package ip

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"net"
	"net/http"
)

const ifconfigURL = "https://ifconfig.me"
const httpMaxRead = 100

// TODO: use a struct, but a baseHTTPClient inside it to perform unit tests
type Getter interface {
	GetCurrentPublicIP(ctx context.Context) (net.IP, error)
}

type concreteIPGetter struct {
}

func (c *concreteIPGetter) GetCurrentPublicIP(ctx context.Context) (net.IP, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, ifconfigURL, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to prepare public IP request: %w", err)
	}
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("failed to get current IP from ifconfig: %w", err)
	}

	if resp.ContentLength > httpMaxRead {
		return nil, fmt.Errorf("response too big: %d/%d", resp.ContentLength, httpMaxRead)
	}

	buf := bytes.NewBuffer([]byte{})
	if _, err := io.CopyN(buf, resp.Body, resp.ContentLength); err != nil {
		return nil, fmt.Errorf("error parsing body: %w", err)
	}

	content := string(buf.Bytes())
	res := net.ParseIP(content)
	if res == nil {
		return nil, fmt.Errorf("got an invalid public IP %q", content)
	}
	return res, nil
}

func New() *concreteIPGetter {
	return &concreteIPGetter{}
}