package mysql

import (
	"context"
	"database/sql"
	"errors"
	"time"

	core "git.yuntuo.hk/k2safe/orbit/model"
	pulse "git.yuntuo.hk/k2safe/orbit/pulse/model"
	"git.yuntuo.hk/k2safe/orbit/pulse/service"
)

// cancelExecutionTask 由已验证所有权的调用方复用；调用前必须持有应用、队列和任务锁。
// 仅已知未开始的任务立即结清，在途执行保留许可并等待结果，历史未知效果不能变成已取消。
func cancelExecutionTask(ctx context.Context, tx *sql.Tx, ns core.ID, task executionTask, now time.Time, reason string) (service.TaskView, error) {
	var out service.TaskView
	view := task.view
	if view.State.Terminal() || view.CancelRequestedAt != nil {
		return view, nil
	}
	id := view.ID
	var err error
	var attempt *pulse.Attempt
	if view.State == pulse.TaskLeased || view.State == pulse.TaskRunning {
		if task.current == nil {
			return out, errors.New("active task lacks attempt")
		}
		a, err := readAttempt(ctx, tx, ns, *task.current)
		if err != nil {
			return out, err
		}
		if a.TaskID != id || a.Epoch != task.epoch || string(a.State) != string(view.State) {
			return out, errors.New("task attempt identity or state mismatch")
		}
		attempt = &a
	}
	next := view.State
	lease := task.lease
	var completed *time.Time
	if view.State == pulse.TaskWaiting || view.State == pulse.TaskLeased {
		next = pulse.TaskCancelled
		completed = &now
		lease = nil
		if view.EffectUncertain {
			next, completed = pulse.TaskNeedsReview, nil
		}
		if attempt != nil {
			if attempt.AuthorizedAt != nil {
				return out, errors.New("leased attempt already authorized")
			}
			result, err := tx.ExecContext(ctx, `UPDATE pulse_attempts SET state='CANCELLED',ended_at=?,error_code='CANCELLED_BEFORE_START',revision=revision+1,updated_at=? WHERE namespace_id=? AND id=? AND revision=?`, now, now, ns, attempt.ID, attempt.Revision)
			if err := exactlyOne(result, err); err != nil {
				return out, err
			}
			if err := releasePermits(ctx, tx, ns, attempt.ID, now); err != nil {
				return out, err
			}
		}
	}
	result, err := tx.ExecContext(ctx, `UPDATE pulse_tasks SET state=?,cancel_requested_at=?,lease_until=?,completed_at=?,updated_at=?,revision=revision+1 WHERE namespace_id=? AND id=? AND revision=?`, next, now, lease, completed, now, ns, id, view.Revision)
	if err := exactlyOne(result, err); err != nil {
		return out, err
	}
	if next.Terminal() {
		if err := releaseQueueTask(ctx, tx, ns, view.QueueID); err != nil {
			return out, err
		}
	}
	out, err = readTask(ctx, tx, ns, id, false)
	if err != nil {
		return out, err
	}
	event := resultEvent(next)
	if next == view.State {
		event = "task.cancel_requested"
	}
	if err := emitEvent(ctx, tx, ns, id, out.Revision, "task", event, map[string]any{"task_id": id, "state": next, "reason": reason, "effect_uncertain": view.EffectUncertain}); err != nil {
		return out, err
	}
	return out, nil
}