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package spring.turbo.util.collection;

import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;
import spring.turbo.lang.Singleton;
import spring.turbo.util.Asserts;
import spring.turbo.util.StringPool;

import java.util.Comparator;
import java.util.Objects;

/**
 * 版本号比较器
 *
 * @author 应卓
 * @see #getInstance()
 * @since 1.1.4
 */
@Singleton
public class VersionComparator implements Comparator {

    /**
     * 私有构造方法
     */
    private VersionComparator() {
        super();
    }

    public static VersionComparator getInstance() {
        return AsyncAvoid.INSTANCE;
    }

    /**
     * 比较两个版本

     * null版本排在最小：即：
     *      * compare(null, "v1") < 0
     * compare("v1", "v1") = 0
     * compare(null, null) = 0
     * compare("v1", null) > 0
     * compare("1.0.0", "1.0.2") < 0
     * compare("1.0.2", "1.0.2a") < 0
     * compare("1.13.0", "1.12.1c") > 0
     * compare("V0.0.20170102", "V0.0.20170101") > 0
     * 
     *
     * @param version1 版本1
     * @param version2 版本2
     */
    @Override
    public int compare(@Nullable String version1, @Nullable String version2) {
        if (Objects.equals(version1, version2)) {
            return 0;
        }

        if (version1 == null) {// null视为最小版本，排在前
            return -1;
        }

        if (version2 == null) {
            return 1;
        }

        final String[] v1s = StringUtils.split(version1, StringPool.DOT);
        final String[] v2s = StringUtils.split(version2, StringPool.DOT);

        Asserts.notNull(v1s);
        Asserts.notNull(v2s);

        int diff = 0;
        int minLength = Math.min(v1s.length, v2s.length);// 取最小长度值
        String v1;
        String v2;
        for (int i = 0; i < minLength; i++) {
            v1 = v1s[i];
            v2 = v2s[i];
            // 先比较长度
            diff = v1.length() - v2.length();
            if (0 == diff) {
                diff = v1.compareTo(v2);
            }
            if (diff != 0) {
                //已有结果，结束
                break;
            }
        }

        // 如果已经分出大小，则直接返回，如果未分出大小，则再比较位数，有子版本的为大；
        return (diff != 0) ? diff : v1s.length - v2s.length;
    }

    // -----------------------------------------------------------------------------------------------------------------

    private static class AsyncAvoid {
        public static final VersionComparator INSTANCE = new VersionComparator();
    }

}