using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using System.Reflection;
using MLEM.Misc;

namespace MLEM.Data {
    /// <summary>
    /// A dynamic enum is a class that represents enum-like single-instance value behavior with additional capabilities, including dynamic addition of new arbitrary values.
    /// A dynamic enum uses <see cref="BigInteger"/> as its underlying type, allowing for an arbitrary number of enum values to be created, even when a <see cref="FlagsAttribute"/>-like structure is used that would only allow for up to 64 values in a regular enum.
    /// All enum operations including <see cref="And{T}"/>, <see cref="Or{T}"/>, <see cref="Xor{T}"/> and <see cref="Neg{T}"/> are supported and can be implemented in derived classes using operator overloads.
    /// To create a custom dynamic enum, simply create a class that extends <see cref="DynamicEnum"/>. New values can then be added using <see cref="Add{T}"/>, <see cref="AddValue{T}"/> or <see cref="AddFlag{T}"/>.
    /// </summary>
    /// <remarks>
    /// To include enum-like operator overloads in a dynamic enum named MyEnum, the following code can be used:
    /// <code>
    /// public static implicit operator BigInteger(MyEnum value) => GetValue(value);
    /// public static implicit operator MyEnum(BigInteger value) => GetEnumValue&lt;MyEnum&gt;(value);
    /// public static MyEnum operator |(MyEnum left, MyEnum right) => Or(left, right);
    /// public static MyEnum operator &amp;(MyEnum left, MyEnum right) => And(left, right);
    /// public static MyEnum operator ^(MyEnum left, MyEnum right) => Xor(left, right);
    /// public static MyEnum operator ~(MyEnum value) => Neg(value);
    /// </code>
    /// </remarks>
    public abstract class DynamicEnum : GenericDataHolder {

        private static readonly Dictionary<Type, Dictionary<BigInteger, DynamicEnum>> Values = new Dictionary<Type, Dictionary<BigInteger, DynamicEnum>>();
        private static readonly Dictionary<Type, Dictionary<BigInteger, DynamicEnum>> FlagCache = new Dictionary<Type, Dictionary<BigInteger, DynamicEnum>>();
        private static readonly Dictionary<string, DynamicEnum> ParseCache = new Dictionary<string, DynamicEnum>();

        private readonly BigInteger value;
        private string name;

        /// <summary>
        /// Creates a new dynamic enum instance.
        /// This constructor is protected as it is only invoked via reflection.
        /// </summary>
        /// <param name="name">The name of the enum value</param>
        /// <param name="value">The value</param>
        protected DynamicEnum(string name, BigInteger value) {
            this.value = value;
            this.name = name;
        }

        /// <summary>
        /// Returns true if this enum value has the given <see cref="DynamicEnum"/> flag on it.
        /// This operation is equivalent to <see cref="Enum.HasFlag"/>.
        /// </summary>
        /// <param name="flag">The flag to query</param>
        /// <returns>True if the flag is present, false otherwise</returns>
        public bool HasFlag(DynamicEnum flag) {
            return (GetValue(this) & GetValue(flag)) == GetValue(flag);
        }

        /// <inheritdoc />
        public override string ToString() {
            if (this.name == null) {
                var included = new List<DynamicEnum>();
                if (GetValue(this) != 0) {
                    foreach (var v in GetValues(this.GetType())) {
                        if (this.HasFlag(v) && GetValue(v) != 0)
                            included.Add(v);
                    }
                }
                this.name = included.Count > 0 ? string.Join(" | ", included) : GetValue(this).ToString();
            }
            return this.name;
        }

        /// <summary>
        /// Adds a new enum value to the given enum type <typeparamref name="T"/>
        /// </summary>
        /// <param name="name">The name of the enum value to add</param>
        /// <param name="value">The value to add</param>
        /// <typeparam name="T">The type to add this value to</typeparam>
        /// <returns>The newly created enum value</returns>
        /// <exception cref="ArgumentException">Thrown if the name or value passed are already present</exception>
        public static T Add<T>(string name, BigInteger value) where T : DynamicEnum {
            if (!Values.TryGetValue(typeof(T), out var dict)) {
                dict = new Dictionary<BigInteger, DynamicEnum>();
                Values.Add(typeof(T), dict);
            }

            if (dict.ContainsKey(value))
                throw new ArgumentException($"Duplicate value {value}", nameof(value));
            if (dict.Values.Any(v => v.name == name))
                throw new ArgumentException($"Duplicate name {name}", nameof(name));

            var ret = Construct(typeof(T), name, value);
            dict.Add(value, ret);
            return (T) ret;
        }

        /// <summary>
        /// Adds a new enum value to the given enum type <typeparamref name="T"/>.
        /// This method differs from <see cref="Add{T}"/> in that it automatically determines a value.
        /// The value determined will be the next free number in a sequence, which represents the default behavior in an enum if enum values are not explicitly numbered.
        /// </summary>
        /// <param name="name">The name of the enum value to add</param>
        /// <typeparam name="T">The type to add this value to</typeparam>
        /// <returns>The newly created enum value</returns>
        public static T AddValue<T>(string name) where T : DynamicEnum {
            BigInteger value = 0;
            if (Values.TryGetValue(typeof(T), out var defined)) {
                while (defined.ContainsKey(value))
                    value++;
            }
            return Add<T>(name, value);
        }

        /// <summary>
        /// Adds a new flag enum value to the given enum type <typeparamref name="T"/>.
        /// This method differs from <see cref="Add{T}"/> in that it automatically determines a value.
        /// The value determined will be the next free power of two, allowing enum values to be combined using bitwise operations to create <see cref="FlagsAttribute"/>-like behavior.
        /// </summary>
        /// <param name="name">The name of the enum value to add</param>
        /// <typeparam name="T">The type to add this value to</typeparam>
        /// <returns>The newly created enum value</returns>
        public static T AddFlag<T>(string name) where T : DynamicEnum {
            BigInteger value = 0;
            if (Values.TryGetValue(typeof(T), out var defined)) {
                while (defined.ContainsKey(value))
                    value <<= 1;
            }
            return Add<T>(name, value);
        }

        /// <summary>
        /// Returns a collection of all of the enum values that are explicitly defined for the given dynamic enum type <typeparamref name="T"/>.
        /// A value counts as explicitly defined if it has been added using <see cref="Add{T}"/>, <see cref="AddValue{T}"/> or <see cref="AddFlag{T}"/>.
        /// </summary>
        /// <typeparam name="T">The type whose values to get</typeparam>
        /// <returns>The defined values for the given type</returns>
        public static IEnumerable<T> GetValues<T>() where T : DynamicEnum {
            return GetValues(typeof(T)).Cast<T>();
        }

        /// <summary>
        /// Returns a collection of all of the enum values that are explicitly defined for the given dynamic enum type <paramref name="type"/>.
        /// A value counts as explicitly defined if it has been added using <see cref="Add{T}"/>, <see cref="AddValue{T}"/> or <see cref="AddFlag{T}"/>.
        /// </summary>
        /// <param name="type">The type whose values to get</param>
        /// <returns>The defined values for the given type</returns>
        public static IEnumerable<DynamicEnum> GetValues(Type type) {
            return Values.TryGetValue(type, out var ret) ? ret.Values : Enumerable.Empty<DynamicEnum>();
        }

        /// <summary>
        /// Returns the bitwise OR (|) combination of the two dynamic enum values
        /// </summary>
        /// <param name="left">The left value</param>
        /// <param name="right">The right value</param>
        /// <typeparam name="T">The type of the values</typeparam>
        /// <returns>The bitwise OR (|) combination</returns>
        public static T Or<T>(T left, T right) where T : DynamicEnum {
            return GetEnumValue<T>(GetValue(left) | GetValue(right));
        }

        /// <summary>
        /// Returns the bitwise AND (&amp;) combination of the two dynamic enum values
        /// </summary>
        /// <param name="left">The left value</param>
        /// <param name="right">The right value</param>
        /// <typeparam name="T">The type of the values</typeparam>
        /// <returns>The bitwise AND (&amp;) combination</returns>
        public static T And<T>(T left, T right) where T : DynamicEnum {
            return GetEnumValue<T>(GetValue(left) & GetValue(right));
        }

        /// <summary>
        /// Returns the bitwise XOR (^) combination of the two dynamic enum values
        /// </summary>
        /// <param name="left">The left value</param>
        /// <param name="right">The right value</param>
        /// <typeparam name="T">The type of the values</typeparam>
        /// <returns>The bitwise XOR (^) combination</returns>
        public static T Xor<T>(T left, T right) where T : DynamicEnum {
            return GetEnumValue<T>(GetValue(left) ^ GetValue(right));
        }

        /// <summary>
        /// Returns the bitwise NEG (~) combination of the dynamic enum value
        /// </summary>
        /// <param name="value">The value</param>
        /// <typeparam name="T">The type of the values</typeparam>
        /// <returns>The bitwise NEG (~) value</returns>
        public static T Neg<T>(T value) where T : DynamicEnum {
            return GetEnumValue<T>(~GetValue(value));
        }

        /// <summary>
        /// Returns the <see cref="BigInteger"/> representation of the given dynamic enum value
        /// </summary>
        /// <param name="value">The value whose number representation to get</param>
        /// <returns>The value's number representation</returns>
        public static BigInteger GetValue(DynamicEnum value) {
            return value?.value ?? 0;
        }

        /// <summary>
        /// Returns the defined or combined dynamic enum value for the given <see cref="BigInteger"/> representation
        /// </summary>
        /// <param name="value">The value whose dynamic enum value to get</param>
        /// <typeparam name="T">The type that the returned dynamic enum should have</typeparam>
        /// <returns>The defined or combined dynamic enum value</returns>
        public static T GetEnumValue<T>(BigInteger value) where T : DynamicEnum {
            return (T) GetEnumValue(typeof(T), value);
        }

        /// <summary>
        /// Returns the defined or combined dynamic enum value for the given <see cref="BigInteger"/> representation
        /// </summary>
        /// <param name="type">The type that the returned dynamic enum should have</param>
        /// <param name="value">The value whose dynamic enum value to get</param>
        /// <returns>The defined or combined dynamic enum value</returns>
        public static DynamicEnum GetEnumValue(Type type, BigInteger value) {
            // get the defined value if it exists
            if (Values.TryGetValue(type, out var values) && values.TryGetValue(value, out var defined))
                return defined;

            // otherwise, cache the combined value
            if (!FlagCache.TryGetValue(type, out var cache)) {
                cache = new Dictionary<BigInteger, DynamicEnum>();
                FlagCache.Add(type, cache);
            }
            if (!cache.TryGetValue(value, out var combined)) {
                combined = Construct(type, null, value);
                cache.Add(value, combined);
            }
            return combined;
        }

        /// <summary>
        /// Parses the given <see cref="string"/> into a dynamic enum value and returns the result.
        /// This method supports defined enum values as well as values combined using the pipe (|) character and any number of spaces.
        /// If no enum value can be parsed, null is returned.
        /// </summary>
        /// <param name="strg">The string to parse into a dynamic enum value</param>
        /// <typeparam name="T">The type of the dynamic enum value to parse</typeparam>
        /// <returns>The parsed enum value, or null if parsing fails</returns>
        public static T Parse<T>(string strg) where T : DynamicEnum {
            return (T) Parse(typeof(T), strg);
        }

        /// <summary>
        /// Parses the given <see cref="string"/> into a dynamic enum value and returns the result.
        /// This method supports defined enum values as well as values combined using the pipe (|) character and any number of spaces.
        /// If no enum value can be parsed, null is returned.        /// </summary>
        /// <param name="type">The type of the dynamic enum value to parse</param>
        /// <param name="strg">The string to parse into a dynamic enum value</param>
        /// <returns>The parsed enum value, or null if parsing fails</returns>
        public static DynamicEnum Parse(Type type, string strg) {
            if (!ParseCache.TryGetValue(strg, out var cached)) {
                BigInteger? accum = null;
                foreach (var val in strg.Split('|')) {
                    foreach (var defined in GetValues(type)) {
                        if (defined.name == val.Trim()) {
                            accum = (accum ?? 0) | GetValue(defined);
                            break;
                        }
                    }
                }
                if (accum != null)
                    cached = GetEnumValue(type, accum.Value);
                ParseCache.Add(strg, cached);
            }
            return cached;
        }

        private static DynamicEnum Construct(Type type, string name, BigInteger value) {
            var constructor = type.GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, new[] {typeof(string), typeof(BigInteger)}, null);
            return (DynamicEnum) constructor.Invoke(new object[] {name, value});
        }

    }
}