## xxHash Integration for NexusOS
##
## This module provides xxh3-128 hashing for Content-Addressable Storage (CAS).
## xxh3 is chosen for its exceptional speed (40-60 GiB/s) and 128-bit collision
## resistance, making it ideal for non-cryptographic CAS operations.
##
## Performance: xxh3-128 is 20-80% faster than BLAKE3 for CAS operations
## Collision Safety: 128-bit output provides < 2^-100 collision probability
##
## Note: This is a wrapper around the xxhash Nim library.
## Install with: nimble install xxhash

import std/[strutils]

# We'll use a conditional import to handle the case where xxhash isn't installed yet
when defined(useXXHash):
  import xxhash
else:
  # Fallback implementation using a simple hash for development
  # This will be replaced with actual xxhash once the library is installed
  import std/hashes as stdhashes

type
  XXH3Hash* = distinct string
  ## xxh3-128 hash value (128-bit)

proc `==`*(a, b: XXH3Hash): bool =
  string(a) == string(b)

proc `$`*(h: XXH3Hash): string =
  string(h)

when defined(useXXHash):
  proc calculateXXH3*(data: string): XXH3Hash =
    ## Calculate xxh3-128 hash of a string
    ## Returns hash in format: "xxh3-<hex-digest>"
    let hash128 = XXH3_128bits(data)
    let hexDigest = hash128.toHex().toLowerAscii()
    result = XXH3Hash("xxh3-" & hexDigest)

  proc calculateXXH3*(data: seq[byte]): XXH3Hash =
    ## Calculate xxh3-128 hash of a byte sequence
    ## Returns hash in format: "xxh3-<hex-digest>"
    let hash128 = XXH3_128bits(cast[ptr UncheckedArray[byte]](unsafeAddr data[0]), data.len)
    let hexDigest = hash128.toHex().toLowerAscii()
    result = XXH3Hash("xxh3-" & hexDigest)

  proc calculateFileXXH3*(path: string): XXH3Hash =
    ## Calculate xxh3-128 hash of a file
    ## Returns hash in format: "xxh3-<hex-digest>"
    let data = readFile(path)
    result = calculateXXH3(data)

else:
  # Fallback implementation for development/testing
  # This uses a simple hash and should NOT be used in production
  proc calculateXXH3*(data: string): XXH3Hash =
    ## FALLBACK: Simple hash for development (NOT production-ready)
    ## Install xxhash library for actual xxh3-128 hashing
    let simpleHash = stdhashes.hash(data)
    let hexDigest = simpleHash.toHex(16).toLowerAscii()
    result = XXH3Hash("xxh3-fallback-" & hexDigest)

  proc calculateXXH3*(data: seq[byte]): XXH3Hash =
    ## FALLBACK: Simple hash for development (NOT production-ready)
    var str = newString(data.len)
    for i, b in data:
      str[i] = char(b)
    result = calculateXXH3(str)

  proc calculateFileXXH3*(path: string): XXH3Hash =
    ## FALLBACK: Simple hash for development (NOT production-ready)
    let data = readFile(path)
    result = calculateXXH3(data)

proc verifyXXH3*(data: string, expectedHash: XXH3Hash): bool =
  ## Verify that data matches the expected xxh3 hash
  let calculatedHash = calculateXXH3(data)
  result = calculatedHash == expectedHash

proc verifyXXH3*(data: seq[byte], expectedHash: XXH3Hash): bool =
  ## Verify that data matches the expected xxh3 hash
  let calculatedHash = calculateXXH3(data)
  result = calculatedHash == expectedHash

proc parseXXH3Hash*(hashStr: string): XXH3Hash =
  ## Parse a hash string into XXH3Hash type
  ## Validates that it starts with "xxh3-" prefix
  if not hashStr.startsWith("xxh3-"):
    raise newException(ValueError, "Invalid xxh3 hash format: must start with 'xxh3-'")
  result = XXH3Hash(hashStr)

proc isValidXXH3Hash*(hashStr: string): bool =
  ## Check if a string is a valid xxh3 hash format
  result = hashStr.startsWith("xxh3-") and hashStr.len > 5

when isMainModule:
  echo "Testing xxHash Integration..."

  # Test basic hashing
  let testData = "Hello, NexusOS with xxh3-128 hashing!"
  let hash = calculateXXH3(testData)
  echo "Hash: ", $hash

  # Test verification
  if verifyXXH3(testData, hash):
    echo "✓ Hash verification passed"
  else:
    echo "✗ Hash verification failed"

  # Test byte sequence hashing
  let testBytes = @[byte(72), byte(101), byte(108), byte(108), byte(111)]  # "Hello"
  let bytesHash = calculateXXH3(testBytes)
  echo "Bytes hash: ", $bytesHash

  # Test hash parsing
  try:
    let parsed = parseXXH3Hash($hash)
    echo "✓ Hash parsing successful"
  except ValueError as e:
    echo "✗ Hash parsing failed: ", e.msg

  # Test invalid hash
  if not isValidXXH3Hash("invalid-hash"):
    echo "✓ Invalid hash detection works"

  when defined(useXXHash):
    echo "✓ Using actual xxhash library"
  else:
    echo "⚠ Using fallback implementation (install xxhash for production)"
