using System.Diagnostics.CodeAnalysis;
using Jint.Native;
using Jint.Native.Iterator;
using Jint.Runtime.Environments;
using Jint.Runtime.Interpreter.Expressions;
using Environment = Jint.Runtime.Environments.Environment;

namespace Jint.Runtime.Interpreter.Statements
{
    /// <summary>
    /// https://tc39.es/ecma262/#sec-for-in-and-for-of-statements
    /// </summary>
    internal sealed class JintForInForOfStatement : JintStatement<Statement>
    {
        private readonly Node _leftNode;
        private readonly Statement _forBody;
        private readonly Expression _rightExpression;
        private readonly IterationKind _iterationKind;

        private ProbablyBlockStatement _body;
        private JintExpression? _expr;
        private DestructuringPattern? _assignmentPattern;
        private JintExpression _right = null!;
        private List<Key>? _tdzNames;
        private bool _destructuring;
        private LhsKind _lhsKind;

        public JintForInForOfStatement(ForInStatement statement) : base(statement)
        {
            _leftNode = statement.Left;
            _rightExpression = statement.Right;
            _forBody = statement.Body;
            _iterationKind = IterationKind.Enumerate;
        }

        public JintForInForOfStatement(ForOfStatement statement) : base(statement)
        {
            _leftNode = statement.Left;
            _rightExpression = statement.Right;
            _forBody = statement.Body;
            _iterationKind = IterationKind.Iterate;
        }

        protected override void Initialize(EvaluationContext context)
        {
            _lhsKind = LhsKind.Assignment;
            var engine = context.Engine;
            if (_leftNode is VariableDeclaration variableDeclaration)
            {
                _lhsKind = variableDeclaration.Kind == VariableDeclarationKind.Var
                    ? LhsKind.VarBinding
                    : LhsKind.LexicalBinding;

                var variableDeclarationDeclaration = variableDeclaration.Declarations[0];
                var id = variableDeclarationDeclaration.Id;
                if (_lhsKind == LhsKind.LexicalBinding)
                {
                    _tdzNames = new List<Key>(1);
                    id.GetBoundNames(_tdzNames);
                }

                if (id is DestructuringPattern pattern)
                {
                    _destructuring = true;
                    _assignmentPattern = pattern;
                }
                else
                {
                    var identifier = (Identifier) id;
                    _expr = new JintIdentifierExpression(identifier);
                }
            }
            else if (_leftNode is DestructuringPattern pattern)
            {
                _destructuring = true;
                _assignmentPattern = pattern;
            }
            else if (_leftNode is MemberExpression memberExpression)
            {
                _expr = new JintMemberExpression(memberExpression);
            }
            else
            {
                _expr = new JintIdentifierExpression((Identifier) _leftNode);
            }

            _body = new ProbablyBlockStatement(_forBody);
            _right = JintExpression.Build(_rightExpression);
        }

        protected override Completion ExecuteInternal(EvaluationContext context)
        {
            if (!HeadEvaluation(context, out var keyResult))
            {
                return new Completion(CompletionType.Normal, JsValue.Undefined, _statement);
            }

            return BodyEvaluation(context, _expr, _body, keyResult, IterationKind.Enumerate, _lhsKind);
        }

        /// <summary>
        /// https://tc39.es/ecma262/#sec-runtime-semantics-forin-div-ofheadevaluation-tdznames-expr-iterationkind
        /// </summary>
        private bool HeadEvaluation(EvaluationContext context, [NotNullWhen(true)] out IteratorInstance? result)
        {
            var engine = context.Engine;
            var oldEnv = engine.ExecutionContext.LexicalEnvironment;
            var tdz = JintEnvironment.NewDeclarativeEnvironment(engine, oldEnv);
            if (_tdzNames != null)
            {
                var TDZEnvRec = tdz;
                foreach (var name in _tdzNames)
                {
                    TDZEnvRec.CreateMutableBinding(name);
                }
            }

            engine.UpdateLexicalEnvironment(tdz);
            var exprValue = _right.GetValue(context);
            engine.UpdateLexicalEnvironment(oldEnv);

            if (_iterationKind == IterationKind.Enumerate)
            {
                if (exprValue.IsNullOrUndefined())
                {
                    result = null;
                    return false;
                }

                var obj = TypeConverter.ToObject(engine.Realm, exprValue);
                result = new IteratorInstance.EnumerableIterator(engine, obj.GetKeys());
            }
            else
            {
                result = exprValue as IteratorInstance ?? exprValue.GetIterator(engine.Realm);
            }

            return true;
        }

        /// <summary>
        /// https://tc39.es/ecma262/#sec-runtime-semantics-forin-div-ofbodyevaluation-lhs-stmt-iterator-lhskind-labelset
        /// </summary>
        private Completion BodyEvaluation(
            EvaluationContext context,
            JintExpression? lhs,
            in ProbablyBlockStatement stmt,
            IteratorInstance iteratorRecord,
            IterationKind iterationKind,
            LhsKind lhsKind,
            IteratorKind iteratorKind = IteratorKind.Sync)
        {
            var engine = context.Engine;
            var oldEnv = engine.ExecutionContext.LexicalEnvironment;
            var v = JsValue.Undefined;
            var destructuring = _destructuring;
            string? lhsName = null;

            var completionType = CompletionType.Normal;
            var close = false;

            try
            {
                while (true)
                {
                    Environment? iterationEnv = null;
                    if (!iteratorRecord.TryIteratorStep(out var nextResult))
                    {
                        close = true;
                        return new Completion(CompletionType.Normal, v, _statement!);
                    }

                    if (iteratorKind == IteratorKind.Async)
                    {
                        // nextResult = await nextResult;
                        ExceptionHelper.ThrowNotImplementedException("await");
                    }

                    var nextValue = nextResult.Get(CommonProperties.Value);
                    close = true;

                    object lhsRef = null!;
                    if (lhsKind != LhsKind.LexicalBinding)
                    {
                        if (!destructuring)
                        {
                            lhsRef = lhs!.Evaluate(context);
                        }
                    }
                    else
                    {
                        iterationEnv = JintEnvironment.NewDeclarativeEnvironment(engine, oldEnv);
                        if (_tdzNames != null)
                        {
                            BindingInstantiation(iterationEnv);
                        }
                        engine.UpdateLexicalEnvironment(iterationEnv);

                        if (!destructuring)
                        {
                            var identifier = (Identifier) ((VariableDeclaration) _leftNode).Declarations[0].Id;
                            lhsName ??= identifier.Name;
                            lhsRef = engine.ResolveBinding(lhsName);
                        }
                    }

                    if (context.DebugMode)
                    {
                        context.Engine.Debugger.OnStep(_leftNode);
                    }

                    var status = CompletionType.Normal;
                    if (!destructuring)
                    {
                        if (context.IsAbrupt())
                        {
                            close = true;
                            status = context.Completion;
                        }
                        else
                        {
                            var reference = (Reference) lhsRef;
                            if (lhsKind == LhsKind.LexicalBinding || _leftNode.Type == NodeType.Identifier && !reference.IsUnresolvableReference)
                            {
                                reference.InitializeReferencedBinding(nextValue);
                            }
                            else
                            {
                                engine.PutValue(reference, nextValue);
                            }
                        }
                    }
                    else
                    {
                        nextValue = DestructuringPatternAssignmentExpression.ProcessPatterns(
                            context,
                            _assignmentPattern!,
                            nextValue,
                            iterationEnv,
                            checkPatternPropertyReference: _lhsKind != LhsKind.VarBinding);

                        status = context.Completion;

                        if (lhsKind == LhsKind.Assignment)
                        {
                            // DestructuringAssignmentEvaluation of assignmentPattern using nextValue as the argument.
                        }
#pragma warning disable MA0140
                        else if (lhsKind == LhsKind.VarBinding)
                        {
                            // BindingInitialization for lhs passing nextValue and undefined as the arguments.
                        }
                        else
                        {
                            // BindingInitialization for lhs passing nextValue and iterationEnv as arguments
                        }
#pragma warning restore MA0140
                    }

                    if (status != CompletionType.Normal)
                    {
                        engine.UpdateLexicalEnvironment(oldEnv);
                        if (_iterationKind == IterationKind.AsyncIterate)
                        {
                            iteratorRecord.Close(status);
                            return new Completion(status, nextValue, context.LastSyntaxElement);
                        }

                        if (iterationKind == IterationKind.Enumerate)
                        {
                            return new Completion(status, nextValue, context.LastSyntaxElement);
                        }

                        iteratorRecord.Close(status);
                        return new Completion(status, nextValue, context.LastSyntaxElement);
                    }

                    var result = stmt.Execute(context);
                    engine.UpdateLexicalEnvironment(oldEnv);

                    if (!result.Value.IsEmpty)
                    {
                        v = result.Value;
                    }

                    if (result.Type == CompletionType.Break && (context.Target == null || string.Equals(context.Target, _statement?.LabelSet?.Name, StringComparison.Ordinal)))
                    {
                        completionType = CompletionType.Normal;
                        return new Completion(CompletionType.Normal, v, _statement!);
                    }

                    if (result.Type != CompletionType.Continue || (context.Target != null && !string.Equals(context.Target, _statement?.LabelSet?.Name, StringComparison.Ordinal)))
                    {
                        completionType = result.Type;
                        if (iterationKind == IterationKind.Enumerate)
                        {
                            // TODO es6-generators make sure we can start from where we left off
                            //return result;
                        }
                        if (result.IsAbrupt())
                        {
                            close = true;
                            return result;
                        }
                    }
                }
            }
            catch
            {
                completionType = CompletionType.Throw;
                throw;
            }
            finally
            {
                if (close)
                {
                    try
                    {
                        iteratorRecord.Close(completionType);
                    }
                    catch
                    {
                        // if we already have and exception, use it
                        if (completionType != CompletionType.Throw)
                        {
#pragma warning disable CA2219
#pragma warning disable MA0072
                            throw;
#pragma warning restore MA0072
#pragma warning restore CA2219
                        }
                    }
                }
                engine.UpdateLexicalEnvironment(oldEnv);
            }
        }

        private void BindingInstantiation(Environment environment)
        {
            var envRec = (DeclarativeEnvironment) environment;
            var variableDeclaration = (VariableDeclaration) _leftNode;
            var boundNames = new List<Key>();
            variableDeclaration.GetBoundNames(boundNames);
            for (var i = 0; i < boundNames.Count; i++)
            {
                var name = boundNames[i];
                if (variableDeclaration.Kind == VariableDeclarationKind.Const)
                {
                    envRec.CreateImmutableBinding(name, strict: true);
                }
                else
                {
                    envRec.CreateMutableBinding(name, canBeDeleted: false);
                }
            }
        }

        private enum LhsKind
        {
            Assignment,
            VarBinding,
            LexicalBinding
        }

        private enum IteratorKind
        {
            Sync,
            Async
        }

        private enum IterationKind
        {
            Enumerate,
            Iterate,
            AsyncIterate
        }
    }
}