/*
   Copyright Docker attest 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 tuf

import (
	"fmt"
	"strings"

	"github.com/Masterminds/semver/v3"
	"github.com/docker/attest/version"
)

const ThisModulePath = "github.com/docker/attest"

type VersionChecker interface {
	// CheckVersion checks if the current version of this library meets the constraints from the TUF repo
	CheckVersion(tufClient Downloader) error
}

type InvalidVersionError struct {
	AttestVersion     string
	VersionConstraint string
	Errors            []error
}

func (e *InvalidVersionError) Error() string {
	var errsStr strings.Builder
	for i, err := range e.Errors {
		if i > 0 {
			errsStr.WriteString("; ")
		}
		errsStr.WriteString(err.Error())
	}
	return fmt.Sprintf("%s version %s does not satisfy constraints %s: %s", ThisModulePath, e.AttestVersion, e.VersionConstraint, errsStr.String())
}

func NewDefaultVersionChecker() *DefaultVersionChecker {
	return &DefaultVersionChecker{
		VersionFetcher: version.NewGoVersionFetcher(),
	}
}

type DefaultVersionChecker struct {
	VersionFetcher version.Fetcher
}

func (vc *DefaultVersionChecker) CheckVersion(client Downloader) error {
	attestVersion, err := vc.VersionFetcher.Get()
	if err != nil {
		return fmt.Errorf("failed to get version: %w", err)
	}
	if attestVersion == nil {
		return nil
	}
	// see https://github.com/Masterminds/semver/blob/v3.2.1/README.md#checking-version-constraints
	// for more information on the expected format of the version constraints in the TUF repo
	target, err := client.DownloadTarget("version-constraints", "")
	if err != nil {
		return fmt.Errorf("failed to download version-constraints: %w", err)
	}
	versionConstraints, err := semver.NewConstraint(string(target.Data))
	if err != nil {
		return fmt.Errorf("failed to parse minimum version: %w", err)
	}

	ok, errs := versionConstraints.Validate(attestVersion)
	if !ok {
		return &InvalidVersionError{
			AttestVersion:     attestVersion.String(),
			VersionConstraint: versionConstraints.String(),
			Errors:            errs,
		}
	}

	return nil
}