/*
Copyright 2022 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Originally copied from pkg/credentialproviders/gcp
package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"

	credentialproviderv1 "k8s.io/kubelet/pkg/apis/credentialprovider/v1"
)

const (
	maxReadLength = 10 * 1 << 20 // 10MB
)

var containerRegistryUrls = []string{"container.cloud.google.com", "gcr.io", "*.gcr.io", "*.pkg.dev"}

// HTTPError wraps a non-StatusOK error code as an error.
type HTTPError struct {
	StatusCode int
	URL        string
}

var _ error = &HTTPError{}

// Error implements error
func (h *HTTPError) Error() string {
	return fmt.Sprintf("http status code: %d while fetching url %s",
		h.StatusCode, h.URL)
}

// TokenBlob is used to decode the JSON blob containing an access token
// that is returned by GCE metadata.
type TokenBlob struct {
	AccessToken string `json:"access_token"`
}

type provider struct {
	client        *http.Client
	tokenEndpoint string
}

func (p *provider) Provide(image string) (map[string]credentialproviderv1.AuthConfig, error) {
	cfg := map[string]credentialproviderv1.AuthConfig{}

	tokenJSONBlob, err := readURL(p.tokenEndpoint, p.client)
	if err != nil {
		return cfg, err
	}

	var parsedBlob TokenBlob
	if err := json.Unmarshal(tokenJSONBlob, &parsedBlob); err != nil {
		return cfg, err
	}

	authConfig := credentialproviderv1.AuthConfig{
		Username: "_token",
		Password: parsedBlob.AccessToken,
	}

	// Add our entry for each of the supported container registry URLs
	for _, k := range containerRegistryUrls {
		cfg[k] = authConfig
	}
	return cfg, nil
}

func readURL(url string, client *http.Client) (body []byte, err error) {
	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return nil, err
	}

	req.Header = http.Header{
		"Metadata-Flavor": []string{"Google"},
	}

	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, &HTTPError{
			StatusCode: resp.StatusCode,
			URL:        url,
		}
	}

	limitedReader := &io.LimitedReader{R: resp.Body, N: maxReadLength}
	contents, err := io.ReadAll(limitedReader)
	if err != nil {
		return nil, err
	}

	if limitedReader.N <= 0 {
		return nil, errors.New("the read limit is reached")
	}

	return contents, nil
}