package rest

import (
	"encoding/json"
	"io"
	"log/slog"
	"net/http"
	"strconv"
)

const (
	maxRequestBody = 1 << 20
	defaultLimit   = 50
	maxLimit       = 200
)

type errorResponse struct {
	Error string `json:"error"`
}

func writeJson(w http.ResponseWriter, status int, value any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	if value == nil {
		return
	}
	if err := json.NewEncoder(w).Encode(value); err != nil {
		slog.Error("encode response", slog.String("op", "rest.writeJson"), slog.Any("error", err))
	}
}

func writeError(w http.ResponseWriter, status int, message string) {
	writeJson(w, status, errorResponse{Error: message})
}

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

func decodeJson(r *http.Request, dst any) error {
	decoder := json.NewDecoder(io.LimitReader(r.Body, maxRequestBody))
	decoder.DisallowUnknownFields()
	return decoder.Decode(dst)
}

func pagination(r *http.Request) (limit, offset int64) {
	limit = defaultLimit
	query := r.URL.Query()

	if value := query.Get("limit"); value != "" {
		if parsed, err := strconv.ParseInt(value, 10, 64); err == nil && parsed > 0 {
			limit = parsed
		}
	}
	if limit > maxLimit {
		limit = maxLimit
	}

	if value := query.Get("offset"); value != "" {
		if parsed, err := strconv.ParseInt(value, 10, 64); err == nil && parsed >= 0 {
			offset = parsed
		}
	}

	return limit, offset
}