// Package common contains cross-provider helper code used by weatherfeeder normalizers.
//
// Purpose
// -------
// Normalizers convert provider-specific RAW payloads into canonical internal/model types.
// Some small utilities are naturally reusable across multiple providers (unit conversions,
// payload extraction, common parsing, shared fallbacks). Those belong here.
//
// This package is intentionally "boring":
//   - pure helpers (deterministic, no I/O)
//   - minimal abstractions (prefer straightforward functions)
//   - easy to unit test
//
// What belongs here
// -----------------
// Put code in internal/normalizers/common when it is:
//
//   - potentially reusable by more than one provider
//   - provider-agnostic (no NWS/OpenWeather/Open-Meteo specific assumptions)
//   - stable, small, and readable
//
// Typical examples:
//   - unit conversion helpers (°F <-> °C, m/s <-> km/h, hPa <-> Pa, etc.)
//   - json.RawMessage payload extraction helpers (with good error messages)
//   - shared parsing helpers (timestamps, simple numeric coercions)
//   - generic fallbacks (e.g., mapping a human text description into a coarse canonical code),
//     so long as the logic truly applies across providers
//
// What does NOT belong here
// -------------------------
// Do NOT put the following in this package:
//
//   - Normalizer implementations (types that satisfy feedkit/normalize.Normalizer)
//   - provider-specific JSON structs or mapping logic (put those under
//     internal/normalizers/<provider>/)
//   - network or filesystem I/O (sources fetch; normalizers transform)
//   - code that depends on event.Source naming, config fields, or driver-specific params
//
// Style and API guidelines
// ------------------------
//   - Prefer small, single-purpose functions.
//   - Keep function names explicit (avoid clever generic “DoThing” helpers).
//   - Return typed errors with context (include schema/field names where helpful).
//   - Keep dependencies minimal: standard library + weatherfeeder packages only.
//   - Add unit tests for any non-trivial logic (especially parsing and fallbacks).
//
// Keeping this clean matters: common is shared by all providers, so complexity here
// multiplies across the project.
package common