﻿//  Author:
//    Alexandru Ciobanu alex+git@ciobanu.org
//
//  Copyright (c) 2015-2018, Alexandru Ciobanu (alex+git@ciobanu.org)
//
//  All rights reserved.
//
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//
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namespace XtraLiteTemplates.Dialects.Standard.Directives
{
    using System;
    using System.Diagnostics;
    using System.Linq;

    using JetBrains.Annotations;

    using XtraLiteTemplates.Expressions;
    using XtraLiteTemplates.Introspection;
    using XtraLiteTemplates.Parsing;

    /// <summary>
    /// The IF directive implementation.
    /// </summary>
    [PublicAPI]
    public sealed class IfDirective : StandardDirective    
    {
        private readonly int _conditionalExpressionComponentIndex;

        /// <summary>
        /// Initializes a new instance of the <see cref="IfDirective" /> class.
        /// </summary>
        /// <param name="startTagMarkup">The start tag markup.</param>
        /// <param name="endTagMarkup">The end tag markup.</param>
        /// <param name="typeConverter">The type converter.</param>
        /// <exception cref="InvalidOperationException">Argument <paramref name="startTagMarkup" /> does not correspond to the expressed rules.</exception>
        /// <exception cref="System.FormatException">Argument <paramref name="startTagMarkup" /> or <paramref name="endTagMarkup" /> cannot be parsed.</exception>
        /// <remarks>
        /// The <paramref name="startTagMarkup" /> is expected to contain exactly one expression components - the conditional expression.
        /// </remarks>
        public IfDirective([NotNull] string startTagMarkup, [NotNull] string endTagMarkup, [NotNull] IPrimitiveTypeConverter typeConverter)
            : base(typeConverter, Tag.Parse(startTagMarkup), Tag.Parse(endTagMarkup))
        {
            Debug.Assert(Tags.Count == 2, "Expected a tag count of 2.");

            /* Find all expressions. */
            var tag = Tags[0];
            var expressionComponents = Enumerable.Range(0, tag.ComponentCount)
                .Where(index => tag.MatchesExpression(index)).Select(index => index).ToArray();

            Expect.IsTrue(nameof(expressionComponents), expressionComponents.Length == 1);

            _conditionalExpressionComponentIndex = expressionComponents[0];
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="IfDirective" /> class using the standard markup {IF $ THEN}...{END}.
        /// </summary>
        /// <param name="typeConverter">The type converter.</param>
        public IfDirective([NotNull] IPrimitiveTypeConverter typeConverter)
            : this("IF $ THEN", "END", typeConverter)
        {
        }

        /// <summary>
        /// Executes the current directive.
        /// </summary>
        /// <param name="tagIndex">The index of the tag that triggered the execution.</param>
        /// <param name="components">The tag components as provided by the lexical analyzer.</param>
        /// <param name="state">A general-purpose state object. Initially set to <c>null</c>.</param>
        /// <param name="context">The evaluation context.</param>
        /// <param name="text">Always <c>null</c>.</param>
        /// <returns>
        /// A value indicating the next step for the evaluation environment.
        /// </returns>
        /// <remarks>
        /// The directive evaluates only if the expression evaluates to <c>true</c>.
        /// </remarks>
        protected internal override FlowDecision Execute(
            int tagIndex,
            object[] components, 
            ref object state,
            IExpressionEvaluationContext context, 
            out string text)
        {
            Debug.Assert(tagIndex >= 0 && tagIndex <= 1, "tagIndex must be between 0 and 1.");
            Debug.Assert(components != null, "components cannot be null.");
            Debug.Assert(components.Length == Tags[tagIndex].ComponentCount, "component length must match tag component length.");
            Debug.Assert(context != null, "context cannot be null.");

            text = null;
            if (tagIndex == 0)
            {
                if (TypeConverter.ConvertToBoolean(components[_conditionalExpressionComponentIndex]))
                {
                    return FlowDecision.Evaluate;
                }
            }
            
            return FlowDecision.Terminate;
        }
    }
}