GitNex/app/src/main/java/org/mian/gitnex/helpers/SyntaxHighlightedArea.java

package org.mian.gitnex.helpers;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.Typeface;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.View;
import android.view.ViewGroup;
import android.widget.HorizontalScrollView;
import android.widget.LinearLayout;
import android.widget.TextView;
import androidx.annotation.ColorInt;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import org.mian.gitnex.core.MainGrammarLocator;
import io.noties.markwon.syntax.Prism4jSyntaxHighlight;
import io.noties.markwon.syntax.Prism4jTheme;
import io.noties.markwon.syntax.Prism4jThemeDarkula;
import io.noties.markwon.syntax.Prism4jThemeDefault;
import io.noties.prism4j.Prism4j;

/**
 * @author opyale
 */

public class SyntaxHighlightedArea extends LinearLayout {

	private Prism4jTheme prism4jTheme;

	private TextView sourceView;
	private LinesView linesView;

	public SyntaxHighlightedArea(@NonNull Context context) {

		super(context);
		setup();
	}

	public SyntaxHighlightedArea(@NonNull Context context, @Nullable AttributeSet attrs) {

		super(context, attrs);
		setup();
	}

	public SyntaxHighlightedArea(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {

		super(context, attrs, defStyleAttr);
		setup();
	}

	public void setup() {

		prism4jTheme = TinyDB.getInstance(getContext()).getString("currentTheme").equals("dark") ?
			Prism4jThemeDarkula.create() :
			Prism4jThemeDefault.create();

		sourceView = new TextView(getContext());

		sourceView.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
		sourceView.setTextSize(TypedValue.COMPLEX_UNIT_SP, 14);
		sourceView.setTypeface(Typeface.createFromAsset(getContext().getAssets(), "fonts/sourcecodeproregular.ttf"));
		sourceView.setTextColor(prism4jTheme.textColor());

		int padding = AppUtil.getPixelsFromDensity(getContext(), 5);
		sourceView.setPadding(padding, 0, padding, 0);

		HorizontalScrollView horizontalScrollView = new HorizontalScrollView(getContext());
		horizontalScrollView.setLayoutParams(new LinearLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT));
		horizontalScrollView.addView(sourceView);

		linesView = new LinesView(getContext());

		linesView.setLayoutParams(new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.MATCH_PARENT));
		linesView.setPadding(
			AppUtil.getPixelsFromDensity(getContext(), 3), 0,
			AppUtil.getPixelsFromDensity(getContext(), 6), 0);

		linesView.getPaint().setTypeface(sourceView.getTypeface());
		linesView.getPaint().setTextSize(sourceView.getTextSize());

		linesView.setBackgroundColor(prism4jTheme.background());
		linesView.setTextColor(prism4jTheme.textColor());
		linesView.setLineColor(prism4jTheme.textColor());

		setOrientation(HORIZONTAL);
		setBackgroundColor(prism4jTheme.background());
		addView(linesView);
		addView(horizontalScrollView);

	}

	public void setContent(@NonNull String source, @NonNull String extension) {

		if(source.length() > 0) {
			linesView.setLineCount(AppUtil.getLineCount(source));

			try {

				MainGrammarLocator mainGrammarLocator = MainGrammarLocator.getInstance();
				Prism4j prism4j = new Prism4j(mainGrammarLocator);

				CharSequence highlightedSource = Prism4jSyntaxHighlight.create(prism4j, prism4jTheme, MainGrammarLocator.DEFAULT_FALLBACK_LANGUAGE)
					.highlight(mainGrammarLocator.fromExtension(extension), source);

				if(highlightedSource.charAt(highlightedSource.length() - 1) == '\n') {
					// Removes a line break which is probably added by Prism4j but not actually present in the source.
					// This line should be altered in case this gets fixed.
					sourceView.setText(highlightedSource.subSequence(0, highlightedSource.length() - 1));
				}
				else {
					sourceView.setText(highlightedSource);
				}

			} catch(Throwable ignored) {
				// Fall back to plaintext if something fails
				sourceView.setText(source);
			}
		}
	}

    public String getContent() {

		return sourceView.getText().toString();
    }

	private static class LinesView extends View {

		private final Paint paint = new Paint();
		private final Rect textBounds = new Rect();

		@ColorInt private int backgroundColor;
		@ColorInt private int textColor;
		@ColorInt private int lineColor;

		private int lineCount;

	    public LinesView(Context context) {
	    	super(context);
	    }

		public void setLineCount(int lineCount) {
			this.lineCount = lineCount;
		}

		@Override
		public void setBackgroundColor(@ColorInt int backgroundColor) {
			this.backgroundColor = backgroundColor;
		}

		public void setTextColor(@ColorInt int textColor) {
			this.textColor = textColor;
		}

		public void setLineColor(@ColorInt int lineColor) {
			this.lineColor = lineColor;
		}

		public Paint getPaint() {
			return paint;
		}

	    @Override
	    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

		    String highestLineNumber = String.valueOf(lineCount);

		    paint.getTextBounds(highestLineNumber, 0, highestLineNumber.length(), textBounds);

	    	setMeasuredDimension(getPaddingLeft() + textBounds.width() + getPaddingRight(), MeasureSpec.getSize(heightMeasureSpec));

	    }

	    @Override
	    protected void onDraw(Canvas canvas) {

	    	paint.setColor(backgroundColor);

	    	canvas.drawRect(0, 0, getWidth(), getHeight(), paint);

		    float marginTopBottom = (float) (getHeight() - (textBounds.height() / 2)) / lineCount;

		    paint.setColor(textColor);

		    canvas.save();
		    canvas.translate(getPaddingLeft(), marginTopBottom);

		    for(int currentLine = 1; currentLine <= lineCount; currentLine++) {

			    canvas.drawText(String.valueOf(currentLine), 0, 0, paint);
			    canvas.translate(0, marginTopBottom);

		    }

		    paint.setColor(lineColor);

		    int dividerX = getWidth() - 1;
		    int dividerY = getHeight();

		    canvas.restore();
		    canvas.drawLine(dividerX,0, dividerX, dividerY, paint);

	    }

    }

}