// 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.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Internal.Log;
using Microsoft.CodeAnalysis.Options;
using Microsoft.VisualStudio.Telemetry;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.Telemetry
{
    internal abstract class TelemetryLogger : ILogger
    {
        private sealed class Implementation : TelemetryLogger
        {
            private readonly TelemetrySession _session;
 
            public Implementation(TelemetrySession session, bool logDelta)
            {
                _session = session;
                LogDelta = logDelta;
            }
 
            protected override bool LogDelta { get; }
 
            public override bool IsEnabled(FunctionId functionId)
                => _session.IsOptedIn;
 
            protected override void PostEvent(TelemetryEvent telemetryEvent)
                => _session.PostEvent(telemetryEvent);
 
            protected override object Start(string eventName, LogType type)
                => type switch
                {
                    LogType.Trace => _session.StartOperation(eventName),
                    LogType.UserAction => _session.StartUserTask(eventName),
                    _ => throw ExceptionUtilities.UnexpectedValue(type),
                };
 
            protected override TelemetryEvent GetEndEvent(object scope)
                => scope switch
                {
                    TelemetryScope<OperationEvent> operation => operation.EndEvent,
                    TelemetryScope<UserTaskEvent> userTask => userTask.EndEvent,
                    _ => throw ExceptionUtilities.UnexpectedValue(scope)
                };
 
            protected override void End(object scope, TelemetryResult result)
            {
                if (scope is TelemetryScope<OperationEvent> operation)
                    operation.End(result);
                else if (scope is TelemetryScope<UserTaskEvent> userTask)
                    userTask.End(result);
                else
                    throw ExceptionUtilities.UnexpectedValue(scope);
            }
        }
 
        private readonly ConcurrentDictionary<int, object> _pendingScopes = new(concurrencyLevel: 2, capacity: 10);
 
        private const string EventPrefix = "vs/ide/vbcs/";
        private const string PropertyPrefix = "vs.ide.vbcs.";
 
        // these don't have concurrency limit on purpose to reduce chance of lock contention. 
        // if that becomes a problem - by showing up in our perf investigation, then we will consider adding concurrency limit.
        private static readonly ConcurrentDictionary<FunctionId, string> s_eventMap = new();
        private static readonly ConcurrentDictionary<(FunctionId id, string name), string> s_propertyMap = new();
 
        protected abstract bool LogDelta { get; }
 
        internal static string GetEventName(FunctionId id)
             => s_eventMap.GetOrAdd(id, id => EventPrefix + GetTelemetryName(id, separator: '/'));
 
        internal static string GetPropertyName(FunctionId id, string name)
            => s_propertyMap.GetOrAdd((id, name), key => PropertyPrefix + GetTelemetryName(id, separator: '.') + "." + key.name.ToLowerInvariant());
 
        private static string GetTelemetryName(FunctionId id, char separator)
            => Enum.GetName(typeof(FunctionId), id)!.Replace('_', separator).ToLowerInvariant();
 
        public static TelemetryLogger Create(TelemetrySession session, bool logDelta)
            => new Implementation(session, logDelta);
 
        public abstract bool IsEnabled(FunctionId functionId);
        protected abstract void PostEvent(TelemetryEvent telemetryEvent);
        protected abstract object Start(string eventName, LogType type);
        protected abstract void End(object scope, TelemetryResult result);
        protected abstract TelemetryEvent GetEndEvent(object scope);
 
        public void Log(FunctionId functionId, LogMessage logMessage)
        {
            if (IgnoreMessage(logMessage))
            {
                return;
            }
 
            var telemetryEvent = new TelemetryEvent(GetEventName(functionId));
            SetProperties(telemetryEvent, functionId, logMessage);
 
            try
            {
                PostEvent(telemetryEvent);
            }
            catch
            {
            }
        }
 
        public void LogBlockStart(FunctionId functionId, LogMessage logMessage, int blockId, CancellationToken cancellationToken)
        {
            if (IgnoreMessage(logMessage))
            {
                return;
            }
 
            var eventName = GetEventName(functionId);
            var kind = GetKind(logMessage);
 
            try
            {
                _pendingScopes[blockId] = Start(eventName, kind);
            }
            catch
            {
            }
        }
 
        public void LogBlockEnd(FunctionId functionId, LogMessage logMessage, int blockId, int delta, CancellationToken cancellationToken)
        {
            if (IgnoreMessage(logMessage))
            {
                return;
            }
 
            Contract.ThrowIfFalse(_pendingScopes.TryRemove(blockId, out var scope));
 
            var endEvent = GetEndEvent(scope);
            SetProperties(endEvent, functionId, logMessage, LogDelta ? delta : null);
 
            var result = cancellationToken.IsCancellationRequested ? TelemetryResult.UserCancel : TelemetryResult.Success;
 
            try
            {
                End(scope, result);
            }
            catch
            {
            }
        }
 
        private static bool IgnoreMessage(LogMessage logMessage)
            => logMessage.LogLevel < LogLevel.Information;
 
        private static LogType GetKind(LogMessage logMessage)
            => logMessage is KeyValueLogMessage kvLogMessage
                                ? kvLogMessage.Kind
                                : logMessage.LogLevel switch
                                {
                                    >= LogLevel.Information => LogType.UserAction,
                                    _ => LogType.Trace
                                };
 
        private static void SetProperties(TelemetryEvent telemetryEvent, FunctionId functionId, LogMessage logMessage, int? delta = null)
        {
            if (logMessage is KeyValueLogMessage kvLogMessage)
            {
                AppendProperties(telemetryEvent, functionId, kvLogMessage);
            }
            else
            {
                var message = logMessage.GetMessage();
                if (!string.IsNullOrWhiteSpace(message))
                {
                    var propertyName = GetPropertyName(functionId, "Message");
                    telemetryEvent.Properties.Add(propertyName, message);
                }
            }
 
            if (delta.HasValue)
            {
                var propertyName = GetPropertyName(functionId, "Delta");
                telemetryEvent.Properties.Add(propertyName, delta.Value);
            }
        }
 
        private static void AppendProperties(TelemetryEvent telemetryEvent, FunctionId functionId, KeyValueLogMessage logMessage)
        {
            foreach (var (name, value) in logMessage.Properties)
            {
                // call SetProperty. VS telemetry will take care of finding correct
                // API based on given object type for us.
                // 
                // numeric data will show up in ES with measurement prefix.
 
                telemetryEvent.Properties.Add(GetPropertyName(functionId, name), value switch
                {
                    PiiValue pii => new TelemetryPiiProperty(pii.Value),
                    IEnumerable<object> items => new TelemetryComplexProperty(items.Select(item => (item is PiiValue pii) ? new TelemetryPiiProperty(pii.Value) : item)),
                    _ => value
                });
            }
        }
    }
}