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

namespace SharepointToolbox.Services;

/// <summary>
/// CSOM-based storage metrics scanner.
/// Port of PowerShell Collect-FolderStorage / Get-PnPFolderStorageMetric pattern.
/// </summary>
public class StorageService : IStorageService
{
    /// <summary>
    /// Collects per-library and per-folder storage metrics for a single
    /// SharePoint site. Depth and indentation are controlled via
    /// <paramref name="options"/>; libraries flagged <c>Hidden</c> are skipped.
    /// Traversal is breadth-first and leans on <see cref="SharePointPaginationHelper"/>
    /// so libraries above the 5,000-item threshold remain scannable.
    /// </summary>
    public async Task<IReadOnlyList<StorageNode>> CollectStorageAsync(
        ClientContext ctx,
        StorageScanOptions options,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        ct.ThrowIfCancellationRequested();

        // Load web-level metadata in one round-trip
        ctx.Load(ctx.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.RootFolder.ServerRelativeUrl));
        await ExecuteQueryRetryHelper.ExecuteQueryRetryAsync(ctx, progress, ct);

        string webSrl = ctx.Web.ServerRelativeUrl.TrimEnd('/');
        string siteTitle = ctx.Web.Title;

        var result = new List<StorageNode>();
        var libs = ctx.Web.Lists
            .Where(l => !l.Hidden && l.BaseType == BaseType.DocumentLibrary)
            .ToList();

        int idx = 0;
        foreach (var lib in libs)
        {
            ct.ThrowIfCancellationRequested();
            idx++;
            progress.Report(new OperationProgress(idx, libs.Count,
                $"Loading storage metrics: {lib.Title} ({idx}/{libs.Count})"));

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

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

            result.Add(libNode);
        }

        return result;
    }

    /// <summary>
    /// Aggregates file counts and total sizes by extension across every
    /// non-hidden document library on the site. Extensions are normalised to
    /// lowercase; files without an extension roll up into a single bucket.
    /// </summary>
    public async Task<IReadOnlyList<FileTypeMetric>> CollectFileTypeMetricsAsync(
        ClientContext ctx,
        IProgress<OperationProgress> progress,
        CancellationToken ct)
    {
        ct.ThrowIfCancellationRequested();

        // Load all non-hidden document libraries
        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();

        // Accumulate file sizes by extension across all libraries
        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})"));

            // Paginated CAML without a WHERE clause — WHERE on non-indexed fields
            // (FSObjType) throws list-view threshold on libraries > 5,000 items.
            // Filter files client-side via FSObjType.
            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; // skip folders

                    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);
        }

        // Convert to FileTypeMetric list, sorted by size descending
        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)
    {
        // Find root-level library nodes that have any zero-valued nodes in their tree
        var libNodes = nodes.Where(n => n.IndentLevel == 0).ToList();
        var needsBackfill = libNodes.Where(lib =>
            lib.TotalFileCount == 0 || HasZeroChild(lib)).ToList();
        if (needsBackfill.Count == 0) return;

        // Load libraries to get RootFolder.ServerRelativeUrl for path matching
        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.Hidden && 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.Name, out var lib)) continue;

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

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

            // Build a lookup of all folder nodes in this library's tree (by server-relative path)
            var folderLookup = new Dictionary<string, StorageNode>(StringComparer.OrdinalIgnoreCase);
            BuildFolderLookup(libNode, libRootSrl, folderLookup);

            // Capture original TotalSizeBytes before reset — StorageMetrics.TotalSize
            // includes version overhead, which cannot be rederived from a file scan
            // (File_x0020_Size is the current stream size only).
            var originalTotals = new Dictionary<StorageNode, long>();
            CaptureTotals(libNode, originalTotals);

            // Reset all nodes in this tree to zero before accumulating
            ResetNodeCounts(libNode);

            // Paginated CAML without WHERE (filter folders client-side via FSObjType).
            // SMTotalSize = per-file total including all versions (version-aware).
            // SMTotalFileStreamSize = current stream only. File_x0020_Size is a fallback
            // when SMTotalSize is unavailable (older tenants / custom fields stripped).
            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; // skip folders

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

                    // Prefer SM fields when present; fall back to File_x0020_Size otherwise.
                    if (smStream > 0) streamSize = smStream;
                    long totalSize = smTotal > 0 ? smTotal : streamSize;

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

                    // Always count toward the library root
                    libNode.TotalSizeBytes += totalSize;
                    libNode.FileStreamSizeBytes += streamSize;
                    libNode.TotalFileCount++;

                    // Also count toward the most specific matching subfolder
                    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);

            // Restore original TotalSizeBytes where it exceeded the recomputed value.
            // Preserves StorageMetrics.TotalSize for nodes whose original metrics were
            // valid but SMTotalSize was missing on individual files.
            foreach (var kv in originalTotals)
            {
                if (kv.Value > kv.Key.TotalSizeBytes)
                    kv.Key.TotalSizeBytes = kv.Value;
            }
        }
    }

    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)
    {
        // fileDirRef is the server-relative folder path, e.g. "/sites/hr/Shared Documents/Reports"
        // Try exact match, then walk up until we find a match
        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;
    }

    // -- Private helpers -----------------------------------------------------

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

        // Enumerate direct child folders via paginated CAML scoped to the parent.
        // Folder.Folders lazy loading hits the list-view threshold on libraries
        // > 5,000 items; a paged CAML query with no WHERE bypasses it.
        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; // folders only

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

            // Skip SharePoint system folders
            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, progress, ct);

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

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