use anyhow::{Context, Result};
use serde::Deserialize;
use std::path::{Path, PathBuf};

#[derive(Debug, Deserialize)]
struct Release {
    assets: Vec<Asset>,
}

#[derive(Debug, Deserialize)]
struct Asset {
    name: String,
    browser_download_url: String,
}

/// Downloads the release asset named exactly `asset_name` for `repo`@`tag`
/// into `dest_dir`, returning the local path.
pub fn download_asset(
    client: &reqwest::blocking::Client,
    repo: &str,
    tag: &str,
    asset_name: &str,
    dest_dir: &Path,
) -> Result<PathBuf> {
    let api_url = format!("https://api.github.com/repos/{repo}/releases/tags/{tag}");
    let release: Release = client
        .get(&api_url)
        .send()?
        .error_for_status()
        .with_context(|| format!("fetching release metadata from {api_url}"))?
        .json()?;

    let asset = release
        .assets
        .iter()
        .find(|a| a.name == asset_name)
        .with_context(|| format!("no asset named '{asset_name}' in {repo}@{tag}"))?;

    std::fs::create_dir_all(dest_dir)?;
    let dest_path = dest_dir.join(&asset.name);
    let bytes = client
        .get(&asset.browser_download_url)
        .send()?
        .error_for_status()?
        .bytes()?;
    std::fs::write(&dest_path, &bytes)?;
    Ok(dest_path)
}