using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace FlowScope.Config
{
    public sealed class InMemoryConfigSource : IConfigSource
    {
        private readonly Dictionary<string, string> _files;

        public InMemoryConfigSource(
            IReadOnlyDictionary<string, string> files,
            string name = "InMemory")
        {
            _files = files != null
                ? new Dictionary<string, string>(files)
                : throw new ArgumentNullException(nameof(files));
            Name = string.IsNullOrWhiteSpace(name)
                ? throw new ArgumentException("Config source name is required.", nameof(name))
                : name;
        }

        public string Name { get; }

        public Task<string> LoadTextAsync(string fileName, CancellationToken cancellationToken)
        {
            cancellationToken.ThrowIfCancellationRequested();
            if (!_files.TryGetValue(fileName, out var text))
            {
                throw new InvalidOperationException($"Config file is missing: {fileName}");
            }

            return Task.FromResult(text);
        }
    }
}