/*
Copyright 2019 The Knative 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 version

import (
	"fmt"
	"os"
	"strings"

	"github.com/blang/semver/v4"
	"k8s.io/client-go/discovery"
)

const (
	// KubernetesMinVersionKey is the environment variable that can be used to override
	// the Kubernetes minimum version required by Knative.
	KubernetesMinVersionKey = "KUBERNETES_MIN_VERSION"

	// NOTE: If you are changing this line, please also update the minimum kubernetes
	// version listed here:
	// https://github.com/knative/docs/blob/master/docs/install/any-kubernetes-cluster.md#before-you-begin
	defaultMinimumVersion = "v1.17.0"
)

func getMinimumVersion() string {
	if v := os.Getenv(KubernetesMinVersionKey); v != "" {
		return v
	}
	return defaultMinimumVersion
}

// CheckMinimumVersion checks if the currently installed version of
// Kubernetes is compatible with the minimum version required.
// Returns an error if its not.
//
// A Kubernetes discovery client can be passed in as the versioner
// like `CheckMinimumVersion(kubeClient.Discovery())`.
func CheckMinimumVersion(versioner discovery.ServerVersionInterface) error {
	v, err := versioner.ServerVersion()
	if err != nil {
		return err
	}

	currentVersion, err := semver.Make(normalizeVersion(v.GitVersion))
	if err != nil {
		return err
	}
	minimumVersion, err := semver.Make(normalizeVersion(getMinimumVersion()))
	if err != nil {
		return err
	}

	// If no specific pre-release requirement is set, we default to "-0" to always allow
	// pre-release versions of the same Major.Minor.Patch version.
	if len(minimumVersion.Pre) == 0 {
		minimumVersion.Pre = []semver.PRVersion{{VersionNum: 0}}
	}

	// Compare returns 1 if the first version is greater than the
	// second version.
	if currentVersion.LT(minimumVersion) {
		if len(currentVersion.Pre) > 0 {
			return fmt.Errorf("pre-release kubernetes version %q is not compatible, need at least %q (this can be overridden with the env var %q); note pre-release version is smaller than the corresponding release version (e.g. 1.x.y-z < 1.x.y), using 1.x.y-0 as the minimum version is likely to help in this case",
				currentVersion, minimumVersion, KubernetesMinVersionKey)
		}
		return fmt.Errorf("kubernetes version %q is not compatible, need at least %q (this can be overridden with the env var %q)",
			currentVersion, minimumVersion, KubernetesMinVersionKey)
	}
	return nil
}

func normalizeVersion(v string) string {
	if strings.HasPrefix(v, "v") {
		// No need to account for unicode widths.
		return v[1:]
	}
	return v
}
