using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Debug = UnityEngine.Debug;
using Stopwatch = System.Diagnostics.Stopwatch;

namespace io.github.hatayama.uLoopMCP
{
    /// <summary>
    /// Dynamic compilation service for execute-dynamic-code.
    /// Keeps the orchestration flow in one place and delegates low-level compiler concerns to helpers.
    /// </summary>
    public sealed class DynamicCodeCompiler : IDynamicCompilationService, IDisposable
    {
        private readonly DynamicCodeSecurityLevel _securityLevel;
        private readonly IDynamicCompilationPlanner _planner;
        private readonly ICompiledAssemblyBuilder _assemblyBuilder;
        private readonly ICompiledAssemblyLoader _assemblyLoader;
        private readonly CompilationCacheManager _cacheManager = new();
        private bool _disposed;

        internal int LastBuildCount { get; private set; }

        public DynamicCodeCompiler(DynamicCodeSecurityLevel securityLevel)
            : this(
                securityLevel,
                DynamicCodeServices.CompilationPlanner,
                DynamicCodeServices.AssemblyBuilder,
                DynamicCodeServices.AssemblyLoadService)
        {
        }

        internal DynamicCodeCompiler(
            DynamicCodeSecurityLevel securityLevel,
            IDynamicCompilationPlanner planner,
            ICompiledAssemblyBuilder assemblyBuilder,
            ICompiledAssemblyLoader assemblyLoader)
        {
            _securityLevel = securityLevel;
            _planner = planner ?? throw new ArgumentNullException(nameof(planner));
            _assemblyBuilder = assemblyBuilder ?? throw new ArgumentNullException(nameof(assemblyBuilder));
            _assemblyLoader = assemblyLoader ?? throw new ArgumentNullException(nameof(assemblyLoader));
        }

        public void Dispose()
        {
            if (_disposed)
            {
                return;
            }

            _cacheManager.ClearCache();
            _disposed = true;
        }

        public async Task<CompilationResult> CompileAsync(CompilationRequest request, CancellationToken ct = default)
        {
            Debug.Assert(request != null, "request must not be null");
            Debug.Assert(!string.IsNullOrWhiteSpace(request.Code), "request.Code must not be empty");

            ct.ThrowIfCancellationRequested();
            LastBuildCount = 0;
            Stopwatch compilerTotalStopwatch = Stopwatch.StartNew();
            Stopwatch planStopwatch = Stopwatch.StartNew();

            DynamicCompilationPlan plan = _planner.CreatePlan(request);
            planStopwatch.Stop();

            Stopwatch cacheStopwatch = Stopwatch.StartNew();
            CompilationResult cachedResult = TryGetCachedResult(plan);
            cacheStopwatch.Stop();
            if (cachedResult != null)
            {
                AppendCompilerStageTimings(
                    cachedResult.Timings,
                    planStopwatch.Elapsed.TotalMilliseconds,
                    cacheStopwatch.Elapsed.TotalMilliseconds,
                    0,
                    compilerTotalStopwatch.Elapsed.TotalMilliseconds);
                return cachedResult;
            }

            Stopwatch sourceSecurityStopwatch = Stopwatch.StartNew();
            CompilationResult sourceSecurityFailure = CreateSourceSecurityFailure(request.Code);
            sourceSecurityStopwatch.Stop();
            if (sourceSecurityFailure != null)
            {
                AppendCompilerStageTimings(
                    sourceSecurityFailure.Timings,
                    planStopwatch.Elapsed.TotalMilliseconds,
                    cacheStopwatch.Elapsed.TotalMilliseconds,
                    0,
                    compilerTotalStopwatch.Elapsed.TotalMilliseconds);
                return sourceSecurityFailure;
            }

            if (plan.PreparedCode.PreparedSource == null)
            {
                CompilationResult mixedModeFailure = CreateMixedModeFailureResult(request.Code, 0, 0);
                AppendCompilerStageTimings(
                    mixedModeFailure.Timings,
                    planStopwatch.Elapsed.TotalMilliseconds,
                    cacheStopwatch.Elapsed.TotalMilliseconds,
                    0,
                    compilerTotalStopwatch.Elapsed.TotalMilliseconds);
                return mixedModeFailure;
            }

            Stopwatch builderTotalStopwatch = Stopwatch.StartNew();
            CompiledAssemblyBuildResult buildResult = await _assemblyBuilder.BuildAsync(plan, ct);
            builderTotalStopwatch.Stop();
            LastBuildCount = buildResult.BuildCount;

            if (buildResult.Diagnostics.Errors.Count > 0)
            {
                CompilationResult failureResult = new CompilationResult
                {
                    Success = false,
                    Errors = buildResult.Diagnostics.Errors,
                    Warnings = buildResult.Diagnostics.Warnings,
                    UpdatedCode = buildResult.UpdatedSource,
                    FailureReason = CompilationFailureReason.CompilationError,
                    AmbiguousTypeCandidates = buildResult.AmbiguousTypeCandidates,
                    AutoInjectedNamespaces = buildResult.AutoInjectedNamespaces,
                    AdvisoryLogs = BuildAdvisoryLogs(buildResult.CompilationBackendKind),
                    CompilationBackendKind = buildResult.CompilationBackendKind,
                    Timings = DynamicCompilationTimingFormatter.CreateCompilationTimings(
                        buildResult.ReferenceResolutionMilliseconds,
                        buildResult.BuildMilliseconds,
                        0,
                        buildResult.CompilationBackendKind)
                };
                AppendCompilerStageTimings(
                    failureResult.Timings,
                    planStopwatch.Elapsed.TotalMilliseconds,
                    cacheStopwatch.Elapsed.TotalMilliseconds,
                    builderTotalStopwatch.Elapsed.TotalMilliseconds,
                    compilerTotalStopwatch.Elapsed.TotalMilliseconds);
                return failureResult;
            }

            CompiledAssemblyLoadResult assemblyLoadResult = _assemblyLoader.Load(
                _securityLevel,
                buildResult.AssemblyBytes);
            if (!assemblyLoadResult.Success)
            {
                CompilationResult assemblySecurityFailure = CreateAssemblySecurityFailure(
                    assemblyLoadResult.SecurityViolations,
                    buildResult.Diagnostics.Warnings,
                    buildResult.UpdatedSource,
                    buildResult.AmbiguousTypeCandidates,
                    buildResult.AutoInjectedNamespaces,
                    buildResult.ReferenceResolutionMilliseconds,
                    buildResult.BuildMilliseconds,
                    assemblyLoadResult.AssemblyLoadMilliseconds,
                    buildResult.CompilationBackendKind);
                AppendCompilerStageTimings(
                    assemblySecurityFailure.Timings,
                    planStopwatch.Elapsed.TotalMilliseconds,
                    cacheStopwatch.Elapsed.TotalMilliseconds,
                    builderTotalStopwatch.Elapsed.TotalMilliseconds,
                    compilerTotalStopwatch.Elapsed.TotalMilliseconds);
                return assemblySecurityFailure;
            }

            CompilationResult result = new CompilationResult
            {
                Success = true,
                CompiledAssembly = assemblyLoadResult.CompiledAssembly,
                Warnings = buildResult.Diagnostics.Warnings,
                UpdatedCode = buildResult.UpdatedSource,
                AmbiguousTypeCandidates = buildResult.AmbiguousTypeCandidates,
                AutoInjectedNamespaces = buildResult.AutoInjectedNamespaces,
                AdvisoryLogs = BuildAdvisoryLogs(buildResult.CompilationBackendKind),
                CompilationBackendKind = buildResult.CompilationBackendKind,
                Timings = DynamicCompilationTimingFormatter.CreateCompilationTimings(
                    buildResult.ReferenceResolutionMilliseconds,
                    buildResult.BuildMilliseconds,
                    assemblyLoadResult.AssemblyLoadMilliseconds,
                    buildResult.CompilationBackendKind)
            };
            AppendCompilerStageTimings(
                result.Timings,
                planStopwatch.Elapsed.TotalMilliseconds,
                cacheStopwatch.Elapsed.TotalMilliseconds,
                builderTotalStopwatch.Elapsed.TotalMilliseconds,
                compilerTotalStopwatch.Elapsed.TotalMilliseconds);

            if (buildResult.ShouldCacheResult)
            {
                _cacheManager.CacheResultIfSuccessful(result, plan.NormalizedRequest);
            }
            return result;
        }

        private CompilationResult TryGetCachedResult(
            DynamicCompilationPlan plan)
        {
            return _cacheManager.CheckCache(plan.NormalizedRequest);
        }

        private CompilationResult CreateSourceSecurityFailure(string originalCode)
        {
            if (_securityLevel != DynamicCodeSecurityLevel.Restricted)
            {
                return null;
            }

            SecurityValidationResult sourceSecurityResult = SourceSecurityScanner.Scan(originalCode);
            if (sourceSecurityResult.IsValid)
            {
                return null;
            }

            return new CompilationResult
            {
                Success = false,
                HasSecurityViolations = true,
                SecurityViolations = sourceSecurityResult.Violations,
                UpdatedCode = originalCode,
                FailureReason = CompilationFailureReason.SecurityViolation,
                CompilationBackendKind = DynamicCompilationBackendKind.Unknown,
                Timings = DynamicCompilationTimingFormatter.CreateCompilationTimings(0, 0, 0)
            };
        }

        private static CompilationResult CreateMixedModeFailureResult(
            string originalCode,
            double referenceResolutionMilliseconds,
            double buildMilliseconds)
        {
            return new CompilationResult
            {
                Success = false,
                Errors = new List<CompilationError>
                {
                    new CompilationError
                    {
                        Message = "Mixed top-level statements and type declarations are not supported. Use a full class definition instead.",
                        ErrorCode = "MIXED_MODE",
                        Line = 0,
                        Column = 0
                    }
                },
                FailureReason = CompilationFailureReason.CompilationError,
                UpdatedCode = originalCode,
                CompilationBackendKind = DynamicCompilationBackendKind.Unknown,
                Timings = DynamicCompilationTimingFormatter.CreateCompilationTimings(
                    referenceResolutionMilliseconds,
                    buildMilliseconds,
                    0)
            };
        }

        private static CompilationResult CreateAssemblySecurityFailure(
            List<SecurityViolation> securityViolations,
            List<string> warnings,
            string updatedCode,
            Dictionary<string, List<string>> ambiguousTypeCandidates,
            List<string> autoInjectedNamespaces,
            double referenceResolutionMilliseconds,
            double buildMilliseconds,
            double assemblyLoadMilliseconds,
            DynamicCompilationBackendKind compilationBackendKind)
        {
            return new CompilationResult
            {
                Success = false,
                HasSecurityViolations = true,
                SecurityViolations = securityViolations,
                Warnings = warnings,
                UpdatedCode = updatedCode,
                FailureReason = CompilationFailureReason.SecurityViolation,
                AmbiguousTypeCandidates = ambiguousTypeCandidates,
                AutoInjectedNamespaces = autoInjectedNamespaces,
                AdvisoryLogs = BuildAdvisoryLogs(compilationBackendKind),
                CompilationBackendKind = compilationBackendKind,
                Timings = DynamicCompilationTimingFormatter.CreateCompilationTimings(
                    referenceResolutionMilliseconds,
                    buildMilliseconds,
                    assemblyLoadMilliseconds,
                    compilationBackendKind)
            };
        }

        private static List<string> BuildAdvisoryLogs(DynamicCompilationBackendKind compilationBackendKind)
        {
            return compilationBackendKind == DynamicCompilationBackendKind.AssemblyBuilderFallback
                ? new List<string>
                {
                    "Warning: Fast Roslyn path is unavailable; execute-dynamic-code is using AssemblyBuilder fallback, so new snippets compile slower."
                }
                : new List<string>();
        }

        private static void AppendCompilerStageTimings(
            List<string> timings,
            double planMilliseconds,
            double cacheMilliseconds,
            double builderTotalMilliseconds,
            double compilerTotalMilliseconds)
        {
            if (timings == null)
            {
                return;
            }

            timings.Add($"[Perf] CompilePlan: {planMilliseconds:F1}ms");
            timings.Add($"[Perf] CompileCacheCheck: {cacheMilliseconds:F1}ms");
            if (builderTotalMilliseconds > 0)
            {
                timings.Add($"[Perf] BuilderTotal: {builderTotalMilliseconds:F1}ms");
            }
            timings.Add($"[Perf] CompilerTotal: {compilerTotalMilliseconds:F1}ms");
        }

    }
}