//! Downloads a named release asset (from GitHub or Forgejo) to a local
//! path. The only module that talks to the releases API for asset bytes —
//! `checker` only resolves version tags, never downloads.

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,
}

/// A downloaded release asset: its local path plus the URL it came from,
/// the latter needed for the `source=` line of a generated PKGBUILD (see
/// `builder`) — `makepkg` uses it only as a fallback if the pre-seeded
/// local copy ever goes missing.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DownloadedAsset {
    pub path: PathBuf,
    pub download_url: String,
}

/// Downloads the release asset named exactly `asset_name` for `repo`@`tag`
/// into `dest_dir`, returning the local path and its origin URL. `api` is
/// the releases API root (see `source::Endpoints::api`); GitHub and Forgejo
/// serve the same endpoint and JSON shape under it.
pub fn download_asset(
    client: &reqwest::blocking::Client,
    api: &str,
    repo: &str,
    tag: &str,
    asset_name: &str,
    dest_dir: &Path,
) -> Result<DownloadedAsset> {
    let api_url = format!("{api}/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(DownloadedAsset {
        path: dest_path,
        download_url: asset.browser_download_url.clone(),
    })
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn download_asset_writes_matching_asset_to_dest_dir() {
        let mut server = mockito::Server::new();
        let api = server.url();
        let asset_url = format!("{}/download/thing.tar.gz", server.url());
        let release_body = format!(
            r#"{{"assets": [{{"name": "thing.tar.gz", "browser_download_url": "{asset_url}"}}]}}"#
        );
        let _release = server
            .mock("GET", "/repos/o/r/releases/tags/v1.0.0")
            .with_status(200)
            .with_body(release_body)
            .create();
        let _download = server
            .mock("GET", "/download/thing.tar.gz")
            .with_status(200)
            .with_body(b"artifact-bytes".as_slice())
            .create();

        let client = reqwest::blocking::Client::new();
        let dest_dir = tempfile::tempdir().unwrap();
        let asset = download_asset(
            &client,
            &api,
            "o/r",
            "v1.0.0",
            "thing.tar.gz",
            dest_dir.path(),
        )
        .unwrap();

        assert_eq!(asset.path, dest_dir.path().join("thing.tar.gz"));
        assert_eq!(asset.download_url, asset_url);
        assert_eq!(std::fs::read(&asset.path).unwrap(), b"artifact-bytes");
    }

    #[test]
    fn download_asset_errors_when_no_asset_matches() {
        let mut server = mockito::Server::new();
        let api = server.url();
        let _release = server
            .mock("GET", "/repos/o/r/releases/tags/v1.0.0")
            .with_status(200)
            .with_body(r#"{"assets": [{"name": "other", "browser_download_url": "https://example.invalid/other"}]}"#)
            .create();

        let client = reqwest::blocking::Client::new();
        let dest_dir = tempfile::tempdir().unwrap();
        let err = download_asset(
            &client,
            &api,
            "o/r",
            "v1.0.0",
            "thing.tar.gz",
            dest_dir.path(),
        )
        .unwrap_err();
        assert!(err.to_string().contains("no asset named"));
    }

    #[test]
    fn download_asset_errors_when_release_not_found() {
        let mut server = mockito::Server::new();
        let api = server.url();
        let _release = server
            .mock("GET", "/repos/o/r/releases/tags/v1.0.0")
            .with_status(404)
            .create();

        let client = reqwest::blocking::Client::new();
        let dest_dir = tempfile::tempdir().unwrap();
        let err = download_asset(
            &client,
            &api,
            "o/r",
            "v1.0.0",
            "thing.tar.gz",
            dest_dir.path(),
        )
        .unwrap_err();
        assert!(err.to_string().contains("fetching release metadata"));
    }
}