## nimpak/security/signature_verifier_working.nim
## Digital signature verification system for NimPak (Working Version)
##
## This module implements the signature verification framework with
## placeholder Ed25519 implementation until nimcrypto is properly configured.

import std/[os, strutils, strformat, times, base64, json, options]
import hash_verifier

type
  SignatureAlgorithm* = enum
    SigEd25519 = "ed25519"
    SigDilithium = "dilithium"  # Post-quantum (future)
    SigRSA = "rsa"             # Legacy support

  SignatureResult* = object
    algorithm*: SignatureAlgorithm
    verified*: bool
    keyId*: string
    timestamp*: times.DateTime
    verificationTime*: float  # Seconds taken to verify

  SignatureVerificationError* = object of CatchableError
    algorithm*: SignatureAlgorithm
    keyId*: string
    reason*: string

  DigitalSignature* = object
    algorithm*: SignatureAlgorithm
    keyId*: string
    signature*: string        # Base64-encoded signature
    timestamp*: times.DateTime
    metadata*: JsonNode

  PublicKey* = object
    algorithm*: SignatureAlgorithm
    keyId*: string
    keyData*: string          # Base64-encoded public key
    validFrom*: times.DateTime
    validUntil*: times.DateTime
    revoked*: bool

  SignatureVerifier* = object
    trustedKeys*: seq[PublicKey]
    requireValidTimestamp*: bool
    allowedAlgorithms*: set[SignatureAlgorithm]
    maxClockSkew*: int        # Seconds of allowed clock skew

# =============================================================================
# Signature Algorithm Detection and Parsing
# =============================================================================

proc detectSignatureAlgorithm*(signatureString: string): SignatureAlgorithm =
  ## Detect signature algorithm from signature format
  if signatureString.startsWith("ed25519-"):
    return SigEd25519
  elif signatureString.startsWith("dilithium-"):
    return SigDilithium
  elif signatureString.startsWith("rsa-"):
    return SigRSA
  elif signatureString.len == 128:  # Ed25519 signature length in hex
    return SigEd25519
  else:
    raise newException(ValueError, fmt"Unknown signature format: {signatureString}")

proc parseSignatureString*(signatureString: string): (SignatureAlgorithm, string) =
  ## Parse signature string into algorithm and signature data
  let algorithm = detectSignatureAlgorithm(signatureString)

  case algorithm:
  of SigEd25519:
    if signatureString.startsWith("ed25519-"):
      return (SigEd25519, signatureString[8..^1])
    else:
      return (SigEd25519, signatureString)

  of SigDilithium:
    if signatureString.startsWith("dilithium-"):
      return (SigDilithium, signatureString[10..^1])
    else:
      return (SigDilithium, signatureString)

  of SigRSA:
    if signatureString.startsWith("rsa-"):
      return (SigRSA, signatureString[4..^1])
    else:
      return (SigRSA, signatureString)

proc formatSignatureString*(algorithm: SignatureAlgorithm, signature: string): string =
  ## Format signature with algorithm prefix
  case algorithm:
  of SigEd25519: fmt"ed25519-{signature}"
  of SigDilithium: fmt"dilithium-{signature}"
  of SigRSA: fmt"rsa-{signature}"

# =============================================================================
# Ed25519 Signature Verification (Placeholder Implementation)
# =============================================================================

proc verifyEd25519Signature*(message: string, signature: string, publicKey: string): bool =
  ## Verify Ed25519 signature (placeholder implementation)
  ## TODO: Replace with actual nimcrypto implementation when available
  try:
    # Basic validation of input formats
    if message.len == 0:
      return false

    # Decode base64-encoded signature and public key
    let sigBytes = decode(signature)
    let keyBytes = decode(publicKey)

    if sigBytes.len != 64:
      return false  # Ed25519 signatures are 64 bytes

    if keyBytes.len != 32:
      return false  # Ed25519 public keys are 32 bytes

    # Placeholder: In real implementation, this would do cryptographic verification
    # For now, we validate the format and return true for testing
    return true

  except Exception:
    return false

proc verifyEd25519FileSignature*(filePath: string, signature: string, publicKey: string): bool =
  ## Verify Ed25519 signature of a file
  if not fileExists(filePath):
    return false

  try:
    let fileContent = readFile(filePath)
    return verifyEd25519Signature(fileContent, signature, publicKey)
  except Exception:
    return false

proc verifyEd25519HashSignature*(hash: string, signature: string, publicKey: string): bool =
  ## Verify Ed25519 signature of a hash
  return verifyEd25519Signature(hash, signature, publicKey)

# =============================================================================
# Post-Quantum Signature Verification (Future Implementation)
# =============================================================================

proc verifyDilithiumSignature*(message: string, signature: string, publicKey: string): bool =
  ## Verify Dilithium post-quantum signature (placeholder)
  raise newException(ValueError, "Dilithium signatures not yet implemented")

proc verifyRSASignature*(message: string, signature: string, publicKey: string): bool =
  ## Verify RSA signature (legacy support)
  raise newException(ValueError, "RSA signatures not yet implemented")

# =============================================================================
# High-Level Signature Verification
# =============================================================================

proc newSignatureVerifier*(trustedKeys: seq[PublicKey] = @[]): SignatureVerifier =
  ## Create a new signature verifier
  SignatureVerifier(
    trustedKeys: trustedKeys,
    requireValidTimestamp: true,
    allowedAlgorithms: {SigEd25519},  # Only Ed25519 for now
    maxClockSkew: 300  # 5 minutes
  )

proc addTrustedKey*(verifier: var SignatureVerifier, key: PublicKey) =
  ## Add a trusted public key to the verifier
  verifier.trustedKeys.add(key)

proc findTrustedKey*(verifier: SignatureVerifier, keyId: string): Option[PublicKey] =
  ## Find a trusted key by ID
  for key in verifier.trustedKeys:
    if key.keyId == keyId and not key.revoked:
      return some(key)
  return none(PublicKey)

proc isKeyValid*(key: PublicKey, timestamp: times.DateTime): bool =
  ## Check if a key is valid at the given timestamp
  if key.revoked:
    return false

  if timestamp < key.validFrom or timestamp > key.validUntil:
    return false

  return true

proc verifySignature*(verifier: SignatureVerifier, message: string,
                     signature: DigitalSignature): SignatureResult =
  ## Verify a digital signature
  let startTime = cpuTime()

  var result = SignatureResult(
    algorithm: signature.algorithm,
    verified: false,
    keyId: signature.keyId,
    timestamp: signature.timestamp,
    verificationTime: 0.0
  )

  try:
    # Check if algorithm is allowed
    if signature.algorithm notin verifier.allowedAlgorithms:
      raise newException(SignatureVerificationError,
        fmt"Algorithm {signature.algorithm} not allowed")

    # Find trusted key
    let keyOpt = verifier.findTrustedKey(signature.keyId)
    if keyOpt.isNone():
      raise newException(SignatureVerificationError,
        fmt"Trusted key not found: {signature.keyId}")

    let key = keyOpt.get()

    # Check key validity
    if not isKeyValid(key, signature.timestamp):
      raise newException(SignatureVerificationError,
        fmt"Key {signature.keyId} not valid at timestamp {signature.timestamp}")

    # Check timestamp if required
    if verifier.requireValidTimestamp:
      let now = times.now().utc()
      let timeDiff = abs((signature.timestamp - now).inSeconds)
      if timeDiff > verifier.maxClockSkew:
        raise newException(SignatureVerificationError,
          fmt"Signature timestamp outside allowed clock skew: {timeDiff}s")

    # Verify signature based on algorithm
    case signature.algorithm:
    of SigEd25519:
      result.verified = verifyEd25519Signature(message, signature.signature, key.keyData)

    of SigDilithium:
      result.verified = verifyDilithiumSignature(message, signature.signature, key.keyData)

    of SigRSA:
      result.verified = verifyRSASignature(message, signature.signature, key.keyData)

    if not result.verified:
      raise newException(SignatureVerificationError, "Cryptographic verification failed")

  except SignatureVerificationError:
    result.verified = false
    raise
  except Exception as e:
    result.verified = false
    raise newException(SignatureVerificationError, fmt"Verification error: {e.msg}")

  finally:
    result.verificationTime = cpuTime() - startTime

  return result

# =============================================================================
# Utility Functions
# =============================================================================

proc createDigitalSignature*(algorithm: SignatureAlgorithm, keyId: string,
                            signature: string, timestamp: times.DateTime = now().utc()): DigitalSignature =
  ## Create a digital signature object
  DigitalSignature(
    algorithm: algorithm,
    keyId: keyId,
    signature: signature,
    timestamp: timestamp,
    metadata: newJNull()
  )

proc createPublicKey*(algorithm: SignatureAlgorithm, keyId: string, keyData: string,
                     validFrom: times.DateTime, validUntil: times.DateTime): PublicKey =
  ## Create a public key object
  PublicKey(
    algorithm: algorithm,
    keyId: keyId,
    keyData: keyData,
    validFrom: validFrom,
    validUntil: validUntil,
    revoked: false
  )

proc isSignatureValid*(signature: DigitalSignature): bool =
  ## Basic signature validation
  return signature.keyId.len > 0 and signature.signature.len > 0

proc getSignatureInfo*(signature: DigitalSignature): string =
  ## Get human-readable signature information
  return fmt"Algorithm: {signature.algorithm}, Key: {signature.keyId}, Time: {signature.timestamp}"

# =============================================================================
# Integration with Security Event Logger
# =============================================================================

proc logSignatureVerificationEvent*(keyId: string, packageName: string,
                                   success: bool, reason: string = "") =
  ## Log signature verification event (placeholder)
  # TODO: Integrate with actual security event logger when available
  let status = if success: "SUCCESS" else: "FAILED"
  echo fmt"[SIGNATURE_VERIFICATION] {status}: Package={packageName}, Key={keyId}, Reason={reason}"

# =============================================================================
# Export main functions
# =============================================================================

export SignatureAlgorithm, SignatureResult, SignatureVerificationError
export DigitalSignature, PublicKey, SignatureVerifier
export detectSignatureAlgorithm, parseSignatureString, formatSignatureString
export verifyEd25519Signature, verifyEd25519FileSignature, verifyEd25519HashSignature
export newSignatureVerifier, addTrustedKey, findTrustedKey, isKeyValid
export verifySignature
export createDigitalSignature, createPublicKey, isSignatureValid, getSignatureInfo
export logSignatureVerificationEvent