package publicrelease

import (
	"crypto/ed25519"
	"encoding/base64"
	"errors"
	"regexp"
	"strings"
)

// ErrSums is every way a checksum list can fail VerifySums.
var ErrSums = errors.New("publicrelease: signed checksum list refused")

var sumLine = regexp.MustCompile(`^([0-9a-f]{64})  (\S+)$`)

// VerifySums checks a release's SHA256SUMS.txt against its .sig with pubKey
// (base64 ed25519, over the raw sums bytes, as Feed.Sums checks it) and
// returns asset name to sha256. Unlike Feed.Sums it is strict, because its
// caller signs what it returns into deployment authority: every line must be
// sha256sum's text form, "<64 lowercase hex>  <name>", each name once, and a
// list with no lines is refused. It reads nothing from the network.
func VerifySums(pubKey string, sums []byte, sig string) (map[string]string, error) {
	pub, err := base64.StdEncoding.DecodeString(pubKey)
	if err != nil || len(pub) != ed25519.PublicKeySize {
		return nil, ErrSums
	}
	raw, err := base64.StdEncoding.DecodeString(strings.TrimSpace(sig))
	if err != nil || len(raw) != ed25519.SignatureSize || !ed25519.Verify(ed25519.PublicKey(pub), sums, raw) {
		return nil, ErrSums
	}
	text := string(sums)
	if !strings.HasSuffix(text, "\n") {
		return nil, ErrSums
	}
	out := map[string]string{}
	for _, line := range strings.Split(strings.TrimSuffix(text, "\n"), "\n") {
		m := sumLine.FindStringSubmatch(line)
		if m == nil {
			return nil, ErrSums
		}
		if _, dup := out[m[2]]; dup {
			return nil, ErrSums
		}
		out[m[2]] = m[1]
	}
	return out, nil
}