1 files changed, 86 insertions, 0 deletions
diff --git a/u/trace/logger.ts b/u/trace/logger.ts
new file mode 100644
index 0000000..79da367
--- /dev/null
+++ b/u/trace/logger.ts
@@ -0,0 +1,86 @@
+import {
+  isDebug,
+  isObject,
+  type ITrace,
+  type SideEffect,
+  type Supplier,
+} from "@emprespresso/utils";
+
+export interface ILogger {
+  log: (...args: unknown[]) => void;
+  debug: (...args: unknown[]) => void;
+  warn: (...args: unknown[]) => void;
+  error: (...args: unknown[]) => void;
+}
+export type ILoggerLevel = "UNKNOWN" | "INFO" | "WARN" | "DEBUG" | "ERROR";
+const logLevelOrder: Array<ILoggerLevel> = ["DEBUG", "INFO", "WARN", "ERROR"];
+const defaultAllowedLevels = () =>
+  [
+    "UNKNOWN",
+    ...(isDebug() ? ["DEBUG"] : []),
+    "INFO",
+    "WARN",
+    "ERROR",
+  ] as Array<ILoggerLevel>;
+
+export const logWithLevel = (
+  logger: ILogger,
+  level: ILoggerLevel,
+): SideEffect<unknown> => {
+  switch (level) {
+    case "UNKNOWN":
+    case "INFO":
+      return logger.log;
+    case "DEBUG":
+      return logger.debug;
+    case "WARN":
+      return logger.warn;
+    case "ERROR":
+      return logger.error;
+  }
+};
+
+export const LoggerImpl = console;
+
+export type LogTraceSupplier = string | Supplier<string> | {
+  level: ILoggerLevel;
+};
+
+const foldTraces = (traces: Array<LogTraceSupplier>) => {
+  const { line, level } = traces.reduce(
+    (acc: { line: string; level: number }, t) => {
+      if (isObject(t) && "level" in t) {
+        return {
+          ...acc,
+          level: Math.max(logLevelOrder.indexOf(t.level), acc.level),
+        };
+      }
+      const prefix = [
+        acc.line,
+        typeof t === "function" ? t() : t,
+      ].join(" ");
+      return { ...acc, prefix };
+    },
+    { line: "", level: -1 },
+  );
+  return { line, level: logLevelOrder[level] ?? "UNKNOWN" };
+};
+
+const defaultTrace = () => `[${new Date().toISOString()}]`;
+export const LogTrace = (
+  logger: ILogger,
+  traces: Array<LogTraceSupplier> = [defaultTrace],
+  allowedLevels: Supplier<Array<ILoggerLevel>> = defaultAllowedLevels,
+  defaultLevel: ILoggerLevel = "INFO",
+): ITrace<LogTraceSupplier> => {
+  return {
+    addTrace: (trace: LogTraceSupplier) =>
+      LogTrace(logger, traces.concat(trace)),
+    trace: (trace: LogTraceSupplier) => {
+      const { line, level: _level } = foldTraces(traces.concat(trace));
+      if (!allowedLevels().includes(_level)) return;
+      const level = _level === "UNKNOWN" ? defaultLevel : _level;
+      logWithLevel(logger, level)(`[${level}]${line}`);
+    },
+  };
+};