Add project-level DORA lead time graphs

app/assets/javascripts/lib/utils/datetime_utility.js

@@ -254,6 +254,37 @@ export const timeIntervalInWords = (intervalInSeconds) => {
     : secondsText;
 };
 
+/**
+ * Similar to `timeIntervalInWords`, but rounds the return value
+ * to 1/10th of the largest time unit. For example:
+ *
+ * 30 => 30 seconds
+ * 90 => 1.5 minutes
+ * 7200 => 2 hours
+ * 86400 => 1 day
+ * ... etc.
+ *
+ * The largest supported unit is "days".
+ *
+ * @param {Number} intervalInSeconds The time interval in seconds
+ * @returns {String} A humanized description of the time interval
+ */
+export const humanizeTimeInterval = (intervalInSeconds) => {
+  if (intervalInSeconds < 60 /* = 1 minute */) {
+    const seconds = Math.round(intervalInSeconds * 10) / 10;
+    return n__('%d second', '%d seconds', seconds);
+  } else if (intervalInSeconds < 3600 /* = 1 hour */) {
+    const minutes = Math.round(intervalInSeconds / 6) / 10;
+    return n__('%d minute', '%d minutes', minutes);
+  } else if (intervalInSeconds < 86400 /* = 1 day */) {
+    const hours = Math.round(intervalInSeconds / 360) / 10;
+    return n__('%d hour', '%d hours', hours);
+  }
+
+  const days = Math.round(intervalInSeconds / 8640) / 10;
+  return n__('%d day', '%d days', days);
+};
+
 export const dateInWords = (date, abbreviated = false, hideYear = false) => {
   if (!date) return date;
 

app/assets/javascripts/projects/pipelines/charts/components/app.vue

@@ -3,8 +3,6 @@ import { GlTabs, GlTab } from '@gitlab/ui';
 import { mergeUrlParams, updateHistory, getParameterValues } from '~/lib/utils/url_utility';
 import PipelineCharts from './pipeline_charts.vue';
 
-const charts = ['pipelines', 'deployments'];
-
 export default {
   components: {
     GlTabs,
@@ -12,6 +10,8 @@ export default {
     PipelineCharts,
     DeploymentFrequencyCharts: () =>
       import('ee_component/projects/pipelines/charts/components/deployment_frequency_charts.vue'),
+    LeadTimeCharts: () =>
+      import('ee_component/projects/pipelines/charts/components/lead_time_charts.vue'),
   },
   inject: {
     shouldRenderDeploymentFrequencyCharts: {
@@ -24,20 +24,29 @@ export default {
       selectedTab: 0,
     };
   },
+  computed: {
+    charts() {
+      if (this.shouldRenderDeploymentFrequencyCharts) {
+        return ['pipelines', 'deployments', 'lead-time'];
+      }
+
+      return ['pipelines', 'lead-time'];
+    },
+  },
   created() {
     this.selectTab();
     window.addEventListener('popstate', this.selectTab);
   },
   methods: {
     selectTab() {
-      const [chart] = getParameterValues('chart') || charts;
-      const tab = charts.indexOf(chart);
+      const [chart] = getParameterValues('chart') || this.charts;
+      const tab = this.charts.indexOf(chart);
       this.selectedTab = tab >= 0 ? tab : 0;
     },
     onTabChange(index) {
       if (index !== this.selectedTab) {
         this.selectedTab = index;
-        const path = mergeUrlParams({ chart: charts[index] }, window.location.pathname);
+        const path = mergeUrlParams({ chart: this.charts[index] }, window.location.pathname);
         updateHistory({ url: path, title: window.title });
       }
     },
@@ -46,14 +55,16 @@ export default {
 </script>
 <template>
   <div>
-    <gl-tabs v-if="shouldRenderDeploymentFrequencyCharts" :value="selectedTab" @input="onTabChange">
+    <gl-tabs :value="selectedTab" @input="onTabChange">
       <gl-tab :title="__('Pipelines')">
         <pipeline-charts />
       </gl-tab>
-      <gl-tab :title="__('Deployments')">
+      <gl-tab v-if="shouldRenderDeploymentFrequencyCharts" :title="__('Deployments')">
         <deployment-frequency-charts />
       </gl-tab>
+      <gl-tab :title="__('Lead Time')">
+        <lead-time-charts />
+      </gl-tab>
     </gl-tabs>
-    <pipeline-charts v-else />
   </div>
 </template>

ee/app/assets/javascripts/projects/pipelines/charts/components/lead_time_charts.vue

+<script>
+import { GlLink } from '@gitlab/ui';
+import * as DoraApi from 'ee/api/dora_api';
+import createFlash from '~/flash';
+import { humanizeTimeInterval } from '~/lib/utils/datetime_utility';
+import { s__ } from '~/locale';
+import CiCdAnalyticsCharts from '~/projects/pipelines/charts/components/ci_cd_analytics_charts.vue';
+import {
+  allChartDefinitions,
+  areaChartOptions,
+  chartDescriptionText,
+  chartDocumentationHref,
+  LAST_WEEK,
+  LAST_MONTH,
+  LAST_90_DAYS,
+  CHART_TITLE,
+} from './static_data/lead_time';
+import { buildNullSeriesForLeadTimeChart, apiDataToChartSeries } from './util';
+
+export default {
+  name: 'LeadTimeCharts',
+  components: {
+    GlLink,
+    CiCdAnalyticsCharts,
+  },
+  inject: {
+    projectPath: {
+      type: String,
+      default: '',
+    },
+  },
+  data() {
+    return {
+      chartData: {
+        [LAST_WEEK]: [],
+        [LAST_MONTH]: [],
+        [LAST_90_DAYS]: [],
+      },
+      tooltipTitle: null,
+      tooltipValue: null,
+    };
+  },
+  computed: {
+    charts() {
+      return allChartDefinitions.map((chart) => ({
+        ...chart,
+        data: this.chartData[chart.id],
+      }));
+    },
+  },
+  async mounted() {
+    const results = await Promise.allSettled(
+      allChartDefinitions.map(async ({ id, requestParams, startDate, endDate }) => {
+        const { data: apiData } = await DoraApi.getProjectDoraMetrics(
+          this.projectPath,
+          DoraApi.LEAD_TIME_FOR_CHANGES,
+          requestParams,
+        );
+
+        this.chartData[id] = buildNullSeriesForLeadTimeChart(
+          apiDataToChartSeries(apiData, startDate, endDate, CHART_TITLE, null),
+        );
+      }),
+    );
+
+    const requestErrors = results.filter((r) => r.status === 'rejected').map((r) => r.reason);
+
+    if (requestErrors.length) {
+      const allErrorMessages = requestErrors.join('\n');
+
+      createFlash({
+        message: s__('DORA4Metrics|Something went wrong while getting lead time data.'),
+        error: new Error(`Something went wrong while getting lead time data:\n${allErrorMessages}`),
+        captureError: true,
+      });
+    }
+  },
+  methods: {
+    formatTooltipText(params) {
+      this.tooltipTitle = params.value;
+      const seconds = params.seriesData[1].data[1];
+
+      this.tooltipValue = seconds != null ? humanizeTimeInterval(seconds) : null;
+    },
+  },
+  allChartDefinitions,
+  areaChartOptions,
+  chartDescriptionText,
+  chartDocumentationHref,
+};
+</script>
+<template>
+  <div>
+    <h4 class="gl-my-4">{{ s__('DORA4|Lead time charts') }}</h4>
+    <p data-testid="help-text">
+      {{ $options.chartDescriptionText }}
+      <gl-link :href="$options.chartDocumentationHref">
+        {{ __('Learn more.') }}
+      </gl-link>
+    </p>
+
+    <!-- Using renderer="canvas" here, otherwise the area chart coloring doesn't work if the
+         first value in the series is `null`. This appears to have been fixed in ECharts v5,
+         so once we upgrade, we can go back to using the default renderer (SVG). -->
+    <ci-cd-analytics-charts
+      :charts="charts"
+      :chart-options="$options.areaChartOptions"
+      :format-tooltip-text="formatTooltipText"
+      renderer="canvas"
+    >
+      <template #tooltip-title> {{ tooltipTitle }} </template>
+      <template #tooltip-content>
+        <template v-if="tooltipValue === null">
+          {{ s__('DORA4Metrics|No merge requests were deployed during this period') }}
+        </template>
+        <div v-else class="gl-display-flex gl-align-items-flex-end">
+          <div class="gl-mr-5">{{ s__('DORA4Metrics|Median lead time') }}</div>
+          <div class="gl-font-weight-bold" data-testid="tooltip-value">{{ tooltipValue }}</div>
+        </div>
+      </template>
+    </ci-cd-analytics-charts>
+  </div>
+</template>

ee/app/assets/javascripts/projects/pipelines/charts/components/static_data/lead_time.js

+import { helpPagePath } from '~/helpers/help_page_helper';
+import { s__ } from '~/locale';
+
+export * from './shared';
+
+export const CHART_TITLE = s__('DORA4Metrics|Lead time');
+
+export const areaChartOptions = {
+  xAxis: {
+    name: s__('DORA4Metrics|Date'),
+    type: 'category',
+  },
+  yAxis: {
+    name: s__('DORA4Metrics|Days from merge to deploy'),
+    type: 'value',
+    minInterval: 1,
+    axisLabel: {
+      formatter(seconds) {
+        // 86400 = the number of seconds in 1 day
+        return (seconds / 86400).toFixed(1);
+      },
+    },
+  },
+};
+
+export const chartDescriptionText = s__(
+  'DORA4Metrics|These charts display the median time between a merge request being merged and deployed to production, as part of the DORA 4 metrics.',
+);
+
+export const chartDocumentationHref = helpPagePath('user/analytics/ci_cd_analytics.html', {
+  anchor: 'lead-time-charts',
+});

ee/app/assets/javascripts/projects/pipelines/charts/components/util.js

+import { dataVizBlue500, dataVizOrange600 } from '@gitlab/ui/scss_to_js/scss_variables';
 import dateFormat from 'dateformat';
+import { merge, cloneDeep } from 'lodash';
 import { getDatesInRange, nDaysBefore, getStartOfDay } from '~/lib/utils/datetime_utility';
+import { s__ } from '~/locale';
 
 /**
  * Converts the raw data fetched from the
@@ -45,3 +48,99 @@ export const apiDataToChartSeries = (apiData, startDate, endDate, seriesName, em
     },
   ];
 };
+
+/**
+ * Linearly interpolates between two values
+ *
+ * @param {Number} valueAtT0 The value at t = 0
+ * @param {Number} valueAtT1 The value at t = 1
+ * @param {Number} t The current value of t
+ *
+ * @returns {Number} The result of the linear interpolation.
+ */
+const lerp = (valueAtT0, valueAtT1, t) => {
+  return valueAtT0 * (1 - t) + valueAtT1 * t;
+};
+
+/**
+ * Builds a second series that visually represents the "no data" (i.e. "null")
+ * data points, and returns a new series Array that includes both the "null"
+ * and "non-null" data sets.
+ * This function returns new series data and does not modify the original instance.
+ *
+ * @param {Array} seriesData The lead time series data that has already been processed
+ * by the `apiDataToChartSeries` function above.
+ * @returns {Array} A new series Array
+ */
+export const buildNullSeriesForLeadTimeChart = (seriesData) => {
+  const nonNullSeries = cloneDeep(seriesData[0]);
+
+  // Loop through the series data and build a list of all the "gaps". A "gap" is
+  // a section of the data set that only include `null` values. Each gap object
+  // includes the start and end indices and the start and end values of the gap.
+  const seriesGaps = [];
+  let currentGap = null;
+  nonNullSeries.data.forEach(([, value], index) => {
+    if (value == null && currentGap == null) {
+      currentGap = {};
+
+      if (index > 0) {
+        currentGap.startIndex = index - 1;
+        const [, previousValue] = nonNullSeries.data[index - 1];
+        currentGap.startValue = previousValue;
+      }
+
+      seriesGaps.push(currentGap);
+    } else if (value != null && currentGap != null) {
+      currentGap.endIndex = index;
+      currentGap.endValue = value;
+      currentGap = null;
+    }
+  });
+
+  // Create a copy of the non-null series, but with all the data point values set to `null`
+  const nullSeriesData = nonNullSeries.data.map(([date]) => [date, null]);
+
+  // Render each of the gaps to the "null" series. Values are determined by linearly
+  // interpolating between the start and end values.
+  seriesGaps.forEach((gap) => {
+    const startIndex = gap.startIndex ?? 0;
+    const startValue = gap.startValue ?? gap.endValue ?? 0;
+    const endIndex = gap.endIndex ?? nonNullSeries.data.length - 1;
+    const endValue = gap.endValue ?? gap.startValue ?? 0;
+
+    for (let i = startIndex; i <= endIndex; i += 1) {
+      const t = (i - startIndex) / (endIndex - startIndex);
+      nullSeriesData[i][1] = lerp(startValue, endValue, t);
+    }
+  });
+
+  merge(nonNullSeries, {
+    lineStyle: {
+      color: dataVizBlue500,
+    },
+    areaStyle: {
+      color: dataVizBlue500,
+    },
+    itemStyle: {
+      color: dataVizBlue500,
+    },
+  });
+
+  const nullSeries = {
+    name: s__('DORA4Metrics|No merge requests were deployed during this period'),
+    data: nullSeriesData,
+    lineStyle: {
+      type: 'dashed',
+      color: dataVizOrange600,
+    },
+    areaStyle: {
+      color: 'none',
+    },
+    itemStyle: {
+      color: dataVizOrange600,
+    },
+  };
+
+  return [nullSeries, nonNullSeries];
+};

ee/changelogs/unreleased/nfriend-add-project-lead-time-graphs.yml

+---
+title: Add DORA 4 lead time charts to project-level CI/CD Analytics page
+merge_request: 57872
+author:
+type: added

ee/spec/frontend/projects/pipelines/charts/components/__snapshots__/deployment_frequency_charts_spec.js.snap

 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`ee_component/projects/pipelines/charts/components/deployment_frequency_charts.vue when there are no network errors converts the data from the API into data usable by the chart component 1`] = `
+exports[`deployment_frequency_charts.vue when there are no network errors converts the data from the API into data usable by the chart component 1`] = `
 Array [
   Object {
     "data": Array [

ee/spec/frontend/projects/pipelines/charts/components/__snapshots__/util_spec.js.snap

+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`ee/projects/pipelines/charts/components/util.js lead time data returns the correct lead time chart data after all processing of the API response 1`] = `
+Array [
+  Object {
+    "areaStyle": Object {
+      "color": "none",
+    },
+    "data": Array [
+      Array [
+        "Jun 27",
+        86400,
+      ],
+      Array [
+        "Jun 28",
+        86400,
+      ],
+      Array [
+        "Jun 29",
+        86400,
+      ],
+      Array [
+        "Jun 30",
+        86400,
+      ],
+      Array [
+        "Jul 1",
+        432000,
+      ],
+      Array [
+        "Jul 2",
+        518400,
+      ],
+      Array [
+        "Jul 3",
+        604800,
+      ],
+    ],
+    "itemStyle": Object {
+      "color": "#b24800",
+    },
+    "lineStyle": Object {
+      "color": "#b24800",
+      "type": "dashed",
+    },
+    "name": "No merge requests were deployed during this period",
+  },
+  Object {
+    "areaStyle": Object {
+      "color": "#5772ff",
+    },
+    "data": Array [
+      Array [
+        "Jun 27",
+        null,
+      ],
+      Array [
+        "Jun 28",
+        null,
+      ],
+      Array [
+        "Jun 29",
+        null,
+      ],
+      Array [
+        "Jun 30",
+        86400,
+      ],
+      Array [
+        "Jul 1",
+        432000,
+      ],
+      Array [
+        "Jul 2",
+        null,
+      ],
+      Array [
+        "Jul 3",
+        604800,
+      ],
+    ],
+    "itemStyle": Object {
+      "color": "#5772ff",
+    },
+    "lineStyle": Object {
+      "color": "#5772ff",
+    },
+    "name": "Lead time",
+  },
+]
+`;

ee/spec/frontend/projects/pipelines/charts/components/deployment_frequency_charts_spec.js

@@ -20,7 +20,7 @@ const last90DaysData = getJSONFixture(
   'api/dora/metrics/daily_deployment_frequency_for_last_90_days.json',
 );
 
-describe('ee_component/projects/pipelines/charts/components/deployment_frequency_charts.vue', () => {
+describe('deployment_frequency_charts.vue', () => {
   useFixturesFakeDate();
 
   let DeploymentFrequencyCharts;

ee/spec/frontend/projects/pipelines/charts/components/lead_time_charts_spec.js

+import { GlSprintf, GlLink } from '@gitlab/ui';
+import { mount, shallowMount } from '@vue/test-utils';
+import MockAdapter from 'axios-mock-adapter';
+import { useFixturesFakeDate } from 'helpers/fake_date';
+import createFlash from '~/flash';
+import axios from '~/lib/utils/axios_utils';
+import httpStatus from '~/lib/utils/http_status';
+import CiCdAnalyticsCharts from '~/projects/pipelines/charts/components/ci_cd_analytics_charts.vue';
+
+jest.mock('~/flash');
+
+const lastWeekData = getJSONFixture(
+  'api/dora/metrics/daily_lead_time_for_changes_for_last_week.json',
+);
+const lastMonthData = getJSONFixture(
+  'api/dora/metrics/daily_lead_time_for_changes_for_last_month.json',
+);
+const last90DaysData = getJSONFixture(
+  'api/dora/metrics/daily_lead_time_for_changes_for_last_90_days.json',
+);
+
+describe('lead_time_charts.vue', () => {
+  useFixturesFakeDate();
+
+  let LeadTimeCharts;
+
+  // Import the component _after_ the date has been set using `useFakeDate`, so
+  // that any calls to `new Date()` during module initialization use the fake date
+  beforeAll(async () => {
+    LeadTimeCharts = (
+      await import('ee_component/projects/pipelines/charts/components/lead_time_charts.vue')
+    ).default;
+  });
+
+  let wrapper;
+  let mock;
+
+  const createComponent = (mountFn = shallowMount) => {
+    wrapper = mountFn(LeadTimeCharts, {
+      provide: {
+        projectPath: 'test/project',
+      },
+      stubs: { GlSprintf },
+    });
+  };
+
+  // Initializes the mock endpoint to return a specific set of lead time data for a given "from" date.
+  const setUpMockLeadTime = ({ start_date, data }) => {
+    mock
+      .onGet(/projects\/test%2Fproject\/dora\/metrics/, {
+        params: {
+          metric: 'lead_time_for_changes',
+          interval: 'daily',
+          per_page: 100,
+          end_date: '2015-07-04T00:00:00+0000',
+          start_date,
+        },
+      })
+      .replyOnce(httpStatus.OK, data);
+  };
+
+  afterEach(() => {
+    wrapper.destroy();
+    mock.restore();
+  });
+
+  const findHelpText = () => wrapper.find('[data-testid="help-text"]');
+  const findDocLink = () => findHelpText().find(GlLink);
+  const getTooltipValue = () => wrapper.find('[data-testid="tooltip-value"]').text();
+  const findCiCdAnalyticsCharts = () => wrapper.find(CiCdAnalyticsCharts);
+
+  describe('when there are no network errors', () => {
+    beforeEach(async () => {
+      mock = new MockAdapter(axios);
+
+      setUpMockLeadTime({
+        start_date: '2015-06-27T00:00:00+0000',
+        data: lastWeekData,
+      });
+      setUpMockLeadTime({
+        start_date: '2015-06-04T00:00:00+0000',
+        data: lastMonthData,
+      });
+      setUpMockLeadTime({
+        start_date: '2015-04-05T00:00:00+0000',
+        data: last90DaysData,
+      });
+
+      createComponent();
+
+      await axios.waitForAll();
+    });
+
+    it('makes 3 GET requests - one for each chart', () => {
+      expect(mock.history.get).toHaveLength(3);
+    });
+
+    it('does not show a flash message', () => {
+      expect(createFlash).not.toHaveBeenCalled();
+    });
+
+    it('renders description text', () => {
+      expect(findHelpText().text()).toMatchInterpolatedText(
+        'These charts display the median time between a merge request being merged and deployed to production, as part of the DORA 4 metrics. Learn more.',
+      );
+    });
+
+    it('renders a link to the documentation', () => {
+      expect(findDocLink().attributes().href).toBe(
+        '/help/user/analytics/ci_cd_analytics.html#lead-time-charts',
+      );
+    });
+
+    describe('methods', () => {
+      describe('formatTooltipText', () => {
+        it('displays a humanized version of the time interval in the tooltip', async () => {
+          createComponent(mount);
+
+          await axios.waitForAll();
+
+          const params = { seriesData: [{}, { data: ['Apr 7', 5328] }] };
+
+          // Simulate the child CiCdAnalyticsCharts component calling the
+          // function bound to the `format-tooltip-text`.
+          const formatTooltipText = findCiCdAnalyticsCharts().vm.$attrs['format-tooltip-text'];
+          formatTooltipText(params);
+
+          await wrapper.vm.$nextTick();
+
+          expect(getTooltipValue()).toBe('1.5 hours');
+        });
+      });
+    });
+  });
+
+  describe('when there are network errors', () => {
+    beforeEach(async () => {
+      mock = new MockAdapter(axios);
+
+      createComponent();
+
+      await axios.waitForAll();
+    });
+
+    it('shows a flash message', () => {
+      expect(createFlash).toHaveBeenCalledTimes(1);
+      expect(createFlash.mock.calls[0]).toEqual([
+        {
+          message: 'Something went wrong while getting lead time data.',
+          captureError: true,
+          error: expect.any(Error),
+        },
+      ]);
+    });
+  });
+});

ee/spec/frontend/projects/pipelines/charts/components/util_spec.js

-import { apiDataToChartSeries } from 'ee/projects/pipelines/charts/components/util';
+import {
+  apiDataToChartSeries,
+  buildNullSeriesForLeadTimeChart,
+} from 'ee/projects/pipelines/charts/components/util';
+
+const lastWeekData = getJSONFixture(
+  'api/dora/metrics/daily_lead_time_for_changes_for_last_week.json',
+);
 
 describe('ee/projects/pipelines/charts/components/util.js', () => {
   describe('apiDataToChartSeries', () => {
@@ -35,4 +42,174 @@ describe('ee/projects/pipelines/charts/components/util.js', () => {
       expect(apiDataToChartSeries(apiData, startDate, endDate, chartTitle)).toEqual(expected);
     });
   });
+
+  describe('buildNullSeriesForLeadTimeChart', () => {
+    it('returns series data with the expected styles and text', () => {
+      const inputSeries = [
+        {
+          name: 'Chart title',
+          data: [],
+        },
+      ];
+
+      const expectedSeries = [
+        {
+          name: 'No merge requests were deployed during this period',
+          data: expect.any(Array),
+          lineStyle: {
+            color: expect.any(String),
+            type: 'dashed',
+          },
+          areaStyle: {
+            color: 'none',
+          },
+          itemStyle: {
+            color: expect.any(String),
+          },
+        },
+        {
+          name: 'Chart title',
+          data: expect.any(Array),
+          lineStyle: {
+            color: expect.any(String),
+          },
+          areaStyle: {
+            color: expect.any(String),
+          },
+          itemStyle: {
+            color: expect.any(String),
+          },
+        },
+      ];
+
+      expect(buildNullSeriesForLeadTimeChart(inputSeries)).toEqual(expectedSeries);
+    });
+
+    describe('series data', () => {
+      describe('non-empty series', () => {
+        it('returns the provided non-empty series data unmodified as the second series', () => {
+          const inputSeries = [
+            {
+              data: [
+                ['Mar 1', 4],
+                ['Mar 2', null],
+                ['Mar 3', null],
+                ['Mar 4', 10],
+              ],
+            },
+          ];
+
+          const actualSeries = buildNullSeriesForLeadTimeChart(inputSeries);
+
+          expect(actualSeries[1]).toMatchObject(inputSeries[0]);
+        });
+      });
+
+      describe('empty series', () => {
+        const compareSeriesData = (inputSeriesData, expectedEmptySeriesData) => {
+          const actualEmptySeriesData = buildNullSeriesForLeadTimeChart([
+            { data: inputSeriesData },
+          ])[0].data;
+
+          expect(actualEmptySeriesData).toEqual(expectedEmptySeriesData);
+        };
+
+        describe('when the data contains a gap in the middle of the data set', () => {
+          it('builds the "no data" series by linealy interpolating between the provided data points', () => {
+            const inputSeriesData = [
+              ['Mar 1', 4],
+              ['Mar 2', null],
+              ['Mar 3', null],
+              ['Mar 4', 10],
+            ];
+
+            const expectedEmptySeriesData = [
+              ['Mar 1', 4],
+              ['Mar 2', 6],
+              ['Mar 3', 8],
+              ['Mar 4', 10],
+            ];
+
+            compareSeriesData(inputSeriesData, expectedEmptySeriesData);
+          });
+        });
+
+        describe('when the data contains a gap at the beginning of the data set', () => {
+          it('fills in the gap using the first non-null data point value', () => {
+            const inputSeriesData = [
+              ['Mar 1', null],
+              ['Mar 2', null],
+              ['Mar 3', null],
+              ['Mar 4', 10],
+            ];
+
+            const expectedEmptySeriesData = [
+              ['Mar 1', 10],
+              ['Mar 2', 10],
+              ['Mar 3', 10],
+              ['Mar 4', 10],
+            ];
+
+            compareSeriesData(inputSeriesData, expectedEmptySeriesData);
+          });
+        });
+
+        describe('when the data contains a gap at the end of the data set', () => {
+          it('fills in the gap using the last non-null data point value', () => {
+            const inputSeriesData = [
+              ['Mar 1', 10],
+              ['Mar 2', null],
+              ['Mar 3', null],
+              ['Mar 4', null],
+            ];
+
+            const expectedEmptySeriesData = [
+              ['Mar 1', 10],
+              ['Mar 2', 10],
+              ['Mar 3', 10],
+              ['Mar 4', 10],
+            ];
+
+            compareSeriesData(inputSeriesData, expectedEmptySeriesData);
+          });
+        });
+
+        describe('when the data contains all null values', () => {
+          it('fills the empty series with all zeros', () => {
+            const inputSeriesData = [
+              ['Mar 1', null],
+              ['Mar 2', null],
+              ['Mar 3', null],
+              ['Mar 4', null],
+            ];
+
+            const expectedEmptySeriesData = [
+              ['Mar 1', 0],
+              ['Mar 2', 0],
+              ['Mar 3', 0],
+              ['Mar 4', 0],
+            ];
+
+            compareSeriesData(inputSeriesData, expectedEmptySeriesData);
+          });
+        });
+      });
+    });
+  });
+
+  describe('lead time data', () => {
+    it('returns the correct lead time chart data after all processing of the API response', () => {
+      const chartData = buildNullSeriesForLeadTimeChart(
+        apiDataToChartSeries(
+          lastWeekData,
+          new Date(2015, 5, 27, 10),
+          new Date(2015, 6, 4, 10),
+          'Lead time',
+          null,
+        ),
+      );
+
+      expect(chartData).toMatchSnapshot();
+    });
+  });
 });

locale/gitlab.pot

@@ -9690,18 +9690,39 @@ msgstr ""
 msgid "DORA4Metrics|Date"
 msgstr ""
 
+msgid "DORA4Metrics|Days from merge to deploy"
+msgstr ""
+
 msgid "DORA4Metrics|Deployments"
 msgstr ""
 
 msgid "DORA4Metrics|Deployments charts"
 msgstr ""
 
+msgid "DORA4Metrics|Lead time"
+msgstr ""
+
+msgid "DORA4Metrics|Median lead time"
+msgstr ""
+
+msgid "DORA4Metrics|No merge requests were deployed during this period"
+msgstr ""
+
 msgid "DORA4Metrics|Something went wrong while getting deployment frequency data"
 msgstr ""
 
+msgid "DORA4Metrics|Something went wrong while getting lead time data."
+msgstr ""
+
 msgid "DORA4Metrics|These charts display the frequency of deployments to the production environment, as part of the DORA 4 metrics. The environment must be named %{codeStart}production%{codeEnd} for its data to appear in these charts."
 msgstr ""
 
+msgid "DORA4Metrics|These charts display the median time between a merge request being merged and deployed to production, as part of the DORA 4 metrics."
+msgstr ""
+
+msgid "DORA4|Lead time charts"
+msgstr ""
+
 msgid "Dashboard"
 msgstr ""
 

spec/frontend/lib/utils/datetime_utility_spec.js

@@ -178,6 +178,30 @@ describe('timeIntervalInWords', () => {
   });
 });
 
+describe('humanizeTimeInterval', () => {
+  it.each`
+    intervalInSeconds | expected
+    ${0}              | ${'0 seconds'}
+    ${1}              | ${'1 second'}
+    ${1.48}           | ${'1.5 seconds'}
+    ${2}              | ${'2 seconds'}
+    ${60}             | ${'1 minute'}
+    ${91}             | ${'1.5 minutes'}
+    ${120}            | ${'2 minutes'}
+    ${3600}           | ${'1 hour'}
+    ${5401}           | ${'1.5 hours'}
+    ${7200}           | ${'2 hours'}
+    ${86400}          | ${'1 day'}
+    ${129601}         | ${'1.5 days'}
+    ${172800}         | ${'2 days'}
+  `(
+    'returns "$expected" when the time interval is $intervalInSeconds seconds',
+    ({ intervalInSeconds, expected }) => {
+      expect(datetimeUtility.humanizeTimeInterval(intervalInSeconds)).toBe(expected);
+    },
+  );
+});
+
 describe('dateInWords', () => {
   const date = new Date('07/01/2016');
 

spec/frontend/projects/pipelines/charts/components/app_spec.js

@@ -10,6 +10,7 @@ import PipelineCharts from '~/projects/pipelines/charts/components/pipeline_char
 jest.mock('~/lib/utils/url_utility');
 
 const DeploymentFrequencyChartsStub = { name: 'DeploymentFrequencyCharts', render: () => {} };
+const LeadTimeChartsStub = { name: 'LeadTimeCharts', render: () => {} };
 
 describe('ProjectsPipelinesChartsApp', () => {
   let wrapper;
@@ -25,6 +26,7 @@ describe('ProjectsPipelinesChartsApp', () => {
           },
           stubs: {
             DeploymentFrequencyCharts: DeploymentFrequencyChartsStub,
+            LeadTimeCharts: LeadTimeChartsStub,
           },
         },
         mountOptions,
@@ -44,6 +46,7 @@ describe('ProjectsPipelinesChartsApp', () => {
   const findGlTabs = () => wrapper.find(GlTabs);
   const findAllGlTab = () => wrapper.findAll(GlTab);
   const findGlTabAt = (i) => findAllGlTab().at(i);
+  const findLeadTimeCharts = () => wrapper.find(LeadTimeChartsStub);
   const findDeploymentFrequencyCharts = () => wrapper.find(DeploymentFrequencyChartsStub);
   const findPipelineCharts = () => wrapper.find(PipelineCharts);
 
@@ -51,15 +54,23 @@ describe('ProjectsPipelinesChartsApp', () => {
     expect(findPipelineCharts().exists()).toBe(true);
   });
 
+  it('renders the lead time charts', () => {
+    expect(findLeadTimeCharts().exists()).toBe(true);
+  });
+
   describe('when shouldRenderDeploymentFrequencyCharts is true', () => {
     beforeEach(() => {
       createComponent({ provide: { shouldRenderDeploymentFrequencyCharts: true } });
     });
 
-    it('renders the deployment frequency charts in a tab', () => {
+    it('renders the expected tabs', () => {
       expect(findGlTabs().exists()).toBe(true);
       expect(findGlTabAt(0).attributes('title')).toBe('Pipelines');
       expect(findGlTabAt(1).attributes('title')).toBe('Deployments');
+      expect(findGlTabAt(2).attributes('title')).toBe('Lead Time');
+    });
+
+    it('renders the deployment frequency charts', () => {
       expect(findDeploymentFrequencyCharts().exists()).toBe(true);
     });
 
@@ -108,6 +119,7 @@ describe('ProjectsPipelinesChartsApp', () => {
   describe('when provided with a query param', () => {
     it.each`
       chart            | tab
+      ${'lead-time'}   | ${'2'}
       ${'deployments'} | ${'1'}
       ${'pipelines'}   | ${'0'}
       ${'fake'}        | ${'0'}
@@ -160,8 +172,13 @@ describe('ProjectsPipelinesChartsApp', () => {
       createComponent({ provide: { shouldRenderDeploymentFrequencyCharts: false } });
     });
 
+    it('renders the expected tabs', () => {
+      expect(findGlTabs().exists()).toBe(true);
+      expect(findGlTabAt(0).attributes('title')).toBe('Pipelines');
+      expect(findGlTabAt(1).attributes('title')).toBe('Lead Time');
+    });
+
     it('does not render the deployment frequency charts in a tab', () => {
-      expect(findGlTabs().exists()).toBe(false);
       expect(findDeploymentFrequencyCharts().exists()).toBe(false);
     });
   });