using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

namespace BulkArchiveMailer.Core
{
    /// <summary>
    /// Minimal placeholder substitution for Subject/BodyHtml templates.
    /// Deliberately simple (no conditionals/loops) - templates are short,
    /// hand-edited strings, not a general templating language.
    /// </summary>
    public static class TemplateEngine
    {
        private static readonly Regex PlaceholderPattern = new Regex(@"\{(?<name>[A-Za-z0-9_]+)\}", RegexOptions.Compiled);

        /// <summary>
        /// Replaces every "{Name}" placeholder with the matching value from
        /// <paramref name="values"/> (case-insensitive lookup). Unknown
        /// placeholders are left untouched rather than throwing, so a typo
        /// in a hand-edited template shows up visibly in the preview
        /// instead of crashing the scan.
        /// </summary>
        public static string Render(string template, IDictionary<string, string> values)
        {
            if (string.IsNullOrEmpty(template))
            {
                return template ?? string.Empty;
            }

            return PlaceholderPattern.Replace(template, match =>
            {
                var name = match.Groups["name"].Value;
                foreach (var kvp in values)
                {
                    if (string.Equals(kvp.Key, name, StringComparison.OrdinalIgnoreCase))
                    {
                        return kvp.Value ?? string.Empty;
                    }
                }

                return match.Value; // leave "{Unknown}" as-is
            });
        }

        /// <summary>Renders both Subject and BodyHtml of a template for one recipient.</summary>
        public static MailTemplate Render(MailTemplate template, string login, string email)
        {
            var values = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
            {
                ["Login"] = login ?? "",
                ["Email"] = email ?? "",
                ["Date"] = DateTime.Now.ToString("dd.MM.yyyy"),
            };

            return new MailTemplate
            {
                Subject = Render(template?.Subject ?? "", values),
                BodyHtml = Render(template?.BodyHtml ?? "", values),
            };
        }
    }
}