package observability

import (
	"context"
	"encoding/json"
	"log"
	"net/http"
	"regexp"
	"strconv"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"

	"github.com/forgeo/forgebucket/internal/events"
)

// ── Metric definitions ────────────────────────────────────────────────────────

var (
	HttpRequestsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "forgebucket_http_requests_total",
		Help: "Total HTTP requests by method, normalized path, and status code.",
	}, []string{"method", "path", "status"})

	HttpRequestDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "forgebucket_http_request_duration_seconds",
		Help:    "HTTP request latency by method and normalized path.",
		Buckets: prometheus.DefBuckets,
	}, []string{"method", "path"})

	PipelineRunsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "forgebucket_pipeline_runs_total",
		Help: "Pipeline runs by terminal status.",
	}, []string{"status"})

	DeploymentsTotal = promauto.NewCounterVec(prometheus.CounterOpts{
		Name: "forgebucket_deployments_total",
		Help: "Deployments by terminal status.",
	}, []string{"status"})

	ActivePipelineRuns = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "forgebucket_active_pipeline_runs",
		Help: "Pipeline runs currently in queued or running state.",
	})
)

func init() {
	// Pre-initialize all label combinations so the metrics are visible in
	// /metrics immediately from startup (no gaps on first scrape).
	for _, s := range []string{"succeeded", "failed", "cancelled"} {
		PipelineRunsTotal.With(prometheus.Labels{"status": s})
	}
	for _, s := range []string{"pending", "success", "failure", "cancelled"} {
		DeploymentsTotal.With(prometheus.Labels{"status": s})
	}
}

// ── HTTP instrumentation middleware ──────────────────────────────────────────

type statusRecorder struct {
	http.ResponseWriter
	status int
}

func (r *statusRecorder) WriteHeader(code int) {
	r.status = code
	r.ResponseWriter.WriteHeader(code)
}

// Middleware records request count and latency for every HTTP request.
// Path labels are normalized to prevent high cardinality (numeric segments
// and positional path variables are replaced with placeholder tokens).
func Middleware() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			start := time.Now()
			rec := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
			next.ServeHTTP(rec, r)

			path := normalizePath(r.URL.Path)
			status := strconv.Itoa(rec.status)
			elapsed := time.Since(start).Seconds()

			HttpRequestsTotal.WithLabelValues(r.Method, path, status).Inc()
			HttpRequestDuration.WithLabelValues(r.Method, path).Observe(elapsed)
		})
	}
}

// normalizePath replaces volatile path segments with placeholders so that
// Prometheus label cardinality stays bounded.
//
// Examples:
//
//	/api/v1/repos/alice/myrepo/runs/42/jobs/7/logs
//	  → /api/v1/repos/:owner/:repo/runs/:id/jobs/:id/logs
//
//	/alice/myrepo.git/info/refs
//	  → /:owner/:repo.git/info/refs
var reNumeric = regexp.MustCompile(`/\d+`)

func normalizePath(path string) string {
	// Replace all-numeric segments first.
	path = reNumeric.ReplaceAllString(path, "/:id")

	// Normalize repo smart-HTTP paths: /{owner}/{repo}.git/...
	path = reGitPath.ReplaceAllString(path, "/:owner/:repo.git$1")

	// Normalize /api/v1/repos/{owner}/{repo}/...
	path = reRepoPath.ReplaceAllString(path, "/api/v1/repos/:owner/:repo$1")

	// Normalize /api/v1/workspaces/{handle}/...
	path = reWorkspacePath.ReplaceAllString(path, "/api/v1/workspaces/:handle$1")

	return path
}

var (
	reGitPath       = regexp.MustCompile(`^/[^/]+/[^/]+\.git(/.*)$`)
	reRepoPath      = regexp.MustCompile(`^/api/v1/repos/[^/]+/[^/]+(/.*)$`)
	reWorkspacePath = regexp.MustCompile(`^/api/v1/workspaces/[^/]+(/.*)$`)
)

// ── NATS event watcher ────────────────────────────────────────────────────────

// StartNATSWatcher subscribes to pipeline and deployment NATS events and
// increments the corresponding Prometheus counters. Runs until ctx is cancelled.
func StartNATSWatcher(ctx context.Context, bus events.EventBus) {
	type statusPayload struct {
		Status string `json:"status"`
	}

	unsub1, err := bus.Subscribe("pipeline.>", func(subject string, data []byte) {
		switch subject {
		case events.SubjectPipelineTriggered:
			ActivePipelineRuns.Inc()
		case events.SubjectPipelineCompleted:
			ActivePipelineRuns.Dec()
			PipelineRunsTotal.WithLabelValues("succeeded").Inc()
		case events.SubjectPipelineFailed:
			ActivePipelineRuns.Dec()
			PipelineRunsTotal.WithLabelValues("failed").Inc()
		}
	})
	if err != nil {
		log.Printf("observability: subscribe pipeline.*: %v", err)
	} else {
		defer unsub1()
	}

	unsub2, err := bus.Subscribe("deployment.>", func(subject string, data []byte) {
		var p statusPayload
		json.Unmarshal(data, &p) //nolint:errcheck
		switch subject {
		case events.SubjectDeploymentSucceeded:
			DeploymentsTotal.WithLabelValues("success").Inc()
		case events.SubjectDeploymentFailed:
			DeploymentsTotal.WithLabelValues("failure").Inc()
		case events.SubjectDeploymentStarted:
			DeploymentsTotal.WithLabelValues("pending").Inc()
		}
	})
	if err != nil {
		log.Printf("observability: subscribe deployment.*: %v", err)
	} else {
		defer unsub2()
	}

	log.Printf("observability: NATS metric watcher started")
	<-ctx.Done()
}