src/main/java/net/glowstone/inventory/crafting/GlowBannerMatcher.java

package net.glowstone.inventory.crafting;

import org.bukkit.DyeColor;
import org.bukkit.Material;
import org.bukkit.block.banner.Pattern;
import org.bukkit.block.banner.PatternType;
import org.bukkit.inventory.ItemMatcher;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.BannerMeta;
import org.bukkit.material.Dye;

import java.util.List;

/**
 * Recipe for adding patterns to a banner item.
 */
public class GlowBannerMatcher extends ItemMatcher {

    ItemStack result = new ItemStack(Material.BANNER); // Default result

    @Override
    public ItemStack getResult(ItemStack[] matrix) {
        DyeColor color = null;
        Pattern texture = null;
        ItemStack banner = null;

        for (ItemStack item : matrix) {
            if (item == null) continue;
            if (item.getType() == Material.BANNER) {
                if (banner != null) {
                    return null; // Multiple banners found
                }
                banner = item;
                continue;
            }
            if (item.getType() == Material.INK_SACK) {
                DyeColor itemColor = ((Dye) item.getData()).getColor();
                if (color != null && itemColor != color) {
                    return null; // Can't have multiple colors
                }
                color = itemColor;
            }
        }
        if  (banner == null) {
            return null; // Couldn't found a banner to alter
        }

        recipe:
        for (LayerRecipe recipe : LayerRecipe.values()) {
            if (recipe.hasItem()) {
                boolean foundDye = false;
                for (ItemStack item : matrix) {
                    if (item == null) continue; // Ignore blanks

                    if (item.getType() == Material.BANNER) continue; // Banner is already checked

                    if (item.getType() == Material.INK_SACK) {
                        if (foundDye) continue recipe; // Can't have multiple dyes
                        foundDye = true;
                        continue;
                    }

                    if (item.getType() == recipe.getType() && item.getDurability() == recipe.getData()) {
                        if (texture != null) return null; // Can't have multiple of same item
                        texture = recipe.getPattern(); // Matches texture type
                        continue;
                    }
                    continue recipe; // Non-recipe item in grid
                }
                if (texture == null) {
                    continue; // No item type for this recipe found
                }
                if (color == null) {
                    color = DyeColor.BLACK;
                }
                break; // Recipe matches
            } else {
                if (matrix.length != 9) return null; // Non-item recipes only work on 3x3

                for (int i = 0; i < 9; i++) {
                    boolean hasValue = recipe.getValues()[i] == '#';
                    ItemStack item = matrix[i];
                    if (hasValue && item != null && item.getType() == Material.INK_SACK) {
                        continue;
                    }
                    if (!hasValue && (item == null || item.getType() == Material.BANNER)) {
                        continue; // Allow banner and blanks
                    }
                    continue recipe; // Non-recipe item found or no dye where dye should be
                }
                texture = recipe.getPattern();
                break; // Recipe matches
            }
        }

        if (texture == null) return null; // No texture found

        // Create result banner
        BannerMeta meta = (BannerMeta) banner.getItemMeta();
        List<Pattern> layers = meta.getPatterns();
        meta.setPatterns(layers);
        result = banner.clone();
        result.setItemMeta(meta);
        return result;
    }

    private enum LayerRecipe {
        BORDER("###", "# #", "###"),
        BOTTOM_HALF("   ", "###", "###"),
        BRICK(Material.BRICK),
        CIRCLE("   ", " # ", "   "),
        CREEPER(Material.SKULL_ITEM, (short) 4),
        CURLY_BORDER(Material.VINE),
        DIAGONAL_CROSS("# #", " # ", "# #"),
        FLOWER(Material.RED_ROSE, (short) 8),
        GRADIENT("# #", " # ", " # "),
        GRADIENT_UP(" # ", " # ", "# #"),
        LEFT_HALF("## ", "## ", "## "),
        MOJANG(Material.GOLDEN_APPLE),
        RIGHT_HALF(" ##", " ##", " ##"),
        RHOMBUS(" # ", "# #", " # "),
        SAW_BOTTOM("   ", "# #", " # "),
        SAW_TOP(" # ", "# #", "   "),
        SKULL(Material.SKULL_ITEM, (short) 1),
        STRIPES("# #", "# #", "   "),
        SQUARE_BOTTOM_LEFT("   ", "   ", "#  "),
        SQUARE_BOTTOM_RIGHT("   ", "   ", "  #"),
        SQUARE_TOP_LEFT("#  ", "   ", "   "),
        SQUARE_TOP_RIGHT("  #", "   ", "   "),
        STRIPE_BOTTOM("   ", "   ", "###"),
        STRAIGHT_CROSS(" # ", "###", " # "),
        STRIPE_DOWN_LEFT("  #", " # ", "#  "),
        STRIPE_DOWN_RIGHT("#  ", " # ", "  #"),
        STRIPE_LEFT("#  ", "#  ", "#  "),
        STRIPE_HORIZONTAL("   ", "###", "   "),
        STRIPE_RIGHT("  #", "  #", "  #"),
        STRIPE_TOP("###", "   ", "   "),
        STRIPE_VERTICAL(" # ", " # ", " # "),
        TOP_HALF("###", "###", "   "),
        TRIANGLE_BOTTOM("   ", " # ", "# #"),
        TRIANGLE_BOTTOM_LEFT("   ", "#  ", "## "),
        TRIANGLE_BOTTOM_RIGHT("   ", "  #", " ##"),
        TRIANGLE_TOP("# #", " # ", "   "),
        TRIANGLE_TOP_LEFT("## ", "#  ", "   "),
        TRIANGLE_TOP_RIGHT(" ##", "  #", "   ");

        char[] values;
        Material item;
        short data;

        private LayerRecipe(String... rows) {
            values = new char[9];
            int index = 0;
            for (String row : rows) {
                for (char c : row.toCharArray()) {
                    values[index++] = c;
                }
            }
        }

        private LayerRecipe(Material item) {
            this.item = item;
        }

        private LayerRecipe(Material item, short data) {
            this.item = item;
            this.data = data;
        }

        public char[] getValues() {
            return values;
        }

        public boolean hasItem() {
            return item != null;
        }

        public Material getType() {
            return item;
        }

        public short getData() {
            return data;
        }

        public Pattern getPattern() {
            DyeColor dyeColor = DyeColor.getByDyeData((byte) data);
            PatternType patternType = PatternType.getByIdentifier(this.toString());
            return new Pattern(dyeColor, patternType);
        }
    }
}