package reconcile

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"time"
)

// Scheduler drives Reconciler.RunOnce on a fixed cadence until ctx is
// cancelled. Spec accepts either "@every <duration>" (robfig/cron compat) or a
// bare Go duration string ("30s", "5m"). Keeping it to those two shapes buys
// us zero external deps while still matching the cron.Spec convention the
// parent issue asked for.
type Scheduler struct {
	Spec       string
	Reconciler *Reconciler
	Logger     *slog.Logger
}

// Run blocks until ctx is cancelled. Returns ctx.Err() in that case; returns
// any other error immediately. Each tick's error is logged and swallowed —
// the whole point of the reconciler is retry-until-success.
func (s *Scheduler) Run(ctx context.Context) error {
	if s.Reconciler == nil {
		return errors.New("reconcile.Scheduler: Reconciler is nil")
	}
	interval, err := ParseSpec(s.Spec)
	if err != nil {
		return fmt.Errorf("parse spec %q: %w", s.Spec, err)
	}
	if s.Logger != nil {
		s.Logger.Info("reconciler scheduler started", "interval", interval.String())
	}
	// Fire once immediately so pending rows don't sit a full interval on boot.
	s.tick(ctx)
	t := time.NewTicker(interval)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			if s.Logger != nil {
				s.Logger.Info("reconciler scheduler stopping", "reason", ctx.Err())
			}
			return ctx.Err()
		case <-t.C:
			s.tick(ctx)
		}
	}
}

func (s *Scheduler) tick(ctx context.Context) {
	rep, err := s.Reconciler.RunOnce(ctx)
	if err != nil {
		if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
			return
		}
		if s.Logger != nil {
			s.Logger.Error("reconciler tick failed", "err", err)
		}
		return
	}
	if s.Logger != nil && (rep.DirtyRows > 0 || rep.Failures > 0) {
		s.Logger.Info("reconciler tick",
			"dirty_rows", rep.DirtyRows,
			"attempts", rep.Attempts,
			"successes", rep.Successes,
			"failures", rep.Failures)
	}
}

// ParseSpec accepts "@every <duration>" or a bare Go duration. Anything else
// is rejected so operators who try a full crontab line get a loud error
// rather than a silent default.
func ParseSpec(spec string) (time.Duration, error) {
	s := strings.TrimSpace(spec)
	if s == "" {
		return 0, errors.New("empty spec")
	}
	if strings.HasPrefix(s, "@every ") {
		s = strings.TrimSpace(strings.TrimPrefix(s, "@every "))
	} else if strings.ContainsAny(s, "* ") {
		return 0, fmt.Errorf("spec %q: only @every <duration> and bare Go durations are supported", spec)
	}
	d, err := time.ParseDuration(s)
	if err != nil {
		return 0, err
	}
	if d <= 0 {
		return 0, fmt.Errorf("spec %q: duration must be positive", spec)
	}
	return d, nil
}