package httpapi

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

const (
	internalErrorDetail = "an internal error occurred"
	badGatewayDetail    = "upstream request failed"
	notFoundDetail      = "resource not found"
	invalidInputDetail  = "invalid request data"
	cdnExtractDetail    = "could not extract prefixes from source"
	csvInvalidRowDetail = "invalid row in csv file"
)

// Problem is RFC 9457 application/problem+json.
type Problem struct {
	Type     string `json:"type,omitempty"`
	Title    string `json:"title"`
	Status   int    `json:"status"`
	Detail   string `json:"detail,omitempty"`
	Instance string `json:"instance,omitempty"`
}

func writeProblem(w http.ResponseWriter, status int, title, detail string) {
	w.Header().Set("Content-Type", "application/problem+json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(Problem{
		Type:   "about:blank",
		Title:  title,
		Status: status,
		Detail: detail,
	})
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func writeNoContent(w http.ResponseWriter) {
	w.WriteHeader(http.StatusNoContent)
}

// writeInternalError logs err server-side and returns a generic 500 problem (ERR-01).
func writeInternalError(w http.ResponseWriter, operation string, err error) {
	if err != nil {
		log.Printf("httpapi: %s: %v", operation, err)
	}
	writeProblem(w, http.StatusInternalServerError, "Internal Error", internalErrorDetail)
}

// writeBadGateway logs err server-side and returns a generic 502 problem (ERR-01).
func writeBadGateway(w http.ResponseWriter, operation string, err error) {
	if err != nil {
		log.Printf("httpapi: %s: %v", operation, err)
	}
	writeProblem(w, http.StatusBadGateway, "Bad Gateway", badGatewayDetail)
}