/*
Copyright The ORAS 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 registry

import (
	"fmt"
	"net/url"
	"regexp"
	"strings"

	"github.com/opencontainers/go-digest"
	errdef "oras.land/oras-go/pkg/content"
)

// regular expressions for components.
var (
	// repositoryRegexp is adapted from the distribution implementation.
	// The repository name set under OCI distribution spec is a subset of the
	// the docker spec. For maximum compability, the docker spec is verified at
	// the client side. Further check is left to the server side.
	// References:
	// - https://github.com/distribution/distribution/blob/v2.7.1/reference/regexp.go#L53
	// - https://github.com/opencontainers/distribution-spec/blob/main/spec.md#pulling-manifests
	repositoryRegexp = regexp.MustCompile(`^[a-z0-9]+(?:(?:[._]|__|[-]*)[a-z0-9]+)*(?:/[a-z0-9]+(?:(?:[._]|__|[-]*)[a-z0-9]+)*)*$`)

	// tagRegexp checks the tag name.
	// The docker and OCI spec have the same regular expression.
	// Reference: https://github.com/opencontainers/distribution-spec/blob/main/spec.md#pulling-manifests
	tagRegexp = regexp.MustCompile(`^[\w][\w.-]{0,127}$`)
)

// Reference references to a descriptor in the registry.
type Reference struct {
	// Registry is the name of the registry.
	// It is usually the domain name of the registry optionally with a port.
	Registry string

	// Repository is the name of the repository.
	Repository string

	// Reference is the reference of the object in the repository.
	// A reference can be a tag or a digest.
	Reference string
}

// ParseReference parses a string into a artifact reference.
// If the reference contains both the tag and the digest, the tag will be
// dropped.
// Digest is recognized only if the corresponding algorithm is available.
func ParseReference(raw string) (Reference, error) {
	parts := strings.SplitN(raw, "/", 2)
	if len(parts) == 1 {
		return Reference{}, fmt.Errorf("%w: missing repository", errdef.ErrInvalidReference)
	}
	registry, path := parts[0], parts[1]
	var repository string
	var reference string
	if index := strings.Index(path, "@"); index != -1 {
		// digest found
		repository = path[:index]
		reference = path[index+1:]

		// drop tag since the digest is present.
		if index := strings.Index(repository, ":"); index != -1 {
			repository = repository[:index]
		}
	} else if index := strings.Index(path, ":"); index != -1 {
		// tag found
		repository = path[:index]
		reference = path[index+1:]
	} else {
		// empty reference
		repository = path
	}
	res := Reference{
		Registry:   registry,
		Repository: repository,
		Reference:  reference,
	}
	if err := res.Validate(); err != nil {
		return Reference{}, err
	}
	return res, nil
}

// Validate validates the entire reference.
func (r Reference) Validate() error {
	err := r.ValidateRegistry()
	if err != nil {
		return err
	}
	err = r.ValidateRepository()
	if err != nil {
		return err
	}
	return r.ValidateReference()
}

// ValidateRegistry validates the registry.
func (r Reference) ValidateRegistry() error {
	uri, err := url.ParseRequestURI("dummy://" + r.Registry)
	if err != nil || uri.Host != r.Registry {
		return fmt.Errorf("%w: invalid registry", errdef.ErrInvalidReference)
	}
	return nil
}

// ValidateRepository validates the repository.
func (r Reference) ValidateRepository() error {
	if !repositoryRegexp.MatchString(r.Repository) {
		return fmt.Errorf("%w: invalid repository", errdef.ErrInvalidReference)
	}
	return nil
}

// ValidateReference validates the reference.
func (r Reference) ValidateReference() error {
	if r.Reference == "" {
		return nil
	}
	if _, err := r.Digest(); err == nil {
		return nil
	}
	if !tagRegexp.MatchString(r.Reference) {
		return fmt.Errorf("%w: invalid tag", errdef.ErrInvalidReference)
	}
	return nil
}

// Host returns the host name of the registry.
func (r Reference) Host() string {
	if r.Registry == "docker.io" {
		return "registry-1.docker.io"
	}
	return r.Registry
}

// ReferenceOrDefault returns the reference or the default reference if empty.
func (r Reference) ReferenceOrDefault() string {
	if r.Reference == "" {
		return "latest"
	}
	return r.Reference
}

// Digest returns the reference as a digest.
func (r Reference) Digest() (digest.Digest, error) {
	return digest.Parse(r.Reference)
}

// String implements `fmt.Stringer` and returns the reference string.
// The resulted string is meaningful only if the reference is valid.
func (r Reference) String() string {
	if r.Repository == "" {
		return r.Registry
	}
	ref := r.Registry + "/" + r.Repository
	if r.Reference == "" {
		return ref
	}
	if d, err := r.Digest(); err == nil {
		return ref + "@" + d.String()
	}
	return ref + ":" + r.Reference
}