package com.codechecker.cache.git;

import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.List;

/**
 * 基于 git 命令的差异扫描与双版本文件内容读取。
 *
 * <p>通过 {@code git diff --name-only} 获取变更的 .java 文件，通过 {@code git show sha:path}
 * 读取指定提交下的文件内容，避免检出两个完整 worktree。</p>
 */
public class GitDiffScanner {

    private final Path repoRoot;

    public GitDiffScanner(Path repoRoot) {
        this.repoRoot = repoRoot;
    }

    /**
     * 返回 old..new 之间变更的 Java 文件路径（相对仓库根，使用 / 分隔）。
     */
    public List<String> changedJavaFiles(String oldSha, String newSha) throws GitException {
        List<String> lines = runLines(
                "git", "diff", "--name-only", "--diff-filter=ACMR", oldSha, newSha, "--", "*.java");
        List<String> result = new ArrayList<>();
        for (String line : lines) {
            String trimmed = line.trim();
            if (!trimmed.isEmpty() && trimmed.endsWith(".java")) {
                result.add(trimmed);
            }
        }
        return result;
    }

    /**
     * 读取某提交下指定文件的内容；文件在该提交不存在时返回 null。
     */
    public String fileContentAt(String sha, String path) throws GitException {
        try {
            ProcessResult pr = run("git", "show", sha + ":" + path);
            if (pr.exitCode != 0) {
                return null;
            }
            return pr.stdout;
        } catch (GitException e) {
            return null;
        }
    }

    private List<String> runLines(String... command) throws GitException {
        ProcessResult pr = run(command);
        if (pr.exitCode != 0) {
            throw new GitException("git 命令执行失败(exit=" + pr.exitCode + "): " + String.join(" ", command)
                    + "\n" + pr.stderr);
        }
        List<String> lines = new ArrayList<>();
        try (BufferedReader reader = new BufferedReader(
                new InputStreamReader(new java.io.ByteArrayInputStream(
                        pr.stdout.getBytes(StandardCharsets.UTF_8)), StandardCharsets.UTF_8))) {
            String line;
            while ((line = reader.readLine()) != null) {
                lines.add(line);
            }
        } catch (IOException e) {
            throw new GitException("读取 git 输出失败", e);
        }
        return lines;
    }

    private ProcessResult run(String... command) throws GitException {
        ProcessBuilder pb = new ProcessBuilder(command);
        pb.directory(repoRoot.toFile());
        pb.redirectErrorStream(false);
        try {
            Process process = pb.start();
            String stdout = readStream(process.getInputStream());
            String stderr = readStream(process.getErrorStream());
            int exit = process.waitFor();
            return new ProcessResult(exit, stdout, stderr);
        } catch (IOException e) {
            throw new GitException("无法启动 git 进程: " + String.join(" ", command), e);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw new GitException("git 进程被中断", e);
        }
    }

    private static String readStream(InputStream in) throws IOException {
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        byte[] chunk = new byte[8192];
        int read;
        while ((read = in.read(chunk)) != -1) {
            buffer.write(chunk, 0, read);
        }
        return new String(buffer.toByteArray(), StandardCharsets.UTF_8);
    }

    private static final class ProcessResult {
        final int exitCode;
        final String stdout;
        final String stderr;

        ProcessResult(int exitCode, String stdout, String stderr) {
            this.exitCode = exitCode;
            this.stdout = stdout;
            this.stderr = stderr;
        }
    }
}