#nullable enable

namespace Terminal.Gui;


internal abstract class AnsiResponseParserBase : IAnsiResponseParser
{
    protected object lockExpectedResponses = new object();

    protected object lockState = new object ();
    /// <summary>
    /// Responses we are expecting to come in.
    /// </summary>
    protected readonly List<AnsiResponseExpectation> expectedResponses = new ();

    /// <summary>
    /// Collection of responses that we <see cref="StopExpecting"/>.
    /// </summary>
    protected readonly List<AnsiResponseExpectation> lateResponses = new ();

    /// <summary>
    /// Responses that you want to look out for that will come in continuously e.g. mouse events.
    /// Key is the terminator.
    /// </summary>
    protected readonly List<AnsiResponseExpectation> persistentExpectations = new ();

    private AnsiResponseParserState _state = AnsiResponseParserState.Normal;

    // Current state of the parser
    public AnsiResponseParserState State
    {
        get => _state;
        protected set
        {
            StateChangedAt = DateTime.Now;
            _state = value;
        }
    }

    protected readonly IHeld heldContent;

    /// <summary>
    ///     When <see cref="State"/> was last changed.
    /// </summary>
    public DateTime StateChangedAt { get; private set; } = DateTime.Now;

    // These all are valid terminators on ansi responses,
    // see CSI in https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Functions-using-CSI-_-ordered-by-the-final-character_s
    // No - N or O
    protected readonly HashSet<char> _knownTerminators = new (new []
    {
        '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
        // No - N or O
        'P', 'Q', 'R', 'S', 'T', 'W', 'X', 'Z',
        '^', '`', '~',
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
        'l', 'm', 'n',
        'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
    });

    protected AnsiResponseParserBase (IHeld heldContent)
    {
        this.heldContent = heldContent;
    }

    protected void ResetState ()
    {
        State = AnsiResponseParserState.Normal;
        heldContent.ClearHeld ();
    }

    /// <summary>
    ///     Processes an input collection of objects <paramref name="inputLength"/> long.
    ///     You must provide the indexers to return the objects and the action to append
    ///     to output stream.
    /// </summary>
    /// <param name="getCharAtIndex">The character representation of element i of your input collection</param>
    /// <param name="getObjectAtIndex">The actual element in the collection (e.g. char or Tuple&lt;char,T&gt;)</param>
    /// <param name="appendOutput">
    ///     Action to invoke when parser confirms an element of the current collection or a previous
    ///     call's collection should be appended to the current output (i.e. append to your output List/StringBuilder).
    /// </param>
    /// <param name="inputLength">The total number of elements in your collection</param>
    protected void ProcessInputBase (
        Func<int, char> getCharAtIndex,
        Func<int, object> getObjectAtIndex,
        Action<object> appendOutput,
        int inputLength
    )
    {
        lock (lockState)
        {
            ProcessInputBaseImpl (getCharAtIndex, getObjectAtIndex, appendOutput, inputLength);
        }
    }

    private void ProcessInputBaseImpl (
        Func<int, char> getCharAtIndex,
        Func<int, object> getObjectAtIndex,
        Action<object> appendOutput,
        int inputLength
    )
    {
        var index = 0; // Tracks position in the input string

        while (index < inputLength)
        {
            char currentChar = getCharAtIndex (index);
            object currentObj = getObjectAtIndex (index);

            bool isEscape = currentChar == '\x1B';

            switch (State)
            {
                case AnsiResponseParserState.Normal:
                    if (isEscape)
                    {
                        // Escape character detected, move to ExpectingBracket state
                        State = AnsiResponseParserState.ExpectingBracket;
                        heldContent.AddToHeld (currentObj); // Hold the escape character
                    }
                    else
                    {
                        // Normal character, append to output
                        appendOutput (currentObj);
                    }

                    break;

                case AnsiResponseParserState.ExpectingBracket:
                    if (isEscape)
                    {
                        // Second escape so we must release first
                        ReleaseHeld (appendOutput, AnsiResponseParserState.ExpectingBracket);
                        heldContent.AddToHeld (currentObj); // Hold the new escape
                    }
                    else if (currentChar == '[')
                    {
                        // Detected '[', transition to InResponse state
                        State = AnsiResponseParserState.InResponse;
                        heldContent.AddToHeld (currentObj); // Hold the '['
                    }
                    else
                    {
                        // Invalid sequence, release held characters and reset to Normal
                        ReleaseHeld (appendOutput);
                        appendOutput (currentObj); // Add current character
                    }

                    break;

                case AnsiResponseParserState.InResponse:
                    heldContent.AddToHeld (currentObj);

                    // Check if the held content should be released
                    if (ShouldReleaseHeldContent ())
                    {
                        ReleaseHeld (appendOutput);
                    }

                    break;
            }

            index++;
        }
    }

    private void ReleaseHeld (Action<object> appendOutput, AnsiResponseParserState newState = AnsiResponseParserState.Normal)
    {
        foreach (object o in heldContent.HeldToObjects ())
        {
            appendOutput (o);
        }

        State = newState;
        heldContent.ClearHeld ();
    }

    // Common response handler logic
    protected bool ShouldReleaseHeldContent ()
    {
        string cur = heldContent.HeldToString ();

        lock (lockExpectedResponses)
        {
            // Look for an expected response for what is accumulated so far (since Esc)
            if (MatchResponse (
                               cur,
                               expectedResponses,
                               invokeCallback: true,
                               removeExpectation: true))
            {
                return false;
            }

            // Also try looking for late requests - in which case we do not invoke but still swallow content to avoid corrupting downstream
            if (MatchResponse (
                               cur,
                               lateResponses,
                               invokeCallback: false,
                               removeExpectation: true))
            {
                return false;
            }

            // Look for persistent requests
            if (MatchResponse (
                               cur,
                               persistentExpectations,
                               invokeCallback: true,
                               removeExpectation: false))
            {
                return false;
            }
        }

        // Finally if it is a valid ansi response but not one we are expect (e.g. its mouse activity)
        // then we can release it back to input processing stream
        if (_knownTerminators.Contains (cur.Last ()) && cur.StartsWith (EscSeqUtils.CSI))
        {
            // We have found a terminator so bail
            State = AnsiResponseParserState.Normal;

            // Maybe swallow anyway if user has custom delegate
            var swallow =  ShouldSwallowUnexpectedResponse ();

            if (swallow)
            {
                heldContent.ClearHeld ();
                // Do not send back to input stream
                return false;
            }

            // Do release back to input stream
            return true;
        }

        return false; // Continue accumulating
    }

    /// <summary>
    /// <para>
    /// When overriden in a derived class, indicates whether the unexpected response
    /// currently in <see cref="heldContent"/> should be released or swallowed.
    /// Use this to enable default event for escape codes.
    /// </para>
    /// 
    /// <remarks>Note this is only called for complete responses.
    /// Based on <see cref="_knownTerminators"/></remarks>
    /// </summary>
    /// <returns></returns>
    protected abstract bool ShouldSwallowUnexpectedResponse ();

    private bool MatchResponse (string cur, List<AnsiResponseExpectation> collection, bool invokeCallback, bool removeExpectation)
    {
        // Check for expected responses
        var matchingResponse = collection.FirstOrDefault (r => r.Matches (cur));

        if (matchingResponse?.Response != null)
        {
            if (invokeCallback)
            {
                matchingResponse.Response.Invoke (heldContent);
            }
            ResetState ();

            if (removeExpectation)
            {
                collection.Remove (matchingResponse);
            }

            return true;
        }

        return false;
    }

    /// <inheritdoc />
    public void ExpectResponse (string terminator, Action<string> response, bool persistent)
    {
        lock (lockExpectedResponses)
        {
            if (persistent)
            {
                persistentExpectations.Add (new (terminator, (h) => response.Invoke (h.HeldToString ())));
            }
            else
            {
                expectedResponses.Add (new (terminator, (h) => response.Invoke (h.HeldToString ())));
            }
        }
    }

    /// <inheritdoc />
    public bool IsExpecting (string terminator)
    {
        lock (lockExpectedResponses)
        {
            // If any of the new terminator matches any existing terminators characters it's a collision so true.
            return expectedResponses.Any (r => r.Terminator.Intersect (terminator).Any ());
        }
    }

    /// <inheritdoc />
    public void StopExpecting (string terminator, bool persistent)
    {

        lock (lockExpectedResponses)
        {
            if (persistent)
            {
                persistentExpectations.RemoveAll (r => r.Matches (terminator));
            }
            else
            {
                var removed = expectedResponses.Where (r => r.Terminator == terminator).ToArray ();

                foreach (var r in removed)
                {
                    expectedResponses.Remove (r);
                    lateResponses.Add (r);
                }
            }
        }
    }
}

internal class AnsiResponseParser<T> : AnsiResponseParserBase
{
    public AnsiResponseParser () : base (new GenericHeld<T> ()) { }


    /// <inheritdoc cref="AnsiResponseParser.UnknownResponseHandler"/>
    public Func<IEnumerable<Tuple<char, T>>, bool> UnexpectedResponseHandler { get; set; } = (_) => false;


    public IEnumerable<Tuple<char, T>> ProcessInput (params Tuple<char, T> [] input)
    {
        List<Tuple<char, T>> output = new List<Tuple<char, T>> ();

        ProcessInputBase (
                          i => input [i].Item1,
                          i => input [i],
                          c => output.Add ((Tuple<char, T>)c),
                          input.Length);

        return output;
    }

    public IEnumerable<Tuple<char, T>> Release ()
    {
        // Lock in case Release is called from different Thread from parse
        lock (lockState)
        {
            foreach (Tuple<char, T> h in HeldToEnumerable())
            {
                yield return h;
            }

            ResetState ();
        }

    }

    private IEnumerable<Tuple<char, T>> HeldToEnumerable ()
    {
        return (IEnumerable<Tuple<char, T>>)heldContent.HeldToObjects ();
    }

    /// <summary>
    /// 'Overload' for specifying an expectation that requires the metadata as well as characters. Has
    /// a unique name because otherwise most lamdas will give ambiguous overload errors.
    /// </summary>
    /// <param name="terminator"></param>
    /// <param name="response"></param>
    /// <param name="persistent"></param>
    public void ExpectResponseT (string terminator, Action<IEnumerable<Tuple<char,T>>> response, bool persistent)
    {
        lock (lockExpectedResponses)
        {
            if (persistent)
            {
                persistentExpectations.Add (new (terminator, (h) => response.Invoke (HeldToEnumerable ())));
            }
            else
            {
                expectedResponses.Add (new (terminator, (h) => response.Invoke (HeldToEnumerable ())));
            }
        }
    }

    /// <inheritdoc />
    protected override bool ShouldSwallowUnexpectedResponse ()
    {
        return UnexpectedResponseHandler.Invoke (HeldToEnumerable ());
    }
}

internal class AnsiResponseParser : AnsiResponseParserBase
{
    /// <summary>
    /// <para>
    /// Delegate for handling unrecognized escape codes. Default behaviour
    /// is to return <see langword="false"/> which simply releases the
    /// characters back to input stream for downstream processing.
    /// </para>
    /// <para>
    /// Implement a method to handle if you want and return <see langword="true"/> if you want the
    /// keystrokes 'swallowed' (i.e. not returned to input stream).
    /// </para>
    /// </summary>
    public Func<string, bool> UnknownResponseHandler { get; set; } = (_) => false;

    public AnsiResponseParser () : base (new StringHeld ()) { }

    public string ProcessInput (string input)
    {
        var output = new StringBuilder ();

        ProcessInputBase (
                          i => input [i],
                          i => input [i], // For string there is no T so object is same as char
                          c => output.Append ((char)c),
                          input.Length);

        return output.ToString ();
    }

    public string Release ()
    {
        lock (lockState)
        {
            var output = heldContent.HeldToString ();
            ResetState ();

            return output;
        }
    }

    /// <inheritdoc />
    protected override bool ShouldSwallowUnexpectedResponse ()
    {
        return UnknownResponseHandler.Invoke (heldContent.HeldToString ());
    }
}