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📜 WAYPOINT LESSON

Checkpoint — The Layered Config Engine

⭐⭐ intermediate⏳ 25 min read📍 Lesson 125 of 265

Combine JSON, environment overrides, typed options, and validation into one provider that fails fast and keeps secrets out of code.

The gate (mini-build)

A layered configuration engine — the shape every real host uses:

  1. JsonConfig(string json) — parses { "Section": { "Key": "value" } }; Get("Section:Key") returns the value or null.
  2. LayeredConfig(IConfigProvider file, string envPrefix) — looks up env first (envPrefix__SECTION__KEY, upper-cased, : → __), then falls back to the file provider.
  3. BindRetry(IConfigProvider config) → typed RetryOptions (defaults 3 / 200) reading Retry:MaxAttempts and Retry:DelayMs as ints, with non-numeric values throwing FormatException.
  4. Validate(RetryOptions) — MaxAttempts >= 1, DelayMs >= 0; all problems in one message: "Retry: <p1>; <p2>".
  5. Secrets rule baked in: Require(config, key) returns the value or throws InvalidOperationException("Configuration key <key> is required") — no fallbacks.

Provided: IConfigProvider / MemoryConfig (same as the practice).