using Microsoft.Extensions.Hosting;
using System.Text;
using System.Text.Json;

namespace StellaOps.Policy.Engine.Overlay;

/// <summary>
/// Persists overlay projections as NDJSON files under overlay/{tenant}/{ruleId}/{version}.ndjson.
/// </summary>
internal sealed class FileOverlayStore : IOverlayStore
{
    private readonly string _root;

    public FileOverlayStore(IHostEnvironment env)
    {
        _root = Path.Combine(env.ContentRootPath, "overlay");
    }

    public async Task SaveAsync(OverlayProjection projection, CancellationToken cancellationToken = default)
    {
        if (projection is null)
        {
            throw new ArgumentNullException(nameof(projection));
        }

        var tenant = Sanitize(projection.Tenant);
        var rule = Sanitize(projection.RuleId);
        var dir = Path.Combine(_root, tenant, rule);
        Directory.CreateDirectory(dir);

        var path = Path.Combine(dir, $"{projection.Version}.ndjson");
        var lines = new[]
        {
            JsonSerializer.Serialize(new OverlayProjectionHeader("overlay-projection-v1")),
            JsonSerializer.Serialize(projection)
        };
        await File.WriteAllLinesAsync(path, lines, Encoding.UTF8, cancellationToken).ConfigureAwait(false);
    }

    private static string Sanitize(string value)
    {
        foreach (var ch in Path.GetInvalidFileNameChars())
        {
            value = value.Replace(ch, '_');
        }

        return string.IsNullOrWhiteSpace(value) ? "unknown" : value;
    }
}