package attesto

import (
	"bytes"
	"crypto/ed25519"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"math"
	"sort"
	"strconv"
	"strings"
	"time"
)

var ProofstreamDomains = map[string]string{
	"anchor":         "attesto.v2.anchor",
	"bundle":         "attesto.v2.bundle",
	"checkpoint":     "attesto.v2.checkpoint",
	"consistency":    "attesto.v2.consistency",
	"event":          "attesto.v2.event",
	"fork":           "attesto.v2.fork",
	"ivc":            "attesto.v2.ivc",
	"receipt":        "attesto.v2.receipt",
	"stream":         "attesto.v2.stream",
	"window":         "attesto.v2.window",
	"witness":        "attesto.v2.witness",
	"witness_policy": "attesto.v2.witness_policy",
}

func CanonicalJSON(value any) ([]byte, error) {
	normalized, err := normalizeCanonical(value)
	if err != nil {
		return nil, err
	}
	var buf bytes.Buffer
	encoder := json.NewEncoder(&buf)
	encoder.SetEscapeHTML(false)
	if err := encoder.Encode(normalized); err != nil {
		return nil, err
	}
	return bytes.TrimSuffix(buf.Bytes(), []byte("\n")), nil
}

func CanonicalJSONHex(value any) (string, error) {
	raw, err := CanonicalJSON(value)
	if err != nil {
		return "", err
	}
	return hex.EncodeToString(raw), nil
}

func DomainHashHex(domain string, value any) (string, error) {
	raw, err := CanonicalJSON(value)
	if err != nil {
		return "", err
	}
	h := sha256.New()
	h.Write([]byte(domain))
	h.Write([]byte{0})
	h.Write(raw)
	return hex.EncodeToString(h.Sum(nil)), nil
}

func SHA256Hex(value []byte) string {
	sum := sha256.Sum256(value)
	return hex.EncodeToString(sum[:])
}

// maxSafeInteger mirrors JavaScript's Number.MAX_SAFE_INTEGER (2^53 - 1).
// Integers beyond this lose precision when a JS verifier parses them, so they
// would re-serialize to different canonical bytes across languages.
const maxSafeInteger = int64(1)<<53 - 1

// UnsafeNumberError reports a committed payload/metadata number whose
// canonical-JSON bytes diverge across Python, Go, and JavaScript (a non-integer,
// or an integer outside +/-(2^53 - 1)). Path is the JSON path to the offender.
type UnsafeNumberError struct {
	Path    string
	Message string
}

func (e *UnsafeNumberError) Error() string { return e.Message }

func nonIntegerError(path string) *UnsafeNumberError {
	return &UnsafeNumberError{
		Path: path,
		Message: fmt.Sprintf(
			"non-integer numbers are not permitted in committed payloads (%s); "+
				"encode decimals as strings", path),
	}
}

func unsafeIntegerError(path string) *UnsafeNumberError {
	return &UnsafeNumberError{
		Path: path,
		Message: fmt.Sprintf(
			"integers beyond +/-2^53-1 are not permitted in committed payloads (%s); "+
				"encode large integers as strings", path),
	}
}

func assertSafeFloat(v float64, path string) error {
	if math.IsInf(v, 0) || math.IsNaN(v) || math.Trunc(v) != v {
		return nonIntegerError(path)
	}
	if math.Abs(v) > float64(maxSafeInteger) {
		return unsafeIntegerError(path)
	}
	return nil
}

func assertSafeInt64(v int64, path string) error {
	if v > maxSafeInteger || v < -maxSafeInteger {
		return unsafeIntegerError(path)
	}
	return nil
}

func assertSafeNumberString(s, path string) error {
	if strings.ContainsAny(s, ".eE") {
		f, err := strconv.ParseFloat(s, 64)
		if err != nil {
			return nonIntegerError(path)
		}
		return assertSafeFloat(f, path)
	}
	n, err := strconv.ParseInt(s, 10, 64)
	if err != nil {
		// Outside int64 range is necessarily outside the safe integer range.
		return unsafeIntegerError(path)
	}
	return assertSafeInt64(n, path)
}

// AssertCommitmentSafeNumbers rejects numbers whose canonical-JSON bytes diverge
// across Python, Go, and JavaScript, so a commitment computed here matches the
// backend's byte-for-byte. Mirrors assert_commitment_safe_numbers in the backend:
// non-integer numbers are rejected outright; integers must be within +/-(2^53 - 1).
// Booleans are exempt. Returns an *UnsafeNumberError on the first offending value.
func AssertCommitmentSafeNumbers(value any, path string) error {
	switch v := value.(type) {
	case nil, bool, string:
		return nil
	case json.Number:
		return assertSafeNumberString(v.String(), path)
	case float64:
		return assertSafeFloat(v, path)
	case float32:
		return assertSafeFloat(float64(v), path)
	case int:
		return assertSafeInt64(int64(v), path)
	case int8:
		return assertSafeInt64(int64(v), path)
	case int16:
		return assertSafeInt64(int64(v), path)
	case int32:
		return assertSafeInt64(int64(v), path)
	case int64:
		return assertSafeInt64(v, path)
	case uint:
		return assertSafeUint64(uint64(v), path)
	case uint8:
		return assertSafeInt64(int64(v), path)
	case uint16:
		return assertSafeInt64(int64(v), path)
	case uint32:
		return assertSafeInt64(int64(v), path)
	case uint64:
		return assertSafeUint64(v, path)
	case []any:
		for i, item := range v {
			if err := AssertCommitmentSafeNumbers(item, fmt.Sprintf("%s[%d]", path, i)); err != nil {
				return err
			}
		}
		return nil
	case []M:
		for i, item := range v {
			if err := AssertCommitmentSafeNumbers(item, fmt.Sprintf("%s[%d]", path, i)); err != nil {
				return err
			}
		}
		return nil
	case map[string]any:
		return assertSafeMap(v, path)
	case M:
		return assertSafeMap(map[string]any(v), path)
	default:
		// Structs and other types: normalize through JSON exactly as the
		// canonical encoder does, then re-check the plain representation.
		raw, err := json.Marshal(v)
		if err != nil {
			return err
		}
		var decoded any
		dec := json.NewDecoder(bytes.NewReader(raw))
		dec.UseNumber()
		if err := dec.Decode(&decoded); err != nil {
			return err
		}
		return AssertCommitmentSafeNumbers(decoded, path)
	}
}

func assertSafeUint64(v uint64, path string) error {
	if v > uint64(maxSafeInteger) {
		return unsafeIntegerError(path)
	}
	return nil
}

func assertSafeMap(m map[string]any, path string) error {
	for key, item := range m {
		if err := AssertCommitmentSafeNumbers(item, fmt.Sprintf("%s.%s", path, key)); err != nil {
			return err
		}
	}
	return nil
}

// PayloadCommitment returns a deterministic commitment to an event payload,
// byte-identical to the server's stored payload_commitment. Call
// AssertCommitmentSafeNumbers first if the payload is not yet known to be safe.
func PayloadCommitment(payload any) (map[string]string, error) {
	raw, err := CanonicalJSON(payload)
	if err != nil {
		return nil, err
	}
	return map[string]string{
		"hash_alg":               "sha256",
		"canonical_payload_hash": SHA256Hex(raw),
	}, nil
}

// MetadataCommitment returns a deterministic commitment to event metadata,
// byte-identical to the server's stored metadata_commitment.
func MetadataCommitment(metadata any) (map[string]string, error) {
	raw, err := CanonicalJSON(metadata)
	if err != nil {
		return nil, err
	}
	return map[string]string{
		"hash_alg":                "sha256",
		"canonical_metadata_hash": SHA256Hex(raw),
	}, nil
}

func storedCommitmentHash(event map[string]any, commitmentKey, hashKey string) string {
	containers := []any{event, event["envelope"], event["envelope_json"]}
	for _, container := range containers {
		obj, ok := container.(map[string]any)
		if !ok {
			continue
		}
		commitment, ok := obj[commitmentKey].(map[string]any)
		if !ok {
			continue
		}
		if stored, ok := commitment[hashKey].(string); ok {
			return stored
		}
	}
	return ""
}

// VerifyPayloadCommitment recomputes the payload commitment locally and compares
// it to the value stored on an event (payload_commitment.canonical_payload_hash,
// whether the event is given flat or under envelope / envelope_json). Returns
// false when the stored commitment is absent or differs.
func VerifyPayloadCommitment(payload any, event map[string]any) (bool, error) {
	stored := storedCommitmentHash(event, "payload_commitment", "canonical_payload_hash")
	if stored == "" {
		return false, nil
	}
	commitment, err := PayloadCommitment(payload)
	if err != nil {
		return false, err
	}
	return commitment["canonical_payload_hash"] == stored, nil
}

// VerifyMetadataCommitment recomputes the metadata commitment locally and
// compares it to the value stored on an event.
func VerifyMetadataCommitment(metadata any, event map[string]any) (bool, error) {
	stored := storedCommitmentHash(event, "metadata_commitment", "canonical_metadata_hash")
	if stored == "" {
		return false, nil
	}
	commitment, err := MetadataCommitment(metadata)
	if err != nil {
		return false, err
	}
	return commitment["canonical_metadata_hash"] == stored, nil
}

func windowNodeHash(left, right string) (string, error) {
	return DomainHashHex(ProofstreamDomains["window"], map[string]any{
		"kind": "node", "left_hash": left, "right_hash": right,
	})
}

func checkpointNodeHash(left, right string) (string, error) {
	return DomainHashHex(ProofstreamDomains["checkpoint"], map[string]any{
		"kind": "node", "left_hash": left, "right_hash": right,
	})
}

// InclusionStep is one node of a window inclusion proof.
type InclusionStep struct {
	Side string `json:"side"`
	Hash string `json:"hash"`
}

// VerifyInclusionProof folds a window inclusion proof from a leaf up to the
// window root. Mirrors verify_inclusion_proof in the backend windows.py: a left
// sibling hashes as node(sibling, current), a right sibling as node(current, sibling).
func VerifyInclusionProof(leafHash string, proof []InclusionStep, rootHash string) (bool, error) {
	current := leafHash
	for _, step := range proof {
		var err error
		switch step.Side {
		case "left":
			if step.Hash == "" {
				return false, nil
			}
			current, err = windowNodeHash(step.Hash, current)
		case "right":
			if step.Hash == "" {
				return false, nil
			}
			current, err = windowNodeHash(current, step.Hash)
		default:
			return false, nil
		}
		if err != nil {
			return false, err
		}
	}
	return current == rootHash, nil
}

// VerifyCheckpointRoot recomputes a checkpoint root from its window hashes and
// compares. Mirrors checkpoint_root_hash in the backend checkpoints.py: an odd
// node at any level is promoted unchanged (never duplicated/hashed with itself).
func VerifyCheckpointRoot(windowHashes []string, expectedRoot string) (bool, error) {
	if len(windowHashes) == 0 {
		return false, nil
	}
	level := append([]string{}, windowHashes...)
	for len(level) > 1 {
		next := make([]string, 0, (len(level)+1)/2)
		for offset := 0; offset < len(level); offset += 2 {
			if offset+1 >= len(level) {
				next = append(next, level[offset]) // promote, do not duplicate
			} else {
				h, err := checkpointNodeHash(level[offset], level[offset+1])
				if err != nil {
					return false, err
				}
				next = append(next, h)
			}
		}
		level = next
	}
	return level[0] == expectedRoot, nil
}

// VerifyCheckpointExtension checks that current continues previous: contiguous
// sequence (current.from_seq_no == previous.to_seq_no + 1) and back-link
// (current.previous_checkpoint_hash == previous.checkpoint_hash).
func VerifyCheckpointExtension(previous, current map[string]any) VerifyReport {
	problems := make([]string, 0)
	if asFloat(current["from_seq_no"]) != asFloat(previous["to_seq_no"])+1 {
		problems = append(problems, "checkpoint does not extend previous (sequence gap)")
	}
	if !sameString(current["previous_checkpoint_hash"], previous["checkpoint_hash"]) {
		problems = append(problems, "checkpoint previous_checkpoint_hash does not match previous")
	}
	return VerifyReport{Kind: "checkpoint-extension", OK: len(problems) == 0, Problems: problems}
}

// VerifyCompleteness proves no events were omitted in [fromSeqNo, toSeqNo]: the
// sequence numbers must be gap-free and every event's prev_event_hash must equal
// the previous event's event_hash (the per-stream hash chain).
func VerifyCompleteness(events []map[string]any, fromSeqNo, toSeqNo int) VerifyReport {
	problems := make([]string, 0)
	ordered := append([]map[string]any{}, events...)
	sort.Slice(ordered, func(i, j int) bool {
		return asFloat(ordered[i]["seq_no"]) < asFloat(ordered[j]["seq_no"])
	})
	gapFree := len(ordered) == toSeqNo-fromSeqNo+1
	if gapFree {
		for i, event := range ordered {
			if int(asFloat(event["seq_no"])) != fromSeqNo+i {
				gapFree = false
				break
			}
		}
	}
	if !gapFree {
		problems = append(problems, "sequence range is not gap-free")
	} else {
		for i := 1; i < len(ordered); i++ {
			if !sameString(ordered[i]["prev_event_hash"], ordered[i-1]["event_hash"]) {
				problems = append(problems, fmt.Sprintf(
					"event chain broken at seq_no %d", int(asFloat(ordered[i]["seq_no"]))))
				break
			}
		}
	}
	return VerifyReport{Kind: "completeness", OK: len(problems) == 0, Problems: problems}
}

func asFloat(v any) float64 {
	switch n := v.(type) {
	case float64:
		return n
	case int:
		return float64(n)
	case int64:
		return float64(n)
	case json.Number:
		f, _ := n.Float64()
		return f
	}
	return 0
}

func sameString(a, b any) bool {
	as, aok := a.(string)
	bs, bok := b.(string)
	if aok && bok {
		return as == bs
	}
	return a == nil && b == nil
}

func SignConnectorWebhookPayload(secret string, body []byte, timestamp int64) (string, string) {
	if timestamp == 0 {
		timestamp = time.Now().Unix()
	}
	ts := fmt.Sprintf("%d", timestamp)
	mac := hmac.New(sha256.New, []byte(secret))
	mac.Write([]byte(ts))
	mac.Write([]byte("."))
	mac.Write(body)
	return ts, hex.EncodeToString(mac.Sum(nil))
}

func SignedConnectorWebhookHeaders(secret string, body []byte, timestamp int64) map[string]string {
	ts, sig := SignConnectorWebhookPayload(secret, body, timestamp)
	return map[string]string{
		"X-Attesto-Connector-Timestamp": ts,
		"X-Attesto-Connector-Signature": sig,
	}
}

func VerifyReceiptOffline(receipt SignedReceipt, publicKeyHex string) VerifyReport {
	problems := make([]string, 0)
	hash, err := DomainHashHex(ProofstreamDomains["receipt"], receipt.Payload)
	if err != nil {
		problems = append(problems, "receipt payload is not canonical-json compatible")
	} else if hash != receipt.ReceiptHash {
		problems = append(problems, "receipt hash mismatch")
	}
	if strings.ToLower(receipt.Signature.Alg) != "ed25519" {
		problems = append(problems, "unsupported receipt signature algorithm")
	}
	signatureHex := receipt.Signature.SignatureHex
	if signatureHex == "" {
		problems = append(problems, "receipt signature missing")
	}
	if err == nil && signatureHex != "" {
		publicKey, keyErr := hex.DecodeString(strings.TrimPrefix(strings.ToLower(publicKeyHex), "0x"))
		signature, sigErr := hex.DecodeString(strings.TrimPrefix(strings.ToLower(signatureHex), "0x"))
		payloadBytes, payloadErr := CanonicalJSON(receipt.Payload)
		if keyErr != nil || len(publicKey) != ed25519.PublicKeySize {
			problems = append(problems, "invalid public key")
		} else if sigErr != nil || len(signature) != ed25519.SignatureSize {
			problems = append(problems, "invalid receipt signature")
		} else if payloadErr != nil {
			problems = append(problems, "receipt payload is not canonical-json compatible")
		} else {
			message := make([]byte, 0, len(ProofstreamDomains["receipt"])+1+len(payloadBytes))
			message = append(message, []byte(ProofstreamDomains["receipt"])...)
			message = append(message, 0)
			message = append(message, payloadBytes...)
			if !ed25519.Verify(ed25519.PublicKey(publicKey), message, signature) {
				problems = append(problems, "receipt signature mismatch")
			}
		}
	}
	ok := len(problems) == 0
	result := "failed"
	if ok {
		result = "accepted"
	}
	eventHash, _ := receipt.Payload["event_hash"].(string)
	if eventHash == "" {
		eventHash, _ = receipt.Payload["eventHash"].(string)
	}
	return VerifyReport{
		Kind:            VerifyReceipt,
		OK:              ok,
		ReceiptHash:     hash,
		EventHash:       eventHash,
		Problems:        problems,
		Protocol:        ProofstreamProtocol,
		ProtocolVersion: ProtocolVersionAlpha,
		Subject:         subjectFromPayload(receipt.Payload),
		Result:          result,
		Checks: []VerificationCheck{{
			Name:    "receipt",
			Result:  result,
			Details: M{"problems": problems},
		}},
	}
}

func normalizeCanonical(value any) (any, error) {
	switch v := value.(type) {
	case nil, string, bool:
		return v, nil
	case time.Time:
		return v.UTC().Format("2006-01-02T15:04:05.000Z"), nil
	case []byte:
		return hex.EncodeToString(v), nil
	case int:
		return v, nil
	case int8:
		return int64(v), nil
	case int16:
		return int64(v), nil
	case int32:
		return int64(v), nil
	case int64:
		return v, nil
	case uint:
		return v, nil
	case uint8:
		return uint64(v), nil
	case uint16:
		return uint64(v), nil
	case uint32:
		return uint64(v), nil
	case uint64:
		return v, nil
	case float32:
		if math.IsInf(float64(v), 0) || math.IsNaN(float64(v)) {
			return nil, errors.New("canonical JSON cannot encode non-finite numbers")
		}
		return v, nil
	case float64:
		if math.IsInf(v, 0) || math.IsNaN(v) {
			return nil, errors.New("canonical JSON cannot encode non-finite numbers")
		}
		return v, nil
	case []any:
		out := make([]any, len(v))
		for i, item := range v {
			normalized, err := normalizeCanonical(item)
			if err != nil {
				return nil, err
			}
			out[i] = normalized
		}
		return out, nil
	case []M:
		out := make([]any, len(v))
		for i, item := range v {
			normalized, err := normalizeCanonical(item)
			if err != nil {
				return nil, err
			}
			out[i] = normalized
		}
		return out, nil
	case map[string]any:
		return normalizeMap(v)
	case M:
		return normalizeMap(map[string]any(v))
	default:
		raw, err := json.Marshal(v)
		if err != nil {
			return nil, err
		}
		var decoded any
		if err := json.Unmarshal(raw, &decoded); err != nil {
			return nil, err
		}
		return normalizeCanonical(decoded)
	}
}

func normalizeMap(in map[string]any) (map[string]any, error) {
	out := make(map[string]any, len(in))
	keys := make([]string, 0, len(in))
	for key := range in {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	for _, key := range keys {
		normalized, err := normalizeCanonical(in[key])
		if err != nil {
			return nil, err
		}
		out[key] = normalized
	}
	return out, nil
}

func subjectFromPayload(payload M) M {
	subject := M{}
	for _, key := range []string{"tenant_id", "system_id", "stream_id", "stream_event_id", "seq_no", "from_seq_no", "to_seq_no", "checkpoint_id", "from_checkpoint_id", "to_checkpoint_id"} {
		if value, ok := payload[key]; ok {
			subject[key] = value
		}
	}
	return subject
}