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package main

import (
	"fmt"
	"net/http"
	"os"
	"os/exec"
	"runtime"
	"time"
)

func main() {
	if len(os.Args) < 2 {
		fmt.Fprintln(os.Stderr, "usage: git-credential-cosmocr <get|store|erase>")
		os.Exit(2)
	}
	op := os.Args[1]
	attrs := parseAttrs(os.Stdin)
	c := cache{path: defaultCachePath()}
	host := attrs["host"]

	switch op {
	case "get":
		runGet(c, host, os.Stdout)
	case "erase":
		// git calls erase after the credential was rejected (e.g. token expired
		// server-side); drop it so the next get re-authenticates.
		_ = c.del(host)
	case "store":
		// The helper manages its own cache; nothing to do.
	default:
		fmt.Fprintf(os.Stderr, "git-credential-cosmocr: unknown operation %q\n", op)
		os.Exit(2)
	}
}

func runGet(c cache, host string, out *os.File) {
	// Serve a cached, still-valid token without a round trip.
	if tok, ok := c.get(host); ok && !expired(tok, time.Now()) {
		emit(out, tok)
		return
	}

	cfg := configFromEnv()
	tok, err := cfg.login(useDeviceFlow())
	if err != nil {
		fmt.Fprintf(cfg.stderr, "git-credential-cosmocr: %v\n", err)
		os.Exit(1)
	}
	if err := c.set(host, tok); err != nil {
		fmt.Fprintf(cfg.stderr, "git-credential-cosmocr: warning: could not cache token: %v\n", err)
	}
	emit(out, tok)
}

// emit writes the token to git as Basic-auth credentials. The username is the
// token's subject; git ignores it for our server but including it keeps the
// credential record meaningful.
func emit(out *os.File, tok string) {
	info, _ := decodeToken(tok)
	attrs := map[string]string{"username": info.Sub, "password": tok}
	if info.Exp > 0 {
		attrs["password_expiry_utc"] = fmt.Sprintf("%d", info.Exp)
	}
	writeAttrs(out, attrs)
}

func configFromEnv() config {
	vaultURL := os.Getenv("COSMOCR_VAULT_URL")
	if vaultURL == "" {
		vaultURL = "https://vault.cosmocr.at"
	}
	aud := os.Getenv("COSMOCR_AUDIENCE")
	if aud == "" {
		aud = "gitweb"
	}
	return config{
		vaultURL: vaultURL,
		audience: aud,
		client:   &http.Client{Timeout: 30 * time.Second},
		openURL:  openBrowser,
		stderr:   os.Stderr,
		timeout:  3 * time.Minute,
	}
}

// useDeviceFlow reports whether to skip the browser and use the device-code
// flow: when explicitly requested, or on a headless machine with no display.
func useDeviceFlow() bool {
	if os.Getenv("COSMOCR_DEVICE") == "1" {
		return true
	}
	switch runtime.GOOS {
	case "linux":
		return os.Getenv("DISPLAY") == "" && os.Getenv("WAYLAND_DISPLAY") == ""
	default:
		return false
	}
}

// openBrowser best-effort launches the user's browser at url.
func openBrowser(url string) {
	var cmd string
	var args []string
	switch runtime.GOOS {
	case "darwin":
		cmd = "open"
	case "windows":
		cmd, args = "rundll32", []string{"url.dll,FileProtocolHandler"}
	default:
		cmd = "xdg-open"
	}
	_ = exec.Command(cmd, append(args, url)...).Start()
}