// Package httputil holds the small HTTP response helpers shared by every API
// handler package (docs, suggestions, vocab, …). Keeping them in one place means
// JSON encoding and — crucially — error handling behave identically everywhere:
// internal errors are logged in full but never leaked to the client.
package httputil

import (
	"encoding/json"
	"log"
	"net/http"
)

// WriteJSON encodes v as the response body with the given status code.
func WriteJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

// ErrorJSON sends a {"error": msg} body with the given status. The message is
// caller-chosen and safe to show the client.
func ErrorJSON(w http.ResponseWriter, status int, msg string) {
	WriteJSON(w, status, map[string]string{"error": msg})
}

// BadRequest is the common 400 shorthand.
func BadRequest(w http.ResponseWriter, msg string) {
	ErrorJSON(w, http.StatusBadRequest, msg)
}

// ServerError logs the real error (with full detail, for the operator) and
// returns a generic 500 to the client — raw database/internal errors must never
// reach the browser, where they leak schema and implementation details.
func ServerError(w http.ResponseWriter, err error) {
	log.Printf("internal error: %v", err)
	ErrorJSON(w, http.StatusInternalServerError, "something went wrong")
}

// UpstreamError is ServerError's counterpart for a dependency Petal calls out
// to — the model, chiefly. Same discipline, and for a sharper reason: a dial
// failure's error text contains the endpoint it failed to dial, so relaying it
// hands anyone who can reach Petal the address of the inference box on the far
// side of the VPN, along with which backend is running there.
//
// `what` names the pass for the operator's log ("checkpoint", "chat"). The
// browser is told only that the helper is unreachable, which is all the client
// ever did anything with: every LLM route's 502 renders as the same warm
// "小助手在休息 · Petal's helper is resting".
func UpstreamError(w http.ResponseWriter, what string, err error) {
	log.Printf("upstream error (%s): %v", what, err)
	ErrorJSON(w, http.StatusBadGateway, "Petal's helper is out of reach right now")
}