hash

type Hash interface {
    io.Writer
    Sum(b []byte) []byte
    Reset()
    Size() int
    BlockSize() int
}

import "hash/crc32"

func calculateCRC32(data []byte) uint32 {
    return crc32.ChecksumIEEE(data)
}

func crc32Example() {
    h := crc32.NewIEEE()
    h.Write([]byte("hello world"))
    checksum := h.Sum32()
    fmt.Printf("CRC32: %x\n", checksum)
}

import "hash/crc64"

func calculateCRC64(data []byte) uint64 {
    table := crc64.MakeTable(crc64.ISO)
    return crc64.Checksum(data, table)
}

import "hash/fnv"

func hashFNV(s string) uint64 {
    h := fnv.New64a()
    h.Write([]byte(s))
    return h.Sum64()
}

import "hash/adler32"

func calculateAdler32(data []byte) uint32 {
    return adler32.Checksum(data)
}

import "hash/maphash"

func hashString(s string) uint64 {
    var h maphash.Hash
    h.WriteString(s)
    return h.Sum64()
}

// With seed for consistency
func hashWithSeed(s string, seed maphash.Seed) uint64 {
    var h maphash.Hash
    h.SetSeed(seed)
    h.WriteString(s)
    return h.Sum64()
}

import (
    "crypto/sha256"
    "hash"
    "io"
    "os"
)

func fileChecksum(filename string, h hash.Hash) ([]byte, error) {
    f, err := os.Open(filename)
    if err != nil {
        return nil, err
    }
    defer f.Close()
    
    if _, err := io.Copy(h, f); err != nil {
        return nil, err
    }
    
    return h.Sum(nil), nil
}

func sha256File(filename string) (string, error) {
    checksum, err := fileChecksum(filename, sha256.New())
    if err != nil {
        return "", err
    }
    return fmt.Sprintf("%x", checksum), nil
}

func verifyFile(filename, expectedHash string) (bool, error) {
    actualHash, err := sha256File(filename)
    if err != nil {
        return false, err
    }
    return actualHash == expectedHash, nil
}

type FileRegistry struct {
    files map[string][]string // hash -> filenames
}

func NewFileRegistry() *FileRegistry {
    return &FileRegistry{
        files: make(map[string][]string),
    }
}

func (r *FileRegistry) AddFile(filename string) error {
    hash, err := sha256File(filename)
    if err != nil {
        return err
    }
    
    r.files[hash] = append(r.files[hash], filename)
    return nil
}

func (r *FileRegistry) FindDuplicates() map[string][]string {
    duplicates := make(map[string][]string)
    
    for hash, files := range r.files {
        if len(files) > 1 {
            duplicates[hash] = files
        }
    }
    
    return duplicates
}

type HashTable struct {
    seed    maphash.Seed
    buckets [][]entry
}

type entry struct {
    key   string
    value interface{}
}

func NewHashTable(size int) *HashTable {
    return &HashTable{
        seed:    maphash.MakeSeed(),
        buckets: make([][]entry, size),
    }
}

func (ht *HashTable) hash(key string) int {
    var h maphash.Hash
    h.SetSeed(ht.seed)
    h.WriteString(key)
    return int(h.Sum64() % uint64(len(ht.buckets)))
}

func (ht *HashTable) Set(key string, value interface{}) {
    idx := ht.hash(key)
    bucket := ht.buckets[idx]
    
    for i, e := range bucket {
        if e.key == key {
            bucket[i].value = value
            return
        }
    }
    
    ht.buckets[idx] = append(bucket, entry{key, value})
}

func (ht *HashTable) Get(key string) (interface{}, bool) {
    idx := ht.hash(key)
    
    for _, e := range ht.buckets[idx] {
        if e.key == key {
            return e.value, true
        }
    }
    
    return nil, false
}

import "crypto/sha256"

type ContentStore struct {
    basePath string
}

func (cs *ContentStore) Store(data []byte) (string, error) {
    hash := sha256.Sum256(data)
    hashStr := fmt.Sprintf("%x", hash)
    
    // Store in subdirectory based on first 2 chars
    dir := filepath.Join(cs.basePath, hashStr[:2])
    if err := os.MkdirAll(dir, 0755); err != nil {
        return "", err
    }
    
    path := filepath.Join(dir, hashStr[2:])
    if err := os.WriteFile(path, data, 0644); err != nil {
        return "", err
    }
    
    return hashStr, nil
}

func (cs *ContentStore) Retrieve(hash string) ([]byte, error) {
    path := filepath.Join(cs.basePath, hash[:2], hash[2:])
    return os.ReadFile(path)
}