package update

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
)

// Release mirrors the subset of the GitHub releases API response that the
// self-updater consumes.
type Release struct {
	TagName string  `json:"tag_name"`
	Name    string  `json:"name"`
	Body    string  `json:"body"`
	Assets  []Asset `json:"assets"`
}

// Asset is a single downloadable artifact attached to a release.
type Asset struct {
	Name               string `json:"name"`
	BrowserDownloadURL string `json:"browser_download_url"`
	Size               int64  `json:"size"`
}

const githubAPI = "https://api.github.com"

// LatestRelease fetches the newest published release for repo (form
// "owner/name"). A non-empty token is sent as a Bearer header, which is
// required for private repositories and lifts the unauthenticated rate limit.
func LatestRelease(ctx context.Context, repo, token string) (*Release, error) {
	repo = strings.TrimSpace(repo)
	if repo == "" {
		return nil, fmt.Errorf("update: repository not configured (set --repo or VOCAT_REPO)")
	}
	if strings.Count(repo, "/") != 1 {
		return nil, fmt.Errorf("update: invalid repository %q (expected owner/name)", repo)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, githubAPI+"/repos/"+repo+"/releases/latest", nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Accept", "application/vnd.github+json")
	if token != "" {
		req.Header.Set("Authorization", "Bearer "+token)
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("update: fetch latest release: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode == http.StatusForbidden {
		// The releases API returns 403 (not 404) when rate-limited.
		body, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
		return nil, fmt.Errorf("update: GitHub API rejected the request (likely rate-limited): %s", strings.TrimSpace(string(body)))
	}
	if resp.StatusCode == http.StatusNotFound {
		return nil, fmt.Errorf("update: no published release found for %s", repo)
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("update: GitHub API returned %s", resp.Status)
	}

	var release Release
	if err := json.NewDecoder(resp.Body).Decode(&release); err != nil {
		return nil, fmt.Errorf("update: decode release JSON: %w", err)
	}
	return &release, nil
}

// downloadAsset streams a release asset into dst, honoring the request context.
// The token is applied for consistency with the API call (GitHub release assets
// redirect to a pre-signed S3 URL; the token is dropped on redirect, which is
// the expected public-CDN flow).
func downloadAsset(ctx context.Context, url, token string, dst io.Writer) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return err
	}
	req.Header.Set("Accept", "application/octet-stream")
	if token != "" {
		req.Header.Set("Authorization", "Bearer "+token)
	}
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return fmt.Errorf("update: download asset: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("update: asset download returned %s", resp.Status)
	}
	if _, err := io.Copy(dst, resp.Body); err != nil {
		return fmt.Errorf("update: read asset body: %w", err)
	}
	return nil
}