using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace HtmlAgilityPack
{
    /// <summary>
    /// 
    /// </summary>
    public static class HtmlVarExtension
    {
        /// <summary>
        /// 根据XPath来获取属性值
        /// </summary>
        /// <param name="original"></param>
        /// <param name="xpath"></param>
        /// <param name="attr">属性名,为空则输出InnerText,-1则输出InnerHtml,-2则输出OuterHtml</param>
        /// <param name="defValue"></param>
        /// <returns></returns>
        static public string GetAttr(this HtmlNode original, string xpath,string attr,string defValue)
        {
            if (original == null) { return defValue; }
            HtmlDocument htmlItem = new HtmlDocument();
            htmlItem.LoadHtml(original.OuterHtml);
            HtmlNodeCollection anchors = htmlItem.DocumentNode.SelectNodes(xpath);
            if (anchors != null && anchors.Count >= 0)
            {
                if (attr.Length == 0)
                { return System.Web.HttpUtility.HtmlDecode(anchors[0].InnerText); }
                else if (attr == "-1")
                { return anchors[0].InnerHtml; }
                else if (attr == "-2")
                { return anchors[0].OuterHtml; }
                else
                {
                    return anchors[0].GetAttributeValue(attr, defValue);
                }
            }
            return defValue;
        }
        /// <summary>
        /// 根据当前节点生成HtmlDocument
        /// </summary>
        /// <param name="original"></param>
        /// <returns></returns>
        static public HtmlDocument GetHtmlDocument(this HtmlNode original)
        {
            if (original == null) { return null; }
            HtmlDocument htmlItem = new HtmlDocument();
            htmlItem.LoadHtml(original.OuterHtml);
            return htmlItem;
        }
        /// <summary>
        /// 根据XPath来获取属性值
        /// </summary>
        /// <param name="htmlItem"></param>
        /// <param name="xpath"></param>
        /// <param name="attr">属性名,为空则输出InnerText,-1则输出InnerHtml,-2则输出OuterHtml</param>
        /// <param name="defValue"></param>
        /// <returns></returns>
        static public string GetAttr(this HtmlDocument htmlItem, string xpath, string attr, string defValue)
        {
            if(htmlItem == null) { return defValue;}
            HtmlNodeCollection item = htmlItem.DocumentNode.SelectNodes(xpath);
            if (item != null && item.Count >= 0)
            {
                if (attr.Length == 0)
                { return System.Web.HttpUtility.HtmlDecode(item[0].InnerText); }
                else if (attr == "-1")
                { return item[0].InnerHtml; }
                else if (attr == "-2")
                { return item[0].OuterHtml; }
                else
                {
                    return item[0].GetAttributeValue(attr, defValue);
                }
            }
            return defValue;
        }
        /// <summary>
        /// 根据XPath来查找节点
        /// </summary>
        /// <param name="htmlDoc"></param>
        /// <param name="xpath"></param>
        /// <returns></returns>
        static public HtmlNode GetHtmlNode(this HtmlDocument htmlDoc, string xpath)
        {
            HtmlNodeCollection anchors = htmlDoc.DocumentNode.SelectNodes(xpath);//筛选出网站的链接
            if (anchors != null)
            {
                return anchors[0];
            }
            return null;
        }
        /// <summary>
        /// 在当前节点下根据xpath来查找符合的第一个节点
        /// </summary>
        /// <param name="node"></param>
        /// <param name="xpath"></param>
        /// <returns></returns>
        static public HtmlNode GetHtmlNode(this HtmlNode node, string xpath)
        {
            if(node == null) { return null; }   
            HtmlDocument htmlItem = new HtmlDocument();
            htmlItem.LoadHtml(node.OuterHtml);
            HtmlNodeCollection anchors = htmlItem.DocumentNode.SelectNodes(xpath);//筛选出网站的链接
            if (anchors != null)
            {
                return anchors[0];
            }
            return null;
        }
        /// <summary>
        /// 在当前节点下根据xpath来查找所有符合的节点
        /// </summary>
        /// <param name="node"></param>
        /// <param name="xpath"></param>
        /// <returns></returns>
        static public HtmlNodeCollection GetHtmlNodes(this HtmlNode node, string xpath)
        {
            if (node == null) { return null; }
            HtmlDocument htmlItem = new HtmlDocument();
            htmlItem.LoadHtml(node.OuterHtml);
            HtmlNodeCollection anchors = htmlItem.DocumentNode.SelectNodes(xpath);//筛选出网站的链接
            return anchors;
        }
    }
}