using System.Diagnostics.CodeAnalysis;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace DodoSSH.Client.Domain;

/// <summary>A decoded Spelunk key payload, together with the schema version it was written at.</summary>
/// <param name="Key">The key.</param>
/// <param name="SchemaVersion">The version the writing client used.</param>
public sealed record SpelunkKeySecretDocument(SpelunkKeySecret Key, int SchemaVersion)
{
    /// <inheritdoc cref="HostSecretDocument.IsReadOnly" />
    public bool IsReadOnly => SchemaVersion > SpelunkKeySecretCodec.CurrentSchemaVersion;
}

/// <summary>
/// Encodes and decodes the plaintext inside a Spelunk key item's encrypted payload.
/// </summary>
/// <remarks>
/// Mirrors <see cref="ObjectStoreSecretCodec"/>, for the same reasons and with the same guarantees.
/// </remarks>
public static class SpelunkKeySecretCodec
{
    /// <summary>The schema version this build writes.</summary>
    public const int CurrentSchemaVersion = 1;

    /// <summary>Serialises a key to the bytes that get sealed.</summary>
    /// <exception cref="ArgumentException">The key is not valid for storage.</exception>
    public static byte[] Encode(SpelunkKeySecret key)
    {
        ArgumentNullException.ThrowIfNull(key);

        if (!key.TryValidate(out var reason))
        {
            throw new ArgumentException(reason, nameof(key));
        }

        var document = new SpelunkKeyPayloadDocument
        {
            SchemaVersion = CurrentSchemaVersion,
            Label = key.Label,
            ApiBase = key.ApiBase,
            ApiKey = key.ApiKey,
        };

        return JsonSerializer.SerializeToUtf8Bytes(
            document, SpelunkKeyPayloadJsonContext.Default.SpelunkKeyPayloadDocument);
    }

    /// <summary>Parses a decrypted payload.</summary>
    /// <inheritdoc cref="HostSecretCodec.TryDecode" path="/remarks" />
    public static bool TryDecode(
        ReadOnlySpan<byte> payload,
        [NotNullWhen(true)] out SpelunkKeySecretDocument? document)
    {
        document = null;

        SpelunkKeyPayloadDocument? parsed;
        try
        {
            parsed = JsonSerializer.Deserialize(
                payload, SpelunkKeyPayloadJsonContext.Default.SpelunkKeyPayloadDocument);
        }
        catch (JsonException)
        {
            return false;
        }

        if (parsed is null || parsed.SchemaVersion < 1)
        {
            return false;
        }

        var candidate = new SpelunkKeySecret
        {
            Label = parsed.Label ?? string.Empty,
            ApiBase = parsed.ApiBase ?? string.Empty,
            ApiKey = parsed.ApiKey ?? string.Empty,
        };

        // A key whose address is not in its normal form is refused rather than normalised here: the address
        // is what decides where the key may go, and a payload that disagrees with how every client writes it
        // is not one to guess about.
        if (!candidate.TryValidate(out _))
        {
            return false;
        }

        document = new SpelunkKeySecretDocument(candidate, parsed.SchemaVersion);
        return true;
    }
}

/// <summary>The serialised shape. Mutable and nullable because it models untrusted input.</summary>
/// <inheritdoc cref="HostPayloadDocument" path="/remarks" />
internal sealed class SpelunkKeyPayloadDocument
{
    public int SchemaVersion { get; set; }

    public string? Label { get; set; }

    public string? ApiBase { get; set; }

    public string? ApiKey { get; set; }
}

[JsonSourceGenerationOptions(
    PropertyNamingPolicy = JsonKnownNamingPolicy.CamelCase,
    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
    UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip)]
[JsonSerializable(typeof(SpelunkKeyPayloadDocument))]
internal sealed partial class SpelunkKeyPayloadJsonContext : JsonSerializerContext;