package monitor

import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"

	"golang.org/x/mod/sumdb/note"
	"golang.org/x/mod/sumdb/tlog"
)

const userAgent = "gosumdbaudit/1.0 (+https://bnbl.io/gosumdbaudit)"

type Database struct {
	URL string
	Key string

	c http.Client
}

func (db *Database) readRemote(path string) ([]byte, error) {
	log.Printf("GET %s", path)
	req, err := http.NewRequest(http.MethodGet, "https://"+db.URL+path, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("user-agent", userAgent)
	resp, err := db.c.Do(req)
	if err != nil {
		return nil, err
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("get %s: expected HTTP OK but got %s", path, resp.Status)
	}
	if resp.ContentLength > 1e6 {
		return nil, fmt.Errorf("get %s: body too large (%d bytes)", path, resp.ContentLength)
	}
	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("get %s: %v", path, err)
	}
	return body, nil
}

func (db *Database) VerifyNote(msg []byte) (*note.Note, error) {
	verifier, err := note.NewVerifier(db.Key)
	if err != nil {
		return nil, err
	}
	return note.Open(msg, note.VerifierList(verifier))
}

func (db *Database) FetchSTH() (tlog.Tree, error) {
	resp, err := db.readRemote("/latest")
	if err != nil {
		return tlog.Tree{}, err
	}
	note, err := db.VerifyNote(resp)
	if err != nil {
		return tlog.Tree{}, err
	}
	return tlog.ParseTree([]byte(note.Text))
}