using System.Text.Json;

namespace OpenNest.Data;

/// <summary>
/// One settings document every workstation shares through the nest server
/// (<c>/api/settings</c>): a machine configuration, a post's settings, the clamp rail or the
/// nest defaults. <see cref="Json"/> is the document exactly as its owner serializes it;
/// <see cref="Revision"/> guards every change.
/// </summary>
public sealed class SharedSettingRecord
{
    public string Kind { get; set; } = "";

    public string Key { get; set; } = "";

    public int Revision { get; set; }

    public string Json { get; set; } = "";

    public DateTime SavedAt { get; set; }

    public string SavedBy { get; set; } = "";
}

/// <summary>The body of a shared settings create or update.</summary>
public sealed class SharedSettingWrite
{
    public string Json { get; set; } = "";

    public string SavedBy { get; set; } = "";
}

/// <summary>The kinds of shared settings and the keys of the single-document kinds.</summary>
public static class SharedSettingKinds
{
    /// <summary>A <see cref="MachineConfig"/>, keyed by its id.</summary>
    public const string Machine = "machine";

    /// <summary>A post processor's settings, keyed by the post's type name.</summary>
    public const string Post = "post";

    /// <summary>The <see cref="ClampSettings"/> new nests start from, under <see cref="DefaultKey"/>.</summary>
    public const string Clamps = "clamps";

    /// <summary>The <see cref="NestDefaults"/> new nests start from, under <see cref="DefaultKey"/>.</summary>
    public const string NestDefaults = "nest-defaults";

    /// <summary>The key of the clamp settings and nest defaults documents.</summary>
    public const string DefaultKey = "default";

    public static IReadOnlyList<string> All { get; } = [Machine, Post, Clamps, NestDefaults];

    public static bool IsKnown(string? kind) => kind is not null && All.Contains(kind);
}

/// <summary>Validation shared by the nest server and its clients.</summary>
public static class SharedSettingRules
{
    public const int MaxKeyLength = 200;

    public const int MaxSavedByLength = 200;

    /// <summary>
    /// A settings document's limit in characters: far above the largest post configuration, and
    /// small enough that the escaped document fits the server's request limit.
    /// </summary>
    public const int MaxJsonLength = 512 * 1024;

    /// <summary>
    /// The key as stored: a machine id in lower-case "D" form, any other key as given. Null when
    /// the key is not valid for the kind.
    /// </summary>
    public static string? NormalizeKey(string? kind, string? key)
    {
        if (!SharedSettingKinds.IsKnown(kind) || string.IsNullOrEmpty(key) || key.Length > MaxKeyLength)
            return null;
        if (kind == SharedSettingKinds.Machine)
            return Guid.TryParse(key, out var id) && id != Guid.Empty ? id.ToString("D") : null;
        if (kind is SharedSettingKinds.Clamps or SharedSettingKinds.NestDefaults)
            return key == SharedSettingKinds.DefaultKey ? key : null;
        return key.All(c => char.IsAsciiLetterOrDigit(c) || c is '.' or '_' or '-' or '+') ? key : null;
    }

    /// <summary>Why the document cannot be stored under the kind and key, or null when it can.</summary>
    public static string? GetError(string? kind, string? key, SharedSettingWrite? write)
    {
        if (!SharedSettingKinds.IsKnown(kind))
            return $"Unknown settings kind '{kind}'.";
        var normalized = NormalizeKey(kind, key);
        if (normalized is null)
            return $"Invalid {kind} settings key.";
        if (write is null || string.IsNullOrEmpty(write.Json))
            return "The settings document is required.";
        if (write.Json.Length > MaxJsonLength)
            return "The settings document is too large.";
        if ((write.SavedBy ?? "").Length > MaxSavedByLength)
            return "savedBy is too long.";

        try
        {
            using var document = JsonDocument.Parse(write.Json);
            if (document.RootElement.ValueKind != JsonValueKind.Object)
                return "The settings document must be a JSON object.";
        }
        catch (JsonException)
        {
            return "The settings document is not valid JSON.";
        }

        if (kind == SharedSettingKinds.Machine)
        {
            MachineConfig? machine;
            try { machine = JsonSerializer.Deserialize<MachineConfig>(write.Json, LocalJsonProvider.JsonOptions); }
            catch (JsonException) { return "The machine configuration is not valid."; }
            if (machine is null || machine.Id.ToString("D") != normalized)
                return "The machine configuration's id does not match its key.";
        }
        return null;
    }
}