// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System;
using System.Diagnostics;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.CodeAnalysis.PooledObjects;
using System.Diagnostics.CodeAnalysis;
 
namespace Microsoft.CodeAnalysis.Internal.Log
{
    /// <summary>
    /// LogMessage that creates key value map lazily
    /// </summary>
    internal sealed class KeyValueLogMessage : LogMessage
    {
        private static readonly ObjectPool<KeyValueLogMessage> s_pool = new(() => new KeyValueLogMessage(), 20);
 
        public static readonly KeyValueLogMessage NoProperty = new();
 
        /// <summary>
        /// Creates a <see cref="KeyValueLogMessage"/> with default <see cref="LogLevel.Information"/>, since
        /// KV Log Messages are by default more informational and should be logged as such. 
        /// </summary>
        public static KeyValueLogMessage Create(Action<Dictionary<string, object?>> propertySetter, LogLevel logLevel = LogLevel.Information)
        {
            var logMessage = s_pool.Allocate();
            logMessage.Initialize(LogType.Trace, propertySetter, logLevel);
 
            return logMessage;
        }
 
        public static KeyValueLogMessage Create(LogType kind, LogLevel logLevel = LogLevel.Information)
            => Create(kind, propertySetter: null, logLevel);
 
        public static KeyValueLogMessage Create(LogType kind, Action<Dictionary<string, object?>>? propertySetter, LogLevel logLevel = LogLevel.Information)
        {
            var logMessage = s_pool.Allocate();
            logMessage.Initialize(kind, propertySetter, logLevel);
 
            return logMessage;
        }
 
        private LogType _kind;
        private Dictionary<string, object?>? _lazyMap;
        private Action<Dictionary<string, object?>>? _propertySetter;
 
        private KeyValueLogMessage()
        {
            // prevent it from being created directly
            _kind = LogType.Trace;
        }
 
        private void Initialize(LogType kind, Action<Dictionary<string, object?>>? propertySetter, LogLevel logLevel)
        {
            _kind = kind;
            _propertySetter = propertySetter;
            LogLevel = logLevel;
        }
 
        public LogType Kind => _kind;
 
        public bool ContainsProperty
        {
            get
            {
                EnsureMap();
                return _lazyMap.Count > 0;
            }
        }
 
        public IEnumerable<KeyValuePair<string, object?>> Properties
        {
            get
            {
                EnsureMap();
                return _lazyMap;
            }
        }
 
        protected override string CreateMessage()
        {
            EnsureMap();
 
            const char PairSeparator = '|';
            const char KeyValueSeparator = '=';
            const char ItemSeparator = ',';
 
            using var _ = PooledStringBuilder.GetInstance(out var builder);
 
            foreach (var entry in _lazyMap)
            {
                if (builder.Length > 0)
                {
                    builder.Append(PairSeparator);
                }
 
                Append(builder, entry.Key);
                builder.Append(KeyValueSeparator);
 
                if (entry.Value is IEnumerable<object> items)
                {
                    var first = true;
                    foreach (var item in items)
                    {
                        if (first)
                        {
                            first = false;
                        }
                        else
                        {
                            builder.Append(ItemSeparator);
                        }
 
                        Append(builder, item);
                    }
                }
                else
                {
                    Append(builder, entry.Value);
                }
            }
 
            static void Append(StringBuilder builder, object? value)
            {
                if (value != null)
                {
                    var str = value.ToString();
                    Debug.Assert(str != null && !str.Contains(PairSeparator) && !str.Contains(KeyValueSeparator) && !str.Contains(ItemSeparator));
                    builder.Append(str);
                }
            }
 
            return builder.ToString();
        }
 
        protected override void FreeCore()
        {
            if (this == NoProperty)
            {
                return;
            }
 
            if (_lazyMap != null)
            {
                SharedPools.Default<Dictionary<string, object?>>().ClearAndFree(_lazyMap);
                _lazyMap = null;
            }
 
            _propertySetter = null;
 
            // always pool it back
            s_pool.Free(this);
        }
 
        [MemberNotNull(nameof(_lazyMap))]
        private void EnsureMap()
        {
            // always create _map
            if (_lazyMap == null)
            {
                _lazyMap = SharedPools.Default<Dictionary<string, object?>>().AllocateAndClear();
                _propertySetter?.Invoke(_lazyMap);
            }
        }
    }
 
    /// <summary>
    /// Type of log it is making.
    /// </summary>
    internal enum LogType
    {
        /// <summary>
        /// Log some traces of an activity (default)
        /// </summary>
        Trace,
 
        /// <summary>
        /// Log an user explicit action
        /// </summary>
        UserAction,
    }
}