using System.IO;
using System.Text;
using SharepointToolbox.Core.Models;

namespace SharepointToolbox.Services.Export;

/// <summary>
/// Exports user access audit results to CSV format.
/// Produces one CSV file per audited user with a summary section at the top.
/// </summary>
public class UserAccessCsvExportService
{
    private const string DataHeader =
        "\"Site\",\"Object Type\",\"Object\",\"URL\",\"Permission Level\",\"Access Type\",\"Granted Through\"";

    /// <summary>
    /// Builds a CSV string for a single user's access entries.
    /// Includes a summary section at the top followed by data rows.
    /// </summary>
    public string BuildCsv(string userDisplayName, string userLogin, IReadOnlyList<UserAccessEntry> entries)
    {
        var sb = new StringBuilder();

        // Summary section
        var sitesCount = entries.Select(e => e.SiteUrl).Distinct().Count();
        var highPrivCount = entries.Count(e => e.IsHighPrivilege);

        sb.AppendLine($"\"User Access Audit Report\"");
        sb.AppendLine($"\"User\",\"{Csv(userDisplayName)} ({Csv(userLogin)})\"");
        sb.AppendLine($"\"Total Accesses\",\"{entries.Count}\"");
        sb.AppendLine($"\"Sites\",\"{sitesCount}\"");
        sb.AppendLine($"\"High Privilege\",\"{highPrivCount}\"");
        sb.AppendLine($"\"Generated\",\"{DateTime.Now:yyyy-MM-dd HH:mm:ss}\"");
        sb.AppendLine(); // Blank line separating summary from data

        // Data rows
        sb.AppendLine(DataHeader);
        foreach (var entry in entries)
        {
            sb.AppendLine(string.Join(",", new[]
            {
                Csv(entry.SiteTitle),
                Csv(entry.ObjectType),
                Csv(entry.ObjectTitle),
                Csv(entry.ObjectUrl),
                Csv(entry.PermissionLevel),
                Csv(entry.AccessType.ToString()),
                Csv(entry.GrantedThrough)
            }));
        }

        return sb.ToString();
    }

    /// <summary>
    /// Writes one CSV file per user to the specified directory.
    /// File names: audit_{email}_{date}.csv
    /// </summary>
    public async Task WriteAsync(
        IReadOnlyList<UserAccessEntry> allEntries,
        string directoryPath,
        CancellationToken ct)
    {
        Directory.CreateDirectory(directoryPath);
        var dateStr = DateTime.Now.ToString("yyyy-MM-dd");

        // Group by user
        var byUser = allEntries.GroupBy(e => e.UserLogin);

        foreach (var group in byUser)
        {
            ct.ThrowIfCancellationRequested();

            var userLogin = group.Key;
            var displayName = group.First().UserDisplayName;
            var entries = group.ToList();

            // Sanitize email for filename (replace @ and other invalid chars)
            var safeLogin = SanitizeFileName(userLogin);
            var fileName = $"audit_{safeLogin}_{dateStr}.csv";
            var filePath = Path.Combine(directoryPath, fileName);

            var csv = BuildCsv(displayName, userLogin, entries);
            await File.WriteAllTextAsync(filePath, csv,
                new UTF8Encoding(encoderShouldEmitUTF8Identifier: true), ct);
        }
    }

    /// <summary>
    /// Writes all entries to a single CSV file (alternative for single-file export).
    /// Used when the ViewModel export command picks a single file path.
    /// </summary>
    public async Task WriteSingleFileAsync(
        IReadOnlyList<UserAccessEntry> entries,
        string filePath,
        CancellationToken ct)
    {
        var sb = new StringBuilder();
        var fullHeader = "\"User\",\"User Login\"," + DataHeader;

        // Summary
        var users = entries.Select(e => e.UserLogin).Distinct().ToList();
        sb.AppendLine($"\"User Access Audit Report\"");
        sb.AppendLine($"\"Users Audited\",\"{users.Count}\"");
        sb.AppendLine($"\"Total Accesses\",\"{entries.Count}\"");
        sb.AppendLine($"\"Generated\",\"{DateTime.Now:yyyy-MM-dd HH:mm:ss}\"");
        sb.AppendLine();

        sb.AppendLine(fullHeader);
        foreach (var entry in entries)
        {
            sb.AppendLine(string.Join(",", new[]
            {
                Csv(entry.UserDisplayName),
                Csv(entry.UserLogin),
                Csv(entry.SiteTitle),
                Csv(entry.ObjectType),
                Csv(entry.ObjectTitle),
                Csv(entry.ObjectUrl),
                Csv(entry.PermissionLevel),
                Csv(entry.AccessType.ToString()),
                Csv(entry.GrantedThrough)
            }));
        }

        await File.WriteAllTextAsync(filePath, sb.ToString(),
            new UTF8Encoding(encoderShouldEmitUTF8Identifier: true), ct);
    }

    /// <summary>RFC 4180 CSV field escaping: wrap in double quotes, double internal quotes.</summary>
    private static string Csv(string value)
    {
        if (string.IsNullOrEmpty(value)) return "\"\"";
        return $"\"{value.Replace("\"", "\"\"")}\"";
    }

    private static string SanitizeFileName(string name)
    {
        var invalid = Path.GetInvalidFileNameChars();
        var sb = new StringBuilder(name.Length);
        foreach (var c in name)
            sb.Append(invalid.Contains(c) ? '_' : c);
        return sb.ToString();
    }
}