package main

import (
	_ "embed"
	"fmt"
	"html/template"
	"net/http"
	_ "net/http/pprof"
	"os"
	"strings"
	"time"

	"github.com/coder/websocket"
	"github.com/coder/websocket/wsjson"
	"k8s.io/klog"
)

var (
	//go:embed index.html
	templateIndexText string
	templateIndex     = template.Must(template.New("index").Parse(templateIndexText))
)

func formatVolts(v float32) string {
	return fmt.Sprintf("%.3f V", v)
}

// formatMbar formats a millibar value using scientific notation and returns a
// HTML fragment (for superscript support).
func formatMbar(v float32) template.HTML {
	exp := 0
	for v < 1 {
		v *= 10
		exp -= 1
	}
	for v >= 10 {
		v /= 10
		exp += 1
	}
	res := fmt.Sprintf("%.3f", v)
	res += fmt.Sprintf(" x 10<sup>%d</sup>", exp)
	res += " mbar"
	return template.HTML(res)
}

// httpIndex is the / view.
func (d *daemon) httpIndex(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" {
		http.NotFound(w, r)
		return
	}

	volts, mbar := d.pirani()

	loadB, err := os.ReadFile("/proc/loadavg")
	load := "unknown"
	if err == nil {
		parts := strings.Fields(string(loadB))
		load = strings.Join(parts[:3], " ")
	}

	hostname, err := os.Hostname()
	if err != nil {
		hostname = "unknown"
	}

	templateIndex.Execute(w, map[string]any{
		"volts":    formatVolts(volts),
		"mbar":     formatMbar(mbar),
		"hostname": hostname,
		"load":     load,
	})
}

// httpStream is the websocket clientwards data hose, returning a 10Hz update
// stream of pressure/voltage.
func (d *daemon) httpStream(w http.ResponseWriter, r *http.Request) {
	c, err := websocket.Accept(w, r, nil)
	if err != nil {
		return
	}
	defer c.CloseNow()

	t := time.NewTicker(time.Second / 10)
	defer t.Stop()

	ctx := c.CloseRead(r.Context())
	for {
		select {
		case <-ctx.Done():
			c.Close(websocket.StatusNormalClosure, "")
			return
		case <-t.C:
			// TODO(q3k): don't poll, get notified when new ADC readout is available.
			volts, mbar := d.pirani()
			v := struct {
				Volts     string
				Mbar      string
				MbarFloat float32
			}{
				Volts:     formatVolts(volts),
				Mbar:      string(formatMbar(mbar)),
				MbarFloat: mbar,
			}
			if err := wsjson.Write(ctx, c, v); err != nil {
				klog.Errorf("Websocket write failed: %v", err)
				return
			}
		}
	}
}

// httpMetrics serves minimalistic Prometheus-compatible metrics.
func (d *daemon) httpMetrics(w http.ResponseWriter, r *http.Request) {
	// TODO(q3k): also serve Go stuff using the actual Prometheus metrics client
	// library.
	_, mbar := d.pirani()
	fmt.Fprintf(w, "# HELP sem_pressure_mbar Pressure in the SEM chamber, in millibar\n")
	fmt.Fprintf(w, "# TYPE sem_pressure_mbar gauge\n")
	fmt.Fprintf(w, "sem_pressure_mbar %f\n", mbar)
}