First commit

1 files changed, 147 insertions, 0 deletions

diff --git a/pkg/gitdiff/apply.go b/pkg/gitdiff/apply.go
new file mode 100644
index 0000000..44bbcca
--- /dev/null
+++ b/pkg/gitdiff/apply.go
@@ -0,0 +1,147 @@
+package gitdiff
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"sort"
+)
+
+// Conflict indicates an apply failed due to a conflict between the patch and
+// the source content.
+//
+// Users can test if an error was caused by a conflict by using errors.Is with
+// an empty Conflict:
+//
+//	    if errors.Is(err, &Conflict{}) {
+//		       // handle conflict
+//	    }
+type Conflict struct {
+	msg string
+}
+
+func (c *Conflict) Error() string {
+	return "conflict: " + c.msg
+}
+
+// Is implements error matching for Conflict. Passing an empty instance of
+// Conflict always returns true.
+func (c *Conflict) Is(other error) bool {
+	if other, ok := other.(*Conflict); ok {
+		return other.msg == "" || other.msg == c.msg
+	}
+	return false
+}
+
+// ApplyError wraps an error that occurs during patch application with
+// additional location information, if it is available.
+type ApplyError struct {
+	// Line is the one-indexed line number in the source data
+	Line int64
+	// Fragment is the one-indexed fragment number in the file
+	Fragment int
+	// FragmentLine is the one-indexed line number in the fragment
+	FragmentLine int
+
+	err error
+}
+
+// Unwrap returns the wrapped error.
+func (e *ApplyError) Unwrap() error {
+	return e.err
+}
+
+func (e *ApplyError) Error() string {
+	return fmt.Sprintf("%v", e.err)
+}
+
+type lineNum int
+type fragNum int
+type fragLineNum int
+
+// applyError creates a new *ApplyError wrapping err or augments the information
+// in err with args if it is already an *ApplyError. Returns nil if err is nil.
+func applyError(err error, args ...interface{}) error {
+	if err == nil {
+		return nil
+	}
+
+	e, ok := err.(*ApplyError)
+	if !ok {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		e = &ApplyError{err: err}
+	}
+	for _, arg := range args {
+		switch v := arg.(type) {
+		case lineNum:
+			e.Line = int64(v) + 1
+		case fragNum:
+			e.Fragment = int(v) + 1
+		case fragLineNum:
+			e.FragmentLine = int(v) + 1
+		}
+	}
+	return e
+}
+
+var (
+	errApplyInProgress = errors.New("gitdiff: incompatible apply in progress")
+	errApplierClosed   = errors.New("gitdiff: applier is closed")
+)
+
+// Apply applies the changes in f to src, writing the result to dst. It can
+// apply both text and binary changes.
+//
+// If an error occurs while applying, Apply returns an *ApplyError that
+// annotates the error with additional information. If the error is because of
+// a conflict with the source, the wrapped error will be a *Conflict.
+func Apply(dst io.Writer, src io.ReaderAt, f *File) error {
+	if f.IsBinary {
+		if len(f.TextFragments) > 0 {
+			return applyError(errors.New("binary file contains text fragments"))
+		}
+		if f.BinaryFragment == nil {
+			return applyError(errors.New("binary file does not contain a binary fragment"))
+		}
+	} else {
+		if f.BinaryFragment != nil {
+			return applyError(errors.New("text file contains a binary fragment"))
+		}
+	}
+
+	switch {
+	case f.BinaryFragment != nil:
+		applier := NewBinaryApplier(dst, src)
+		if err := applier.ApplyFragment(f.BinaryFragment); err != nil {
+			return err
+		}
+		return applier.Close()
+
+	case len(f.TextFragments) > 0:
+		frags := make([]*TextFragment, len(f.TextFragments))
+		copy(frags, f.TextFragments)
+
+		sort.Slice(frags, func(i, j int) bool {
+			return frags[i].OldPosition < frags[j].OldPosition
+		})
+
+		// TODO(bkeyes): consider merging overlapping fragments
+		// right now, the application fails if fragments overlap, but it should be
+		// possible to precompute the result of applying them in order
+
+		applier := NewTextApplier(dst, src)
+		for i, frag := range frags {
+			if err := applier.ApplyFragment(frag); err != nil {
+				return applyError(err, fragNum(i))
+			}
+		}
+		return applier.Close()
+
+	default:
+		// nothing to apply, just copy all the data
+		_, err := copyFrom(dst, src, 0)
+		return err
+	}
+}