using System;
using System.IO;
using Vellum;

namespace Amphora.Vellum
{
    /// <summary>
    /// Saves a StringView as the whole of the string it looks into, and where in it the view starts and ends.
    /// </summary>
    /// <remarks>
    /// The string is saved the way any string is, so views of one string, and the string itself, share it in the save
    /// and load over a single string.
    /// </remarks>
    public sealed class StringViewConverter : SaveConverter<StringView>
    {
        public const string TextKey = "text";
        public const string StartIndexKey = "startIndex";
        public const string EndIndexKey = "endIndex";

        public override SaveNode Write(StringView value, SaveSession session)
        {
            // A default view has no text at all, and saves as a view of an empty one.
            string text = value.Text ?? "";
            SaveNode returnMe = SaveNode.NewTable();
            returnMe.Entries[TextKey] = session.ToNode(text);
            returnMe.Entries[StartIndexKey] = session.ToNode(value.StartIndex);
            returnMe.Entries[EndIndexKey] = session.ToNode(value.EndIndex);
            return returnMe;
        }

        public override StringView Read(SaveNode node, SaveSession session)
        {
            var reader = new SaveReader(node, session);
            string text = reader.Require<string>(TextKey);
            int startIndex = reader.Require<int>(StartIndexKey);
            int endIndex = reader.Require<int>(EndIndexKey);
            if (text == null)
            {
                throw new InvalidDataException("A saved string view has no text to look into.");
            }

            try
            {
                return new StringView(text, startIndex, endIndex);
            }
            catch (ArgumentException exception)
            {
                throw new InvalidDataException("A saved string view runs from " + startIndex + " to " + endIndex +
                    ", which doesn't fit the " + text.Length + " characters it looks into.", exception);
            }
        }

        public override bool TryListChildren(SaveNode node, ChildList children)
        {
            // Everything it reads is built-in, and so left out.
            SaveNode text;
            return node.TryGetEntry(TextKey, out text);
        }
    }
}