package main

import (
	"context"
	"errors"
	"fmt"
	"net/url"
	"os"
	"os/exec"
	"strings"
	"time"
)

type commandRunner func(context.Context, string, ...string) ([]byte, error)

func resolveToken(endpoint string) (string, error) {
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	return resolveTokenWith(ctx, endpoint, os.Getenv, runCommand)
}

func resolveTokenWith(ctx context.Context, endpoint string, getenv func(string) string, run commandRunner) (string, error) {
	if token := firstNonEmpty(
		getenv("GH_TOKEN"),
		getenv("GITHUB_TOKEN"),
		getenv("GH_ENTERPRISE_TOKEN"),
		getenv("GITHUB_ENTERPRISE_TOKEN"),
	); token != "" {
		return token, nil
	}

	host, err := githubHost(endpoint)
	if err != nil {
		return "", err
	}
	output, err := run(ctx, "gh", "auth", "token", "--hostname", host)
	if err != nil {
		if errors.Is(err, exec.ErrNotFound) {
			return "", errors.New("no environment token found and gh is not installed; install gh and run `gh auth login`, or set GH_TOKEN")
		}
		if ctx.Err() != nil {
			return "", fmt.Errorf("read authentication from gh: %w", ctx.Err())
		}
		return "", fmt.Errorf("no usable authentication for %s; run `gh auth login --hostname %s`, or set GH_TOKEN: %w", host, host, err)
	}
	token := strings.TrimSpace(string(output))
	if token == "" {
		return "", fmt.Errorf("gh returned an empty token for %s; run `gh auth login --hostname %s`", host, host)
	}
	return token, nil
}

func githubHost(endpoint string) (string, error) {
	parsed, err := url.Parse(endpoint)
	if err != nil || parsed.Scheme == "" || parsed.Hostname() == "" {
		return "", fmt.Errorf("invalid GitHub GraphQL endpoint %q", endpoint)
	}
	if parsed.Hostname() == "api.github.com" {
		return "github.com", nil
	}
	return parsed.Hostname(), nil
}

func runCommand(ctx context.Context, name string, args ...string) ([]byte, error) {
	return exec.CommandContext(ctx, name, args...).Output()
}