package merkletrie import ( "fmt" "io" "gopkg.in/src-d/go-git.v4/utils/merkletrie/internal/frame" "gopkg.in/src-d/go-git.v4/utils/merkletrie/noder" ) // Iter is an iterator for merkletries (only the trie part of the // merkletrie is relevant here, it does not use the Hasher interface). // // The iteration is performed in depth-first pre-order. Entries at each // depth are traversed in (case-sensitive) alphabetical order. // // This is the kind of traversal you will expect when listing ordinary // files and directories recursively, for example: // // Trie Traversal order // ---- --------------- // . // / | \ c // / | \ d/ // d c z ===> d/a // / \ d/b // b a z // // // This iterator is somewhat especial as you can chose to skip whole // "directories" when iterating: // // - The Step method will iterate normally. // // - the Next method will not descend deeper into the tree. // // For example, if the iterator is at `d/`, the Step method will return // `d/a` while the Next would have returned `z` instead (skipping `d/` // and its descendants). The name of the these two methods are based on // the well known "next" and "step" operations, quite common in // debuggers, like gdb. // // The paths returned by the iterator will be relative, if the iterator // was created from a single node, or absolute, if the iterator was // created from the path to the node (the path will be prefixed to all // returned paths). type Iter struct { // Tells if the iteration has started. hasStarted bool // The top of this stack has the current node and its siblings. The // rest of the stack keeps the ancestors of the current node and // their corresponding siblings. The current element is always the // top element of the top frame. // // When "step"ping into a node, its children are pushed as a new // frame. // // When "next"ing pass a node, the current element is dropped by // popping the top frame. frameStack []*frame.Frame // The base path used to turn the relative paths used internally by // the iterator into absolute paths used by external applications. // For relative iterator this will be nil. base noder.Path } // NewIter returns a new relative iterator using the provider noder as // its unnamed root. When iterating, all returned paths will be // relative to node. func NewIter(n noder.Noder) (*Iter, error) { return newIter(n, nil) } // NewIterFromPath returns a new absolute iterator from the noder at the // end of the path p. When iterating, all returned paths will be // absolute, using the root of the path p as their root. func NewIterFromPath(p noder.Path) (*Iter, error) { return newIter(p, p) // Path implements Noder } func newIter(root noder.Noder, base noder.Path) (*Iter, error) { ret := &Iter{ base: base, } if root == nil { return ret, nil } frame, err := frame.New(root) if err != nil { return nil, err } ret.push(frame) return ret, nil } func (iter *Iter) top() (*frame.Frame, bool) { if len(iter.frameStack) == 0 { return nil, false } top := len(iter.frameStack) - 1 return iter.frameStack[top], true } func (iter *Iter) push(f *frame.Frame) { iter.frameStack = append(iter.frameStack, f) } const ( doDescend = true dontDescend = false ) // Next returns the path of the next node without descending deeper into // the trie and nil. If there are no more entries in the trie it // returns nil and io.EOF. In case of error, it will return nil and the // error. func (iter *Iter) Next() (noder.Path, error) { return iter.advance(dontDescend) } // Step returns the path to the next node in the trie, descending deeper // into it if needed, and nil. If there are no more nodes in the trie, // it returns nil and io.EOF. In case of error, it will return nil and // the error. func (iter *Iter) Step() (noder.Path, error) { return iter.advance(doDescend) } // Advances the iterator in the desired direction: descend or // dontDescend. // // Returns the new current element and a nil error on success. If there // are no more elements in the trie below the base, it returns nil, and // io.EOF. Returns nil and an error in case of errors. func (iter *Iter) advance(wantDescend bool) (noder.Path, error) { current, err := iter.current() if err != nil { return nil, err } // The first time we just return the current node. if !iter.hasStarted { iter.hasStarted = true return current, nil } // Advances means getting a next current node, either its first child or // its next sibling, depending if we must descend or not. numChildren, err := current.NumChildren() if err != nil { return nil, err } mustDescend := numChildren != 0 && wantDescend if mustDescend { // descend: add a new frame with the current's children. frame, err := frame.New(current) if err != nil { return nil, err } iter.push(frame) } else { // don't descend: just drop the current node iter.drop() } return iter.current() } // Returns the path to the current node, adding the base if there was // one, and a nil error. If there were no noders left, it returns nil // and io.EOF. If an error occurred, it returns nil and the error. func (iter *Iter) current() (noder.Path, error) { if topFrame, ok := iter.top(); !ok { return nil, io.EOF } else if _, ok := topFrame.First(); !ok { return nil, io.EOF } ret := make(noder.Path, 0, len(iter.base)+len(iter.frameStack)) // concat the base... ret = append(ret, iter.base...) // ... and the current node and all its ancestors for i, f := range iter.frameStack { t, ok := f.First() if !ok { panic(fmt.Sprintf("frame %d is empty", i)) } ret = append(ret, t) } return ret, nil } // removes the current node if any, and all the frames that become empty as a // consecuence of this action. func (iter *Iter) drop() { frame, ok := iter.top() if !ok { return } frame.Drop() // if the frame is empty, remove it and its parent, recursively if frame.Len() == 0 { top := len(iter.frameStack) - 1 iter.frameStack[top] = nil iter.frameStack = iter.frameStack[:top] iter.drop() } }