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// <copyright file="SmallBasicEngine.cs" company="MIT License">
// Licensed under the MIT License. See LICENSE file in the project root for license information.
// </copyright>
namespace SmallBasic.Compiler
    using System;
    using System.Collections.Generic;
    using System.Diagnostics;
    using System.Linq;
    using System.Threading.Tasks;
    using SmallBasic.Compiler.Binding;
    using SmallBasic.Compiler.Runtime;
    using SmallBasic.Utilities;
    public enum ExecutionMode
        RunToEnd,
        Debug,
        NextLine
    public enum ExecutionState
        Running,
        Paused,
        BlockedOnStringInput,
        BlockedOnNumberInput,
        Terminated,
    public sealed class SmallBasicEngine
        private readonly SmallBasicCompilation compilation;
        private readonly Dictionary<string, string> eventCallbacks;
        public SmallBasicEngine(SmallBasicCompilation compilation, IEngineLibraries libraries)
            Debug.Assert(!compilation.Diagnostics.Any(), "Cannot execute a compilation with errors.");
            this.compilation = compilation;
            this.eventCallbacks = new Dictionary<string, string>(StringComparer.CurrentCultureIgnoreCase);
            this.CurrentSourceLine = 0;
            this.Mode = ExecutionMode.RunToEnd;
            this.State = ExecutionState.Running;
            this.ExecutionStack = new LinkedList<Frame>();
            this.EvaluationStack = new Stack<BaseValue>();
            this.Memory = new Dictionary<string, BaseValue>();
            this.Modules = new Dictionary<string, RuntimeModule>();
            this.Libraries = libraries;
            this.Libraries.SetEventCallbacks(this);
            RuntimeModule mainModule = this.EmitAndSaveModule("Program", compilation.MainModule);
            foreach (BoundSubModule subModule in compilation.SubModules.Values)
                this.EmitAndSaveModule(subModule.Name, subModule.Body);
            this.ExecutionStack.AddLast(new Frame(mainModule));
        public ExecutionMode Mode { get; set; }
        public ExecutionState State { get; private set; }
        public int CurrentSourceLine { get; private set; }
        internal LinkedList<Frame> ExecutionStack { get; private set; }
        internal Stack<BaseValue> EvaluationStack { get; private set; }
        internal Dictionary<string, BaseValue> Memory { get; private set; }
        internal Dictionary<string, RuntimeModule> Modules { get; private set; }
        internal IEngineLibraries Libraries { get; private set; }
        public DebuggerSnapshot GetSnapshot()
            return new DebuggerSnapshot(this.CurrentSourceLine, this.ExecutionStack, this.Memory);
        public async Task Execute()
            Debug.Assert(this.State == ExecutionState.Running || this.State == ExecutionState.Paused, "Engine is not in a executable state.");
            while (this.State == ExecutionState.Running)
                if (this.ExecutionStack.Count == 0)
                    if (!this.compilation.Analysis.ListensToEvents)
                        this.Terminate();
                    break;
                Frame frame = this.ExecutionStack.Last();
                if (frame.InstructionIndex == frame.Module.Instructions.Count)
                    this.ExecutionStack.RemoveLast();
                    continue;
                BaseInstruction instruction = frame.Module.Instructions[frame.InstructionIndex];
                int instructionLine = instruction.Range.Start.Line;
                bool shouldPause = this.Mode == ExecutionMode.NextLine && this.CurrentSourceLine != instructionLine;
                this.CurrentSourceLine = instructionLine;
                if (shouldPause)
                    this.Pause();
                    return;
                    await instruction.Execute(this, frame).ConfigureAwait(false);
        public void InputReceived()
            switch (this.State)
                case ExecutionState.BlockedOnNumberInput:
                case ExecutionState.BlockedOnStringInput:
                    this.State = ExecutionState.Running;
                    break;
                default:
                    throw ExceptionUtilities.UnexpectedValue(this.State);
        public void Pause()
            if (this.Mode != ExecutionMode.RunToEnd)
                this.State = ExecutionState.Paused;
        public void Continue()
            if (this.Mode != ExecutionMode.RunToEnd)
                this.State = ExecutionState.Running;
        public void Terminate()
            this.State = ExecutionState.Terminated;
            this.ExecutionStack.Clear();
        internal void SetEventCallback(string library, string eventName, string subModule)
            this.eventCallbacks[$"{library}.${eventName}"] = subModule;
        internal void RaiseEvent(string library, string eventName)
            if (this.eventCallbacks.TryGetValue($"{library}.${eventName}", out string subModule))
                var existing = this.ExecutionStack.Take(this.ExecutionStack.Count - 1).FirstOrDefault(frame => frame.Module.Name == subModule);
                if (!existing.IsDefault())
                    this.ExecutionStack.Remove(existing);
                this.ExecutionStack.AddFirst(new Frame(this.Modules[subModule]));
        internal void BlockOnStringInput()
            this.State = ExecutionState.BlockedOnStringInput;
        internal void BlockOnNumberInput()
            this.State = ExecutionState.BlockedOnNumberInput;
        private RuntimeModule EmitAndSaveModule(string name, BoundStatementBlock body)
            ModuleEmitter emitter = new ModuleEmitter(body);
            RuntimeModule module = new RuntimeModule(name, emitter.Instructions, body.Syntax);
            this.Modules.Add(module.Name, module);
            return module;
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