vn/code/vn_text_op.h

/* date = May 7th 2023 7:16 pm */

#ifndef VN_TEXT_OP_H
#define VN_TEXT_OP_H

struct text_op
{
    range1_s64 Range;
    string ReplaceString;
    string CopyString;
    s64 NewCursor;
    s64 NewMark;
};

struct text_edit_state
{
    s64 Cursor;
    s64 Mark;
};

typedef u32 text_action_flags;
enum
{
    TextActionFlag_WordScan                = (1<<0),
    TextActionFlag_KeepMark                = (1<<1),
    TextActionFlag_Delete                  = (1<<2),
    TextActionFlag_ZeroDeltaWithSelection  = (1<<3),
    TextActionFlag_DeltaPicksSelectionSide = (1<<4),
};

struct text_action
{
    text_action_flags Flags;
    s64 Delta;
    u32 Codepoint;
};

inline b32 IsValid(text_action *Action)
{
    b32 Result = !(Action->Flags == 0 && Action->Delta == 0 && Action->Codepoint == 0);
    return(Result);
}

static text_action SingleLineTextActionFromEvent(platform_event *Event)
{
    text_action Action = {};
    
    if(Event->Type == PlatformEvent_Text)
    {
        if(Event->Codepoint != '\n')
        {
            Action.Codepoint = Event->Codepoint;
        }
    }
    else if(Event->Type == PlatformEvent_Press)
    {
        if(Event->Modifiers & PlatformModifier_Ctrl)
        {
            Action.Flags |= TextActionFlag_WordScan;
        }
        if(Event->Modifiers & PlatformModifier_Shift)
        {
            Action.Flags |= TextActionFlag_KeepMark;
        }
        
        switch(Event->Key)
        {
            case Key_Right:
            {
                Action.Delta = +1;
                Action.Flags |= TextActionFlag_DeltaPicksSelectionSide;
            } break;
            
            case Key_Left:
            {
                Action.Delta = -1;
                Action.Flags |= TextActionFlag_DeltaPicksSelectionSide;
            } break;
            
            case Key_Home:  { Action.Delta = S64_Min; } break;
            case Key_End:   { Action.Delta = S64_Max; } break;
            
            case Key_Backspace:
            {
                Action.Delta = -1;
                Action.Flags |= TextActionFlag_Delete|TextActionFlag_ZeroDeltaWithSelection;
            } break;
            
            case Key_Delete:
            {
                Action.Delta = +1;
                Action.Flags |= TextActionFlag_Delete|TextActionFlag_ZeroDeltaWithSelection;
            } break;
            
            default: {} break;
        }
    }
    return(Action);
}

inline s64 CodepointScan(string String, s64 Index, s64 Delta)
{
    s64 Result = 0;
    if(Delta > 0)
    {
        while(Index < String.Count && Delta)
        {
            u8 Base = String.Data[Index];
            s64 ToMove = 0;
            
            if((Base & 0x80) == 0x00)
            {
                ToMove = 1;
            }
            else if((Base & 0xE0) == 0xC0)
            {
                ToMove = 2;
            }
            else if((Base & 0xF0) == 0xE0)
            {
                ToMove = 3;
            }
            else if((Base & 0xF8) == 0xF0)
            {
                ToMove = 4;
            }
            
            Result += ToMove;
            Index += ToMove;
            
            --Delta;
        }
    }
    else
    {
        Index -= 1;
        
        while(Index >= 0 && (Delta != 0))
        {
            u8 Base = String.Data[Index];
            if(((Base & 0x80) == 0) || !((Base & 0xC0) == 0x80))
            {
                ++Delta;
            }
            
            --Result;
            --Index;
        }
    }
    
    return(Result);
}

inline b32 IsWordBoundary(string String, s64 Index)
{
    b32 Result;
    if(Index > 0)
    {
        Result = IsWhitespace(String.Data[Index - 1]) && !(IsWhitespace(String.Data[Index]));
    }
    else
    {
        Result = true;
    }
    return(Result);
}

static s64 WordScan(string String, s64 Index, s64 Delta)
{
    s64 Result = 0;
    
    while(Delta)
    {
        if(Delta > 0)
        {
            ++Index;
            ++Result;
            
            while(Index < String.Count && !IsWordBoundary(String, Index))
            {
                ++Index;
                ++Result;
            }
            
            if(Index > String.Count)
            {
                Result -= Index - String.Count;
                Index = String.Count;
                goto End;
            }
            
            --Delta;
        }
        else
        {
            --Index;
            --Result;
            
            while(Index >= 0 && !IsWordBoundary(String, Index))
            {
                --Index;
                --Result;
            }
            
            if(Index < 0)
            {
                Result -= Index;
                Index = 0;
                goto End;
            }
            
            ++Delta;
        }
    }
    
    End:
    return(Result);
}

static text_op TextOpFromAction(memory_arena *Arena, string String,
                                text_edit_state *State, text_action *Action)
{
    text_op Op = {};
    
    Op.NewCursor = State->Cursor;
    Op.NewMark = State->Mark;
    Op.Range = Range1S64(0, 0);
    Op.ReplaceString = StrLit("");
    
    s64 Delta = 0;
    if(Action->Flags & TextActionFlag_WordScan)
    {
        Delta = WordScan(String, State->Cursor, Action->Delta);
    }
    else
    {
        Delta = CodepointScan(String, State->Cursor, Action->Delta);
    }
    
    if(State->Cursor != State->Mark &&
       Action->Flags & TextActionFlag_ZeroDeltaWithSelection)
    {
        Delta = 0;
    }
    
    if(State->Cursor != State->Mark &&
       Action->Flags & TextActionFlag_DeltaPicksSelectionSide &&
       !(Action->Flags & TextActionFlag_KeepMark))
    {
        Delta = 0;
        if(Action->Delta > 0)
        {
            Op.NewCursor = Maximum(State->Cursor, State->Mark);
        }
        else if(Action->Delta < 0)
        {
            Op.NewCursor = Minimum(State->Cursor, State->Mark);
        }
    }
    else
    {
        Op.NewCursor = State->Cursor + Delta;
    }
    
    if(Action->Flags & TextActionFlag_Delete)
    {
        Op.Range = Range1S64(Op.NewCursor, Op.NewMark);
        Op.NewCursor = Op.NewMark = Op.Range.Min;
    }
    
    if(Action->Codepoint != 0)
    {
        Op.ReplaceString = StringFromCodepoint(Arena, Action->Codepoint);
        
        if(State->Cursor == State->Mark)
        {
            Op.NewCursor += Op.ReplaceString.Count;
            Op.Range = Range1S64(State->Cursor, State->Cursor);
        }
        else
        {
            Op.NewCursor += Op.ReplaceString.Count;
            Op.Range = Range1S64(State->Cursor, State->Mark);
        }
    }
    
    if(!(Action->Flags & TextActionFlag_KeepMark))
    {
        Op.NewMark = Op.NewCursor;
    }
    
    return(Op);
}

#endif //VN_TEXT_OP_H