package instrumentation

import (
	"context"
	"slices"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"go.opentelemetry.io/otel/metric"
	sdk_metric "go.opentelemetry.io/otel/sdk/metric"
	"go.opentelemetry.io/otel/sdk/metric/metricdata"
	"go.opentelemetry.io/otel/sdk/resource"
)

func TestMetricConfig_SetLegacyConfig(t *testing.T) {
	tests := []struct {
		name   string // description of this test case
		target MetricConfig
		lc     *LegacyMetricConfig
		want   MetricConfig
	}{
		{
			name: "nil legacy config does not change target",
			target: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeNone,
				},
			},
			lc: nil,
			want: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeNone,
				},
			},
		},
		{
			name: "non-none target type does not change target",
			target: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeStdOut,
				},
			},
			lc: &LegacyMetricConfig{
				Type: "otel",
			},
			want: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeStdOut,
				},
			},
		},
		{
			name: "sets fields from legacy config (type none)",
			target: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeNone,
				},
			},
			lc: &LegacyMetricConfig{
				Type: "otel",
			},
			want: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypePrometheus,
				},
			},
		},
		{
			name: "sets fields from legacy config (type unspecified)",
			target: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeUnspecified,
				},
			},
			lc: &LegacyMetricConfig{
				Type: "otel",
			},
			want: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypePrometheus,
				},
			},
		},
		{
			name: "auto type is not overridden by legacy config",
			target: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
			lc: &LegacyMetricConfig{
				Type: "otel",
			},
			want: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
		},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			tt.target.SetLegacyConfig(tt.lc)
			assert.Equal(t, tt.want, tt.target)
		})
	}
}

func Test_newMeterProvider(t *testing.T) {
	resource, err := resource.New(t.Context())
	require.NoError(t, err)

	tests := []struct {
		name string // description of this test case
		// Named input parameters for target function.
		cfg     MetricConfig
		wantErr bool
	}{
		{
			name: "none exporter returns no error",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeNone,
				},
			},
			wantErr: false,
		},
		{
			name: "unsupported exporter returns error",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterType(-1),
				},
			},
			wantErr: true,
		},
		{
			name: "prometheus exporter returns no error",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypePrometheus,
				},
			},
			wantErr: false,
		},
		{
			name: "stdout exporter returns no error",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeStdOut,
				},
			},
			wantErr: false,
		},
		{
			name: "stderr exporter returns no error",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeStdErr,
				},
			},
			wantErr: false,
		},
		{
			name: "http exporter returns no error",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type:     ExporterTypeHTTP,
					Endpoint: "localhost:4318",
				},
			},
			wantErr: false,
		},
		{
			name: "google exporter return error (no credentials)",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeGoogle,
				},
			},
			wantErr: true,
		},
		{
			name: "grpc exporter returns no error",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type:     ExporterTypeGRPC,
					Endpoint: "localhost:4317",
				},
			},
			wantErr: false,
		},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got, gotErr := newMeterProvider(t.Context(), tt.cfg, resource)
			if tt.wantErr {
				assert.Error(t, gotErr)
				assert.Nil(t, got)
			} else {
				assert.NoError(t, gotErr)
				assert.NotNil(t, got)
			}
		})
	}
}

func TestMeter_RegisterCounterObserver(t *testing.T) {
	reader := sdk_metric.NewManualReader()
	provider := sdk_metric.NewMeterProvider(sdk_metric.WithReader(reader))
	m := &Meter{Meter: provider.Meter(t.Name())}

	callback := func(_ context.Context, o metric.Int64Observer) error {
		o.Observe(42)
		return nil
	}

	err := m.RegisterCounterObserver("test.counter.observer", "test counter observer", callback)
	require.NoError(t, err)

	// registering the same name again is a no-op, not an error.
	err = m.RegisterCounterObserver("test.counter.observer", "test counter observer", callback)
	require.NoError(t, err)

	_, exists := m.CounterObservers.Load("test.counter.observer")
	assert.True(t, exists)

	var rm metricdata.ResourceMetrics
	require.NoError(t, reader.Collect(t.Context(), &rm))

	got := findMetric(t, rm, "test.counter.observer")
	sum, ok := got.Data.(metricdata.Sum[int64])
	require.True(t, ok, "expected an observable counter (Sum[int64]), got %T", got.Data)
	assert.True(t, sum.IsMonotonic)
	require.Len(t, sum.DataPoints, 1)
	assert.Equal(t, int64(42), sum.DataPoints[0].Value)
}

// findMetric locates a metric by name across all scopes collected from a reader.
func findMetric(t *testing.T, rm metricdata.ResourceMetrics, name string) metricdata.Metrics {
	t.Helper()
	for _, sm := range rm.ScopeMetrics {
		if i := slices.IndexFunc(sm.Metrics, func(m metricdata.Metrics) bool { return m.Name == name }); i >= 0 {
			return sm.Metrics[i]
		}
	}
	t.Fatalf("metric %q not found in collected data", name)
	return metricdata.Metrics{}
}

func Test_newMeterProvider_autoexport(t *testing.T) {
	resource, err := resource.New(t.Context())
	require.NoError(t, err)

	tests := []struct {
		name    string
		cfg     MetricConfig
		envVars map[string]string
		wantErr bool
	}{
		{
			name: "auto type with OTEL_METRICS_EXPORTER=console creates provider",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
			envVars: map[string]string{
				"OTEL_METRICS_EXPORTER": "console",
			},
		},
		{
			name: "auto type with no OTEL env vars creates provider (noop fallback)",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
		},
		{
			name: "auto type with OTEL_METRICS_EXPORTER=none creates provider (autoexport none)",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
			envVars: map[string]string{
				"OTEL_METRICS_EXPORTER": "none",
			},
		},
		{
			name: "auto type with only OTEL_EXPORTER_OTLP_ENDPOINT uses OTLP default",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
			envVars: map[string]string{
				"OTEL_EXPORTER_OTLP_ENDPOINT": "http://localhost:4318",
			},
		},
		{
			name: "auto type with only OTEL_EXPORTER_OTLP_METRICS_ENDPOINT uses OTLP default",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
			envVars: map[string]string{
				"OTEL_EXPORTER_OTLP_METRICS_ENDPOINT": "http://localhost:4318",
			},
		},
		{
			name: "auto type with only OTEL_EXPORTER_OTLP_PROTOCOL uses OTLP default",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
			envVars: map[string]string{
				"OTEL_EXPORTER_OTLP_PROTOCOL": "http/protobuf",
			},
		},
		{
			name: "auto type with only OTEL_EXPORTER_OTLP_METRICS_PROTOCOL uses OTLP default",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeAuto,
				},
			},
			envVars: map[string]string{
				"OTEL_EXPORTER_OTLP_METRICS_PROTOCOL": "http/protobuf",
			},
		},
		{
			name: "none type ignores OTEL env vars (explicit disable)",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeNone,
				},
			},
			envVars: map[string]string{
				"OTEL_METRICS_EXPORTER": "invalid_exporter",
			},
		},
		// Backward compatibility: ExporterTypeNone ignores global OTEL endpoint
		{
			name: "none type ignores OTEL_EXPORTER_OTLP_ENDPOINT",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeNone,
				},
			},
			envVars: map[string]string{
				"OTEL_EXPORTER_OTLP_ENDPOINT": "http://localhost:4318",
			},
		},
		// Backward compatibility: ExporterTypeNone ignores per-signal OTEL var
		{
			name: "none type ignores OTEL_METRICS_EXPORTER=console",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeNone,
				},
			},
			envVars: map[string]string{
				"OTEL_METRICS_EXPORTER": "console",
			},
		},
		// Backward compatibility: explicit ZITADEL types take priority over OTEL env vars
		{
			name: "stdout type ignores OTEL_METRICS_EXPORTER",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type: ExporterTypeStdOut,
				},
			},
			envVars: map[string]string{
				"OTEL_METRICS_EXPORTER": "grpc",
			},
		},
		{
			name: "grpc type ignores OTEL_EXPORTER_OTLP_ENDPOINT",
			cfg: MetricConfig{
				Exporter: ExporterConfig{
					Type:     ExporterTypeGRPC,
					Endpoint: "localhost:4317",
				},
			},
			envVars: map[string]string{
				"OTEL_EXPORTER_OTLP_ENDPOINT": "http://some-other-host:4318",
			},
		},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			for k, v := range tt.envVars {
				t.Setenv(k, v)
			}
			got, gotErr := newMeterProvider(t.Context(), tt.cfg, resource)
			if tt.wantErr {
				assert.Error(t, gotErr)
				assert.Nil(t, got)
			} else {
				assert.NoError(t, gotErr)
				assert.NotNil(t, got)
			}
		})
	}
}