git.stella-ops.org/src/Notifier/StellaOps.Notifier/StellaOps.Notifier.Worker/Processing/SimpleTemplateRenderer.cs

using System.Text.Json.Nodes;
using System.Text.RegularExpressions;
using StellaOps.Notify.Models;

namespace StellaOps.Notifier.Worker.Processing;

/// <summary>
/// Simple Handlebars-like template renderer supporting {{property}} and {{#each}} blocks.
/// </summary>
public sealed partial class SimpleTemplateRenderer : INotifyTemplateRenderer
{
    private static readonly Regex PlaceholderPattern = PlaceholderRegex();
    private static readonly Regex EachBlockPattern = EachBlockRegex();

    public string Render(NotifyTemplate template, JsonNode? payload)
    {
        ArgumentNullException.ThrowIfNull(template);

        var body = template.Body;
        if (string.IsNullOrWhiteSpace(body))
        {
            return string.Empty;
        }

        // Process {{#each}} blocks first
        body = ProcessEachBlocks(body, payload);

        // Then substitute simple placeholders
        body = SubstitutePlaceholders(body, payload);

        return body;
    }

    private static string ProcessEachBlocks(string body, JsonNode? payload)
    {
        return EachBlockPattern.Replace(body, match =>
        {
            var collectionPath = match.Groups[1].Value.Trim();
            var innerTemplate = match.Groups[2].Value;

            var collection = ResolvePath(payload, collectionPath);
            if (collection is not JsonObject obj)
            {
                return string.Empty;
            }

            var results = new List<string>();
            foreach (var (key, value) in obj)
            {
                var itemResult = innerTemplate
                    .Replace("{{@key}}", key)
                    .Replace("{{this}}", value?.ToString() ?? string.Empty);
                results.Add(itemResult);
            }

            return string.Join(string.Empty, results);
        });
    }

    private static string SubstitutePlaceholders(string body, JsonNode? payload)
    {
        return PlaceholderPattern.Replace(body, match =>
        {
            var path = match.Groups[1].Value.Trim();
            var resolved = ResolvePath(payload, path);
            return resolved?.ToString() ?? string.Empty;
        });
    }

    private static JsonNode? ResolvePath(JsonNode? root, string path)
    {
        if (root is null || string.IsNullOrWhiteSpace(path))
        {
            return null;
        }

        var segments = path.Split('.');
        var current = root;

        foreach (var segment in segments)
        {
            if (current is JsonObject obj && obj.TryGetPropertyValue(segment, out var next))
            {
                current = next;
            }
            else
            {
                return null;
            }
        }

        return current;
    }

    [GeneratedRegex(@"\{\{([^#/}]+)\}\}", RegexOptions.Compiled)]
    private static partial Regex PlaceholderRegex();

    [GeneratedRegex(@"\{\{#each\s+([^}]+)\}\}(.*?)\{\{/each\}\}", RegexOptions.Compiled | RegexOptions.Singleline)]
    private static partial Regex EachBlockRegex();
}