package nsqd

type inFlightPqueue []*Message

func newInFlightPqueue(capacity int) inFlightPqueue {
    return make(inFlightPqueue, 0, capacity)
}

func (pq inFlightPqueue) Swap(i, j int) {
    pq[i], pq[j] = pq[j], pq[i]
    pq[i].index = i
    pq[j].index = j
}

func (pq *inFlightPqueue) Push(x *Message) {
    n := len(*pq)
    c := cap(*pq)
    if n+1 > c {
        npq := make(inFlightPqueue, n, c*2)
        copy(npq, *pq)
        *pq = npq
    }
    *pq = (*pq)[0 : n+1]
    x.index = n
    (*pq)[n] = x
    pq.up(n)
}

func (pq *inFlightPqueue) Pop() *Message {
    n := len(*pq)
    c := cap(*pq)
    pq.Swap(0, n-1)
    pq.down(0, n-1)
    if n < (c/2) && c > 25 {
        npq := make(inFlightPqueue, n, c/2)
        copy(npq, *pq)
        *pq = npq
    }
    x := (*pq)[n-1]
    x.index = -1
    *pq = (*pq)[0 : n-1]
    return x
}

func (pq *inFlightPqueue) Remove(i int) *Message {
    n := len(*pq)
    if n-1 != i {
        pq.Swap(i, n-1)
        pq.down(i, n-1)
        pq.up(i)
    }
    x := (*pq)[n-1]
    x.index = -1
    *pq = (*pq)[0 : n-1]
    return x
}

func (pq *inFlightPqueue) PeekAndShift(max int64) (*Message, int64) {
    if len(*pq) == 0 {
        return nil, 0
    }

    x := (*pq)[0]
    if x.pri > max {
        return nil, x.pri - max
    }
    pq.Pop()

    return x, 0
}

func (pq *inFlightPqueue) up(j int) {
    for {
        i := (j - 1) / 2 // parent
        if i == j || (*pq)[j].pri >= (*pq)[i].pri {
            break
        }
        pq.Swap(i, j)
        j = i
    }
}

func (pq *inFlightPqueue) down(i, n int) {
    for {
        j1 := 2*i + 1
        if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
            break
        }
        j := j1 // left child
        if j2 := j1 + 1; j2 < n && (*pq)[j1].pri >= (*pq)[j2].pri {
            j = j2 // = 2*i + 2  // right child
        }
        if (*pq)[j].pri >= (*pq)[i].pri {
            break
        }
        pq.Swap(i, j)
        i = j
    }
}