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package thread
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import (
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"context"
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"fmt"
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"strconv"
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"strings"
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"github.com/barerepo/server/internal/gitx"
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// Anchor is chapter 43's four fields, of which the blob hash recovers what the commenter saw.
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type Anchor struct {
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Path string
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Line int
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Blob string // the file's blob hash at comment time
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Side string // old | new
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// ParseAnchor reads the "config.go:43" form.
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func ParseAnchor(s string) (Anchor, bool) {
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path, num, ok := strings.Cut(s, ":")
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if !ok {
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return Anchor{}, false
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line, err := strconv.Atoi(num)
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if err != nil || line <= 0 || !gitx.ValidPath(path) {
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return Anchor{}, false
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return Anchor{Path: path, Line: line}, true
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func (a Anchor) String() string { return fmt.Sprintf("%s:%d", a.Path, a.Line) }
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// Placement is where a comment lands once its file moved on, in chapter 43.3's three outcomes.
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type Placement string
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const (
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// Exact means the blob is the one the commenter saw.
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Exact Placement = "exact"
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// Moved means the line survived at a different number.
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Moved Placement = "moved"
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// Outdated keeps the comment and shows the code it meant, never hidden or deleted. 43.4.
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Outdated Placement = "outdated"
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// Lost means the retained revision expired, and 43.5 asks this to degrade, not pretend.
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Lost Placement = "lost"
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// Resolved is an anchor after the file has changed.
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type Resolved struct {
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Placement Placement
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Line int // where to show it now
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Excerpt string // the line as the commenter saw it
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// Resolve maps an anchor forward from its blob hash, because a bare line number retrieves nothing.
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func Resolve(ctx context.Context, dir string, a Anchor, currentRef string) Resolved {
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if a.Blob == "" {
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return Resolved{Placement: Lost, Line: a.Line}
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oldBody, err := gitx.Run(ctx, dir, "cat-file", "blob", a.Blob)
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if err != nil {
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return Resolved{Placement: Lost, Line: a.Line}
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oldLines := strings.Split(strings.TrimSuffix(oldBody, "\n"), "\n")
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excerpt := ""
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if a.Line-1 < len(oldLines) {
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excerpt = oldLines[a.Line-1]
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newBlob, err := currentBlob(ctx, dir, currentRef, a.Path)
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if err != nil {
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return Resolved{Placement: Outdated, Line: a.Line, Excerpt: excerpt}
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if newBlob == a.Blob {
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return Resolved{Placement: Exact, Line: a.Line, Excerpt: excerpt}
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line, ok := mapLine(ctx, dir, a.Blob, newBlob, a.Line)
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switch {
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case !ok:
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return Resolved{Placement: Outdated, Line: a.Line, Excerpt: excerpt}
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case line == a.Line:
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return Resolved{Placement: Exact, Line: line, Excerpt: excerpt}
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default:
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return Resolved{Placement: Moved, Line: line, Excerpt: excerpt}
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func currentBlob(ctx context.Context, dir, ref, path string) (string, error) {
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if !gitx.ValidRev(ref) || !gitx.ValidPath(path) {
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return "", fmt.Errorf("bad ref or path")
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out, err := gitx.Run(ctx, dir, "rev-parse", "--verify", "--quiet", ref+":"+path)
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return strings.TrimSpace(out), err
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// mapLine walks a line between blobs through their diff, and reports false once it was touched.
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func mapLine(ctx context.Context, dir, oldBlob, newBlob string, line int) (int, bool) {
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patch, err := gitx.Run(ctx, dir, "diff", "--unified=0", "--no-color", oldBlob, newBlob)
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if err != nil {
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return 0, false
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}
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// A hunk before the line shifts it, and a hunk containing it makes the line outdated.
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shift := 0
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for _, h := range strings.Split(patch, "\n") {
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if !strings.HasPrefix(h, "@@") {
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continue
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}
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oldStart, oldCount, _, newCount, ok := parseHunkHeader(h)
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if !ok {
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continue
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}
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switch {
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case oldCount == 0:
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// git writes @@ -2,0 +3,2 @@ for lines put after old line 2, so line 2 stays put.
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if oldStart < line {
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shift += newCount
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}
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case oldStart+oldCount <= line:
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shift += (newCount - oldCount)
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case oldStart <= line:
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// The line is inside this hunk's removed range.
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return 0, false
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}
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}
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return line + shift, true
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// parseHunkHeader reads "@@ -a,b +c,d @@".
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func parseHunkHeader(h string) (oldStart, oldCount, newStart, newCount int, ok bool) {
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body := strings.TrimPrefix(h, "@@ ")
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if i := strings.Index(body, " @@"); i >= 0 {
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body = body[:i]
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}
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oldPart, newPart, found := strings.Cut(body, " ")
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if !found {
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return 0, 0, 0, 0, false
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}
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oldStart, oldCount, ok1 := parseRange(strings.TrimPrefix(oldPart, "-"))
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newStart, newCount, ok2 := parseRange(strings.TrimPrefix(newPart, "+"))
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return oldStart, oldCount, newStart, newCount, ok1 && ok2
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func parseRange(s string) (start, count int, ok bool) {
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startText, countText, found := strings.Cut(s, ",")
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start, err := strconv.Atoi(startText)
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if err != nil {
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return 0, 0, false
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}
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count = 1
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if found {
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count, err = strconv.Atoi(countText)
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if err != nil {
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return 0, 0, false
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}
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}
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return start, count, true