//! CLI 侧夹具：一个「别的启动器铺好了 `.minecraft`」的数据根 + 全量快照工具。

use std::collections::hash_map::DefaultHasher;
use std::collections::BTreeMap;
use std::hash::{Hash, Hasher};
use std::path::Path;
use std::time::UNIX_EPOCH;

/// 造一份「别的启动器已经铺好的」数据根（`<root>/.minecraft` + `<root>/.ULL`）：
///
/// | 路径 | 用意 |
/// | --- | --- |
/// | `versions/1.20.1/` | 正常版本（清单 + jar），可登记、可 `launch --dry-run` |
/// | `versions/1.20.1-orphan/` | 缺父版本 ⇒ 不可登记 |
/// | `libraries/` `assets/` | 恒共享层（登记不该碰） |
/// | `mods/` `saves/` | 玩家数据（登记不该碰） |
/// | `launcher_profiles.json` | 别的启动器的元数据（连读都不该读，更不该写） |
pub fn foreign_data_root(root: &Path) {
    let minecraft = root.join(".minecraft");
    let versions = minecraft.join("versions");
    write_version(&versions, "1.20.1", MANIFEST_OK, true);
    write_version(&versions, "1.20.1-orphan", MANIFEST_ORPHAN, true);
    write_file(
        &minecraft.join("libraries/com/mojang/brigadier/1.0.18/brigadier-1.0.18.jar"),
        b"library-bytes",
    );
    write_file(
        &minecraft.join("assets/indexes/5.json"),
        b"{\"objects\":{}}",
    );
    write_file(&minecraft.join("mods/jei.jar"), b"mod-bytes");
    write_file(&minecraft.join("saves/World/level.dat"), b"save-bytes");
    write_file(
        &minecraft.join("launcher_profiles.json"),
        br#"{"profiles":{"1.20.1":{"name":"1.20.1","lastVersionId":"1.20.1"}}}"#,
    );
}

/// 全量快照：相对路径 → (字节数, mtime 纳秒, 内容哈希)。
pub fn snapshot(dir: &Path) -> BTreeMap<String, (u64, u128, u64)> {
    let mut out = BTreeMap::new();
    walk(dir, dir, &mut out);
    out
}

fn walk(root: &Path, dir: &Path, out: &mut BTreeMap<String, (u64, u128, u64)>) {
    let Ok(entries) = std::fs::read_dir(dir) else {
        return;
    };
    for entry in entries.flatten() {
        let path = entry.path();
        let Ok(meta) = std::fs::symlink_metadata(&path) else {
            continue;
        };
        if meta.is_dir() {
            walk(root, &path, out);
            continue;
        }
        let relative = path
            .strip_prefix(root)
            .unwrap_or(&path)
            .to_string_lossy()
            .into_owned();
        let bytes = std::fs::read(&path).expect("文件应可读");
        let mtime = meta
            .modified()
            .ok()
            .and_then(|time| time.duration_since(UNIX_EPOCH).ok())
            .map_or(0, |duration| duration.as_nanos());
        out.insert(relative, (bytes.len() as u64, mtime, hash(&bytes)));
    }
}

fn hash(bytes: &[u8]) -> u64 {
    let mut hasher = DefaultHasher::new();
    bytes.hash(&mut hasher);
    hasher.finish()
}

/// 断言两次快照完全一致（路径集合 / 字节数 / 内容哈希 / mtime）。
///
/// 抓得住：命令写了、删了、改了任何外部文件（含「内容相同但重写一遍」——mtime 会变）。
/// 抓不住：只读打开（没有可观测痕迹）。
pub fn assert_unchanged(
    before: &BTreeMap<String, (u64, u128, u64)>,
    after: &BTreeMap<String, (u64, u128, u64)>,
    what: &str,
) {
    assert_eq!(
        before.keys().collect::<Vec<_>>(),
        after.keys().collect::<Vec<_>>(),
        "{what}：路径集合变了"
    );
    for (path, before) in before {
        assert_eq!(
            before,
            after.get(path).expect("同一路径"),
            "{what}：文件被改动 -> {path}"
        );
    }
}

fn write_version(versions: &Path, id: &str, manifest: &str, jar: bool) {
    let dir = versions.join(id);
    std::fs::create_dir_all(&dir).expect("建版本目录");
    std::fs::write(dir.join(format!("{id}.json")), manifest.as_bytes()).expect("写清单");
    if jar {
        std::fs::write(dir.join(format!("{id}.jar")), b"junk").expect("写 jar");
    }
}

fn write_file(path: &Path, bytes: &[u8]) {
    if let Some(parent) = path.parent() {
        std::fs::create_dir_all(parent).expect("建父目录");
    }
    std::fs::write(path, bytes).expect("写文件");
}

const MANIFEST_OK: &str = r#"{
  "id": "1.20.1",
  "type": "release",
  "mainClass": "net.minecraft.client.main.Main",
  "assets": "5",
  "assetIndex": { "id": "5" },
  "arguments": {
    "game": ["--username", "${auth_player_name}", "--version", "${version_name}",
             "--gameDir", "${game_directory}"],
    "jvm": ["-Djava.library.path=${natives_directory}", "-cp", "${classpath}"]
  },
  "libraries": [],
  "downloads": { "client": { "size": 4, "url": "http://example.invalid/client.jar" } }
}"#;

const MANIFEST_ORPHAN: &str = r#"{
  "id": "1.20.1-orphan",
  "type": "release",
  "inheritsFrom": "1.20.1-not-on-disk",
  "mainClass": "net.minecraft.client.main.Main",
  "libraries": []
}"#;