using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace AsbCloudDb
{
    public static class EFExtentions
    {
        static Dictionary<Type, IQueryStringFactory> QueryFactories { get; set; } = new Dictionary<Type, IQueryStringFactory>();

        static IQueryStringFactory GetQueryStringFactory<T>(DbSet<T> dbset)
            where T : class
        {
            var t = typeof(T);
            QueryStringFactory<T> factory = (QueryStringFactory<T>)QueryFactories.GetValueOrDefault(t);
            if (factory is null)
            {
                factory = new QueryStringFactory<T>(dbset);
                QueryFactories.Add(t, factory);
            }
            
            return factory;
        }

        public static Task<int> ExecInsertOrUpdateAsync<T>(this Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade database, DbSet<T> dbset, IEnumerable<T> items, CancellationToken token)
            where T : class
        {
            var factory = (QueryStringFactory<T>)GetQueryStringFactory(dbset);
            var query = factory.MakeInsertOrUpdateSql(items);
            return database.ExecuteSqlRawAsync(query, token);
        }
    }

    interface IQueryStringFactory{}

    class QueryStringFactory<T> : IQueryStringFactory
        where T : class
    {
        private readonly string pk;
        private readonly string tableName;
        private readonly string colunmsString;
        private readonly string conflictUpdateSet;
        private readonly IEnumerable<IClrPropertyGetter> getters;

        public QueryStringFactory(DbSet<T> dbset)
        {
            var ps = dbset.EntityType.GetProperties();
            var pkColsNames = dbset.EntityType.FindPrimaryKey()?.Properties.Select(p => p.GetColumnBaseName());
            pk = pkColsNames is null ? string.Empty : $"({string.Join(", ", pkColsNames)})";

            tableName = dbset.EntityType.GetTableName();
            getters = ps.Select(p => p.GetGetter());
            var colNames = ps.Select(p => $"\"{p.GetColumnBaseName()}\"");
            colunmsString = $"({string.Join(", ", colNames)})";
            conflictUpdateSet = string.Join(", ", colNames.Select(n => $"{n} = excluded.{n}"));
        }

        public string MakeInsertOrUpdateSql(IEnumerable<T> items)
        {
            /* EXAMPLE:
                INSERT INTO the_table (id, column_1, column_2) 
                VALUES (1, 'A', 'X'), (2, 'B', 'Y'), (3, 'C', 'Z')
                ON CONFLICT (id) DO UPDATE 
                  SET column_1 = excluded.column_1, 
                      column_2 = excluded.column_2;
             */
            var sqlBuilder = new StringBuilder("INSERT INTO ", 7);
            sqlBuilder.Append(tableName);
            sqlBuilder.Append(colunmsString);
            sqlBuilder.AppendLine(" VALUES ");
            sqlBuilder.Append(MakeQueryValues(items));
            sqlBuilder.AppendLine(" ON CONFLICT ");
            if (string.IsNullOrEmpty(pk))
            {
                sqlBuilder.Append("DO NOTHING;");
            }
            else
            {
                sqlBuilder.Append(pk);
                sqlBuilder.Append(" DO UPDATE SET ");
                sqlBuilder.AppendLine(conflictUpdateSet);
                sqlBuilder.Append(';');
            }

            return sqlBuilder.ToString();
        }

        private string MakeQueryValues(IEnumerable<T> items)
        {
            var rows = items.Select(item => MakeRow(item));
            return string.Join(",", rows);
        }

        private string MakeRow(T item)
        {
            var values = getters.Select(getter => FormatValue(getter.GetClrValue(item)));
            return $"({string.Join(",", values)})";
        }

        private static string FormatValue(object v)
        => v switch
            {
                string vStr => $"'{vStr}'",
                DateTime vDate => $"'{FormatDateValue(vDate)}'",
                IFormattable vFormattable=> FormatFormattableValue(vFormattable),
                _ => System.Text.Json.JsonSerializer.Serialize(v),
            };

        private static string FormatFormattableValue(IFormattable v)
        => v switch
        {
            double vt => vt.ToString(System.Globalization.CultureInfo.InvariantCulture),
            float vt => vt.ToString(System.Globalization.CultureInfo.InvariantCulture),
            decimal vt => vt.ToString(System.Globalization.CultureInfo.InvariantCulture),
            int vt => vt.ToString(System.Globalization.CultureInfo.InvariantCulture),
            short vt => vt.ToString(System.Globalization.CultureInfo.InvariantCulture),
            uint vt => vt.ToString(System.Globalization.CultureInfo.InvariantCulture),
            ushort vt => vt.ToString(System.Globalization.CultureInfo.InvariantCulture),
            _ => v.ToString(null, System.Globalization.CultureInfo.InvariantCulture),
        };

        private static string FormatDateValue(DateTime vDate)
        {
            if (vDate.Kind == DateTimeKind.Unspecified)
                vDate = DateTime.SpecifyKind(vDate, DateTimeKind.Utc);
            return vDate.ToUniversalTime().ToString("yyyy-MM-dd HH:mm:ss.ffffff zzz");
        }

    }
}