using System.Text.RegularExpressions;

namespace Terminal.Gui.Views;

/// <summary>Regex Provider for TextValidateField.</summary>
public class TextRegexProvider : ITextValidateProvider
{
    private List<Rune> _pattern = null!;
    private Regex _regex = null!;
    private List<Rune> _text = null!;

    /// <summary>Empty Constructor.</summary>
    public TextRegexProvider (string pattern) { Pattern = pattern; }

    /// <summary>Regex pattern property.</summary>
    public string Pattern
    {
        get => StringExtensions.ToString (_pattern);
        set
        {
            _pattern = value.ToRuneList ();
            CompileMask ();
            SetupText ();
        }
    }

    /// <summary>When true, validates with the regex pattern on each input, preventing the input if it's not valid.</summary>
    public bool ValidateOnInput { get; set; } = true;

    /// <inheritdoc/>
    public event EventHandler<EventArgs<string>> TextChanged = null!;

    /// <inheritdoc/>
    public string Text
    {
        get => StringExtensions.ToString (_text);
        set
        {
            _text = (value != string.Empty ? value.ToRuneList () : null)!;
            SetupText ();
        }
    }

    /// <inheritdoc/>
    public string DisplayText => Text;

    /// <inheritdoc/>
    public bool IsValid => Validate (_text);

    /// <inheritdoc/>
    public bool Fixed => false;

    /// <inheritdoc/>
    public int Cursor (int pos)
    {
        if (pos < 0)
        {
            return CursorStart ();
        }

        if (pos >= _text.Count)
        {
            return CursorEnd ();
        }

        return pos;
    }

    /// <inheritdoc/>
    public int CursorStart () { return 0; }

    /// <inheritdoc/>
    public int CursorEnd () { return _text.Count; }

    /// <inheritdoc/>
    public int CursorLeft (int pos)
    {
        if (pos > 0)
        {
            return pos - 1;
        }

        return pos;
    }

    /// <inheritdoc/>
    public int CursorRight (int pos)
    {
        if (pos < _text.Count)
        {
            return pos + 1;
        }

        return pos;
    }

    /// <inheritdoc/>
    public bool Delete (int pos)
    {
        if (_text.Count > 0 && pos < _text.Count)
        {
            string oldValue = Text;
            _text.RemoveAt (pos);
            OnTextChanged (new (in oldValue));
        }

        return true;
    }

    /// <inheritdoc/>
    public bool InsertAt (char ch, int pos)
    {
        List<Rune> aux = _text.ToList ();
        aux.Insert (pos, (Rune)ch);

        if (Validate (aux) || ValidateOnInput == false)
        {
            string oldValue = Text;
            _text.Insert (pos, (Rune)ch);
            OnTextChanged (new (in oldValue));

            return true;
        }

        return false;
    }

    /// <inheritdoc/>
    public void OnTextChanged (EventArgs<string> args) { TextChanged?.Invoke (this, args); }

    /// <summary>Compiles the regex pattern for validation./></summary>
    private void CompileMask () { _regex = new (StringExtensions.ToString (_pattern), RegexOptions.Compiled); }

    private void SetupText ()
    {
        if (_text is { } && IsValid)
        {
            return;
        }

        _text = new ();
    }

    private bool Validate (List<Rune> text)
    {
        Match match = _regex.Match (StringExtensions.ToString (text));

        return match.Success;
    }
}