use anyhow::{Context, Result};
use std::io::Write;

const GITEA_BASE: &str  = "https://gitea.whitlocktech.com";
const REPO_OWNER: &str  = "whitlocktech";
const REPO_NAME: &str   = "tickr";
const ASSET_NAME: &str  = "tickr.exe";

/// Check whether a newer release exists on Gitea.
/// Returns `Some((tag_name, download_url))` when the remote version is strictly
/// greater than the running binary, `None` when already up-to-date.
pub async fn check_for_update() -> Result<Option<(String, String)>> {
    let url = format!(
        "{GITEA_BASE}/api/v1/repos/{REPO_OWNER}/{REPO_NAME}/releases/latest"
    );

    let resp = reqwest::Client::new()
        .get(&url)
        .header("User-Agent", format!("tickr/{}", crate::VERSION))
        .send()
        .await
        .context("Failed to reach Gitea")?;

    if !resp.status().is_success() {
        // 404 = no releases yet; treat as up-to-date rather than an error
        return Ok(None);
    }

    let body: serde_json::Value = resp.json().await.context("Invalid JSON from Gitea")?;

    let tag = body["tag_name"]
        .as_str()
        .context("Missing tag_name in release")?
        .to_string();

    let download_url = body["assets"]
        .as_array()
        .and_then(|assets| {
            assets
                .iter()
                .find(|a| a["name"].as_str() == Some(ASSET_NAME))
                .and_then(|a| a["browser_download_url"].as_str())
        })
        .context("Asset not found in release")?
        .to_string();

    // Strip leading 'v' and compare semver
    let remote_str = tag.trim_start_matches('v');
    let remote_ver = semver::Version::parse(remote_str)
        .with_context(|| format!("Bad remote version: {remote_str}"))?;
    let local_ver = semver::Version::parse(crate::VERSION)
        .with_context(|| format!("Bad local version: {}", crate::VERSION))?;

    if remote_ver > local_ver {
        Ok(Some((tag, download_url)))
    } else {
        Ok(None)
    }
}

/// Download the new binary and schedule a swap on next launch.
///
/// The download is streamed in chunks to avoid loading the whole binary into
/// memory. A small bat script is written alongside it; the bat waits 2 seconds
/// for the current process to exit, moves the new exe into place, relaunches
/// it, then deletes itself.
pub async fn download_and_swap(download_url: &str) -> Result<()> {
    let exe_path = std::env::current_exe().context("Cannot resolve current exe path")?;
    let exe_dir = exe_path.parent().context("Cannot resolve exe directory")?;

    let update_path = exe_dir.join("tickr_update.exe");
    let bat_path    = exe_dir.join("tickr_swap.bat");

    // ── Stream download ───────────────────────────────────────────────────
    let mut resp = reqwest::Client::new()
        .get(download_url)
        .header("User-Agent", format!("tickr/{}", crate::VERSION))
        .send()
        .await
        .context("Download request failed")?;

    if !resp.status().is_success() {
        anyhow::bail!("Download returned HTTP {}", resp.status());
    }

    let mut file = std::fs::File::create(&update_path)
        .with_context(|| format!("Cannot create {}", update_path.display()))?;

    while let Some(chunk) = resp.chunk().await.context("Download interrupted")? {
        file.write_all(&chunk).context("Write error during download")?;
    }
    drop(file);

    // ── Write swap bat ────────────────────────────────────────────────────
    let bat = "@echo off\r\ntimeout /t 2 /nobreak >nul\r\nmove /y tickr_update.exe tickr.exe\r\nstart \"\" tickr.exe\r\ndel \"%~f0\"\r\n";
    std::fs::write(&bat_path, bat)
        .with_context(|| format!("Cannot write {}", bat_path.display()))?;

    // ── Launch bat detached and exit ──────────────────────────────────────
    std::process::Command::new("cmd")
        .args(["/c", "tickr_swap.bat"])
        .current_dir(exe_dir)
        .spawn()
        .context("Failed to launch swap bat")?;

    std::process::exit(0);
}