using System.Diagnostics;
using System.Reflection;

namespace w4c_workflows.Services;

/// <summary>
/// Static self-description of this workflows-api instance, served at
/// <c>GET /api/about</c>. Used by the platform to show a runtime's name/version in
/// the runtime selector and by self-hosted runtimes to report themselves when they
/// connect over the outbound channel.
/// </summary>
public sealed record RuntimeSelfInfo(
    string Name,
    string Version,
    DateTimeOffset StartedAt,
    bool MultiTenant);

/// <summary>
/// Produces <see cref="RuntimeSelfInfo"/> from configuration + process state.
/// <c>name</c> ← <c>Runtime:Name</c> (default <c>APP_NAME</c> / app name),
/// <c>version</c> ← assembly informational version, <c>startedAt</c> ← process
/// start, <c>multiTenant</c> ← <c>!UseLiteMode</c> (overridable via
/// <c>Runtime:MultiTenant</c>).
/// </summary>
public sealed class RuntimeSelfInfoProvider
{
    private readonly RuntimeSelfInfo _info;

    public RuntimeSelfInfoProvider(IConfiguration config)
    {
        var name = FirstNonEmpty(
            config["Runtime:Name"],
            config["APP_NAME"],
            "w4c-workflows-api")!;

        var version =
            Assembly.GetExecutingAssembly()
                .GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion
            ?? Assembly.GetExecutingAssembly().GetName().Version?.ToString()
            ?? "unknown";

        DateTimeOffset startedAt;
        try
        {
            startedAt = Process.GetCurrentProcess().StartTime.ToUniversalTime();
        }
        catch
        {
            startedAt = DateTimeOffset.UtcNow;
        }

        var liteMode = config.GetValue<bool>("UseLiteMode");
        var multiTenant = !liteMode;
        if (config["Runtime:MultiTenant"] is { Length: > 0 } raw &&
            bool.TryParse(raw, out var parsed))
        {
            multiTenant = parsed;
        }

        _info = new RuntimeSelfInfo(name, version, startedAt, multiTenant);
    }

    public RuntimeSelfInfo Get() => _info;

    private static string? FirstNonEmpty(params string?[] values)
    {
        foreach (var value in values)
            if (!string.IsNullOrWhiteSpace(value))
                return value.Trim();
        return null;
    }
}