using Microsoft.SharePoint.Client;
using Microsoft.SharePoint.Client.Search.Query;
using SharepointToolbox.Core.Helpers;
using SharepointToolbox.Core.Models;
using System.Text.RegularExpressions;

namespace SharepointToolbox.Services;

/// <summary>
/// File search using SharePoint KQL Search API.
/// Port of PS Search-SPOFiles pattern (PS lines 4747-4987).
/// Pagination: 500 rows per batch, hard cap StartRow=50,000 (SharePoint Search boundary).
/// </summary>
public class SearchService : ISearchService
{
    private const int BatchSize = 500;
    private const int MaxStartRow = 50_000;

    public async Task<IReadOnlyList<SearchResult>> SearchFilesAsync(
        ClientContext ctx,
        SearchOptions options,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        ct.ThrowIfCancellationRequested();

        string kql = BuildKql(options);
        ValidateKqlLength(kql);

        Regex? regexFilter = null;
        if (!string.IsNullOrWhiteSpace(options.Regex))
        {
            regexFilter = new Regex(options.Regex,
                RegexOptions.IgnoreCase | RegexOptions.Compiled,
                TimeSpan.FromSeconds(2));
        }

        var allResults = new List<SearchResult>();
        int startRow = 0;
        int maxResults = Math.Min(options.MaxResults, MaxStartRow);

        do
        {
            ct.ThrowIfCancellationRequested();

            var kq = new KeywordQuery(ctx)
            {
                QueryText      = kql,
                StartRow       = startRow,
                RowLimit       = BatchSize,
                TrimDuplicates = false
            };
            foreach (var prop in new[] { "Title", "Path", "Author", "LastModifiedTime",
                "FileExtension", "Created", "ModifiedBy", "Size" })
                kq.SelectProperties.Add(prop);

            var executor = new SearchExecutor(ctx);
            ClientResult<ResultTableCollection> clientResult = executor.ExecuteQuery(kq);
            await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

            var table = clientResult.Value
                .FirstOrDefault(t => t.TableType == KnownTableTypes.RelevantResults);
            if (table == null || table.RowCount == 0) break;

            foreach (System.Collections.Hashtable row in table.ResultRows)
            {
                var dict = row.Cast<System.Collections.DictionaryEntry>()
                    .ToDictionary(e => e.Key.ToString()!, e => e.Value ?? (object)string.Empty);

                // Skip SharePoint version history paths
                string path = Str(dict, "Path");
                if (path.Contains("/_vti_history/", StringComparison.OrdinalIgnoreCase))
                    continue;

                var result = ParseRow(dict);

                // Client-side Regex filter on file name
                if (regexFilter != null)
                {
                    string fileName = System.IO.Path.GetFileName(result.Path);
                    if (!regexFilter.IsMatch(fileName) && !regexFilter.IsMatch(result.Title))
                        continue;
                }

                allResults.Add(result);
                if (allResults.Count >= maxResults) goto done;
            }

            progress.Report(new OperationProgress(allResults.Count, maxResults,
                $"Retrieved {allResults.Count:N0} results\u2026"));

            startRow += BatchSize;
        }
        while (startRow <= MaxStartRow && allResults.Count < maxResults);

        done:
        return allResults;
    }

    // ── Extension point: bypassing the 50,000-item cap ───────────────────────
    //
    // The StartRow approach has a hard ceiling at 50,000 (SharePoint Search boundary).
    // To go beyond it, replace the StartRow loop with a DocId cursor:
    //
    //   1. Add "DocId" to SelectProperties.
    //   2. Add query.SortList.Add("DocId", SortDirection.Ascending).
    //   3. First page KQL: unchanged.
    //      Subsequent pages: append "AND DocId>{lastDocId}" to the KQL (StartRow stays 0).
    //   4. Track lastDocId = Convert.ToInt64(lastRow["DocId"]) after each batch.
    //   5. Stop when batch.RowCount < BatchSize.
    //
    // Caveats:
    //   - DocId is per-site-collection; for multi-site searches, maintain a separate
    //     cursor per ClientContext (site URL).
    //   - The search index can shift between batches (new items indexed mid-scan);
    //     the DocId cursor is safer than StartRow but cannot guarantee zero drift.
    //   - DocId is not returned by default — it must be in SelectProperties.
    //
    // This is deliberately not implemented here because SRCH-02 caps results at 50,000,
    // which the StartRow approach already covers exactly (100 pages × 500 rows).
    // Implement the DocId cursor if the cap needs to be lifted in a future version.

    // ── KQL builder ───────────────────────────────────────────────────────────

    internal static string BuildKql(SearchOptions opts)
    {
        var parts = new List<string> { "ContentType:Document" };

        if (opts.Extensions.Length > 0)
        {
            var extParts = opts.Extensions
                .Select(e => $"FileExtension:{e.TrimStart('.').ToLowerInvariant()}");
            parts.Add($"({string.Join(" OR ", extParts)})");
        }
        if (opts.CreatedAfter.HasValue)
            parts.Add($"Created>={opts.CreatedAfter.Value:yyyy-MM-dd}");
        if (opts.CreatedBefore.HasValue)
            parts.Add($"Created<={opts.CreatedBefore.Value:yyyy-MM-dd}");
        if (opts.ModifiedAfter.HasValue)
            parts.Add($"Write>={opts.ModifiedAfter.Value:yyyy-MM-dd}");
        if (opts.ModifiedBefore.HasValue)
            parts.Add($"Write<={opts.ModifiedBefore.Value:yyyy-MM-dd}");
        if (!string.IsNullOrEmpty(opts.CreatedBy))
            parts.Add($"Author:\"{opts.CreatedBy}\"");
        if (!string.IsNullOrEmpty(opts.ModifiedBy))
            parts.Add($"ModifiedBy:\"{opts.ModifiedBy}\"");
        if (!string.IsNullOrEmpty(opts.Library) && !string.IsNullOrEmpty(opts.SiteUrl))
            parts.Add($"Path:\"{opts.SiteUrl.TrimEnd('/')}/{opts.Library.TrimStart('/')}*\"");

        return string.Join(" AND ", parts);
    }

    private static void ValidateKqlLength(string kql)
    {
        // SharePoint Search KQL text hard cap is 4096 characters
        if (kql.Length > 4096)
            throw new InvalidOperationException(
                $"KQL query exceeds 4096-character SharePoint Search limit ({kql.Length} chars). " +
                "Reduce the number of extension filters.");
    }

    // ── Row parser ────────────────────────────────────────────────────────────

    private static SearchResult ParseRow(IDictionary<string, object> row)
    {
        static string Str(IDictionary<string, object> r, string key) =>
            r.TryGetValue(key, out var v) ? v?.ToString() ?? string.Empty : string.Empty;

        static DateTime? Date(IDictionary<string, object> r, string key)
        {
            var s = Str(r, key);
            return DateTime.TryParse(s, out var dt) ? dt : (DateTime?)null;
        }

        static long ParseSize(IDictionary<string, object> r, string key)
        {
            var raw = Str(r, key);
            var digits = Regex.Replace(raw, "[^0-9]", "");
            return long.TryParse(digits, out var v) ? v : 0L;
        }

        return new SearchResult
        {
            Title         = Str(row, "Title"),
            Path          = Str(row, "Path"),
            FileExtension = Str(row, "FileExtension"),
            Created       = Date(row, "Created"),
            LastModified  = Date(row, "LastModifiedTime"),
            Author        = Str(row, "Author"),
            ModifiedBy    = Str(row, "ModifiedBy"),
            SizeBytes     = ParseSize(row, "Size")
        };
    }

    private static string Str(IDictionary<string, object> r, string key) =>
        r.TryGetValue(key, out var v) ? v?.ToString() ?? string.Empty : string.Empty;
}