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|
package snap
import (
"strings"
"log"
"os"
"strconv"
)
var die = log.New(os.Stderr, "", 0)
func isEscaped(str string) bool {
n := len(str)
return n > 1 && str[0] == '"' && str[n - 1] == '"';
}
func parseEscaped(snapish string) *Relative {
if isEscaped(snapish) {
snapshot := strings.Trim(snapish, `"`);
if(snapshot == "") {
die.Fatal("Snapshot cannot be empty \"\"")
}
return &Relative {
snapshot: snapshot,
}
}
return nil
}
func parseRelativeSyntax(snapish, directionToken string) *Relative {
parts := strings.Split(snapish, directionToken)
n_parts := len(parts)
if n_parts == 1 {
return nil;
}
// Test if the last the last token is a numeric offset
if offset, err := strconv.Atoi(parts[n_parts - 1]);
err == nil {
// Two tokens (e.g. ++ or --) indicates increment syntax
if n_parts > 2 && parts[n_parts - 2] == "" {
die.Fatal("A snapshot reference cannot be a mix of increment syntax (e.g. my_snap++) and literal syntax (e.g. my_snap+4).")
}
snapshot := strings.TrimRight(snapish, directionToken + "0123456789")
return &Relative {
offset: offset,
snapshot: snapshot,
}
}
// Parse the increment / decrement syntax
// E.g. snapshot+++ or snapshot---
offset := 0;
for i := n_parts - 1; i >= 1 && parts[i] == ""; i-- {
offset += 1
}
return &Relative {
offset: offset,
snapshot: snapish[:len(snapish) - offset],
}
}
func ToRelative(snapish string) * Relative {
if ref := parseEscaped(snapish); ref != nil {
return ref;
}
if ref := parseRelativeSyntax(snapish, "+"); ref != nil {
return ref;
}
if ref := parseRelativeSyntax(snapish, "-"); ref != nil {
ref.offset = -ref.offset;
return ref;
}
return &Relative{
snapshot: snapish,
};
}
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