package main

import (
	"context"
	"fmt"
	"io"
	"time"
)

// WatchEvery is how often the watch looks at the pools.
const WatchEvery = time.Minute

// The module's one long-running process (`zfs-tools watch`), run by the node-engine. It is what the
// module's health is declared on (novox/hq ADR 0240: a tool check stands on a long-running resource): the
// node-engine judges the process alive, and asks zfs_health whether the pools are. The watch itself
// writes no file and changes nothing: each minute it reads the pools, and says in its journal when their
// health changes, so the journal holds when a pool went DEGRADED and when it came back.

// Watch keeps the last verdict, to say only changes.
type Watch struct {
	M    *Machine
	Out  io.Writer
	last string
}

// Look reads the pools once and says the verdict when it changed.
func (w *Watch) Look(ctx context.Context) {
	h := w.M.Health(ctx)
	verdict := "healthy"
	if !h.Healthy {
		verdict = "UNHEALTHY"
	}
	line := verdict + ": " + h.Why
	if line != w.last {
		fmt.Fprintf(w.Out, "%s %s\n", w.M.Now().Format(time.RFC3339), line)
		w.last = line
	}
}

// Run looks every WatchEvery until the context ends.
func (w *Watch) Run(ctx context.Context) {
	w.Look(ctx)
	t := time.NewTicker(WatchEvery)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
			w.Look(ctx)
		}
	}
}