOffset CreatedAt { get; init; }
}

/// <summary>
/// Result of on-call resolution.
/// </summary>
public sealed record OnCallResolution
{
    /// <summary>
    /// Whether someone is on-call.
    /// </summary>
    public required bool HasOnCall { get; init; }

    /// <summary>
    /// The on-call user (if any).
    /// </summary>
    public OnCallUser? OnCallUser { get; init; }

    /// <summary>
    /// Which layer resolved the on-call.
    /// </summary>
    public string? ResolvedFromLayer { get; init; }

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

    /// <summary>
    /// Override details if applicable.
    /// </summary>
    public OnCallOverride? Override { get; init; }

    /// <summary>
    /// Whether this is the fallback user.
    /// </summary>
    public bool IsFallback { get; init; }

    /// <summary>
    /// When the current on-call shift ends.
    /// </summary>
    public DateTimeOffset? ShiftEndsAt { get; init; }

    /// <summary>
    /// The time this resolution was calculated for.
    /// </summary>
    public DateTimeOffset AsOf { get; init; }

    public static OnCallResolution NoOneOnCall(DateTimeOffset asOf) =>
        new() { HasOnCall = false, AsOf = asOf };

    public static OnCallResolution FromUser(OnCallUser user, string layer, DateTimeOffset asOf, DateTimeOffset? shiftEnds = null) =>
        new()
        {
            HasOnCall = true,
            OnCallUser = user,
            ResolvedFromLayer = layer,
            AsOf = asOf,
            ShiftEndsAt = shiftEnds
        };

    public static OnCallResolution FromOverride(OnCallUser user, OnCallOverride @override, DateTimeOffset asOf) =>
        new()
        {
            HasOnCall = true,
            OnCallUser = user,
            IsOverride = true,
            Override = @override,
            AsOf = asOf,
            ShiftEndsAt = @override.EndTime
        };

    public static OnCallResolution FromFallback(OnCallUser user, DateTimeOffset asOf) =>
        new()
        {
            HasOnCall = true,
            OnCallUser = user,
            IsFallback = true,
            AsOf = asOf
        };
}

/// <summary>
/// On-call coverage for a time period.
/// </summary>
public sealed record OnCallCoverage
{
    /// <summary>
    /// Start of this coverage period.
    /// </summary>
    public required DateTimeOffset From { get; init; }

    /// <summary>
    /// End of this coverage period.
    /// </summary>
    public required DateTimeOffset To { get; init; }

    /// <summary>
    /// User on-call during this period.
    /// </summary>
    public required OnCallUser User { get; init; }

    /// <summary>
    /// Layer providing coverage.
    /// </summary>
    public string? Layer { get; init; }

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