using System.Net;
using System.Text.RegularExpressions;
using YamlDotNet.Serialization;
using YamlDotNet.Serialization.NamingConventions;
using YamlDotNet.RepresentationModel;

namespace Agent.App.Configuration;

public static partial class ConfigurationLoader
{
    public static AgentConfiguration Load(string path)
    {
        string absolutePath = Path.GetFullPath(path);
        if (!File.Exists(absolutePath))
        {
            throw new ConfigurationException($"Configuration file does not exist: {absolutePath}");
        }

        try
        {
            string yaml = File.ReadAllText(absolutePath);
            string localPath = Path.Combine(Path.GetDirectoryName(absolutePath)!, "agent.local.yaml");
            if (!string.Equals(absolutePath, localPath, StringComparison.OrdinalIgnoreCase) && File.Exists(localPath))
                yaml = MergeYaml(yaml, File.ReadAllText(localPath));
            var deserializer = new DeserializerBuilder()
                .WithNamingConvention(UnderscoredNamingConvention.Instance)
                .Build();
            AgentConfiguration configuration = deserializer.Deserialize<AgentConfiguration>(yaml)
                ?? throw new ConfigurationException("Configuration document is empty.");
            Validate(configuration, Path.GetDirectoryName(absolutePath)!);
            return configuration;
        }
        catch (ConfigurationException)
        {
            throw;
        }
        catch (Exception ex)
        {
            throw new ConfigurationException($"Could not parse YAML: {ex.Message}", ex);
        }
    }

    public static void Validate(AgentConfiguration value, string baseDirectory)
    {
        if (value.SchemaVersion != 1) Throw("schema_version must be 1.");
        if (string.IsNullOrWhiteSpace(value.Application.Language)) Throw("application.language is required.");
        if (value.Mcp.Transport is not ("stdio" or "http")) Throw("mcp.transport must be stdio or http.");
        if (!IPAddress.TryParse(value.Mcp.Http.Host, out IPAddress? host) || !IPAddress.IsLoopback(host)) Throw("mcp.http.host must be 127.0.0.1 or ::1.");
        if (value.Mcp.Http.Port is < 1 or > 65535) Throw("mcp.http.port is outside 1..65535.");
        if (value.Mcp.Images.MaxCount < 0 || value.Mcp.Images.MaxBytesEach <= 0 || value.Mcp.Images.MaxTotalBytes <= 0) Throw("mcp.images limits must be positive.");
        if (value.Mcp.Images.MaxTotalBytes < value.Mcp.Images.MaxBytesEach) Throw("mcp.images.max_total_bytes must be >= max_bytes_each.");
        if (value.Mcp.Tasks.TimeToLiveHours <= 0 || value.Mcp.Tasks.PollIntervalMs <= 0) Throw("mcp.tasks TTL and poll interval must be positive.");
        if (value.Agent.MaxIterations <= 0 || value.Agent.SameFailureLimit <= 0) Throw("agent iteration limits must be positive.");
        if (!Uri.TryCreate(value.Ollama.Endpoint, UriKind.Absolute, out Uri? endpoint) || endpoint.Scheme is not ("http" or "https")) Throw("ollama.endpoint must be an absolute HTTP(S) URI.");
        if (string.IsNullOrWhiteSpace(value.Ollama.Model)) Throw("ollama.model is required.");
        if (value.Ollama.Options.NumCtx is <= 0) Throw("ollama.options.num_ctx must be positive.");
        if (value.Ollama.Options.Temperature is < 0 or > 2) Throw("ollama.options.temperature must be in 0..2.");
        if (value.Planner.MaxTasks is < 1 or > 32) Throw("planner.max_tasks must be in 1..32.");
        if (value.Sandbox.Process.MaxProcesses <= 0 || value.Sandbox.Resources.MemoryMb <= 0 || value.Sandbox.Resources.ProcessTimeoutSeconds <= 0) Throw("sandbox resource limits must be positive.");
        if (value.Sandbox.Network.Mode is not ("deny" or "allow")) Throw("sandbox.network.mode must be deny or allow.");
        foreach (NetworkAllowance allowance in value.Sandbox.Network.Allow)
        {
            if (string.IsNullOrWhiteSpace(allowance.Host) || allowance.Ports.Count == 0 || allowance.Ports.Any(static p => p is < 1 or > 65535)) Throw("sandbox.network.allow contains an invalid host or port.");
        }
        foreach (ExecutableApproval approval in value.Sandbox.Process.Approvals)
        {
            if (!Path.IsPathFullyQualified(approval.Path) || !Sha256Regex().IsMatch(approval.Sha256)) Throw("process approval requires an absolute path and 64 hexadecimal SHA-256 characters.");
            string approvalPath = Path.GetFullPath(approval.Path);
            bool executable = value.Sandbox.Filesystem.Execute.Any(entry => ContainsPath(baseDirectory, entry, approvalPath));
            if (!executable) Throw($"sandbox.process.approvals path is not covered by sandbox.filesystem.execute: {approvalPath}. Add the path or an ancestor directory to sandbox.filesystem.execute.");
        }
        foreach (string executeEntry in value.Sandbox.Filesystem.Execute)
        {
            string executePath = Path.IsPathFullyQualified(executeEntry) ? Path.GetFullPath(executeEntry) : Resolve(baseDirectory, executeEntry);
            if (File.Exists(executePath) && !value.Sandbox.Process.Approvals.Any(approval =>
                    string.Equals(Path.GetFullPath(approval.Path), executePath, StringComparison.OrdinalIgnoreCase)))
                Throw($"sandbox.filesystem.execute file has no sandbox.process.approvals entry: {executePath}. Add canonical path and SHA-256 under sandbox.process.approvals.");
        }
        if (value.FileEdit.MemoryBackupLimitMb <= 0 || value.Limits.WholeReadBytes <= 0 || value.Limits.SearchMaxResults <= 0 || value.Limits.TailMaxLines <= 0 || value.Limits.ContextSummaryRatio is <= 0 or >= 1) Throw("file/context limits are invalid.");
        if (value.Logging.MaxFileBytes <= 0 || value.Logging.RetainedFiles < 1) Throw("logging limits are invalid.");
        if (value.Logging.Level is not ("information" or "warning" or "error" or "fatal")) Throw("logging.level must be information, warning, error, or fatal.");

        RequireFile(baseDirectory, value.Agent.UserSystemPrompt, "agent.user_system_prompt");
        RequireDirectory(baseDirectory, value.Localization.Directory, "localization.directory");
        RequireDirectory(baseDirectory, value.Skills.Directory, "skills.directory");
    }

    private static void RequireFile(string baseDirectory, string path, string key)
    {
        if (!File.Exists(Resolve(baseDirectory, path))) Throw($"{key} does not exist: {path}");
    }

    private static void RequireDirectory(string baseDirectory, string path, string key)
    {
        if (!Directory.Exists(Resolve(baseDirectory, path))) Throw($"{key} does not exist: {path}");
    }

    public static string Resolve(string baseDirectory, string path) => Path.GetFullPath(path, baseDirectory);

    private static bool ContainsPath(string baseDirectory, string configuredPath, string target)
    {
        string allowed = Path.IsPathFullyQualified(configuredPath) ? Path.GetFullPath(configuredPath) : Resolve(baseDirectory, configuredPath);
        if (string.Equals(allowed, target, StringComparison.OrdinalIgnoreCase)) return true;
        string prefix = allowed.TrimEnd(Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar) + Path.DirectorySeparatorChar;
        return target.StartsWith(prefix, StringComparison.OrdinalIgnoreCase);
    }

    private static string MergeYaml(string baseYaml, string localYaml)
    {
        YamlNode baseRoot = LoadRoot(baseYaml, "base configuration");
        YamlNode localRoot = LoadRoot(localYaml, "agent.local.yaml");
        YamlNode merged = MergeNode(baseRoot, localRoot);
        var stream = new YamlStream(new YamlDocument(merged));
        using var writer = new StringWriter(System.Globalization.CultureInfo.InvariantCulture);
        stream.Save(writer, assignAnchors: false);
        return writer.ToString();
    }

    private static YamlNode LoadRoot(string yaml, string source)
    {
        var stream = new YamlStream();
        using var reader = new StringReader(yaml);
        stream.Load(reader);
        if (stream.Documents.Count != 1) Throw($"{source} must contain exactly one YAML document.");
        return stream.Documents[0].RootNode;
    }

    private static YamlNode MergeNode(YamlNode baseNode, YamlNode localNode)
    {
        if (baseNode is not YamlMappingNode baseMap || localNode is not YamlMappingNode localMap)
            return Clone(localNode);

        var result = (YamlMappingNode)Clone(baseMap);
        foreach ((YamlNode key, YamlNode localValue) in localMap.Children)
        {
            YamlNode? existingKey = result.Children.Keys.FirstOrDefault(candidate => candidate is YamlScalarNode a && key is YamlScalarNode b && string.Equals(a.Value, b.Value, StringComparison.Ordinal));
            if (existingKey is null) result.Add(Clone(key), Clone(localValue));
            else result.Children[existingKey] = MergeNode(result.Children[existingKey], localValue);
        }
        return result;
    }

    private static YamlNode Clone(YamlNode node)
    {
        var stream = new YamlStream(new YamlDocument(node));
        using var writer = new StringWriter(System.Globalization.CultureInfo.InvariantCulture);
        stream.Save(writer, assignAnchors: false);
        return LoadRoot(writer.ToString(), "merged configuration");
    }

    private static void Throw(string message) => throw new ConfigurationException(message);
    [GeneratedRegex("^[0-9a-fA-F]{64}$", RegexOptions.CultureInvariant)]
    private static partial Regex Sha256Regex();
}