package imgcache

import (
	"fmt"

	"github.com/prometheus/client_golang/prometheus"
)

// registerMetrics makes the cache's metrics and registers them on
// metricsRegistry. The metrics are kept in memory, so updating one waits
// for nothing and makes no database call. It fails when metricsRegistry
// already holds metrics of the same names.
func (c *Cache) registerMetrics(metricsRegistry prometheus.Registerer) error {
	c.cacheHits = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_cache_hits_total",
		Help: "Image requests served from the cache.",
	})
	c.cacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_cache_misses_total",
		Help: "Image requests not served from the cache.",
	})
	c.sourceCacheHits = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_source_cache_hits_total",
		Help: "Variants made or checked whose source was in the cache.",
	})
	c.sourceCacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_source_cache_misses_total",
		Help: "Variants made or checked whose source was not in the cache.",
	})
	c.usageBytes = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "pixa_cache_usage_bytes",
		Help: "Bytes of sources and variants in the cache, as eviction last read them.",
	})
	c.maxBytes = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "pixa_cache_max_bytes",
		Help: "The disk cache limit in bytes, cache_max_bytes.",
	})
	c.evictions = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_cache_evictions_total",
		Help: "Sources and variants removed by eviction.",
	})
	c.evictedBytes = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_cache_evicted_bytes_total",
		Help: "Bytes of the sources and variants removed by eviction.",
	})

	c.maxBytes.Set(float64(c.config.MaxBytes))

	for _, metric := range []prometheus.Collector{
		c.cacheHits, c.cacheMisses, c.sourceCacheHits, c.sourceCacheMisses,
		c.usageBytes, c.maxBytes, c.evictions, c.evictedBytes,
	} {
		err := metricsRegistry.Register(metric)
		if err != nil {
			return fmt.Errorf("failed to register the cache's metrics: %w", err)
		}
	}

	return nil
}

// IncrementStats counts a cache hit or miss of an image request. It only
// adds to the cache's counters in memory, so it never waits for the
// database or fails.
func (c *Cache) IncrementStats(hit bool) {
	if hit {
		c.cacheHits.Inc()
	} else {
		c.cacheMisses.Inc()
	}
}

// IncrementSourceStats counts whether a variant being made or checked found
// its source in the cache. Like IncrementStats, it never waits or fails.
func (c *Cache) IncrementSourceStats(hit bool) {
	if hit {
		c.sourceCacheHits.Inc()
	} else {
		c.sourceCacheMisses.Inc()
	}
}

// countEviction counts one source or variant of sizeBytes bytes removed by
// eviction.
func (c *Cache) countEviction(sizeBytes int64) {
	c.evictions.Inc()
	c.evictedBytes.Add(float64(sizeBytes))
}