Avalonia/src/Windows/Avalonia.Win32/Input/Imm32InputMethod.cs

using System;
using System.Diagnostics.CodeAnalysis;
using System.Text;
using Avalonia.Input.TextInput;
using Avalonia.Threading;

using static Avalonia.Win32.Interop.UnmanagedMethods;

namespace Avalonia.Win32.Input
{
    /// <summary>
    /// A Windows input method editor based on Windows Input Method Manager (IMM32).
    /// </summary>
    internal class Imm32InputMethod : ITextInputMethodImpl
    {
        public IntPtr Hwnd { get; private set; }
        private IntPtr _currentHimc;
        private WindowImpl? _parent;

        private Imm32CaretManager _caretManager;

        private ushort _langId;
        private const int CaretMargin = 1;

        public ITextInputMethodClient? Client { get; private set; }

        [MemberNotNullWhen(true, nameof(Client))]
        public bool IsActive => Client != null;

        public bool IsComposing { get; set; }

        public bool ShowCompositionWindow => false;

        public string? Composition { get; internal set; }

        public void CreateCaret()
        {
            _caretManager.TryCreate(Hwnd);
        }

        public void EnableImm()
        {
            var himc = ImmGetContext(Hwnd);

            if(himc == IntPtr.Zero)
            {
                himc = ImmCreateContext();
            }

            if(himc != _currentHimc)
            {
                if(_currentHimc != IntPtr.Zero)
                {
                    DisableImm();
                }

                ImmAssociateContext(Hwnd, himc);

                ImmReleaseContext(Hwnd, himc);

                _currentHimc = himc;

                _caretManager.TryCreate(Hwnd);
            }
        }

        public void DisableImm()
        {
            _caretManager.TryDestroy();

            Reset();

            ImmAssociateContext(Hwnd, IntPtr.Zero);

            _caretManager.TryDestroy();

            _currentHimc = IntPtr.Zero;
        }

        public void SetLanguageAndWindow(WindowImpl parent, IntPtr hwnd, IntPtr HKL)
        {
            Hwnd = hwnd;
            _parent = parent;
            _langId = PRIMARYLANGID(LGID(HKL));

            _parent = parent;

            var langId= PRIMARYLANGID(LGID(HKL));

            if(langId != _langId)
            {
                DisableImm();
            }

            _langId = langId;

            EnableImm();
        }

        public void ClearLanguageAndWindow()
        {
            DisableImm();

            Hwnd = IntPtr.Zero;
            _parent = null;
            Client = null;
            _langId = 0;

            IsComposing = false;
        }

        //Dependant on CurrentThread. When Avalonia will support Multiple Dispatchers -
        //every Dispatcher should have their own InputMethod.
        public static Imm32InputMethod Current { get; } = new();

        public void Reset()
        {
            Dispatcher.UIThread.Post(() =>
            {
                var himc = ImmGetContext(Hwnd);

                if (IsComposing)
                {
                    ImmNotifyIME(himc, NI_COMPOSITIONSTR, CPS_COMPLETE, 0);
                   
                    IsComposing = false;
                }

                ImmReleaseContext(Hwnd, himc);
            });
        }

        public void SetClient(ITextInputMethodClient? client)
        {
            Client = client;

            Dispatcher.UIThread.Post(() =>
            {
                if (IsActive)
                {
                    EnableImm();
                }
                else
                {
                    // A renderer process have moved its input focus to a password input
                    // when there is an ongoing composition, e.g. a user has clicked a
                    // mouse button and selected a password input while composing a text.
                    // For this case, we have to complete the ongoing composition and
                    // clean up the resources attached to this object BEFORE DISABLING THE IME.

                    DisableImm();
                }
            });
        }

        public void SetCursorRect(Rect rect)
        {
            var focused = GetActiveWindow() == Hwnd;

            if (!focused)
            {
                return;
            }

            Dispatcher.UIThread.Post(() =>
            {
                var himc = ImmGetContext(Hwnd);

                if (himc == IntPtr.Zero)
                {
                    return;
                }

                MoveImeWindow(rect, himc);

                ImmReleaseContext(Hwnd, himc);
            });
        }
        
        // see: https://chromium.googlesource.com/experimental/chromium/src/+/bf09a5036ccfb77d2277247c66dc55daf41df3fe/chrome/browser/ime_input.cc
        // see: https://engine.chinmaygarde.com/window__win32_8cc_source.html
        private void MoveImeWindow(Rect rect, IntPtr himc)
        {
            var p1 = rect.TopLeft;
            var p2 = rect.BottomRight;
            var s = _parent?.DesktopScaling ?? 1;
            var (x1, y1, x2, y2) = ((int) (p1.X * s), (int) (p1.Y * s), (int) (p2.X * s), (int) (p2.Y * s));

            if (!ShowCompositionWindow && _langId == LANG_ZH)
            {
                // Chinese IMEs ignore function calls to ::ImmSetCandidateWindow()
                // when a user disables TSF (Text Service Framework) and CUAS (Cicero
                // Unaware Application Support).
                // On the other hand, when a user enables TSF and CUAS, Chinese IMEs
                // ignore the position of the current system caret and uses the
                // parameters given to ::ImmSetCandidateWindow() with its 'dwStyle'
                // parameter CFS_CANDIDATEPOS.
                // Therefore, we do not only call ::ImmSetCandidateWindow() but also
                // set the positions of the temporary system caret.
                var candidateForm = new CANDIDATEFORM
                {
                    dwIndex = 0,
                    dwStyle = CFS_CANDIDATEPOS,
                    ptCurrentPos = new POINT {X = x2, Y = y2}
                };

                ImmSetCandidateWindow(himc, ref candidateForm);
            }

            _caretManager.TryMove(x2, y2);

            if (ShowCompositionWindow)
            {
                ConfigureCompositionWindow(x1, y1, himc, y2 - y1);
                // Don't need to set the position of candidate window.
                return;
            }

            if (_langId == LANG_KO)
            {
                // Chinese IMEs and Japanese IMEs require the upper-left corner of
                // the caret to move the position of their candidate windows.
                // On the other hand, Korean IMEs require the lower-left corner of the
                // caret to move their candidate windows.
                y2 += CaretMargin;
            }

            // Need to return here since some Chinese IMEs would stuck if set
            // candidate window position with CFS_EXCLUDE style.
            if (_langId == LANG_ZH)
            {
                return;
            }

            // Japanese IMEs and Korean IMEs also use the rectangle given to
            // ::ImmSetCandidateWindow() with its 'dwStyle' parameter CFS_EXCLUDE
            // to move their candidate windows when a user disables TSF and CUAS.
            // Therefore, we also set this parameter here.
            var excludeRectangle = new CANDIDATEFORM
            {
                dwIndex = 0,
                dwStyle = CFS_EXCLUDE,
                ptCurrentPos = new POINT {X = x1, Y = y1},
                rcArea = new RECT {left = x1, top = y1, right = x2, bottom = y2 + CaretMargin}
            };

            ImmSetCandidateWindow(himc, ref excludeRectangle);
        }

        private static void ConfigureCompositionWindow(int x1, int y1, IntPtr himc, int height)
        {
            var compForm = new COMPOSITIONFORM
            {
                dwStyle = CFS_POINT,
                ptCurrentPos = new POINT {X = x1, Y = y1},
            };

            ImmSetCompositionWindow(himc, ref compForm);

            var logFont = new LOGFONT()
            {
                lfHeight = height,
                lfQuality = 5 //CLEARTYPE_QUALITY
            };

            ImmSetCompositionFont(himc, ref logFont);
        }
        
        public void SetOptions(TextInputOptions options)
        {
            // we're skipping this. not usable on windows
        }

        public void CompositionChanged(string? composition)
        {
            Composition = composition;

            if (!IsActive || !Client.SupportsPreedit)
            {
                return;
            }

            Client.SetPreeditText(composition);
        }
        
        public string? GetCompositionString(GCS flag)
        {
            if (!IsComposing)
            {
                return null;
            }

            var himc = ImmGetContext(Hwnd);

            return ImmGetCompositionString(himc, flag);
        }

        ~Imm32InputMethod()
        {
            _caretManager.TryDestroy();
        }
    }
}