Add a second type of player with a different strategy.

exceptions/IllegalArgumentException.php

@@ -0,0 +1,4 @@
+<?php
+
+class IllegalArgumentException extends Exception {
+}

line.php

@@ -42,6 +42,39 @@ public function length() {
     return count($this->placements);
   }
 
+  public function contains($searchTile) {
+    foreach ($this->tiles() as $tile) {
+      if ($tile === $searchTile) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  public function sharedProperty() {
+    $sharedProperty = null;
+    foreach (Color::colors() as $color) {
+      foreach ($this->tiles() as $tile) {
+        if ($sharedProperty === null || $sharedProperty === $tile->color()) {
+          $sharedProperty = $tile->color();
+        } else {
+          $sharedProperty = null;
+          break 2;
+        }
+      }
+    }
+    foreach (Shape::shapes() as $shape) {
+      foreach ($this->tiles() as $tile) {
+        if ($sharedProperty === null || $sharedProperty === $tile->shape()) {
+          $sharedProperty = $tile->shape();
+        } else {
+          return null;
+        }
+      }
+    }
+    return $sharedProperty;
+  }
+
   public function __toString() {
     $a = [];
     foreach ($this->placements as $placement) {

player.php

@@ -65,15 +65,16 @@ public function move(Board $board, $bagIsEmpty) {
     if ($board->isEmpty()) {
       return $this->startingMove($tiles);
     }
+    return $this->chooseMove($tiles, $board, $bagIsEmpty);
+  }
+
+  protected function chooseMove(array $tiles, Board $board, $bagIsEmpty) {
     $usefulSets = $this->usefulSets($tiles);
     list($max, $bestMove) = [0, new Move([])];
     foreach ($usefulSets as $usefulSet) {
       $move = $this->bestMoveWith($usefulSet, $board);
       if ($move) {
-        $score = $board->score($move);
-        if (count($move->placements()) === count($tiles) && $bagIsEmpty) {
-          $score += Score::FINISHING_BONUS;
-        }
+        $score = $this->evaluate($tiles, $move, $board, $bagIsEmpty);
         if ($score > $max) {
           $max = $score;
           $bestMove = $move;
@@ -83,6 +84,14 @@ public function move(Board $board, $bagIsEmpty) {
     return $bestMove;
   }
 
+  protected function evaluate(array $tiles, Move $move, Board $board, $bagIsEmpty) {
+    $score = $board->score($move);
+    if (count($move->placements()) === count($tiles) && $bagIsEmpty) {
+      $score += Score::FINISHING_BONUS;
+    }
+    return $score;
+  }
+
   private function usefulSets(array $tiles) {
     Assert::type($tiles, Tile);
     if (array_unique($tiles) !== $tiles) {

players/cautiousplayer.php

@@ -0,0 +1,65 @@
+<?php
+
+class CautiousPlayer extends Player {
+  public function evaluate(array $tiles, Move $move, Board $board, $bagIsEmpty) {
+    $score = $board->score($move);
+    if (count($move->placements()) === count($tiles) && $bagIsEmpty) {
+      $score += Score::FINISHING_BONUS;
+    } elseif ($this->enablesQwirkle($move, $board, $bagIsEmpty) && $score < 9) {
+      $score -= 3.5;
+    }
+    return $score;
+  }
+
+  private function enablesQwirkle(Move $move, Board $board, $bagIsEmpty) {
+    foreach ($move->lines($board) as $line) {
+      if ($line->length() === count(Color::colors()) - 1) {
+        $missingPiece = $this->missingPieces($line)[0];
+        if ($this->notAccountedFor($missingPiece, $board)) {
+          return false;
+        }
+      }
+    }
+    return false;
+  }
+
+  private function missingPieces($line) {
+    if ($line->length() <= 1) {
+      throw new IllegalArgumentException("Qwirkle this lines is part of is ambiguous ($line).");
+    }
+    $sharedProperty = $line->sharedProperty();
+    if ($sharedProperty === null) {
+      throw new IllegalArgumentException("This line does not have a shared property ($line).");
+    }
+    $missing = [];
+    if (get_class($sharedProperty) === Shape) {
+      foreach (Color::colors() as $color) {
+        $tile = Tile::getTile($color, $sharedProperty);
+        if (!$line->contains($tile)) {
+          $missing[] = $tile;
+        }
+      }
+    } elseif (get_class($sharedProperty) === Color) {
+      foreach (Shape::shapes() as $shape) {
+        $tile = Tile::getTile($sharedProperty, $shape);
+        if (!$line->contains($tile)) {
+          $missing[] = $tile;
+        }
+      }
+    } else {
+      throw new IllegalArgumentException("Unrecognized property $sharedProperty");
+    }
+    return $missing;
+  }
+
+  private function notAccountedFor($searchTile, Board $board) {
+    $tiles = Tile::allTiles();
+    foreach ($board->tiles() as $tile) {
+      if ($tile === $searchTile) {
+        $pos = array_search($tile, $tiles);
+        unset($tiles[$pos]);
+      }
+    }
+    return in_array($tile, $tiles);
+  }
+}