using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using System.Diagnostics.CodeAnalysis;

namespace OpenArchival.DataAccess;

public class ArtifactGroupingProvider : IArtifactGroupingProvider
{
    private readonly IDbContextFactory<ApplicationDbContext>  _context;
    private readonly ILogger<ArtifactGroupingProvider> _logger;

    [SetsRequiredMembers]
    public ArtifactGroupingProvider(IDbContextFactory<ApplicationDbContext> context, ILogger<ArtifactGroupingProvider> logger)
    {
        _context = context;
        _logger = logger;
    }

    public async Task<ArtifactGrouping?> GetGroupingAsync(int id)
    {
        await using var context = await _context.CreateDbContextAsync();
        return await context.ArtifactGroupings
            .Include(g => g.Category)
            .Include(g => g.IdentifierFields)
            .Include(g => g.Type)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.StorageLocation)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Type)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Files)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Tags)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.ListedNames)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Defects)
            .Where(g => g.Id == id)
            .FirstOrDefaultAsync();
    }

    public async Task<ArtifactGrouping?> GetGroupingAsync(string artifactGroupingIdentifier)
    {
        await using var context = await _context.CreateDbContextAsync();
        return await context.ArtifactGroupings
            .Include(g => g.Category)
            .Include(g => g.IdentifierFields)
            .Include(g => g.Type)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.StorageLocation)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Type)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Files)
            .Include(g=> g.ChildArtifactEntries)
                .ThenInclude(e => e.Tags)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.ListedNames)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Defects)
            .Where(g => g.ArtifactGroupingIdentifier == artifactGroupingIdentifier)
            .FirstOrDefaultAsync();
    }

    public async Task CreateGroupingAsync(ArtifactGrouping grouping)
    {
        await using var context = await _context.CreateDbContextAsync();

        // Attach the Category to the context. If it has a key, it will be tracked.
        context.Attach(grouping.Category);

        var processedTypes = new Dictionary<string, ArtifactType>();

        // Helper function to get a de-duplicated type
        async Task<ArtifactType> GetUniqueTypeAsync(ArtifactType typeToProcess)
        {
            // If the type is null or has no name, do nothing.
            if (string.IsNullOrEmpty(typeToProcess?.Name))
            {
                return typeToProcess;
            }

            // A. First, check our local cache for the type.
            if (processedTypes.TryGetValue(typeToProcess.Name, out var uniqueType))
            {
                // Found it in the cache! Return the single instance we're tracking.
                return uniqueType;
            }

            // B. If not in the cache, check the database.
            var dbType = await context.ArtifactTypes.FirstOrDefaultAsync(t => t.Name == typeToProcess.Name);
            if (dbType != null)
            {
                // Found it in the database. Add it to our cache for next time.
                processedTypes[dbType.Name] = dbType;
                return dbType;
            }

            // C. It's a brand new type. Add the new instance to our cache.
            processedTypes[typeToProcess.Name] = typeToProcess;
            return typeToProcess;
        }

        // 2. De-duplicate the main grouping's type
        grouping.Type = await GetUniqueTypeAsync(grouping.Type);

        // Iterate through all child entries to handle their related entities.
        foreach (var entry in grouping.ChildArtifactEntries)
        {
            // Handle Artifact Types
            // Check if the type exists in the database.
            var existingType = await GetUniqueTypeAsync(entry.Type);
            entry.Type = existingType;

            // Handle Storage Location
            // Check if the storage location exists in the database.
            var existingLocation = await context.ArtifactStorageLocations.FirstOrDefaultAsync(l => l.Location == entry.StorageLocation.Location);
            if (existingLocation != null)
            {
                // If it exists, replace the disconnected object with the tracked one.
                entry.StorageLocation = existingLocation;
            }

            // Handle Tags
            // Create a temporary list to hold the managed tag entities.
            var managedTags = new List<ArtifactEntryTag>();
            foreach (var tag in entry.Tags)
            {
                // Attempt to find the tag in the database.
                var existingTag = await context.ArtifactEntryTags.FirstOrDefaultAsync(t => t.Name == tag.Name);
                if (existingTag != null)
                {
                    // The tag already exists. Use the tracked instance.
                    managedTags.Add(existingTag);
                }
                else
                {
                    // The tag is new. Add it to the managed list.
                    managedTags.Add(tag);
                }
            }
            // Replace the disconnected tag objects on the entry with the managed ones.
            entry.Tags = managedTags;

            // Handle Listed Names
            // Create a temporary list to hold the managed name entities.
            var managedNames = new List<ListedName>();
            foreach (var name in entry.ListedNames)
            {
                // Attempt to find the listed name in the database.
                var existingName = await context.ArtifactAssociatedNames.FirstOrDefaultAsync(n => n.Value == name.Value);
                if (existingName != null)
                {
                    // The name already exists. Use the tracked instance.
                    managedNames.Add(existingName);
                }
                else
                {
                    // The name is new. Add it to the managed list.
                    managedNames.Add(name);
                }
            }
            // Replace the disconnected name objects on the entry with the managed ones.
            entry.ListedNames = managedNames;

            // Handle Defects
            // Create a temporary list to hold the managed defect entities.
            var managedDefects = new List<ArtifactDefect>();
            foreach (var defect in entry.Defects)
            {
                // Attempt to find the defect in the database.
                var existingDefect = await context.ArtifactDefects.FirstOrDefaultAsync(d => d.Description == defect.Description);
                if (existingDefect != null)
                {
                    // The defect already exists. Use the tracked instance.
                    managedDefects.Add(existingDefect);
                }
                else
                {
                    // The defect is new. Add it to the managed list.
                    managedDefects.Add(defect);
                }
            }
            // Replace the disconnected defect objects on the entry with the managed ones.
            entry.Defects = managedDefects;

            // Handle file paths. This is the original logic you provided.
            var managedFilePaths = new List<FilePathListing>();
            foreach (var filepath in entry.Files)
            {
                // Attempt to find the file path in the database.
                var existingFilePath = await context.ArtifactFilePaths.FirstOrDefaultAsync(f => f.Path == filepath.Path);

                if (existingFilePath != null)
                {
                    // The file path already exists. Use the tracked instance.
                    managedFilePaths.Add(existingFilePath);
                }
                else
                {
                    // The file path is new. Add it to the managed list.
                    managedFilePaths.Add(filepath);
                }
            }

            // Replace the disconnected file path objects on the entry with the managed ones.
            entry.Files = managedFilePaths;
        }
    
        // Concatinate all of the text to be searchable by postgres
        grouping.GenerateSearchIndex();

        // Add the new grouping and save changes.
        //context.ArtifactGroupings.Add(grouping);
        context.ChangeTracker.TrackGraph(grouping, node =>
        {
            // If the entity's key is set, EF should treat it as an existing, unchanged entity.
            if (node.Entry.IsKeySet)
            {
                node.Entry.State = EntityState.Unchanged;
            }
            // Otherwise, it's a new entity that needs to be inserted.
            else
            {
                node.Entry.State = EntityState.Added;
            }
        });

        await context.SaveChangesAsync();
    }

    public async Task UpdateGroupingAsync(ArtifactGrouping updatedGrouping)
    {
        // The DbContext is provided externally, so we will use it as is.
        // Assuming you have an instance available, e.g., via a constructor or method parameter.
        await using var context = await _context.CreateDbContextAsync();

        // 1. Retrieve the existing grouping object from the database, eagerly loading all related data.
        // This is crucial for correctly handling all relationships.
        var existingGrouping = await context.ArtifactGroupings
            .Include(g => g.Category)
            .Include(g => g.IdentifierFields)
            .Include(g => g.Type)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.StorageLocation)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Type)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Files)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Tags)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.ListedNames)
            .Include(g => g.ChildArtifactEntries)
                .ThenInclude(e => e.Defects)
            .Where(g => g.Id == updatedGrouping.Id)
            .FirstOrDefaultAsync();

        if (existingGrouping == null)
        {
            // The grouping does not exist. You may want to throw an exception or handle this case.
            return;
        }

        // 2. Manually copy over primitive properties.
        existingGrouping.Title = updatedGrouping.Title;
        existingGrouping.Description = updatedGrouping.Description;
        existingGrouping.IsPublicallyVisible = updatedGrouping.IsPublicallyVisible;
        existingGrouping.IdentifierFields = updatedGrouping.IdentifierFields;

        // Handle one-to-many relationships (Type, Category).
        // Find the existing related entity and attach it to the tracked graph.
        var existingGroupingType = await context.ArtifactTypes.FirstOrDefaultAsync(t => t.Name == updatedGrouping.Type.Name);
        if (existingGroupingType != null)
        {
            existingGrouping.Type = existingGroupingType;
        }
        else
        {
            existingGrouping.Type = updatedGrouping.Type;
        }

        // Attach the category as specified
        if (existingGrouping.Category.Name != updatedGrouping.Category.Name)
        {
            existingGrouping.Category = updatedGrouping.Category;
            context.Add(existingGrouping.Category);
        }

        // Update top-level properties.
        existingGrouping.Title = updatedGrouping.Title;
        existingGrouping.IsPublicallyVisible = updatedGrouping.IsPublicallyVisible;
        existingGrouping.Description = updatedGrouping.Description;

        // 3. Synchronize the ChildArtifactEntries collection.
        // First, remove any entries that were deleted in the DTO.
        var updatedEntryIds = updatedGrouping.ChildArtifactEntries.Select(e => e.Id).ToList();
        var entriesToRemove = existingGrouping.ChildArtifactEntries
            .Where(e => !updatedEntryIds.Contains(e.Id))
            .ToList();

        foreach (var entryToRemove in entriesToRemove)
        {
            existingGrouping.ChildArtifactEntries.Remove(entryToRemove);
        }

        // Now, loop through the updated entries to handle updates and additions.
        foreach (var updatedEntry in updatedGrouping.ChildArtifactEntries)
        {
            // FIRST, de-duplicate all related entities on the incoming entry.

            var existingEntry = existingGrouping.ChildArtifactEntries
                .FirstOrDefault(e => e.Id == updatedEntry.Id);
            
            await DeDuplicateEntryRelationsAsync(context, updatedEntry);

            if (existingEntry != null)
            {
                // The entry exists, so manually update its properties.
                existingEntry.Title = updatedEntry.Title;
                existingEntry.Description = updatedEntry.Description;
                existingEntry.ArtifactNumber = updatedEntry.ArtifactNumber;
                existingEntry.IsPubliclyVisible = updatedEntry.IsPubliclyVisible;
                existingEntry.AssociatedDates = updatedEntry.AssociatedDates;
                existingEntry.FileTextContent = updatedEntry.FileTextContent;
                existingEntry.Files = updatedEntry.Files;

                // The relations on updatedEntry are already de-duplicated, so just assign them.
                existingEntry.StorageLocation = updatedEntry.StorageLocation;
                existingEntry.Type = updatedEntry.Type;

                // For collections, clear the old ones and add the new de-duplicated ones.
                existingEntry.Tags.Clear();
                updatedEntry.Tags.ForEach(tag => existingEntry.Tags.Add(tag));

                existingEntry.ListedNames.Clear();
                updatedEntry.ListedNames.ForEach(name => existingEntry.ListedNames.Add(name));

                existingEntry.Defects.Clear();
                updatedEntry.Defects.ForEach(defect => existingEntry.Defects.Add(defect));
            }
            else
            {
                // The entry is new and its children are already de-duplicated, so just add it.
                existingGrouping.ChildArtifactEntries.Add(updatedEntry);
            }
        }

        existingGrouping.GenerateSearchIndex();

        // 4. Save all changes.
        await context.SaveChangesAsync();
    }

    private async Task DeDuplicateEntryRelationsAsync(ApplicationDbContext context, ArtifactEntry entry)
    {
        // --- Handle One-to-Many Relationships ---
        var existingLocation = await context.ArtifactStorageLocations.FirstOrDefaultAsync(l => l.Location == entry.StorageLocation.Location);
        if (existingLocation != null)
        {
            entry.StorageLocation = existingLocation;
        }

        var existingType = await context.ArtifactTypes.FirstOrDefaultAsync(t => t.Name == entry.Type.Name);
        if (existingType != null)
        {
            entry.Type = existingType;
        }

        // --- Handle Many-to-Many Relationships ---

        // De-duplicate Tags
        var processedTags = new List<ArtifactEntryTag>();
        foreach (var tag in entry.Tags)
        {
            var existingTag = await context.ArtifactEntryTags.FirstOrDefaultAsync(t => t.Name == tag.Name) ?? tag;
            processedTags.Add(existingTag);
        }
        entry.Tags = processedTags;

        // De-duplicate ListedNames
        var processedNames = new List<ListedName>();
        if (entry.ListedNames != null)
                {
            foreach (var name in entry.ListedNames)
                    {
                var existingName = await context.ArtifactAssociatedNames.FirstOrDefaultAsync(n => n.Value == name.Value) ?? name;
                processedNames.Add(existingName);
            }
            entry.ListedNames = processedNames;
                    }

        // De-duplicate Defects
        var processedDefects = new List<ArtifactDefect>();
        if (entry.Defects != null)
        {
            foreach (var defect in entry.Defects)
            {
                var existingDefect = await context.ArtifactDefects.FirstOrDefaultAsync(d => d.Description == defect.Description) ?? defect;
                processedDefects.Add(existingDefect);
                }
            entry.Defects = processedDefects;
            }

        if (entry.Files.Any())
            {
            // 1. Get the IDs from the incoming, untracked file objects.
            var inputFileIds = entry.Files.Select(f => f.Id).ToList();

            // 2. Fetch the actual, tracked entities from the database.
            var trackedFiles = await context.ArtifactFilePaths
                .Where(dbFile => inputFileIds.Contains(dbFile.Id))
                    .ToListAsync();

            // 3. Replace the untracked collection with the tracked one.
            entry.Files = trackedFiles;
        }
    }

    /// <summary>
    /// A helper method to synchronize many-to-many collections.
    /// </summary>
    private async Task SyncCollectionAsync<TEntity, TKey>(
    DbContext context,
    ICollection<TEntity> existingItems,
    ICollection<TEntity> updatedItems,
    Func<TEntity, TKey> keySelector) where TEntity : class
    {
        var existingKeys = existingItems.Select(keySelector).ToHashSet();
        var updatedKeys = updatedItems.Select(keySelector).ToHashSet();

        // 1. Remove items that are no longer in the updated collection
        var keysToRemove = existingKeys.Except(updatedKeys);
        var itemsToRemove = existingItems.Where(item => keysToRemove.Contains(keySelector(item))).ToList();
        foreach (var item in itemsToRemove)
        {
            existingItems.Remove(item);
        }

        // 2. Identify keys for brand new items
        var keysToAdd = updatedKeys.Except(existingKeys).ToList();
        if (!keysToAdd.Any())
                {
            return; // Nothing to add
                }

        // 3. Batch-fetch all entities from the DB that match the new keys.
        // This is the key change to make the query translatable to SQL.
        Dictionary<TKey, TEntity> existingDbItemsMap = [];
        if (typeof(TEntity) == typeof(ArtifactEntryTag))
        {
            var tagKeys = keysToAdd.Cast<string>().ToList();
            var tags = await context.Set<ArtifactEntryTag>()
                .Where(t => tagKeys.Contains(t.Name))
                .ToListAsync();
            existingDbItemsMap = tags.ToDictionary(t => (TKey)(object)t.Name) as Dictionary<TKey, TEntity>;
        }
        else if (typeof(TEntity) == typeof(ListedName))
        {
            var nameKeys = keysToAdd.Cast<string>().ToList();
            var names = await context.Set<ListedName>()
                .Where(n => nameKeys.Contains(n.Value))
                .ToListAsync();
            existingDbItemsMap = names.ToDictionary(n => (TKey)(object)n.Value) as Dictionary<TKey, TEntity>;
            }
        else if (typeof(TEntity) == typeof(ArtifactDefect))
        {
            var defectKeys = keysToAdd.Cast<string>().ToList();
            var defects = await context.Set<ArtifactDefect>()
                .Where(d => defectKeys.Contains(d.Description))
                .ToListAsync();
            existingDbItemsMap = defects.ToDictionary(d => (TKey)(object)d.Description) as Dictionary<TKey, TEntity>;
        }


        // 4. Add the items, using the tracked entity from the DB if it exists.
        foreach (var updatedItem in updatedItems.Where(i => keysToAdd.Contains(keySelector(i))))
        {
            var key = keySelector(updatedItem);
            if (existingDbItemsMap.TryGetValue(key, out var dbItem))
            {
                // The item already exists in the DB, so add the tracked version.
                existingItems.Add(dbItem);
            }
            else
            {
                // This is a brand new item, so add the untracked one from the input.
                existingItems.Add(updatedItem);
            }
        }
    }

    public async Task DeleteGroupingAsync(int id)
    {
        await using var context = await _context.CreateDbContextAsync();
        await context.ArtifactGroupings
            .Where(p => p.Id == id)
            .ExecuteDeleteAsync();

        await context.SaveChangesAsync();
    }

    public async Task DeleteGroupingAsync(ArtifactGrouping grouping)
    {
        await using var context = await _context.CreateDbContextAsync();
        context.ArtifactGroupings.Remove(grouping);
        await context.SaveChangesAsync();
    }
    
    public async Task<List<ArtifactGrouping>> GetGroupingsPaged(int pageNumber, int resultsCount)
    {
        await using var context = await _context.CreateDbContextAsync();
        if (pageNumber < 1 || resultsCount < 1)
        {
            throw new ArgumentOutOfRangeException($"Either page number or number of results was less than or equal to 0. {nameof(pageNumber)}={pageNumber} {nameof(resultsCount)}={resultsCount}");
        }

        var totalCount = await context.ArtifactGroupings.CountAsync();

        var items = await context.ArtifactGroupings
            .Include(g => g.ChildArtifactEntries)
            .Include(g => g.Category)
            .OrderBy(g => g.Id)
            .Skip((pageNumber - 1) * resultsCount)
            .Take(resultsCount)
            .ToListAsync();
        
        return items;
    }

    public async Task<int> GetTotalCount()
    {
        await using var context = await _context.CreateDbContextAsync();
        return context.ArtifactGroupings.Count();
    }
}