package authority

import (
	"crypto/ed25519"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
)

const (
	AuthoritySchemaVersion = "rap.cluster_authority.v1"
	SignatureSchemaVersion = "rap.cluster_authority.signature.v1"
	QuorumSchemaVersion    = "rap.cluster_authority.quorum.v1"
	QuorumEnvelopeVersion  = "rap.cluster_authority.quorum_envelope.v1"
	AlgorithmEd25519       = "ed25519"
)

var (
	ErrInvalidKey       = errors.New("invalid cluster authority key")
	ErrInvalidSignature = errors.New("invalid cluster authority signature")
	ErrInvalidPayload   = errors.New("invalid cluster authority payload")
)

type Signature struct {
	SchemaVersion  string `json:"schema_version"`
	Algorithm      string `json:"algorithm"`
	KeyFingerprint string `json:"key_fingerprint"`
	Signature      string `json:"signature"`
}

type QuorumMember struct {
	NodeID               string   `json:"node_id,omitempty"`
	Role                 string   `json:"role,omitempty"`
	PublicKey            string   `json:"public_key"`
	PublicKeyFingerprint string   `json:"public_key_fingerprint"`
	Scopes               []string `json:"scopes,omitempty"`
}

type QuorumDescriptor struct {
	SchemaVersion string         `json:"schema_version"`
	ClusterID     string         `json:"cluster_id"`
	Epoch         string         `json:"epoch"`
	Threshold     int            `json:"threshold"`
	Members       []QuorumMember `json:"members"`
}

type QuorumEnvelope struct {
	SchemaVersion  string      `json:"schema_version"`
	ClusterID      string      `json:"cluster_id"`
	Epoch          string      `json:"epoch"`
	Threshold      int         `json:"threshold"`
	PayloadSHA256  string      `json:"payload_sha256"`
	QuorumSHA256   string      `json:"quorum_sha256"`
	Signatures     []Signature `json:"signatures"`
	AllowedScopes  []string    `json:"allowed_scopes,omitempty"`
	DecisionReason string      `json:"decision_reason,omitempty"`
}

func VerifyRaw(publicKeyB64 string, payload json.RawMessage, signature Signature) error {
	if signature.SchemaVersion != SignatureSchemaVersion {
		return fmt.Errorf("%w: schema_version must be %s", ErrInvalidSignature, SignatureSchemaVersion)
	}
	if signature.Algorithm != AlgorithmEd25519 {
		return fmt.Errorf("%w: algorithm must be %s", ErrInvalidSignature, AlgorithmEd25519)
	}
	publicKey, err := decodePublicKey(publicKeyB64)
	if err != nil {
		return err
	}
	if signature.KeyFingerprint != Fingerprint(publicKey) {
		return fmt.Errorf("%w: key fingerprint mismatch", ErrInvalidSignature)
	}
	canonical, err := CanonicalJSON(payload)
	if err != nil {
		return err
	}
	decodedSignature, err := decodeBase64(strings.TrimSpace(signature.Signature))
	if err != nil || len(decodedSignature) != ed25519.SignatureSize {
		return fmt.Errorf("%w: signature must be base64 ed25519 signature", ErrInvalidSignature)
	}
	if !ed25519.Verify(publicKey, canonical, decodedSignature) {
		return ErrInvalidSignature
	}
	return nil
}

func VerifyQuorumRaw(descriptor QuorumDescriptor, payload json.RawMessage, envelope QuorumEnvelope, requiredScope string) error {
	if descriptor.SchemaVersion != QuorumSchemaVersion {
		return fmt.Errorf("%w: quorum schema_version must be %s", ErrInvalidSignature, QuorumSchemaVersion)
	}
	if envelope.SchemaVersion != QuorumEnvelopeVersion {
		return fmt.Errorf("%w: quorum envelope schema_version must be %s", ErrInvalidSignature, QuorumEnvelopeVersion)
	}
	if strings.TrimSpace(descriptor.ClusterID) == "" || descriptor.ClusterID != envelope.ClusterID {
		return fmt.Errorf("%w: quorum cluster mismatch", ErrInvalidSignature)
	}
	if strings.TrimSpace(descriptor.Epoch) == "" || descriptor.Epoch != envelope.Epoch {
		return fmt.Errorf("%w: quorum epoch mismatch", ErrInvalidSignature)
	}
	threshold := descriptor.Threshold
	if envelope.Threshold > threshold {
		threshold = envelope.Threshold
	}
	if threshold <= 0 || threshold > len(descriptor.Members) {
		return fmt.Errorf("%w: invalid quorum threshold", ErrInvalidSignature)
	}
	payloadHash, err := HashRaw(payload)
	if err != nil {
		return err
	}
	if envelope.PayloadSHA256 != payloadHash {
		return fmt.Errorf("%w: quorum payload hash mismatch", ErrInvalidSignature)
	}
	descriptorHash, err := HashRaw(mustMarshalQuorumDescriptor(descriptor))
	if err != nil {
		return err
	}
	if envelope.QuorumSHA256 != descriptorHash {
		return fmt.Errorf("%w: quorum descriptor hash mismatch", ErrInvalidSignature)
	}
	members := map[string]QuorumMember{}
	for _, member := range descriptor.Members {
		fingerprint := strings.TrimSpace(member.PublicKeyFingerprint)
		if fingerprint == "" {
			publicKey, err := decodePublicKey(member.PublicKey)
			if err != nil {
				return err
			}
			fingerprint = Fingerprint(publicKey)
		}
		if _, exists := members[fingerprint]; exists {
			return fmt.Errorf("%w: duplicate quorum member", ErrInvalidSignature)
		}
		member.PublicKeyFingerprint = fingerprint
		members[fingerprint] = member
	}
	seen := map[string]bool{}
	valid := 0
	for _, signature := range envelope.Signatures {
		fingerprint := strings.TrimSpace(signature.KeyFingerprint)
		if seen[fingerprint] {
			continue
		}
		member, ok := members[fingerprint]
		if !ok {
			return fmt.Errorf("%w: quorum signer is not a member", ErrInvalidSignature)
		}
		if requiredScope != "" && !memberAllowsScope(member, requiredScope) {
			return fmt.Errorf("%w: quorum signer scope mismatch", ErrInvalidSignature)
		}
		if err := VerifyRaw(member.PublicKey, payload, signature); err != nil {
			return err
		}
		seen[fingerprint] = true
		valid++
	}
	if valid < threshold {
		return fmt.Errorf("%w: quorum threshold not met", ErrInvalidSignature)
	}
	return nil
}

func QuorumDescriptorHash(descriptor QuorumDescriptor) (string, error) {
	return HashRaw(mustMarshalQuorumDescriptor(descriptor))
}

func Fingerprint(publicKey ed25519.PublicKey) string {
	sum := sha256.Sum256(publicKey)
	return "rap-ca-ed25519-" + hex.EncodeToString(sum[:16])
}

func HashRaw(raw json.RawMessage) (string, error) {
	canonical, err := CanonicalJSON(raw)
	if err != nil {
		return "", err
	}
	sum := sha256.Sum256(canonical)
	return hex.EncodeToString(sum[:]), nil
}

func mustMarshalQuorumDescriptor(descriptor QuorumDescriptor) json.RawMessage {
	raw, err := json.Marshal(descriptor)
	if err != nil {
		return nil
	}
	return raw
}

func memberAllowsScope(member QuorumMember, requiredScope string) bool {
	requiredScope = strings.TrimSpace(requiredScope)
	if requiredScope == "" {
		return true
	}
	for _, scope := range member.Scopes {
		scope = strings.TrimSpace(scope)
		if scope == "*" || scope == requiredScope {
			return true
		}
	}
	return false
}

func CanonicalJSON(raw json.RawMessage) ([]byte, error) {
	if len(raw) == 0 {
		return nil, fmt.Errorf("%w: empty payload", ErrInvalidPayload)
	}
	var value any
	if err := json.Unmarshal(raw, &value); err != nil {
		return nil, fmt.Errorf("%w: invalid json: %v", ErrInvalidPayload, err)
	}
	canonical, err := json.Marshal(value)
	if err != nil {
		return nil, fmt.Errorf("%w: canonical json: %v", ErrInvalidPayload, err)
	}
	return canonical, nil
}

func decodePublicKey(value string) (ed25519.PublicKey, error) {
	decoded, err := decodeBase64(strings.TrimSpace(value))
	if err != nil {
		return nil, fmt.Errorf("%w: public key must be base64 encoded", ErrInvalidKey)
	}
	if len(decoded) != ed25519.PublicKeySize {
		return nil, fmt.Errorf("%w: public key must decode to %d bytes", ErrInvalidKey, ed25519.PublicKeySize)
	}
	return ed25519.PublicKey(decoded), nil
}

func decodeBase64(value string) ([]byte, error) {
	if value == "" {
		return nil, errors.New("empty base64 value")
	}
	decoded, err := base64.StdEncoding.DecodeString(value)
	if err == nil {
		return decoded, nil
	}
	return base64.RawStdEncoding.DecodeString(value)
}