package git
import (
"bytes"
"errors"
"fmt"
"strconv"
"strings"
"time"
"unicode/utf8"
"github.com/go-git/go-git/v5/plumbing"
"github.com/go-git/go-git/v5/plumbing/object"
"github.com/go-git/go-git/v5/utils/diff"
)
// BlameResult represents the result of a Blame operation.
type BlameResult struct {
// Path is the path of the File that we're blaming.
Path string
// Rev (Revision) is the hash of the specified Commit used to generate this result.
Rev plumbing.Hash
// Lines contains every line with its authorship.
Lines []*Line
}
// Blame returns a BlameResult with the information about the last author of
// each line from file `path` at commit `c`.
func Blame(c *object.Commit, path string) (*BlameResult, error) {
// The file to blame is identified by the input arguments:
// commit and path. commit is a Commit object obtained from a Repository. Path
// represents a path to a specific file contained into the repository.
//
// Blaming a file is a two step process:
//
// 1. Create a linear history of the commits affecting a file. We use
// revlist.New for that.
//
// 2. Then build a graph with a node for every line in every file in
// the history of the file.
//
// Each node is assigned a commit: Start by the nodes in the first
// commit. Assign that commit as the creator of all its lines.
//
// Then jump to the nodes in the next commit, and calculate the diff
// between the two files. Newly created lines get
// assigned the new commit as its origin. Modified lines also get
// this new commit. Untouched lines retain the old commit.
//
// All this work is done in the assignOrigin function which holds all
// the internal relevant data in a "blame" struct, that is not
// exported.
//
// TODO: ways to improve the efficiency of this function:
// 1. Improve revlist
// 2. Improve how to traverse the history (example a backward traversal will
// be much more efficient)
//
// TODO: ways to improve the function in general:
// 1. Add memoization between revlist and assign.
// 2. It is using much more memory than needed, see the TODOs below.
b := new(blame)
b.fRev = c
b.path = path
// get all the file revisions
if err := b.fillRevs(); err != nil {
return nil, err
}
// calculate the line tracking graph and fill in
// file contents in data.
if err := b.fillGraphAndData(); err != nil {
return nil, err
}
file, err := b.fRev.File(b.path)
if err != nil {
return nil, err
}
finalLines, err := file.Lines()
if err != nil {
return nil, err
}
// Each node (line) holds the commit where it was introduced or
// last modified. To achieve that we use the FORWARD algorithm
// described in Zimmermann, et al. "Mining Version Archives for
// Co-changed Lines", in proceedings of the Mining Software
// Repositories workshop, Shanghai, May 22-23, 2006.
lines, err := newLines(finalLines, b.sliceGraph(len(b.graph)-1))
if err != nil {
return nil, err
}
return &BlameResult{
Path: path,
Rev: c.Hash,
Lines: lines,
}, nil
}
// Line values represent the contents and author of a line in BlamedResult values.
type Line struct {
// Author is the email address of the last author that modified the line.
Author string
// Text is the original text of the line.
Text string
// Date is when the original text of the line was introduced
Date time.Time
// Hash is the commit hash that introduced the original line
Hash plumbing.Hash
}
func newLine(author, text string, date time.Time, hash plumbing.Hash) *Line {
return &Line{
Author: author,
Text: text,
Hash: hash,
Date: date,
}
}
func newLines(contents []string, commits []*object.Commit) ([]*Line, error) {
lcontents := len(contents)
lcommits := len(commits)
if lcontents != lcommits {
if lcontents == lcommits-1 && contents[lcontents-1] != "\n" {
contents = append(contents, "\n")
} else {
return nil, errors.New("contents and commits have different length")
}
}
result := make([]*Line, 0, lcontents)
for i := range contents {
result = append(result, newLine(
commits[i].Author.Email, contents[i],
commits[i].Author.When, commits[i].Hash,
))
}
return result, nil
}
// this struct is internally used by the blame function to hold its
// inputs, outputs and state.
type blame struct {
// the path of the file to blame
path string
// the commit of the final revision of the file to blame
fRev *object.Commit
// the chain of revisions affecting the the file to blame
revs []*object.Commit
// the contents of the file across all its revisions
data []string
// the graph of the lines in the file across all the revisions
graph [][]*object.Commit
}
// calculate the history of a file "path", starting from commit "from", sorted by commit date.
func (b *blame) fillRevs() error {
var err error
b.revs, err = references(b.fRev, b.path)
return err
}
// build graph of a file from its revision history
func (b *blame) fillGraphAndData() error {
//TODO: not all commits are needed, only the current rev and the prev
b.graph = make([][]*object.Commit, len(b.revs))
b.data = make([]string, len(b.revs)) // file contents in all the revisions
// for every revision of the file, starting with the first
// one...
for i, rev := range b.revs {
// get the contents of the file
file, err := rev.File(b.path)
if err != nil {
return nil
}
b.data[i], err = file.Contents()
if err != nil {
return err
}
nLines := countLines(b.data[i])
// create a node for each line
b.graph[i] = make([]*object.Commit, nLines)
// assign a commit to each node
// if this is the first revision, then the node is assigned to
// this first commit.
if i == 0 {
for j := 0; j < nLines; j++ {
b.graph[i][j] = b.revs[i]
}
} else {
// if this is not the first commit, then assign to the old
// commit or to the new one, depending on what the diff
// says.
b.assignOrigin(i, i-1)
}
}
return nil
}
// sliceGraph returns a slice of commits (one per line) for a particular
// revision of a file (0=first revision).
func (b *blame) sliceGraph(i int) []*object.Commit {
fVs := b.graph[i]
result := make([]*object.Commit, 0, len(fVs))
for _, v := range fVs {
c := *v
result = append(result, &c)
}
return result
}
// Assigns origin to vertexes in current (c) rev from data in its previous (p)
// revision
func (b *blame) assignOrigin(c, p int) {
// assign origin based on diff info
hunks := diff.Do(b.data[p], b.data[c])
sl := -1 // source line
dl := -1 // destination line
for h := range hunks {
hLines := countLines(hunks[h].Text)
for hl := 0; hl < hLines; hl++ {
switch {
case hunks[h].Type == 0:
sl++
dl++
b.graph[c][dl] = b.graph[p][sl]
case hunks[h].Type == 1:
dl++
b.graph[c][dl] = b.revs[c]
case hunks[h].Type == -1:
sl++
default:
panic("unreachable")
}
}
}
}
// GoString prints the results of a Blame using git-blame's style.
func (b *blame) GoString() string {
var buf bytes.Buffer
file, err := b.fRev.File(b.path)
if err != nil {
panic("PrettyPrint: internal error in repo.Data")
}
contents, err := file.Contents()
if err != nil {
panic("PrettyPrint: internal error in repo.Data")
}
lines := strings.Split(contents, "\n")
// max line number length
mlnl := len(strconv.Itoa(len(lines)))
// max author length
mal := b.maxAuthorLength()
format := fmt.Sprintf("%%s (%%-%ds %%%dd) %%s\n",
mal, mlnl)
fVs := b.graph[len(b.graph)-1]
for ln, v := range fVs {
fmt.Fprintf(&buf, format, v.Hash.String()[:8],
prettyPrintAuthor(fVs[ln]), ln+1, lines[ln])
}
return buf.String()
}
// utility function to pretty print the author.
func prettyPrintAuthor(c *object.Commit) string {
return fmt.Sprintf("%s %s", c.Author.Name, c.Author.When.Format("2006-01-02"))
}
// utility function to calculate the number of runes needed
// to print the longest author name in the blame of a file.
func (b *blame) maxAuthorLength() int {
memo := make(map[plumbing.Hash]struct{}, len(b.graph)-1)
fVs := b.graph[len(b.graph)-1]
m := 0
for ln := range fVs {
if _, ok := memo[fVs[ln].Hash]; ok {
continue
}
memo[fVs[ln].Hash] = struct{}{}
m = max(m, utf8.RuneCountInString(prettyPrintAuthor(fVs[ln])))
}
return m
}
func max(a, b int) int {
if a > b {
return a
}
return b
}
