// Package api provides small HTTP helpers shared by the HTTP handlers.
package api

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

// Error is an error that serializes to the shape {"error": message}.
type Error struct {
	Err string `json:"error"`
}

// Error returns the error message.
func (e Error) Error() string { return e.Err }

// NewError returns an Error with the given message.
func NewError(msg string) error { return Error{Err: msg} }

// WriteJSON writes a JSON response. A nil payload writes only the status code.
func WriteJSON(w http.ResponseWriter, status int, payload any) {
	if payload == nil {
		w.WriteHeader(status)
		return
	}

	data, err := json.Marshal(payload)

	if err != nil {
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusInternalServerError)
		_, _ = w.Write([]byte(`{"error":"Failed to encode JSON response"}`))
		return
	}

	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_, _ = w.Write(data)
}

// WriteError writes an error response with the given status code.
func WriteError(w http.ResponseWriter, status int, msg string) {
	WriteJSON(w, status, Error{Err: msg})
}

// DecodeJSON decodes a JSON request body into a new value of type T.
func DecodeJSON[T any](r *http.Request) (*T, error) {
	defer r.Body.Close()

	decoder := json.NewDecoder(r.Body)
	var data *T

	if err := decoder.Decode(&data); err != nil {
		return nil, NewError("Failed to deserialize request")
	}

	return data, nil
}