package org.sample;

import com.google.gson.JsonElement;
import com.google.gson.JsonParser;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.Reader;
import java.time.Instant;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAccessor;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.TimeUnit;

/**
 * This class finds CREATE_COMPLETE stacks that are more than five days old,
 * and output a aws cloudformation delete command to stdout.
 * This simply outputs the result, no actual stacks will be deleted.
 * <p>
 * First run this command:
 * export AWS_DEFAULT_REGION=us-east-1
 * aws cloudformation describe-stacks --query 'Stacks[?StackStatus==`CREATE_COMPLETE`]' --output json > /tmp/cfn-output-json
 * This shows all create_complete stacks in a given region
 * <p>
 * Then, run this class.
 * Finally, run the output in bash.
 * <p>
 * Requirements:
 * gson library should be in classpath
 */
public class CloudformationStackDeleter {

    private static final int OLDER_THAN_DAYS = 4;
    private static final String CFN_DESCRIBE_STACK_JSON_OUTPUT = "/tmp/cfn-output-json";

    public static void main(String[] args) throws FileNotFoundException {
        Reader r = new FileReader(CFN_DESCRIBE_STACK_JSON_OUTPUT);
        JsonParser parser = new JsonParser();
        final JsonElement parsed = parser.parse(r);
//        final JsonElement parsed = parser.parse("{id: 123}");

        List<String> stacksToDel = new ArrayList<>();
        for (JsonElement element : parsed.getAsJsonArray()) {
            final JsonElement creationTime = element.getAsJsonObject().get("CreationTime");
            String creationTimeAsString = creationTime.getAsString();
            DateTimeFormatter timeFormatter = DateTimeFormatter.ISO_INSTANT;
            TemporalAccessor accessor = timeFormatter.parse(creationTimeAsString);
            final Instant ctI = Instant.from(accessor);
            Date date = Date.from(ctI);
            Date now = new Date();

            final long diff = Math.abs(now.getTime() - date.getTime());
            final long days = TimeUnit.DAYS.convert(diff, TimeUnit.MILLISECONDS);
            if (days > OLDER_THAN_DAYS) {
                final JsonElement stackName = element.getAsJsonObject().get("StackName");
                stacksToDel.add(stackName.getAsString());
            }
        }

        System.out.println("Stacks to delete: " + stacksToDel.size());
        for (String name : stacksToDel) {
            System.out.println("aws cloudformation delete-stack --stack-name " + name);
        }
    }
}