passing

board/fen.go

@@ -1,12 +1,15 @@
 package board
 
 import (
+	"errors"
 	"strconv"
 	"strings"
 
 	"github.com/maaslalani/gambit/piece"
 )
 
+var ErrInvalidFEN = errors.New("Invalid FEN")
+
 func (b Board) ToFen() string {
 	var sb strings.Builder
 	// Loop through the entire board and build the FEN string for each rank
@@ -30,7 +33,7 @@ func (b Board) ToFen() string {
 			}
 
 			// Display the piece's Fen representation
-			sb.WriteString(p.Fen())
+			sb.WriteString(p.ToFen())
 		}
 
 		// If we have reached the end of the rank and we have encountered
@@ -44,7 +47,7 @@ func (b Board) ToFen() string {
 		}
 	}
 
-	sb.WriteString(" w ")
+	sb.WriteString(" " + string(b.Turn) + " ")
 	// TODO: Add castling
 	sb.WriteString("KQkq")
 	sb.WriteString(" - ")
@@ -53,5 +56,32 @@ func (b Board) ToFen() string {
 }
 
 func FromFen(fen string) (Board, error) {
-	return Board{}, nil
+	var b Board
+
+	parts := strings.Split(fen, " ")
+	if len(parts) != 6 {
+		return b, ErrInvalidFEN
+	}
+
+	b.Turn = piece.Color(parts[1])
+
+	ranks := strings.Split(parts[0], "/")
+
+	for r, rank := range ranks {
+		for c, char := range rank {
+			// Empty squares, append n empty pieces into the board
+			if char >= '1' && char <= '8' {
+				n := int(char - '0')
+				for i := 0; i < n; i++ {
+					b.Grid[7-r][c+i] = piece.Empty()
+				}
+				continue
+			}
+
+			p := piece.FromFen(string(char))
+			b.Grid[7-r][c] = p
+		}
+	}
+
+	return b, nil
 }

piece/fen.go

@@ -0,0 +1,26 @@
+package piece
+
+import "strings"
+
+func (p Piece) ToFen() string {
+	if p.Color == NoColor {
+		return ""
+	}
+
+	if p.Color == Black {
+		return strings.ToLower(string(p.Type))
+	}
+
+	return string(p.Type)
+}
+
+func FromFen(fen string) Piece {
+	t := Type(strings.ToUpper(fen))
+	var c Color
+	if strings.ToUpper(fen) == fen {
+		c = White
+	} else {
+		c = Black
+	}
+	return Piece{Type: t, Color: c}
+}

piece/piece.go

@@ -1,7 +1,5 @@
 package piece
 
-import "strings"
-
 type Piece struct {
 	Type  Type
 	Color Color
@@ -15,18 +13,6 @@ func (p Piece) String() string {
 	return Display[p.Type]
 }
 
-func (p Piece) Fen() string {
-	if p.Color == NoColor {
-		return ""
-	}
-
-	if p.Color == Black {
-		return strings.ToLower(string(p.Type))
-	}
-
-	return string(p.Type)
-}
-
 var (
 	BW = Piece{Bishop, White}
 	KW = Piece{King, White}