// Copyright 2019, 2020 OCI Contributors
// Copyright 2017 Docker, Inc.
//
// 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
//
//     https://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 digest

import (
	"errors"
	"fmt"
	"hash"
	"io"
	"regexp"
	"strings"
)

// Digest allows simple protection of hex formatted digest strings, prefixed
// by their algorithm. Strings of type Digest have some guarantee of being in
// the correct format and it provides quick access to the components of a
// digest string.
//
// The following is an example of the contents of Digest types:
//
//	sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc
//
// This allows to abstract the digest behind this type and work only in those
// terms.
type Digest string

// NewDigest returns a Digest from alg and a hash.Hash object.
func NewDigest(alg Algorithm, h hash.Hash) Digest {
	return NewDigestFromBytes(alg, h.Sum(nil))
}

// NewDigestFromBytes returns a new digest from the byte contents of p.
// Typically, this can come from hash.Hash.Sum(...) or xxx.SumXXX(...)
// functions. This is also useful for rebuilding digests from binary
// serializations.
func NewDigestFromBytes(alg Algorithm, p []byte) Digest {
	return Digest(string(alg) + ":" + alg.Encode(p))
}

// NewDigestFromHex returns a Digest from alg and the hex encoded digest.
//
// Deprecated: use [NewDigestFromEncoded] instead.
func NewDigestFromHex(alg, hex string) Digest {
	return Digest(alg + ":" + hex)
}

// NewDigestFromEncoded returns a Digest from alg and the encoded digest.
func NewDigestFromEncoded(alg Algorithm, encoded string) Digest {
	return Digest(string(alg) + ":" + encoded)
}

// DigestRegexp matches valid digest types.
var DigestRegexp = regexp.MustCompile(`[a-z0-9]+(?:[.+_-][a-z0-9]+)*:[a-zA-Z0-9=_-]+`)

// DigestRegexpAnchored matches valid digest types, anchored to the start and end of the match.
var DigestRegexpAnchored = regexp.MustCompile(`^` + DigestRegexp.String() + `$`)

var (
	// ErrDigestInvalidFormat returned when digest format invalid.
	ErrDigestInvalidFormat = errors.New("invalid checksum digest format")

	// ErrDigestInvalidLength returned when digest has invalid length.
	ErrDigestInvalidLength = errors.New("invalid checksum digest length")

	// ErrDigestUnsupported returned when the digest algorithm is unsupported.
	ErrDigestUnsupported = errors.New("unsupported digest algorithm")
)

// Parse parses s and returns the validated digest object. An error will
// be returned if the format is invalid.
func Parse(s string) (Digest, error) {
	d := Digest(s)
	return d, d.Validate()
}

// FromReader consumes the content of rd until io.EOF, returning canonical digest.
func FromReader(rd io.Reader) (Digest, error) {
	return Canonical.FromReader(rd)
}

// FromBytes digests the input and returns a Digest.
func FromBytes(p []byte) Digest {
	return Canonical.FromBytes(p)
}

// FromString digests the input and returns a Digest.
func FromString(s string) Digest {
	return Canonical.FromString(s)
}

// Validate checks that the contents of d is a valid digest, returning an
// error if not.
func (d Digest) Validate() error {
	alg, encoded, ok := strings.Cut(string(d), ":")
	if !ok || encoded == "" {
		return ErrDigestInvalidFormat
	}
	algorithm := Algorithm(alg)
	if !algorithm.Available() {
		if !DigestRegexpAnchored.MatchString(string(d)) {
			return ErrDigestInvalidFormat
		}
		return ErrDigestUnsupported
	}
	return algorithm.Validate(encoded)
}

// Algorithm returns the algorithm portion of the digest. It panics if
// the underlying digest is not in a valid format.
func (d Digest) Algorithm() Algorithm {
	alg, _, ok := strings.Cut(string(d), ":")
	if !ok {
		panic(fmt.Sprintf("no ':' separator in digest %q", d))
	}
	return Algorithm(alg)
}

// Verifier returns a writer object that can be used to verify a stream of
// content against the digest. If the digest is invalid, the method will panic.
func (d Digest) Verifier() Verifier {
	return hashVerifier{
		hash:   d.Algorithm().Hash(),
		digest: d,
	}
}

// Encoded returns the encoded portion of the digest. It panics if the
// underlying digest is not in a valid format.
func (d Digest) Encoded() string {
	_, encoded, ok := strings.Cut(string(d), ":")
	if !ok {
		panic(fmt.Sprintf("no ':' separator in digest %q", d))
	}
	return encoded
}

// Hex returns the encoded portion of the digest. This will panic if the
// underlying digest is not in a valid format.
//
// Deprecated: [Digest.Encoded] instead.
func (d Digest) Hex() string {
	return d.Encoded()
}

func (d Digest) String() string {
	return string(d)
}