diff --git a/README.md b/README.md
index 1ce1e2c..0b5b469 100644
--- a/README.md
+++ b/README.md
@@ -94,7 +94,6 @@ or changed without updating this reference. Search for `SettingsStorage`.
 ```
 {
   log: 'info', // default log level
-  allowTemplateAugmenting: false, // sloppy mode
   retryTemplate: 30,    // retry attempts within one template
   attemptTemplates: 50, // number of templates to try on failure
   svgEffects: false,    // fancy mode
@@ -125,19 +124,20 @@ Algorithm Quirks
 
 Every board must be solvable, otherwise it wouldn't be much of a game. Generating a valid board
 turned out quite a bit more challenging than I thought. My algorithm is based in some heuristics
-and good deal of luck. 
+and luck.
 
 To make things more fun, besides the marble matching rules, the board must be laid out in one of 
 several pre-defined shapes of exactly 55 tiles. The algorithm can sometimes get itself into a dead 
-end while placing marbles on the board. I experimented with backtracking, but the current version 
-simply retries the whole thing with a different random seed. There are configurable retry limits
-as a failsafe. If the given template fails many consecutive times, the algorithm opts to switch to 
+end while placing marbles on the board. After some experimentation I settled on a recursive algorithm
+with a heuristic and backtracking. There are configurable retry limits and max recursion / retry
+counter as a failsafe. If the given template fails many consecutive times, the algorithm opts to switch to 
 a different template. Some templates are harder than others, and some random seeds just seem to 
 have a problem.
 
-A workaround I added is called Sloppy Mode. When the algorithm can't place a marble, it may choose
-to add a new tile to the template, trying to keep the overall shape as tidy as possible. This may
-hurt game difficulty, but is generally much faster than retrying over and over.
+I added a few extra rules to the generation algorithm to make the boards harder: Vitae and Mors should not
+appear as the first few marbles to remove, since they tend to eliminate any choice; and metals start a few
+levels deeper still. This gives the player a lot more room to make a mistake in the beginning. 
+At least you can enjoy the Undo and Try Again buttons!
 
 If you're curious about the inner workings, open dev tools and enable debug logging with the `debug=1`
 GET parameter.
diff --git a/index.html b/index.html
index 97b7b7c..93f7192 100644
--- a/index.html
+++ b/index.html
@@ -8,7 +8,7 @@
     <meta name="apple-mobile-web-app-capable" content="yes">
 
     <title>Sigmar's Garden Online</title>
-    <link rel="stylesheet" href="style.css?cache=2019-12-10b">
+    <link rel="stylesheet" href="style.css?cache=2019-12-15">
 
     <meta name="author" content="Ondřej Hruška">
     <meta name="description" content="Play Sigmar's Garden online. Opus Magnum minigame re-implemented in JavaScript and SVG.">
@@ -90,6 +90,6 @@
         </div>
     </div>
 </div>
-<script src="script.js?cache=2019-12-10b"></script>
+<script src="script.js?cache=2019-12-15"></script>
 </body>
 </html>
diff --git a/script.js b/script.js
index 3d7e1f8..5220fe9 100644
--- a/script.js
+++ b/script.js
@@ -262,6 +262,15 @@ class Board {
     this.removeOrbByIndex(index)
   }
 
+  /**
+   * Count orbs in the game board
+   *
+   * @return {number}
+   */
+  countOrbs() {
+    return this.grid.reduce((acu, x) => acu + (x !== null), 0);
+  }
+
   /**
    * Remove orb by array index
    *
@@ -642,41 +651,115 @@ class Board {
     return this.grid[n];
   }
 
+  /**
+   * Check if a cell is available for selection in-game
+   * (checking surroundings only). This should work the same regardless
+   * of whether the cell is occupied or not.
+   *
+   * @param n
+   * @return {boolean}
+   */
+  isAvailable(n) {
+    return this.getCellInfo(n).freeSequence >= 3;
+  }
+
+  /**
+   * Get info about a cell surroundings and position
+   *
+   * neighbours - number of occupied neighbouring cells
+   * centerWeight - distance from the board center
+   * freeSequence - number of contiguous free tiles in the direct neighbourhood
+   *
+   * @param n
+   * @return {{neighbours: number, centerWeight: number, freeSequence: number}}
+   */
+  getCellInfo(n) {
+    let {x, y} = gridIndexToXy(n);
+
+    let freeSpaces = [
+      isXyOutside(x - 1, y) || !this.grid[n - 1],
+      isXyOutside(x - 1, y - 1) || !this.grid[n - 12],
+      isXyOutside(x, y - 1) || !this.grid[n - 11],
+      isXyOutside(x + 1, y) || !this.grid[n + 1],
+      isXyOutside(x + 1, y + 1) || !this.grid[n + 12],
+      isXyOutside(x, y + 1) || !this.grid[n + 11],
+    ];
+
+    let nOccupied = 0;
+    for (let i = 0; i < 6; i++) {
+      if (!freeSpaces[i]) {
+        nOccupied++;
+      }
+    }
+
+    let freeSequence = 0;
+    let maxFreeSequence = 0;
+    for (let i = 0; i < 12; i++) {
+      if (freeSpaces[i % 6]) {
+        freeSequence++;
+        if (freeSequence >= 6) {
+          maxFreeSequence = freeSequence;
+          break;
+        }
+        if (freeSequence > maxFreeSequence) {
+          maxFreeSequence = freeSequence;
+        }
+      } else {
+        freeSequence = 0;
+      }
+    }
+
+    let { rx, ry } = this.gridXyToCoord(x, y);
+
+    return {
+      neighbours: nOccupied,
+      freeSequence: maxFreeSequence,
+      centerWeight: Math.round(Math.sqrt(Math.pow(rx, 2) + Math.pow(ry, 2))),
+    };
+  }
+
+  /**
+   * Build the game GUI (buttons, links)
+   */
   buildGui() {
+    const addButton = (x, y, text, classes='') => {
+      let { rx, ry } = this.guiXyToCoord(x, y);
+      let button = Svg.fromXML(`<text class="button-text${classes?' '+classes:''}" x="${rx}" y="${ry}">${text}</text>`);
+      this.$root.appendChild(button);
+      return button;
+    };
+
     const y0 = 0.05;
     const x0 = 0;
     const ysp = 0.75;
     const ysp2 = 0.6;
 
-    this.buttons.randomize = this.addButton(x0, y0, 'Randomize');
-    this.buttons.restart = this.addButton(x0, y0 + ysp, 'Try Again', 'disabled');
-    this.buttons.undo = this.addButton(x0, y0 + ysp*2, 'Undo', 'disabled');
+    this.buttons.randomize = addButton(x0, y0, 'Randomize');
+    this.buttons.restart = addButton(x0, y0 + ysp, 'Try Again', 'disabled');
+    this.buttons.undo = addButton(x0, y0 + ysp*2, 'Undo', 'disabled');
+    this.buttons.working = addButton(x0, y0 + ysp*3, 'Working…', 'working');
 
-    const cfgy0 = 10;
+    const cfgy0 = 10.5;
 
-    this.buttons.optFancy = this.addButton(x0, cfgy0, 'Effects:', 'config');
-    this.buttons.optBlockedEffect = this.addButton(x0, cfgy0+ysp2, 'Dim Blocked:', 'config');
-    this.buttons.optSloppy = this.addButton(x0, cfgy0+ysp2*2, 'Sloppy Mode:', 'config');
-    this.buttons.toggleFullscreen = this.addButton(x0, cfgy0+ysp2*-1.5, 'Fullscreen', 'config');
+    this.buttons.optFancy = addButton(x0, cfgy0, 'Effects:', 'config');
+    this.buttons.optBlockedEffect = addButton(x0, cfgy0+ysp2, 'Dim Blocked:', 'config');
+    this.buttons.toggleFullscreen = addButton(x0, cfgy0+ysp2*-1.5, 'Fullscreen', 'config');
 
-    this.buttons.btnAbout = this.addButton(x0, cfgy0+ysp2*-2.5, 'Help', 'config');
+    this.buttons.btnAbout = addButton(x0, cfgy0+ysp2*-2.5, 'Help', 'config');
 
     let youWin = Svg.fromXML(`<text class="you-win" opacity="0" x="0" y="0">Good work!</text>`);
     this.$root.appendChild(youWin);
     this.youWin = youWin;
   }
 
+  /**
+   * Update toggles
+   *
+   * @param cfg
+   */
   updateSettingsGUI(cfg) {
     this.buttons.optFancy.textContent = 'Effects: '+(cfg.svgEffects ? 'On' : 'Off');
     this.buttons.optBlockedEffect.textContent = 'Dim Blocked: '+(cfg.dimBlocked ? 'On' : 'Off');
-    this.buttons.optSloppy.textContent = 'Sloppy Mode: '+(cfg.allowTemplateAugmenting ? 'On' : 'Off');
-  }
-
-  addButton(x, y, text, classes='') {
-    let { rx, ry } = this.guiXyToCoord(x, y);
-    let button = Svg.fromXML(`<text class="button-text${classes?' '+classes:''}" x="${rx}" y="${ry}">${text}</text>`);
-    this.$root.appendChild(button);
-    return button;
   }
 }
 
@@ -733,6 +816,56 @@ class Rng {
   nextInt(max) {
     return Math.floor((max + 1) * this.next());
   }
+
+  /**
+   * Shuffle an array.
+   * The array is shuffled in place.
+   *
+   * @return the array
+   */
+  arrayShuffle(a) {
+    let j, x, i;
+    for (i = a.length - 1; i > 0; i--) {
+      j = this.nextInt(i);
+      x = a[i];
+      a[i] = a[j];
+      a[j] = x;
+    }
+    return a;
+  }
+
+  /**
+   * Choose a random member of an array
+   *
+   * @param array
+   * @return {number}
+   */
+  arrayChoose(array) {
+    return array[Math.floor(this.next() * array.length)];
+  }
+
+  /**
+   * Sneak items in the given order into another array
+   *
+   * @param array - the modified array
+   * @param startKeepout - how many leading lements to leave untouched
+   * @param endKeepout - how many trailing elements to leave untouched
+   * @param items - items to sneak in
+   * @return the modified array
+   */
+  arraySneak(array, startKeepout, endKeepout, items) {
+    let positions = [];
+    for (let i = 0; i < items.length; i++) {
+      positions.push(startKeepout + this.nextInt(array.length - startKeepout - endKeepout))
+    }
+    positions.sort((a, b) => a - b);
+    // inject them into the array
+    items.forEach((pair, i) => {
+      array.splice(positions[i] + i, 0, pair);
+    });
+
+    return array;
+  }
 }
 
 class SettingsStorage {
@@ -741,13 +874,12 @@ class SettingsStorage {
     this.defaults = {
       version: 1,
       log: 'info',
-      allowTemplateAugmenting: false,
-      retryTemplate: 120,
+      retryTemplate: 70,
       attemptTemplates: 20,
-      difficulty: 35,
       svgEffects: false,
       dimBlocked: true,
       logSolution: false,
+      highlightTemplate: false,
     };
     this.settings = Object.assign({}, this.defaults);
   }
@@ -932,7 +1064,7 @@ class Game {
 
     // Defer start to give browser time to render the background
     setTimeout(() => {
-      this.newGame(args.seed)
+      this.newGameWithLoader(args.seed)
     }, 50);
   }
 
@@ -1101,358 +1233,9 @@ class Game {
     };
   }
 
-  isAvailable(n) {
-    return this.getNeighbours(n).freeSequence >= 3;
-  }
-
-  getNeighbours(n) {
-    let {x, y} = gridIndexToXy(n);
-
-    let freeSpaces = [
-      isXyOutside(x - 1, y) || !this.board.grid[n - 1],
-      isXyOutside(x - 1, y - 1) || !this.board.grid[n - 12],
-      isXyOutside(x, y - 1) || !this.board.grid[n - 11],
-      isXyOutside(x + 1, y) || !this.board.grid[n + 1],
-      isXyOutside(x + 1, y + 1) || !this.board.grid[n + 12],
-      isXyOutside(x, y + 1) || !this.board.grid[n + 11],
-    ];
-
-    let nOccupied = 0;
-    for (let i = 0; i < 6; i++) {
-      if (!freeSpaces[i]) {
-        nOccupied++;
-      }
-    }
-
-    let freeSequence = 0;
-    let maxFreeSequence = 0;
-    for (let i = 0; i < 12; i++) {
-      if (freeSpaces[i % 6]) {
-        freeSequence++;
-        if (freeSequence >= 6) {
-          maxFreeSequence = freeSequence;
-          break;
-        }
-        if (freeSequence > maxFreeSequence) {
-          maxFreeSequence = freeSequence;
-        }
-      } else {
-        freeSequence = 0;
-      }
-    }
-
-    let { rx, ry } = this.board.gridXyToCoord(x, y);
-
-    return {
-      neighbours: nOccupied,
-      freeSequence: maxFreeSequence,
-      centerWeight: Math.round(Math.sqrt(Math.pow(rx, 2) + Math.pow(ry, 2))),
-    };
-  }
-
   placeOrbs(template) {
-    let tilesAdded = 0;
-
-    this.board.removeAllOrbs();
-
-    let allowedTable = [];
-    let outsideTemplate = [];
-    for (let i = 0; i < BOARD_SIZE; i++) {
-      const allo = template.includes(i);
-      allowedTable.push(allo);
-
-      let {x, y} = gridIndexToXy(i);
-      if (!allo && !isXyOutside(x, y)) {
-        outsideTemplate.push(i);
-      }
-
-      // Highlight pattern shape
-
-      // if (this.board.tiles[i]) {
-      //   if (allo) {
-      //     this.board.tiles[i].setAttribute('opacity', 1)
-      //   } else {
-      //     this.board.tiles[i].setAttribute('opacity', 0.6)
-      //   }
-      // }
-    }
-
-    const place = (n, symbol) => {
-      this.trace(`Place ${n} <- ${symbol}`);
-      if (!allowedTable[n]) throw Error(`Position ${n} not allowed by template`);
-      if (this.board.grid[n]) throw Error(`Position ${n} is occupied by ${this.board.grid[n]}`);
-      // we use a hack to speed up generation here - SVG is not altered until we have a solution
-      this.board.grid[n] = symbol;
-    };
-
-    const unplace = (n) => {
-      this.trace(`Unplace ${n}`);
-      this.board.grid[n] = null;
-    };
-
-    const findBestCandidate = (except = null) => {
-      let candidates = [];
-      for (let n of template) {
-        if (except && except.includes(n)) continue;
-
-        if (!this.board.grid[n]) {
-          // is free
-          const neigh = this.getNeighbours(n);
-          if (neigh.freeSequence >= 3) {
-            candidates.push({
-              n,
-              cw: neigh.centerWeight
-            });
-          }
-        }
-      }
-
-      candidates.sort((a, b) => a.cw - b.cw);
-
-      if (candidates.length) {
-        // return candidates[0].n;
-        let top = [];
-        let topw = candidates[0].cw;
-        for(let cand of candidates) {
-          if (cand.cw <= topw + this.cfg.difficulty) { // TODO this could vary by template
-            top.push(cand);
-          }
-        }
-
-        //the neighbor count is not used for anything anymore, oops
-
-        // console.log('Got a choice of '+top.length+' tiles');
-
-        return this.arrayChoose(top).n;
-      }
-
-      return false;
-    };
-
-    const findAvailableIndex = (except = null) => {
-      const n = findBestCandidate(except);
-      if (n !== false) return n;
-
-      // this corrupts the template, but makes the likelihood of quickly finding a valid solution much higher.
-      if (template.length !== BOARD_SIZE && this.cfg.allowTemplateAugmenting) {
-        // Prefer tile with more neighbours to make the game harder
-        let candidates = [];
-        outsideTemplate.forEach((n) => {
-          if (!allowedTable[n] && this.isAvailable(n)) {
-            const neigh = this.getNeighbours(n);
-            if (!candidates[neigh.neighbours]) {
-              candidates[neigh.neighbours] = [n];
-            } else {
-              candidates[neigh.neighbours].push(n);
-            }
-          }
-        });
-
-        for (let i = 6; i >= 0; i--) {
-          if (!candidates[i]) continue;
-          let toAdd = this.arrayChoose(candidates[i]);
-          allowedTable[toAdd] = true;
-          outsideTemplate.splice(outsideTemplate.indexOf(toAdd), 1);
-
-          template.push(toAdd);
-          tilesAdded++;
-
-          this.warn(`Adding extra tile to template: ${toAdd}`);
-          return toAdd;
-        }
-      }
-
-      throw Error("Failed to find available board tile.");
-    };
-
-    place(60, 'gold');
-
-    const toPlace = this.buildPlacementList();
-
-    let solution = [
-      ['gold', 60],
-    ];
-    while (toPlace.length > 0) {
-      this.trace('placing a pair.');
-
-      let symbol1 = toPlace.pop();
-      let index1 = findAvailableIndex();
-      place(index1, symbol1);
-      solution.push([symbol1, index1]);
-
-      let symbol2 = toPlace.pop();
-      let index2 = findAvailableIndex();
-      place(index2, symbol2);
-
-      if (!this.isAvailable(index1)) {
-        this.debug(`Deadlock, trying to work around it - ${index1}, ${index2}`);
-
-        unplace(index2);
-        let except = [index2];
-
-        let suc = false;
-        for (let i = 0; i < 5; i++) {
-          this.trace(`try #${i + 1}`);
-          let index = findAvailableIndex(except);
-          place(index, symbol2);
-
-          if (this.isAvailable(index1)) {
-            suc = true;
-            index2 = index;
-            break;
-          } else {
-            unplace(index);
-            except.push(index);
-          }
-        }
-
-        if (!suc) {
-          throw new Error("Solution contains a deadlock.");
-        }
-      }
-
-      // index2 is updated in the fixing loop
-      solution.push([symbol2, index2]);
-    }
-
-    // Show the solution for debug
-
-    solution.reverse();
-    this.info("Found a valid board!");
-
-    solution.forEach((a) => {
-      let p = gridIndexToXy(a[1]);
-      a[1] = `${p.x}×${p.y}`;
-    });
-
-    this.debug('Solution:', solution);
-
-    return {
-      solution,
-      tilesAdded: tilesAdded,
-    };
-  }
-
-  /**
-   * Shuffle an array.
-   * The array is shuffled in place.
-   *
-   * @return the array
-   */
-  arrayShuffle(a) {
-    let j, x, i;
-    for (i = a.length - 1; i > 0; i--) {
-      j = this.rng.nextInt(i);
-      x = a[i];
-      a[i] = a[j];
-      a[j] = x;
-    }
-    return a;
-  }
-
-  /**
-   * Count orbs in the game board
-   *
-   * @return {number}
-   */
-  countOrbs() {
-    return this.board.grid.reduce((acu, x) => acu + (x !== null), 0);
-  }
-
-  /**
-   * Choose a random emember of an array
-   *
-   * @param array
-   * @return {number}
-   */
-  arrayChoose(array) {
-    return array[Math.floor(this.rng.next() * array.length)];
-  }
-
-  buildPlacementList() {
-    let toPlace = [
-      ['air', 'air'],
-      ['air', 'air'],
-      ['air', 'air'],
-      ['air', 'air'],
-
-      ['fire', 'fire'],
-      ['fire', 'fire'],
-      ['fire', 'fire'],
-      ['fire', 'fire'],
-
-      ['water', 'water'],
-      ['water', 'water'],
-      ['water', 'water'],
-      ['water', 'water'],
-
-      ['earth', 'earth'],
-      ['earth', 'earth'],
-      ['earth', 'earth'],
-      ['earth', 'earth'],
-    ];
-
-    let newSaltedPairs = [];
-    const nsalted = this.rng.nextInt(2);
-    for (let i = 0; i < nsalted; i++) {
-      while (true) {
-        const n = this.rng.nextInt(toPlace.length - 1);
-        if (toPlace[n][1] !== 'salt') {
-          this.trace(`Pairing ${toPlace[n][1]} with salt.`);
-          newSaltedPairs.push([toPlace[n][1], 'salt']);
-          toPlace[n][1] = 'salt';
-          break;
-        }
-      }
-    }
-    toPlace = toPlace.concat(newSaltedPairs);
-    // if we have some salt pairs left
-    for (let i = 0; i < 2 - nsalted; i++) {
-      toPlace.push(['salt', 'salt']);
-    }
-
-    // these are always paired like this, and don't support salt
-    toPlace = toPlace.concat([
-      ['mors', 'vitae'],
-      ['mors', 'vitae'],
-      ['mors', 'vitae'],
-      ['mors', 'vitae'],
-    ]);
-
-    // shuffle the pairs that have random order (i.e. not metals)
-    this.arrayShuffle(toPlace);
-
-    // the order here is actually significant, so let's pay attention...
-    const metals = [
-      ['lead', 'mercury'],
-      ['tin', 'mercury'],
-      ['iron', 'mercury'],
-      ['copper', 'mercury'],
-      ['silver', 'mercury'],
-    ];
-    let mPos = [];
-    for (let i = 0; i < metals.length; i++) {
-      let x;
-      // find a unique position
-      do {
-        x = this.rng.nextInt(toPlace.length + i);
-      } while (mPos.includes(x));
-      mPos.push(x)
-    }
-    mPos.sort((a, b) => a - b);
-    this.trace('Metal positions ', mPos);
-    // inject them into the array
-    metals.forEach((pair, i) => {
-      toPlace.splice(mPos[i] + i, 0, pair);
-    });
-
-    this.debug('Placement order (last first):', toPlace);
-
-    return toPlace.reduce((a, c) => {
-      a.push(c[0]);
-      a.push(c[1]);
-      return a;
-    }, []);
+    let placer = new RecursiveOrbPlacer(this, template);
+    return placer.place();
   }
 
   getPairSymbols(first) {
@@ -1500,7 +1283,7 @@ class Game {
    * @return {Boolean}
    */
   isAvailableAtPlaytime(n) {
-    let ava = this.isAvailable(n);
+    let ava = this.board.isAvailable(n);
 
     const sym = this.board.grid[n].symbol;
     if (METAL_SEQ.includes(sym)) {
@@ -1623,7 +1406,7 @@ class Game {
     }
 
     if (wantRefresh) {
-      if (this.countOrbs() === 0) {
+      if (this.board.countOrbs() === 0) {
         this.info("Good work!");
 
         if (removed) {
@@ -1643,12 +1426,14 @@ class Game {
   installButtonHandlers() {
     this.board.buttons.restart.addEventListener('click', () => {
       this.info("New Game with the same seed");
-      this.newGame(this.rng.seed);
+      while (this.undoStack.length) {
+        this.undo();
+      }
     });
 
     this.board.buttons.randomize.addEventListener('click', () => {
       this.info("New Game with a random seed");
-      this.newGame(+new Date);
+      this.newGameWithLoader(+new Date);
     });
 
     this.board.buttons.btnAbout.addEventListener('click', () => {
@@ -1679,13 +1464,6 @@ class Game {
       })
     });
 
-    this.board.buttons.optSloppy.addEventListener('click', () => {
-      this.info("Toggle sloppy placement mode");
-      this.setCfg({
-        allowTemplateAugmenting: !this.cfg.allowTemplateAugmenting,
-      })
-    });
-
     this.board.buttons.toggleFullscreen.addEventListener('click', () => {
       this.info("Toggle Fullscreen");
       if (document.fullscreenElement) {
@@ -1700,7 +1478,7 @@ class Game {
    * Update button hiding attributes, disabled orb effects, etc
    */
   updateGameGui() {
-    let nOrbs = this.countOrbs();
+    let nOrbs = this.board.countOrbs();
 
     this.board.buttons.restart
       .classList.toggle('disabled', nOrbs === 55);
@@ -1724,6 +1502,15 @@ class Game {
     }
   }
 
+  newGameWithLoader(seed) {
+    this.board.buttons.working.classList.add('show');
+
+    setTimeout(() => {
+      this.newGame(seed);
+      this.board.buttons.working.classList.remove('show');
+    }, 20);
+  }
+
   newGame(seed) {
     if (seed !== null) {
       this.rng.setSeed(seed);
@@ -1773,11 +1560,7 @@ class Game {
           break;
         } catch (e) {
           retry_count++;
-          if (this.logging_trace) {
-            this.error(e);
-          } else {
-            this.warn(e.message);
-          }
+          this.warn(e.message);
         }
       }
 
@@ -1792,10 +1575,7 @@ class Game {
     if (!suc) {
       alert(`Sorry, could not find a valid board setup after ${retry_count} retries.`);
     } else {
-      this.info(
-        `Board set up with ${retry_count} retries:\n` +
-        `teplate "${board_info.template.name}"` +
-        (this.cfg.allowTemplateAugmenting ? ` with ${board_info.tilesAdded} extra tiles` : ''));
+      this.info(`Board set up with ${retry_count} retries.`);
 
       if (this.cfg.logSolution) {
         this.info('Reference solution:\n  ' + board_info.solution.reduce((s, entry, i) => {
@@ -1816,6 +1596,306 @@ class Game {
   }
 }
 
+/**
+ * Base class for orb placer.
+ */
+class BaseOrbPlacer {
+  constructor(game, template) {
+    this.template = template;
+    this.rng = game.rng;
+    this.cfg = game.cfg;
+    this.game = game;
+    this.board = game.board;
+  }
+
+  /**
+   * Place an orb. The position must be inside template and free.
+   *
+   * @param n - position
+   * @param symbol - symbol to place
+   */
+  placeOrb(n, symbol) {
+    if (!this.templateMap[n]) {
+      throw Error(`Position ${n} not allowed by template`);
+    }
+    if (this.board.grid[n]) {
+      throw Error(`Position ${n} is occupied by ${this.board.grid[n]}`);
+    }
+    this.trace(`Place ${n} <- ${symbol}`);
+    this.board.grid[n] = symbol;
+  }
+
+  /**
+   * Remove an orb, if any.
+   *
+   * @param n - position
+   */
+  removeOrb(n) {
+    let old = this.board.grid[n];
+    this.board.grid[n] = null;
+    this.trace(`Unplace ${n} (${old})`);
+    return old;
+  }
+
+  /** Check if a cell is available for selection - 3 free slots */
+  isAvailable(n) {
+    return this.board.isAvailable(n);
+  }
+
+  /** Get cell info by number */
+  getCellInfo(n) {
+    return this.board.getCellInfo(n);
+  }
+
+  trace(...args) {
+    this.game.debug(...args);
+  }
+
+  debug(...args) {
+    this.game.debug(...args);
+  }
+
+  info(...args) {
+    this.game.info(...args);
+  }
+
+  warn(...args) {
+    this.game.warn(...args);
+  }
+
+  error(...args) {
+    this.game.error(...args);
+  }
+
+  /**
+   * Build a list of orbs in the right order.
+   * They are always grouped in matching pairs, and metals are always in
+   * the correct reaction order.
+   *
+   * @return {string[]}
+   */
+  buildPlacementList() {
+    let toPlace = [
+      ['air', 'air'],
+      ['air', 'air'],
+      ['air', 'air'],
+      ['air', 'air'],
+
+      ['fire', 'fire'],
+      ['fire', 'fire'],
+      ['fire', 'fire'],
+      ['fire', 'fire'],
+
+      ['water', 'water'],
+      ['water', 'water'],
+      ['water', 'water'],
+      ['water', 'water'],
+
+      ['earth', 'earth'],
+      ['earth', 'earth'],
+      ['earth', 'earth'],
+      ['earth', 'earth'],
+    ];
+
+    let newSaltedPairs = [];
+    const nsalted = this.rng.nextInt(2);
+    for (let i = 0; i < nsalted; i++) {
+      while (true) {
+        const n = this.rng.nextInt(toPlace.length - 1);
+        if (toPlace[n][1] !== 'salt') {
+          this.trace(`Pairing ${toPlace[n][1]} with salt.`);
+          newSaltedPairs.push([toPlace[n][1], 'salt']);
+          toPlace[n][1] = 'salt';
+          break;
+        }
+      }
+    }
+    toPlace = toPlace.concat(newSaltedPairs);
+    // if we have some salt pairs left
+    for (let i = 0; i < 2 - nsalted; i++) {
+      toPlace.push(['salt', 'salt']);
+    }
+
+    // shuffle the pairs that have random order (i.e. not metals)
+    this.rng.arrayShuffle(toPlace);
+
+    this.rng.arraySneak(toPlace, 3, 0, [
+      ['mors', 'vitae'],
+      ['mors', 'vitae'],
+      ['mors', 'vitae'],
+      ['mors', 'vitae'],
+    ]);
+
+    this.rng.arraySneak(toPlace, 4, 0, [
+      ['lead', 'mercury'],
+      ['tin', 'mercury'],
+      ['iron', 'mercury'],
+      ['copper', 'mercury'],
+      ['silver', 'mercury'],
+    ]);
+
+    this.debug('Placement order (last first):', toPlace);
+
+    return toPlace.reduce((a, c) => {
+      a.push(c[0]);
+      a.push(c[1]);
+      return a;
+    }, []);
+  }
+
+  /**
+   * Run the placement logic.
+   */
+  place() {
+    this.board.removeAllOrbs();
+    this.solution = [];
+
+    let allowedTable = [];
+    let outsideTemplate = [];
+    for (let i = 0; i < BOARD_SIZE; i++) {
+      const allo = this.template.includes(i);
+      allowedTable.push(allo);
+
+      let {x, y} = gridIndexToXy(i);
+      if (!allo && !isXyOutside(x, y)) {
+        outsideTemplate.push(i);
+      }
+
+      // Highlight pattern shape
+
+      if (this.cfg.highlightTemplate) {
+        if (this.board.tiles[i]) {
+          if (allo) {
+            this.board.tiles[i].setAttribute('opacity', 1)
+          } else {
+            this.board.tiles[i].setAttribute('opacity', 0.6)
+          }
+        }
+      }
+    }
+    this.templateMap = allowedTable;
+    this.outsideTemplate = outsideTemplate;
+
+    this.placeOrb(60, 'gold');
+    this.solution.push(['gold', 60]);
+
+    let toPlace = this.buildPlacementList();
+    let rv = this.doPlace(toPlace);
+
+    let solution = this.solution;
+
+    solution.reverse();
+    this.info("Found a valid board!");
+
+    solution.forEach((a) => {
+      let p = gridIndexToXy(a[1]);
+      a[1] = `${p.x}×${p.y}`;
+    });
+
+    this.debug('Solution:', solution);
+
+    rv.solution = solution;
+    return rv;
+  }
+
+  /**
+   * Perform the orbs placement.
+   *
+   * Orb symbols to place are given as an argument.
+   *
+   * The layout template is in `this.template`, also `this.templateMap` as an array
+   * with indices 0-121 containing true/false to indicate template membership.
+   *
+   * `this.outsideTemplate` is a list of cell indices that are not in the template.
+   *
+   * this.solution is an array to populate with orb placements in the format [n, symbol].
+   *
+   * The board is cleared now. When the function ends, the board should contain
+   * the new layout (as symbol name strings)
+   *
+   * After placing each orb, make sure to call `this.solution.push([symbol, index])`;
+   * in case of backtracking, pop it again.
+   *
+   * Return object to return to parent; 'solution' will be added automatically.
+   */
+  doPlace(toPlace) {
+    throw new Error("Not implemented");
+  }
+}
+
+class RecursiveOrbPlacer extends BaseOrbPlacer {
+  doPlace(toPlace) {
+    this.toPlace = toPlace;
+    this.recDepth = 0;
+
+    this.placeOne(0);
+
+    return {};
+  }
+
+  placeOne() {
+    this.recDepth++;
+    if (this.recDepth > 1000) {
+      throw new Error("Too many backtracks");
+    }
+
+    let symbol = this.toPlace.pop();
+
+    let candidates = [[],[],[],[],[],[],[]];
+    for (let n of this.template) {
+      if (!this.board.grid[n]) {
+        // is free
+        const cell = this.getCellInfo(n);
+        if (cell.freeSequence >= 3) {
+          candidates[cell.neighbours].push(n);
+        }
+      }
+    }
+
+    for (let neighs = 6; neighs >= 0; neighs--) {
+      this.rng.arrayShuffle(candidates[neighs]);
+    }
+
+    for (let i = 6; i >= 0; i--) {
+      if (candidates[i].length) {
+        for (let n of candidates[i]) {
+          this.placeOrb(n, symbol);
+
+          // avoid deadlocking
+          if (this.solution.length % 2 === 0) {
+            // this is the second orb in a pair (solution starts with gold)
+            let prevn = this.solution[this.solution.length-1][1];
+            if (!this.isAvailable(prevn)) {
+              this.trace("Avoid deadlock (this is the second of a pair)");
+              this.removeOrb(n);
+              continue;
+            }
+          }
+
+          this.solution.push([symbol, n]);
+
+          if (this.toPlace.length) {
+            if (this.placeOne()) {
+              return true;
+            } else {
+              this.trace("Undo and continue");
+              this.removeOrb(n);
+              this.solution.pop();
+              // and continue the iteration
+            }
+          } else {
+            return true;
+          }
+        }
+      }
+    }
+
+    // give it back
+    this.toPlace.push(symbol);
+    return false;
+  }
+}
+
 /* Start */
 
 window.game = new Game();
diff --git a/style.css b/style.css
index 1d2e6c4..705e8bb 100644
--- a/style.css
+++ b/style.css
@@ -122,6 +122,24 @@ text {
 	stroke-width: 2px;
 	cursor: pointer;
 }
+.button-text.working,
+.button-text.working:hover {
+	fill: #8d7761;
+	font-size: 26px;
+	opacity: 0;
+}
+
+.button-text.working {
+	transition: opacity linear 0.2s;
+}
+
+.cfg-no-anim .button-text.working {
+	transition: none;
+}
+
+.button-text.working.show {
+	opacity: 1;
+}
 
 .you-win {
 	font-size: 80px;
@@ -160,6 +178,8 @@ text {
 	transform: translateY(1px);
 }
 
+
+
 .button-text.disabled,
 .button-text.disabled:hover,
 .button-text.disabled:active {