package agent

import (
	"context"
	"encoding/json"
	"io"
	"net/http"
	"net/http/httptest"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

// TestSensorMux_CloseFlushesBuffer confirms Close() empties the
// pending buffer through the HTTP client before returning. Without
// this guarantee a Burn run would drop the last 2 s of samples when
// the stage tears down, which is exactly the window that contains the
// peak-load PSU / thermal readings we care about.
func TestSensorMux_CloseFlushesBuffer(t *testing.T) {
	var batches int32
	var totalSamples int32
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !strings.HasSuffix(r.URL.Path, "/sensor") {
			t.Errorf("unexpected path %s", r.URL.Path)
		}
		body, _ := io.ReadAll(r.Body)
		var env struct {
			Samples []SensorSample `json:"samples"`
		}
		if err := json.Unmarshal(body, &env); err != nil {
			t.Errorf("decode: %v", err)
		}
		atomic.AddInt32(&batches, 1)
		atomic.AddInt32(&totalSamples, int32(len(env.Samples)))
		w.WriteHeader(http.StatusOK)
	}))
	defer srv.Close()

	c := &Client{
		BaseURL: srv.URL,
		RunID:   1,
		Token:   "t",
		HTTP:    srv.Client(),
	}
	mux := NewSensorMux(context.Background(), c)
	mux.Send([]SensorSample{
		{Kind: "temp", Key: "cpu/0", Value: 72.5, Unit: "C"},
		{Kind: "psu_volt", Key: "+12V", Value: 12.05, Unit: "V"},
	})
	mux.Send([]SensorSample{
		{Kind: "mce", Key: "0", Value: 0, Unit: "count"},
	})
	mux.Close()

	if got := atomic.LoadInt32(&totalSamples); got != 3 {
		t.Errorf("expected 3 samples flushed, got %d across %d batch(es)", got, atomic.LoadInt32(&batches))
	}
	if atomic.LoadInt32(&batches) == 0 {
		t.Errorf("expected at least one batch HTTP post")
	}
}

// TestSensorMux_ChunksOversizedBatch verifies flushChunks splits a
// single oversized input into maxBatch-sized HTTP requests. The plan's
// Burn stage can legitimately push a single input larger than the cap
// (e.g. a workload goroutine dumping a backlog), and a single giant
// POST would defeat the point of the multiplexer.
func TestSensorMux_ChunksOversizedBatch(t *testing.T) {
	var batchSizes []int
	var mu sync.Mutex
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		body, _ := io.ReadAll(r.Body)
		var env struct {
			Samples []SensorSample `json:"samples"`
		}
		_ = json.Unmarshal(body, &env)
		mu.Lock()
		batchSizes = append(batchSizes, len(env.Samples))
		mu.Unlock()
		w.WriteHeader(http.StatusOK)
	}))
	defer srv.Close()

	c := &Client{BaseURL: srv.URL, RunID: 1, Token: "t", HTTP: srv.Client()}
	mux := NewSensorMux(context.Background(), c)

	// One input with 1200 samples → expect chunks of 500 + 500 + 200
	// given the default maxBatch of 500.
	big := make([]SensorSample, 1200)
	for i := range big {
		big[i] = SensorSample{Kind: "burn/throughput_mbps", Key: "eth0", Value: float64(i), Unit: "Mbps"}
	}
	mux.Send(big)
	mux.Close()

	mu.Lock()
	defer mu.Unlock()
	total := 0
	for _, n := range batchSizes {
		total += n
		if n > 500 {
			t.Errorf("batch size %d exceeds maxBatch=500", n)
		}
	}
	if total != 1200 {
		t.Errorf("sum of batch sizes = %d, want 1200 (sizes=%v)", total, batchSizes)
	}
	if len(batchSizes) < 3 {
		t.Errorf("expected at least 3 chunks for a 1200-sample input, got %d (%v)", len(batchSizes), batchSizes)
	}
}

// TestSensorMux_EmptyAndNilSafe covers the defensive guards around
// Send(nil) / Send([]) / a nil *SensorMux. Callers with conditional
// sample lists (storage probe that skipped a disk, GPU stage with no
// devices) should be able to call Send unconditionally without adding
// their own nil check.
func TestSensorMux_EmptyAndNilSafe(t *testing.T) {
	var batches int32
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
		atomic.AddInt32(&batches, 1)
		w.WriteHeader(http.StatusOK)
	}))
	defer srv.Close()

	// Nil receiver must be a no-op.
	var nilMux *SensorMux
	nilMux.Send([]SensorSample{{Kind: "x", Key: "y"}})
	nilMux.Close()

	c := &Client{BaseURL: srv.URL, RunID: 1, Token: "t", HTTP: srv.Client()}
	mux := NewSensorMux(context.Background(), c)
	mux.Send(nil)
	mux.Send([]SensorSample{})
	mux.Close()

	// Give any spurious goroutine a chance to surprise us.
	time.Sleep(50 * time.Millisecond)
	if atomic.LoadInt32(&batches) != 0 {
		t.Errorf("empty/nil Send must not produce HTTP batches, got %d", atomic.LoadInt32(&batches))
	}
}