1 files changed, 92 insertions, 0 deletions
diff --git a/shared/logger/src/composite.ts b/shared/logger/src/composite.ts
new file mode 100644
index 0000000..a3c4d69
--- /dev/null
+++ b/shared/logger/src/composite.ts
@@ -0,0 +1,92 @@
+import type { LoggerFactory, Logger } from './types';
+
+export class CompositeLoggerFactory implements LoggerFactory {
+    private readonly factories: LoggerFactory[];
+
+    constructor(factories: LoggerFactory[]) {
+        this.factories = factories;
+    }
+
+    loggerFor(name: string): Logger {
+        return new CompositeLogger(
+            this.factories.map((factory) => factory.loggerFor(name)),
+        );
+    }
+}
+
+export class CompositeLogger implements Logger {
+    private readonly loggers: Logger[];
+
+    constructor(loggers: Logger[]) {
+        this.loggers = loggers;
+    }
+
+    /**
+     * Log a debug level message.
+     * Appropriate for verbose logging that explains steps/details of the inner state of
+     * a code unit.
+     *
+     * Example uses include in a size-constrain datastructure, logging when the size
+     * exceeds the threshold and elements are removed, or in a virtual scrolling
+     * component logging when a scroll event causes a new page of elements to be loaded.
+     *
+     * @param args Arguments to log (same as console.debug)
+     * @return empty string (for use in brackets {} in svelte components)
+     */
+    debug(...args: unknown[]): string {
+        return this.callAll('debug', args);
+    }
+
+    /**
+     * Log an info level message.
+     * Appropriate for informational messages that may be relevant to consumers of a code
+     * unit.
+     *
+     * Example uses include a router logging when transitions occur or a button logging
+     * clicks.
+     *
+     * @param args Arguments to log (same as console.info)
+     * @return empty string (for use in brackets {} in svelte components)
+     */
+    info(...args: unknown[]): string {
+        return this.callAll('info', args);
+    }
+
+    /**
+     * Log a warn level message.
+     * Appropriate for situations where state has been (or likely will be) corrupted or
+     * invariants have been broken.
+     *
+     * Example uses include a data structure warning when it is used before being fully
+     * initialized.
+     *
+     * @param args Arguments to log (same as console.warn)
+     * @return empty string (for use in brackets {} in svelte components)
+     */
+    warn(...args: unknown[]): string {
+        return this.callAll('warn', args);
+    }
+
+    /**
+     * Log an error message.
+     * Appropriate for thrown errors or situations where the apps breaks or has to
+     * engage in fallback behavior to avoid a more catastrophic failure.
+     *
+     * @param args Arguments to log (same as console.error)
+     * @return empty string (for use in brackets {} in svelte components)
+     */
+    error(...args: unknown[]): string {
+        return this.callAll('error', args);
+    }
+
+    private callAll(
+        method: 'debug' | 'info' | 'warn' | 'error',
+        args: unknown[],
+    ): string {
+        for (const logger of this.loggers) {
+            logger[method](...args);
+        }
+
+        return '';
+    }
+}