basic features working

.eslintrc

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+{
+  "env": {
+    "es6": true,
+    "mocha": true,
+    "node": true
+  },
+  "extends": "semistandard",
+  "plugins": [
+    "standard"
+  ],
+  "rules": {
+    "no-unused-vars": [2, { "vars": "all", "args": "after-used" }]
+  }
+}

.gitignore

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+# Logs
+logs
+*.log
+
+# Runtime data
+pids
+*.pid
+*.seed
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+lib-cov
+
+# Coverage directory used by tools like istanbul
+coverage
+
+# Grunt intermediate storage (http://gruntjs.com/creating-plugins#storing-task-files)
+.grunt
+
+# node-waf configuration
+.lock-wscript
+
+# Compiled binary addons (http://nodejs.org/api/addons.html)
+build/Release
+
+# Dependency directory
+# https://www.npmjs.org/doc/misc/npm-faq.html#should-i-check-my-node_modules-folder-into-git
+node_modules

index.js

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+'use strict';
+
+// TODO add maxAge (i.e. support expiration)
+
+function buildCache (client, opts) {
+  if (typeof opts === 'number') {
+    opts = {max: opts};
+  }
+
+  opts = Object.assign({
+    namespace: 'LRU-CACHE!'
+  }, opts);
+
+  if (!opts.max) {
+    throw Error('max number of items in cache must be specified.');
+  }
+
+  const ZSET_KEY = `${opts.namespace}-i`;
+
+  function namedKey (key) {
+    if (!typeof key === 'string') {
+      throw Error('key should be a string.');
+    }
+
+    return `${opts.namespace}-k-${key}`;
+  }
+
+  /*
+  * Gets the value for the given key and updates its timestamp score, only if
+  * already present in the zset. The result is JSON.parsed before returned.
+  */
+  const get = (key) => new Promise((resolve, reject) => {
+    const score = -new Date().getTime();
+    key = namedKey(key);
+
+    client.multi()
+      .get(key)
+      .zadd(ZSET_KEY, 'XX', score, key)
+      .exec((err, results) => {
+        if (err) return reject(err);
+
+        const value = results[0] && JSON.parse(results[0]);
+        resolve(value);
+      });
+  });
+
+  /*
+  * Save (add/update) the new value for the given key, and update its timestamp
+  * score. The value is JSON.stringified before saving.
+  *
+  * If there are more than opts.max items in the cache after the operation
+  * then remove each exceeded key from the zset index and its value from the
+  * cache (in a single transaction).
+  */
+  const set = (key, value) => new Promise((resolve, reject) => {
+    const score = -new Date().getTime();
+    key = namedKey(key);
+
+    client.multi()
+      .set(key, JSON.stringify(value))
+      .zadd(ZSET_KEY, score, key)
+      .zrange(ZSET_KEY, opts.max, -1)
+      .exec((err, results) => {
+        if (err) return reject(err);
+
+        // we get zrange first then zrem each one instead of just zremrange,
+        // that way we guarantee that zset is always in sync with available data in the cache
+
+        const exceededKeys = results[2];
+        if (exceededKeys.length) {
+          return client.multi()
+            .zrem(ZSET_KEY, exceededKeys)
+            .del(exceededKeys)
+            .exec((err) => {
+              if (err) return reject(err);
+              resolve();
+            });
+        }
+
+        return resolve();
+      });
+  });
+
+  /*
+  * Retrieve the value for key in the cache (if present), without updating the
+  * timestamp score. The result is JSON.parsed before returned.
+  */
+  const peek = (key) => new Promise((resolve, reject) =>
+    client.get(namedKey(key), (err, result) => {
+      if (err) return reject(err);
+
+      const value = result && JSON.parse(result);
+      resolve(value);
+    }));
+
+  /*
+  * Remove the value of key from the cache (and the zset index).
+  */
+  function del (key) {
+    // del from key
+    // zrem from zset
+  }
+
+  /*
+  * Remove all items from cache (and the zset index).
+  */
+  function reset () {
+    // get all from zet
+    // del all keys from result
+    // del zset
+  }
+
+  /*
+  * Return true if the given key is in the cache
+  */
+  function has (key) {
+    // !! zscore
+  }
+
+  /*
+  * Return an array of the keys currenlty in the cache, most reacently accessed
+  * first.
+  */
+  function keys () {
+    // get all from zset
+    // remove prefix from all
+  }
+
+  /*
+  * Return an array of the values currenlty in the cache, most reacently accessed
+  * first.
+  */
+  function values () {
+    // get all from zset
+    // get each value from result keys
+  }
+
+  /*
+  * Return the amount of items currenlty in the cache.
+  */
+  function count () {
+
+  }
+
+  return {
+    get: get,
+    set: set,
+    peek: peek,
+    del: del,
+    reset: reset,
+    has: has,
+    keys: keys,
+    values: values,
+    count: count
+  };
+}
+
+module.exports = buildCache;

package.json

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+{
+  "name": "redis-lru",
+  "version": "1.0.0",
+  "description": "redis-backed LRU cache",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "devDependencies": {
+    "eslint": "^3.8.0",
+    "eslint-config-semistandard": "^6.0.1",
+    "eslint-config-standard": "^5.1.0",
+    "eslint-plugin-promise": "^1.1.0",
+    "eslint-plugin-standard": "^1.3.2",
+    "mocha": "^2.4.5"
+  },
+  "author": "Facundo Olano",
+  "license": "MIT"
+}