package util

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
)

// DecodeJSON reads and decodes JSON from r into v. It limits body size to maxBytes.
func DecodeJSON(r io.Reader, maxBytes int64, v any) error {
	lr := io.LimitReader(r, maxBytes+1)
	body, err := io.ReadAll(lr)
	if err != nil {
		return err
	}
	if int64(len(body)) > maxBytes {
		return fmt.Errorf("json body exceeds max size %d", maxBytes)
	}
	dec := json.NewDecoder(bytes.NewReader(body))
	dec.DisallowUnknownFields()
	return dec.Decode(v)
}

// WriteJSON writes v as JSON with Content-Type application/json.
func WriteJSON(w http.ResponseWriter, status int, v any) error {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	enc := json.NewEncoder(w)
	enc.SetEscapeHTML(true)
	return enc.Encode(v)
}

// MergeHeaders copies named headers from src to dst if present.
func MergeHeaders(dst, src http.Header, names ...string) {
	for _, n := range names {
		if v := src.Get(n); v != "" {
			dst.Set(n, v)
		}
	}
}