chore: adds SLO retries metrics

src/context.ts

@@ -0,0 +1,90 @@
+/**
+ * Context object allows to pass a context-chain (number of contexts, linked by "parent" field) thru function calls stack.
+ *
+ * To do this, you need to call functions like "context.do(() => [some function])".  And in this "some function" at the
+ * beginning execute "const context = getContext();".
+ *
+ * Create a new context - "new Context(context?)".  If context is provided, then new context considers it as a child-context.
+ * Otherwise, it's new context with an id, if newId() function was specified.
+ *
+ * Getting the context fields "... = context...".  Also, context might have methods.
+ *
+ * Specific part of context-chain can be obtained thru findContextByClass() method.
+ */
+export class Context {
+
+    readonly id?: any;
+    readonly parent?: Context;
+
+    constructor(parent?: Context) {
+        if (parent) {
+            if (parent.id) {
+                this.id = parent.id;
+            }
+            this.parent = parent;
+        } else {
+            const id = newId();
+            if (id) {
+                this.id = id;
+            }
+        }
+    }
+
+    do<T>(func: () => T): T {
+        const prevContext = _context;
+        try {
+            _context = this;
+            return func();
+        } finally {
+            _context = prevContext;
+        }
+    }
+
+    findContextByClass<T extends Context>(type: Function): T | null {
+        let ctx: Context | undefined = this;
+
+        while (ctx) {
+            if (ctx instanceof type) {
+                return ctx as T;
+            }
+            ctx = ctx.parent;
+        }
+
+        return null;
+    }
+
+    toString() {
+        return this.id ? `${this.id}: ` : '';
+    }
+}
+
+/**
+ * This is an object that does not contain any context, but allows to execute context.do().
+ */
+const NOT_A_CONTEXT = Object.create(Context.prototype);
+
+/**
+ * The current context so that it can be retrieved via getConext().
+ */
+let _context: any = NOT_A_CONTEXT;
+
+/**
+ * Method of generating a new id for a new context.
+ */
+let newId: () => any = () => undefined;
+
+/**
+ * Sets the id generator. By default, the id remain undefined.
+ */
+export function setContextNewId(generateNewId: () => any) {
+    newId = generateNewId;
+}
+
+/**
+ * The context must be taken in the begining of a function before a first 'await'.
+ *
+ * Ex.: const context = getContext();
+ */
+export function getContext(): Context {
+    return _context;
+}