package keeper

import (
	"github.com/prometheus/client_golang/prometheus"
	wasmvmtypes "wasmvm.mleku.dev/types"
)

const (
	labelPinned = "pinned"
	labelMemory = "memory"
	labelFs     = "fs"
)

// metricSource source of wasmvm metrics
type metricSource interface {
	GetMetrics() (*wasmvmtypes.Metrics, error)
	GetPinnedMetrics() (*wasmvmtypes.PinnedMetrics, error)
}

var _ prometheus.Collector = (*WasmVMMetricsCollector)(nil)

// WasmVMMetricsCollector custom metrics collector to be used with Prometheus
type WasmVMMetricsCollector struct {
	source             metricSource
	CacheHitsDescr     *prometheus.Desc
	CacheMissesDescr   *prometheus.Desc
	CacheElementsDescr *prometheus.Desc
	CacheSizeDescr     *prometheus.Desc
	PinnedHitsDescr    *prometheus.Desc
	PinnedSizeDescr    *prometheus.Desc
}

// NewWasmVMMetricsCollector constructor
func NewWasmVMMetricsCollector(s metricSource) *WasmVMMetricsCollector {
	if s == nil {
		panic("wasmvm instance must not be nil")
	}
	return &WasmVMMetricsCollector{
		source:           s,
		CacheHitsDescr:   prometheus.NewDesc("wasmvm_cache_hits_total", "Total number of cache hits", []string{"type"}, nil),
		CacheMissesDescr: prometheus.NewDesc("wasmvm_cache_misses_total", "Total number of cache misses", nil, nil),
		CacheElementsDescr: prometheus.NewDesc("wasmvm_cache_elements_total", "Total number of elements in the cache",
			[]string{"type"}, nil),
		CacheSizeDescr: prometheus.NewDesc("wasmvm_cache_size_bytes", "Total number of elements in the cache",
			[]string{"type"}, nil),
		PinnedHitsDescr: prometheus.NewDesc("wasmvm_pinned_contract_hits", "Number of hits of a pinned contract",
			[]string{"checksum"}, nil),
		PinnedSizeDescr: prometheus.NewDesc("wasmvm_pinned_contract_size", "Size of a pinned contract", []string{"checksum"},
			nil),
	}
}

// Register registers all metrics
func (p *WasmVMMetricsCollector) Register(r prometheus.Registerer) {
	r.MustRegister(p)
}

// Describe sends the super-set of all possible descriptors of metrics
func (p *WasmVMMetricsCollector) Describe(descs chan<- *prometheus.Desc) {
	descs <- p.CacheHitsDescr
	descs <- p.CacheMissesDescr
	descs <- p.CacheElementsDescr
	descs <- p.CacheSizeDescr
}

// Collect is called by the Prometheus registry when collecting metrics.
func (p *WasmVMMetricsCollector) Collect(c chan<- prometheus.Metric) {
	m, err := p.source.GetMetrics()
	if err == nil {
		c <- prometheus.MustNewConstMetric(p.CacheHitsDescr, prometheus.CounterValue, float64(m.HitsPinnedMemoryCache),
			labelPinned)
		c <- prometheus.MustNewConstMetric(p.CacheHitsDescr, prometheus.CounterValue, float64(m.HitsMemoryCache), labelMemory)
		c <- prometheus.MustNewConstMetric(p.CacheHitsDescr, prometheus.CounterValue, float64(m.HitsFsCache), labelFs)
		c <- prometheus.MustNewConstMetric(p.CacheMissesDescr, prometheus.CounterValue, float64(m.Misses))
		c <- prometheus.MustNewConstMetric(p.CacheElementsDescr, prometheus.GaugeValue, float64(m.ElementsPinnedMemoryCache),
			labelPinned)
		c <- prometheus.MustNewConstMetric(p.CacheElementsDescr, prometheus.GaugeValue, float64(m.ElementsMemoryCache),
			labelMemory)
		c <- prometheus.MustNewConstMetric(p.CacheSizeDescr, prometheus.GaugeValue, float64(m.SizeMemoryCache), labelMemory)
		c <- prometheus.MustNewConstMetric(p.CacheSizeDescr, prometheus.GaugeValue, float64(m.SizePinnedMemoryCache),
			labelPinned)
	}

	pm, err := p.source.GetPinnedMetrics()
	if err == nil {
		for _, mod := range pm.PerModule {
			c <- prometheus.MustNewConstMetric(p.PinnedHitsDescr, prometheus.CounterValue, float64(mod.Metrics.Hits),
				mod.Checksum.String())
			c <- prometheus.MustNewConstMetric(p.PinnedSizeDescr, prometheus.GaugeValue, float64(mod.Metrics.Size),
				mod.Checksum.String())
		}
	}

	// Node about fs metrics:
	// The number of elements and the size of elements in the file system cache cannot easily be obtained.
	// We had to either scan the whole directory of potentially thousands of files or track the values when files are added or removed.
	// Such a tracking would need to be on disk such that the values are not cleared when the node is restarted.
}
