// Copyright (c) .NET Foundation and contributors. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

using System;
using System.Collections.Generic;
using System.Linq;
using Mono.Cecil;
using Mono.Cecil.Cil;

namespace TLens.Analyzers
{
    sealed class InverterCtorsChainAnalyzer : Analyzer
    {
        readonly List<(MethodDefinition, MethodDefinition)> ctors = new List<(MethodDefinition, MethodDefinition)>();

        protected override void ProcessMethod(MethodDefinition method)
        {
            if (!method.IsConstructor || !method.DeclaringType.IsClass)
                return;

            foreach (var instr in method.Body.Instructions)
            {
                switch (instr.OpCode.Code)
                {
                    case Code.Call:
                        var mr = (MethodReference)instr.Operand;
                        var md = mr.Resolve();
                        if (md == null)
                            return;

                        if (!md.IsConstructor)
                            return;

                        if (md.DeclaringType != method.DeclaringType)
                            return;

                        if (md.Parameters.Count <= method.Parameters.Count)
                            return;

                        var prev = instr.Previous.OpCode.Code;
                        if (prev == Code.Ldnull || prev == Code.Ldc_I4_0)
                            ctors.Add((method, md));

                        break;
                }
            }
        }

        public override void PrintResults(int maxCount)
        {
            var entries = ctors.OrderByDescending(l => l.Item2.GetEstimatedSize()).Take(maxCount);
            if (!entries.Any())
                return;

            PrintHeader("Constructors with possibly inverted initializations");

            foreach (var entry in entries)
            {
                Console.WriteLine($"Constructor '{entry.Item1.ToDisplay()}' calls possibly unnecessary initialization in '{entry.Item2.ToDisplay(showSize: true)}'");
            }
        }
    }
}