// Reports that arrive from devices over MQTT: presence and telemetry
// (AGENTS.md §7, §11 Phase 3).
//
// The broker is transport only. Every report is written to SQLite here, because
// SQLite is the source of truth (SYSTEM_MAP.md). A malformed or hostile report
// must never take the service down: callers validate first, and a failed insert
// is logged and dropped.
package store

import (
	"context"
	"database/sql"
	"fmt"
	"time"
)

// SetPresence records that a device was seen and whether it is online now. It
// returns whether the online flag changed.
//
// Presence comes from the broker's Last Will and Testament: a device publishes
// a retained "online" status, and the broker publishes its retained will
// ("online": false) when the connection drops without a clean disconnect.
//
// last_seen is refreshed on every report. The audit log only gets an entry when
// the online flag changes, so a chatty device does not flood the log (FR-15).
func (s *Store) SetPresence(ctx context.Context, id int64, online bool, at time.Time, actor string) (bool, error) {
	if at.IsZero() {
		at = time.Now()
	}
	at = at.UTC()

	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return false, fmt.Errorf("set presence: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	var current int
	if err := tx.QueryRowContext(ctx, `SELECT online FROM devices WHERE id = ?`, id).Scan(&current); err != nil {
		return false, fmt.Errorf("set presence: %w", err)
	}

	if _, err := tx.ExecContext(ctx,
		`UPDATE devices SET online = ?, last_seen = ?, updated_at = datetime('now') WHERE id = ?`,
		boolToInt(online), at.Format(time.RFC3339), id); err != nil {
		return false, fmt.Errorf("set presence: %w", err)
	}

	changed := (current != 0) != online
	if changed {
		action, detail := "device.offline", "last will received"
		if online {
			action, detail = "device.online", "status report"
		}
		if err := insertAudit(ctx, tx, actor, action, &id, detail); err != nil {
			return false, err
		}
	}
	if err := tx.Commit(); err != nil {
		return false, fmt.Errorf("commit presence: %w", err)
	}
	return changed, nil
}

// TelemetryEntry is one app or domain row of a usage report.
type TelemetryEntry struct {
	App     string
	Domain  string
	Seconds int
}

// InsertTelemetry upserts a rolling daily usage total per (device, day, app,
// domain). Reports are repeats, not deltas: a later report for the same key
// replaces the earlier total (migration 002). The affected days are rolled up
// in the same transaction (migration 003). It returns the number of rows
// written.
func (s *Store) InsertTelemetry(ctx context.Context, id int64, day string, entries []TelemetryEntry) (int, error) {
	if len(entries) == 0 {
		return 0, nil
	}

	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return 0, fmt.Errorf("insert telemetry: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	n := 0
	days := make(map[string]struct{}, 1)
	for _, e := range entries {
		if e.Seconds < 0 {
			continue
		}
		if _, err := tx.ExecContext(ctx, `
			INSERT INTO telemetry (device_id, app, domain, seconds, day)
			VALUES (?, ?, ?, ?, ?)
			ON CONFLICT(device_id, day, app, domain) DO UPDATE SET
				seconds = excluded.seconds,
				created_at = datetime('now')`,
			id, e.App, e.Domain, e.Seconds, day); err != nil {
			return n, fmt.Errorf("insert telemetry: %w", err)
		}
		days[day] = struct{}{}
		n++
	}
	for d := range days {
		if err := rollupDay(ctx, tx, id, d); err != nil {
			return n, err
		}
	}
	if err := tx.Commit(); err != nil {
		return n, fmt.Errorf("commit telemetry: %w", err)
	}
	return n, nil
}

// rollupDay recomputes one device/day row of telemetry_daily from the detail
// table. Apps and domains are summed separately so a report that carries both
// is not double-counted.
func rollupDay(ctx context.Context, ex interface {
	ExecContext(context.Context, string, ...any) (sql.Result, error)
}, id int64, day string) error {
	if _, err := ex.ExecContext(ctx, `
		INSERT INTO telemetry_daily
			(device_id, day, app_seconds, domain_seconds, app_count, domain_count, updated_at)
		SELECT ?, ?,
		       COALESCE(SUM(CASE WHEN app <> '' THEN seconds END), 0),
		       COALESCE(SUM(CASE WHEN domain <> '' THEN seconds END), 0),
		       COALESCE(SUM(CASE WHEN app <> '' THEN 1 END), 0),
		       COALESCE(SUM(CASE WHEN domain <> '' THEN 1 END), 0),
		       datetime('now')
		FROM telemetry WHERE device_id = ? AND day = ?
		ON CONFLICT(device_id, day) DO UPDATE SET
			app_seconds = excluded.app_seconds,
			domain_seconds = excluded.domain_seconds,
			app_count = excluded.app_count,
			domain_count = excluded.domain_count,
			updated_at = datetime('now')`,
		id, day, id, day); err != nil {
		return fmt.Errorf("rollup day: %w", err)
	}
	return nil
}

// RebuildRollups recomputes every telemetry_daily row from the detail table. It
// is idempotent and is how the rollup is backfilled after an upgrade or
// repaired after an import. It returns the number of rows inserted or updated.
func (s *Store) RebuildRollups(ctx context.Context) (int, error) {
	res, err := s.db.ExecContext(ctx, `
		INSERT INTO telemetry_daily
			(device_id, day, app_seconds, domain_seconds, app_count, domain_count, updated_at)
		SELECT device_id, day,
		       COALESCE(SUM(CASE WHEN app <> '' THEN seconds END), 0),
		       COALESCE(SUM(CASE WHEN domain <> '' THEN seconds END), 0),
		       COALESCE(SUM(CASE WHEN app <> '' THEN 1 END), 0),
		       COALESCE(SUM(CASE WHEN domain <> '' THEN 1 END), 0),
		       datetime('now')
		FROM telemetry
		GROUP BY device_id, day
		ON CONFLICT(device_id, day) DO UPDATE SET
			app_seconds = excluded.app_seconds,
			domain_seconds = excluded.domain_seconds,
			app_count = excluded.app_count,
			domain_count = excluded.domain_count,
			updated_at = datetime('now')`)
	if err != nil {
		return 0, fmt.Errorf("rebuild rollups: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return 0, fmt.Errorf("rebuild rollups: %w", err)
	}
	return int(n), nil
}

// DayUsage is one day of rolled-up usage for a device. AppSeconds and
// DomainSeconds are kept apart because a report may carry both.
type DayUsage struct {
	Day           string
	AppSeconds    int
	DomainSeconds int
	AppCount      int
	DomainCount   int
}

// UsageRange returns the daily rollup for a device in [from, to] inclusive,
// oldest first. Days without a report are absent; the caller fills the gaps.
func (s *Store) UsageRange(ctx context.Context, id int64, from, to string) ([]DayUsage, error) {
	rows, err := s.db.QueryContext(ctx, `
		SELECT day, app_seconds, domain_seconds, app_count, domain_count
		FROM telemetry_daily
		WHERE device_id = ? AND day BETWEEN ? AND ?
		ORDER BY day`, id, from, to)
	if err != nil {
		return nil, fmt.Errorf("usage range: %w", err)
	}
	defer rows.Close()

	out := make([]DayUsage, 0, 8)
	for rows.Next() {
		var d DayUsage
		if err := rows.Scan(&d.Day, &d.AppSeconds, &d.DomainSeconds, &d.AppCount, &d.DomainCount); err != nil {
			return nil, fmt.Errorf("scan usage day: %w", err)
		}
		out = append(out, d)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("usage range: %w", err)
	}
	return out, nil
}

// UsageTotal is one app or domain total over a range.
type UsageTotal struct {
	Name    string
	Seconds int
}

// TopUsage returns the biggest apps or domains for a device in [from, to]
// inclusive. kind is "app" or "domain"; anything else returns no rows. The
// column is chosen by a switch, never interpolated, so the argument can never
// reach SQL as text.
func (s *Store) TopUsage(ctx context.Context, id int64, from, to, kind string, limit int) ([]UsageTotal, error) {
	column := ""
	switch kind {
	case "app":
		column = "app"
	case "domain":
		column = "domain"
	default:
		return nil, nil
	}
	if limit <= 0 || limit > 100 {
		limit = 10
	}

	rows, err := s.db.QueryContext(ctx, `
		SELECT `+column+`, SUM(seconds)
		FROM telemetry
		WHERE device_id = ? AND day BETWEEN ? AND ? AND `+column+` <> ''
		GROUP BY `+column+`
		ORDER BY SUM(seconds) DESC, `+column+` ASC
		LIMIT ?`, id, from, to, limit)
	if err != nil {
		return nil, fmt.Errorf("top %s: %w", column, err)
	}
	defer rows.Close()

	out := make([]UsageTotal, 0, limit)
	for rows.Next() {
		var t UsageTotal
		if err := rows.Scan(&t.Name, &t.Seconds); err != nil {
			return nil, fmt.Errorf("scan top %s: %w", column, err)
		}
		out = append(out, t)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("top %s: %w", column, err)
	}
	return out, nil
}

// DeviceDayUsage is one device's rolled-up usage for one day. AppSeconds and
// DomainSeconds are kept apart for the same reason as the rollup: a report may
// carry both for one session, so adding them together would double-count time.
// The screen-time answer decides how to combine them (internal/hub).
type DeviceDayUsage struct {
	DeviceID      int64
	Name          string
	Child         string
	AppSeconds    int
	DomainSeconds int
}

// UsageByDeviceForDay returns the daily rollup for every device that reported
// anything on day (YYYY-MM-DD). It is the read the screen-time answer is built
// from. Devices with no row are absent; the caller treats them as zero.
func (s *Store) UsageByDeviceForDay(ctx context.Context, day string) ([]DeviceDayUsage, error) {
	rows, err := s.db.QueryContext(ctx, `
		SELECT d.id, d.name, d.child, td.app_seconds, td.domain_seconds
		FROM telemetry_daily td
		JOIN devices d ON d.id = td.device_id
		WHERE td.day = ?
		ORDER BY d.id`, day)
	if err != nil {
		return nil, fmt.Errorf("usage by device for day: %w", err)
	}
	defer rows.Close()

	out := make([]DeviceDayUsage, 0, 8)
	for rows.Next() {
		var u DeviceDayUsage
		if err := rows.Scan(&u.DeviceID, &u.Name, &u.Child, &u.AppSeconds, &u.DomainSeconds); err != nil {
			return nil, fmt.Errorf("scan device day usage: %w", err)
		}
		out = append(out, u)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("usage by device for day: %w", err)
	}
	return out, nil
}

// DetailUsageByDeviceForDay is the same measure computed straight from the
// telemetry detail table instead of the derived rollup. It exists so an
// operator can independently check the rollup the daily answer reads.
func (s *Store) DetailUsageByDeviceForDay(ctx context.Context, day string) ([]DeviceDayUsage, error) {
	rows, err := s.db.QueryContext(ctx, `
		SELECT d.id, d.name, d.child,
		       COALESCE(SUM(CASE WHEN t.app <> '' THEN t.seconds END), 0),
		       COALESCE(SUM(CASE WHEN t.domain <> '' THEN t.seconds END), 0)
		FROM telemetry t
		JOIN devices d ON d.id = t.device_id
		WHERE t.day = ?
		GROUP BY d.id
		ORDER BY d.id`, day)
	if err != nil {
		return nil, fmt.Errorf("detail usage by device for day: %w", err)
	}
	defer rows.Close()

	out := make([]DeviceDayUsage, 0, 8)
	for rows.Next() {
		var u DeviceDayUsage
		if err := rows.Scan(&u.DeviceID, &u.Name, &u.Child, &u.AppSeconds, &u.DomainSeconds); err != nil {
			return nil, fmt.Errorf("scan detail device day usage: %w", err)
		}
		out = append(out, u)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("detail usage by device for day: %w", err)
	}
	return out, nil
}

// CapAudit keeps the newest max audit rows and deletes the oldest beyond that,
// so the append-only log cannot grow without bound (AGENTS.md §7 retention). It
// returns how many rows it removed. Nothing in the audit log is ever edited.
func (s *Store) CapAudit(ctx context.Context, max int) (int, error) {
	if max <= 0 {
		return 0, nil
	}
	res, err := s.db.ExecContext(ctx, `
		DELETE FROM audit WHERE id NOT IN (
			SELECT id FROM audit ORDER BY id DESC LIMIT ?
		)`, max)
	if err != nil {
		return 0, fmt.Errorf("cap audit: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return 0, fmt.Errorf("cap audit: %w", err)
	}
	return int(n), nil
}

// TelemetryForDay returns one device's usage rows for a day, biggest first.
func (s *Store) TelemetryForDay(ctx context.Context, id int64, day string) ([]TelemetryEntry, error) {
	rows, err := s.db.QueryContext(ctx, `
		SELECT app, domain, seconds FROM telemetry
		WHERE device_id = ? AND day = ?
		ORDER BY seconds DESC`, id, day)
	if err != nil {
		return nil, fmt.Errorf("telemetry for day: %w", err)
	}
	defer rows.Close()

	out := make([]TelemetryEntry, 0, 8)
	for rows.Next() {
		var e TelemetryEntry
		if err := rows.Scan(&e.App, &e.Domain, &e.Seconds); err != nil {
			return nil, fmt.Errorf("scan telemetry: %w", err)
		}
		out = append(out, e)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("telemetry for day: %w", err)
	}
	return out, nil
}