using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;
using System.Threading;
using System.Collections.Concurrent;
using System.Threading.Tasks;

namespace Tango.CSV
{
    /// <summary>
    /// Represents a CSV file reader.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <seealso cref="Tango.CSV.CsvFile" />
    /// <seealso cref="System.Collections.Generic.IEnumerable{T}" />
    /// <seealso cref="System.Collections.Generic.IEnumerator{T}" />
    internal class CsvFileReader<T> : CsvFile, IEnumerable<T>, IEnumerator<T>
     where T : new()
    {
        private readonly Dictionary<Type, List<Action<T, String>>> allSetters = new Dictionary<Type, List<Action<T, String>>>();
        private string[] columns;
        private char curChar;
        private int len;
        private string line;
        private int pos;
        private T record;
        private readonly char fieldSeparator;
        private readonly TextReader textReader;
        private readonly char textQualifier;
        private readonly StringBuilder parseFieldResult = new StringBuilder();



        /// <summary>
        /// Initializes a new instance of the <see cref="CsvFileReader{T}"/> class.
        /// </summary>
        /// <param name="csvSource">The CSV source.</param>
        public CsvFileReader(CsvSource csvSource)
            : this(csvSource, null)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="CsvFileReader{T}"/> class.
        /// </summary>
        /// <param name="csvSource">The CSV source.</param>
        /// <param name="csvDefinition">The CSV definition.</param>
        public CsvFileReader(CsvSource csvSource, CsvDefinition csvDefinition)
        {
            var streamReader = csvSource.TextReader as StreamReader;
            if (streamReader != null)
                this.BaseStream = streamReader.BaseStream;
            if (csvDefinition == null)
                csvDefinition = DefaultCsvDefinition;
            this.fieldSeparator = csvDefinition.FieldSeparator;
            this.textQualifier = csvDefinition.TextQualifier;

            this.textReader = csvSource.TextReader;// new FileStream(csvSource.TextReader, FileMode.Open);

            this.ReadHeader(csvDefinition.Header);

        }

        /// <summary>
        /// Gets the element in the collection at the current position of the enumerator.
        /// </summary>
        public T Current
        {
            get { return this.record; }
        }

        /// <summary>
        /// Gets a value indicating whether this <see cref="CsvFileReader{T}"/> is EOF.
        /// </summary>
        public bool Eof
        {
            get { return this.line == null; }
        }

        /// <summary>
        /// Gets the element in the collection at the current position of the enumerator.
        /// </summary>
        object IEnumerator.Current
        {
            get { return this.Current; }
        }

        /// <summary>
        /// Releases unmanaged and - optionally - managed resources.
        /// </summary>
        /// <param name="disposing"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged resources.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                // free managed resources
                this.textReader.Dispose();
            }
        }

        /// <summary>
        /// Returns an enumerator that iterates through a collection.
        /// </summary>
        /// <returns>
        /// An <see cref="T:System.Collections.IEnumerator" /> object that can be used to iterate through the collection.
        /// </returns>
        IEnumerator IEnumerable.GetEnumerator()
        {
            return this.GetEnumerator();
        }

        /// <summary>
        /// Returns an enumerator that iterates through the collection.
        /// </summary>
        /// <returns>
        /// An enumerator that can be used to iterate through the collection.
        /// </returns>
        public IEnumerator<T> GetEnumerator()
        {
            return this;
        }

        /// <summary>
        /// Advances the enumerator to the next element of the collection.
        /// </summary>
        /// <returns>
        /// true if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the collection.
        /// </returns>
        public bool MoveNext()
        {
            this.ReadNextLine();
            if (this.line == null && (this.line = this.textReader.ReadLine()) == null)
            {
                this.record = default(T);
            }
            else
            {
                this.record = new T();
                Type recordType = typeof(T);
                List<Action<T, String>> setters;
                if (!this.allSetters.TryGetValue(recordType, out setters))
                {
                    setters = this.CreateSetters();
                    this.allSetters[recordType] = setters;
                }

                var fieldValues = new string[setters.Count];
                for (int i = 0; i < setters.Count; i++)
                {
                    fieldValues[i] = this.ParseField();
                    if (this.curChar == this.fieldSeparator)
                        this.NextChar();
                    else
                        break;
                }
                for (int i = 0; i < setters.Count; i++)
                {
                    var setter = setters[i];
                    if (setter != null)
                    {
                        setter(this.record, fieldValues[i]);
                    }
                }
            }
            return (this.record != null);
        }

        /// <summary>
        /// Sets the enumerator to its initial position, which is before the first element in the collection.
        /// </summary>
        /// <exception cref="System.NotImplementedException">Cannot reset CsvFileReader enumeration.</exception>
        public void Reset()
        {
            throw new NotImplementedException("Cannot reset CsvFileReader enumeration.");
        }

        /// <summary>
        /// Emits the set value action.
        /// </summary>
        /// <param name="mi">The mi.</param>
        /// <param name="func">The function.</param>
        /// <returns></returns>
        /// <exception cref="System.NotImplementedException"></exception>
        private static Action<T, string> EmitSetValueAction(MemberInfo mi, Func<string, object> func)
        {
            ParameterExpression paramExpObj = Expression.Parameter(typeof(object), "obj");
            ParameterExpression paramExpT = Expression.Parameter(typeof(T), "instance");

            {
                var pi = mi as PropertyInfo;
                if (pi != null)
                {
                    if (CsvFile.UseLambdas)
                    {
                        var callExpr = Expression.Call(
                            paramExpT,
                            pi.GetSetMethod(),
                            Expression.ConvertChecked(paramExpObj, pi.PropertyType));
                        var setter = Expression.Lambda<Action<T, object>>(
                            callExpr,
                            paramExpT,
                            paramExpObj).Compile();
                        return (o, s) => setter(o, func(s));
                    }
                    return (o, v) => pi.SetValue(o, (object)func(v), null);

                }
            }
            {
                var fi = mi as FieldInfo;
                if (fi != null)
                {
                    if (CsvFile.UseLambdas)
                    {
                        //ParameterExpression valueExp = Expression.Parameter(typeof(string), "value");
                        var valueExp = Expression.ConvertChecked(paramExpObj, fi.FieldType);

                        // Expression.Property can be used here as well
                        MemberExpression fieldExp = Expression.Field(paramExpT, fi);
                        BinaryExpression assignExp = Expression.Assign(fieldExp, valueExp);

                        var setter = Expression.Lambda<Action<T, object>>
                            (assignExp, paramExpT, paramExpObj).Compile();

                        return (o, s) => setter(o, func(s));
                    }
                    return ((o, v) => fi.SetValue(o, func(v)));
                }
            }
            throw new NotImplementedException();
        }

        /// <summary>
        /// Finds the setter.
        /// </summary>
        /// <param name="c">The c.</param>
        /// <param name="staticMember">if set to <c>true</c> [static member].</param>
        /// <returns></returns>
        private static Action<T, string> FindSetter(string c, bool staticMember, int? index = null)
        {
            var flags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.IgnoreCase | (staticMember ? BindingFlags.Static : BindingFlags.Instance);
            Action<T, string> action = null;

            var propByIndex = typeof(T).GetProperties(flags).SingleOrDefault(x => x.GetCustomAttribute<CsvOrderAttribute>() != null && x.GetCustomAttribute<CsvOrderAttribute>().Index == index);

            if (propByIndex != null)
            {
                var pFunc = StringToObject(propByIndex.PropertyType);
                action = EmitSetValueAction(propByIndex, pFunc);
                return action;
            }

            PropertyInfo pi = typeof(T).GetProperty(c, flags);
            if (pi != null)
            {
                var pFunc = StringToObject(pi.PropertyType);
                action = EmitSetValueAction(pi, pFunc);
            }

            if (action == null)
            {
                FieldInfo fi = typeof(T).GetField(c, flags);
                if (fi != null)
                {
                    var fFunc = StringToObject(fi.FieldType);
                    action = EmitSetValueAction(fi, fFunc);
                }
            }

            return action;
        }

        /// <summary>
        /// Strings to object.
        /// </summary>
        /// <param name="propertyType">Type of the property.</param>
        /// <returns></returns>
        /// <exception cref="System.NotImplementedException"></exception>
        private static Func<string, object> StringToObject(Type propertyType)
        {
            if (propertyType == typeof(string))
                return (s) => s ?? String.Empty;
            else if (propertyType == typeof(Int32))
                return (s) => String.IsNullOrEmpty(s) ? 0 : Int32.Parse(s);
            if (propertyType == typeof(DateTime))
                return (s) => String.IsNullOrEmpty(s) ? DateTimeZero : DateTime.Parse(s);
            else if (propertyType == typeof(Double))
                return (s) => String.IsNullOrEmpty(s) ? 0.0 : Double.Parse(s);
            else
                throw new NotImplementedException();
        }

        /// <summary>
        /// Creates the setters.
        /// </summary>
        /// <returns></returns>
        private List<Action<T, string>> CreateSetters()
        {
            var list = new List<Action<T, string>>();
            for (int i = 0; i < this.columns.Length; i++)
            {
                string columnName = this.columns[i];
                Action<T, string> action = null;
                if (columnName.IndexOf(' ') >= 0)
                    columnName = columnName.Replace(" ", "");
                action = FindSetter(columnName, false, i) ?? FindSetter(columnName, true, i);

                list.Add(action);
            }
            return list;
        }

        /// <summary>
        /// Next character.
        /// </summary>
        private void NextChar()
        {
            if (this.pos < this.len)
            {
                this.pos++;
                this.curChar = this.pos < this.len ? this.line[this.pos] : '\0';
            }
        }

        /// <summary>
        /// Parses the end of line.
        /// </summary>
        /// <exception cref="System.NotImplementedException"></exception>
        private void ParseEndOfLine()
        {
            throw new NotImplementedException();
        }

        /// <summary>
        /// Parses the field.
        /// </summary>
        /// <returns></returns>
        private string ParseField()
        {
            parseFieldResult.Length = 0;
            if (this.line == null || this.pos >= this.len)
                return null;
            while (this.curChar == ' ' || this.curChar == '\t')
            {
                this.NextChar();
            }
            if (this.curChar == this.textQualifier)
            {
                this.NextChar();
                while (this.curChar != 0)
                {
                    if (this.curChar == this.textQualifier)
                    {
                        this.NextChar();
                        if (this.curChar == this.textQualifier)
                        {
                            this.NextChar();
                            parseFieldResult.Append(this.textQualifier);
                        }
                        else
                            return parseFieldResult.ToString();
                    }
                    else if (this.curChar == '\0')
                    {
                        if (this.line == null)
                            return parseFieldResult.ToString();
                        this.ReadNextLine();
                    }
                    else
                    {
                        parseFieldResult.Append(this.curChar);
                        this.NextChar();
                    }
                }
            }
            else
            {
                while (this.curChar != 0 && this.curChar != this.fieldSeparator && this.curChar != '\r' && this.curChar != '\n')
                {
                    parseFieldResult.Append(this.curChar);
                    this.NextChar();
                }
            }
            return parseFieldResult.ToString();
        }

        /// <summary>
        /// Reads the header.
        /// </summary>
        /// <param name="header">The header.</param>
        private void ReadHeader(string header)
        {
            if (header == null)
            {
                this.ReadNextLine();
            }
            else
            {
                // we read the first line from the given header
                this.line = header;
                this.pos = -1;
                this.len = this.line.Length;
                this.NextChar();
            }

            var readColumns = new List<string>();
            string columnName;
            while ((columnName = this.ParseField()) != null)
            {
                readColumns.Add(columnName);
                if (this.curChar == this.fieldSeparator)
                    this.NextChar();
                else
                    break;
            }
            this.columns = readColumns.ToArray();
            Columns = this.columns;
        }

        /// <summary>
        /// Reads the next line.
        /// </summary>
        private void ReadNextLine()
        {
            this.line = this.textReader.ReadLine();
            this.pos = -1;
            if (this.line == null)
            {
                this.len = 0;
                this.curChar = '\0';
            }
            else
            {
                this.len = this.line.Length;
                this.NextChar();
            }
        }
    }
}