wip

src/ledger/file.go

@@ -1,6 +1,8 @@
 package ledger
 
 import (
+	"bufio"
+	"bytes"
 	"fmt"
 	"io"
 	"io/fs"
@@ -20,6 +22,41 @@ func NewFiles(p string, q ...string) (Files, error) {
 	return f, err
 }
 
+func (files Files) TempGetLastNLines(n int) ([]string, error) {
+	p := files.paths()[0]
+	f, err := os.Open(p)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	return peekLastNLines(io.Discard, bufio.NewReader(f), n)
+}
+
+func (files Files) TempSetLastNLines(n int, lines []string) error {
+	panic("e")
+}
+
+func peekLastNLines(w io.Writer, r *bufio.Reader, n int) ([]string, error) {
+	lastNLines := make([]string, 0, n)
+	for {
+		line, err := r.ReadBytes('\n')
+		if len(line) > 0 {
+			lastNLines = append(lastNLines, string(bytes.TrimRight(line, "\n")))
+			for i := 0; i < len(lastNLines)-n; i++ {
+				fmt.Fprintln(w, lastNLines[i])
+			}
+			lastNLines = lastNLines[max(0, len(lastNLines)-n):]
+		}
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+	}
+	return lastNLines, nil
+}
+
 func (files Files) paths() []string {
 	result := make([]string, 0, len(files))
 	for i := range files {