package dehub

import (
	"bytes"
	"errors"
	"fmt"
	"sort"
	"strings"

	"dehub.dev/src/dehub.git/fs"
	"dehub.dev/src/dehub.git/sigcred"
	"dehub.dev/src/dehub.git/yamlutil"

	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/plumbing/object"
)

// CommitChange describes the structure of a change commit message.
type CommitChange struct {
	Message    string        `yaml:"message"`
	ChangeHash yamlutil.Blob `yaml:"change_hash"`
}

var _ CommitInterface = CommitChange{}

// NewCommitChange constructs a Commit populated with a CommitChange
// encompassing the currently staged file changes. The Credentials of the
// returned Commit will _not_ be filled in.
func (r *Repo) NewCommitChange(msg string) (Commit, error) {
	headTree := new(object.Tree)
	if head, err := r.GetGitHead(); err != nil && !errors.Is(err, ErrHeadIsZero) {
		return Commit{}, fmt.Errorf("getting HEAD commit: %w", err)
	} else if err == nil {
		headTree = head.GitTree
	}

	_, stagedTree, err := fs.FromStagedChangesTree(r.GitRepo)
	if err != nil {
		return Commit{}, err
	}

	changedFiles, err := ChangedFilesBetweenTrees(headTree, stagedTree)
	if err != nil {
		return Commit{}, fmt.Errorf("calculating diff between HEAD and staged changes: %w", err)
	}

	cc := CommitChange{Message: msg}
	if cc.ChangeHash, err = cc.ExpectedHash(changedFiles); err != nil {
		return Commit{}, err
	}

	return Commit{
		Change: &cc,
	}, nil
}

// MessageHead implements the method for the CommitInterface interface.
func (cc CommitChange) MessageHead(CommitCommon) (string, error) {
	return abbrevCommitMessage(cc.Message), nil
}

// ExpectedHash implements the method for the CommitInterface interface.
func (cc CommitChange) ExpectedHash(changedFiles []ChangedFile) ([]byte, error) {
	return genChangeHash(nil, cc.Message, changedFiles), nil
}

// StoredHash implements the method for the CommitInterface interface.
func (cc CommitChange) StoredHash() []byte {
	return cc.ChangeHash
}

// CombineCommitChanges takes all changes in the given range and combines them
// into a single change Commit. The resulting Commit will have the same message
// as the latest change commit in the range, and will contain all Credentials
// for the resulting change hash that it finds in the range as well.
//
// The combined commit is then committed to the repo with the given revision as
// its parent. If the diff between start/end and onto/end is different then this
// will return an error, as the change hash which has been accredited in
// start/end will be different than the one which needs to be accredited in
// onto/end.
func (r *Repo) CombineCommitChanges(commits []GitCommit, onto plumbing.ReferenceName) (GitCommit, error) {
	info, err := r.changeRangeInfo(commits)
	if err != nil {
		return GitCommit{}, err
	}

	authors := make([]string, 0, len(info.authors))
	for author := range info.authors {
		authors = append(authors, author)
	}
	sort.Strings(authors)

	ontoBranchName, err := r.ReferenceToBranchName(onto)
	if err != nil {
		return GitCommit{}, fmt.Errorf("resolving %q into a branch name: %w", onto, err)
	}

	// now determine the change hash from onto->end, to ensure that it remains
	// the same as from start->end
	ontoCommit, err := r.GetGitRevision(plumbing.Revision(onto))
	if err != nil {
		return GitCommit{}, fmt.Errorf("resolving revision %q: %w", onto, err)
	}

	ontoEndChangedFiles, err := ChangedFilesBetweenTrees(ontoCommit.GitTree, info.endTree)
	if err != nil {
		return GitCommit{}, fmt.Errorf("calculating file changes between %q and %q: %w",
			ontoCommit.GitCommit.Hash, commits[len(commits)-1].GitCommit.Hash, err)
	}

	ontoEndChangeHash := genChangeHash(nil, info.msg, ontoEndChangedFiles)
	if !bytes.Equal(ontoEndChangeHash, info.changeHash) {
		// TODO figure out what files to show as being the "problem files" in
		// the error message
		return GitCommit{}, fmt.Errorf("combining onto %q would cause the change hash to change, aborting combine", onto.Short())
	}

	var creds []sigcred.Credential
	for _, commit := range commits {
		if bytes.Equal(commit.Interface.StoredHash(), info.changeHash) {
			creds = append(creds, commit.Commit.Common.Credentials...)
		}
	}

	// this is mostly to make tests easier
	sort.Slice(creds, func(i, j int) bool {
		return creds[i].AccountID < creds[j].AccountID
	})

	commit := Commit{
		Change: &CommitChange{
			Message:    info.msg,
			ChangeHash: info.changeHash,
		},
		Common: CommitCommon{Credentials: creds},
	}

	gitCommit, err := r.CommitBare(CommitBareParams{
		Commit:     commit,
		Author:     strings.Join(authors, ","),
		ParentHash: ontoCommit.GitCommit.Hash,
		GitTree:    info.endTree,
	})
	if err != nil {
		return GitCommit{}, fmt.Errorf("storing commit: %w", err)
	}

	// set the onto branch to this new commit
	newHeadRef := plumbing.NewHashReference(ontoBranchName, gitCommit.GitCommit.Hash)
	if err := r.GitRepo.Storer.SetReference(newHeadRef); err != nil {
		return GitCommit{}, fmt.Errorf("setting reference %q to new commit hash %q: %w",
			ontoBranchName, gitCommit.GitCommit.Hash, err)
	}
	return gitCommit, nil
}