// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Diagnostics;
using System.Xml;
using System.Xml.XPath;
using System.Xml.Xsl;
using FT = MS.Internal.Xml.XPath.Function.FunctionType;

namespace MS.Internal.Xml.XPath
{
    internal sealed class BooleanFunctions : ValueQuery
    {
        private readonly Query? _arg;
        private readonly FT _funcType;

        public BooleanFunctions(FT funcType, Query? arg)
        {
            _arg = arg;
            _funcType = funcType;
        }
        private BooleanFunctions(BooleanFunctions other) : base(other)
        {
            _arg = Clone(other._arg);
            _funcType = other._funcType;
        }

        public override void SetXsltContext(XsltContext context)
        {
            _arg?.SetXsltContext(context);
        }

        public override object Evaluate(XPathNodeIterator nodeIterator) =>
            _funcType switch
            {
                FT.FuncBoolean => toBoolean(nodeIterator),
                FT.FuncNot => Not(nodeIterator),
                FT.FuncTrue => true,
                FT.FuncFalse => false,
                FT.FuncLang => Lang(nodeIterator!),
                _ => false,
            };

        internal static bool toBoolean(double number)
        {
            return number != 0 && !double.IsNaN(number);
        }
        internal static bool toBoolean(string str)
        {
            return str.Length > 0;
        }

        internal bool toBoolean(XPathNodeIterator nodeIterator)
        {
            object result = _arg!.Evaluate(nodeIterator);
            if (result is XPathNodeIterator) return _arg.Advance() != null;

            string? str = result as string;
            if (str != null)
                return toBoolean(str);

            if (result is double) return toBoolean((double)result);
            if (result is bool) return (bool)result;
            Debug.Assert(result is XPathNavigator, "Unknown value type");
            return true;
        }

        public override XPathResultType StaticType { get { return XPathResultType.Boolean; } }

        private bool Not(XPathNodeIterator nodeIterator)
        {
            return !(bool)_arg!.Evaluate(nodeIterator);
        }

        private bool Lang(XPathNodeIterator nodeIterator)
        {
            string str = _arg!.Evaluate(nodeIterator).ToString()!;
            Debug.Assert(nodeIterator.Current != null);
            string lang = nodeIterator.Current.XmlLang;
            return (
               lang.StartsWith(str, StringComparison.OrdinalIgnoreCase) &&
               (lang.Length == str.Length || lang[str.Length] == '-')
            );
        }

        public override XPathNodeIterator Clone() { return new BooleanFunctions(this); }
    }
}