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+package merkletrie
+
+// The focus of this difftree implementation is to save time by
+// skipping whole directories if their hash is the same in both
+// trees.
+//
+// The diff algorithm implemented here is based on the doubleiter
+// type defined in this same package; we will iterate over both
+// trees at the same time, while comparing the current noders in
+// each iterator. Depending on how they differ we will output the
+// corresponding chages and move the iterators further over both
+// trees.
+//
+// The table bellow show all the possible comparison results, along
+// with what changes should we produce and how to advance the
+// iterators.
+//
+// The table is implemented by the switches in this function,
+// diffTwoNodes, diffTwoNodesSameName and diffTwoDirs.
+//
+// Many Bothans died to bring us this information, make sure you
+// understand the table before modifying this code.
+
+// # Cases
+//
+// When comparing noders in both trees you will found yourself in
+// one of 169 possible cases, but if we ignore moves, we can
+// simplify a lot the search space into the following table:
+//
+// - "-": nothing, no file or directory
+// - a<>: an empty file named "a".
+// - a<1>: a file named "a", with "1" as its contents.
+// - a<2>: a file named "a", with "2" as its contents.
+// - a(): an empty dir named "a".
+// - a(...): a dir named "a", with some files and/or dirs inside (possibly
+// empty).
+// - a(;;;): a dir named "a", with some other files and/or dirs inside
+// (possibly empty), which different from the ones in "a(...)".
+//
+// \ to - a<> a<1> a<2> a() a(...) a(;;;)
+// from \
+// - 00 01 02 03 04 05 06
+// a<> 10 11 12 13 14 15 16
+// a<1> 20 21 22 23 24 25 26
+// a<2> 30 31 32 33 34 35 36
+// a() 40 41 42 43 44 45 46
+// a(...) 50 51 52 53 54 55 56
+// a(;;;) 60 61 62 63 64 65 66
+//
+// Every (from, to) combination in the table is a special case, but
+// some of them can be merged into some more general cases, for
+// instance 11 and 22 can be merged into the general case: both
+// noders are equal.
+//
+// Here is a full list of all the cases that are similar and how to
+// merge them together into more general cases. Each general case
+// is labeled wiht an uppercase letter for further reference, and it
+// is followed by the pseudocode of the checks you have to perfrom
+// on both noders to see if you are in such a case, the actions to
+// perform (i.e. what changes to output) and how to advance the
+// iterators of each tree to continue the comparison process.
+//
+// ## A. Impossible: 00
+//
+// ## B. Same thing on both sides: 11, 22, 33, 44, 55, 66
+// - check: `SameName() && SameHash()`
+// - action: do nothing.
+// - advance: `FromNext(); ToNext()`
+//
+// ### C. To was created: 01, 02, 03, 04, 05, 06
+// - check: `DifferentName() && ToBeforeFrom()`
+// - action: inserRecursively(to)
+// - advance: `ToNext()`
+//
+// ### D. From was deleted: 10, 20, 30, 40, 50, 60
+// - check: `DifferentName() && FromBeforeTo()`
+// - action: `DeleteRecursively(from)`
+// - advance: `FromNext()`
+//
+// ### E. Empty file to file with contents: 12, 13
+// - check: `SameName() && DifferentHash() && FromIsFile() &&
+// ToIsFile() && FromIsEmpty()`
+// - action: `modifyFile(from, to)`
+// - advance: `FromNext()` or `FromStep()`
+//
+// ### E'. file with contents to empty file: 21, 31
+// - check: `SameName() && DifferentHash() && FromIsFile() &&
+// ToIsFile() && ToIsEmpty()`
+// - action: `modifyFile(from, to)`
+// - advance: `FromNext()` or `FromStep()`
+//
+// ### F. empty file to empty dir with the same name: 14
+// - check: `SameName() && FromIsFile() && FromIsEmpty() &&
+// ToIsDir() && ToIsEmpty()`
+// - action: `DeleteFile(from); InsertEmptyDir(to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### F'. empty dir to empty file of the same name: 41
+// - check: `SameName() && FromIsDir() && FromIsEmpty &&
+// ToIsFile() && ToIsEmpty()`
+// - action: `DeleteEmptyDir(from); InsertFile(to)`
+// - advance: `FromNext(); ToNext()` or step for any of them.
+//
+// ### G. empty file to non-empty dir of the same name: 15, 16
+// - check: `SameName() && FromIsFile() && ToIsDir() &&
+// FromIsEmpty() && ToIsNotEmpty()`
+// - action: `DeleteFile(from); InsertDirRecursively(to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### G'. non-empty dir to empty file of the same name: 51, 61
+// - check: `SameName() && FromIsDir() && FromIsNotEmpty() &&
+// ToIsFile() && FromIsEmpty()`
+// - action: `DeleteDirRecursively(from); InsertFile(to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### H. modify file contents: 23, 32
+// - check: `SameName() && FromIsFile() && ToIsFile() &&
+// FromIsNotEmpty() && ToIsNotEmpty()`
+// - action: `ModifyFile(from, to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### I. file with contents to empty dir: 24, 34
+// - check: `SameName() && DifferentHash() && FromIsFile() &&
+// FromIsNotEmpty() && ToIsDir() && ToIsEmpty()`
+// - action: `DeleteFile(from); InsertEmptyDir(to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### I'. empty dir to file with contents: 42, 43
+// - check: `SameName() && DifferentHash() && FromIsDir() &&
+// FromIsEmpty() && ToIsFile() && ToIsEmpty()`
+// - action: `DeleteDir(from); InsertFile(to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### J. file with contents to dir with contetns: 25, 26, 35, 36
+// - check: `SameName() && DifferentHash() && FromIsFile() &&
+// FromIsNotEmpty() && ToIsDir() && ToIsNotEmpty()`
+// - action: `DeleteFile(from); InsertDirRecursively(to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### J'. dir with contetns to file with contents: 52, 62, 53, 63
+// - check: `SameName() && DifferentHash() && FromIsDir() &&
+// FromIsNotEmpty() && ToIsFile() && ToIsNotEmpty()`
+// - action: `DeleteDirRecursively(from); InsertFile(to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### K. empty dir to dir with contents: 45, 46
+// - check: `SameName() && DifferentHash() && FromIsDir() &&
+// FromIsEmpty() && ToIsDir() && ToIsNotEmpty()`
+// - action: `InsertChildrenRecursively(to)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### K'. dir with contents to empty dir: 54, 64
+// - check: `SameName() && DifferentHash() && FromIsDir() &&
+// FromIsEmpty() && ToIsDir() && ToIsNotEmpty()`
+// - action: `DeleteChildrenRecursively(from)`
+// - advance: `FromNext(); ToNext()`
+//
+// ### L. dir with contents to dir with different contents: 56, 65
+// - check: `SameName() && DifferentHash() && FromIsDir() &&
+// FromIsNotEmpty() && ToIsDir() && ToIsNotEmpty()`
+// - action: nothing
+// - advance: `FromStep(); ToStep()`
+//
+//
+
+// All these cases can be further simplified by a truth table
+// reduction process, in which we gather similar checks together to
+// make the final code easier to read and understand.
+//
+// The first 6 columns are the outputs of the checks to perform on
+// both noders. I have labeled them 1 to 6, this is what they mean:
+//
+// 1: SameName()
+// 2: SameHash()
+// 3: FromIsDir()
+// 4: ToIsDir()
+// 5: FromIsEmpty()
+// 6: ToIsEmpty()
+//
+// The from and to columns are a fsnoder example of the elements
+// that you will find on each tree under the specified comparison
+// results (columns 1 to 6).
+//
+// The type column identifies the case we are into, from the list above.
+//
+// The type' column identifies the new set of reduced cases, using
+// lowercase letters, and they are explained after the table.
+//
+// The last column is the set of actions and advances for each case.
+//
+// "---" means impossible except in case of hash collision.
+//
+// advance meaning:
+// - NN: from.Next(); to.Next()
+// - SS: from.Step(); to.Step()
+//
+// 1 2 3 4 5 6 | from | to |type|type'|action ; advance
+// ------------+--------+--------+----+------------------------------------
+// 0 0 0 0 0 0 | | | | | if !SameName() {
+// . | | | | | if FromBeforeTo() {
+// . | | | D | d | delete(from); from.Next()
+// . | | | | | } else {
+// . | | | C | c | insert(to); to.Next()
+// . | | | | | }
+// 0 1 1 1 1 1 | | | | | }
+// 1 0 0 0 0 0 | a<1> | a<2> | H | e | modify(from, to); NN
+// 1 0 0 0 0 1 | a<1> | a<> | E' | e | modify(from, to); NN
+// 1 0 0 0 1 0 | a<> | a<1> | E | e | modify(from, to); NN
+// 1 0 0 0 1 1 | ---- | ---- | | e |
+// 1 0 0 1 0 0 | a<1> | a(...) | J | f | delete(from); insert(to); NN
+// 1 0 0 1 0 1 | a<1> | a() | I | f | delete(from); insert(to); NN
+// 1 0 0 1 1 0 | a<> | a(...) | G | f | delete(from); insert(to); NN
+// 1 0 0 1 1 1 | a<> | a() | F | f | delete(from); insert(to); NN
+// 1 0 1 0 0 0 | a(...) | a<1> | J' | f | delete(from); insert(to); NN
+// 1 0 1 0 0 1 | a(...) | a<> | G' | f | delete(from); insert(to); NN
+// 1 0 1 0 1 0 | a() | a<1> | I' | f | delete(from); insert(to); NN
+// 1 0 1 0 1 1 | a() | a<> | F' | f | delete(from); insert(to); NN
+// 1 0 1 1 0 0 | a(...) | a(;;;) | L | g | nothing; SS
+// 1 0 1 1 0 1 | a(...) | a() | K' | h | deleteChidren(from); NN
+// 1 0 1 1 1 0 | a() | a(...) | K | i | insertChildren(to); NN
+// 1 0 1 1 1 1 | ---- | ---- | | |
+// 1 1 0 0 0 0 | a<1> | a<1> | B | b | nothing; NN
+// 1 1 0 0 0 1 | ---- | ---- | | b |
+// 1 1 0 0 1 0 | ---- | ---- | | b |
+// 1 1 0 0 1 1 | a<> | a<> | B | b | nothing; NN
+// 1 1 0 1 0 0 | ---- | ---- | | b |
+// 1 1 0 1 0 1 | ---- | ---- | | b |
+// 1 1 0 1 1 0 | ---- | ---- | | b |
+// 1 1 0 1 1 1 | ---- | ---- | | b |
+// 1 1 1 0 0 0 | ---- | ---- | | b |
+// 1 1 1 0 0 1 | ---- | ---- | | b |
+// 1 1 1 0 1 0 | ---- | ---- | | b |
+// 1 1 1 0 1 1 | ---- | ---- | | b |
+// 1 1 1 1 0 0 | a(...) | a(...) | B | b | nothing; NN
+// 1 1 1 1 0 1 | ---- | ---- | | b |
+// 1 1 1 1 1 0 | ---- | ---- | | b |
+// 1 1 1 1 1 1 | a() | a() | B | b | nothing; NN
+//
+// c and d:
+// if !SameName()
+// d if FromBeforeTo()
+// c else
+// b: SameName) && sameHash()
+// e: SameName() && !sameHash() && BothAreFiles()
+// f: SameName() && !sameHash() && FileAndDir()
+// g: SameName() && !sameHash() && BothAreDirs() && NoneIsEmpty
+// i: SameName() && !sameHash() && BothAreDirs() && FromIsEmpty
+// h: else of i
+
+import (
+ "fmt"
+ "strings"
+
+ "srcd.works/go-git.v4/utils/merkletrie/noder"
+)
+
+// DiffTree calculates the list of changes between two merkletries. It
+// uses the provided hashEqual callback to compare noders.
+func DiffTree(fromTree, toTree noder.Noder,
+ hashEqual noder.Equal) (Changes, error) {
+ ret := NewChanges()
+
+ ii, err := newDoubleIter(fromTree, toTree, hashEqual)
+ if err != nil {
+ return nil, err
+ }
+
+ for {
+ from := ii.from.current
+ to := ii.to.current
+
+ switch r := ii.remaining(); r {
+ case noMoreNoders:
+ return ret, nil
+ case onlyFromRemains:
+ if err = ret.AddRecursiveDelete(from); err != nil {
+ return nil, err
+ }
+ if err = ii.nextFrom(); err != nil {
+ return nil, err
+ }
+ case onlyToRemains:
+ if err = ret.AddRecursiveInsert(to); err != nil {
+ return nil, err
+ }
+ if err = ii.nextTo(); err != nil {
+ return nil, err
+ }
+ case bothHaveNodes:
+ if err = diffNodes(&ret, ii); err != nil {
+ return nil, err
+ }
+ default:
+ panic(fmt.Sprintf("unknown remaining value: %d", r))
+ }
+ }
+}
+
+func diffNodes(changes *Changes, ii *doubleIter) error {
+ from := ii.from.current
+ to := ii.to.current
+ var err error
+
+ // compare their full paths as strings
+ switch strings.Compare(from.String(), to.String()) {
+ case -1:
+ if err = changes.AddRecursiveDelete(from); err != nil {
+ return err
+ }
+ if err = ii.nextFrom(); err != nil {
+ return err
+ }
+ case 1:
+ if err = changes.AddRecursiveInsert(to); err != nil {
+ return err
+ }
+ if err = ii.nextTo(); err != nil {
+ return err
+ }
+ default:
+ if err := diffNodesSameName(changes, ii); err != nil {
+ return err
+ }
+ }
+
+ return nil
+}
+
+func diffNodesSameName(changes *Changes, ii *doubleIter) error {
+ from := ii.from.current
+ to := ii.to.current
+
+ status, err := ii.compare()
+ if err != nil {
+ return err
+ }
+
+ switch {
+ case status.sameHash:
+ // do nothing
+ if err = ii.nextBoth(); err != nil {
+ return err
+ }
+ case status.bothAreFiles:
+ changes.Add(NewModify(from, to))
+ if err = ii.nextBoth(); err != nil {
+ return err
+ }
+ case status.fileAndDir:
+ if err = changes.AddRecursiveDelete(from); err != nil {
+ return err
+ }
+ if err = changes.AddRecursiveInsert(to); err != nil {
+ return err
+ }
+ if err = ii.nextBoth(); err != nil {
+ return err
+ }
+ case status.bothAreDirs:
+ if err = diffDirs(changes, ii); err != nil {
+ return err
+ }
+ default:
+ return fmt.Errorf("bad status from double iterator")
+ }
+
+ return nil
+}
+
+func diffDirs(changes *Changes, ii *doubleIter) error {
+ from := ii.from.current
+ to := ii.to.current
+
+ status, err := ii.compare()
+ if err != nil {
+ return err
+ }
+
+ switch {
+ case status.fromIsEmptyDir:
+ if err = changes.AddRecursiveInsert(to); err != nil {
+ return err
+ }
+ if err = ii.nextBoth(); err != nil {
+ return err
+ }
+ case status.toIsEmptyDir:
+ if err = changes.AddRecursiveDelete(from); err != nil {
+ return err
+ }
+ if err = ii.nextBoth(); err != nil {
+ return err
+ }
+ case !status.fromIsEmptyDir && !status.toIsEmptyDir:
+ // do nothing
+ if err = ii.stepBoth(); err != nil {
+ return err
+ }
+ default:
+ return fmt.Errorf("both dirs are empty but has different hash")
+ }
+
+ return nil
+}