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relative.go
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relative.go
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package reference
import (
"errors"
"fmt"
"regexp"
"strconv"
)
var (
ErrInvalidOffsetFormat = errors.New("invalid offset format")
)
// Relative defines a relative reference.
// It is made of a base and an offset.
// Base is the reference on which the offset must be applied to get
// an absolute reference.
type Relative struct {
ref Reference
offset uint
}
// RelativeFromReferenceAndOffset returns a new Relative reference base on the given
// reference and offset.
func RelativeFromReferenceAndOffset(ref Reference, offset uint) Relative {
return Relative{ref: ref, offset: offset}
}
var offsetRegex = regexp.MustCompile(`(~\d+|\^+)$`)
// RelativeFromString parses the given string and returns relative reference
// after validating and normalizing it. An error is returned if the reference is invalid.
func RelativeFromString(ref string) (Relative, error) {
index := offsetRegex.FindStringIndex(ref)
offset := uint(0)
// Parse offset if there is one
if index != nil {
var err error
offset, err = parseOffset(ref[index[0]:index[1]])
if err != nil {
return Relative{}, fmt.Errorf("failed to parse offset: %w", err)
}
// Strip offset from ref
ref = ref[:index[0]]
if ref[len(ref)-1] == ':' {
ref = ref[:len(ref)-1]
}
}
// Parse base reference
baseRef, err := LocalRefFromString(ref)
if err != nil {
return Relative{}, err
}
return RelativeFromReferenceAndOffset(
baseRef,
offset,
), nil
}
// Base returns the base of the relative reference
func (r Relative) Base() Reference {
return r.ref
}
// Offset returns the offset part of the relative reference.
func (r Relative) Offset() uint {
return r.offset
}
// parseOffset returns the offset value of a relative reference string.
// NOTE: this function must not be called directly, RelativeFromString should
// be used instead.
func parseOffset(offset string) (uint, error) {
if len(offset) == 0 {
panic("offset string is empty")
}
switch offset[0] {
case '^':
return uint(len(offset)), nil
case '~':
if len(offset) == 1 {
return 1, nil
}
result, err := strconv.Atoi(offset[1:])
if err != nil {
return 0, fmt.Errorf("failed to parse integer of relative reference: %w", err)
}
return uint(result), nil
default:
return 0, ErrInvalidOffsetFormat
}
}
// String implements fmt.Stringer.
func (r Relative) String() string {
return fmt.Sprintf("%v~%d", r.ref.String(), r.offset)
}