66 lines
2.2 KiB
JavaScript
66 lines
2.2 KiB
JavaScript
// MAP DATA CACHE ///////////////////////////////////
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// cache for map data tiles.
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window.DataCache = function() {
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this.REQUEST_CACHE_FRESH_AGE = 90; // if younger than this, use data in the cache rather than fetching from the server
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this.REQUEST_CACHE_MAX_AGE = 60*60; // maximum cache age. entries are deleted from the cache after this time
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this.REQUEST_CACHE_MIN_SIZE = 200; // if fewer than this many entries, don't expire any
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this.REQUEST_CACHE_MAX_SIZE = 2000; // if more than this many entries, expire early
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this._cache = {};
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}
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window.DataCache.prototype.store = function(qk,data,date) {
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// fixme? common behaviour for objects is that properties are kept in the order they're added
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// this is handy, as it allows easy retrieval of the oldest entries for expiring
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// however, this is not guaranteed by the standards, but all our supported browsers work this way
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delete this._cache[qk];
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if (date === undefined) date = new Date();
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this._cache[qk] = { time: date.getTime(), data: data };
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}
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window.DataCache.prototype.get = function(qk) {
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if (qk in this._cache) return this._cache[qk].data;
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else return undefined;
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}
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window.DataCache.prototype.getTime = function(qk) {
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if (qk in this._cache) return this._cache[qk].time;
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else return 0;
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}
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window.DataCache.prototype.isFresh = function(qk) {
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if (qk in this._cache) {
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var d = new Date();
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var t = d.getTime() - this.REQUEST_CACHE_FRESH_AGE*1000;
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if (this._cache[qk].time >= t) return true;
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else return false;
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}
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return undefined;
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}
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window.DataCache.prototype.expire = function() {
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var d = new Date();
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var t = d.getTime()-this.REQUEST_CACHE_MAX_AGE*1000;
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var cacheSize = Object.keys(this._cache).length;
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for(var qk in this._cache) {
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// stop processing once we hit the minimum size
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if (cacheSize < this.REQUEST_CACHE_MIN_SIZE) break;
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// fixme? our MAX_SIZE test here assumes we're processing the oldest first. this relies
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// on looping over object properties in the order they were added. this is true in most browsers,
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// but is not a requirement of the standards
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if (cacheSize > this.REQUEST_CACHE_MAX_SIZE || this._cache[qk].time < t) {
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delete this._cache[qk];
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cacheSize--;
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}
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}
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}
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