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"
"gopkg.in/src-d/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 from.Compare(to) {
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
}
