package main

import "fmt"

type Cell struct {
    val int
    next *Cell
}

type LinkedList struct {
    head *Cell
}

func (l *LinkedList) Print() {
    cell := l.head
    for cell != nil {
        fmt.Printf("val: %d\n", cell.val)
        cell = cell.next
    }
}

func (l *LinkedList) Insert(val int, previous *Cell) {
    cell := NewCell(val)
    if previous == nil {
        fmt.Println("ERROR: Given previous cell does not exist yet.")
        return
    }
    cell.next = previous.next
    previous.next = cell
}

func (l *LinkedList) Prepend(val int) {
    cell := NewCell(val)
    cell.next = l.head
    l.head = cell
}

func (l *LinkedList) Append(val int) {
    cell := NewCell(val)
    last := l.head
    if last == nil {
        l.head = cell
        return
    }
    for last.next != nil {
        last = last.next
    }
    last.next = cell
}

func (l *LinkedList) Delete(val int) {
    if l.head == nil {
        fmt.Println("ERROR: linked list does not exist yet.")
        return
    }
    target := l.head
    var prev *Cell
    for target.next != nil {
        if target.val == val {
            break
        }
        prev = target
        target = target.next
    }
    if target == l.head {
        l.head = l.head.next
        return
    }
    prev.next = target.next
    target.next = nil
}

func NewCell(val int) *Cell {
    return &Cell{val: val, next: nil}
}

func NewLinkedList() *LinkedList {
    return &LinkedList{head: nil}
}

func main() {
    l0 := NewLinkedList()
    l0.head = NewCell(0)
    c1 := NewCell(1)
    c2 := NewCell(2)
    l0.head.next = c1
    c1.next = c2
    l0.Print()
    // val: 0
    // val: 1
    // val: 2

    l0.Prepend(-1)
    fmt.Println()
    l0.Print()
    // val: -1
    // val: 0
    // val: 1
    // val: 2

    l0.Append(99)
    fmt.Println()
    l0.Print()
    // val: -1
    // val: 0
    // val: 1
    // val: 2
    // val: 99

    l0.Insert(77, c2)
    fmt.Println()
    l0.Print()
    // val: -1
    // val: 0
    // val: 1
    // val: 2
    // val: 77
    // val: 99

    l0.Delete(0)
    fmt.Println()
    l0.Print()

    // val: -1
    // val: 1
    // val: 2
    // val: 77
    // val: 99
}