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package reachability
import (
"errors"
"fmt"
"iter"
"codeberg.org/lindenii/furgit/object"
"codeberg.org/lindenii/furgit/objectid"
"codeberg.org/lindenii/furgit/objecttype"
)
// Walk is one single-use iterator-style traversal.
type Walk struct {
reachability *Reachability
domain Domain
haves map[objectid.ObjectID]struct{}
wants map[objectid.ObjectID]struct{}
seqUsed bool
err error
}
// Seq returns the traversal sequence. It is single-use.
func (walk *Walk) Seq() iter.Seq[objectid.ObjectID] {
if walk.seqUsed {
return func(yield func(objectid.ObjectID) bool) {
_ = yield
if walk.err == nil {
walk.err = errors.New("reachability: walk sequence already consumed")
}
}
}
walk.seqUsed = true
return func(yield func(objectid.ObjectID) bool) {
if walk.err != nil {
return
}
stack := walk.initialStack()
var err error
visited := make(map[objectid.ObjectID]struct{}, len(stack))
for len(stack) > 0 {
item := stack[len(stack)-1]
stack = stack[:len(stack)-1]
if containsOID(walk.haves, item.id) {
continue
}
if _, ok := visited[item.id]; ok {
continue
}
visited[item.id] = struct{}{}
var next []walkItem
next, err = walk.expand(item)
if err != nil {
walk.err = err
return
}
if !yield(item.id) {
return
}
stack = append(stack, next...)
}
}
}
// Err returns the terminal error, if any, once Seq has been consumed.
func (walk *Walk) Err() error {
return walk.err
}
type walkItem struct {
id objectid.ObjectID
want objecttype.Type
}
func (walk *Walk) initialStack() []walkItem {
if len(walk.wants) == 0 {
return nil
}
stack := make([]walkItem, 0, len(walk.wants))
for want := range walk.wants {
stack = append(stack, walkItem{id: want, want: objecttype.TypeInvalid})
}
return stack
}
func (walk *Walk) expand(item walkItem) ([]walkItem, error) {
if walk.domain == DomainCommits {
return walk.expandCommits(item)
}
return walk.expandObjects(item)
}
func (walk *Walk) expandCommits(item walkItem) ([]walkItem, error) {
ty, err := walk.readHeaderType(item.id)
if err != nil {
return nil, err
}
switch ty {
case objecttype.TypeCommit:
content, err := walk.readBytesContent(item.id)
if err != nil {
return nil, err
}
commit, err := object.ParseCommit(content, item.id.Algorithm())
if err != nil {
return nil, err
}
next := make([]walkItem, 0, len(commit.Parents))
for _, parent := range commit.Parents {
next = append(next, walkItem{id: parent, want: objecttype.TypeInvalid})
}
return next, nil
case objecttype.TypeTag:
content, err := walk.readBytesContent(item.id)
if err != nil {
return nil, err
}
tag, err := object.ParseTag(content, item.id.Algorithm())
if err != nil {
return nil, err
}
return []walkItem{{id: tag.Target, want: objecttype.TypeInvalid}}, nil
case objecttype.TypeTree, objecttype.TypeBlob, objecttype.TypeInvalid,
objecttype.TypeFuture, objecttype.TypeOfsDelta, objecttype.TypeRefDelta:
return nil, &ErrObjectType{OID: item.id, Got: ty, Want: objecttype.TypeCommit}
}
return nil, fmt.Errorf("reachability: unreachable object type %d", ty)
}
func (walk *Walk) expandObjects(item walkItem) ([]walkItem, error) {
ty, err := walk.readHeaderType(item.id)
if err != nil {
return nil, err
}
if item.want != objecttype.TypeInvalid && ty != item.want {
return nil, &ErrObjectType{OID: item.id, Got: ty, Want: item.want}
}
switch ty {
case objecttype.TypeBlob:
return nil, nil
case objecttype.TypeCommit:
content, err := walk.readBytesContent(item.id)
if err != nil {
return nil, err
}
commit, err := object.ParseCommit(content, item.id.Algorithm())
if err != nil {
return nil, err
}
next := make([]walkItem, 0, len(commit.Parents)+1)
next = append(next, walkItem{id: commit.Tree, want: objecttype.TypeTree})
for _, parent := range commit.Parents {
next = append(next, walkItem{id: parent, want: objecttype.TypeCommit})
}
return next, nil
case objecttype.TypeTree:
content, err := walk.readBytesContent(item.id)
if err != nil {
return nil, err
}
tree, err := object.ParseTree(content, item.id.Algorithm())
if err != nil {
return nil, err
}
next := make([]walkItem, 0, len(tree.Entries))
for _, entry := range tree.Entries {
switch entry.Mode {
case object.FileModeGitlink:
continue
case object.FileModeDir:
next = append(next, walkItem{id: entry.ID, want: objecttype.TypeTree})
case object.FileModeRegular, object.FileModeExecutable, object.FileModeSymlink:
next = append(next, walkItem{id: entry.ID, want: objecttype.TypeBlob})
}
}
return next, nil
case objecttype.TypeTag:
content, err := walk.readBytesContent(item.id)
if err != nil {
return nil, err
}
tag, err := object.ParseTag(content, item.id.Algorithm())
if err != nil {
return nil, err
}
return []walkItem{{id: tag.Target, want: tag.TargetType}}, nil
case objecttype.TypeInvalid, objecttype.TypeFuture, objecttype.TypeOfsDelta, objecttype.TypeRefDelta:
return nil, &ErrObjectType{OID: item.id, Got: ty, Want: item.want}
}
return nil, fmt.Errorf("reachability: unreachable object type %d", ty)
}
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