using Jint.Runtime.Environments;
using System.Collections;
using Environment = Jint.Runtime.Environments.Environment;

namespace Jint.Runtime.Debugger;

public sealed class DebugScopes : IReadOnlyList<DebugScope>
{
    private readonly List<DebugScope> _scopes = new();

    internal DebugScopes(Environment environment)
    {
        Populate(environment);
    }

    public DebugScope this[int index] => _scopes[index];
    public int Count => _scopes.Count;

    private void Populate(Environment? environment)
    {
        bool inLocalScope = true;
        while (environment is not null)
        {
            var record = environment;
            switch (record)
            {
                case GlobalEnvironment global:
                    // Similarly to Chromium, we split the Global environment into Global and Script scopes
                    AddScope(DebugScopeType.Script, global._declarativeRecord);
                    AddScope(DebugScopeType.Global, new ObjectEnvironment(environment._engine, global._global, false, false));
                    break;
                case FunctionEnvironment:
                    AddScope(inLocalScope ? DebugScopeType.Local : DebugScopeType.Closure, record);
                    // We're now in closure territory
                    inLocalScope = false;
                    break;
                case ObjectEnvironment:
                    // If an ObjectEnvironmentRecord is not a GlobalEnvironmentRecord, it's With
                    AddScope(DebugScopeType.With, record);
                    break;
                case ModuleEnvironment:
                    AddScope(DebugScopeType.Module, record);
                    break;
                case DeclarativeEnvironment der:
                    if (der._catchEnvironment)
                    {
                        AddScope(DebugScopeType.Catch, record);
                    }
                    else
                    {
                        bool isTopLevel = environment._outerEnv is FunctionEnvironment;
                        AddScope(DebugScopeType.Block, record, isTopLevel: isTopLevel);
                    }
                    break;
            }

            environment = environment._outerEnv;
        }
    }

    private void AddScope(DebugScopeType type, Environment record, bool isTopLevel = false)
    {
        if (record.HasBindings())
        {
            var scope = new DebugScope(type, record, isTopLevel);
            _scopes.Add(scope);
        }
    }

    public IEnumerator<DebugScope> GetEnumerator()
    {
        return _scopes.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return _scopes.GetEnumerator();
    }
}