// src/updater.rs
use anyhow::{Context, Result};
use futures::StreamExt;
use serde::Deserialize;
use tokio::io::AsyncWriteExt;
use tokio::sync::mpsc::UnboundedSender;

#[derive(Debug, Clone)]
pub struct UpdateInfo {
    pub current_version: String,
    pub new_version: String,
    pub download_url: String,
    pub size: u64,
}

#[derive(Deserialize)]
struct Release {
    tag_name: String,
    prerelease: bool,
    assets: Vec<ReleaseAsset>,
}

#[derive(Deserialize)]
struct ReleaseAsset {
    name: String,
    browser_download_url: String,
    size: u64,
}

/// Checks Gitea releases API for latest stable (non-prerelease) release.
/// Returns Ok(None) if already up to date or no matching asset found.
pub async fn check(api_base: &str, timeout_sec: u64) -> Result<Option<UpdateInfo>> {
    let url = format!("{}/releases?limit=10&page=1", api_base);

    let client = reqwest::Client::builder()
        .timeout(std::time::Duration::from_secs(timeout_sec))
        .build()
        .context("failed to build HTTP client")?;

    let releases: Vec<Release> = client
        .get(&url)
        .send()
        .await
        .context("failed to fetch releases")?
        .json()
        .await
        .context("failed to parse releases JSON")?;

    let current_version = env!("CARGO_PKG_VERSION").to_string();

    // Find the latest non-prerelease release
    let latest = releases.into_iter().find(|r| !r.prerelease);
    let release = match latest {
        Some(r) => r,
        None => return Ok(None),
    };

    // Strip "v" prefix and anything after "@" (e.g. "v1.0.0@master" → "1.0.0")
    let tag = release.tag_name.as_str();
    let tag = tag.strip_prefix('v').unwrap_or(tag);
    let tag = tag.split('@').next().unwrap_or(tag).trim();
    let new_version = tag.to_string();

    // Already up to date
    if new_version == current_version {
        return Ok(None);
    }

    // Find a matching asset
    let asset_prefix = format!(
        "{}-{}-{}",
        env!("CARGO_PKG_NAME"),
        std::env::consts::OS,
        std::env::consts::ARCH
    );

    let asset = release
        .assets
        .into_iter()
        .find(|a| a.name.starts_with(&asset_prefix));

    let asset = match asset {
        Some(a) => a,
        None => return Ok(None),
    };

    Ok(Some(UpdateInfo {
        current_version,
        new_version,
        download_url: asset.browser_download_url,
        size: asset.size,
    }))
}

/// Downloads binary to temp file with streaming progress, atomically replaces
/// current exe, sets chmod 755.
/// Returns the path of the replaced executable (captured before rename so it
/// remains valid even after the old inode is marked "(deleted)" by the kernel).
pub async fn download_and_apply(
    info: &UpdateInfo,
    progress_tx: UnboundedSender<u64>,
) -> Result<std::path::PathBuf> {
    let client = reqwest::Client::new();

    let response = client
        .get(&info.download_url)
        .send()
        .await
        .context("failed to start download")?
        .error_for_status()
        .context("download request failed with error status")?;

    // Write to a temp file next to the current exe so rename is atomic
    let current_exe = std::env::current_exe().context("failed to get current exe path")?;
    let exe_dir = current_exe
        .parent()
        .context("current exe has no parent directory")?;

    let tmp_path = exe_dir.join(format!(".{}.tmp", env!("CARGO_PKG_NAME")));

    let mut file = tokio::fs::File::create(&tmp_path)
        .await
        .context("failed to create temp file")?;

    let mut stream = response.bytes_stream();
    let mut downloaded: u64 = 0;

    while let Some(chunk) = stream.next().await {
        let chunk = chunk.context("error reading download chunk")?;
        downloaded += chunk.len() as u64;
        file.write_all(&chunk)
            .await
            .context("failed to write to temp file")?;
        let _ = progress_tx.send(downloaded);
    }

    // Flush and close
    drop(file);

    // chmod 755
    #[cfg(unix)]
    {
        use std::os::unix::fs::PermissionsExt;
        let perms = std::fs::Permissions::from_mode(0o755);
        std::fs::set_permissions(&tmp_path, perms).context("failed to set permissions")?;
    }

    // Atomically replace current exe.
    // current_exe is captured BEFORE this rename — after rename, /proc/self/exe
    // on Linux returns the path with " (deleted)" appended, but the PathBuf we
    // hold still refers to the correct filesystem path of the new binary.
    std::fs::rename(&tmp_path, &current_exe).context("failed to replace current exe")?;

    Ok(current_exe)
}

// ── Update-target file ───────────────────────────────────────────────────────
// Written just before exec. On next startup we compare the expected version
// with CARGO_PKG_VERSION. A mismatch means the replacement didn't work
// (wrong asset, failed rename, etc.) and we show an error instead of looping.

fn update_target_path() -> std::path::PathBuf {
    crate::config::config_path()
        .parent()
        .expect("config dir has parent")
        .join(".update_target")
}

/// Write the expected version to disk before exec'ing the new binary.
pub fn write_update_target(new_version: &str) {
    let _ = std::fs::write(update_target_path(), new_version);
}

/// Read and delete the update-target file.
/// Returns `Some(expected_version)` if a previous run attempted an update.
/// The caller should compare it with `env!("CARGO_PKG_VERSION")` and show
/// an error if they differ.
pub fn take_update_target() -> Option<String> {
    let path = update_target_path();
    if !path.exists() {
        return None;
    }
    let version = std::fs::read_to_string(&path).ok()?;
    let _ = std::fs::remove_file(&path);
    Some(version.trim().to_string())
}

/// Replaces current process via execv (Unix). Never returns on success.
/// `exe_path` must be the path captured *before* the binary was replaced —
/// do NOT call std::env::current_exe() here, it returns "(deleted)" on Linux.
#[cfg(unix)]
pub fn exec_updated(exe_path: &std::path::Path) -> ! {
    use std::os::unix::process::CommandExt;

    let args: Vec<String> = std::env::args().collect();

    let err = std::process::Command::new(exe_path)
        .args(&args[1..])
        .exec();

    eprintln!("Failed to exec updated binary: {}", err);
    std::process::exit(1);
}