// Package httputil provides typed handler adapters and HTTP response helpers.
//
// Handler adapters eliminate HTTP boilerplate — business functions stay pure Go
// with no knowledge of request parsing or response encoding. All errors flow
// through a centralized [Error] handler that logs once at the correct level and
// writes a standardized JSON response body.
//
// # Typed handler adapters
//
//	type CreateUserReq struct {
//	    Email string `json:"email" validate:"required,email"`
//	}
//	type CreateUserRes struct {
//	    ID string `json:"id"`
//	}
//
//	r.Post("/users", httputil.Handle(v, logger, func(ctx context.Context, req CreateUserReq) (CreateUserRes, error) {
//	    u, err := svc.CreateUser(ctx, req.Email)
//	    if err != nil {
//	        return CreateUserRes{}, err // propagates to Error — logged once, correct HTTP status
//	    }
//	    return CreateUserRes{ID: u.ID}, nil
//	}))
//
// # Request binding
//
// [Bind] and [BindEmpty] extend the same decode → validate → call → encode pipeline
// to requests that carry more than a JSON body. Each field declares its source with
// a struct tag — path:, query: or json: — and the assembled struct is validated once:
//
//	type getRoleReq struct {
//	    RoleID uuid.UUID `path:"roleID"  validate:"required"`
//	    Expand []string  `query:"expand"`
//	}
//
//	r.Get("/roles/{roleID}", httputil.Bind(v, logger, func(ctx context.Context, req getRoleReq) (RoleRes, error) {
//	    return svc.GetRole(ctx, req.RoleID)
//	}))
//
// A malformed value is a 400 naming the parameter (never a 500), uuid.UUID and
// time.Time bind via [encoding.TextUnmarshaler], and a mis-tagged struct fails at
// wiring rather than on a request. Use these instead of [HandlerFunc] for any route
// with an identifier or a filter.
//
// # Centralized error handler
//
// [Error] is the single point of error processing for all handlers:
//   - 5xx → Error level  (logz auto-enriches with error_code and WithContext fields)
//   - 4xx → Warn level   (client mistake — not a server failure)
//   - 499 → Info level   (client cancelled the request intentionally)
//
// Call it directly from [HandlerFunc] for genuinely custom responses — streaming,
// file downloads, non-JSON content types:
//
//	r.Get("/reports/{id}.csv", httputil.HandlerFunc(func(w http.ResponseWriter, r *http.Request) error {
//	    rows, err := svc.Export(r.Context(), chi.URLParam(r, "id"))
//	    if err != nil {
//	        httputil.Error(logger, w, r, err)
//	        return nil
//	    }
//	    w.Header().Set("Content-Type", "text/csv")
//	    return csv.NewWriter(w).WriteAll(rows)
//	}).ServeHTTP)
package httputil