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package main
import (
"log"
"net/http"
"fmt"
"time"
"sync"
"slices"
"strings"
"github.com/wcharczuk/go-chart/v2"
)
type ChartHandler struct {
building Building
}
func (h ChartHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
log.Println(r.Method, r.URL)
if r.Method != http.MethodGet {
w.WriteHeader(http.StatusMethodNotAllowed)
fmt.Fprintf(w, "invalid method: '%s'", r.Method)
return
}
graph := chart.Chart{
Background: chart.Style{
Padding: chart.Box{Top: 20, Left: 20},
},
Series: buildSortedSeries(h.building),
}
graph.Elements = []chart.Renderable{
chart.Legend(&graph),
}
w.Header().Set("Content-Type", "image/png")
if err := graph.Render(chart.PNG, w); err != nil {
log.Println(err)
}
}
// Build a time series for each humidity record in the building.
// The returned series' are sorted by room name.
func buildSortedSeries(building Building) []chart.Series {
seriesChan := make(chan chart.TimeSeries)
sortedSeriesChan := make(chan []chart.Series)
go sortSeriesByName(seriesChan, sortedSeriesChan)
var wg sync.WaitGroup
for room, record := range building {
entries := make(chan Entry[Humidity])
record.get <- entries
wg.Add(1)
go func() {
buildSeries(room, entries, seriesChan)
wg.Done()
}()
}
wg.Wait()
close(seriesChan)
return <-sortedSeriesChan
}
// Sort a sequence of series' by name.
func sortSeriesByName(in <-chan chart.TimeSeries, out chan<- []chart.Series) {
series := make([]chart.Series, 0)
cmp := func(a chart.Series, b chart.TimeSeries) int {
return strings.Compare(a.GetName(), b.GetName())
}
// Insertion sort.
for s := range in {
i, _ := slices.BinarySearchFunc(series, s, cmp)
series = slices.Insert(series, i, chart.Series(s))
}
out <- series
close(out)
}
// Build a time series from a sequence of record entries.
func buildSeries(room RoomID, in <-chan Entry[Humidity], out chan<- chart.TimeSeries) {
var x []time.Time
var y []float64
for e := range in {
x = append(x, e.t)
y = append(y, float64(e.v))
}
out <- chart.TimeSeries{
Name: string(room),
XValues: x,
YValues: y,
}
}
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