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

namespace SharepointToolbox.Services.Export;

/// <summary>
/// Exports DuplicateGroup list to CSV. Each duplicate item becomes one row;
/// the Group column ties copies together and a Copies column gives the group size.
/// Header row is built at write-time so culture switches are honoured.
/// </summary>
public class DuplicatesCsvExportService
{
    /// <summary>Writes the CSV to <paramref name="filePath"/> with UTF-8 BOM (Excel-compatible).</summary>
    public async Task WriteAsync(
        IReadOnlyList<DuplicateGroup> groups,
        string filePath,
        CancellationToken ct)
    {
        var csv = BuildCsv(groups);
        await ExportFileWriter.WriteCsvAsync(filePath, csv, ct);
    }

    /// <summary>
    /// Writes one or more CSVs depending on <paramref name="splitMode"/>.
    /// Single → <paramref name="basePath"/> as-is. BySite → one file per site,
    /// filenames derived from <paramref name="basePath"/> with a site suffix.
    /// </summary>
    public Task WriteAsync(
        IReadOnlyList<DuplicateGroup> groups,
        string basePath,
        ReportSplitMode splitMode,
        CancellationToken ct)
        => ReportSplitHelper.WritePartitionedAsync(
            groups, basePath, splitMode,
            PartitionBySite,
            (part, path, c) => WriteAsync(part, path, c),
            ct);

    internal static IEnumerable<(string Label, IReadOnlyList<DuplicateGroup> Partition)> PartitionBySite(
        IReadOnlyList<DuplicateGroup> groups)
    {
        return groups
            .GroupBy(g =>
            {
                var first = g.Items.FirstOrDefault();
                return (Url: first?.SiteUrl ?? string.Empty, Title: first?.SiteTitle ?? string.Empty);
            })
            .Select(g => (
                Label: ReportSplitHelper.DeriveSiteLabel(g.Key.Url, g.Key.Title),
                Partition: (IReadOnlyList<DuplicateGroup>)g.ToList()));
    }

    /// <summary>
    /// Builds the CSV payload. Emits a header summary (group count, generated
    /// timestamp), then one row per duplicate item with its group index and
    /// group size. CSV fields are escaped via <see cref="CsvSanitizer.Escape"/>.
    /// </summary>
    public string BuildCsv(IReadOnlyList<DuplicateGroup> groups)
    {
        var T = TranslationSource.Instance;
        var sb = new StringBuilder();

        // Summary
        sb.AppendLine($"\"{T["report.title.duplicates_short"]}\"");
        sb.AppendLine($"\"{T["report.text.duplicate_groups_found"]}\",\"{groups.Count}\"");
        sb.AppendLine($"\"{T["report.text.generated"]}\",\"{DateTime.Now:yyyy-MM-dd HH:mm:ss}\"");
        sb.AppendLine();

        // Header
        sb.AppendLine(string.Join(",", new[]
        {
            Csv(T["report.col.number"]),
            Csv(T["report.col.group"]),
            Csv(T["report.text.copies"]),
            Csv(T["report.col.site"]),
            Csv(T["report.col.name"]),
            Csv(T["report.col.library"]),
            Csv(T["report.col.path"]),
            Csv(T["report.col.size_bytes"]),
            Csv(T["report.col.created"]),
            Csv(T["report.col.modified"]),
        }));

        foreach (var g in groups)
        {
            int i = 0;
            foreach (var item in g.Items)
            {
                i++;
                sb.AppendLine(string.Join(",", new[]
                {
                    Csv(i.ToString()),
                    Csv(g.Name),
                    Csv(g.Items.Count.ToString()),
                    Csv(item.SiteTitle),
                    Csv(item.Name),
                    Csv(item.Library),
                    Csv(item.Path),
                    Csv(item.SizeBytes?.ToString() ?? string.Empty),
                    Csv(item.Created?.ToString("yyyy-MM-dd") ?? string.Empty),
                    Csv(item.Modified?.ToString("yyyy-MM-dd") ?? string.Empty),
                }));
            }
        }

        return sb.ToString();
    }

    private static string Csv(string value) => CsvSanitizer.Escape(value);
}