using System.Text.Json;
using System.Text.Json.Serialization;

namespace StellaOps.Microservice.Validation;

/// <summary>
/// RFC 7807 Problem Details for schema validation failures.
/// Returns HTTP 422 Unprocessable Entity.
/// </summary>
public sealed class ValidationProblemDetails
{
    private static readonly JsonSerializerOptions SerializerOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
    };

    /// <summary>
    /// A URI reference identifying the problem type.
    /// </summary>
    [JsonPropertyName("type")]
    public string Type { get; init; } = "https://stellaops.io/errors/schema-validation";

    /// <summary>
    /// A short, human-readable summary of the problem.
    /// </summary>
    [JsonPropertyName("title")]
    public string Title { get; init; } = "Schema Validation Failed";

    /// <summary>
    /// The HTTP status code (422).
    /// </summary>
    [JsonPropertyName("status")]
    public int Status { get; init; } = 422;

    /// <summary>
    /// A human-readable explanation specific to this occurrence.
    /// </summary>
    [JsonPropertyName("detail")]
    public string? Detail { get; init; }

    /// <summary>
    /// A URI reference identifying the specific occurrence (the endpoint path).
    /// </summary>
    [JsonPropertyName("instance")]
    public string? Instance { get; init; }

    /// <summary>
    /// The trace/correlation ID for distributed tracing.
    /// </summary>
    [JsonPropertyName("traceId")]
    public string? TraceId { get; init; }

    /// <summary>
    /// The list of validation errors.
    /// </summary>
    [JsonPropertyName("errors")]
    public IReadOnlyList<SchemaValidationError> Errors { get; init; } = [];

    /// <summary>
    /// Creates a ValidationProblemDetails for schema validation failures.
    /// </summary>
    /// <param name="method">The HTTP method.</param>
    /// <param name="path">The endpoint path.</param>
    /// <param name="direction">Request or response validation.</param>
    /// <param name="errors">The validation errors.</param>
    /// <param name="correlationId">Optional correlation ID.</param>
    public static ValidationProblemDetails Create(
        string method,
        string path,
        SchemaDirection direction,
        IReadOnlyList<SchemaValidationError> errors,
        string? correlationId = null)
    {
        var directionText = direction == SchemaDirection.Request ? "request" : "response";
        return new ValidationProblemDetails
        {
            Detail = $"{char.ToUpperInvariant(directionText[0])}{directionText[1..]} body failed schema validation for {method} {path}",
            Instance = path,
            TraceId = correlationId,
            Errors = errors
        };
    }

    /// <summary>
    /// Converts this problem details to a RawResponse.
    /// </summary>
    public RawResponse ToRawResponse()
    {
        var json = JsonSerializer.SerializeToUtf8Bytes(this, SerializerOptions);
        var headers = new HeaderCollection();
        headers.Set("Content-Type", "application/problem+json; charset=utf-8");

        return new RawResponse
        {
            StatusCode = Status,
            Headers = headers,
            Body = new MemoryStream(json)
        };
    }
}