refactor(src): introduce submodules

src/filter.ts

@@ -0,0 +1,114 @@
+import { LogRecord } from './log-record';
+
+//---------------------------------------------------------------------------
+// Filter classes and functions
+//---------------------------------------------------------------------------
+
+export type FilterCallable = (record: LogRecord) => boolean;
+
+/**
+ * Filter instances are used to perform arbitrary filtering of LogRecords.
+ *
+ * Loggers and Handlers can optionally use Filter instances to filter records as
+ * desired. The base filter class only allows events which are below a certain
+ * point in the logger hierarchy. For example, a filter initialized with "A.B"
+ * will allow events logged by loggers "A.B", initialized with the empty string,
+ * all events are passed.
+ */
+export class Filter {
+    public readonly scope: string;
+    public readonly slen: number;
+
+    /**
+     * Initialize with the name of the logger which ,together with its children,
+     * will have its events allowed through the filter. If no name is specified,
+     * allow every event.
+     *
+     * @param name - name of logging scope
+     */
+    constructor(scope: string) {
+        this.scope = scope ?? '';
+        this.slen = this.scope.length;
+    }
+
+    /**
+     * Inspect a record, if it should be logged.
+     *
+     * Returns true if the record should be logged, or false otherwise. If
+     * deemed appropriate, the record may be modified in-place.
+     *
+     * @param - scope of log record to inspect
+     * @param - log record to inspect
+     */
+    filter(record: LogRecord): boolean {
+        if (this.slen == 0 || this.scope == record.scope) { return true }
+        else if (!record.scope.substring(0, this.slen)) { return false }
+        return (record.scope[this.slen] == '.')
+    }
+}
+
+export class Filterer {
+    filters: Filter[] = [];
+
+    /**
+     * Add the specified filter to this handler.
+     *
+     * @param filter
+     */
+    addFilter(filter: Filter) {
+        if (!this.filters.includes(filter)) { this.filters.push(filter) }
+    }
+
+    /**
+     * Remove the specified filter from this handler.
+     *
+     * @param filter
+     */
+    removeFilter(filter: Filter) {
+        if (this.filters.includes(filter)) {
+            this.filters.splice(this.filters.indexOf(filter), 1)
+        }
+    }
+
+    /**
+     * Determine if a record is loggable by consulting all the filters.
+     *
+     * The default is to allow the record to be logged; any filter can veto this
+     * by returning a false value.
+     * If a filter attached to a handler returns a log record instance, then
+     * that instance is used in place of the original log record in any further
+     * processing of the event by that handler.
+     * If a filter returns any other true value, the original log record is used
+     * in any further processing of the event by that handler.
+     *
+     * If none of the filters return false values, this method returns a log
+     * record.
+     *
+     * If any of the filters return a false value, this method returns a false
+     * value.
+     *
+     * @param filter
+     */
+    filter(record: LogRecord): LogRecord|null {
+
+        for (var i = 0; i < this.filters.length; i += 1) {
+            let result: boolean|LogRecord = false;
+
+            let filter = this.filters[i];
+
+            if (typeof (filter as Filter).filter == 'function') {
+                result = (filter as Filter).filter(record)
+            }
+            else {
+                result = (filter as unknown as FilterCallable)(record)
+            }
+
+            if (!result) { return null }
+
+            if ((result as any) instanceof LogRecord) { record = result as unknown as LogRecord }
+        }
+
+        return record
+    }
+}
+