Began implementing the befunge field data structure

pkg/field/field.go

@@ -0,0 +1,81 @@
+package field
+
+import (
+	"bytes"
+	"io"
+)
+
+//            32-bit Befunge-98
+//           =================
+//                   |-2,147,483,648
+//                   |
+//                   |    x
+//              -----+-----
+// -2,147,483,648    |    2,147,483,647
+//                   |
+//                  y|2,147,483,647
+
+type Field struct {
+	firstLineIndex int
+	length         int
+	lines          []Line
+}
+
+type Line struct {
+	firstColumnIndex int
+	length           int
+	columns          []byte
+}
+
+func LoadFile(fd io.Reader) (*Field, error) {
+	f := new(Field)
+	l := new(Line)
+	trailingSpaces := 0
+	for {
+		data := make([]byte, 4096)
+		if n, errRead := fd.Read(data); errRead != nil {
+			if errRead == io.EOF {
+				if f.length == 0 && l.length == 0 {
+					return nil, newDecodeError("No instruction on the first line of the file produces an unusable program in Befunge98")
+				}
+				if l.length > 0 {
+					f.length++
+					f.lines = append(f.lines, *l)
+				}
+				break
+			} else {
+				return nil, newReadError(errRead)
+			}
+		} else {
+			for i := 0; i < n; i++ {
+				if data[i] == '\n' || data[i] == '\r' {
+					if f.length == 0 && l.length == 0 {
+						return nil, newDecodeError("No instruction on the first line of the file produces an unusable program in Befunge98")
+					}
+					f.length++
+					f.lines = append(f.lines, *l)
+					l = new(Line)
+					trailingSpaces = 0
+					if i+1 < n && data[i] == '\r' && data[i+1] == '\n' {
+						i++
+					}
+				} else {
+					if l.length == 0 && data[i] == ' ' {
+						l.firstColumnIndex++ // trim leading spaces
+					} else {
+						if data[i] == ' ' {
+							trailingSpaces++
+						} else {
+							l.columns = append(l.columns, bytes.Repeat([]byte{' '}, trailingSpaces)...)
+							l.length += trailingSpaces
+							trailingSpaces = 0
+							l.length++
+							l.columns = append(l.columns, data[i])
+						}
+					}
+				}
+			}
+		}
+	}
+	return f, nil
+}