/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.juneau.console;

import static java.nio.charset.StandardCharsets.*;

import java.io.*;
import java.util.*;

import org.apache.juneau.marshall.collections.*;

/**
 * Loads {@code juneau-page.schema.json} from the classpath and validates contracts against it, plus
 * the cross-reference rules R-1..R-4 the schema cannot express. Used by {@code PageCapture} in dev
 * mode and by {@code PageContractAssert} in tests.
 *
 * <h5 class='section'>Example:</h5>
 * <p class='bjava'>
 *    List&lt;String&gt; <jv>errors</jv> = PageContractSchema.<jsm>get</jsm>().validate(<jv>contractJson</jv>);
 *    <jk>if</jk> (! <jv>errors</jv>.isEmpty())
 *       <jk>throw new</jk> IllegalStateException(String.<jsm>join</jsm>(<js>"\n"</js>, <jv>errors</jv>));
 *
 *    <jc>// With the &lt;template&gt; ids found in the rendered page, R-4 is checked too:</jc>
 *    <jv>errors</jv> = PageContractSchema.<jsm>get</jsm>().validate(<jv>contractJson</jv>, Set.<jsm>of</jsm>(<js>"jc-seg-1"</js>, <js>"header.banner"</js>));
 * </p>
 *
 * @since 10.0.0
 */
@SuppressWarnings({
   "unchecked" // validate() casts the parsed JSON contract (nav, cards, activeNav) to List/Map, after the schema validator has checked those shapes
})
public final class PageContractSchema {

   /** Classpath location of the schema. */
   public static final String RESOURCE = "org/apache/juneau/console/juneau-page.schema.json";

   private static final PageContractSchema INSTANCE = new PageContractSchema();

   private final String schemaJson;
   private final SchemaSubsetValidator validator;

   private PageContractSchema() {
      try (var in = PageContractSchema.class.getClassLoader().getResourceAsStream(RESOURCE)) {
         if (in == null)
            throw new IllegalStateException("Missing classpath resource: " + RESOURCE);
         schemaJson = new String(in.readAllBytes(), UTF_8);
         validator = new SchemaSubsetValidator(JsonMap.ofString(schemaJson));
      } catch (IOException e) {
         throw new UncheckedIOException(e);
      } catch (Exception e) {
         throw new IllegalStateException("Unparseable " + RESOURCE, e);
      }
   }

   /**
    * Returns the shared instance.
    *
    * @return The shared instance, never <jk>null</jk>.
    */
   public static PageContractSchema get() {
      return INSTANCE;
   }

   /**
    * Returns the schema text exactly as shipped.
    *
    * @return The schema JSON.
    */
   public String schemaJson() {
      return schemaJson;
   }

   /**
    * Validates a contract against the schema and rules R-1..R-3.
    *
    * @param contractJson The contract JSON.
    * @return The findings, empty when valid.
    */
   public List<String> validate(String contractJson) {
      return validate(contractJson, null);
   }

   /**
    * Validates a contract against the schema and rules R-1..R-4.
    *
    * @param contractJson The contract JSON.
    * @param templateIds The {@code <template data-card|data-slot>} ids present in the page, or <jk>null</jk> to skip R-4.
    * @return The findings, empty when valid.
    */
   @SuppressWarnings({
      "java:S3776" // Rules R-1..R-4 read best as one straight-line pass.
   })
   public List<String> validate(String contractJson, Set<String> templateIds) {
      Map<String,Object> c;
      try {
         c = JsonMap.ofString(contractJson);
      } catch (Exception e) {
         return List.of("$: unparseable JSON: " + e.getMessage());
      }
      var errors = new ArrayList<>(validator.validate(c));
      if (! errors.isEmpty())
         return errors;
      var nav = (List<Object>)c.get("nav");
      checkSiblingIds(nav, "nav", errors);                                   // R-1
      var cardIds = new HashSet<String>();
      for (var o : (List<Object>)c.get("cards")) {                           // R-2
         var id = (String)((Map<String,Object>)o).get("id");
         if (! cardIds.add(id))
            errors.add("R-2: duplicate card id '" + id + "'");
      }
      var level = nav;                                                        // R-3
      for (var id : (List<String>)c.get("activeNav")) {
         var next = level == null ? null : level.stream().map(x -> (Map<String,Object>)x)
            .filter(n -> id.equals(n.get("id"))).findFirst().orElse(null);
         if (next == null) {
            errors.add("R-3: activeNav " + c.get("activeNav") + " is not a path in nav (failed at '" + id + "')");
            break;
         }
         level = (List<Object>)next.get("children");
      }
      if (templateIds != null)                                                // R-4
         for (var ref : templateRefs(c))
            if (! templateIds.contains(ref))
               errors.add("R-4: template '" + ref + "' is referenced but not present");
      return errors;
   }

   private static void checkSiblingIds(List<Object> nodes, String where, List<String> errors) {
      if (nodes == null)
         return;
      var seen = new HashSet<String>();
      for (var o : nodes) {
         var n = (Map<String,Object>)o;
         var id = (String)n.get("id");
         if (! seen.add(id))
            errors.add("R-1: duplicate nav id '" + id + "' under " + where);
         checkSiblingIds((List<Object>)n.get("children"), where + "/" + id, errors);
      }
   }

   static List<String> templateRefs(Map<String,Object> c) {
      var refs = new ArrayList<String>();
      for (var scope : List.of("header", "footer")) {
         var sec = (Map<String,Object>)c.get(scope);
         if (sec != null && sec.get("slots") instanceof Map<?,?> slots)
            for (var v : slots.values())
               refs.add((String)v);
      }
      for (var o : (List<Object>)c.get("cards")) {
         var t = ((Map<String,Object>)o).get("template");
         if (t != null)
            refs.add((String)t);
      }
      return refs;
   }
}