package com.mes.update;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;

/**
 * 本地/远程版本读写与三段数字比较。
 */
public final class VersionUtil {

    private VersionUtil() {
    }

    /**
     * 读取本地版本：优先安装目录旁 app.version，否则使用配置中的默认版本。
     */
    public static String resolveLocalVersion(File installDir, String configVersion) {
        if (installDir != null) {
            File versionFile = new File(installDir, "app.version");
            String fromFile = readVersionFile(versionFile);
            if (fromFile != null && !fromFile.isEmpty()) {
                return fromFile;
            }
        }
        if (configVersion != null && !configVersion.trim().isEmpty()) {
            return configVersion.trim();
        }
        return "0.0.0";
    }

    public static String readVersionFile(File versionFile) {
        if (versionFile == null || !versionFile.isFile()) {
            return null;
        }
        try (BufferedReader reader = new BufferedReader(
                new InputStreamReader(new FileInputStream(versionFile), StandardCharsets.UTF_8))) {
            String line = reader.readLine();
            if (line == null) {
                return null;
            }
            return line.trim();
        } catch (Exception e) {
            return null;
        }
    }

    /**
     * 比较两个版本号。返回 >0 表示 a 更新，<0 表示 b 更新，0 表示相等。
     */
    public static int compare(String a, String b) {
        int[] pa = parse(a);
        int[] pb = parse(b);
        int len = Math.max(pa.length, pb.length);
        for (int i = 0; i < len; i++) {
            int va = i < pa.length ? pa[i] : 0;
            int vb = i < pb.length ? pb[i] : 0;
            if (va != vb) {
                return va - vb;
            }
        }
        return 0;
    }

    public static boolean isNewer(String remote, String local) {
        return compare(remote, local) > 0;
    }

    private static int[] parse(String version) {
        if (version == null || version.trim().isEmpty()) {
            return new int[]{0, 0, 0};
        }
        String cleaned = version.trim();
        if (cleaned.startsWith("v") || cleaned.startsWith("V")) {
            cleaned = cleaned.substring(1);
        }
        String[] parts = cleaned.split("[^0-9]+");
        int[] result = new int[Math.max(3, parts.length)];
        int idx = 0;
        for (String part : parts) {
            if (part == null || part.isEmpty()) {
                continue;
            }
            try {
                result[idx++] = Integer.parseInt(part);
            } catch (NumberFormatException ignored) {
                result[idx++] = 0;
            }
        }
        if (idx == 0) {
            return new int[]{0, 0, 0};
        }
        if (idx < 3) {
            int[] padded = new int[3];
            System.arraycopy(result, 0, padded, 0, idx);
            return padded;
        }
        int[] exact = new int[idx];
        System.arraycopy(result, 0, exact, 0, idx);
        return exact;
    }
}