package inventory

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/jackc/pgx/v5"
)

// The durations the core's bounds are set from (novox/hq to-be 45 Phase 0): see migration 0066.

// The kinds of duration recorded.
const (
	DurationApply        = "apply"
	DurationHeartbeatGap = "heartbeat-gap"
	DurationPlanTier     = "plan-tier"
	DurationBuild        = "build"
)

// DurationKinds are every kind, in the order `durations` shows them.
var DurationKinds = []string{DurationApply, DurationHeartbeatGap, DurationPlanTier, DurationBuild}

// DurationsKeptFor is how long a duration is kept: long enough to set a bound from, and to correct it
// in Phase 1's first live week.
const DurationsKeptFor = 30 * 24 * time.Hour

// Duration is one measurement.
type Duration struct {
	Kind    string        `json:"kind"`
	Subject string        `json:"subject"`
	Node    string        `json:"node,omitempty"`
	Ref     string        `json:"ref"`
	Started time.Time     `json:"started"`
	Took    time.Duration `json:"took"`
	Detail  string        `json:"detail,omitempty"`
}

// RecordDuration keeps one measurement, once: the same thing measured again is not a second row.
func (i *Inventory) RecordDuration(ctx context.Context, d Duration) error {
	if d.Took < 0 {
		return nil // a clock that went back measures nothing
	}
	_, err := i.store.Pool().Exec(ctx,
		`insert into duration (kind, subject, node, ref, started, took_ms, detail)
		 values ($1, $2, $3, $4, $5, $6, $7) on conflict do nothing`,
		d.Kind, d.Subject, d.Node, d.Ref, d.Started, d.Took.Milliseconds(), d.Detail)
	return err
}

// RecordApplyDuration measures a machine's report of the declaration it was last sent: from the send
// to the first report of it. A report of anything else, or of a send already measured, measures
// nothing — a machine reconciling reports the same declaration every few minutes.
func (i *Inventory) RecordApplyDuration(ctx context.Context, node, declared, outcome string) error {
	if declared == "" {
		return nil
	}
	_, err := i.store.Pool().Exec(ctx,
		`insert into duration (kind, subject, node, ref, started, took_ms, detail)
		 select $1, n.name, n.name, n.sent || '@' || to_char(n.sent_at at time zone 'UTC', 'YYYY-MM-DD"T"HH24:MI:SS.US'),
		        n.sent_at, (extract(epoch from (now() - n.sent_at)) * 1000)::bigint, $4
		   from node n
		  where n.name = $2 and n.sent = $3 and n.sent_at is not null
		 on conflict do nothing`,
		DurationApply, node, declared, outcome)
	return err
}

// RecordHeartbeatGap measures the silence before a machine's word: from the last word heard before
// it, which the caller read before recording this one.
func (i *Inventory) RecordHeartbeatGap(ctx context.Context, node string, before time.Time) error {
	if before.IsZero() {
		return nil
	}
	now := time.Now()
	return i.RecordDuration(ctx, Duration{Kind: DurationHeartbeatGap, Subject: node, Node: node,
		Ref: before.UTC().Format(time.RFC3339Nano), Started: before, Took: now.Sub(before)})
}

// Durations is every measurement of a kind since a moment, oldest first; every kind when kind is empty.
func (i *Inventory) Durations(ctx context.Context, kind string, since time.Time) ([]Duration, error) {
	rows, err := i.store.Pool().Query(ctx,
		`select kind, subject, node, ref, started, took_ms, detail from duration
		  where ($1 = '' or kind = $1) and recorded >= $2 order by recorded`, kind, since)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []Duration
	for rows.Next() {
		var d Duration
		var ms int64
		if err := rows.Scan(&d.Kind, &d.Subject, &d.Node, &d.Ref, &d.Started, &ms, &d.Detail); err != nil {
			return nil, err
		}
		d.Took = time.Duration(ms) * time.Millisecond
		out = append(out, d)
	}
	return out, rows.Err()
}

// ForgetOldDurations removes what is older than DurationsKeptFor, and says how many.
func (i *Inventory) ForgetOldDurations(ctx context.Context) (int64, error) {
	tag, err := i.store.Pool().Exec(ctx, `delete from duration where recorded < $1`,
		time.Now().Add(-DurationsKeptFor))
	if err != nil {
		return 0, err
	}
	return tag.RowsAffected(), nil
}

// planTierLeft is the measurement a plan's save makes when it leaves a tier: the tier moved on, or
// the plan ended. Read in the save's own transaction, so two saves cannot both measure one tier.
func planTierLeft(ctx context.Context, tx pgx.Tx, p Plan, now time.Time) (entered time.Time, err error) {
	var oldTier int
	var oldState string
	var since time.Time
	err = tx.QueryRow(ctx,
		`select tier, state, coalesce(tier_entered, created) from release_plan where id = $1 for update`,
		p.ID).Scan(&oldTier, &oldState, &since)
	if errors.Is(err, pgx.ErrNoRows) {
		return now, nil // a new plan enters its first tier now
	}
	if err != nil {
		return time.Time{}, err
	}
	wasOpen := oldState == PlanBuilding || oldState == PlanRolling
	if !wasOpen || (oldTier == p.Tier && p.Open()) {
		return since, nil // still in the tier, or already ended
	}
	var modules []string
	if oldTier >= 0 && oldTier < len(p.Tiers) {
		modules = p.Tiers[oldTier]
	}
	detail := fmt.Sprintf("plan %s, tier %d of %d (%v), left %s", p.ID, oldTier, len(p.Tiers), modules, p.State)
	if p.Open() {
		detail = fmt.Sprintf("plan %s, tier %d of %d (%v), moved on to tier %d", p.ID, oldTier, len(p.Tiers), modules, p.Tier)
	}
	_, err = tx.Exec(ctx,
		`insert into duration (kind, subject, node, ref, started, took_ms, detail)
		 values ($1, $2, '', $3, $4, $5, $6) on conflict do nothing`,
		DurationPlanTier, p.Repository, fmt.Sprintf("%s/tier-%d", p.ID, oldTier), since,
		now.Sub(since).Milliseconds(), detail)
	return now, err
}