fixed frontmatter processing, added test

internal/builder/frontmatter_test.go

@@ -2,6 +2,7 @@
 package builder
 
 import (
+	"bytes"
 	"os"
 	"testing"
 )
@@ -89,3 +90,94 @@ This is the body of the document.`
 		t.Fatalf("Expected error for invalid frontmatter, got nil")
 	}
 }
+
+func TestReadFrontmatter(t *testing.T) {
+	tests := []struct {
+		name     string
+		content  string
+		wantErr  bool
+		wantData []byte
+		wantLen  int
+	}{
+		{
+			name: "Valid frontmatter",
+			content: `---
+title: "Test"
+author: "User"
+---
+Content here`,
+			wantErr:  false,
+			wantData: []byte("title: \"Test\"\nauthor: \"User\"\n"),
+			wantLen:  2,
+		},
+		{
+			name: "Missing closing delimiter",
+			content: `---
+title: "Incomplete Frontmatter"`,
+			wantErr: true,
+		},
+		{
+			name: "Frontmatter later in file",
+			content: `This is some content
+---
+title: "Not Frontmatter"
+---`,
+			wantErr:  false,
+			wantData: nil, // Should return nil because `---` is not the first line
+			wantLen:  0,
+		},
+		{
+			name: "Empty frontmatter",
+			content: `---
+---`,
+			wantErr: true,
+		},
+		{
+			name:     "No frontmatter",
+			content:  `This is just a normal file.`,
+			wantErr:  false,
+			wantData: nil, // Should return nil as there's no frontmatter
+			wantLen:  0,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			// Create a temporary file
+			tmpFile, err := os.CreateTemp("", "testfile-*.md")
+			if err != nil {
+				t.Fatalf("failed to create temp file: %v", err)
+			}
+			defer os.Remove(tmpFile.Name())
+
+			// Write test content
+			_, err = tmpFile.WriteString(tc.content)
+			if err != nil {
+				t.Fatalf("failed to write to temp file: %v", err)
+			}
+			tmpFile.Close()
+
+			// Call function under test
+			data, length, err := readFrontmatter(tmpFile.Name())
+
+			// Check for expected error
+			if tc.wantErr {
+				if err == nil {
+					t.Errorf("expected error but got none")
+				}
+			} else {
+				if err != nil {
+					t.Errorf("unexpected error: %v", err)
+				}
+				// Check content
+				if !bytes.Equal(data, tc.wantData) {
+					t.Errorf("expected %q, got %q", tc.wantData, data)
+				}
+				// Check length
+				if length != tc.wantLen {
+					t.Errorf("expected length %d, got %d", tc.wantLen, length)
+				}
+			}
+		})
+	}
+}