MarkdownParse.java

//https://howtodoinjava.com/java/io/java-read-file-to-string-examples/

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;

public class MarkdownParse {

    public static ArrayList<String> getLinks(String markdown) {
        ArrayList<String> toReturn = new ArrayList<>();
        // find the next [, then find the ], then find the (, then read link upto next )
        int currentIndex = 0;

        while(currentIndex < markdown.length()) {
            int openBracket = markdown.indexOf("[", currentIndex);
            if (isEscapeCharacter(markdown, openBracket)){
                openBracket = markdown.indexOf("[", openBracket);
            }
            int closeBracket = markdown.indexOf("]", openBracket);
            if (isEscapeCharacter(markdown, closeBracket)){
                closeBracket = markdown.indexOf("]", closeBracket+1);
            }
            if(closeBracket+1 == markdown.length() && markdown.indexOf("(",currentIndex) != -1){
                closeBracket = -1;
            }
            int openParen;
            if (openBracket == -1 || closeBracket == -1){
                openParen = markdown.indexOf("(",currentIndex);
            }
            else{
                openParen = markdown.indexOf("(", closeBracket+1);
            }
            if (isEscapeCharacter(markdown, openParen)){
                openParen = markdown.indexOf("(", openParen+1);
            }
            int closeParen = -1;
            if (openParen != -1){
                closeParen = markdown.indexOf(")", openParen);
            }
            if (isEscapeCharacter(markdown, closeParen)){
                closeParen = markdown.indexOf(")", closeParen+1);
            }
            if (openParen + 1 <= closeParen){
                //toReturn.add(markdown.substring(openParen + 1, closeParen));
                
                if (beforNewLine(markdown, closeParen)){
                    int innercloseParen = getOuterParen(markdown, closeParen);
                    toReturn.add(trimSpaces(markdown,openParen,innercloseParen));
                }
                else{
                    toReturn.add(trimSpaces(markdown,openParen,closeParen));
                }
                
                if (isNestedLink(markdown, openBracket,closeBracket,closeParen)){
                    openParen = markdown.indexOf("(", closeParen);
                    closeParen = markdown.indexOf(")", openParen);
                    closeParen = getOuterParen(markdown, closeParen);
                    //toReturn.add(markdown.substring(openParen + 1, closeParen));
                    toReturn.add(trimSpaces(markdown,openParen,closeParen));
                }

            }
            else{
                break;
            }
            
            currentIndex = closeParen + 1;
        }
        return toReturn;
   
    }
    public static boolean isNestedLink(String md, int openBra, int closeBra,int closePar){
        openBra = md.indexOf("[",openBra+1);
        int newLine = md.indexOf("\n",closeBra);
        System.out.println(newLine);
        return openBra != -1 && openBra < closeBra && md.substring(closeBra,newLine).contains("]")
        && !isEscapeCharacter(md, openBra);
    }

    public static int getOuterParen(String md, int closeParen){
        
        int newLine = md.indexOf("\n",closeParen);
        /*System.out.println(closeParen+1);
        System.out.println(newLine);*/
        int outerCloseParen = closeParen;
        System.out.println(md.substring(outerCloseParen+1, newLine).contains(")"));
        while (md.substring(outerCloseParen+1, newLine).contains(")")){
            outerCloseParen = md.indexOf(")", outerCloseParen+1);
            
            //System.out.println(closeParen);
        }
        return outerCloseParen;
    }

    private static boolean isEscapeCharacter(String md, int index){
        if (index - 1 > -1 && md.charAt(index-1) == '\\'){
            //System.out.println("true");
            return true;
        }
        return false;
    }

    public static String trimSpaces(String md, int openParen, int closeParen){
        String toTrim = md.substring(openParen+1, closeParen);
        return toTrim.trim();
    }   
    public static boolean beforNewLine(String md, int closeParen){
        int newLine = md.indexOf("\n",closeParen);
        System.out.println("newline: "+ newLine);
        System.out.println("closeParen: " + closeParen);
        if (!md.substring(closeParen,newLine).contains("]")){
            return true;
        }
        return false;
    }



  public static void main(String[] args) throws IOException {
        Path fileName = Path.of(args[0]);
        String content = Files.readString(fileName);
        ArrayList<String> links = getLinks(content);
	    System.out.println(links);
    }

   
}