package main

import (
	"context"
	"fmt"
	"sort"
	"strings"
)

// EventsArgv is ZFS's recent events with their details. ZFS keeps them in memory since the module loaded,
// a bounded number, and gives them to root only.
func EventsArgv() []string { return []string{"events", "-v"} }

// Event is one ZFS event.
type Event struct {
	Time  string `json:"time"`
	Class string `json:"class"`
	// Details are the event's fields that say what and where: pool, vdev, state, error.
	Details map[string]string `json:"details,omitempty"`
}

// eventKeys are the details an event is answered with; the rest are internal identifiers and checksums.
var eventKeys = map[string]bool{
	"pool": true, "pool_state": true, "vdev_path": true, "vdev_type": true, "vdev_state": true, "vdev_laststate": true,
	"vdev_read_errors": true, "vdev_write_errors": true, "vdev_cksum_errors": true, "zio_err": true, "zio_objset": true,
	"zio_object": true, "history_internal_name": true, "history_internal_str": true, "vdev_ashift": true, "eid": true,
	"resilver_type": true,
}

// vdevStates are ZFS's vdev states as numbers, as events give them.
var vdevStates = map[string]string{
	"0x0": "UNKNOWN", "0x1": "CLOSED", "0x2": "OFFLINE", "0x3": "REMOVED", "0x4": "CANT_OPEN", "0x5": "FAULTED",
	"0x6": "DEGRADED", "0x7": "ONLINE",
}

// ParseEvents reads `zpool events -v`: a header line, then for each event a line of its time and class and
// its fields indented under it, `name = value`.
func ParseEvents(out string) []Event {
	var evs []Event
	for _, line := range strings.Split(out, "\n") {
		line = strings.TrimRight(line, "\r")
		if strings.TrimSpace(line) == "" {
			continue
		}
		if droppedLine.MatchString(strings.TrimSpace(line)) {
			continue
		}
		if line[0] != ' ' && line[0] != '\t' {
			f := strings.Fields(line)
			if len(f) < 2 || (f[0] == "TIME" && f[len(f)-1] == "CLASS") {
				continue
			}
			evs = append(evs, Event{Time: strings.Join(f[:len(f)-1], " "), Class: f[len(f)-1]})
			continue
		}
		if len(evs) == 0 {
			continue
		}
		k, v, ok := strings.Cut(strings.TrimSpace(line), " = ")
		if !ok || !eventKeys[k] {
			continue
		}
		v = strings.Trim(strings.TrimSpace(v), `"`)
		if k == "vdev_state" || k == "vdev_laststate" {
			if s, known := vdevStates[v]; known {
				v = s
			}
		}
		e := &evs[len(evs)-1]
		if e.Details == nil {
			e.Details = map[string]string{}
		}
		e.Details[k] = v
	}
	return evs
}

// Notable says whether an event is an error or a change of state: every ereport (an I/O, checksum or
// device error), every resource event (a device's state changed) and ZFS's own events but the history
// it writes for every command and the configuration it syncs.
func Notable(class string) bool {
	switch {
	case strings.HasPrefix(class, "ereport."), strings.HasPrefix(class, "resource."):
		return true
	case class == "sysevent.fs.zfs.history_event", class == "sysevent.fs.zfs.config_sync":
		return false
	case strings.HasPrefix(class, "sysevent.fs.zfs."):
		return true
	}
	return false
}

// EventsAnswer is what zfs_events answers.
type EventsAnswer struct {
	Applicable bool     `json:"applicable"`
	Events     []Event  `json:"events"`
	Shown      int      `json:"shown"`
	Kept       int      `json:"kept"`
	Said       []string `json:"said"`
}

// Events are ZFS's recent errors and changes of state, newest first; with all, every event.
func (m *Machine) Events(ctx context.Context, all bool, limit int) (any, error) {
	r, err := m.AsRoot(ctx, "zpool", EventsArgv()...)
	if err != nil {
		return notHere(err)
	}
	evs := ParseEvents(r.Out)
	a := EventsAnswer{Applicable: true, Events: []Event{}, Kept: len(evs), Said: []string{}}
	for i := len(evs) - 1; i >= 0 && len(a.Events) < limit; i-- {
		if all || Notable(evs[i].Class) {
			a.Events = append(a.Events, evs[i])
		}
	}
	a.Shown = len(a.Events)
	for _, e := range a.Events {
		line := e.Time + " " + strings.TrimPrefix(strings.TrimPrefix(e.Class, "sysevent.fs.zfs."), "ereport.fs.zfs.")
		keys := make([]string, 0, len(e.Details))
		for k := range e.Details {
			keys = append(keys, k)
		}
		sort.Strings(keys)
		for _, k := range keys {
			line += fmt.Sprintf(" %s=%s", k, e.Details[k])
		}
		a.Said = append(a.Said, line)
	}
	which := "errors and changes of state"
	if all {
		which = "events"
	}
	a.Said = append([]string{fmt.Sprintf("%d %s shown, newest first, of the %d events ZFS keeps since its module loaded", a.Shown, which, a.Kept)}, a.Said...)
	return a, nil
}