1 files changed, 147 insertions, 0 deletions
diff --git a/snap/fs.go b/snap/fs.go
new file mode 100644
index 0000000..d0dc83d
--- /dev/null
+++ b/snap/fs.go
@@ -0,0 +1,147 @@
+package snap
+
+import (
+	"time"
+	"path/filepath"
+	"os"
+	"sort"
+)
+
+type Snapshot struct {
+	Name      string
+	ModTime   time.Time
+	Reference string
+}
+
+func getZFSRoot(reference string) string {
+	cursor := filepath.Dir(reference)
+	zfsNotFound := false
+
+	for !zfsNotFound {
+		zfsDir := filepath.Join(cursor, ".zfs")
+		
+		if _, err := os.Stat(zfsDir); !os.IsNotExist(err) {
+			break
+		} 
+
+		cursor = filepath.Join(cursor, "..")
+
+		zfsNotFound = filepath.ToSlash(cursor) == "/"
+	}
+
+	if(zfsNotFound) {
+		die.Fatal("Could not find a .zfs directory. Are you within a zfs dataset?")
+	}
+
+	return cursor
+}
+
+func getSnapshots(reference string) []*Snapshot {
+	zfsRoot := getZFSRoot(reference)
+
+	snapshotDir := filepath.Join(zfsRoot, ".zfs", "snapshot");
+
+	files, err := os.ReadDir(snapshotDir)
+	if err != nil {
+		die.Fatalf("Could not find the snapshots directory inside %s", snapshotDir);
+	}
+
+	relPath, err := filepath.Rel(zfsRoot, reference)
+	if err != nil {
+		die.Fatal("Could not find relative path to reference file: %v", err)
+	}
+
+	snaps := make([]*Snapshot, len(files))
+
+	for i, file := range files {
+
+		info, err := file.Info()
+		if(err != nil) {
+			die.Fatalf("Could not read file %v", err)
+		}
+
+		name := file.Name()
+		snaps[i] = &Snapshot{
+			Name: name,
+			ModTime: info.ModTime(),
+		}
+
+		pathInSnap := filepath.Join(snapshotDir, name, relPath)
+
+		if _, err := os.Stat(pathInSnap); err != nil {
+			if !os.IsNotExist(err) {
+				die.Fatalf("Error encountered while attempting to read reference file in snapshot:\n%v", err)
+			}
+		} else {
+			snaps[i].Reference = pathInSnap
+		}
+
+	}
+
+	return snaps
+}
+
+func GetTimeseries(reference string) []*Snapshot {
+	reference, err := filepath.Abs(reference)
+
+	if err != nil {
+	  die.Fatal(err)
+	}
+	
+	snaps := getSnapshots(reference)
+
+	sort.Slice(snaps, func(i, j int) bool {
+		return snaps[i].ModTime.Before(snaps[j].ModTime)
+	})
+
+	return snaps
+}
+
+func buildNameMap(snapTs []*Snapshot) map[string] int {
+	namemap := make(map[string] int)
+
+	for i, snap := range snapTs {
+		namemap[snap.Name] = i
+	}
+
+	return namemap
+}
+
+type SnapshotOracle struct {
+	timeseries []*Snapshot
+	namemap    map[string] int
+};
+
+func GetOracle(reference string) *SnapshotOracle {
+	timeseries := GetTimeseries(reference)
+	namemap := buildNameMap(timeseries)
+
+
+	return &SnapshotOracle {
+		timeseries,
+		namemap,
+	}
+}
+
+func (oracle *SnapshotOracle) ResolveRelative(ref *Relative) string {
+	n_ts := len(oracle.timeseries)
+	wanted := n_ts - 1
+
+	if ref.snapshot != "" {
+		id, ok := oracle.namemap[ref.snapshot]
+
+		if !ok {
+			die.Fatal("Could not find the snapshot %s", ref.snapshot)
+		}
+
+		wanted = id
+	}
+
+	wanted += ref.offset
+
+	if wanted < 0 || wanted >= n_ts {
+		die.Fatal("The snapshot you requested is out of range.")
+	}
+
+	return oracle.timeseries[wanted].Reference
+}
+\ No newline at end of file