// 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.Collections.Generic;
using System.Diagnostics;
using Microsoft.CodeAnalysis.PooledObjects;
 
namespace Microsoft.CodeAnalysis.Internal.Log
{
    /// <summary>
    /// Defines a log aggregator to create a histogram
    /// </summary>
    internal sealed class HistogramLogAggregator<TKey> : AbstractLogAggregator<TKey, HistogramLogAggregator<TKey>.HistogramCounter> where TKey : notnull
    {
        private readonly int _bucketSize;
        private readonly int _maxBucketValue;
        private readonly int _bucketCount;
 
        public HistogramLogAggregator(int bucketSize, int maxBucketValue)
        {
            if (bucketSize <= 0 || maxBucketValue <= 0 || maxBucketValue % bucketSize != 0)
            {
                throw new ArgumentException();
            }
 
            _bucketSize = bucketSize;
            _maxBucketValue = maxBucketValue;
            _bucketCount = maxBucketValue / bucketSize + 1;
        }
 
        protected override HistogramCounter CreateCounter()
            => new(_bucketSize, _maxBucketValue, _bucketCount);
 
        public void IncreaseCount(TKey key, int value)
        {
            var counter = GetCounter(key);
            counter.IncreaseCount(value);
        }
 
        public void LogTime(TKey key, TimeSpan timeSpan)
        {
            var counter = GetCounter(key);
            counter.IncreaseCount((int)timeSpan.TotalMilliseconds);
        }
 
        public HistogramCounter? GetValue(TKey key)
        {
            TryGetCounter(key, out var counter);
            return counter;
        }
 
        internal sealed class HistogramCounter
        {
            private readonly int[] _buckets;
 
            public int BucketCount { get; }
            public int BucketSize { get; }
            public int MaxBucketValue { get; }
 
            public HistogramCounter(int bucketSize, int maxBucketValue, int bucketCount)
            {
                Debug.Assert(bucketSize > 0 && maxBucketValue > 0 && bucketCount > 0);
 
                BucketSize = bucketSize;
                MaxBucketValue = maxBucketValue;
                BucketCount = bucketCount;
                _buckets = new int[BucketCount];
            }
 
            public void IncreaseCount(int value)
            {
                var bucket = GetBucket(value);
                _buckets[bucket]++;
            }
 
            public string GetBucketsAsString()
            {
                var pooledStringBuilder = PooledStringBuilder.GetInstance();
                var builder = pooledStringBuilder.Builder;
 
                builder.Append('[');
                builder.Append(_buckets[0]);
 
                for (var i = 1; i < _buckets.Length; ++i)
                {
                    builder.Append(',');
                    builder.Append(_buckets[i]);
                }
 
                builder.Append(']');
                return pooledStringBuilder.ToStringAndFree();
            }
 
            private int GetBucket(int value)
            {
                var bucket = value / BucketSize;
                if (bucket >= BucketCount)
                {
                    bucket = BucketCount - 1;
                }
 
                return bucket;
            }
 
            /// <summary>
            /// Writes out these statistics to a property bag for sending to telemetry.
            /// </summary>
            /// <param name="prefix">The prefix given to any properties written. A period is used to delimit between the 
            /// prefix and the value.</param>
            public void WriteTelemetryPropertiesTo(Dictionary<string, object?> properties, string prefix)
            {
                prefix += ".";
 
                properties.Add(prefix + nameof(BucketSize), BucketSize);
                properties.Add(prefix + nameof(MaxBucketValue), MaxBucketValue);
                properties.Add(prefix + "Buckets", GetBucketsAsString());
            }
        }
    }
}