package mijia

import (
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"net/http"
	"strings"
)

const maxHTTPResponseBytes = 16 << 20

func readHTTPResponse(response *http.Response) ([]byte, error) {
	rawBody, err := readBounded(response.Body, maxHTTPResponseBytes)
	if err != nil {
		return nil, fmt.Errorf("read raw HTTP response: %w", err)
	}
	if !headerContainsToken(response.Header.Get("Content-Encoding"), "gzip") {
		return rawBody, nil
	}

	reader, err := gzip.NewReader(bytes.NewReader(rawBody))
	if err != nil {
		return nil, fmt.Errorf("open gzip HTTP response: %w", err)
	}
	body, readErr := readBounded(reader, maxHTTPResponseBytes)
	closeErr := reader.Close()
	if readErr != nil {
		return nil, fmt.Errorf("decompress gzip HTTP response: %w", readErr)
	}
	if closeErr != nil {
		return nil, fmt.Errorf("close gzip HTTP response: %w", closeErr)
	}
	return body, nil
}

func readBounded(reader io.Reader, maximum int64) ([]byte, error) {
	body, err := io.ReadAll(io.LimitReader(reader, maximum+1))
	if err != nil {
		return nil, err
	}
	if int64(len(body)) > maximum {
		return nil, fmt.Errorf("response exceeds %d bytes", maximum)
	}
	return body, nil
}

func headerContainsToken(value, token string) bool {
	for _, encoding := range strings.Split(value, ",") {
		if strings.EqualFold(strings.TrimSpace(encoding), token) {
			return true
		}
	}
	return false
}