package slurm

import (
	"context"
	"sync"
	"time"
)

type TokenCache struct {
	mu       sync.RWMutex
	token    string
	expireAt time.Time

	refresh func(ctx context.Context) (string, error)
	ttl     time.Duration
	leeway  time.Duration
}

func NewTokenCache(refresh func(ctx context.Context) (string, error), ttl time.Duration, leeway time.Duration) *TokenCache {
	return &TokenCache{
		refresh: refresh,
		ttl:     ttl,
		leeway:  leeway,
	}
}

func (c *TokenCache) Token(ctx context.Context) (string, error) {
	c.mu.RLock()
	if c.token != "" && time.Now().Before(c.expireAt.Add(-c.leeway)) {
		token := c.token
		c.mu.RUnlock()
		return token, nil
	}
	c.mu.RUnlock()

	c.mu.Lock()
	defer c.mu.Unlock()

	if c.token != "" && time.Now().Before(c.expireAt.Add(-c.leeway)) {
		return c.token, nil
	}

	token, err := c.refresh(ctx)
	if err != nil {
		return "", err
	}

	c.token = token
	c.expireAt = time.Now().Add(c.ttl)
	return token, nil
}