// <copyright file="CompositeMetricReader.cs" company="OpenTelemetry Authors">
// Copyright The OpenTelemetry Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// </copyright>

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;
using OpenTelemetry.Internal;

namespace OpenTelemetry.Metrics
{
    /// <summary>
    /// CompositeMetricReader that does not deal with adding metrics and recording measurements.
    /// </summary>
    internal sealed partial class CompositeMetricReader : MetricReader
    {
        public readonly DoublyLinkedListNode Head;
        private DoublyLinkedListNode tail;
        private bool disposed;
        private int count;

        public CompositeMetricReader(IEnumerable<MetricReader> readers)
        {
            Guard.ThrowIfNull(readers);

            using var iter = readers.GetEnumerator();
            if (!iter.MoveNext())
            {
                throw new ArgumentException($"'{iter}' is null or empty", nameof(iter));
            }

            this.Head = new DoublyLinkedListNode(iter.Current);
            this.tail = this.Head;
            this.count++;

            while (iter.MoveNext())
            {
                this.AddReader(iter.Current);
            }
        }

        public CompositeMetricReader AddReader(MetricReader reader)
        {
            Guard.ThrowIfNull(reader);

            var node = new DoublyLinkedListNode(reader)
            {
                Previous = this.tail,
            };
            this.tail.Next = node;
            this.tail = node;
            this.count++;

            return this;
        }

        public Enumerator GetEnumerator() => new(this.Head);

        /// <inheritdoc/>
        internal override bool ProcessMetrics(in Batch<Metric> metrics, int timeoutMilliseconds)
        {
            // CompositeMetricReader delegates the work to its underlying readers,
            // so CompositeMetricReader.ProcessMetrics should never be called.
            throw new NotSupportedException();
        }

        /// <inheritdoc/>
        protected override bool OnCollect(int timeoutMilliseconds = Timeout.Infinite)
        {
            var result = true;
            var sw = timeoutMilliseconds == Timeout.Infinite
                ? null
                : Stopwatch.StartNew();

            for (var cur = this.Head; cur != null; cur = cur.Next)
            {
                if (sw == null)
                {
                    result = cur.Value.Collect(Timeout.Infinite) && result;
                }
                else
                {
                    var timeout = timeoutMilliseconds - sw.ElapsedMilliseconds;

                    // notify all the readers, even if we run overtime
                    result = cur.Value.Collect((int)Math.Max(timeout, 0)) && result;
                }
            }

            return result;
        }

        /// <inheritdoc/>
        protected override bool OnShutdown(int timeoutMilliseconds)
        {
            var result = true;
            var sw = timeoutMilliseconds == Timeout.Infinite
                ? null
                : Stopwatch.StartNew();

            for (var cur = this.Head; cur != null; cur = cur.Next)
            {
                if (sw == null)
                {
                    result = cur.Value.Shutdown(Timeout.Infinite) && result;
                }
                else
                {
                    var timeout = timeoutMilliseconds - sw.ElapsedMilliseconds;

                    // notify all the readers, even if we run overtime
                    result = cur.Value.Shutdown((int)Math.Max(timeout, 0)) && result;
                }
            }

            return result;
        }

        protected override void Dispose(bool disposing)
        {
            if (!this.disposed)
            {
                if (disposing)
                {
                    for (var cur = this.Head; cur != null; cur = cur.Next)
                    {
                        try
                        {
                            cur.Value?.Dispose();
                        }
                        catch (Exception ex)
                        {
                            OpenTelemetrySdkEventSource.Log.MetricReaderException(nameof(this.Dispose), ex);
                        }
                    }
                }

                this.disposed = true;
            }

            base.Dispose(disposing);
        }

        public struct Enumerator
        {
            private DoublyLinkedListNode node;

            internal Enumerator(DoublyLinkedListNode node)
            {
                this.node = node;
                this.Current = null;
            }

            public MetricReader Current { get; private set; }

            public bool MoveNext()
            {
                if (this.node != null)
                {
                    this.Current = this.node.Value;
                    this.node = this.node.Next;
                    return true;
                }

                return false;
            }
        }

        internal sealed class DoublyLinkedListNode
        {
            public readonly MetricReader Value;

            public DoublyLinkedListNode(MetricReader value)
            {
                this.Value = value;
            }

            public DoublyLinkedListNode Previous { get; set; }

            public DoublyLinkedListNode Next { get; set; }
        }
    }
}
