nim-sds/tests/test_bloom.nim

import unittest, results, strutils
import sds/bloom
from random import rand, randomize

suite "bloom filter":
  setup:
    let nElementsToTest = 10000
    let bfResult = initializeBloomFilter(capacity = nElementsToTest, errorRate = 0.001)
    check bfResult.isOk
    var bf = bfResult.get
    randomize(2882) # Seed the RNG
    var
      sampleChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
      testElements = newSeq[string](nElementsToTest)

    for i in 0 ..< nElementsToTest:
      var newString = ""
      for j in 0 .. 7:
        newString.add(sampleChars[rand(51)])
      testElements[i] = newString

    for item in testElements:
      bf.insert(item)

  test "initialization parameters":
    check bf.capacity == nElementsToTest
    check bf.errorRate == 0.001
    check bf.kHashes == 10
    check bf.mBits div bf.capacity == 15 # bits per element

  test "basic operations":
    check bf.lookup("nonexistent") == false # Test empty lookup

    let bf2Result = initializeBloomFilter(100, 0.01)
    check bf2Result.isOk
    var bf2 = bf2Result.get
    bf2.insert("test string")
    check bf2.lookup("test string") == true
    check bf2.lookup("different string") == false

  test "error rate":
    var falsePositives = 0
    let testSize = nElementsToTest div 2
    for i in 0 ..< testSize:
      var testString = ""
      for j in 0 .. 8: # Different length than setup
        testString.add(sampleChars[rand(51)])
      if bf.lookup(testString):
        falsePositives.inc()

    let actualErrorRate = falsePositives.float / testSize.float
    check actualErrorRate < bf.errorRate * 1.5 # Allow some margin

  test "perfect recall":
    var lookupErrors = 0
    for item in testElements:
      if not bf.lookup(item):
        lookupErrors.inc()
    check lookupErrors == 0

  test "k/m bits specification":
    # Test error case for k > 12
    let errorCase = getMOverNBitsForK(k = 13, targetError = 0.01)
    check errorCase.isErr
    check errorCase.error ==
      "K must be <= 12 if forceNBitsPerElem is not also specified."

    # Test error case for unachievable error rate
    let errorCase2 = getMOverNBitsForK(k = 2, targetError = 0.00001)
    check errorCase2.isErr
    check errorCase2.error ==
      "Specified value of k and error rate not achievable using less than 4 bytes / element."

    # Test success cases
    let case1 = getMOverNBitsForK(k = 2, targetError = 0.1)
    check case1.isOk
    check case1.value == 6

    let case2 = getMOverNBitsForK(k = 7, targetError = 0.01)
    check case2.isOk
    check case2.value == 10

    let case3 = getMOverNBitsForK(k = 7, targetError = 0.001)
    check case3.isOk
    check case3.value == 16

    let bf2Result = initializeBloomFilter(10000, 0.001, k = 4, forceNBitsPerElem = 20)
    check bf2Result.isOk
    let bf2 = bf2Result.get
    check bf2.kHashes == 4
    check bf2.mBits == 200000

  test "string representation":
    let bf3Result = initializeBloomFilter(1000, 0.01, k = 4)
    check bf3Result.isOk
    let bf3 = bf3Result.get
    let str = $bf3
    check str.contains("1000") # Capacity
    check str.contains("4 hash") # Hash functions
    check str.contains("1.0e-02") # Error rate in scientific notation

suite "bloom filter special cases":
  test "different patterns of strings":
    const testSize = 10_000
    let patterns = @[
      "shortstr",
      repeat("a", 1000), # Very long string
      "special@#$%^&*()", # Special characters
      "unicode→★∑≈", # Unicode characters
      repeat("pattern", 10), # Repeating pattern
    ]

    let bfResult = initializeBloomFilter(testSize, 0.01)
    check bfResult.isOk
    var bf = bfResult.get
    var inserted = newSeq[string](testSize)

    # Test pattern handling
    for pattern in patterns:
      bf.insert(pattern)
      assert bf.lookup(pattern), "failed lookup pattern: " & pattern

    # Test general insertion and lookup
    for i in 0 ..< testSize:
      inserted[i] = $i & "test" & $rand(1000)
      bf.insert(inserted[i])

    # Verify all insertions
    var lookupErrors = 0
    for item in inserted:
      if not bf.lookup(item):
        lookupErrors.inc()
    check lookupErrors == 0

    # Check false positive rate
    var falsePositives = 0
    let fpTestSize = testSize div 2
    for i in 0 ..< fpTestSize:
      let testItem = "notpresent" & $i & $rand(1000)
      if bf.lookup(testItem):
        falsePositives.inc()

    let fpRate = falsePositives.float / fpTestSize.float
    check fpRate < bf.errorRate * 1.5 # Allow some margin but should be close to target