'use strict';

var crypto = require('crypto');

function jsonDeepClone(target) {
  return JSON.parse(
    JSON.stringify(target)
  );
}

function mergeObjects() {
  // arguments should be an array of objects. We
  // reverse it because the last argument to set
  // a value wins.
  var args = [].slice.call(arguments).reverse();
  var len = args.length;
  if (len === 1) {
    return args[0];
  }

  // gather the set of keys from all arguments
  var keyLists = args.map(function (arg) {
    return Object.keys(arg);
  });

  var keys = Object.keys(keyLists.reduce(function (all, list) {
    list.forEach(function (k) {
      all[k] = true;
    });
    return all;
  }, {}));

  // for each key
  return keys.reduce(function (target, k) {
    // find the first argument (because of the reverse() above) with the key set
    var values = [];
    var isObject = false;
    for (var i = 0; i < len; i++) {
      var v = args[i];
      var vType = typeof v;

      if (vType === 'object') {
        if (!v) {
          // typeof null is object. null is the only falsey object. null represents
          // a delete or the end of our argument list;
          break;
        }
        // we need to collect values until we get a non-object, so we can merge them
        values.push(v);
        isObject = true;
      } else if (!isObject) {
        if (vType === 'undefined') {
          // if the arg actually has the key set this is effectively a "delete"
          if (keyList[i].indexOf(k) != -1) {
            break;
          }
          // otherwise we need to check the next argument's value, so we don't break the loop
        } else {
          values.push(v);
          break;
        }
      } else {
        // a previous value was an object, this one isn't
        // That means we are done collecting values.
        break;
      }
    }

    if (values.length > 0) {
      target[k] = mergeObjects.apply(null, values);
    }

    return target;
  }, {});
}

function prepareZone(zone, options) {
  var opts = options || {};
  var timestamp = opts.timestamp || Date.now();
  if (!zone.name) {
    zone.name = zone.id;
    zone.id = null;
  }
  if (!zone.id) {
    zone.id = crypto.randomBytes(16).toString('hex');
  }
  if (!zone.createdAt) { zone.createdAt = timestamp; }
  if (!zone.updatedAt || opts.isUpdate) { zone.updatedAt = timestamp; }

  // create a names set for the zone, keyed by record name mapped to
  // an object for the various records with that name, by type (A, MX, TXT, etc.)
  zone.records = zone.records || {};

  return zone;
}

/*
init() should return an object with: {
  save: function -> undefined - changes to in memory representation should be persisted
  This could be considered the equivalent of committing a transaction to the database.
  primaryNameservers: {
    list: function -> list nameservers
  },
  zones: {
    list: function -> list zones,
    create:
    update:
    delete:
  },
  records: {
    list: function -> list records,
    create:
    update:
    delete:
  }
}

All lists will be a deep copy of the data actually stored.
 */

module.exports = function init (opts) {
  // opts = { filepath };

  var db = require(opts.filepath);
  var mtime = require('fs').statSync(opts.filepath).mtime.valueOf();

  //
  // Migration from other formats
  //

  // Convert the primary nameservers from an array of strings to objects with names and IDs.
  // also switch to the 'peers' name, since we are really interested in the other FQDNs that
  // use the same data store and are kept in sync.
  var peerList = (!db.peers || Array.isArray(db.peers))? db.peers : Object.keys(db.peers).map(function (p) {
    return db.peers[p];
  });
  db.peers = [].concat(db.primaryNameservers, peerList).filter(function (p) {
    // filer out empty strings, undefined, etc.
    return !!p;
  }).map(function (ns) {
    var peer = ('string' === typeof ns)? ns : { name: ns };
    if (!ns.id) {
      peer.id = crypto.randomBytes(16).toString('hex');
    }
    return peer;
  }).reduce(function (peers, p) {
    peers[p.name] = p;
    return peers;
  }, {});
  delete db.primaryNameservers;

  // Convert domains to zones and ensure that they have proper IDs and timestamps
  // Organize zones as a set of zone names
  var zoneList = (!db.zones || Array.isArray(db.zones))? db.zones : Object.keys(db.zones).map(function (z) {
    return db.zones[z];
  });

  db.zones = [].concat(db.domains, zoneList).filter(function (z) {
    // filer out empty strings, undefined, etc.
    return !!z;
  }).map(function (zone) {
    return prepareZone(zone, { timestamp: mtime });
  }).reduce(function (zones, z) {
    zones[z.name] = z;
    return zones;
  }, {});
  delete db.domains;

  // NOTE: Records belong to zones, but they previously referred to them only by a
  // zone property. This may pose problems where the whole list of records is not easily
  // filtered / kept in memory / indexed and/or retrieved by zone. Traditionally,
  // records are stored "within a zone" in a zone file. We want to have the store API
  // behave more traditionally, even though some stores (like a SQL database
  // table) might actually store the zone as a property of a record as we currently do.
  // (This fits with the somewhat unexpected and confusing logic of wildcard records.)
  (db.records || []).forEach(function (record) {
    // make sure the record has an ID
    if (!record.id) {
      record.id = crypto.randomBytes(16).toString('hex');
    }

    // put it in it's zone - synthesize one if needed
    db.zones[record.zone] = db.zones[record.zone] || prepareZone({ name: record.zone });
    var zone = db.zones[record.zone];
    zone.records[record.name] = zone.records[record.name] || [];
    var recordsForName = zone.records[record.name];
    recordsForName.push(record);
  });
  delete db.records;

  // Write the migrated data
  require('fs').writeFileSync(opts.filepath, JSON.stringify(db, null, 2));
  //
  // End Migration
  //

  var save = function save (cb) {
    if (save._saving) {
      console.log('make pending');
      save._pending.push(cb);
      return;
    }

    save._saving = true;
    require('fs').writeFile(opts.filepath, JSON.stringify(db, null, 2), function (err) {
      console.log('done writing');
      var pending = save._pending.splice(0);
      save._saving = false;
      cb(err);
      if (!pending.length) {
        return;
      }
      save(function (err) {
        console.log('double save');
        pending.forEach(function (cb) { cb(err); });
      });
    });
  };
  save._pending = [];

  function matchPredicate(predicate) {
    return function (toCheck) {
      // which items match the predicate?
      if (!toCheck) {
        return false;
      }

      // check all the keys in the predicate - only supporting exact match
      // of at least one listed option for all keys right now
      if (Object.keys(predicate || {}).some(function (k) {
        return [].concat(predicate[k]).indexOf(toCheck[k]) === -1;
      })) {
        return false;
      }

      // we have a match
      return true;
    };
  }

  function matchZone(predicate) {
    var zonenames = !!predicate.name ? [].concat(predicate.name) : Object.keys(db.zones);
    var check = matchPredicate(predicate);
    // TODO: swap the filter() for a functional style "loop" recursive function
    // that lets us return early if we have a limit, etc.
    var found = zonenames.filter(function (zonename) {
      /*
      if (predicate.id && predicate.id !== z.id) { return false; }
      if (predicate.name && predicate.name !== z.name) { return false; }
      */
      return check(db.zones[zonename]);
    }).map(function (zonename) {
      return db.zones[zonename];
    });

    return found;
  }

  var dbApi = {
    save: function () {
      // hide _pending and _saving from callers
      var args = [].slice.call(arguments);
      return save.apply(null, args);
    },
    // peers really isn't editable - it's literally the list of FQDN's
    // that this database is replicated to in a multi-master fashion.
    //
    // However, lib/store/index.js does plenty to update these records in support
    // of the SOA records that are built from them (as does this file in the "migration"
    // section). I'm toying with the idea of not storing them seperately or creating the
    // SOA records somewhat immediately.
    peers: function listPeers(cb) {
      // Most data stores are going to have an asynchronous storage API. If we need
      // synchronous access to the data it is going to have to be cached. If it is
      // cached, there is still the issue the cache getting out of sync (a legitimate
      // issue anyway). If we explicitly make all of these operations async then we
      // have greater flexibility for store implmentations to address these issues.
      return setImmediate(cb, null, jsonDeepClone(db.peers));
    },
    zones: {
      /*
      I'm fairly certan that zone names must be unique and therefore are legitimately
      IDs within the zones namespace. This is similarly true of record names within a zone.
      I'm not certain that having a distinct ID adds value and it may add confusion / complexity.
       */
      // NOTE: `opts` exists so we can add options - like properties to read - easily in the future
      // without modifying the function signature
      list: function listZones(predicate, opts, cb) {
        // TODO: consider whether we should just return the zone names
        var found = jsonDeepClone(matchZone(predicate)).map(function (z) {
          // This is fairly inefficient!! Consider alternative storage
          // that does not require deleting the records like this.
          delete z.records;
          return z;
        });
        return setImmediate(cb, null, found);
      },
      // // NOTE: I'm not sure we need a distinct 'find()' operation in the API
      // // unless we are going to limit the output of the
      // // 'list()' operation in some incompatible way.
      // // NOTE: `opts` exists so we can add options - like properties to read - easily in the future
      // // without modifying the function signature
      // find: function getZone(predicate, opts, cb) {
      //   if (!predicate.name || predicate.id) {
      //     return setImmediate(cb, new Error('Finding a zone requires a `name` or `id`'));
      //   }
      //   // TODO: implement a limit / short circuit and possibly offset
      //   // to allow for paging of zone data.
      //   var found = matchZone(predicate);
      //   if (!found[0]) {
      //     // TODO: make error message more specific?
      //     return setImmediate(cb, new Error('Zone not found'));
      //   }

      //   var z = jsonDeepClone(found[0]);
      //   delete z.records;
      //   return setImmediate(cb, null, z);
      // },
      create: function createZone(zone, cb) {
        // We'll need a lock mechanism of some sort that works
        // for simultaneous requests and multiple processes.
        matchZone({ name: zone.name }, function (err, matched) {
          if (err) {
            return setImmediate(cb, err);
          }

          var found = matched[0];
          if (found) {
            return setImmediate(cb, new Error('Zone ' + zone.name + ' already exists'));
          }
          
          db.zones[zone.name] = prepareZone(zone);
          return setImmediate(function () {
            cb(null, jsonDeepClone(db.zones[zone.name]));
            // release lock
          });
        });
      },
      update: function updateZone(zone, cb) {
        // We'll need a lock mechanism of some sort that works
        // for simultaneous requests and multiple processes.
        matchZone({ name: zone.name }, function (err, matched) {
          if (err) {
            return setImmediate(cb, err);
          }
          var found = matched[0];
          if (!found) {
            return setImmediate(cb, new Error('Zone not found'));
          }
          // make sure we are not writing records through this interface
          delete zone.records;

          var combined = mergeObjects(found, zone);
          db.zones[zone.name] = prepareZone(combined, { isUpdate: true });
          return setImmediate(function () {
            cb(null, jsonDeepClone(db.zones[zone.name]));
            // release lock
          });
        });
      },
      delete: function(zone, cb) {
        // We'll need a lock mechanism of some sort that works
        // for simultaneous requests and multiple processes.
        matchZone({ name: zone.name }, function (err, matched) {
          if (err) {
            return setImmediate(cb, err);
          }
          var found = matched[0];
          if (!found) {
            return setImmediate(cb, new Error('Zone not found'));
          }

          delete db.zones[zone.name];
          return setImmediate(function () {
            cb();
            // release lock
          });
        });
      }
    },
    records: {
      list: function listRecords(rPredicate, cb) {
        var recordNames = [].concat(rPredicate.name);
        var check = matchPredicate(rPredicate);

        var found = matchZone({ name: rPredicate.zone }).reduce(function (records, zone) {
          // get the records from the zone that match the record predicate
          var zFound = recordNames.filter(function (name) {
            return !!zone.records[name];
          }).map(function (name) {
            return zone.records[name].filter(check);
          });
          return records.concat(zFound);
        }, []);

        return setImmediate(cb, null, jsonDeepClone(found));
      },
      // find: function getRecord(rPredicate, cb) {
      //   var recordNames = [].concat(rPredicate.name);
      //   var check = matchPredicate(rPredicate);

      //   // TODO: swap the `filter()` and `map()` for a functional style "loop"
      //   // recursive function that lets us return early if we have a limit, etc.
      //   var found = matchZone({ name: rPredicate.zone }).reduce(function (records, zone) {
      //     // get the records from the zone that match the record predicate
      //     var zFound = recordNames.filter(function (name) {
      //       return !!zone.records[name];
      //     }).map(function (name) {
      //       return zone.records[name].filter(check);
      //     });
      //     return records.concat(zFound);
      //   }, []);

      //   return setImmediate(cb, null, jsonDeepClone(found[0]));
      // },
      create: function(record, cb) {
        var zone = matchZone({ name: record.zone })[0];
        if (!zone) {
          return setImmediate(cb, new Error('Unble to find zone ' + record.zone + ' to create record'));
        }

        var records = zone.records[record.name] = zone.records[record.name] || [];
        var check = matchPredicate(record);
        if (records.filter(check)[0]) {
          return setImmediate(cb, new Error('Exact record already exists in zone ' + record.zone ));
        }

        return setImmediate(cb, null, jsonDeepClone(found));
      },
      update: function(record, cb) {},
      delete: function(record, cb) {}
    }
  };

  return dbApi;
};