package hostevidence

import (
	"bytes"
	"context"
	"crypto/ed25519"
	"errors"
	"strings"

	"github.com/carlosframework/platform/internal/release"
)

var ErrSignature = errors.New("hostevidence: invalid receipt signature")

func message(key string, body []byte) ([]byte, error) {
	parts := strings.Split(key, "/")
	if len(parts) < 6 || parts[0] != "control" || parts[1] != "hosts" ||
		!((len(parts) == 7 && parts[3] == "evidence") || (len(parts) == 6 && parts[3] == "serving-evidence")) ||
		!strings.HasSuffix(key, ".json") || strings.ContainsAny(key, "\\\x00\r\n") {
		return nil, ErrSignature
	}
	for _, part := range parts {
		if part == "" || part == "." || part == ".." {
			return nil, ErrSignature
		}
	}
	out := append([]byte("carlos-host-stop-v1\x00"+key+"\x00"), body...)
	return out, nil
}
func Verify(pub ed25519.PublicKey, key string, body, signature []byte) error {
	wire, err := message(key, body)
	if err != nil || len(pub) != ed25519.PublicKeySize || len(signature) != ed25519.SignatureSize || !ed25519.Verify(pub, wire, signature) {
		return ErrSignature
	}
	return nil
}
func immutable(ctx context.Context, s release.Store, key string, body []byte) error {
	if _, err := s.Put(ctx, key, body, ""); err == nil {
		return nil
	} else if !errors.Is(err, release.ErrCASConflict) {
		return err
	}
	existing, _, err := s.Get(ctx, key)
	if err != nil {
		return err
	}
	if !bytes.Equal(existing, body) {
		return ErrSignature
	}
	return nil
}
func Publish(ctx context.Context, s release.Store, private ed25519.PrivateKey, key string, body []byte) error {
	wire, err := message(key, body)
	if err != nil || s == nil || len(private) != ed25519.PrivateKeySize {
		return ErrSignature
	}
	signature := ed25519.Sign(private, wire)
	if err = immutable(ctx, s, key, body); err != nil {
		return err
	}
	return immutable(ctx, s, key+".sig", signature)
}