using FluentValidation;
using Microsoft.Extensions.Logging;
using Raven.Client.Documents;
using Raven.Client.Documents.Linq;
using Raven.Client.Documents.Session;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using zero.Core.Database.Indexes;
using zero.Core.Entities;
using zero.Core.Extensions;
using zero.Core.Handlers;
using zero.Core.Options;

namespace zero.Core.Api
{
  public class PagesApi : BackofficeApi, IPagesApi
  {
    const string RECYCLE_BIN_GROUP = "pages";

    protected IZeroOptions Options { get; private set; }

    protected IRecycleBinApi RecycleBinApi { get; private set; }

    protected ILogger<PagesApi> Logger { get; private set; }

    protected IHandlerHolder Handler { get; private set; }


    public PagesApi(IZeroOptions options, IBackofficeStore store, IRecycleBinApi recycleBinApi, ILogger<PagesApi> logger, IHandlerHolder handler) : base(store)
    {
      Options = options;
      RecycleBinApi = recycleBinApi;
      Logger = logger;
      Handler = handler;
    }


    /// <inheritdoc />
    public Task<IPage> GetEmpty(string pageType, string parentId = null)
    {
      PageType type = GetPageType(pageType);

      if (type == null)
      {
        return Task.FromResult<IPage>(null);
      }

      try
      {
        IPage model = Activator.CreateInstance(type.ContentType) as IPage;

        model.PageTypeAlias = type.Alias;
        model.ParentId = parentId; // TODO validate if type is allowed and if parentid is allowed

        Handler.Get<IPageCreationHandler>()?.OnCreate(model);

        return Task.FromResult(model);
      }
      catch
      {
        Logger.LogWarning("Could not create page with type {type}", type);
      }

      return Task.FromResult<IPage>(null);
    }


    /// <inheritdoc />
    public async Task<IPage> GetById(string id)
    {
      return await GetById<IPage>(id);
    }


    /// <inheritdoc />
    public async Task<Dictionary<string, IPage>> GetByIds(params string[] ids)
    {
      return await GetByIds<IPage>(ids);
    }


    /// <inheritdoc />
    public IList<PageType> GetPageTypes()
    {
      return Options.Pages.GetAllItems().ToList();
    }


    /// <inheritdoc />
    public async Task<IList<PageType>> GetAllowedPageTypes(string parentId = null)
    {    
      IEnumerable<PageType> types = Options.Pages.GetAllItems();

      if (parentId.IsNullOrEmpty())
      {
        return types.Where(x => x.AllowAsRoot || x.OnlyAtRoot).ToList();
      }

      Page page = await GetById<Page>(parentId);
      PageType pageType = page != null ? types.FirstOrDefault(x => x.Alias == page.PageTypeAlias) : null;

      if (pageType == null)
      {
        return new List<PageType>();
      }

      if (pageType.AllowAllChildrenTypes)
      {
        return types.Where(x => !x.OnlyAtRoot).ToList();
      }

      return types.Where(x => !x.OnlyAtRoot && pageType.AllowedChildrenTypes.Contains(x.Alias)).ToList();
    }


    /// <inheritdoc />
    public PageType GetPageType(string alias) 
    {
      return Options.Pages.GetAllItems().FirstOrDefault(x => x.Alias == alias);
    }


    /// <inheritdoc />
    public async Task<EntityResult<IPage>> Save(IPage model)
    {
      return await SaveModel(model, null);
    }


    /// <inheritdoc />
    public async Task<EntityResult<IList<IPage>>> SaveSorting(string[] sortedIds)
    {
      Dictionary<string, IPage> items = await GetByIds<IPage>(sortedIds);
      uint index = 0;

      // contains multiple parents, therefore fail
      if (items.Select(x => x.Value?.ParentId).Distinct().Count() > 1)
      {
        return EntityResult<IList<IPage>>.Fail("@errors.page.sortingmultipleparents");
      }

      using (IAsyncDocumentSession session = Store.OpenAsyncSession())
      {
        session.Advanced.WaitForIndexesAfterSaveChanges(throwOnTimeout: false);

        foreach (var item in items)
        {
          item.Value.Sort = index;
          index += 10;
          await session.StoreAsync(item.Value);
          //session.Advanced.Patch<T, uint>(item.Value.Id, x => x.Sort, index++);
        }

        await session.SaveChangesAsync();
      }

      return EntityResult<IList<IPage>>.Success(items.Select(x => x.Value).ToList());
    }


    /// <inheritdoc />
    public async Task<EntityResult<IPage>> Move(string id, string parentId)
    {
      IPage model = await GetById<IPage>(id);
      IPage parent = await GetById<IPage>(parentId);

      if (model == null || (!parentId.IsNullOrEmpty() && parent == null))
      {
        return EntityResult<IPage>.Fail("@errors.idnotfound");
      }

      IList<PageType> pageTypes = await GetAllowedPageTypes(parentId);

      if (!pageTypes.Any(x => x.Alias == model.PageTypeAlias))
      {
        return EntityResult<IPage>.Fail("@errors.page.parentnotallowed");
      }

      model.ParentId = parent?.Id;

      return await Save(model);
    }


    /// <inheritdoc />
    public async Task<EntityResult<IPage>> Copy(string id, string destinationId, bool includeDescendants = false)
    {
      IPage model = await GetById<IPage>(id);
      IPage parent = await GetById<IPage>(destinationId);

      if (model == null || (!destinationId.IsNullOrEmpty() && parent == null))
      {
        return EntityResult<IPage>.Fail("@errors.idnotfound");
      }

      string baseId = model.Id;

      // update new page properties
      model.Id = null;
      model.ParentId = parent?.Id;
      model.IsActive = false;
      model.CreatedDate = DateTimeOffset.Now;

      // check if new parent is allowed
      IList<PageType> pageTypes = await GetAllowedPageTypes(destinationId);

      if (!pageTypes.Any(x => x.Alias == model.PageTypeAlias))
      {
        return EntityResult<IPage>.Fail("@errors.page.parentnotallowed");
      }

      using (IAsyncDocumentSession session = Store.OpenAsyncSession())
      {
        session.Advanced.WaitForIndexesAfterSaveChanges(throwOnTimeout: false);

        // recursive function to store descendants
        async Task AddChildren(string oldParentId, string newParentId)
        {
          Pages_WithChildren.Result childrenResult = await session.Query<Pages_WithChildren.Result, Pages_WithChildren>()
            .ProjectInto<Pages_WithChildren.Result>()
            .Include<Pages_WithChildren.Result, IPage>(x => x.Id)
            .Where(x => x.Id == oldParentId)
            .FirstOrDefaultAsync();

          if (childrenResult == null || childrenResult.ChildrenIds.Length < 1)
          {
            return;
          }

          Dictionary<string, IPage> childrenPages = await session.LoadAsync<IPage>(childrenResult.ChildrenIds);

          foreach (var child in childrenPages)
          {
            IPage childPage = child.Value.Clone();
            childPage.Id = null;
            childPage.IsActive = false;
            childPage.ParentId = newParentId;
            childPage.CreatedDate = DateTimeOffset.Now;

            await session.StoreAsync(childPage);
            await AddChildren(child.Key, childPage.Id);
          }
        }

        await session.StoreAsync(model);

        if (includeDescendants)
        {
          await AddChildren(baseId, model.Id);
        }

        await session.SaveChangesAsync();
      }

      return EntityResult<IPage>.Success(model);
    }


    /// <inheritdoc />
    public async Task<EntityResult<string[]>> Delete(string id, bool moveToRecycleBin = true)
    {
      IList<IPage> pages = await GetByIdWithDescendants(id);
      string[] ids = pages.Select(x => x.Id).ToArray();

      if (pages.Count < 1)
      {
        return EntityResult<string[]>.Fail("@errors.ondelete.idnotfound");
      }

      if (moveToRecycleBin)
      {
        await RecycleBinApi.Add(pages, RECYCLE_BIN_GROUP);
      }

      await DeleteByIds<IPage>(ids);

      return EntityResult<string[]>.Success(ids);
    }


    /// <inheritdoc />
    public async Task<EntityResult<string[]>> Restore(string id, bool includeDescendants = false)
    {
      EntityResult<string[]> result = new EntityResult<string[]>();
      IRecycledEntity recycledEntity = await RecycleBinApi.GetById(id);
      List<IRecycledEntity> entities = new List<IRecycledEntity>() { recycledEntity };

      if (recycledEntity == null)
      {
        return EntityResult<string[]>.Fail(); // TODO correct error message
      }

      // get descendants from the operation
      if (includeDescendants && !recycledEntity.OperationId.IsNullOrEmpty())
      {
        entities = (await RecycleBinApi.GetByOperation(recycledEntity.OperationId)).ToList();
      }

      // fill ids
      string[] ids = entities.Select(x => x.OriginalId).ToArray();

      // check if parents are available
      string[] parentIds = entities.Select(x => x.Content as IPage).Where(x => x != null).Select(x => x.ParentId).ToArray();
      parentIds = (await GetByIds<IPage>(parentIds)).Where(x => x.Value != null).Select(x => x.Value.Id).ToArray();

      // validate and restore all items
      foreach (IRecycledEntity entity in entities)
      {
        // check if it contains page data
        if (entity.Group != RECYCLE_BIN_GROUP || !(entity.Content is IPage))
        {
          //result.AddError("Cannot parse recycled entity as an IPage in group \"" + RECYCLE_BIN_GROUP + "\""); // TODO correct error message
          continue;
        }

        // get page
        IPage page = entity.Content as IPage;
        page.IsActive = false;

        // validate app and parent
        if (!page.ParentId.IsNullOrEmpty() && !ids.Contains(page.ParentId) && !parentIds.Contains(page.ParentId))
        {
          // TODO correct error message
          continue;
        }

        // restore to pages
        EntityResult<IPage> saveResult = await SaveModel(page);
      }

      // delete affected entities from recycle bin
      if (!recycledEntity.OperationId.IsNullOrEmpty())
      {
        await RecycleBinApi.DeleteByOperation(recycledEntity.OperationId);
      }

      // set result
      result.Model = ids;
      result.IsSuccess = true;

      return result;
    }


    /// <summary>
    /// Get a page with all its descendants
    /// </summary>
    async Task<List<IPage>> GetByIdWithDescendants(string id)
    {
      List<IPage> items = new List<IPage>();

      IPage model = await GetById<IPage>(id);

      if (model == null)
      {
        return items;
      }

      items.Add(model);

      using (IAsyncDocumentSession session = Store.OpenAsyncSession())
      {
        // recursive function to store descendants
        async Task AddChildren(string parentId)
        {
          Pages_WithChildren.Result childrenResult = await session.Query<Pages_WithChildren.Result, Pages_WithChildren>()
            .ProjectInto<Pages_WithChildren.Result>()
            .Include<Pages_WithChildren.Result, IPage>(x => x.Id)
            .Where(x => x.Id == parentId)
            .FirstOrDefaultAsync();

          if (childrenResult == null || childrenResult.ChildrenIds.Length < 1)
          {
            return;
          }

          Dictionary<string, IPage> childrenPages = await session.LoadAsync<IPage>(childrenResult.ChildrenIds);

          foreach (var child in childrenPages)
          {
            items.Add(child.Value);
            await AddChildren(child.Value.Id);
          }
        }

        await AddChildren(model.Id);
      }

      return items;
    }
  }


  public interface IPagesApi
  {
    /// <summary>
    /// Get a new empty page with the specified type
    /// </summary>
    public Task<IPage> GetEmpty(string pageType, string parentId = null);

    /// <summary>
    /// Get page by Id
    /// </summary>
    Task<IPage> GetById(string id);

    /// <summary>
    /// Get pages by ids
    /// </summary>
    Task<Dictionary<string, IPage>> GetByIds(params string[] ids);

    /// <summary>
    /// Get all available page types
    /// </summary>
    IList<PageType> GetPageTypes();

    /// <summary>
    /// Get all page types which are allowed below a selected parent page
    /// </summary>
    Task<IList<PageType>> GetAllowedPageTypes(string parentId = null);

    /// <summary>
    /// Get a specific page type by alias
    /// </summary>
    PageType GetPageType(string alias);

    /// <summary>
    /// Creates or updates a page
    /// </summary>
    Task<EntityResult<IPage>> Save(IPage model);

    /// <summary>
    /// Update sorting of pages on a specific level
    /// </summary>
    Task<EntityResult<IList<IPage>>> SaveSorting(string[] sortedIds);

    /// <summary>
    /// Move a page to a new parent
    /// </summary>
    Task<EntityResult<IPage>> Move(string id, string parentId);

    /// <summary>
    /// Copies a page (with optional descendants) to a new location
    /// </summary>
    Task<EntityResult<IPage>> Copy(string id, string destinationId, bool includeDescendants = false);

    /// <summary>
    /// Deletes a page by Id (with all it's descendants)
    /// </summary>
    Task<EntityResult<string[]>> Delete(string id, bool moveToRecycleBin = true);

    /// <summary>
    /// Restores a page from the recycle bin
    /// </summary>
    Task<EntityResult<string[]>> Restore(string id, bool includeDescendants = false);
  }
}