use anyhow::{Context, Result};
use reqwest::Client;
use sha2::{Digest, Sha256};
use std::fs::{self, File};
use std::io::Write;
use std::path::{Path, PathBuf};
use tracing::info;

#[cfg(feature = "embed-binaries")]
pub static TLUSTY_BIN: &[u8] = include_bytes!("../../../assets/tlusty_static");
#[cfg(not(feature = "embed-binaries"))]
pub static TLUSTY_BIN: &[u8] = &[];

#[cfg(feature = "embed-binaries")]
pub static SYNSPEC_BIN: &[u8] = include_bytes!("../../../assets/synspec_static");
#[cfg(not(feature = "embed-binaries"))]
pub static SYNSPEC_BIN: &[u8] = &[];

#[derive(Debug, Clone)]
pub struct RuntimePaths {
    pub tlusty_exe: PathBuf,
    pub synspec_exe: PathBuf,
    pub data_dir: PathBuf,
    pub linelist: PathBuf,
}

fn calc_hash(bytes: &[u8]) -> String {
    let mut hasher = Sha256::new();
    hasher.update(bytes);
    hex::encode(hasher.finalize())
}

/// Ensures Fortran runtime binaries are unpacked and common partition function data files are fetched
pub async fn ensure_runtime(
    runtime_dir: &Path,
    server_url: &str,
    client: &Client,
) -> Result<RuntimePaths> {
    fs::create_dir_all(runtime_dir)
        .with_context(|| format!("Failed to create runtime dir: {}", runtime_dir.display()))?;

    let tlusty_exe = runtime_dir.join("tlusty_static");
    let synspec_exe = runtime_dir.join("synspec_static");
    let data_dir = runtime_dir.join("data");
    let linelist = runtime_dir.join("gfVIS99.dat");

    fs::create_dir_all(&data_dir)?;

    // 1. Unpack tlusty_static & synspec_static binaries if embedded
    if !TLUSTY_BIN.is_empty() {
        write_if_changed(&tlusty_exe, TLUSTY_BIN, true)?;
    }
    if !SYNSPEC_BIN.is_empty() {
        write_if_changed(&synspec_exe, SYNSPEC_BIN, true)?;
    }

    // 2. Fetch baseline equation of state partition function tables if missing locally
    let common_files = &[
        "irwin_bc.dat",
        "irwin_orig.dat",
        "tsuji.molec_bc2",
        "tsuji.molec_orig",
    ];
    ensure_specific_data_files(&data_dir, server_url, client, common_files).await?;

    // 3. Check gfVIS99.dat
    if !linelist.exists() {
        let url = format!("{}/api/data/linelist", server_url);
        info!("本地缺失主谱线库 gfVIS99.dat，开始从服务端下载: {}...", url);
        let resp = client.get(&url).send().await?;
        if resp.status().is_success() {
            let bytes = resp.bytes().await?;
            fs::write(&linelist, &bytes)?;
            info!("成功下载并保存主谱线库 gfVIS99.dat");
        } else {
            anyhow::bail!(
                "从服务端下载主谱线库 gfVIS99.dat 失败，HTTP 状态码: {}",
                resp.status()
            );
        }
    }

    let abs_runtime_dir =
        fs::canonicalize(runtime_dir).unwrap_or_else(|_| runtime_dir.to_path_buf());
    let tlusty_exe = abs_runtime_dir.join("tlusty_static");
    let synspec_exe = abs_runtime_dir.join("synspec_static");
    let data_dir = abs_runtime_dir.join("data");
    let linelist = abs_runtime_dir.join("gfVIS99.dat");

    Ok(RuntimePaths {
        tlusty_exe,
        synspec_exe,
        data_dir,
        linelist,
    })
}

static DATA_DOWNLOAD_MUTEX: tokio::sync::Mutex<()> = tokio::sync::Mutex::const_new(());

/// Checks local `./runtime/data/` for specific required files. If missing, downloads ONLY those specific files from Server!
pub async fn ensure_specific_data_files(
    data_dir: &Path,
    server_url: &str,
    client: &Client,
    required_files: &[&str],
) -> Result<()> {
    let _guard = DATA_DOWNLOAD_MUTEX.lock().await;
    tokio::fs::create_dir_all(data_dir).await?;

    for &filename in required_files {
        let local_file = data_dir.join(filename);
        if !local_file.exists() {
            let file_url = format!("{}/api/data/file/{}", server_url, filename);
            info!(
                "本地缺失数据文件 {}，开始从服务端拉取: {}",
                filename, file_url
            );

            let resp = client.get(&file_url).send().await?;
            if resp.status().is_success() {
                let bytes = resp.bytes().await?;
                let tmp_file = data_dir.join(format!(
                    "{}.{}.tmp",
                    filename,
                    uuid::Uuid::new_v4().simple()
                ));
                tokio::fs::write(&tmp_file, &bytes).await?;
                tokio::fs::rename(&tmp_file, &local_file).await?;
                info!("成功保存数据文件: {}", filename);
            } else {
                anyhow::bail!(
                    "服务端返回 HTTP {} 错误，数据文件: {}",
                    resp.status(),
                    filename
                );
            }
        }
    }

    Ok(())
}

fn write_if_changed(target_path: &Path, content: &[u8], executable: bool) -> Result<()> {
    let should_write = if target_path.exists() {
        match fs::read(target_path) {
            Ok(existing) => calc_hash(&existing) != calc_hash(content),
            Err(_) => true,
        }
    } else {
        true
    };

    if should_write {
        // 原子写：先写 .tmp 再 rename，避免半写后崩溃留下截断/损坏的可执行二进制。
        // 历史上直接 File::create 覆盖目标，若 write_all 中途进程被杀/磁盘满，会留下
        // 截断的 tlusty_static，且权限可能已设 0o755（可执行但损坏），node 尝试运行时
        // 产生难以定位的 Fortran 崩溃。tmp + rename 保证目标要么是完整旧版、要么是完整新版。
        let tmp_path = target_path.with_extension("tmp.write");
        {
            let mut file = File::create(&tmp_path)
                .with_context(|| format!("创建临时文件失败: {}", tmp_path.display()))?;
            file.write_all(content)?;
            file.flush()?;
            // drop 前 sync_all 确保数据落盘，降低断电丢数据的概率。
            let _ = file.sync_all();
        }

        #[cfg(unix)]
        if executable {
            use std::os::unix::fs::PermissionsExt;
            let mut perms = fs::metadata(&tmp_path)?.permissions();
            perms.set_mode(0o755);
            fs::set_permissions(&tmp_path, perms)?;
        }

        fs::rename(&tmp_path, target_path).with_context(|| {
            format!(
                "原子重命名 {} -> {} 失败",
                tmp_path.display(),
                target_path.display()
            )
        })?;
    }

    Ok(())
}