/*
Copyright 2016 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.
*/

package util

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"regexp"
	"strings"

	netutil "k8s.io/apimachinery/pkg/util/net"
)

var (
	kubeReleaseBucketURL  = "https://dl.k8s.io"
	kubeReleaseRegex      = regexp.MustCompile(`^v?(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)([-0-9a-zA-Z_\.+]*)?$`)
	kubeReleaseLabelRegex = regexp.MustCompile(`^[[:lower:]]+(-[-\w_\.]+)?$`)
	kubeBucketPrefixes    = regexp.MustCompile(`^((release|ci|ci-cross)/)?([-\w_\.+]+)$`)
)

// KubernetesReleaseVersion is helper function that can fetch
// available version information from release servers based on
// label names, like "stable" or "latest".
//
// If argument is already semantic version string, it
// will return same string.
//
// In case of labels, it tries to fetch from release
// servers and then return actual semantic version.
//
// Available names on release servers:
//  stable      (latest stable release)
//  stable-1    (latest stable release in 1.x)
//  stable-1.0  (and similarly 1.1, 1.2, 1.3, ...)
//  latest      (latest release, including alpha/beta)
//  latest-1    (latest release in 1.x, including alpha/beta)
//  latest-1.0  (and similarly 1.1, 1.2, 1.3, ...)
func KubernetesReleaseVersion(version string) (string, error) {
	ver := normalizedBuildVersion(version)
	if len(ver) != 0 {
		return ver, nil
	}

	bucketURL, versionLabel, err := splitVersion(version)
	if err != nil {
		return "", err
	}

	// revalidate, if exact build from e.g. CI bucket requested.
	ver = normalizedBuildVersion(versionLabel)
	if len(ver) != 0 {
		return ver, nil
	}

	if kubeReleaseLabelRegex.MatchString(versionLabel) {
		url := fmt.Sprintf("%s/%s.txt", bucketURL, versionLabel)
		body, err := fetchFromURL(url)
		if err != nil {
			return "", err
		}
		// Re-validate received version and return.
		return KubernetesReleaseVersion(body)
	}
	return "", fmt.Errorf("version %q doesn't match patterns for neither semantic version nor labels (stable, latest, ...)", version)
}

// KubernetesVersionToImageTag is helper function that replaces all
// non-allowed symbols in tag strings with underscores.
// Image tag can only contain lowercase and uppercase letters, digits,
// underscores, periods and dashes.
// Current usage is for CI images where all of symbols except '+' are valid,
// but function is for generic usage where input can't be always pre-validated.
func KubernetesVersionToImageTag(version string) string {
	allowed := regexp.MustCompile(`[^-a-zA-Z0-9_\.]`)
	return allowed.ReplaceAllString(version, "_")
}

// KubernetesIsCIVersion checks if user requested CI version
func KubernetesIsCIVersion(version string) bool {
	subs := kubeBucketPrefixes.FindAllStringSubmatch(version, 1)
	if len(subs) == 1 && len(subs[0]) == 4 && strings.HasPrefix(subs[0][2], "ci") {
		return true
	}
	return false
}

// Internal helper: returns normalized build version (with "v" prefix if needed)
// If input doesn't match known version pattern, returns empty string.
func normalizedBuildVersion(version string) string {
	if kubeReleaseRegex.MatchString(version) {
		if strings.HasPrefix(version, "v") {
			return version
		}
		return "v" + version
	}
	return ""
}

// Internal helper: split version parts,
// Return base URL and cleaned-up version
func splitVersion(version string) (string, string, error) {
	var urlSuffix string
	subs := kubeBucketPrefixes.FindAllStringSubmatch(version, 1)
	if len(subs) != 1 || len(subs[0]) != 4 {
		return "", "", fmt.Errorf("invalid version %q", version)
	}

	switch {
	case strings.HasPrefix(subs[0][2], "ci"):
		// Just use whichever the user specified
		urlSuffix = subs[0][2]
	default:
		urlSuffix = "release"
	}
	url := fmt.Sprintf("%s/%s", kubeReleaseBucketURL, urlSuffix)
	return url, subs[0][3], nil
}

// Internal helper: return content of URL
func fetchFromURL(url string) (string, error) {
	client := &http.Client{Transport: netutil.SetOldTransportDefaults(&http.Transport{})}
	resp, err := client.Get(url)
	if err != nil {
		return "", fmt.Errorf("unable to get URL %q: %s", url, err.Error())
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("unable to fetch file. URL: %q Status: %v", url, resp.Status)
	}
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return "", fmt.Errorf("unable to read content of URL %q: %s", url, err.Error())
	}
	return strings.TrimSpace(string(body)), nil
}