Add methods concerning the previous line

CHANGELOG.md

@@ -5,6 +5,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.1.4] - 29.07.2023
+
+[Diff](https://github.com/elk-language/go-prompt/compare/v1.1.3...elk-language:go-prompt:v1.1.4)
+
+### Added
+- `func (*prompt.Document).PreviousLineIndentSpaces() int`
+- `func (*prompt.Document).PreviousLineIndentLevel(indentSize int) int`
+- `func (*prompt.Document).PreviousLine() (s string, ok bool)`
+
 ## [1.1.3] - 29.07.2023
 
 [Diff](https://github.com/elk-language/go-prompt/compare/v1.1.2...elk-language:go-prompt:v1.1.3)

document.go

@@ -109,6 +109,25 @@ func (d *Document) CurrentLineIndentLevel(indentSize int) int {
 	return d.IndentLevel(d.TextBeforeCursor(), indentSize)
 }
 
+// Returns the amount of spaces that the previous line (relative to the cursor)
+// is indented with.
+func (d *Document) PreviousLineIndentSpaces() int {
+	line, ok := d.PreviousLine()
+	if !ok {
+		return 0
+	}
+	return d.IndentSpaces(line)
+}
+
+// Returns the indentation level of the previous line (relative to the cursor).
+func (d *Document) PreviousLineIndentLevel(indentSize int) int {
+	line, ok := d.PreviousLine()
+	if !ok {
+		return 0
+	}
+	return d.IndentLevel(line, indentSize)
+}
+
 // TextBeforeCursor returns the text before the cursor.
 func (d *Document) TextBeforeCursor() string {
 	r := []rune(d.Text)
@@ -349,6 +368,21 @@ func (d *Document) CurrentLine() string {
 	return d.CurrentLineBeforeCursor() + d.CurrentLineAfterCursor()
 }
 
+// Return the text of the previous line (relative to the cursor).
+// If the cursor is on the first line then false is returned in the second value
+// to signify that there is no previous line.
+func (d *Document) PreviousLine() (s string, ok bool) {
+	indices := d.lineStartIndices()
+	pos := bisect.Right(indices, d.cursorPosition) - 1
+	if pos == 0 {
+		return "", false
+	}
+
+	prevLineStartIndex := indices[pos-1]
+	lineStartIndex := indices[pos]
+	return d.Text[prevLineStartIndex : lineStartIndex-1], true
+}
+
 // Array pointing to the start indices of all the lines.
 func (d *Document) lineStartIndices() []istrings.RuneNumber {
 	// TODO: Cache, because this is often reused.

document_test.go

@@ -377,6 +377,46 @@ func TestDocument_LastLineIndentLevel(t *testing.T) {
 	}
 }
 
+func TestDocument_PreviousLine(t *testing.T) {
+	tests := []struct {
+		document *Document
+		want     string
+		ok       bool
+	}{
+		{
+			document: &Document{
+				Text:           "line 1\nline 2\nline 3\n      line 4",
+				cursorPosition: 32,
+			},
+			want: "line 3",
+			ok:   true,
+		},
+		{
+			document: &Document{
+				Text:           "line 1\nline 2\nline 3\n      line 4",
+				cursorPosition: 19,
+			},
+			want: "line 2",
+			ok:   true,
+		},
+		{
+			document: &Document{
+				Text:           "line 1\nline 2\nline 3\n      line 4",
+				cursorPosition: 1,
+			},
+			want: "",
+			ok:   false,
+		},
+	}
+
+	for i, tc := range tests {
+		got, ok := tc.document.PreviousLine()
+		if got != tc.want || ok != tc.ok {
+			t.Errorf("[%d] Should be (%#v, %#v), got (%#v, %#v)", i, tc.want, tc.ok, got, ok)
+		}
+	}
+}
+
 func TestDocument_TextAfterCursor(t *testing.T) {
 	pattern := []struct {
 		document *Document