removed accidentally created submodule, broke everything up into JS modules, put CSS in its own file. create game and update state from FEN-formatted strings. also implemented serialization to FEN

app.js

@@ -0,0 +1,49 @@
+import { LETTER_PIECE_NAME_LOOKUP, STARTING_FEN } from './constants.js'
+import { getGameStateFromFEN, toFEN } from './fen.js'
+
+const GREEN = "#779558"
+const BEIGE = "#eeedd3"
+const board = document.getElementById("board")
+
+let gameState = {}
+
+const renderBoard = (fromPerspective = "white")  => {
+    // adapted from https://codepen.io/Staghouse/pen/OzpVya
+    let lastColor = BEIGE
+    let files = Array.from("abcdefgh")
+    let ranks = Array.from("12345678")
+    if (fromPerspective === "white") {
+        ranks.reverse()
+    } else {
+        files.reverse()
+    }
+    ranks.forEach(num => {
+        files.forEach((char, charIndex) => {
+            if (charIndex % 7 || charIndex > 0) {
+                lastColor = lastColor === BEIGE ? GREEN : BEIGE
+            }
+            const box = document.createElement("div")
+            box.classList.add("box")
+            box.id = `${char}${num}`
+            box.style.backgroundColor = lastColor
+            board.appendChild(box)
+        })
+    })
+}
+
+const initializeGameState = () => {
+    gameState = getGameStateFromFEN(STARTING_FEN)
+}
+
+const renderPieces = () => null
+
+const initializeGame = () => {
+    renderBoard()
+    initializeGameState()
+    renderPieces()
+    console.log(gameState)
+    console.log(toFEN(gameState))
+    console.log(toFEN(gameState) === STARTING_FEN)
+    console.log(STARTING_FEN)
+}
+document.addEventListener("DOMContentLoaded", initializeGame)

constants.js

@@ -0,0 +1,20 @@
+
+export const LETTER_PIECE_NAME_LOOKUP = {}
+export const PIECE_NAME_LETTER_LOOKUP = {}
+
+for (const [letter, name] of Object.entries({
+    r: 'rook',
+    b: 'bishop',
+    q: 'queen',
+    k: 'king',
+    p: 'pawn',
+    n: 'knight',
+})) {
+    LETTER_PIECE_NAME_LOOKUP[letter] = `black-${name}`
+    LETTER_PIECE_NAME_LOOKUP[letter.toUpperCase()] = `white-${name}`
+    PIECE_NAME_LETTER_LOOKUP[`black-${name}`] = letter
+    PIECE_NAME_LETTER_LOOKUP[`white-${name}`] = letter.toUpperCase()
+}
+
+export const files = Array.from("abcdefgh")
+export const STARTING_FEN = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"

fen.js

@@ -0,0 +1,131 @@
+import { LETTER_PIECE_NAME_LOOKUP, PIECE_NAME_LETTER_LOOKUP, files } from './constants.js'
+
+const parseCastlingAvailability = castlingAvailability => {
+    let castlingAvailabilityObj = {whiteKing: false, whiteQueen: false, blackKing: false, blackQueen: false}
+    if (castlingAvailability !== "-") {
+        for (const char of castlingAvailability) {
+            if (char === "K") {
+                castlingAvailabilityObj.whiteKing = true
+            } else if (char === "Q") {
+                castlingAvailabilityObj.whiteQueen = true
+            } else if (char === "k") {
+                castlingAvailabilityObj.blackKing = true
+            } else if (char === "q") {
+                castlingAvailabilityObj.blackQueen = true
+            }
+        }
+    }
+    return castlingAvailabilityObj
+}
+
+const castlingAvailabilityToFEN = castlingAvailabilityObj => {
+    let FEN = ""
+    if (castlingAvailabilityObj.whiteKing) {
+        FEN += "K"
+    }
+    if (castlingAvailabilityObj.whiteQueen) {
+        FEN += "Q"
+    }
+    if (castlingAvailabilityObj.blackKing) {
+        FEN += "k"
+    }
+    if (castlingAvailabilityObj.blackQueen) {
+        FEN += "q"
+    }
+    FEN = FEN || "-"
+    return FEN
+}
+
+const parsePositions = positions => {
+    let board = {}
+    const ranks = positions.split('/')
+    ranks.forEach((tokens, rankIndex) => {
+        rankIndex = Math.abs(rankIndex - 7)
+        let rank = rankIndex + 1
+        Array.from(tokens).forEach((token, fileIndex) => {
+            let parsed = parseInt(token)
+            if (isNaN(parsed)) {
+                let file = files[fileIndex]
+                board[`${file}${rank}`] = LETTER_PIECE_NAME_LOOKUP[token]
+            }
+        })
+    })
+    return board
+}
+
+const boardToFEN = board => {
+    let FEN = ""
+    let blanks = 0
+    let files = Array.from("abcdefgh")
+    let ranks = Array.from("12345678").reverse()
+    ranks.forEach((rank, rankIndex) => {
+        if (rankIndex) {
+            if (blanks) {
+                FEN += blanks
+                blanks = 0
+            }
+            FEN += "/"
+        }
+        files.forEach((file, charIndex) => {
+            let cell = `${file}${rank}`
+            if (board.hasOwnProperty(cell)) {
+                if (blanks) {
+                    // it's insane this works, JS casts `blanks` to a String
+                    FEN += blanks
+                    blanks = 0
+                }
+                FEN += PIECE_NAME_LETTER_LOOKUP[board[cell]]
+            } else {
+                blanks++
+            }
+        })
+    })
+    return FEN
+}
+
+export const toFEN = gameState => {
+    let { 
+        board, 
+        whoseTurn, 
+        castlingAvailability, 
+        enPassantTargetSquare, 
+        halfMoveClock, 
+        fullMoveNum 
+    } = gameState
+
+    enPassantTargetSquare = !enPassantTargetSquare ? "-" : enPassantTargetSquare
+
+    return [
+        boardToFEN(board),
+        whoseTurn[0],
+        castlingAvailabilityToFEN(castlingAvailability),
+        enPassantTargetSquare,
+        halfMoveClock,
+        fullMoveNum,
+    ].join(" ")
+}
+
+export const getGameStateFromFEN = FEN => {
+    // https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation
+    let [
+        positions, 
+        whoseTurn, 
+        castlingAvailability,
+        enPassantTargetSquare,
+        halfMoveClock,
+        fullMoveNum
+    ] = FEN.split(" ")
+    whoseTurn = whoseTurn === "w" ? "white" : "black"
+    enPassantTargetSquare = enPassantTargetSquare === "-" ? null : enPassantTargetSquare
+    const castlingAvailabilityObj = parseCastlingAvailability(castlingAvailability)
+    fullMoveNum = parseInt(fullMoveNum)
+    halfMoveClock = parseInt(halfMoveClock)
+    return {
+        board: parsePositions(positions),
+        whoseTurn, 
+        fullMoveNum, 
+        halfMoveClock, 
+        enPassantTargetSquare,
+        castlingAvailability: castlingAvailabilityObj,
+    }
+}

img/pieces/black_king.svg

@@ -1,4 +1,3 @@
-
 <svg xmlns="http://www.w3.org/2000/svg" version="1.1">
     <g style="fill:none; fill-opacity:1; fill-rule:evenodd; stroke:#000000; stroke-width:1.5; stroke-linecap:round;stroke-linejoin:round;stroke-miterlimit:4; stroke-dasharray:none; stroke-opacity:1;" transform="translate(0,45)">
         <path 
@@ -20,5 +19,4 @@
            d="M 11.5,30 C 17,27 27,27 32.5,30 M 11.5,33.5 C 17,30.5 27,30.5 32.5,33.5 M 11.5,37 C 17,34 27,34 32.5,37"
            style="fill:none; stroke:#ffffff;" />
     </g>
-    
-    </svg>
+</svg>

index.html

@@ -3,70 +3,11 @@
 <head>
     <meta charset="utf-8">
     <title></title>
-    <style>
-        #board {
-          margin: auto;
-          padding-top: 4vw;
-          width: 50vw;
-          height: 50vh;
-          display: grid;
-          grid-template-columns: repeat(8, 1fr);
-          grid-template-rows: auto;
-        }
-        .box::before {
-          content: "";
-          display: block;
-          padding-top: 100%;
-        }
-
-        body {
-          padding: 0;
-          margin: 0;
-          background-color: #212121;
-        }
-        body .grid {
-          max-width: 570px;
-          margin: 30px auto;
-          box-sizing: border-box;
-          border: 10px solid #2a351f;
-        }
-    </style>
+    <link rel="stylesheet" href="styles.css">
     <link rel="icon" href="favicon.ico" type="image/x-icon" />
 </head>
-<body onload="renderBoard()">
-    <main id="board">
-    </main>
-    <script>
-        const GREEN = "#779558"
-        const BEIGE = "#eeedd3"
-        const board = document.getElementById("board")
-        // const state = {
-        //     a1: "
-        // }
-        const renderBoard = (fromPerspective = "white")  => {
-            // adapted from https://codepen.io/Staghouse/pen/OzpVya
-            let lastColor = BEIGE
-            let files = Array.from("abcdefgh")
-            let ranks = Array.from("12345678")
-            if (fromPerspective === "white") {
-                ranks.reverse()
-            } else {
-                files.reverse()
-            }
-            ranks.forEach(char => {
-                files.forEach((num, numIndex) => {
-                    if (numIndex % 7 || numIndex > 0) {
-                        lastColor = lastColor === BEIGE ? GREEN : BEIGE
-                    }
-                    const box = document.createElement("div")
-                    box.classList.add("box")
-                    box.id = `${num}${char}`
-                    box.style.backgroundColor = lastColor
-                    board.appendChild(box)
-                })
-            })
-
-        }
-    </script>
+<body>
+    <main id="board"></main>
+    <script type="module" src="app.js"></script>
 </body>
 </html>

styles.css

@@ -0,0 +1,26 @@
+#board {
+  margin: auto;
+  padding-top: 4vw;
+  width: 50vw;
+  height: 50vh;
+  display: grid;
+  grid-template-columns: repeat(8, 1fr);
+  grid-template-rows: auto;
+}
+.box::before {
+  content: "";
+  display: block;
+  padding-top: 100%;
+}
+
+body {
+  padding: 0;
+  margin: 0;
+  background-color: #212121;
+}
+body .grid {
+  max-width: 570px;
+  margin: 30px auto;
+  box-sizing: border-box;
+  border: 10px solid #2a351f;
+}