var path = require('path');
var fs = require('fs');

var winston = require('winston');

// For serving static assets

var StaticHandler = function(path, cacheAssets) {
  this.basePath = path;
  this.defaultPath = '/index.html';
  this.cacheAssets = cacheAssets;
  // Grab the list of available files - and move into hash for quick lookup
  var available = fs.readdirSync(this.basePath);
  this.availablePaths = {};
  for (var i = 0; i < available.length; i++) {
    this.availablePaths['/' + available[i]] = true;
  }
};

StaticHandler.cache = {};

// Determine the content type for a given extension
StaticHandler.contentTypeFor = function(ext) {
  if (ext == '.js') return 'text/javascript';
  else if (ext == '.css') return 'text/css';
  else if (ext == '.html') return 'text/html';
  else if (ext == '.ico') return 'image/ico';
  else {
    winston.error('unable to determine content type for static asset with extension: ' + ext);
    return 'text/plain';
  }
};

// Handle a request, and serve back the asset if it exists
StaticHandler.prototype.handle = function(incPath, response) {
  // Go to index if not found or /
  if (!this.availablePaths[incPath]) incPath = this.defaultPath;
  var filePath = this.basePath + (incPath == '/' ? this.defaultPath : incPath);
  // And then stream the file back - either from the cache or from source
  var cached = this.cacheAssets && this.isCached(filePath);
  var method = cached ? this.serveCached : this.retrieve;
  // Run!
  var _this = this;
  method(filePath, function(error, content) {
    // Get the content
    if (content) {
      var contentType = StaticHandler.contentTypeFor(path.extname(filePath));
      response.writeHead(200, { 'content-type': contentType });
      response.end(content, 'utf-8');
      // Stick it in the cache if its not in there
      if (!cached && _this.cacheAssets) {
        StaticHandler.cache[filePath] = content;
      }
    }
    // Or break down and cry
    else {
      winston.error('unable to read file', { path: filePath, error: error });
      response.writeHead(500, { 'content-type': 'application/json' });
      response.end(JSON.stringify({ message: 'IO: Unable to read file' }));
      // If it was cached, bust the cache
      if (cached) {
        StaticHandler.cache[filePath] = null;
      }
    }
  }); 
};

// Retrieve from the file
StaticHandler.prototype.retrieve = function(filePath, callback) {
  var _this = this;
  winston.verbose('loading static asset', { path: filePath });
  fs.readFile(filePath, function(error, content) {
    callback(error, content);
  });    
};

// Retrieve from memory cache
StaticHandler.prototype.serveCached = function(filePath, callback) {
  callback(undefined, StaticHandler.cache[filePath]);
};

// Determine if a given filePath is cached or not
StaticHandler.prototype.isCached = function(filePath) {
  return !!StaticHandler.cache[filePath];
};

module.exports = StaticHandler;