package pgstore

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

	"github.com/jackc/pgx/v5"

	"textmachine/platform/internal/auth"
)

// Lookup resolves a presented token. Expiry and revocation are clauses of THIS query, not checks a
// caller could forget: a row that comes back is live by construction.
func (s *Store) Lookup(ctx context.Context, digest []byte, now time.Time) (auth.Session, error) {
	const q = `
		select user_id, idle_expires_at, absolute_expires_at
		  from sessions
		 where token_sha256 = $1
		   and revoked_at is null
		   and idle_expires_at > $2
		   and absolute_expires_at > $2`
	var out auth.Session
	err := s.pool.QueryRow(ctx, q, digest, now).
		Scan(&out.UserID, &out.IdleExpiresAt, &out.AbsoluteExpiresAt)
	if errors.Is(err, pgx.ErrNoRows) {
		return auth.Session{}, auth.ErrNoSession
	}
	if err != nil {
		return auth.Session{}, fmt.Errorf("pgstore: lookup session: %w", err)
	}
	return out, nil
}

// Touch slides the idle window. It never moves the absolute expiry — that is the point of having
// two clocks — and it is called only in the window's second half, so reads stay reads.
func (s *Store) Touch(ctx context.Context, digest []byte, now time.Time, idleTTL time.Duration) error {
	// Deadlines are computed in Go and travel as timestamps: one clock, one place, and no interval
	// encoding to reason about.
	const q = `
		update sessions
		   set last_used_at = $2,
		       idle_expires_at = least($3::timestamptz, absolute_expires_at)
		 where token_sha256 = $1
		   and revoked_at is null
		   and absolute_expires_at > $2`
	if _, err := s.pool.Exec(ctx, q, digest, now, now.Add(idleTTL)); err != nil {
		return fmt.Errorf("pgstore: touch session: %w", err)
	}
	return nil
}

// CreateSession stores a freshly minted token's digest. The plaintext never reaches this package.
func (s *Store) CreateSession(ctx context.Context, digest []byte, userID string, now time.Time, idleTTL, maxAge time.Duration) error {
	const q = `
		insert into sessions (token_sha256, user_id, created_at, last_used_at, idle_expires_at, absolute_expires_at)
		values ($1, $2, $3, $3, $4, $5)`
	if _, err := s.pool.Exec(ctx, q, digest, userID, now, now.Add(idleTTL), now.Add(maxAge)); err != nil {
		return fmt.Errorf("pgstore: create session: %w", err)
	}
	return nil
}

// RevokeSession ends one session immediately — the property an opaque server-side session has and
// a self-verifying token does not.
func (s *Store) RevokeSession(ctx context.Context, digest []byte, now time.Time) error {
	const q = `update sessions set revoked_at = $2 where token_sha256 = $1 and revoked_at is null`
	if _, err := s.pool.Exec(ctx, q, digest, now); err != nil {
		return fmt.Errorf("pgstore: revoke session: %w", err)
	}
	return nil
}

// DeleteExpiredSessions is the sweep. Expired rows are deleted rather than kept: a session table is
// not an audit log, and "who was logged in last spring" is not a question we want to be able to
// answer from it.
func (s *Store) DeleteExpiredSessions(ctx context.Context, now time.Time) (int64, error) {
	const q = `delete from sessions where absolute_expires_at <= $1`
	tag, err := s.pool.Exec(ctx, q, now)
	if err != nil {
		return 0, fmt.Errorf("pgstore: sweep sessions: %w", err)
	}
	return tag.RowsAffected(), nil
}