/*
 * Copyright 2002-present the original author or authors.
 *
 * Licensed 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
 *
 *      https://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.grails.undertow.core.reactive;

import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;

import io.undertow.util.HeaderMap;
import io.undertow.util.HeaderValues;
import io.undertow.util.HttpString;

import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;
import org.springframework.util.MultiValueMap;

/**
 * {@code MultiValueMap} implementation for wrapping Undertow HTTP headers.
 *
 * @author Brian Clozel
 * @author Sam Brannen
 * @since 5.1.1
 */
class UndertowHeadersAdapter implements MultiValueMap<String, String> {

    private final HeaderMap headers;

    UndertowHeadersAdapter(HeaderMap headers) {
        this.headers = headers;
    }

    @Override
    public String getFirst(String key) {
        return this.headers.getFirst(key);
    }

    @Override
    public void add(String key, @Nullable String value) {
        this.headers.add(HttpString.tryFromString(key), value);
    }

    @Override
    @SuppressWarnings("unchecked")
    public void addAll(String key, List<? extends String> values) {
        this.headers.addAll(HttpString.tryFromString(key), (List<String>) values);
    }

    @Override
    public void addAll(MultiValueMap<String, String> values) {
        values.forEach((key, list) -> this.headers.addAll(HttpString.tryFromString(key), list));
    }

    @Override
    public void set(String key, @Nullable String value) {
        this.headers.put(HttpString.tryFromString(key), value);
    }

    @Override
    public void setAll(Map<String, String> values) {
        values.forEach((key, list) -> this.headers.put(HttpString.tryFromString(key), list));
    }

    @Override
    public Map<String, String> toSingleValueMap() {
        Map<String, String> singleValueMap = CollectionUtils.newLinkedHashMap(this.headers.size());
        this.headers.forEach(values ->
            singleValueMap.put(values.getHeaderName().toString(), values.getFirst()));
        return singleValueMap;
    }

    @Override
    public int size() {
        return this.headers.size();
    }

    @Override
    public boolean isEmpty() {
        return (this.headers.size() == 0);
    }

    @Override
    public boolean containsKey(Object key) {
        return (key instanceof String headerName && this.headers.contains(headerName));
    }

    @Override
    public boolean containsValue(Object value) {
        return (value instanceof String &&
            this.headers.getHeaderNames().stream()
                .map(this.headers::get)
                .anyMatch(values -> values.contains(value)));
    }

    @Override
    @Nullable
    public List<String> get(Object key) {
        return (key instanceof String headerName ? this.headers.get(headerName) : null);
    }

    @Override
    @Nullable
    public List<String> put(String key, List<String> value) {
        HeaderValues previousValues = this.headers.get(key);
        this.headers.putAll(HttpString.tryFromString(key), value);
        return previousValues;
    }

    @Override
    @Nullable
    public List<String> remove(Object key) {
        if (key instanceof String headerName && this.headers.contains(headerName)) {
            Collection<String> removed = this.headers.remove(headerName);
            if (removed != null) {
                return new ArrayList<>(removed);
            }
        }
        return null;
    }

    @Override
    public void putAll(Map<? extends String, ? extends List<String>> map) {
        map.forEach((key, values) ->
            this.headers.putAll(HttpString.tryFromString(key), values));
    }

    @Override
    public void clear() {
        this.headers.clear();
    }

    @Override
    public Set<String> keySet() {
        return new HeaderNames();
    }

    @Override
    public Collection<List<String>> values() {
        return this.headers.getHeaderNames().stream()
            .map(this.headers::get)
            .collect(Collectors.toList());
    }

    @Override
    public Set<Entry<String, List<String>>> entrySet() {
        return new AbstractSet<>() {
            @Override
            public Iterator<Entry<String, List<String>>> iterator() {
                return new EntryIterator();
            }

            @Override
            public int size() {
                return headers.size();
            }
        };
    }

    @Override
    public String toString() {
        return org.springframework.http.HttpHeaders.formatHeaders(this);
    }

    private class EntryIterator implements Iterator<Entry<String, List<String>>> {

        private final Iterator<HttpString> names = headers.getHeaderNames().iterator();

        @Override
        public boolean hasNext() {
            return this.names.hasNext();
        }

        @Override
        public Entry<String, List<String>> next() {
            return new HeaderEntry(this.names.next());
        }
    }

    private class HeaderEntry implements Entry<String, List<String>> {

        private final HttpString key;

        HeaderEntry(HttpString key) {
            this.key = key;
        }

        @Override
        public String getKey() {
            return this.key.toString();
        }

        @Override
        public List<String> getValue() {
            return headers.get(this.key);
        }

        @Override
        public List<String> setValue(List<String> value) {
            List<String> previousValues = headers.get(this.key);
            headers.putAll(this.key, value);
            return previousValues;
        }
    }

    private class HeaderNames extends AbstractSet<String> {

        @Override
        public Iterator<String> iterator() {
            return new HeaderNamesIterator(headers.getHeaderNames().iterator());
        }

        @Override
        public int size() {
            return headers.getHeaderNames().size();
        }
    }

    private final class HeaderNamesIterator implements Iterator<String> {

        private final Iterator<HttpString> iterator;

        @Nullable
        private String currentName;

        private HeaderNamesIterator(Iterator<HttpString> iterator) {
            this.iterator = iterator;
        }

        @Override
        public boolean hasNext() {
            return this.iterator.hasNext();
        }

        @Override
        public String next() {
            this.currentName = this.iterator.next().toString();
            return this.currentName;
        }

        @Override
        public void remove() {
            if (this.currentName == null) {
                throw new IllegalStateException("No current Header in iterator");
            }
            if (!headers.contains(this.currentName)) {
                throw new IllegalStateException("Header not present: " + this.currentName);
            }
            headers.remove(this.currentName);
        }
    }

}
