using System.Security.Cryptography;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Transport;

namespace ZB.MOM.WW.ScadaBridge.Transport.Serialization;

/// <summary>
/// Outcome of validating a <see cref="BundleManifest"/> against the supplied
/// raw content bytes. Distinct values let the importer surface a precise
/// rejection reason to the operator.
/// </summary>
public enum ManifestValidationResult
{
    Ok,
    UnsupportedFormatVersion,
    ContentHashMismatch,
    MalformedManifest
}

/// <summary>
/// Inspects a deserialized manifest plus the raw content bytes recovered from
/// the bundle ZIP and reports the first integrity failure (or <see cref="ManifestValidationResult.Ok"/>).
/// </summary>
public sealed class ManifestValidator
{
    /// <summary>Validates a deserialized bundle manifest against the raw content bytes and returns the first integrity failure, or <see cref="ManifestValidationResult.Ok"/>.</summary>
    /// <param name="manifest">The deserialized manifest to validate.</param>
    /// <param name="contentBytes">The raw content bytes extracted from the bundle ZIP.</param>
    /// <returns>A <see cref="ManifestValidationResult"/> indicating success or the specific failure kind.</returns>
    public ManifestValidationResult Validate(BundleManifest manifest, byte[] contentBytes)
    {
        if (manifest is null || contentBytes is null)
        {
            return ManifestValidationResult.MalformedManifest;
        }

        if (string.IsNullOrEmpty(manifest.SourceEnvironment) || manifest.Contents is null)
        {
            return ManifestValidationResult.MalformedManifest;
        }

        if (manifest.BundleFormatVersion != ManifestBuilder.CurrentBundleFormatVersion)
        {
            return ManifestValidationResult.UnsupportedFormatVersion;
        }

        var expected = "sha256:" + Convert.ToHexString(SHA256.HashData(contentBytes)).ToLowerInvariant();
        if (!string.Equals(expected, manifest.ContentHash, StringComparison.Ordinal))
        {
            return ManifestValidationResult.ContentHashMismatch;
        }

        return ManifestValidationResult.Ok;
    }
}
