/*
    This code is from https://gist.github.com/jjfiv/2ac5c081e088779f49aa, which is BSD licensed:
    http://lemurproject.org/galago-license
*/
package biz.nellemann.syslogd.parser;

public class JsonUtil {

    public static String encode(String input) {

        StringBuilder output = new StringBuilder();

        for (int i = 0; i < input.length(); i++) {
            char ch = input.charAt(i);

            // let's not put any nulls in our strings
            if ((int) ch == 0) {
                continue;
            }

            if (ch == '\n') {
                output.append("\\n");
            } else if (ch == '\t') {
                output.append("\\t");
            } else if (ch == '\r') {
                output.append("\\r");
            } else if (ch == '\\') {
                output.append("\\\\");
            } else if (ch == '"') {
                output.append("\\\"");
            } else if (ch == '\b') {
                output.append("\\b");
            } else if (ch == '\f') {
                output.append("\\f");
            } else if ((int) ch > 127) {
                output.append(String.format("\\u%04x", (int) ch));
            } else {
                output.append(ch);
            }
        }

        return output.toString();
    }


    public static String decode(String input) {

        StringBuilder builder = new StringBuilder();

        int i = 0;
        while (i < input.length()) {
            char delimiter = input.charAt(i);
            i++; // consume letter or backslash

            if (delimiter == '\\' && i < input.length()) {

                // consume first after backslash
                char ch = input.charAt(i);
                i++;

                if (ch == '\\' || ch == '/' || ch == '"' || ch == '\'') {
                    builder.append(ch);
                } else if (ch == 'n') builder.append('\n');
                else if (ch == 'r') builder.append('\r');
                else if (ch == 't') builder.append('\t');
                else if (ch == 'b') builder.append('\b');
                else if (ch == 'f') builder.append('\f');
                else if (ch == 'u') {

                    StringBuilder hex = new StringBuilder();

                    // expect 4 digits
                    if (i + 4 > input.length()) {
                        throw new RuntimeException("Not enough unicode digits! ");
                    }
                    for (char x : input.substring(i, i + 4).toCharArray()) {
                        if (!Character.isLetterOrDigit(x)) {
                            throw new RuntimeException("Bad character in unicode escape.");
                        }
                        hex.append(Character.toLowerCase(x));
                    }
                    i += 4; // consume those four digits.

                    int code = Integer.parseInt(hex.toString(), 16);
                    builder.append((char) code);
                } else {
                    throw new RuntimeException("Illegal escape sequence: \\" + ch);
                }
            } else { // it's not a backslash, or it's the last character.
                builder.append(delimiter);
            }
        }

        return builder.toString();
    }

}