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merge.go
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merge.go
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// SPDX-FileCopyrightText: 2022 Sascha Brawer <sascha@brawer.ch>
// SPDX-License-Identifier: MIT
package main
import (
"bufio"
"container/heap"
"context"
"io"
)
func mergeTileCounts(r []io.Reader, out chan<- TileCount, ctx context.Context) error {
defer close(out)
if len(r) == 0 {
return nil
}
merger := NewTileCountMerger(r)
for merger.Advance() {
// Check if our task has been canceled. Typically this can happen
// because of an error in another goroutine in the same x.sync.errroup.
select {
case <-ctx.Done():
return ctx.Err()
default:
}
out <- merger.TileCount()
}
if err := merger.Err(); err != nil {
return err
}
return nil
}
type TileCountMerger struct {
heap tileCountHeap
err error
inited bool
}
func NewTileCountMerger(r []io.Reader) *TileCountMerger {
m := &TileCountMerger{}
m.heap = make(tileCountHeap, 0, len(r))
for _, rr := range r {
stream := &tileCountStream{scanner: bufio.NewScanner(rr)}
if stream.scanner.Scan() {
stream.tc = ParseTileCount(stream.scanner.Text())
m.heap = append(m.heap, stream)
}
if err := stream.scanner.Err(); err != nil {
m.err = err
return m
}
}
return m
}
func (m *TileCountMerger) Advance() bool {
if m.err != nil {
return false
}
if len(m.heap) == 0 {
return false
}
if !m.inited {
heap.Init(&m.heap)
m.inited = true
return true
}
stream := m.heap[0]
if stream.scanner.Scan() {
stream.tc = ParseTileCount(stream.scanner.Text())
heap.Fix(&m.heap, 0)
} else {
heap.Remove(&m.heap, 0)
}
if err := stream.scanner.Err(); err != nil {
m.err = err
return false
}
return len(m.heap) > 0
}
func (m *TileCountMerger) Err() error {
return m.err
}
func (m *TileCountMerger) TileCount() TileCount {
n := len(m.heap)
if n > 0 {
return m.heap[0].tc
} else {
return TileCount{NoTile, 0}
}
}
type tileCountStream struct {
tc TileCount
scanner *bufio.Scanner
index int
}
type tileCountHeap []*tileCountStream
func (h tileCountHeap) Len() int { return len(h) }
func (h tileCountHeap) Less(i, j int) bool {
return TileCountLess(h[i].tc, h[j].tc)
}
func (h tileCountHeap) Swap(i, j int) {
h[i], h[j] = h[j], h[i]
h[i].index = i
h[j].index = j
}
func (h *tileCountHeap) Push(x interface{}) {
stream := x.(*tileCountStream)
stream.index = len(*h)
*h = append(*h, stream)
}
func (h *tileCountHeap) Pop() interface{} {
old := *h
n := len(old)
stream := old[n-1]
old[n-1] = nil // avoid memory leak
stream.index = -1
*h = old[0 : n-1]
return stream
}