package dehub

import (
	"errors"
)

// PayloadCredential describes the structure of a credential payload.
type PayloadCredential struct {
	// CommitHashes represents the commits which this credential is accrediting.
	// It is only present for informational purposes, as commits don't not have
	// any bearing on the CredentialedHash itself.
	CommitHashes []string `yaml:"commits,omitempty"`

	// ChangeDescription represents the description which has been credentialed.
	// This field is only relevant if the Credential in the payload is for a
	// change set.
	ChangeDescription string `yaml:"change_description"`
}

var _ Payload = PayloadCredential{}

// NewPayloadCredential constructs and returns a PayloadUnion populated with a
// PayloadCredential for the given fingerprint. The Credentials of the returned
// PayloadUnion will _not_ be filled in.
func (proj *Project) NewPayloadCredential(fingerprint []byte) (PayloadUnion, error) {
	return PayloadUnion{
		Credential: &PayloadCredential{},
		Common:     PayloadCommon{Fingerprint: fingerprint},
	}, nil
}

// NewPayloadCredentialFromChanges constructs and returns a PayloadUnion
// populated with a PayloadCredential. The fingerprint of the payload will be a
// change fingerprint generated from the given description and all changes in
// the given range of Commits.
//
// If an empty description is given then the description of the last change
// payload in the range is used when generating the fingerprint.
func (proj *Project) NewPayloadCredentialFromChanges(descr string, commits []Commit) (PayloadUnion, error) {
	info, err := proj.changeRangeInfo(commits)
	if err != nil {
		return PayloadUnion{}, err
	}

	if descr == "" {
		descr = info.changeDescription
	}
	fingerprint, err := info.changeFingerprint(descr)
	if err != nil {
		return PayloadUnion{}, err
	}

	payCred, err := proj.NewPayloadCredential(fingerprint)
	if err != nil {
		return PayloadUnion{}, err
	}

	payCred.Credential.ChangeDescription = descr
	for _, commit := range info.changeCommits {
		payCred.Credential.CommitHashes = append(
			payCred.Credential.CommitHashes,
			commit.Hash.String(),
		)
	}

	return payCred, nil
}

// MessageHead implements the method for the Payload interface.
func (payCred PayloadCredential) MessageHead(common PayloadCommon) string {
	return "Credential of " + common.Fingerprint.String()
}

// Fingerprint implements the method for the Payload interface.
func (payCred PayloadCredential) Fingerprint(changes []ChangedFile) ([]byte, error) {
	if len(changes) > 0 {
		return nil, errors.New("PayloadCredential cannot have any changed files")
	}
	// a PayloadCredential can't compute its own fingerprint, it's stored in the
	// common.
	return nil, nil
}