package store

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"time"
)

// DigestStatus — the lifecycle state of a digest entry. Go has no enum type;
// the idiom is a defined type plus constants, which is what this is. The point
// is not ceremony: with bare strings nothing stopped a rule name or a body
// hash being passed where a status belongs, and every one of these values
// reaches SQL. A defined type makes that a compile error.
type DigestStatus string

// pending = enqueued, waiting for a drain. drained = spoken as part of a
// bundle. expired = the tick loop's expiry sweep found it past its expires_ts
// before a drain happened — dropped, not delivered late.
const (
	DigestPending DigestStatus = "pending"
	DigestDrained DigestStatus = "drained"
	DigestExpired DigestStatus = "expired"
)

// DigestEntry — one gate-suppressed care candidate durably held for later
// bundled delivery.
type DigestEntry struct {
	ID        int64
	Rule      string
	Severity  int
	Body      string
	CreatedTs time.Time
	ExpiresTs time.Time
}

// DigestBodyHash is the dedupe key for a digest entry: same rule, same
// wording ⇒ the same suppressed nudge repeating across ticks, and he should
// hear it once, not once per tick it kept getting suppressed.
func DigestBodyHash(rule, body string) string {
	sum := sha256.Sum256([]byte(rule + "\x00" + body))
	return hex.EncodeToString(sum[:8])
}

// EnqueueDigestEntry durably records a suppressed care candidate worth
// resurfacing later. If a pending entry with the same rule+body already
// exists, this is a no-op that returns the existing id and deduped=true —
// the same suppressed nudge repeating across ticks must not pile up into
// several copies of itself in the eventual bundle.
func (s *Store) EnqueueDigestEntry(ctx context.Context, rule string, severity int, body string, now, expiresAt time.Time) (id int64, deduped bool, err error) {
	hash := DigestBodyHash(rule, body)
	var existing int64
	err = s.db.QueryRowContext(ctx,
		`SELECT id FROM digest_entries WHERE status = ? AND rule = ? AND body_hash = ? LIMIT 1`,
		DigestPending, rule, hash).Scan(&existing)
	if err == nil {
		return existing, true, nil
	}

	res, err := s.db.ExecContext(ctx,
		`INSERT INTO digest_entries (rule, severity, body, body_hash, status, created_ts, expires_ts)
		 VALUES (?, ?, ?, ?, ?, ?, ?)`,
		rule, severity, body, hash, DigestPending, now.UnixMilli(), expiresAt.UnixMilli())
	if err != nil {
		return 0, false, fmt.Errorf("enqueue digest entry: %w", err)
	}
	id, err = res.LastInsertId()
	if err != nil {
		return 0, false, fmt.Errorf("enqueue digest entry: last insert id: %w", err)
	}
	return id, false, nil
}

// PendingDigestEntries returns the live (not yet expired) pending entries,
// oldest first — the order they were suppressed in, which is also the order
// a bundled readout should mention them.
func (s *Store) PendingDigestEntries(ctx context.Context, now time.Time) ([]DigestEntry, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT id, rule, severity, body, created_ts, expires_ts
		 FROM digest_entries WHERE status = ? AND expires_ts > ? ORDER BY created_ts ASC`,
		DigestPending, now.UnixMilli())
	if err != nil {
		return nil, fmt.Errorf("pending digest entries: %w", err)
	}
	defer rows.Close()

	var out []DigestEntry
	for rows.Next() {
		var e DigestEntry
		var created, expires int64
		if err := rows.Scan(&e.ID, &e.Rule, &e.Severity, &e.Body, &created, &expires); err != nil {
			return nil, fmt.Errorf("pending digest entries: scan: %w", err)
		}
		e.CreatedTs = time.UnixMilli(created)
		e.ExpiresTs = time.UnixMilli(expires)
		out = append(out, e)
	}
	return out, rows.Err()
}

// ExpireStaleDigestEntries marks pending entries whose expires_ts has passed
// as expired — stale information (yesterday's battery warning) is noise, not
// news, so it is dropped rather than delivered late. Called once per tick,
// mirroring ReconcileStaleDeliveryAttempts's "sweep, don't guess" shape.
// Returns the count expired, for logging.
func (s *Store) ExpireStaleDigestEntries(ctx context.Context, now time.Time) (int, error) {
	res, err := s.db.ExecContext(ctx,
		`UPDATE digest_entries SET status = ? WHERE status = ? AND expires_ts <= ?`,
		DigestExpired, DigestPending, now.UnixMilli())
	if err != nil {
		return 0, fmt.Errorf("expire stale digest entries: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return 0, fmt.Errorf("expire stale digest entries: rows affected: %w", err)
	}
	return int(n), nil
}

// DrainDigestEntries marks the given entries drained — they were folded into
// a bundle that was successfully dispatched. Called only after a successful
// send, same rule as the delivery outbox: a failed dispatch must not mark
// entries drained, or the bundle is lost along with the failed send.
func (s *Store) DrainDigestEntries(ctx context.Context, ids []int64, now time.Time) error {
	if len(ids) == 0 {
		return nil
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return fmt.Errorf("drain digest entries: begin: %w", err)
	}
	defer func() { _ = tx.Rollback() }()
	stmt, err := tx.PrepareContext(ctx,
		`UPDATE digest_entries SET status = ? WHERE id = ? AND status = ?`)
	if err != nil {
		return fmt.Errorf("drain digest entries: prepare: %w", err)
	}
	defer stmt.Close()
	for _, id := range ids {
		if _, err := stmt.ExecContext(ctx, DigestDrained, id, DigestPending); err != nil {
			return fmt.Errorf("drain digest entry %d: %w", id, err)
		}
	}
	if err := tx.Commit(); err != nil {
		return fmt.Errorf("drain digest entries: commit: %w", err)
	}
	return nil
}