using System;
using Svrnty.CQRS.Events.Abstractions.Models;
using Svrnty.CQRS.Events.Abstractions.EventStore;

namespace Svrnty.CQRS.Events.Abstractions.Models;

/// <summary>
/// Represents schema information for a versioned event type.
/// </summary>
/// <remarks>
/// <para>
/// Schema information tracks the evolution of event types over time, enabling:
/// - Automatic upcasting from old versions to new versions
/// - JSON schema generation for external consumers
/// - Version compatibility checking
/// </para>
/// <para>
/// <strong>Example:</strong>
/// UserCreatedEventV1 → UserCreatedEventV2 (added Email property)
/// </para>
/// </remarks>
/// <param name="EventType">The fully qualified CLR type name of the event (e.g., "MyApp.UserCreatedEvent")</param>
/// <param name="Version">The semantic version of this schema (e.g., 1, 2, 3)</param>
/// <param name="ClrType">The .NET Type that represents this version</param>
/// <param name="JsonSchema">JSON Schema (Draft 7) describing the event structure (optional, for external consumers)</param>
/// <param name="UpcastFromType">The CLR type of the previous version (null for version 1)</param>
/// <param name="UpcastFromVersion">The version number this version can upcast from (null for version 1)</param>
/// <param name="RegisteredAt">When this schema was registered in the system</param>
public sealed record SchemaInfo(
    string EventType,
    int Version,
    Type ClrType,
    string? JsonSchema,
    Type? UpcastFromType,
    int? UpcastFromVersion,
    DateTimeOffset RegisteredAt)
{
    /// <summary>
    /// Gets a value indicating whether this is the initial version of the event.
    /// </summary>
    public bool IsInitialVersion => Version == 1 && UpcastFromType == null;

    /// <summary>
    /// Gets a value indicating whether this schema can be upcast from a previous version.
    /// </summary>
    public bool SupportsUpcasting => UpcastFromType != null && UpcastFromVersion.HasValue;

    /// <summary>
    /// Gets the schema identifier (EventType:Version).
    /// </summary>
    public string SchemaId => $"{EventType}:v{Version}";

    /// <summary>
    /// Validates the schema information for correctness.
    /// </summary>
    /// <exception cref="InvalidOperationException">Thrown if the schema info is invalid.</exception>
    public void Validate()
    {
        if (string.IsNullOrWhiteSpace(EventType))
            throw new InvalidOperationException("EventType cannot be null or whitespace.");

        if (Version < 1)
            throw new InvalidOperationException($"Version must be >= 1, got {Version}.");

        if (ClrType == null)
            throw new InvalidOperationException("ClrType cannot be null.");

        if (!ClrType.IsAssignableTo(typeof(ICorrelatedEvent)))
            throw new InvalidOperationException($"ClrType {ClrType.FullName} must implement ICorrelatedEvent.");

        // Version 1 should not have upcast information
        if (Version == 1)
        {
            if (UpcastFromType != null)
                throw new InvalidOperationException("Version 1 should not have UpcastFromType.");
            if (UpcastFromVersion.HasValue)
                throw new InvalidOperationException("Version 1 should not have UpcastFromVersion.");
        }
        else
        {
            // Versions > 1 should have upcast information
            if (UpcastFromType == null)
                throw new InvalidOperationException($"Version {Version} must specify UpcastFromType.");
            if (!UpcastFromVersion.HasValue)
                throw new InvalidOperationException($"Version {Version} must specify UpcastFromVersion.");
            if (UpcastFromVersion.Value != Version - 1)
                throw new InvalidOperationException(
                    $"Version {Version} must upcast from version {Version - 1}, got {UpcastFromVersion.Value}.");
        }
    }
}