Implement code frequency graph (#29191)

### Overview
This is the implementation of Code Frequency page. This feature was
mentioned on these issues: #18262, #7392.


It adds another tab to Activity page called Code Frequency. Code
Frequency tab shows additions and deletions over time since the
repository existed.


Before:
<img width="1296" alt="image"
src="https://github.com/go-gitea/gitea/assets/32161460/2603504f-aee7-4929-a8c4-fb3412a7a0f6">

After:
<img width="1296" alt="image"
src="https://github.com/go-gitea/gitea/assets/32161460/58c03721-729f-4536-a663-9f337f240963">

---


#### Features
- See additions deletions over time since repository existed
- Click on "Additions" or "Deletions" legend to show only one type of
contribution
- Use the same cache from Contributors page so that the loading of data
will be fast once it is cached by visiting either one of the pages

---------

Co-authored-by: Giteabot <teabot@gitea.io>

6 files changed, 217 insertions, 30 deletions

diff --git a/web_src/js/components/RepoCodeFrequency.vue b/web_src/js/components/RepoCodeFrequency.vue
new file mode 100644
index 0000000000..ad607a041a
--- /dev/null
+++ b/web_src/js/components/RepoCodeFrequency.vue
@@ -0,0 +1,172 @@
+<script>
+import {SvgIcon} from '../svg.js';
+import {
+  Chart,
+  Legend,
+  LinearScale,
+  TimeScale,
+  PointElement,
+  LineElement,
+  Filler,
+} from 'chart.js';
+import {GET} from '../modules/fetch.js';
+import {Line as ChartLine} from 'vue-chartjs';
+import {
+  startDaysBetween,
+  firstStartDateAfterDate,
+  fillEmptyStartDaysWithZeroes,
+} from '../utils/time.js';
+import {chartJsColors} from '../utils/color.js';
+import {sleep} from '../utils.js';
+import 'chartjs-adapter-dayjs-4/dist/chartjs-adapter-dayjs-4.esm';
+
+const {pageData} = window.config;
+
+Chart.defaults.color = chartJsColors.text;
+Chart.defaults.borderColor = chartJsColors.border;
+
+Chart.register(
+  TimeScale,
+  LinearScale,
+  Legend,
+  PointElement,
+  LineElement,
+  Filler,
+);
+
+export default {
+  components: {ChartLine, SvgIcon},
+  props: {
+    locale: {
+      type: Object,
+      required: true
+    },
+  },
+  data: () => ({
+    isLoading: false,
+    errorText: '',
+    repoLink: pageData.repoLink || [],
+    data: [],
+  }),
+  mounted() {
+    this.fetchGraphData();
+  },
+  methods: {
+    async fetchGraphData() {
+      this.isLoading = true;
+      try {
+        let response;
+        do {
+          response = await GET(`${this.repoLink}/activity/code-frequency/data`);
+          if (response.status === 202) {
+            await sleep(1000); // wait for 1 second before retrying
+          }
+        } while (response.status === 202);
+        if (response.ok) {
+          this.data = await response.json();
+          const weekValues = Object.values(this.data);
+          const start = weekValues[0].week;
+          const end = firstStartDateAfterDate(new Date());
+          const startDays = startDaysBetween(new Date(start), new Date(end));
+          this.data = fillEmptyStartDaysWithZeroes(startDays, this.data);
+          this.errorText = '';
+        } else {
+          this.errorText = response.statusText;
+        }
+      } catch (err) {
+        this.errorText = err.message;
+      } finally {
+        this.isLoading = false;
+      }
+    },
+
+    toGraphData(data) {
+      return {
+        datasets: [
+          {
+            data: data.map((i) => ({x: i.week, y: i.additions})),
+            pointRadius: 0,
+            pointHitRadius: 0,
+            fill: true,
+            label: 'Additions',
+            backgroundColor: chartJsColors['additions'],
+            borderWidth: 0,
+            tension: 0.3,
+          },
+          {
+            data: data.map((i) => ({x: i.week, y: -i.deletions})),
+            pointRadius: 0,
+            pointHitRadius: 0,
+            fill: true,
+            label: 'Deletions',
+            backgroundColor: chartJsColors['deletions'],
+            borderWidth: 0,
+            tension: 0.3,
+          },
+        ],
+      };
+    },
+
+    getOptions() {
+      return {
+        responsive: true,
+        maintainAspectRatio: false,
+        animation: true,
+        plugins: {
+          legend: {
+            display: true,
+          },
+        },
+        scales: {
+          x: {
+            type: 'time',
+            grid: {
+              display: false,
+            },
+            time: {
+              minUnit: 'month',
+            },
+            ticks: {
+              maxRotation: 0,
+              maxTicksLimit: 12
+            },
+          },
+          y: {
+            ticks: {
+              maxTicksLimit: 6
+            },
+          },
+        },
+      };
+    },
+  },
+};
+</script>
+<template>
+  <div>
+    <div class="ui header gt-df gt-ac gt-sb">
+      {{ isLoading ? locale.loadingTitle : errorText ? locale.loadingTitleFailed: `Code frequency over the history of ${repoLink.slice(1)}` }}
+    </div>
+    <div class="gt-df ui segment main-graph">
+      <div v-if="isLoading || errorText !== ''" class="gt-tc gt-m-auto">
+        <div v-if="isLoading">
+          <SvgIcon name="octicon-sync" class="gt-mr-3 job-status-rotate"/>
+          {{ locale.loadingInfo }}
+        </div>
+        <div v-else class="text red">
+          <SvgIcon name="octicon-x-circle-fill"/>
+          {{ errorText }}
+        </div>
+      </div>
+      <ChartLine
+        v-memo="data" v-if="data.length !== 0"
+        :data="toGraphData(data)" :options="getOptions()"
+      />
+    </div>
+  </div>
+</template>
+<style scoped>
+.main-graph {
+  height: 440px;
+}
+</style>
diff --git a/web_src/js/components/RepoContributors.vue b/web_src/js/components/RepoContributors.vue
index fa1545b3df..84fdcae1f6 100644
--- a/web_src/js/components/RepoContributors.vue
+++ b/web_src/js/components/RepoContributors.vue
@@ -3,10 +3,7 @@ import {SvgIcon} from '../svg.js';
 import {
   Chart,
   Title,
-  Tooltip,
-  Legend,
   BarElement,
-  CategoryScale,
   LinearScale,
   TimeScale,
   PointElement,
@@ -21,27 +18,13 @@ import {
   firstStartDateAfterDate,
   fillEmptyStartDaysWithZeroes,
 } from '../utils/time.js';
+import {chartJsColors} from '../utils/color.js';
+import {sleep} from '../utils.js';
 import 'chartjs-adapter-dayjs-4/dist/chartjs-adapter-dayjs-4.esm';
 import $ from 'jquery';
 
 const {pageData} = window.config;
 
-const colors = {
-  text: '--color-text',
-  border: '--color-secondary-alpha-60',
-  commits: '--color-primary-alpha-60',
-  additions: '--color-green',
-  deletions: '--color-red',
-  title: '--color-secondary-dark-4',
-};
-
-const styles = window.getComputedStyle(document.documentElement);
-const getColor = (name) => styles.getPropertyValue(name).trim();
-
-for (const [key, value] of Object.entries(colors)) {
-  colors[key] = getColor(value);
-}
-
 const customEventListener = {
   id: 'customEventListener',
   afterEvent: (chart, args, opts) => {
@@ -54,17 +37,14 @@ const customEventListener = {
   }
 };
 
-Chart.defaults.color = colors.text;
-Chart.defaults.borderColor = colors.border;
+Chart.defaults.color = chartJsColors.text;
+Chart.defaults.borderColor = chartJsColors.border;
 
 Chart.register(
   TimeScale,
-  CategoryScale,
   LinearScale,
   BarElement,
   Title,
-  Tooltip,
-  Legend,
   PointElement,
   LineElement,
   Filler,
@@ -122,7 +102,7 @@ export default {
         do {
           response = await GET(`${this.repoLink}/activity/contributors/data`);
           if (response.status === 202) {
-            await new Promise((resolve) => setTimeout(resolve, 1000)); // wait for 1 second before retrying
+            await sleep(1000); // wait for 1 second before retrying
           }
         } while (response.status === 202);
         if (response.ok) {
@@ -222,7 +202,7 @@ export default {
             pointRadius: 0,
             pointHitRadius: 0,
             fill: 'start',
-            backgroundColor: colors[this.type],
+            backgroundColor: chartJsColors[this.type],
             borderWidth: 0,
             tension: 0.3,
           },
@@ -254,7 +234,6 @@ export default {
           title: {
             display: type === 'main',
             text: 'drag: zoom, shift+drag: pan, double click: reset zoom',
-            color: colors.title,
             position: 'top',
             align: 'center',
           },
@@ -262,9 +241,6 @@ export default {
             chartType: type,
             instance: this,
           },
-          legend: {
-            display: false,
-          },
           zoom: {
             pan: {
               enabled: true,
diff --git a/web_src/js/features/code-frequency.js b/web_src/js/features/code-frequency.js
new file mode 100644
index 0000000000..103d82f6e3
--- /dev/null
+++ b/web_src/js/features/code-frequency.js
@@ -0,0 +1,21 @@
+import {createApp} from 'vue';
+
+export async function initRepoCodeFrequency() {
+  const el = document.getElementById('repo-code-frequency-chart');
+  if (!el) return;
+
+  const {default: RepoCodeFrequency} = await import(/* webpackChunkName: "code-frequency-graph" */'../components/RepoCodeFrequency.vue');
+  try {
+    const View = createApp(RepoCodeFrequency, {
+      locale: {
+        loadingTitle: el.getAttribute('data-locale-loading-title'),
+        loadingTitleFailed: el.getAttribute('data-locale-loading-title-failed'),
+        loadingInfo: el.getAttribute('data-locale-loading-info'),
+      }
+    });
+    View.mount(el);
+  } catch (err) {
+    console.error('RepoCodeFrequency failed to load', err);
+    el.textContent = el.getAttribute('data-locale-component-failed-to-load');
+  }
+}
diff --git a/web_src/js/index.js b/web_src/js/index.js
index ddd435f05e..876e4291ee 100644
--- a/web_src/js/index.js
+++ b/web_src/js/index.js
@@ -87,6 +87,7 @@ import {onDomReady} from './utils/dom.js';
 import {initRepoIssueList} from './features/repo-issue-list.js';
 import {initCommonIssueListQuickGoto} from './features/common-issue-list.js';
 import {initRepoContributors} from './features/contributors.js';
+import {initRepoCodeFrequency} from './features/code-frequency.js';
 import {initRepoDiffCommitBranchesAndTags} from './features/repo-diff-commit.js';
 import {initDirAuto} from './modules/dirauto.js';
 
@@ -177,6 +178,7 @@ onDomReady(() => {
   initRepository();
   initRepositoryActionView();
   initRepoContributors();
+  initRepoCodeFrequency();
 
   initCommitStatuses();
   initCaptcha();
diff --git a/web_src/js/utils.js b/web_src/js/utils.js
index c82e42d349..3a2694335f 100644
--- a/web_src/js/utils.js
+++ b/web_src/js/utils.js
@@ -139,3 +139,5 @@ export function parseDom(text, contentType) {
 export function serializeXml(node) {
   return xmlSerializer.serializeToString(node);
 }
+
+export const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
diff --git a/web_src/js/utils/color.js b/web_src/js/utils/color.js
index 5d9c4ca45d..0ba6af49ee 100644
--- a/web_src/js/utils/color.js
+++ b/web_src/js/utils/color.js
@@ -19,3 +19,17 @@ function getLuminance(r, g, b) {
 export function useLightTextOnBackground(r, g, b) {
   return getLuminance(r, g, b) < 0.453;
 }
+
+function resolveColors(obj) {
+  const styles = window.getComputedStyle(document.documentElement);
+  const getColor = (name) => styles.getPropertyValue(name).trim();
+  return Object.fromEntries(Object.entries(obj).map(([key, value]) => [key, getColor(value)]));
+}
+
+export const chartJsColors = resolveColors({
+  text: '--color-text',
+  border: '--color-secondary-alpha-60',
+  commits: '--color-primary-alpha-60',
+  additions: '--color-green',
+  deletions: '--color-red',
+});