namespace Sms.Environment.Linux;

public sealed class LinuxEnvironmentVariableStore : IEnvironmentVariableStore
{
    private const string ManagedFileName = "99-sms-task-two.conf";

    private readonly string _managedFilePath;
    private readonly string _environmentDirectory;

    public LinuxEnvironmentVariableStore()
        : this(
            Path.Combine(
                System.Environment.GetFolderPath(System.Environment.SpecialFolder.UserProfile),
                ".config",
                "environment.d"),
            ManagedFileName)
    {
    }

    internal LinuxEnvironmentVariableStore(string environmentDirectory, string managedFileName)
    {
        _environmentDirectory = environmentDirectory;
        _managedFilePath = Path.Combine(environmentDirectory, managedFileName);
    }

    public string? Get(string name)
    {
        var fromFiles = LoadMergedFromDirectory();
        if (fromFiles.TryGetValue(name, out var fileValue))
        {
            return fileValue;
        }

        return System.Environment.GetEnvironmentVariable(name);
    }

    public string? GetUserPersistedValue(string name)
    {
        if (LoadMergedFromDirectory().TryGetValue(name, out var value))
        {
            return value;
        }

        return null;
    }

    public void Set(string name, string value)
    {
        try
        {
            Directory.CreateDirectory(_environmentDirectory);
            var managed = LoadManagedFile();
            managed[name] = value;
            WriteManagedFileAtomic(managed);
        }
        catch (Exception ex) when (ex is UnauthorizedAccessException or IOException)
        {
            throw new EnvironmentVariableStoreException(
                $"Failed to write environment variable '{name}' to '{_managedFilePath}'.",
                ex);
        }
    }

    public bool Exists(string name) => Get(name) is not null;

    public IReadOnlyDictionary<string, string> GetAll(IEnumerable<string> names)
    {
        var merged = LoadMergedFromDirectory();
        var result = new Dictionary<string, string>(StringComparer.Ordinal);
        foreach (var name in names)
        {
            if (merged.TryGetValue(name, out var value))
            {
                result[name] = value;
            }
            else
            {
                var processValue = System.Environment.GetEnvironmentVariable(name);
                if (processValue is not null)
                {
                    result[name] = processValue;
                }
            }
        }

        return result;
    }

    public IReadOnlyDictionary<string, string> GetProcessEnvironment() =>
        ToDictionary(System.Environment.GetEnvironmentVariables());

    public IReadOnlyDictionary<string, string> GetUserPersistedEnvironment() =>
        LoadMergedFromDirectory();

    public bool IsPersistedInUserStore(string name) =>
        LoadMergedFromDirectory().ContainsKey(name);

    public void RemoveFromUserStore(string name)
    {
        try
        {
            if (!Directory.Exists(_environmentDirectory))
            {
                return;
            }

            foreach (var file in Directory.EnumerateFiles(_environmentDirectory, "*.conf"))
            {
                var variables = SystemdEnvironmentFileParser.Parse(File.ReadAllText(file));
                if (!variables.Remove(name))
                {
                    continue;
                }

                WriteConfFileAtomic(file, variables);
            }
        }
        catch (Exception ex) when (ex is UnauthorizedAccessException or IOException)
        {
            throw new EnvironmentVariableStoreException(
                $"Failed to remove environment variable '{name}' from '{_environmentDirectory}'.",
                ex);
        }
    }

    private Dictionary<string, string> LoadManagedFile()
    {
        if (!File.Exists(_managedFilePath))
        {
            return new Dictionary<string, string>(StringComparer.Ordinal);
        }

        return SystemdEnvironmentFileParser.Parse(File.ReadAllText(_managedFilePath));
    }

    private Dictionary<string, string> LoadMergedFromDirectory()
    {
        var merged = new Dictionary<string, string>(StringComparer.Ordinal);
        if (!Directory.Exists(_environmentDirectory))
        {
            return merged;
        }

        foreach (var file in Directory.EnumerateFiles(_environmentDirectory, "*.conf").Order(StringComparer.Ordinal))
        {
            var parsed = SystemdEnvironmentFileParser.Parse(File.ReadAllText(file));
            foreach (var pair in parsed)
            {
                merged[pair.Key] = pair.Value;
            }
        }

        return merged;
    }

    private void WriteManagedFileAtomic(Dictionary<string, string> variables) =>
        WriteConfFileAtomic(_managedFilePath, variables);

    private static void WriteConfFileAtomic(string path, Dictionary<string, string> variables)
    {
        var content = SystemdEnvironmentFileParser.Serialize(variables);
        var tempPath = path + ".tmp";
        File.WriteAllText(tempPath, content);
        File.Move(tempPath, path, overwrite: true);
    }

    private static Dictionary<string, string> ToDictionary(System.Collections.IDictionary source)
    {
        var result = new Dictionary<string, string>(StringComparer.Ordinal);
        foreach (string key in source.Keys)
        {
            result[key] = source[key]?.ToString() ?? string.Empty;
        }

        return result;
    }
}