/// <summary>
/// Trigger the build and output of Posts to the STDOUT stream
/// </summary>
public void Handle(Options options, IConsoleStream consoleStream)
{
// Validate that the number of Posts does not exceed 100
if (options.Posts < 1 || options.Posts > 100)
{
consoleStream.WriteErrorLine("Number of posts must be a positive integer not exceeding 100");
return;
}
var postSerializer = new JsonSerializer();
consoleStream.JsonWriter.Formatting = Formatting.Indented;
int postCounter = 1;
// Write the start of the Json Array to the STDOUT stream
consoleStream.JsonWriter.WriteStartArray();
// Write each post to the Array in the STDOUT stream
// This continues to use Linq Lazy Evaluation to write one valid post to the STDOUT stream
// at a time
var posts = service.GetTopPosts(consoleStream)
.Where(PostValidator.Validate)
.Where(p => SerializePost(postSerializer, consoleStream, p, postCounter++))
.Take(options.Posts)
.ToList();
// Write the end of the Json Array to the STDOUT stream
consoleStream.JsonWriter.WriteEndArray();
}
/// <summary>
/// Makes an API call to get the collection of Top Story Ids
/// </summary>
private IEnumerable <long> GetTopPostIdCollection(IConsoleStream consoleStream)
{
IEnumerable <long> storyIds = new List <long>().AsEnumerable();
try
{
var response = client.GetAsync(new Uri("https://hacker-news.firebaseio.com/v0/topstories.json")).Result;
var jsonString = response.Content.ReadAsStringAsync().Result;
storyIds = JsonConvert.DeserializeObject <IEnumerable <long> >(jsonString);
}
catch (Exception e)
{
consoleStream.WriteErrorLine("Error getting latest Post Ids");
consoleStream.WriteErrorLine(e.Message);
}
return(storyIds);
}
/// <summary>
/// Method to write a Post in the required format to the STDOUT stream
/// </summary>
private bool SerializePost(JsonSerializer ser, IConsoleStream consoleStream, Post post, int counter)
{
try
{
ser.Serialize(consoleStream.JsonWriter,
new
{
title = post.title,
uri = post.url,
author = post.by,
points = post.score,
comments = post.descendants,
rank = counter
});
}
catch (Exception e)
{
consoleStream.WriteErrorLine(e.Message);
return(false);
}
return(true);
}
/// <summary>
/// First gets the list of top story Ids and then calls the API for each Id to get the full story data.
/// This method takes advantage of LazyEvaluation which only executes the API call when needed.
/// </summary>
public IEnumerable <Post> GetTopPosts(IConsoleStream consoleStream)
{
var postIds = GetTopPostIdCollection(consoleStream);
foreach (var id in postIds)
{
Post post = null;
try
{
var response = client.GetAsync(new Uri($"https://hacker-news.firebaseio.com/v0/item/{id}.json")).Result;
var jsonString = response.Content.ReadAsStringAsync().Result;
post = JsonConvert.DeserializeObject <Post>(jsonString);
}
catch (Exception e)
{
consoleStream.WriteErrorLine($"Error getting Post for Post Id: {id}");
consoleStream.WriteErrorLine(e.Message);
continue;
}
yield return(post);
}
}
