using Implab.Formats.Json;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Xml;

namespace Implab.Xml {
    public class JsonXmlReader : XmlReader {
        struct JsonContext {
            public string localName;
            public bool skip;
        }

        JsonReader m_parser;
        JsonXmlReaderOptions m_options;
        JsonXmlReaderPosition m_position = JsonXmlReaderPosition.Initial;
        XmlNameTable m_nameTable;

        readonly string m_jsonRootName;
        readonly string m_jsonNamespace;
        readonly string m_jsonPrefix;
        readonly bool m_jsonFlattenArrays;
        readonly string m_jsonArrayItemName;

        string m_jsonLocalName;
        string m_jsonValueName;
        bool m_jsonSkip; // indicates wheather to generate closing tag for objects or arrays

        readonly Stack<JsonContext> m_jsonNameStack = new Stack<JsonContext>();

        XmlQualifiedName m_elementQName;
        string m_elementPrefix;
        int m_elementDepth;
        bool m_elementIsEmpty;

        XmlQualifiedName m_qName;
        string m_prefix;
        int m_xmlDepth;

        XmlSimpleAttribute[] m_attributes;
        string m_value;
        bool m_isEmpty;

        XmlNodeType m_nodeType = XmlNodeType.None;

        bool m_isAttribute; // indicates that we are reading attribute nodes
        int m_currentAttribute;
        bool m_currentAttributeRead;


        XmlNameContext m_context;

        readonly string m_xmlnsPrefix;
        readonly string m_xmlnsNamespace;
        readonly string m_xsiPrefix;
        readonly string m_xsiNamespace;


        public JsonXmlReader(JsonReader parser, JsonXmlReaderOptions options) {
            Safe.ArgumentNotNull(parser, nameof(parser));
            m_parser = parser;

            m_options = options ?? new JsonXmlReaderOptions();

            m_jsonFlattenArrays = m_options.FlattenArrays;
            m_nameTable = m_options.NameTable ?? new NameTable();

            m_jsonRootName = m_nameTable.Add(string.IsNullOrEmpty(m_options.RootName) ? "data" : m_options.RootName);
            m_jsonArrayItemName = m_nameTable.Add(string.IsNullOrEmpty(m_options.ArrayItemName) ? "item" : m_options.ArrayItemName);
            m_jsonNamespace = m_nameTable.Add(m_options.NamespaceUri ?? string.Empty);
            m_jsonPrefix = m_nameTable.Add(m_options.NodesPrefix ?? string.Empty);
            m_xmlnsPrefix = m_nameTable.Add(XmlNameContext.XmlnsPrefix);
            m_xmlnsNamespace = m_nameTable.Add(XmlNameContext.XmlnsNamespace);
            m_xsiPrefix = m_nameTable.Add(XmlNameContext.XsiPrefix);
            m_xsiNamespace = m_nameTable.Add(XmlNameContext.XsiNamespace);

            // TODO validate m_jsonRootName, m_jsonArrayItemName

            m_context = new XmlNameContext(null, 0);
        }

        public override int AttributeCount {
            get {
                return m_attributes == null ? 0 : m_attributes.Length;
            }
        }

        public override string BaseURI {
            get {
                return string.Empty;
            }
        }

        public override int Depth {
            get {
                return m_xmlDepth;
            }
        }

        public override bool EOF {
            get {
                return m_position == JsonXmlReaderPosition.Eof;
            }
        }

        public override bool IsEmptyElement {
            get { return m_isEmpty; }
        }


        public override string LocalName {
            get {
                return m_qName.Name;
            }
        }

        public override string NamespaceURI {
            get {
                return m_qName.Namespace;
            }
        }

        public override XmlNameTable NameTable {
            get {
                return m_nameTable;
            }
        }

        public override XmlNodeType NodeType {
            get {
                return m_nodeType;
            }
        }

        public override string Prefix {
            get {
                return m_prefix;
            }
        }

        public override ReadState ReadState {
            get {
                switch (m_position) {
                    case JsonXmlReaderPosition.Initial:
                        return ReadState.Initial;
                    case JsonXmlReaderPosition.Eof:
                        return ReadState.EndOfFile;
                    case JsonXmlReaderPosition.Closed:
                        return ReadState.Closed;
                    case JsonXmlReaderPosition.Error:
                        return ReadState.Error;
                    default:
                        return ReadState.Interactive;
                };
            }
        }

        public override string Value {
            get {
                return m_value;
            }
        }
        
        public override string GetAttribute(int i) {
            Safe.ArgumentInRange(i, 0, AttributeCount - 1, nameof(i));
            return m_attributes[i].Value;
        }

        public override string GetAttribute(string name) {
            if (m_attributes == null)
                return null;
            var qName = m_context.Resolve(name);
            var attr = Array.Find(m_attributes, x => x.QName == qName);
            var value = attr?.Value;
            return value == string.Empty ? null : value;
        }

        public override string GetAttribute(string name, string namespaceURI) {
            if (m_attributes == null)
                return null;
            var qName = new XmlQualifiedName(name, namespaceURI);
            var attr = Array.Find(m_attributes, x => x.QName == qName);
            var value = attr?.Value;
            return value == string.Empty ? null : value;
        }

        public override string LookupNamespace(string prefix) {
            return m_context.ResolvePrefix(prefix);
        }

        public override bool MoveToAttribute(string name) {
            if (m_attributes == null || m_attributes.Length == 0)
                return false;

            var qName = m_context.Resolve(name);
            var index = Array.FindIndex(m_attributes, x => x.QName == qName);
            if (index >= 0) {
                MoveToAttributeImpl(index);
                return true;
            }
            return false;
        }

        public override bool MoveToAttribute(string name, string ns) {
            if (m_attributes == null || m_attributes.Length == 0)
                return false;

            var qName = m_context.Resolve(name);
            var index = Array.FindIndex(m_attributes, x => x.QName == qName);
            if (index >= 0) {
                MoveToAttributeImpl(index);
                return true;
            }
            return false;
        }

        void MoveToAttributeImpl(int i) {
            if (!m_isAttribute) {
                m_elementQName = m_qName;
                m_elementDepth = m_xmlDepth;
                m_elementPrefix = m_prefix;
                m_elementIsEmpty = m_isEmpty;
                m_isAttribute = true;
            }
            
            var attr = m_attributes[i];


            m_currentAttribute = i;
            m_currentAttributeRead = false;
            m_nodeType = XmlNodeType.Attribute;

            m_xmlDepth = m_elementDepth + 1;
            m_qName = attr.QName;
            m_value = attr.Value;
            m_prefix = attr.Prefix;
        }

        public override bool MoveToElement() {
            if (m_isAttribute) {
                m_value = null;
                m_nodeType = XmlNodeType.Element;
                m_xmlDepth = m_elementDepth;
                m_prefix = m_elementPrefix;
                m_qName = m_elementQName;
                m_isEmpty = m_elementIsEmpty;
                m_isAttribute = false;
                return true;
            }
            return false;
        }

        public override bool MoveToFirstAttribute() {
            if (m_attributes != null && m_attributes.Length > 0) {
                MoveToAttributeImpl(0);
                return true;
            }
            return false;
        }

        public override bool MoveToNextAttribute() {
            if (m_isAttribute) {
                var next = m_currentAttribute + 1;
                if (next < AttributeCount) {
                    MoveToAttributeImpl(next);
                    return true;
                }
                return false;
            } else {
                return MoveToFirstAttribute();
            }

        }

        public override bool ReadAttributeValue() {
            if (!m_isAttribute || m_currentAttributeRead)
                return false;

            ValueNode(m_attributes[m_currentAttribute].Value);
            m_currentAttributeRead = true;
            return true;
        }

        public override void ResolveEntity() {
            /* do nothing */
        }

        /// <summary>
        /// Determines do we need to increase depth after the current node
        /// </summary>
        /// <returns></returns>
        public bool IsSibling() {
            switch (m_nodeType) {
                case XmlNodeType.None: // start document
                case XmlNodeType.Attribute: // after attribute only it's content can be iterated with ReadAttributeValue method
                    return false;
                case XmlNodeType.Element:
                    // if the elemnt is empty the next element will be it's sibling
                    return m_isEmpty;
                default:
                    return true;
            }
        }

        void ValueNode(string value) {
            if (!IsSibling()) // the node is nested
                m_xmlDepth++;

            m_qName = XmlQualifiedName.Empty;
            m_nodeType = XmlNodeType.Text;
            m_prefix = string.Empty;
            m_value = value;
            m_isEmpty = false;
            m_attributes = null;
        }

        void ElementNode(string name, string ns, XmlSimpleAttribute[] attrs, bool empty) {
            if (!IsSibling()) // the node is nested
                m_xmlDepth++;

            var context = m_context;
            List<XmlSimpleAttribute> definedAttrs = null;

            // define new namespaces
            if (attrs != null) {
                foreach (var attr in attrs) {
                    if (attr.QName.Name == "xmlns") {
                        if (context == m_context)
                             context = new XmlNameContext(m_context, m_xmlDepth);
                        context.DefinePrefix(attr.Value, string.Empty);
                    } else if (attr.Prefix == m_xmlnsPrefix) {
                        if (context == m_context)
                            context = new XmlNameContext(m_context, m_xmlDepth);
                        context.DefinePrefix(attr.Value, attr.QName.Name);
                    } else {
                        string attrPrefix;
                        if (string.IsNullOrEmpty(attr.QName.Namespace))
                            continue;

                        // auto-define prefixes
                        if (!context.LookupNamespacePrefix(attr.QName.Namespace, out attrPrefix) || string.IsNullOrEmpty(attrPrefix)) {
                            // new namespace prefix added
                            attrPrefix = context.CreateNamespacePrefix(attr.QName.Namespace);
                            attr.Prefix = attrPrefix;

                            if (definedAttrs == null)
                                definedAttrs = new List<XmlSimpleAttribute>();

                            definedAttrs.Add(new XmlSimpleAttribute(attrPrefix, m_xmlnsNamespace, m_xmlnsPrefix, attr.QName.Namespace));
                        }
                    }
                }
            }

            string p;
            // auto-define prefixes
            if (!context.LookupNamespacePrefix(ns, out p)) {
                if (context == m_context)
                    context = new XmlNameContext(m_context, m_xmlDepth);
                p = context.CreateNamespacePrefix(ns);
                if (definedAttrs == null)
                    definedAttrs = new List<XmlSimpleAttribute>();

                definedAttrs.Add(new XmlSimpleAttribute(p, m_xmlnsNamespace, m_xmlnsPrefix, ns));
            }

            if (definedAttrs != null) {
                if (attrs != null)
                    definedAttrs.AddRange(attrs);
                attrs = definedAttrs.ToArray();
            }

            if (!empty)
                m_context = context;

            m_nodeType = XmlNodeType.Element;
            m_qName = new XmlQualifiedName(name, ns);
            m_prefix = p;
            m_value = null;
            m_isEmpty = empty;
            m_attributes = attrs;
        }

        void EndElementNode(string name, string ns) {
            if (IsSibling()) {
                // closing the element which has children
                m_xmlDepth--;
            }

            string p;
            if (!m_context.LookupNamespacePrefix(ns, out p))
                throw new Exception($"Failed to lookup namespace '{ns}'");

            if (m_context.Depth == m_xmlDepth)
                m_context = m_context.ParentContext;

            m_nodeType = XmlNodeType.EndElement;
            m_prefix = p;
            m_qName = new XmlQualifiedName(name, ns);
            m_value = null;
            m_attributes = null;
            m_isEmpty = false;
        }

        void XmlDeclaration() {
            if (!IsSibling()) // the node is nested
                m_xmlDepth++;
            m_nodeType = XmlNodeType.XmlDeclaration;
            m_qName = new XmlQualifiedName("xml");
            m_value = "version='1.0'";
            m_prefix = string.Empty;
            m_attributes = null;
            m_isEmpty = false;
        }

        public override bool Read() {
            try {
                string elementName;
                XmlSimpleAttribute[] elementAttrs = null;
                MoveToElement();

                switch (m_position) {
                    case JsonXmlReaderPosition.Initial:
                        m_jsonLocalName = m_jsonRootName;
                        m_jsonSkip = false;
                        XmlDeclaration();
                        m_position = JsonXmlReaderPosition.Declaration;
                        return true;
                    case JsonXmlReaderPosition.Declaration:
                        elementAttrs = new[] {
                            new XmlSimpleAttribute(m_xsiPrefix, m_xmlnsNamespace, m_xmlnsPrefix, m_xsiNamespace),
                            string.IsNullOrEmpty(m_jsonPrefix) ?
                                new XmlSimpleAttribute(m_xmlnsPrefix, string.Empty, string.Empty, m_jsonNamespace) :
                                new XmlSimpleAttribute(m_jsonPrefix, m_xmlnsNamespace, m_xmlnsPrefix, m_jsonNamespace)
                        };
                        break;
                    case JsonXmlReaderPosition.ValueElement:
                        if (!m_isEmpty) {
                            if (m_parser.ElementValue != null && !m_parser.ElementValue.Equals(string.Empty))
                                ValueNode(m_parser.ElementValue);
                            else
                                goto case JsonXmlReaderPosition.ValueContent;
                            m_position = JsonXmlReaderPosition.ValueContent;
                            return true;
                        } else {
                            m_position = JsonXmlReaderPosition.ValueEndElement;
                            break;
                        }
                    case JsonXmlReaderPosition.ValueContent:
                        EndElementNode(m_jsonValueName, m_jsonNamespace);
                        m_position = JsonXmlReaderPosition.ValueEndElement;
                        return true;
                    case JsonXmlReaderPosition.Eof:
                    case JsonXmlReaderPosition.Closed:
                    case JsonXmlReaderPosition.Error:
                        return false;
                }

                while (m_parser.Read()) {
                    var jsonName = m_nameTable.Add(m_parser.ElementName);

                    switch (m_parser.ElementType) {
                        case JsonElementType.BeginObject:
                            if (!EnterJsonObject(jsonName, out elementName))
                                continue;

                            m_position = JsonXmlReaderPosition.BeginObject;
                            ElementNode(elementName, m_jsonNamespace, elementAttrs, false);
                            break;
                        case JsonElementType.EndObject:
                            if (!LeaveJsonScope(out elementName))
                                continue;

                            m_position = JsonXmlReaderPosition.EndObject;
                            EndElementNode(elementName, m_jsonNamespace);
                            break;
                        case JsonElementType.BeginArray:
                            if (!EnterJsonArray(jsonName, out elementName))
                                continue;

                            m_position = JsonXmlReaderPosition.BeginArray;
                            ElementNode(elementName, m_jsonNamespace, elementAttrs, false);
                            break;
                        case JsonElementType.EndArray:
                            if (!LeaveJsonScope(out elementName))
                                continue;

                            m_position = JsonXmlReaderPosition.EndArray;
                            EndElementNode(elementName, m_jsonNamespace);
                            break;
                        case JsonElementType.Value:
                            if (!VisitJsonValue(jsonName, out m_jsonValueName))
                                continue;

                            m_position = JsonXmlReaderPosition.ValueElement;
                            if (m_parser.ElementValue == null)
                                // generate empty element with xsi:nil="true" attribute
                                ElementNode(
                                    m_jsonValueName,
                                    m_jsonNamespace,
                                    new[] {
                                        new XmlSimpleAttribute("nil", m_xsiNamespace, m_xsiPrefix, "true")
                                    },
                                    true
                                );
                            else
                                ElementNode(m_jsonValueName, m_jsonNamespace, elementAttrs, m_parser.ElementValue.Equals(string.Empty));
                            break;
                        default:
                            throw new Exception($"Unexpected JSON element {m_parser.ElementType}: {m_parser.ElementName}");
                    }
                    return true;
                }

                m_position = JsonXmlReaderPosition.Eof;
                return false;
            } catch {
                m_position = JsonXmlReaderPosition.Error;
                throw;
            }
        }

        void SaveJsonName() {
            m_jsonNameStack.Push(new JsonContext {
                skip = m_jsonSkip,
                localName = m_jsonLocalName
            });

        }

        bool EnterJsonObject(string name, out string elementName) {
            SaveJsonName();
            m_jsonSkip = false;

            if (string.IsNullOrEmpty(name)) {
                if (m_jsonNameStack.Count != 1 && !m_jsonFlattenArrays)
                    m_jsonLocalName = m_jsonArrayItemName;
            } else {
                m_jsonLocalName = name;
            }

            elementName = m_jsonLocalName;
            return true;
        }

        /// <summary>
        /// Called when JSON parser visits BeginArray ('[') element.
        /// </summary>
        /// <param name="name">Optional property name if the array is the member of an object</param>
        /// <returns>true if element should be emited, false otherwise</returns>
        bool EnterJsonArray(string name, out string elementName) {
            SaveJsonName();

            if (string.IsNullOrEmpty(name)) {
                // m_jsonNameStack.Count == 1 means the root node
                if (m_jsonNameStack.Count != 1 && !m_jsonFlattenArrays)
                    m_jsonLocalName = m_jsonArrayItemName;

                m_jsonSkip = false; // we should not flatten arrays inside arrays or in the document root
            } else {
                m_jsonLocalName = name;
                m_jsonSkip = m_jsonFlattenArrays;
            }
            elementName = m_jsonLocalName;

            return !m_jsonSkip;
        }

        bool VisitJsonValue(string name, out string elementName) {
            if (string.IsNullOrEmpty(name)) {
                // m_jsonNameStack.Count == 0 means that JSON document consists from simple value
                elementName = (m_jsonNameStack.Count == 0 || m_jsonFlattenArrays) ? m_jsonLocalName : m_jsonArrayItemName;
            } else {
                elementName = name;
            }
            return true;
        }

        bool LeaveJsonScope(out string elementName) {
            elementName = m_jsonLocalName;
            var skip = m_jsonSkip;

            var prev = m_jsonNameStack.Pop();
            m_jsonLocalName = prev.localName;
            m_jsonSkip = prev.skip;

            return !skip;
        }

        public override string ToString() {
            switch (NodeType) {
                case XmlNodeType.Element:
                    return $"<{Name} {string.Join(" ", (m_attributes ?? new XmlSimpleAttribute[0]).Select(x => $"{x.Prefix}{(string.IsNullOrEmpty(x.Prefix) ? "" : ":")}{x.QName.Name}='{x.Value}'"))} {(IsEmptyElement ? "/" : "")}>";
                case XmlNodeType.Attribute:
                    return $"@{Name}";
                case XmlNodeType.Text:
                    return $"{Value}";
                case XmlNodeType.CDATA:
                    return $"<![CDATA[{Value}]]>";
                case XmlNodeType.EntityReference:
                    return $"&{Name};";
                case XmlNodeType.EndElement:
                    return $"</{Name}>";
                default:
                    return $".{NodeType} {Name} {Value}";
            }
        }
    }
}