package httpserver

import (
	"context"
	"log/slog"
	"time"

	"github.com/krow/krow-backend/go-api/internal/oauth"
	"github.com/krow/krow-backend/go-api/internal/ratelimit"
)

// Scheduled maintenance for the OAuth and rate-limit tables.
//
// WHY THIS SHAPE AND NOT A NEW ONE
//
// The process already has a scheduled maintenance mechanism: sweepSessions in
// cmd/api/main.go, a ticker goroutine whose context is the server's, which runs
// once at startup and then on an interval, logs a failure and retries at the
// next tick. It is bounded, cancellable, non-blocking and failure-isolated, and
// it has been in production.
//
// So this is the same thing for two more tables rather than a second kind of
// thing. No new process, no cron dependency, no leader election, no library.
// The one addition is that both sweeps live behind a single type, so
// cmd/api/main.go gains one line rather than two more goroutines.
//
// MULTI-INSTANCE SAFETY COMES FROM THE STATEMENTS, NOT FROM COORDINATION
//
// Every instance runs this, on its own schedule, with no lock between them —
// deliberately. A lease or an advisory lock would be state to hold, to expire
// and to recover when the holder dies mid-sweep, in exchange for avoiding work
// that is already harmless: each sweep is a bounded DELETE whose predicate no
// longer matches once a row is gone. Two instances sweeping at the same moment
// delete disjoint sets and neither errors. A row deleted twice is not an error;
// it is a row that was already deleted.
//
// That is the same property Phase 5's concurrent-cleanup test asserts directly:
// four workers, six dead tokens, exactly six removed between them.

// maintenanceInterval is how often the sweep runs.
//
// Hourly. The grace period before anything is deleted is also an hour, so a
// row becomes eligible and is collected within roughly two — soon enough that
// nothing accumulates, and far enough apart that a DELETE never lands on a hot
// path. Shorter would buy nothing: nothing here is a correctness deadline.
//
// Deliberately NOT sweepInterval's fifteen minutes. Sessions churn with every
// sign-in; authorization codes live sixty seconds and tokens fifteen minutes,
// so an hour still collects them promptly while running a quarter as often.
const maintenanceInterval = time.Hour

// maintenanceTimeout bounds one pass.
//
// Generous for three bounded deletes and short enough that a wedged statement
// cannot hold this goroutine past shutdown. Matches sweepSessions' own bound in
// spirit; longer only because there are more statements.
const maintenanceTimeout = 60 * time.Second

// Maintenance sweeps the OAuth and rate-limit tables.
//
// Nil when the deployment does not serve MCP, which is why Server.Maintenance
// returns a pointer and the caller checks it — the same way routeOAuth simply
// registers nothing.
type Maintenance struct {
	store   *oauth.Store
	limiter *ratelimit.Limiter
	log     *slog.Logger
}

// Maintenance exposes the sweeper, or nil when there is nothing to sweep.
//
// Mirrors Server.Sessions(), which exists for exactly this reason: the process
// owns the schedule, the server owns the things being swept.
func (s *Server) Maintenance() *Maintenance {
	if !s.cfg.OAuth.Enabled() {
		return nil
	}
	return &Maintenance{
		store:   oauth.NewStore(s.db.Pool),
		limiter: s.limiter,
		log:     s.log,
	}
}

// MaintenanceResult is what one pass removed.
type MaintenanceResult struct {
	Grants        int64
	AccessTokens  int64
	RefreshTokens int64
	RateLimits    int64
}

// Total is the row count removed, for the log line.
func (r MaintenanceResult) Total() int64 {
	return r.Grants + r.AccessTokens + r.RefreshTokens + r.RateLimits
}

// Sweep runs one maintenance pass.
//
// The two halves are independent on purpose: a failure sweeping OAuth rows must
// not prevent the rate-limit sweep, because the second is the one that would
// otherwise grow without bound. The first error is returned, after both have
// been attempted.
func (m *Maintenance) Sweep(ctx context.Context) (MaintenanceResult, error) {
	var out MaintenanceResult
	var firstErr error

	// OAuth: codes, access tokens, and refresh tokens past their retention.
	// The grace period and the reuse-detection retention are enforced inside
	// Store.Cleanup — this schedules it, it does not reimplement it.
	cleaned, err := m.store.Cleanup(ctx)
	if err != nil {
		firstErr = err
	} else {
		out.Grants = cleaned.Grants
		out.AccessTokens = cleaned.AccessTokens
		out.RefreshTokens = cleaned.RefreshTokens
	}

	if m.limiter != nil {
		swept, err := m.limiter.Sweep(ctx, 0) // 0 = the package's own batch size
		if err != nil && firstErr == nil {
			firstErr = err
		}
		out.RateLimits = swept
	}

	return out, firstErr
}

// SweepMaintenance runs the sweep until the context is cancelled.
//
// Deliberately identical in shape to sweepSessions: one pass immediately so a
// process that has been down does not carry a backlog for a further hour, then
// on the ticker. A failed pass is logged and retried at the next tick — the
// tables being briefly larger than they should be is not worth stopping the API
// for, and it is certainly not worth a panic in a goroutine nobody is watching.
//
// Exported because cmd/api owns the process's goroutines and this package owns
// what they do.
func SweepMaintenance(ctx context.Context, m *Maintenance, log *slog.Logger) {
	if m == nil {
		// No OAuth surface, nothing to sweep. Returning rather than ticking
		// uselessly for the life of the process.
		return
	}

	ticker := time.NewTicker(maintenanceInterval)
	defer ticker.Stop()

	pass := func() {
		// A deadline of its own, so a slow DELETE cannot leave this goroutine
		// blocked past shutdown.
		sweepCtx, cancel := context.WithTimeout(ctx, maintenanceTimeout)
		defer cancel()

		// A panic in a background goroutine takes the process with it, and
		// this one runs unattended for the life of the deployment. Recovering
		// turns a bug here into a logged failure and a retry at the next tick.
		defer func() {
			if p := recover(); p != nil {
				log.Error("maintenance sweep panicked", "panic", p)
			}
		}()

		result, err := m.Sweep(sweepCtx)
		switch {
		case err != nil && ctx.Err() != nil:
			// Shutting down; the cancellation is expected, not a failure.
		case err != nil:
			log.Warn("maintenance sweep failed", "error", err,
				"grants", result.Grants, "access_tokens", result.AccessTokens,
				"refresh_tokens", result.RefreshTokens, "rate_limits", result.RateLimits)
		case result.Total() > 0:
			log.Info("maintenance sweep",
				"grants", result.Grants, "access_tokens", result.AccessTokens,
				"refresh_tokens", result.RefreshTokens, "rate_limits", result.RateLimits)
		default:
			log.Debug("maintenance sweep found nothing to delete")
		}
	}

	pass()
	for {
		select {
		case <-ctx.Done():
			log.Debug("maintenance sweeper stopped")
			return
		case <-ticker.C:
			pass()
		}
	}
}