prog8/examples/pointers/hashtable.p8

; Doubly Linked List with Hash Table Cache
; Demonstrates advanced pointer usage with a combination of doubly linked lists and hash tables
; for efficient data storage and retrieval


%import strings
%import textio
%zeropage basicsafe

main {
    sub start() {
        txt.lowercase()
        txt.print("Doubly Linked List with Hash Table Cache Demo\n")
        txt.print("============================================\n\n")

        ; Initialize the data structure
        cache.init()

        ; Add some sample data
        txt.print("Adding sample data...\n")
        cache.add("Alice", "Engineer", 30)
        cache.add("Bob", "Designer", 25)
        cache.add("Charlie", "Manager", 35)
        cache.add("Diana", "Developer", 28)
        cache.add("Eve", "Analyst", 32)

        txt.print("\nForward traversal:\n")
        cache.print_forward()

        txt.print("\nBackward traversal:\n")
        cache.print_backward()

        txt.print("\nSearching for specific entries:\n")
        txt.print("Looking for 'Charlie': ")
        ^^cache.Entry entry = cache.find("Charlie")
        if entry!=0 {
            txt.print(entry.name)
            txt.print(" - ")
            txt.print(entry.job)
            txt.print(" (")
            txt.print_ub(entry.age)
            txt.print(" years old)\n")
        } else {
            txt.print("Not found\n")
        }

        txt.print("Looking for 'Frank': ")
        entry = cache.find("Frank")
        if entry!=0 {
            txt.print("Found\n")
        } else {
            txt.print("Not found\n")
        }

        txt.print("\nRemoving 'Bob'...\n")
        void cache.remove("Bob")

        txt.print("Forward traversal after removal:\n")
        cache.print_forward()

        txt.print("\nDemonstrating hash collision handling...\n")
        ; Add entries that will likely collide in the hash table
        cache.add("A", "First", 20)
        cache.add("B", "Second", 21)
        cache.add("C", "Third", 22)
        cache.add("D", "Fourth", 23)
        cache.add("E", "Fifth", 24)

        txt.print("Added entries with potential hash collisions.\n")
        txt.print("Forward traversal:\n")
        cache.print_forward()
    }
}

cache {
    struct Entry {
        ^^Entry next          ; Next entry in the list
        ^^Entry prev          ; Previous entry in the list
        ^^Entry hash_next     ; Next entry in the hash bucket
        str name              ; Name (key)
        str job               ; Job description
        ubyte age             ; Age
    }

    const ubyte HASH_TABLE_SIZE = 16
    ^^Entry[HASH_TABLE_SIZE] hash_table    ; Hash table for fast lookups
    ^^Entry head = 0                       ; Head of the doubly linked list
    ^^Entry tail = 0                       ; Tail of the doubly linked list
    uword count = 0                        ; Number of entries

    sub init() {
        ; Initialize hash table buckets to null
        sys.memsetw(hash_table, HASH_TABLE_SIZE, 0)
    }

    sub add(str name, str job, ubyte age) {
        ; Create new entry
        ^^Entry new_entry = arena.alloc(sizeof(Entry))
        ^^ubyte name_copy = arena.alloc(strings.length(name) + 1)
        ^^ubyte job_copy = arena.alloc(strings.length(job) + 1)
        void strings.copy(name, name_copy)
        void strings.copy(job, job_copy)

        new_entry.name = name_copy
        new_entry.job = job_copy
        new_entry.age = age
        new_entry.next = 0
        new_entry.prev = 0
        new_entry.hash_next = 0

        ; Add to the end of the doubly linked list
        if head == 0 {
            ; First entry
            head = new_entry
            tail = new_entry
        } else {
            ; Add to the end
            tail.next = new_entry
            new_entry.prev = tail
            tail = new_entry
        }

        ; Add to hash table
        ubyte bucket = strings.hash(name) % HASH_TABLE_SIZE
        new_entry.hash_next = hash_table[bucket]
        hash_table[bucket] = new_entry

        count++
        txt.print("Added: ")
        txt.print(name)
        txt.print("\n")
    }

    sub find(str name) -> ^^Entry {
        ; Find entry using hash table for O(1) average case
        ubyte bucket = strings.hash(name) % HASH_TABLE_SIZE
        ^^Entry current = hash_table[bucket]

        while current != 0 {
            if strings.compare(current.name, name) == 0
                return current
            current = current.hash_next
        }

        return 0  ; Not found
    }

    sub remove(str name) -> bool {
        ; Find the entry
        ^^Entry to_remove = find(name)
        if to_remove == 0
            return false  ; Not found

        ; Remove from doubly linked list
        if to_remove.prev != 0
            to_remove.prev.next = to_remove.next
        else
            head = to_remove.next  ; Was the head

        if to_remove.next != 0
            to_remove.next.prev = to_remove.prev
        else
            tail = to_remove.prev  ; Was the tail

        ; Remove from hash table
        ubyte bucket = strings.hash(name) % HASH_TABLE_SIZE
        if hash_table[bucket] == to_remove {
            hash_table[bucket] = to_remove.hash_next
        } else {
            ^^Entry current = hash_table[bucket]
            while current.hash_next != 0 {
                if current.hash_next == to_remove {
                    current.hash_next = to_remove.hash_next
                    break
                }
                current = current.hash_next
            }
        }

        count--
        txt.print("Removed: ")
        txt.print(name)
        txt.print("\n")
        return true
    }

    sub print_forward() {
        ^^Entry current = head
        while current != 0 {
            txt.print("- ")
            txt.print(current.name)
            txt.print(" (")
            txt.print(current.job)
            txt.print(", ")
            txt.print_ub(current.age)
            txt.print(")\n")
            current = current.next
        }
        txt.print("Total entries: ")
        txt.print_uw(count)
        txt.print("\n")
    }

    sub print_backward() {
        ^^Entry current = tail
        while current != 0 {
            txt.print("- ")
            txt.print(current.name)
            txt.print(" (")
            txt.print(current.job)
            txt.print(", ")
            txt.print_ub(current.age)
            txt.print(")\n")
            current = current.prev
        }
        txt.print("Total entries: ")
        txt.print_uw(count)
        txt.print("\n")
    }
}

arena {
    ; Simple arena allocator
    uword buffer = memory("arena", 8000, 0)
    uword next = buffer

    sub alloc(ubyte size) -> uword {
        defer next += size
        return next
    }
}