using Jint.Native;
using Jint.Runtime.Environments;
using Jint.Runtime.Interpreter.Expressions;
using Environment = Jint.Runtime.Environments.Environment;

namespace Jint.Runtime.Interpreter.Statements
{
    internal sealed class JintSwitchBlock
    {
        private readonly NodeList<SwitchCase> _switchBlock;
        private JintSwitchCase[] _jintSwitchBlock = Array.Empty<JintSwitchCase>();
        private bool _initialized;

        public JintSwitchBlock(NodeList<SwitchCase> switchBlock)
        {
            _switchBlock = switchBlock;
        }

        private void Initialize()
        {
            _jintSwitchBlock = new JintSwitchCase[_switchBlock.Count];
            for (var i = 0; i < _jintSwitchBlock.Length; i++)
            {
                _jintSwitchBlock[i] = new JintSwitchCase(_switchBlock[i]);
            }
        }

        public Completion Execute(EvaluationContext context, JsValue input)
        {
            if (!_initialized)
            {
                Initialize();
                _initialized = true;
            }

            var v = JsValue.Undefined;
            var l = context.LastSyntaxElement;
            var hit = false;
            var defaultCaseIndex = -1;

            var i = 0;
            Environment? oldEnv = null;
            var temp = _jintSwitchBlock;

            DeclarativeEnvironment? blockEnv = null;

            start:
            for (; i < temp.Length; i++)
            {
                var clause = temp[i];
                if (clause.LexicalDeclarations is not null && oldEnv is null)
                {
                    oldEnv = context.Engine.ExecutionContext.LexicalEnvironment;
                    blockEnv ??= JintEnvironment.NewDeclarativeEnvironment(context.Engine, oldEnv);
                    blockEnv.Clear();

                    JintStatementList.BlockDeclarationInstantiation(blockEnv, clause.LexicalDeclarations);
                    context.Engine.UpdateLexicalEnvironment(blockEnv);
                }

                if (clause.Test == null)
                {
                    defaultCaseIndex = i;
                    if (!hit)
                    {
                        continue;
                    }
                }

                var clauseSelector = clause.Test?.GetValue(context);
                if (clauseSelector == input)
                {
                    hit = true;
                }

                if (!hit)
                {
                    if (oldEnv is not null)
                    {
                        context.Engine.UpdateLexicalEnvironment(oldEnv);
                        oldEnv = null;
                    }
                    continue;
                }

                var r = clause.Consequent.Execute(context);

                if (r.Type != CompletionType.Normal)
                {
                    if (oldEnv is not null)
                    {
                        context.Engine.UpdateLexicalEnvironment(oldEnv);
                    }

                    return r.UpdateEmpty(v);
                }

                l = r._source;
                v = r.Value.IsUndefined() ? v : r.Value;
            }

            // do we need to execute the default case ?
            if (!hit && defaultCaseIndex != -1)
            {
                // jump back to loop and start from default case
                hit = true;
                i = defaultCaseIndex;
                goto start;
            }

            if (oldEnv is not null)
            {
                context.Engine.UpdateLexicalEnvironment(oldEnv);
            }

            return new Completion(CompletionType.Normal, v, l);
        }

        private sealed class JintSwitchCase
        {
            internal readonly JintStatementList Consequent;
            internal readonly JintExpression? Test;
            internal readonly List<Declaration>? LexicalDeclarations;

            public JintSwitchCase(SwitchCase switchCase)
            {
                Consequent = new JintStatementList(statement: null, switchCase.Consequent);
                LexicalDeclarations = HoistingScope.GetLexicalDeclarations(switchCase);

                if (switchCase.Test != null)
                {
                    Test = JintExpression.Build(switchCase.Test);
                }
            }
        }
    }
}