using System.IO;
using Microsoft.SharePoint.Client;
using Serilog;
using SharepointToolbox.Core.Helpers;
using SharepointToolbox.Core.Models;

namespace SharepointToolbox.Services;

/// <summary>
/// Orchestrates server-side file copy/move between two SharePoint libraries
/// (same or different tenants). Uses <see cref="MoveCopyUtil"/> for the
/// transfer itself so bytes never round-trip through the local machine.
/// Folder creation and enumeration are done via CSOM; all ambient retries
/// flow through <see cref="ExecuteQueryRetryHelper"/>.
/// </summary>
public class FileTransferService : IFileTransferService
{
    /// <summary>
    /// Runs the configured <see cref="TransferJob"/>. Enumerates source files
    /// (unless the job is folder-only), pre-creates destination folders, then
    /// copies or moves each file according to <see cref="TransferJob.Mode"/>
    /// and <see cref="TransferJob.ConflictPolicy"/>. Returns a per-item
    /// summary where failures are reported individually — the method does
    /// not abort on first error so partial transfers are recoverable.
    /// </summary>
    public async Task<BulkOperationSummary<string>> TransferAsync(
        ClientContext sourceCtx,
        ClientContext destCtx,
        TransferJob job,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        // 1. Enumerate files from source (unless contents are suppressed).
        IReadOnlyList<string> files;
        if (job.CopyFolderContents)
        {
            progress.Report(new OperationProgress(0, 0, "Enumerating source files..."));
            files = await EnumerateFilesAsync(sourceCtx, job, progress, ct);
        }
        else
        {
            files = Array.Empty<string>();
        }

        // When CopyFolderContents is off, the job is folder-only: ensure the
        // destination folder is created below (IncludeSourceFolder branch) and
        // return without iterating any files.
        if (files.Count == 0 && !job.IncludeSourceFolder)
        {
            progress.Report(new OperationProgress(0, 0, "No files found to transfer."));
            return new BulkOperationSummary<string>(new List<BulkItemResult<string>>());
        }

        // 2. Build source and destination base paths. Resolve library roots via
        // CSOM — constructing from title breaks for localized libraries whose
        // URL segment differs (e.g. title "Documents" → URL "Shared Documents"),
        // causing "Access denied" when CSOM tries to touch a non-existent path.
        var srcBasePath = await ResolveLibraryPathAsync(
            sourceCtx, job.SourceLibrary, job.SourceFolderPath, progress, ct);
        var dstBasePath = await ResolveLibraryPathAsync(
            destCtx, job.DestinationLibrary, job.DestinationFolderPath, progress, ct);

        // When IncludeSourceFolder is set, recreate the source folder name under
        // destination so dest/srcFolderName/... mirrors the source tree. When
        // no SourceFolderPath is set, fall back to the source library name.
        // Also pre-create the folder itself — per-file EnsureFolder only fires
        // for nested paths, so flat files at the root of the source folder
        // would otherwise copy into a missing parent and fail.
        if (job.IncludeSourceFolder)
        {
            var srcFolderName = !string.IsNullOrEmpty(job.SourceFolderPath)
                ? Path.GetFileName(job.SourceFolderPath.TrimEnd('/'))
                : job.SourceLibrary;
            if (!string.IsNullOrEmpty(srcFolderName))
            {
                dstBasePath = $"{dstBasePath}/{srcFolderName}";
                await EnsureFolderAsync(destCtx, dstBasePath, progress, ct);
            }
        }

        // 3. Transfer each file using BulkOperationRunner
        return await BulkOperationRunner.RunAsync(
            files,
            async (fileRelUrl, idx, token) =>
            {
                // Compute destination path by replacing source base with dest base
                var relativePart = fileRelUrl;
                if (fileRelUrl.StartsWith(srcBasePath, StringComparison.OrdinalIgnoreCase))
                    relativePart = fileRelUrl.Substring(srcBasePath.Length).TrimStart('/');

                // Ensure destination folder exists
                var destFolderRelative = dstBasePath;
                var fileFolder = Path.GetDirectoryName(relativePart)?.Replace('\\', '/');
                if (!string.IsNullOrEmpty(fileFolder))
                {
                    destFolderRelative = $"{dstBasePath}/{fileFolder}";
                    await EnsureFolderAsync(destCtx, destFolderRelative, progress, token);
                }

                var fileName = Path.GetFileName(relativePart);
                var destFileUrl = $"{destFolderRelative}/{fileName}";

                await TransferSingleFileAsync(sourceCtx, destCtx, fileRelUrl, destFileUrl, job, progress, token);

                Log.Information("Transferred: {Source} -> {Dest}", fileRelUrl, destFileUrl);
            },
            progress,
            ct);
    }

    private async Task TransferSingleFileAsync(
        ClientContext sourceCtx,
        ClientContext destCtx,
        string srcFileUrl,
        string dstFileUrl,
        TransferJob job,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        // MoveCopyUtil.CopyFileByPath expects absolute URLs (scheme + host),
        // not server-relative paths. Passing "/sites/..." silently fails or
        // returns no error yet copies nothing — especially across site
        // collections. Prefix with the owning site's scheme+host.
        var srcAbs  = ToAbsoluteUrl(sourceCtx, srcFileUrl);
        var dstAbs  = ToAbsoluteUrl(destCtx, dstFileUrl);
        var srcPath = ResourcePath.FromDecodedUrl(srcAbs);
        var dstPath = ResourcePath.FromDecodedUrl(dstAbs);

        bool overwrite = job.ConflictPolicy == ConflictPolicy.Overwrite;
        var options = new MoveCopyOptions
        {
            KeepBoth = job.ConflictPolicy == ConflictPolicy.Rename,
            ResetAuthorAndCreatedOnCopy = false, // best-effort metadata preservation
        };

        try
        {
            if (job.Mode == TransferMode.Copy)
            {
                MoveCopyUtil.CopyFileByPath(sourceCtx, srcPath, dstPath, overwrite, options);
                await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(sourceCtx, progress, ct);
            }
            else // Move
            {
                MoveCopyUtil.MoveFileByPath(sourceCtx, srcPath, dstPath, overwrite, options);
                await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(sourceCtx, progress, ct);
            }
        }
        catch (ServerException ex) when (job.ConflictPolicy == ConflictPolicy.Skip &&
                                          ex.Message.Contains("already exists", StringComparison.OrdinalIgnoreCase))
        {
            Log.Warning("Skipped (already exists): {File}", srcFileUrl);
        }
    }

    private async Task<IReadOnlyList<string>> EnumerateFilesAsync(
        ClientContext ctx,
        TransferJob job,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        var list = ctx.Web.Lists.GetByTitle(job.SourceLibrary);
        var rootFolder = list.RootFolder;
        ctx.Load(rootFolder, f => f.ServerRelativeUrl);
        await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

        var libraryRoot = rootFolder.ServerRelativeUrl.TrimEnd('/');

        // Explicit per-file selection overrides folder enumeration. Paths are
        // library-relative (e.g. "SubFolder/file.docx") and get resolved to
        // full server-relative URLs here.
        if (job.SelectedFilePaths.Count > 0)
        {
            return job.SelectedFilePaths
                .Where(p => !string.IsNullOrWhiteSpace(p))
                .Select(p => $"{libraryRoot}/{p.TrimStart('/')}")
                .ToList();
        }

        var baseFolderUrl = libraryRoot;
        if (!string.IsNullOrEmpty(job.SourceFolderPath))
            baseFolderUrl = $"{baseFolderUrl}/{job.SourceFolderPath.TrimStart('/')}";

        // Paginated recursive CAML query — Folder.Files / Folder.Folders lazy
        // loading hits the list-view threshold on libraries > 5,000 items.
        var files = new List<string>();

        await foreach (var item in SharePointPaginationHelper.GetItemsInFolderAsync(
            ctx, list, baseFolderUrl, recursive: true,
            viewFields: new[] { "FSObjType", "FileRef", "FileDirRef" },
            ct: ct))
        {
            ct.ThrowIfCancellationRequested();

            if (item["FSObjType"]?.ToString() != "0") continue; // files only

            var fileRef = item["FileRef"]?.ToString();
            if (string.IsNullOrEmpty(fileRef)) continue;

            // Skip files under SharePoint system folders (e.g. "Forms", "_*").
            var dir = item["FileDirRef"]?.ToString() ?? string.Empty;
            if (HasSystemFolderSegment(dir, baseFolderUrl)) continue;

            files.Add(fileRef);
        }

        return files;
    }

    private static bool HasSystemFolderSegment(string fileDirRef, string baseFolderUrl)
    {
        if (string.IsNullOrEmpty(fileDirRef)) return false;
        var baseTrim = baseFolderUrl.TrimEnd('/');
        if (!fileDirRef.StartsWith(baseTrim, StringComparison.OrdinalIgnoreCase))
            return false;

        var tail = fileDirRef.Substring(baseTrim.Length).Trim('/');
        if (string.IsNullOrEmpty(tail)) return false;

        foreach (var seg in tail.Split('/', StringSplitOptions.RemoveEmptyEntries))
        {
            if (seg.StartsWith("_", StringComparison.Ordinal) ||
                seg.Equals("Forms", StringComparison.OrdinalIgnoreCase))
                return true;
        }
        return false;
    }

    private async Task EnsureFolderAsync(
        ClientContext ctx,
        string folderServerRelativeUrl,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        folderServerRelativeUrl = folderServerRelativeUrl.TrimEnd('/');

        // Already there?
        try
        {
            var existing = ctx.Web.GetFolderByServerRelativeUrl(folderServerRelativeUrl);
            ctx.Load(existing, f => f.Exists);
            await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);
            if (existing.Exists) return;
        }
        catch { /* not present — fall through to creation */ }

        // Walk the path, creating each missing segment. `Web.Folders.Add(url)` is
        // ambiguous across CSOM versions (some treat the arg as relative to Web,
        // others server-relative), which produces bogus paths + "Access denied".
        // Resolve the parent explicitly and add only the leaf name instead.
        int slash = folderServerRelativeUrl.LastIndexOf('/');
        if (slash <= 0) return;

        var parentUrl = folderServerRelativeUrl.Substring(0, slash);
        var leafName = folderServerRelativeUrl.Substring(slash + 1);
        if (string.IsNullOrEmpty(leafName)) return;

        // Recurse to guarantee the parent exists first.
        await EnsureFolderAsync(ctx, parentUrl, progress, ct);

        var parent = ctx.Web.GetFolderByServerRelativeUrl(parentUrl);
        parent.Folders.Add(leafName);
        try
        {
            await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);
        }
        catch (Exception ex)
        {
            Log.Warning("EnsureFolder failed at {Parent}/{Leaf}: {Error}",
                parentUrl, leafName, ex.Message);
            throw;
        }
    }

    private static string ToAbsoluteUrl(ClientContext ctx, string pathOrUrl)
    {
        if (pathOrUrl.StartsWith("http://", StringComparison.OrdinalIgnoreCase) ||
            pathOrUrl.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
            return pathOrUrl;

        var uri = new Uri(ctx.Url);
        return $"{uri.Scheme}://{uri.Host}{(pathOrUrl.StartsWith("/") ? "" : "/")}{pathOrUrl}";
    }

    private static async Task<string> ResolveLibraryPathAsync(
        ClientContext ctx,
        string libraryTitle,
        string relativeFolderPath,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        var list = ctx.Web.Lists.GetByTitle(libraryTitle);
        ctx.Load(list, l => l.RootFolder.ServerRelativeUrl);
        await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

        var basePath = list.RootFolder.ServerRelativeUrl.TrimEnd('/');
        if (!string.IsNullOrEmpty(relativeFolderPath))
            basePath = $"{basePath}/{relativeFolderPath.TrimStart('/')}";
        return basePath;
    }
}