(#371) Added first definition of log provider interface

Author: s1hofmann

Diff for: lib/provider/io/log-provider.class.ts

@@ -0,0 +1,42 @@
+export type LogFunction = (message: string, data?: {}) => void;
+export type ErrorLogFunction = (error: Error, data?: {}) => void;
+
+export enum LogLevel {
+    TRACE,
+    DEBUG,
+    INFO,
+    WARN,
+    ERROR
+}
+
+export interface ConsoleLogger {
+    trace(message?: any, ...optionalParams: any[]): void;
+    debug(message?: any, ...optionalParams: any[]): void;
+    info(message?: any, ...optionalParams: any[]): void;
+    warn(message?: any, ...optionalParams: any[]): void;
+    error(message?: any, ...optionalParams: any[]): void;
+}
+
+export type ExternalLogger = ConsoleLogger;
+
+/**
+ * LogProviderInterface to implement when adding a new logging provider for internal use
+ *
+ * ATTENTION: Please keep in mind that none of the trace, debug, info, warn or error should cause runtime errors.
+ *            Logging should default to a no-op in case it's not properly set up
+ */
+export interface LogProviderInterface {
+    trace: LogFunction;
+    debug: LogFunction;
+    info: LogFunction;
+    warn: LogFunction;
+    error: ErrorLogFunction;
+
+    /**
+     * connectLogger is meant to wire up an {@link ExternalLogger} to the internal logging provider
+     * @param logger The {@link ExternalLogger} to connect
+     */
+    connectLogger(logger: ExternalLogger): void;
+
+    log(level: LogLevel, message: string, data?: {}): void;
+}