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

namespace SharepointToolbox.Services;

/// <summary>
/// CSOM-based storage metrics scanner.
/// Captures every storage source SharePoint reports for a site:
/// document libraries (visible + hidden), the Preservation Hold Library,
/// list attachments, the recycle bin (1st + 2nd stage), and optionally
/// subsites. Each <see cref="StorageNode"/> carries a <see cref="StorageNodeKind"/>
/// so the caller can filter what appears in the report.
/// </summary>
public class StorageService : IStorageService
{
    // PreservationHoldLibrary base template id.
    private const int PreservationHoldTemplate = 851;

    public async Task<IReadOnlyList<StorageNode>> CollectStorageAsync(
        ClientContext ctx,
        StorageScanOptions options,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        var result = new List<StorageNode>();
        await CollectForWebAsync(ctx, ctx.Web, options, result, progress, ct);
        return result;
    }

    private async Task CollectForWebAsync(
        ClientContext ctx,
        Web web,
        StorageScanOptions options,
        List<StorageNode> result,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        ct.ThrowIfCancellationRequested();

        ctx.Load(web,
            w => w.Title,
            w => w.Url,
            w => w.ServerRelativeUrl,
            w => w.Lists.Include(
                l => l.Title,
                l => l.Hidden,
                l => l.BaseType,
                l => l.BaseTemplate,
                l => l.ItemCount,
                l => l.RootFolder.ServerRelativeUrl));
        if (options.IncludeSubsites)
            ctx.Load(web.Webs, ws => ws.Include(w => w.ServerRelativeUrl, w => w.Title));
        await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

        string siteTitle = web.Title;
        var lists = web.Lists.ToList();

        // ── Document libraries (incl. hidden + Preservation Hold) ───────────
        var docLibs = lists.Where(l => l.BaseType == BaseType.DocumentLibrary).ToList();
        int idx = 0;
        foreach (var lib in docLibs)
        {
            ct.ThrowIfCancellationRequested();
            idx++;

            StorageNodeKind kind = ClassifyLibrary(lib);
            if (kind == StorageNodeKind.HiddenLibrary && !options.IncludeHiddenLibraries) continue;
            if (kind == StorageNodeKind.PreservationHold && !options.IncludePreservationHold) continue;

            progress.Report(new OperationProgress(idx, docLibs.Count,
                $"Loading storage metrics: {lib.Title} ({idx}/{docLibs.Count})"));

            var libNode = await LoadFolderNodeAsync(
                ctx, lib.RootFolder.ServerRelativeUrl, lib.Title,
                siteTitle, lib.Title, 0, kind, progress, ct);

            if (options.FolderDepth > 0)
            {
                await CollectSubfoldersAsync(
                    ctx, lib, lib.RootFolder.ServerRelativeUrl,
                    libNode, 1, options.FolderDepth,
                    siteTitle, lib.Title, kind, progress, ct);
            }

            result.Add(libNode);
        }

        // ── List attachments (non-document-library lists) ───────────────────
        if (options.IncludeListAttachments)
        {
            var nonDocLists = lists
                .Where(l => l.BaseType != BaseType.DocumentLibrary && !l.Hidden && l.ItemCount > 0)
                .ToList();

            int aIdx = 0;
            foreach (var list in nonDocLists)
            {
                ct.ThrowIfCancellationRequested();
                aIdx++;
                progress.Report(new OperationProgress(aIdx, nonDocLists.Count,
                    $"Scanning list attachments: {list.Title} ({aIdx}/{nonDocLists.Count})"));

                var attachNode = await TryLoadAttachmentsNodeAsync(ctx, list, siteTitle, progress, ct);
                if (attachNode != null && attachNode.TotalSizeBytes > 0)
                    result.Add(attachNode);
            }
        }

        // ── Recycle bin (stage 1 + stage 2) ─────────────────────────────────
        if (options.IncludeRecycleBin)
        {
            progress.Report(OperationProgress.Indeterminate(
                $"Scanning recycle bin: {siteTitle}..."));

            var rbNodes = await LoadRecycleBinNodesAsync(ctx, siteTitle, progress, ct);
            result.AddRange(rbNodes);
        }

        // ── Subsites (recursive) ────────────────────────────────────────────
        if (options.IncludeSubsites)
        {
            var subwebs = web.Webs.ToList();
            foreach (var sub in subwebs)
            {
                ct.ThrowIfCancellationRequested();

                // Build a node header so subsite results are visually grouped.
                var subResult = new List<StorageNode>();
                await CollectForWebAsync(ctx, sub, options, subResult, progress, ct);
                if (subResult.Count == 0) continue;

                var subRoot = new StorageNode
                {
                    Name           = sub.Title,
                    Url            = ctx.Url.TrimEnd('/') + sub.ServerRelativeUrl,
                    SiteTitle      = sub.Title,
                    Library        = string.Empty,
                    Kind           = StorageNodeKind.Subsite,
                    IndentLevel    = 0,
                    Children       = subResult,
                    TotalSizeBytes      = subResult.Sum(n => n.TotalSizeBytes),
                    FileStreamSizeBytes = subResult.Sum(n => n.FileStreamSizeBytes),
                    TotalFileCount      = subResult.Sum(n => n.TotalFileCount)
                };
                result.Add(subRoot);
            }
        }
    }

    private static StorageNodeKind ClassifyLibrary(List lib)
    {
        if (lib.BaseTemplate == PreservationHoldTemplate ||
            string.Equals(lib.Title, "Preservation Hold Library", StringComparison.OrdinalIgnoreCase))
            return StorageNodeKind.PreservationHold;
        return lib.Hidden ? StorageNodeKind.HiddenLibrary : StorageNodeKind.Library;
    }

    private static async Task<StorageNode?> TryLoadAttachmentsNodeAsync(
        ClientContext ctx,
        List list,
        string siteTitle,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        // Per-list attachments live in <listRootFolder>/Attachments/<itemId>/<file>.
        // The Attachments folder may or may not exist depending on whether any
        // item ever had an attachment — guard with try/catch.
        string attachmentsUrl = list.RootFolder.ServerRelativeUrl.TrimEnd('/') + "/Attachments";

        try
        {
            var folder = ctx.Web.GetFolderByServerRelativeUrl(attachmentsUrl);
            ctx.Load(folder,
                f => f.Exists,
                f => f.StorageMetrics,
                f => f.TimeLastModified,
                f => f.ServerRelativeUrl);
            await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

            if (!folder.Exists || folder.StorageMetrics.TotalFileCount == 0)
                return null;

            DateTime? lastMod = folder.StorageMetrics.LastModified > DateTime.MinValue
                ? folder.StorageMetrics.LastModified
                : folder.TimeLastModified > DateTime.MinValue
                    ? folder.TimeLastModified
                    : (DateTime?)null;

            return new StorageNode
            {
                Name                = $"[Attachments] {list.Title}",
                Url                 = ctx.Url.TrimEnd('/') + attachmentsUrl,
                SiteTitle           = siteTitle,
                Library             = list.Title,
                Kind                = StorageNodeKind.ListAttachments,
                TotalSizeBytes      = folder.StorageMetrics.TotalSize,
                FileStreamSizeBytes = folder.StorageMetrics.TotalFileStreamSize,
                TotalFileCount      = folder.StorageMetrics.TotalFileCount,
                LastModified        = lastMod,
                IndentLevel         = 0,
                Children            = new List<StorageNode>()
            };
        }
        catch
        {
            // Attachments folder absent for this list — not an error.
            return null;
        }
    }

    private static async Task<List<StorageNode>> LoadRecycleBinNodesAsync(
        ClientContext ctx,
        string siteTitle,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        var nodes = new List<StorageNode>();

        try
        {
            var bin = ctx.Site.RecycleBin;
            ctx.Load(bin, b => b.Include(
                i => i.Size,
                i => i.ItemState,
                i => i.DeletedDate));
            await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

            long stage1Size = 0, stage2Size = 0;
            int stage1Count = 0, stage2Count = 0;
            DateTime? stage1Last = null, stage2Last = null;

            foreach (var item in bin)
            {
                if (item.ItemState == RecycleBinItemState.SecondStageRecycleBin)
                {
                    stage2Size += item.Size;
                    stage2Count++;
                    if (stage2Last is null || item.DeletedDate > stage2Last) stage2Last = item.DeletedDate;
                }
                else
                {
                    stage1Size += item.Size;
                    stage1Count++;
                    if (stage1Last is null || item.DeletedDate > stage1Last) stage1Last = item.DeletedDate;
                }
            }

            if (stage1Count > 0)
                nodes.Add(new StorageNode
                {
                    Name                = "[Recycle Bin] First-stage",
                    SiteTitle           = siteTitle,
                    Library             = "RecycleBin",
                    Kind                = StorageNodeKind.RecycleBin,
                    TotalSizeBytes      = stage1Size,
                    FileStreamSizeBytes = stage1Size,
                    TotalFileCount      = stage1Count,
                    LastModified        = stage1Last,
                    IndentLevel         = 0,
                    Children            = new List<StorageNode>()
                });

            if (stage2Count > 0)
                nodes.Add(new StorageNode
                {
                    Name                = "[Recycle Bin] Second-stage",
                    SiteTitle           = siteTitle,
                    Library             = "RecycleBin",
                    Kind                = StorageNodeKind.RecycleBin,
                    TotalSizeBytes      = stage2Size,
                    FileStreamSizeBytes = stage2Size,
                    TotalFileCount      = stage2Count,
                    LastModified        = stage2Last,
                    IndentLevel         = 0,
                    Children            = new List<StorageNode>()
                });
        }
        catch
        {
            // Insufficient permission to read recycle bin or feature unavailable.
        }

        return nodes;
    }

    public async Task<IReadOnlyList<FileTypeMetric>> CollectFileTypeMetricsAsync(
        ClientContext ctx,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        ct.ThrowIfCancellationRequested();

        ctx.Load(ctx.Web,
            w => w.Lists.Include(
                l => l.Title,
                l => l.Hidden,
                l => l.BaseType,
                l => l.ItemCount));
        await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

        var libs = ctx.Web.Lists
            .Where(l => !l.Hidden && l.BaseType == BaseType.DocumentLibrary)
            .ToList();

        var extensionMap = new Dictionary<string, (long totalSize, int count)>(StringComparer.OrdinalIgnoreCase);

        int libIdx = 0;
        foreach (var lib in libs)
        {
            ct.ThrowIfCancellationRequested();
            libIdx++;
            progress.Report(new OperationProgress(libIdx, libs.Count,
                $"Scanning files by type: {lib.Title} ({libIdx}/{libs.Count})"));

            var query = new CamlQuery
            {
                ViewXml = @"<View Scope='RecursiveAll'>
                    <Query></Query>
                    <ViewFields>
                        <FieldRef Name='FSObjType' />
                        <FieldRef Name='FileLeafRef' />
                        <FieldRef Name='File_x0020_Size' />
                    </ViewFields>
                    <RowLimit Paged='TRUE'>5000</RowLimit>
                </View>"
            };

            ListItemCollection items;
            do
            {
                ct.ThrowIfCancellationRequested();
                items = lib.GetItems(query);
                ctx.Load(items, ic => ic.ListItemCollectionPosition,
                    ic => ic.Include(
                        i => i["FSObjType"],
                        i => i["FileLeafRef"],
                        i => i["File_x0020_Size"]));
                await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

                foreach (var item in items)
                {
                    if (item["FSObjType"]?.ToString() != "0") continue;

                    string fileName = item["FileLeafRef"]?.ToString() ?? string.Empty;
                    string sizeStr = item["File_x0020_Size"]?.ToString() ?? "0";

                    if (!long.TryParse(sizeStr, out long fileSize))
                        fileSize = 0;

                    string ext = Path.GetExtension(fileName).ToLowerInvariant();

                    if (extensionMap.TryGetValue(ext, out var existing))
                        extensionMap[ext] = (existing.totalSize + fileSize, existing.count + 1);
                    else
                        extensionMap[ext] = (fileSize, 1);
                }

                query.ListItemCollectionPosition = items.ListItemCollectionPosition;
            }
            while (items.ListItemCollectionPosition != null);
        }

        return extensionMap
            .Select(kvp => new FileTypeMetric(kvp.Key, kvp.Value.totalSize, kvp.Value.count))
            .OrderByDescending(m => m.TotalSizeBytes)
            .ToList();
    }

    public async Task BackfillZeroNodesAsync(
        ClientContext ctx,
        IReadOnlyList<StorageNode> nodes,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        // Only backfill nodes scanned through CSOM document-library StorageMetrics —
        // synthetic categories (recycle bin, list attachments, subsite headers)
        // cannot be re-derived from File_x0020_Size.
        var libNodes = nodes.Where(n => n.IndentLevel == 0 &&
            (n.Kind == StorageNodeKind.Library ||
             n.Kind == StorageNodeKind.HiddenLibrary ||
             n.Kind == StorageNodeKind.PreservationHold)).ToList();
        var needsBackfill = libNodes.Where(lib =>
            lib.TotalFileCount == 0 || HasZeroChild(lib)).ToList();
        if (needsBackfill.Count == 0) return;

        ctx.Load(ctx.Web, w => w.ServerRelativeUrl,
            w => w.Lists.Include(
                l => l.Title, l => l.Hidden, l => l.BaseType,
                l => l.RootFolder.ServerRelativeUrl));
        await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

        var libs = ctx.Web.Lists
            .Where(l => l.BaseType == BaseType.DocumentLibrary)
            .ToDictionary(l => l.Title, StringComparer.OrdinalIgnoreCase);

        int idx = 0;
        foreach (var libNode in needsBackfill)
        {
            ct.ThrowIfCancellationRequested();
            idx++;

            if (!libs.TryGetValue(libNode.Library, out var lib)) continue;

            progress.Report(new OperationProgress(idx, needsBackfill.Count,
                $"Counting files: {libNode.Name} ({idx}/{needsBackfill.Count})"));

            string libRootSrl = lib.RootFolder.ServerRelativeUrl.TrimEnd('/');

            var folderLookup = new Dictionary<string, StorageNode>(StringComparer.OrdinalIgnoreCase);
            BuildFolderLookup(libNode, libRootSrl, folderLookup);

            var originalTotals = new Dictionary<StorageNode, long>();
            CaptureTotals(libNode, originalTotals);

            ResetNodeCounts(libNode);

            var query = new CamlQuery
            {
                ViewXml = @"<View Scope='RecursiveAll'>
                    <Query></Query>
                    <ViewFields>
                        <FieldRef Name='FSObjType' />
                        <FieldRef Name='FileDirRef' />
                        <FieldRef Name='File_x0020_Size' />
                        <FieldRef Name='SMTotalSize' />
                        <FieldRef Name='SMTotalFileStreamSize' />
                    </ViewFields>
                    <RowLimit Paged='TRUE'>5000</RowLimit>
                </View>"
            };

            ListItemCollection items;
            do
            {
                ct.ThrowIfCancellationRequested();
                items = lib.GetItems(query);
                ctx.Load(items, ic => ic.ListItemCollectionPosition,
                    ic => ic.Include(
                        i => i["FSObjType"],
                        i => i["FileDirRef"],
                        i => i["File_x0020_Size"],
                        i => i["SMTotalSize"],
                        i => i["SMTotalFileStreamSize"]));
                await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

                foreach (var item in items)
                {
                    if (item["FSObjType"]?.ToString() != "0") continue;

                    long streamSize = ParseLong(item["File_x0020_Size"]);
                    long smStream   = ParseLong(SafeGet(item, "SMTotalFileStreamSize"));
                    long smTotal    = ParseLong(SafeGet(item, "SMTotalSize"));

                    if (smStream > 0) streamSize = smStream;
                    long totalSize = smTotal > 0 ? smTotal : streamSize;

                    string fileDirRef = item["FileDirRef"]?.ToString() ?? "";

                    libNode.TotalSizeBytes += totalSize;
                    libNode.FileStreamSizeBytes += streamSize;
                    libNode.TotalFileCount++;

                    var matchedFolder = FindDeepestFolder(fileDirRef, folderLookup);
                    if (matchedFolder != null && matchedFolder != libNode)
                    {
                        matchedFolder.TotalSizeBytes += totalSize;
                        matchedFolder.FileStreamSizeBytes += streamSize;
                        matchedFolder.TotalFileCount++;
                    }
                }

                query.ListItemCollectionPosition = items.ListItemCollectionPosition;
            }
            while (items.ListItemCollectionPosition != null);

            foreach (var kv in originalTotals)
            {
                if (kv.Value > kv.Key.TotalSizeBytes)
                    kv.Key.TotalSizeBytes = kv.Value;
            }
        }
    }

    public async Task<long> GetSiteUsageStorageBytesAsync(
        ClientContext ctx,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        try
        {
            ctx.Load(ctx.Site, s => s.Usage);
            await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);
            return ctx.Site.Usage.Storage;
        }
        catch
        {
            return 0L;
        }
    }

    private static long ParseLong(object? value)
    {
        if (value == null) return 0;
        return long.TryParse(value.ToString(), out long n) ? n : 0;
    }

    private static object? SafeGet(ListItem item, string fieldName)
    {
        try { return item[fieldName]; }
        catch { return null; }
    }

    private static void CaptureTotals(StorageNode node, Dictionary<StorageNode, long> map)
    {
        map[node] = node.TotalSizeBytes;
        foreach (var child in node.Children)
            CaptureTotals(child, map);
    }

    private static bool HasZeroChild(StorageNode node)
    {
        foreach (var child in node.Children)
        {
            if (child.TotalFileCount == 0) return true;
            if (HasZeroChild(child)) return true;
        }
        return false;
    }

    private static void ResetNodeCounts(StorageNode node)
    {
        node.TotalSizeBytes = 0;
        node.FileStreamSizeBytes = 0;
        node.TotalFileCount = 0;
        foreach (var child in node.Children)
            ResetNodeCounts(child);
    }

    private static void BuildFolderLookup(StorageNode node, string parentPath,
        Dictionary<string, StorageNode> lookup)
    {
        string nodePath = node.IndentLevel == 0
            ? parentPath
            : parentPath + "/" + node.Name;
        lookup[nodePath] = node;

        foreach (var child in node.Children)
            BuildFolderLookup(child, nodePath, lookup);
    }

    private static StorageNode? FindDeepestFolder(string fileDirRef,
        Dictionary<string, StorageNode> lookup)
    {
        string path = fileDirRef.TrimEnd('/');
        while (!string.IsNullOrEmpty(path))
        {
            if (lookup.TryGetValue(path, out var node))
                return node;
            int lastSlash = path.LastIndexOf('/');
            if (lastSlash <= 0) break;
            path = path[..lastSlash];
        }
        return null;
    }

    // ── Library/folder loading helpers ──────────────────────────────────────

    private static async Task<StorageNode> LoadFolderNodeAsync(
        ClientContext ctx,
        string serverRelativeUrl,
        string name,
        string siteTitle,
        string library,
        int indentLevel,
        StorageNodeKind kind,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        ct.ThrowIfCancellationRequested();

        Folder folder = ctx.Web.GetFolderByServerRelativeUrl(serverRelativeUrl);
        ctx.Load(folder,
            f => f.StorageMetrics,
            f => f.TimeLastModified,
            f => f.ServerRelativeUrl,
            f => f.Name);
        await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

        DateTime? lastMod = folder.StorageMetrics.LastModified > DateTime.MinValue
            ? folder.StorageMetrics.LastModified
            : folder.TimeLastModified > DateTime.MinValue
                ? folder.TimeLastModified
                : (DateTime?)null;

        return new StorageNode
        {
            Name                = name,
            Url                 = ctx.Url.TrimEnd('/') + serverRelativeUrl,
            SiteTitle           = siteTitle,
            Library             = library,
            Kind                = kind,
            TotalSizeBytes      = folder.StorageMetrics.TotalSize,
            FileStreamSizeBytes = folder.StorageMetrics.TotalFileStreamSize,
            TotalFileCount      = folder.StorageMetrics.TotalFileCount,
            LastModified        = lastMod,
            IndentLevel         = indentLevel,
            Children            = new List<StorageNode>()
        };
    }

    private static async Task CollectSubfoldersAsync(
        ClientContext ctx,
        List list,
        string parentServerRelativeUrl,
        StorageNode parentNode,
        int currentDepth,
        int maxDepth,
        string siteTitle,
        string library,
        StorageNodeKind kind,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        if (currentDepth > maxDepth) return;
        ct.ThrowIfCancellationRequested();

        var subfolders = new List<(string Name, string ServerRelativeUrl)>();

        await foreach (var item in SharePointPaginationHelper.GetItemsInFolderAsync(
            ctx, list, parentServerRelativeUrl, recursive: false,
            viewFields: new[] { "FSObjType", "FileLeafRef", "FileRef" },
            ct: ct))
        {
            if (item["FSObjType"]?.ToString() != "1") continue;

            string name = item["FileLeafRef"]?.ToString() ?? string.Empty;
            string url  = item["FileRef"]?.ToString() ?? string.Empty;
            if (string.IsNullOrEmpty(name) || string.IsNullOrEmpty(url)) continue;

            if (name.Equals("Forms", StringComparison.OrdinalIgnoreCase) ||
                name.StartsWith("_", StringComparison.Ordinal))
                continue;

            subfolders.Add((name, url));
        }

        foreach (var sub in subfolders)
        {
            ct.ThrowIfCancellationRequested();

            var childNode = await LoadFolderNodeAsync(
                ctx, sub.ServerRelativeUrl, sub.Name,
                siteTitle, library, currentDepth, kind, progress, ct);

            if (currentDepth < maxDepth)
            {
                await CollectSubfoldersAsync(
                    ctx, list, sub.ServerRelativeUrl, childNode,
                    currentDepth + 1, maxDepth,
                    siteTitle, library, kind, progress, ct);
            }

            parentNode.Children.Add(childNode);
        }
    }
}