using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Principal;
using System.Text;
using System.Threading.Tasks;

namespace Blog3000.Shared
{
    public class BlogPostSearch
    {
        private readonly Func<IAsyncEnumerable<BlogPost>> postSource;
        private readonly Func<IAsyncEnumerable<BlogPostHeader>> headerSource;
        private readonly string searchTerm;


        private readonly List<string> tokens = new List<string>();

        private bool invalidTermsRemoved;

        /// <summary>
        /// 
        /// </summary>
        /// <param name="searchTerm">searchTerm or NULL to return the latest items only</param>
        public BlogPostSearch(
            Func<IAsyncEnumerable<BlogPost>> postSource,
            Func<IAsyncEnumerable<BlogPostHeader>> headerSource, 
            string searchTerm)
        {
            this.postSource = postSource;
            this.headerSource = headerSource;
            this.searchTerm = searchTerm;
            TokenizeTerm();
        }

        public bool IsNonEmptyTerm
        {
            get { return tokens.Count > 0; }
        }

        public bool InvalidTermsRemoved
        {
            get { return invalidTermsRemoved;  }
        }

        public bool RequiresFullText
        {
            get { return tokens.Where(c => !c.StartsWith("#")).FirstOrDefault() != null; }
        }


        /// <summary>
        /// 
        /// </summary>
        /// <returns>Search results or latest items when searchterm is  null</returns>
        public async Task<List<BlogPostHeader>> ExecAsync(
            int startIdx, int pageMaxSize, bool findLastPage)
        {
            IAsyncEnumerable<BlogPostHeader> fetch;

            if (!IsNonEmptyTerm)
            {
                fetch = headerSource()
                .Where(p => (p.StickyMenuPos ?? -1) < 0)
                .OrderByDescending(p => p.Revisions?.Latest()?.ChangedAt ?? DateTime.MinValue)
                .ThenByDescending(p => p.Title);
            }
            else
            {
                if (!RequiresFullText)
                {
                    var efetch = headerSource();
                    foreach (var tok in tokens)
                    {
                        if (tok.StartsWith("#"))
                        {
                            efetch = efetch
                            .Where(
                                p => (
                                    ((p.Topics != null) && (p.Topics.Find(t => t.ToLowerInvariant().Contains(tok)) != null))
                                 )
                                 );
                        }
                    }
                    fetch = efetch;

                }
                else
                {
                    var efetch = postSource();

                    foreach (var tok in tokens)
                    {
                        System.Diagnostics.Debug.WriteLine($"Tok: {tok}");
                        if (tok.StartsWith("#"))
                        {
                            efetch = efetch
                            .Where(
                                p => (
                                    ((p.Topics != null) && (p.Topics.Find(t => t.ToLowerInvariant().Contains(tok)) != null))
                                 )
                                 );
                        }
                        else
                        {
                            efetch = ((IAsyncEnumerable<BlogPost>)efetch)
                            .Where(
                                p => (
                                    ((p.Title?.ToLowerInvariant() ?? "").Contains(tok)) ||
                                    ((p.Text?.ToLowerInvariant() ?? "").Contains(tok)) ||
                                    ((p.Abstract?.ToLowerInvariant() ?? "").Contains(tok)) ||
                                    ((p.Topics != null) && (p.Topics.Find(t => t.ToLowerInvariant().Contains(tok)) != null))
                                 )
                                 );
                        }
                    }
                    fetch = efetch;

                }

                fetch = fetch
                       .OrderByDescending(p => p.Revisions?.Latest()?.ChangedAt ?? DateTime.MinValue)
                       .OrderByDescending(p => p.Title);
            }

            List<BlogPostHeader> res;
            if (!findLastPage)
            {
                res = await fetch
                .Skip(startIdx)
                .Take(pageMaxSize)
                .ToListAsync();
            }
            else
            {
                var count = await fetch.CountAsync();
                var sidx = count - pageMaxSize;
                if (sidx < 0) sidx = 0;
                res = await fetch
                .Skip(sidx)
                .Take(pageMaxSize)
                .ToListAsync();
            }

            return res;
        }

        private void TokenizeTerm()
        {
            if (searchTerm != null)
            {
                foreach (var t in searchTerm.ToLowerInvariant().Split(" ")) // Improve
                {
                    if (!String.IsNullOrWhiteSpace(t) && (t.Length >= 2))
                    {
                        tokens.Add(t);
                    }
                    else invalidTermsRemoved = true;
                }
            }
        }

    }
}