Prometheus: Make sure "Min Step" has precedence (#115941)

* set minStep value as final step value when set explicitly.

* enhance it with tests

* improve function readability

* a bit more improvement for readability

pkg/promlib/models/interval_test.go

@@ -0,0 +1,602 @@
+package models
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/otel"
+
+	"github.com/grafana/grafana/pkg/promlib/intervalv2"
+)
+
+var (
+	testNow                = time.Now()
+	testIntervalCalculator = intervalv2.NewCalculator()
+	testTracer             = otel.Tracer("test/interval")
+)
+
+func TestCalculatePrometheusInterval(t *testing.T) {
+	_, span := testTracer.Start(context.Background(), "test")
+	defer span.End()
+
+	tests := []struct {
+		name             string
+		queryInterval    string
+		dsScrapeInterval string
+		intervalMs       int64
+		intervalFactor   int64
+		query            backend.DataQuery
+		want             time.Duration
+		wantErr          bool
+	}{
+		{
+			name:             "min step 2m with 300000 intervalMs",
+			queryInterval:    "2m",
+			dsScrapeInterval: "",
+			intervalMs:       300000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval:      5 * time.Minute,
+				MaxDataPoints: 761,
+			},
+			want:    2 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "min step 2m with 900000 intervalMs",
+			queryInterval:    "2m",
+			dsScrapeInterval: "",
+			intervalMs:       900000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval:      15 * time.Minute,
+				MaxDataPoints: 175,
+			},
+			want:    2 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "with step parameter",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(12 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    30 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "without step parameter",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    15 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with high intervalFactor",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   10,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    20 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "with low intervalFactor",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    2 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "with specified scrape-interval in data source",
+			queryInterval:    "",
+			dsScrapeInterval: "240s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    4 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "with zero intervalFactor defaults to 1",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   0,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    15 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with $__interval variable",
+			queryInterval:    "$__interval",
+			dsScrapeInterval: "15s",
+			intervalMs:       60000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    120 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with ${__interval} variable",
+			queryInterval:    "${__interval}",
+			dsScrapeInterval: "15s",
+			intervalMs:       60000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    120 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with ${__interval} variable and explicit interval",
+			queryInterval:    "1m",
+			dsScrapeInterval: "15s",
+			intervalMs:       60000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    1 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "with $__rate_interval variable",
+			queryInterval:    "$__rate_interval",
+			dsScrapeInterval: "30s",
+			intervalMs:       100000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(2 * 24 * time.Hour),
+				},
+				Interval:      100 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    130 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with ${__rate_interval} variable",
+			queryInterval:    "${__rate_interval}",
+			dsScrapeInterval: "30s",
+			intervalMs:       100000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(2 * 24 * time.Hour),
+				},
+				Interval:      100 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    130 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "intervalMs 100s, minStep override 150s and scrape interval 30s",
+			queryInterval:    "150s",
+			dsScrapeInterval: "30s",
+			intervalMs:       100000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(2 * 24 * time.Hour),
+				},
+				Interval:      100 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    150 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "intervalMs 120s, minStep override 150s and ds scrape interval 30s",
+			queryInterval:    "150s",
+			dsScrapeInterval: "30s",
+			intervalMs:       120000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(2 * 24 * time.Hour),
+				},
+				Interval:      120 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    150 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "intervalMs 120s, minStep auto (interval not overridden) and ds scrape interval 30s",
+			queryInterval:    "120s",
+			dsScrapeInterval: "30s",
+			intervalMs:       120000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(2 * 24 * time.Hour),
+				},
+				Interval:      120 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    120 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "interval and minStep are automatically calculated and ds scrape interval 30s and time range 1 hour",
+			queryInterval:    "30s",
+			dsScrapeInterval: "30s",
+			intervalMs:       30000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval:      30 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    30 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "minStep is $__rate_interval and ds scrape interval 30s and time range 1 hour",
+			queryInterval:    "$__rate_interval",
+			dsScrapeInterval: "30s",
+			intervalMs:       30000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval:      30 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    2 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "minStep is $__rate_interval and ds scrape interval 30s and time range 2 days",
+			queryInterval:    "$__rate_interval",
+			dsScrapeInterval: "30s",
+			intervalMs:       120000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(2 * 24 * time.Hour),
+				},
+				Interval:      120 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    150 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "minStep is $__interval and ds scrape interval 15s and time range 2 days",
+			queryInterval:    "$__interval",
+			dsScrapeInterval: "15s",
+			intervalMs:       120000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(2 * 24 * time.Hour),
+				},
+				Interval:      120 * time.Second,
+				MaxDataPoints: 12384,
+			},
+			want:    120 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with empty dsScrapeInterval defaults to 15s",
+			queryInterval:    "",
+			dsScrapeInterval: "",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    15 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with very short time range",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Minute),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    15 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with very long time range",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(30 * 24 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    30 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "with manual interval override",
+			queryInterval:    "5m",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    5 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "minStep is auto and ds scrape interval 30s and time range 1 hour",
+			queryInterval:    "",
+			dsScrapeInterval: "30s",
+			intervalMs:       30000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval:      30 * time.Second,
+				MaxDataPoints: 1613,
+			},
+			want:    30 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "minStep is auto and ds scrape interval 15s and time range 5 minutes",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       15000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(5 * time.Minute),
+				},
+				Interval:      15 * time.Second,
+				MaxDataPoints: 1055,
+			},
+			want:    15 * time.Second,
+			wantErr: false,
+		},
+		// Additional test cases for better coverage
+		{
+			name:             "with $__interval_ms variable",
+			queryInterval:    "$__interval_ms",
+			dsScrapeInterval: "15s",
+			intervalMs:       60000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    120 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with ${__interval_ms} variable",
+			queryInterval:    "${__interval_ms}",
+			dsScrapeInterval: "15s",
+			intervalMs:       60000,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    120 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with MaxDataPoints zero",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval:      1 * time.Minute,
+				MaxDataPoints: 0,
+			},
+			want:    15 * time.Second,
+			wantErr: false,
+		},
+		{
+			name:             "with negative intervalFactor",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   -5,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    -10 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "with invalid interval string that fails parsing",
+			queryInterval:    "invalid-interval",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(48 * time.Hour),
+				},
+				Interval: 1 * time.Minute,
+			},
+			want:    time.Duration(0),
+			wantErr: true,
+		},
+		{
+			name:             "with very small MaxDataPoints",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval:      1 * time.Minute,
+				MaxDataPoints: 10,
+			},
+			want:    5 * time.Minute,
+			wantErr: false,
+		},
+		{
+			name:             "when safeInterval is larger than calculatedInterval",
+			queryInterval:    "",
+			dsScrapeInterval: "15s",
+			intervalMs:       0,
+			intervalFactor:   1,
+			query: backend.DataQuery{
+				TimeRange: backend.TimeRange{
+					From: testNow,
+					To:   testNow.Add(1 * time.Hour),
+				},
+				Interval:      1 * time.Minute,
+				MaxDataPoints: 10000,
+			},
+			want:    15 * time.Second,
+			wantErr: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := calculatePrometheusInterval(
+				tt.queryInterval,
+				tt.dsScrapeInterval,
+				tt.intervalMs,
+				tt.intervalFactor,
+				tt.query,
+				testIntervalCalculator,
+			)
+
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+
+			require.NoError(t, err)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}