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package difftree
import (
"bytes"
"fmt"
"io"
"sort"
"strings"
"gopkg.in/src-d/go-git.v4"
"gopkg.in/src-d/go-git.v4/core"
)
type Action int
func (a Action) String() string {
switch a {
case Insert:
return "Insert"
case Delete:
return "Delete"
case Modify:
return "Modify"
default:
panic(fmt.Sprintf("unsupported action: %d", a))
}
}
const (
Insert Action = iota
Delete
Modify
)
type Change struct {
Action
File *git.File
}
func (c *Change) String() string {
return fmt.Sprintf("<Action: %s, Path: %s, Size: %d>", c.Action, c.File.Name, c.File.Size)
}
type Changes []*Change
func newEmpty() Changes {
return make([]*Change, 0, 0)
}
func New(a, b *git.Tree) (Changes, error) {
if a == b {
return newEmpty(), nil
}
if a == nil || b == nil {
return newWithEmpty(a, b)
}
return newDiffTree(a, b)
}
func (c Changes) Len() int {
return len(c)
}
func (c Changes) Swap(i, j int) {
c[i], c[j] = c[j], c[i]
}
func (c Changes) Less(i, j int) bool {
return strings.Compare(c[i].File.Name, c[j].File.Name) < 0
}
func (c Changes) String() string {
var buffer bytes.Buffer
buffer.WriteString("[")
comma := ""
for _, v := range c {
buffer.WriteString(comma)
buffer.WriteString(v.String())
comma = ", "
}
buffer.WriteString("]")
return buffer.String()
}
func newWithEmpty(a, b *git.Tree) (Changes, error) {
changes := newEmpty()
var action Action
var tree *git.Tree
if a == nil {
action = Insert
tree = b
} else {
action = Delete
tree = a
}
iter := tree.Files()
defer iter.Close()
for {
file, err := iter.Next()
if err == io.EOF {
break
} else if err != nil {
return nil, fmt.Errorf("cannot get next file: %s", err)
}
insert := &Change{
Action: action,
File: file,
}
changes = append(changes, insert)
}
return changes, nil
}
// FIXME: this is very inefficient, but correct.
// The proper way to do this is to implement a diff-tree algorithm,
// while taking advantage of the tree hashes to avoid traversing
// subtrees when the hash is equal in both inputs.
func newDiffTree(a, b *git.Tree) (Changes, error) {
result := newEmpty()
aChanges, err := newWithEmpty(a, nil)
if err != nil {
return nil, fmt.Errorf("cannot create nil-diff of source tree: %s", err)
}
sort.Sort(aChanges)
bChanges, err := newWithEmpty(nil, b)
if err != nil {
return nil, fmt.Errorf("cannot create nil-diff of destination tree: %s", err)
}
sort.Sort(bChanges)
for len(aChanges) > 0 && len(bChanges) > 0 {
switch comp := strings.Compare(aChanges[0].File.Name, bChanges[0].File.Name); {
case comp == 0: // append as "Modify" or ignore if not changed
modified, err := hasChange(a, b, aChanges[0].File.Name)
if err != nil {
return nil, err
}
if modified {
bChanges[0].Action = Modify
result = append(result, bChanges[0])
} else {
}
aChanges = aChanges[1:]
bChanges = bChanges[1:]
case comp < 0: // delete first a change
result = append(result, aChanges[0])
aChanges = aChanges[1:]
case comp > 0: // insert first b change
result = append(result, bChanges[0])
bChanges = bChanges[1:]
}
}
// append all remaining changes in aChanges, if any, as deletes
// append all remaining changes in bChanges, if any, as inserts
result = append(result, aChanges...)
result = append(result, bChanges...)
return result, nil
}
func hasChange(a, b *git.Tree, path string) (bool, error) {
ha, err := hash(a, path)
if err != nil {
return false, err
}
hb, err := hash(b, path)
if err != nil {
return false, err
}
return ha != hb, nil
}
func hash(tree *git.Tree, path string) (core.Hash, error) {
file, err := tree.File(path)
if err != nil {
var empty core.Hash
return empty, fmt.Errorf("cannot find file %s in tree: %s", path, err)
}
return file.Hash, nil
}
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