Missing placeholders mean TileJSON endpoints

Allows TM2 project files to work unmodified, as this now matches its
behavior.

Switches to factory construction to make `tilelive` available without
directly depending on it.

Fixes #2

README.md

@@ -6,7 +6,7 @@ I am an HTTP source for [tilelive](https://github.com/mapbox/tilelive.js).
 
 ```javascript
 var tilelive = require("tilelive");
-require("tilelive-http").registerProtocols(tilelive);
+require("tilelive-http")(tilelive);
 require("mbtiles").registerProtocols(tilelive);
 
 var template = "http://tile.stamen.com/watercolor/{z}/{x}/{y}.jpg";

index.js

@@ -7,66 +7,78 @@ var version = require("./package.json").version;
 
 http.globalAgent.maxSockets = 100;
 
-var HttpSource = function(uri, callback) {
-  this.source = url.format(uri);
+module.exports = function(tilelive, options) {
+  var HttpSource = function(uri, callback) {
+    this.source = url.format(uri);
 
-  return callback(null, this);
-};
-
-HttpSource.prototype.getTile = function(z, x, y, callback) {
-  var tileUrl = this.source
-    .replace(/{z}/i, z)
-    .replace(/{x}/i, x)
-    .replace(/{y}/i, y);
-
-  var headers = {
-    "User-Agent": "tilelive-http/" + version
-  };
+    if (!(this.source.match(/{z}/) &&
+        this.source.match(/{x}/) &&
+        this.source.match(/{y}/))) {
+      console.log("Coordinate placeholders missing; assuming %s is a TileJSON endpoint (tilejson+).", this.source);
 
-  return request.get({
-    uri: tileUrl,
-    encoding: null,
-    headers: headers
-  }, function(err, rsp, body) {
-    if (err) {
-      return callback(err);
+      return tilelive.load("tilejson+" + this.source, callback);
     }
 
-    switch (rsp.statusCode) {
-    case 200:
-      var rspHeaders = {
-        "Content-Type": rsp.headers["content-type"]
-      };
+    return callback(null, this);
+  };
 
-      return callback(null, body, rspHeaders);
+  HttpSource.prototype.getTile = function(z, x, y, callback) {
+    var tileUrl = this.source
+      .replace(/{z}/i, z)
+      .replace(/{x}/i, x)
+      .replace(/{y}/i, y);
+
+    var headers = {
+      "User-Agent": "tilelive-http/" + version
+    };
+
+    return request.get({
+      uri: tileUrl,
+      encoding: null,
+      headers: headers
+    }, function(err, rsp, body) {
+      if (err) {
+        return callback(err);
+      }
+
+      switch (rsp.statusCode) {
+      case 200:
+        var rspHeaders = {
+          "Content-Type": rsp.headers["content-type"]
+        };
+
+        return callback(null, body, rspHeaders);
+
+      case 404:
+        return callback(new Error('Tile does not exist'));
+
+      default:
+        return callback(new Error("Upstream error: " + rsp.statusCode));
+      }
+    });
+  };
 
-    case 404:
-      return callback(new Error('Tile does not exist'));
+  HttpSource.prototype.getInfo = function(callback) {
+    return callback(null, {
+      format: url.parse(this.source).pathname.split(".").pop(),
+      bounds: [-180, -85.0511, 180, 85.0511],
+      minzoom: 0,
+      maxzoom: Infinity
+    });
+  };
 
-    default:
-      return callback(new Error("Upstream error: " + rsp.statusCode));
-    }
-  });
-};
+  HttpSource.prototype.close = function(callback) {
+    callback = callback || function() {};
 
-HttpSource.prototype.getInfo = function(callback) {
-  return callback(null, {
-    format: url.parse(this.source).pathname.split(".").pop(),
-    bounds: [-180, -85.0511, 180, 85.0511],
-    minzoom: 0,
-    maxzoom: Infinity
-  });
-};
+    return callback();
+  };
 
-HttpSource.prototype.close = function(callback) {
-  callback = callback || function() {};
+  HttpSource.registerProtocols = function(tilelive) {
+    tilelive.protocols["http:"] = HttpSource;
+    tilelive.protocols["https:"] = HttpSource;
+  };
 
-  return callback();
-};
+  HttpSource.registerProtocols(tilelive);
 
-HttpSource.registerProtocols = function(tilelive) {
-  tilelive.protocols["http:"] = HttpSource;
-  tilelive.protocols["https:"] = HttpSource;
+  return HttpSource;
 };
-
-module.exports = HttpSource;