package main

import (
	"context"
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"time"
)

// ScrubWarnAfter is how long after the last completed scrub the module warns: a month and a few days, so
// a monthly scrub that ran late is not yet a warning.
const ScrubWarnAfter = 35 * 24 * time.Hour

// HistoryTimeout bounds reading a pool's history, which grows with the pool's life.
const HistoryTimeout = 60 * time.Second

// HistoryArgv is one pool's history with ZFS's internal events, where each scan's start and end are.
func HistoryArgv(pool string) []string { return []string{"history", "-i", pool} }

// Pass is one scan the history records: when it started and how it ended.
type Pass struct {
	Kind    string     `json:"kind"`
	Started *time.Time `json:"started,omitempty"`
	Ended   *time.Time `json:"ended,omitempty"`
	// Outcome is finished or canceled.
	Outcome string `json:"outcome"`
	Errors  *int   `json:"errors,omitempty"`
}

var historyScan = regexp.MustCompile(`^(\d{4}-\d{2}-\d{2}\.\d{2}:\d{2}:\d{2}) \[txg:\d+\] scan (setup|done|cancelled|canceled|aborted)\b(.*)$`)
var historyFunc = regexp.MustCompile(`\bfunc=(\d+)`)
var historyErrors = regexp.MustCompile(`\berrors=(\d+)`)

// ParseHistory reads `zpool history -i` for the last finished scrub and the last finished resilver. ZFS
// writes `scan setup … func=1` for a scrub and `func=2` for a resilver, then `scan done … errors=N` or
// `scan cancelled`.
func ParseHistory(out string) (scrub, resilver *Pass) {
	var open *Pass
	for _, line := range lines(out) {
		m := historyScan.FindStringSubmatch(strings.TrimSpace(line))
		if m == nil {
			continue
		}
		t, err := time.ParseInLocation("2006-01-02.15:04:05", m[1], time.Local)
		if err != nil {
			continue
		}
		switch m[2] {
		case "setup":
			kind := "scan"
			if f := historyFunc.FindStringSubmatch(m[3]); f != nil {
				switch f[1] {
				case "1":
					kind = "scrub"
				case "2":
					kind = "resilver"
				}
			}
			open = &Pass{Kind: kind, Started: &t}
		default:
			if open == nil {
				continue
			}
			open.Ended = &t
			open.Outcome = "finished"
			if m[2] != "done" {
				open.Outcome = "canceled"
			}
			if e := historyErrors.FindStringSubmatch(m[3]); e != nil {
				n, _ := strconv.Atoi(e[1])
				open.Errors = &n
			}
			if open.Outcome == "finished" {
				switch open.Kind {
				case "scrub":
					scrub = open
				case "resilver":
					resilver = open
				}
			}
			open = nil
		}
	}
	return scrub, resilver
}

// ScrubRow is one pool's scans.
type ScrubRow struct {
	Pool string `json:"pool"`
	// Scans are the pool's scan lines as status gives them: its scrub or error scrub, then its resilver.
	Scans []Scan `json:"scans"`
	// LastScrub and LastResilver are the last finished of each, from status, or from the history when it
	// was read and status no longer shows it.
	LastScrub    *Pass    `json:"last_scrub,omitempty"`
	LastResilver *Pass    `json:"last_resilver,omitempty"`
	DaysSince    *float64 `json:"days_since_last_scrub,omitempty"`
	Warning      string   `json:"warning,omitempty"`
	Note         string   `json:"note,omitempty"`
	Said         []string `json:"said"`
}

// ScrubAnswer is what zfs_scrub answers.
type ScrubAnswer struct {
	Applicable bool       `json:"applicable"`
	Pools      []ScrubRow `json:"pools"`
	Schedule   *Schedule  `json:"schedule,omitempty"`
	Said       []string   `json:"said"`
}

// LastScrubEnded is when the pool's last scrub finished, as status shows it; nil when status shows no
// finished scrub.
func LastScrubEnded(p PoolStatus) *time.Time {
	if s := p.Scrub(); s != nil && s.State == "finished" {
		return s.Ended
	}
	return nil
}

// ScrubLate is how long after its last finished scrub a pool is late: its schedule's cadence and margin,
// or ScrubWarnAfter where the module has no schedule for it.
func ScrubLate(pool string, s *Schedule) (time.Duration, string) {
	if s != nil && s.Pool == pool {
		return cadenceAllows[s.Cadence], "its " + s.Cadence + " schedule allows"
	}
	return ScrubWarnAfter, "the module's line for a pool without a schedule"
}

// Scrubs are every pool's scans, its schedule and when it fires next. With history, each pool's history
// is read too (as root), for the scrub and the resilver status no longer shows.
func (m *Machine) Scrubs(ctx context.Context, history bool) (any, error) {
	st, err := m.Status(ctx)
	if err != nil {
		return notHere(err)
	}
	now := m.Now()
	a := ScrubAnswer{Applicable: true, Pools: []ScrubRow{}, Said: []string{}}
	sched, serr := m.ScheduleNow(ctx)
	switch {
	case serr != nil:
		a.Said = append(a.Said, "The scrub schedule's settings are not valid: "+serr.Error()+".")
	case sched == nil:
		a.Said = append(a.Said, "The module has no scrub schedule on this machine (no "+ScrubConfig+").")
	default:
		a.Schedule = sched
		line := fmt.Sprintf("%s scrub of %s, %s at %s (monthly: the first %s of the month), decided by the run %s fires "+
			"every quarter of an hour (%s, %s)", sched.Cadence, sched.Pool, sched.Day, sched.Time, sched.Day,
			sched.Timer, orUnknown(sched.TimerState), orUnknown(sched.Enabled))
		if sched.Cadence == "weekly" {
			line = fmt.Sprintf("weekly scrub of %s, %s at %s, decided by the run %s fires every quarter of an hour (%s, %s)",
				sched.Pool, sched.Day, sched.Time, sched.Timer, orUnknown(sched.TimerState), orUnknown(sched.Enabled))
		}
		if sched.Next != nil {
			line += "; next scheduled scrub of " + sched.Pool + ": " + sched.Next.Local().Format("2006-01-02 15:04")
		}
		if sched.LastResult != "" {
			line += "; last run: " + sched.LastResult
		}
		a.Said = append(a.Said, line)
		if sched.Note != "" {
			a.Said = append(a.Said, sched.Note)
		}
	}
	for _, p := range st {
		r := ScrubRow{Pool: p.Name, Scans: p.Scans, Said: []string{}}
		if ended := LastScrubEnded(p); ended != nil {
			sc := p.Scrub()
			r.LastScrub = &Pass{Kind: "scrub", Started: sc.Started, Ended: ended, Outcome: "finished", Errors: sc.Errors}
		}
		for _, rs := range p.Resilvers() {
			if rs.State == "finished" && rs.Ended != nil && (r.LastResilver == nil || rs.Ended.After(*r.LastResilver.Ended)) {
				r.LastResilver = &Pass{Kind: "resilver", Started: rs.Started, Ended: rs.Ended, Outcome: "finished", Errors: rs.Errors}
			}
		}
		if history {
			hctx, cancel := context.WithTimeout(ctx, HistoryTimeout)
			out, err := m.AsRoot(hctx, "zpool", HistoryArgv(p.Name)...)
			cancel()
			if err != nil {
				r.Note = "the history could not be read: " + err.Error()
			} else {
				scrub, resilver := ParseHistory(out.Out)
				if scrub != nil && (r.LastScrub == nil || scrub.Ended.After(*r.LastScrub.Ended)) {
					r.LastScrub = scrub
				}
				if resilver != nil && (r.LastResilver == nil || resilver.Ended.After(*r.LastResilver.Ended)) {
					r.LastResilver = resilver
				}
			}
		} else if r.LastScrub == nil {
			r.Note = "status shows no finished scrub of this pool; ask with history=true for the last one the pool's history records"
		}
		late, by := ScrubLate(p.Name, sched)
		if r.LastScrub != nil && r.LastScrub.Ended != nil {
			d := round1(now.Sub(*r.LastScrub.Ended).Hours() / 24)
			r.DaysSince = &d
			if now.Sub(*r.LastScrub.Ended) > late {
				r.Warning = fmt.Sprintf("the last scrub of %s finished %.0f days ago, more than %s (%d days)", p.Name, d, by, int(late.Hours()/24))
			}
		} else if history {
			r.Warning = fmt.Sprintf("no finished scrub of %s is on record", p.Name)
		}
		for _, sc := range p.Scans {
			r.Said = append(r.Said, p.Name+": "+scanSaid(sc))
		}
		if len(p.Scans) == 0 {
			r.Said = append(r.Said, p.Name+": no scan was ever asked")
		}
		if r.DaysSince != nil {
			r.Said = append(r.Said, fmt.Sprintf("%s: last finished scrub %.1f days ago", p.Name, *r.DaysSince))
		}
		if r.Warning != "" {
			r.Said = append(r.Said, p.Name+": WARNING: "+r.Warning)
		}
		if r.Note != "" {
			r.Said = append(r.Said, p.Name+": "+r.Note)
		}
		a.Pools = append(a.Pools, r)
		a.Said = append(a.Said, r.Said...)
	}
	return a, nil
}

// scanSaid says one scan in a line: a running one with its progress and the time to go.
func scanSaid(s Scan) string {
	what := s.Kind
	if s.Vdev != "" {
		what += " of " + s.Vdev
	}
	switch s.State {
	case "running", "paused":
		line := fmt.Sprintf("a %s is %s", what, s.State)
		if s.Started != nil {
			line += " (started " + s.Started.Local().Format("2006-01-02 15:04") + ")"
		}
		if s.Done != nil {
			line += fmt.Sprintf(", %.2f %% done", *s.Done)
		}
		switch {
		case s.ToGo != "":
			line += ", " + s.ToGo + " to go"
		case s.NoEstimate:
			line += ", no estimate of the time to go yet"
		}
		return line
	case "finished":
		line := fmt.Sprintf("the last %s finished %s after %s, %s", what, stamp(s.Ended), s.Took, s.Repaired)
		if s.Kind == "scrub" {
			line += " repaired"
		} else if s.Kind == "resilver" {
			line += " resilvered"
		}
		if s.Errors != nil {
			line += fmt.Sprintf(", %d errors", *s.Errors)
		}
		return line
	case "canceled":
		return fmt.Sprintf("the last %s was canceled %s", what, stamp(s.Ended))
	case "none":
		return "no scan was ever asked"
	}
	return "scan: " + firstLine(s.Said)
}

func orUnknown(s string) string {
	if s == "" {
		return "not known"
	}
	return s
}

func stamp(t *time.Time) string {
	if t == nil {
		return "at a time status did not say"
	}
	return t.Local().Format("2006-01-02 15:04")
}

func deref(n *int) int {
	if n == nil {
		return 0
	}
	return *n
}