add support for overwriting existing card (#859)

* frontend

* wip

* minimum viable

* minor simplification

* simplify gradients in duplicate svg

* simplify add-duplicate svg

* colors good

* arrows shape

* disable overwrite if no valid duplicate IDs

* add warning

18 files changed, 274 insertions, 97 deletions

diff --git a/ext/css/display.css b/ext/css/display.css
index 198ff662..9b4e0022 100644
--- a/ext/css/display.css
+++ b/ext/css/display.css
@@ -669,8 +669,13 @@ button.action-button:active {
 .icon[data-icon=view-note]      { background-image: url('/images/view-note.svg'); }
 .icon[data-icon=add-term-kanji] { background-image: url('/images/add-term-kanji.svg'); }
 .icon[data-icon=add-term-kana]  { background-image: url('/images/add-term-kana.svg'); }
+.icon[data-icon=add-kanji]  { background-image: url('/images/add-term-kanji.svg'); }
+.icon[data-icon=overwrite-term-kanji] { background-image: url('/images/overwrite-term-kanji.svg'); }
+.icon[data-icon=overwrite-term-kana]  { background-image: url('/images/overwrite-term-kana.svg'); }
+.icon[data-icon=overwrite-kanji]  { background-image: url('/images/overwrite-term-kanji.svg'); }
 .icon[data-icon=add-duplicate-term-kanji] { background-image: url('/images/add-duplicate-term-kanji.svg'); }
 .icon[data-icon=add-duplicate-term-kana]  { background-image: url('/images/add-duplicate-term-kana.svg'); }
+.icon[data-icon=add-duplicate-kanji]  { background-image: url('/images/add-duplicate-term-kanji.svg'); }
 .icon[data-icon=play-audio]     { background-image: url('/images/play-audio.svg'); }
 .icon[data-icon=source-term]    { background-image: url('/images/source-term.svg'); }
 .icon[data-icon=entry-current]  { background-image: url('/images/entry-current.svg'); }
@@ -1920,7 +1925,7 @@ button.footer-notification-close-button {
     display: none;
 }
 :root[data-anki-enabled=false] .action-button[data-action=view-note],
-:root[data-anki-enabled=false] .action-button[data-action=add-note] {
+:root[data-anki-enabled=false] .action-button[data-action=save-note] {
     display: none;
 }
 :root[data-audio-enabled=false] .action-button[data-action=play-audio] {
diff --git a/ext/data/schemas/options-schema.json b/ext/data/schemas/options-schema.json
index 0cb6db0a..5db4c087 100644
--- a/ext/data/schemas/options-schema.json
+++ b/ext/data/schemas/options-schema.json
@@ -990,7 +990,7 @@
                                     },
                                     "duplicateBehavior": {
                                         "type": "string",
-                                        "enum": ["prevent", "new"],
+                                        "enum": ["prevent", "overwrite", "new"],
                                         "default": "prevent"
                                     },
                                     "fieldTemplates": {
diff --git a/ext/images/add-duplicate-term-kana.svg b/ext/images/add-duplicate-term-kana.svg
index 267c55ec..6bc430e6 100644
--- a/ext/images/add-duplicate-term-kana.svg
+++ b/ext/images/add-duplicate-term-kana.svg
@@ -13,8 +13,8 @@
    <stop stop-opacity=".28986" offset="0"/>
    <stop stop-opacity="0" offset="1"/>
   </radialGradient>
-  <filter id="green-to-red" x="-.083333" y="-.083333" width="1.1667" height="1.1667" color-interpolation-filters="sRGB">
-   <feColorMatrix result="color1" type="hueRotate" values="250"/>
+  <filter id="green-to-purple" x="-.083333" y="-.083333" width="1.1667" height="1.1667" color-interpolation-filters="sRGB">
+   <feColorMatrix result="color1" type="hueRotate" values="180"/>
    <feColorMatrix result="color2" type="saturate" values="1"/>
   </filter>
   <symbol id="plus-in-circle" viewBox="0 0 16 16">
@@ -24,10 +24,10 @@
     <path d="m6 8h1v-1h1v1h1v1h-1v1h-1v-1h-1v-1" fill="#fff"/>
   </symbol>
  </defs>
- <g transform="translate(1,-1)" filter="url(#green-to-red)">
+ <g transform="translate(1,-1)" filter="url(#green-to-purple)">
   <use xlink:href="#plus-in-circle"/>
  </g>
- <g transform="translate(-1,1)" filter="url(#green-to-red)">
+ <g transform="translate(-1,1)" filter="url(#green-to-purple)">
   <use xlink:href="#plus-in-circle"/>
  </g>
 </svg>
diff --git a/ext/images/add-duplicate-term-kanji.svg b/ext/images/add-duplicate-term-kanji.svg
index fc3279d9..da39eb1c 100644
--- a/ext/images/add-duplicate-term-kanji.svg
+++ b/ext/images/add-duplicate-term-kanji.svg
@@ -13,8 +13,8 @@
    <stop stop-opacity=".28986" offset="0"/>
    <stop stop-opacity="0" offset="1"/>
   </radialGradient>
-  <filter id="green-to-red" x="-.038462" y="-.038462" width="1.0769" height="1.0769" color-interpolation-filters="sRGB">
-   <feColorMatrix type="hueRotate" values="250"/>
+  <filter id="green-to-purple" x="-.038462" y="-.038462" width="1.0769" height="1.0769" color-interpolation-filters="sRGB">
+   <feColorMatrix type="hueRotate" values="180"/>
    <feColorMatrix type="saturate" values="1"/>
    <feColorMatrix type="hueRotate" values="0"/>
   </filter>
@@ -28,10 +28,10 @@
   </symbol>
  </defs>
 
- <g transform="matrix(.91504 0 0 .91504 2.2745 -.91504)" filter="url(#green-to-red)">
+ <g transform="matrix(.91504 0 0 .91504 2.2745 -.91504)" filter="url(#green-to-purple)">
   <use xlink:href="#plus-in-circle"/>
  </g>
- <g transform="matrix(.91504 0 0 .91504 -.91504 2.2745)" filter="url(#green-to-red)">
+ <g transform="matrix(.91504 0 0 .91504 -.91504 2.2745)" filter="url(#green-to-purple)">
   <use xlink:href="#plus-in-circle"/>
  </g>
 </svg>
diff --git a/ext/images/overwrite-term-kana.svg b/ext/images/overwrite-term-kana.svg
new file mode 100644
index 00000000..7bcb1926
--- /dev/null
+++ b/ext/images/overwrite-term-kana.svg
@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="16" height="16" version="1.1" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+ <defs>
+  <linearGradient id="inner-fill" x1="-1.7198" x2="-1.7198" y1="2.7781" y2="1.4552" gradientTransform="matrix(3.7795 0 0 3.7795 14 .5)" gradientUnits="userSpaceOnUse">
+   <stop stop-color="#6fb558" offset="0"/>
+   <stop stop-color="#a5db9b" offset="1"/>
+  </linearGradient>
+  <linearGradient id="outer-rim"  x1="2.1167" x2="1.4552" y1="2.3812" y2="1.7198" gradientTransform="scale(3.7795 3.7795)" gradientUnits="userSpaceOnUse">
+   <stop stop-color="#34812c" offset="0"/>
+   <stop stop-color="#87b870" offset="1"/>
+  </linearGradient>
+  <radialGradient id="center-shadow" cx="2.1167" cy="2.1167" r=".66146" gradientTransform="matrix(2.2677 -7.9311e-7 7.9312e-7 2.2677 2.7 3.7)" gradientUnits="userSpaceOnUse">
+   <stop stop-opacity=".28986" offset="0"/>
+   <stop stop-opacity="0" offset="1"/>
+  </radialGradient>
+  <filter id="green-to-orange" x="-.083333" y="-.083333" width="1.1667" height="1.1667" color-interpolation-filters="sRGB">
+   <feColorMatrix result="color1" type="hueRotate" values="280"/>
+   <feColorMatrix result="color2" type="saturate" values="2"/>
+  </filter>
+ </defs>
+ <g filter="url(#green-to-orange)">
+  <circle cx="7.5" cy="8.5" r="3" fill="url(#inner-fill)"/>
+  <circle cx="7.5" cy="8.5" r="3" fill="none" stroke="url(#outer-rim)"/>
+  <path
+       transform="matrix(.49952 0 0 .49952 .84885 3.6971)"
+       d="m15.631 9.9045 0.66159 0.08268c-0.18327 1.4812-1.4463 2.6278-2.9771 2.6278-0.94244 0-1.7834-0.43457-2.3334-1.1143l3.1e-5 1.1143h-0.66667v-2.3333h2.3333v0.66667l-1.2482 3.45e-4c0.42167 0.60433 1.1221 0.99971 1.9149 0.99971 1.1906 0 2.173-0.89179 2.3156-2.0439zm0.68445-3.2895v2.3333h-2.3333v-0.66666l1.2484-5.09e-5c-0.42165-0.60446-1.1222-0.99995-1.9151-0.99995-1.1907 0-2.173 0.8918-2.3156 2.0439l-0.66159-0.082684c0.18327-1.4812 1.4463-2.6279 2.9771-2.6279 0.94244 0 1.7834 0.43457 2.3334 1.1143l-2.9e-5 -1.1143z"
+       fill="#fff"
+       style="stroke:#ffffff;stroke-opacity:1;stroke-width:0.40038437;stroke-dasharray:none" />
+ </g>
+</svg>
diff --git a/ext/images/overwrite-term-kanji.svg b/ext/images/overwrite-term-kanji.svg
new file mode 100644
index 00000000..d7d48ad8
--- /dev/null
+++ b/ext/images/overwrite-term-kanji.svg
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="16" height="16" version="1.1" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+ <defs>
+  <linearGradient id="inner-fill" x1="-1.7198" x2="-1.7198" y1="3.5719" y2=".79375" gradientTransform="matrix(3.7795 0 0 3.7795 14.5 -6.308e-7)" gradientUnits="userSpaceOnUse">
+   <stop stop-color="#6fb558" offset="0"/>
+   <stop stop-color="#a5db9b" offset="1"/>
+  </linearGradient>
+  <linearGradient id="outer-rim" x1="7.5406" x2="5.1594" y1="3.3073" y2=".92604" gradientTransform="matrix(3.7795 0 0 3.7795 -16 -6e-7)" gradientUnits="userSpaceOnUse">
+   <stop stop-color="#34812c" offset="0"/>
+   <stop stop-color="#87b870" offset="1"/>
+  </linearGradient>
+  <radialGradient id="center-shadow" cx="2.1167" cy="2.1167" r=".66146" gradientTransform="matrix(4.5354 8.0301e-7 -8.0301e-7 4.5354 -1.6 -1.6)" gradientUnits="userSpaceOnUse">
+   <stop stop-opacity=".28986" offset="0"/>
+   <stop stop-opacity="0" offset="1"/>
+  </radialGradient>
+  <filter id="green-to-orange" x="-.083333" y="-.083333" width="1.1667" height="1.1667" color-interpolation-filters="sRGB">
+   <feColorMatrix result="color1" type="hueRotate" values="280"/>
+   <feColorMatrix result="color2" type="saturate" values="2"/>
+  </filter>
+ </defs>
+ <g filter="url(#green-to-orange)">
+  <circle cx="8" cy="8" r="6.5" fill="url(#inner-fill)"/>
+  <circle cx="8" cy="8" r="5.75" fill="none" stroke="#fff" stroke-opacity=".50196" stroke-width="1.5"/>
+  <circle cx="8" cy="8" r="6.5" fill="none" stroke="url(#outer-rim)"/>
+	<path
+      d="m10.309 8.2795 0.66159 0.082684c-0.18327 1.4812-1.4463 2.6278-2.9771 2.6278-0.94244 0-1.7834-0.43457-2.3334-1.1143l3.11e-5 1.1143h-0.66667v-2.3333h2.3333v0.66667l-1.2482 3.453e-4c0.42167 0.60433 1.1221 0.99971 1.9149 0.99971 1.1906 0 2.173-0.89179 2.3156-2.0439zm0.68445-3.2895v2.3333h-2.3333v-0.66666l1.2484-5.09e-5c-0.42165-0.60446-1.1222-0.99995-1.9151-0.99995-1.1907 0-2.173 0.8918-2.3156 2.0439l-0.66159-0.082684c0.18327-1.4813 1.4463-2.6279 2.9771-2.6279 0.94244 0 1.7834 0.43457 2.3334 1.1143l-2.9e-5 -1.1143z"
+      fill="#fff"
+      style="stroke:#ffffff;stroke-opacity:1;stroke-width:0.4;stroke-dasharray:none"
+   />
+	</g>
+</svg>
diff --git a/ext/js/background/backend.js b/ext/js/background/backend.js
index dfb85e05..b9e23cbb 100644
--- a/ext/js/background/backend.js
+++ b/ext/js/background/backend.js
@@ -28,7 +28,7 @@ import {logErrorLevelToNumber} from '../core/log-utilities.js';
 import {log} from '../core/log.js';
 import {isObjectNotArray} from '../core/object-utilities.js';
 import {clone, deferPromise, promiseTimeout} from '../core/utilities.js';
-import {invalidNoteId, isNoteDataValid} from '../data/anki-util.js';
+import {INVALID_NOTE_ID, isNoteDataValid} from '../data/anki-util.js';
 import {arrayBufferToBase64} from '../data/array-buffer-util.js';
 import {OptionsUtil} from '../data/options-util.js';
 import {getAllPermissions, hasPermissions, hasRequiredPermissionsForOptions} from '../data/permissions-util.js';
@@ -153,6 +153,7 @@ export class Backend {
             ['getAnkiConnectVersion',        this._onApiGetAnkiConnectVersion.bind(this)],
             ['isAnkiConnected',              this._onApiIsAnkiConnected.bind(this)],
             ['addAnkiNote',                  this._onApiAddAnkiNote.bind(this)],
+            ['updateAnkiNote',               this._onApiUpdateAnkiNote.bind(this)],
             ['getAnkiNoteInfo',              this._onApiGetAnkiNoteInfo.bind(this)],
             ['injectAnkiNoteMedia',          this._onApiInjectAnkiNoteMedia.bind(this)],
             ['viewNotes',                    this._onApiViewNotes.bind(this)],
@@ -539,6 +540,11 @@ export class Backend {
         return await this._anki.addNote(note);
     }
 
+    /** @type {import('api').ApiHandler<'updateAnkiNote'>} */
+    async _onApiUpdateAnkiNote({noteWithId}) {
+        return await this._anki.updateNoteFields(noteWithId);
+    }
+
     /**
      * @param {import('anki').Note[]} notes
      * @returns {Promise<import('backend').CanAddResults>}
@@ -600,7 +606,7 @@ export class Backend {
             const valid = isNoteDataValid(note);
 
             if (isDuplicate && duplicateNoteIds[originalIndices.indexOf(i)].length === 0) {
-                duplicateNoteIds[originalIndices.indexOf(i)] = [invalidNoteId];
+                duplicateNoteIds[originalIndices.indexOf(i)] = [INVALID_NOTE_ID];
             }
 
             const noteIds = isDuplicate ? duplicateNoteIds[originalIndices.indexOf(i)] : null;
diff --git a/ext/js/comm/anki-connect.js b/ext/js/comm/anki-connect.js
index 446b2139..8c5e2c85 100644
--- a/ext/js/comm/anki-connect.js
+++ b/ext/js/comm/anki-connect.js
@@ -144,6 +144,21 @@ export class AnkiConnect {
     }
 
     /**
+     * @param {import('anki').Note} noteWithId
+     * @returns {Promise<null>}
+     */
+    async updateNoteFields(noteWithId) {
+        if (!this._enabled) { return null; }
+        await this._checkVersion();
+        const result = await this._invoke('updateNoteFields', {note: noteWithId});
+        if (result !== null) {
+            throw this._createUnexpectedResultError('null', result);
+        }
+        return result;
+    }
+
+
+    /**
      * @param {import('anki').Note[]} notes
      * @returns {Promise<boolean[]>}
      */
diff --git a/ext/js/comm/api.js b/ext/js/comm/api.js
index e8db7846..b044a783 100644
--- a/ext/js/comm/api.js
+++ b/ext/js/comm/api.js
@@ -96,6 +96,14 @@ export class API {
     }
 
     /**
+     * @param {import('api').ApiParam<'updateAnkiNote', 'noteWithId'>} noteWithId
+     * @returns {Promise<import('api').ApiReturn<'updateAnkiNote'>>}
+     */
+    updateAnkiNote(noteWithId) {
+        return this._invoke('updateAnkiNote', {noteWithId});
+    }
+
+    /**
      * @param {import('api').ApiParam<'getAnkiNoteInfo', 'notes'>} notes
      * @param {import('api').ApiParam<'getAnkiNoteInfo', 'fetchAdditionalInfo'>} fetchAdditionalInfo
      * @returns {Promise<import('api').ApiReturn<'getAnkiNoteInfo'>>}
diff --git a/ext/js/data/anki-util.js b/ext/js/data/anki-util.js
index c076c482..88b3c251 100644
--- a/ext/js/data/anki-util.js
+++ b/ext/js/data/anki-util.js
@@ -83,4 +83,4 @@ export function isNoteDataValid(note) {
     );
 }
 
-export const invalidNoteId = -1;
+export const INVALID_NOTE_ID = -1;
diff --git a/ext/js/display/display-anki.js b/ext/js/display/display-anki.js
index 442319f7..6ac84ede 100644
--- a/ext/js/display/display-anki.js
+++ b/ext/js/display/display-anki.js
@@ -22,7 +22,7 @@ import {toError} from '../core/to-error.js';
 import {deferPromise} from '../core/utilities.js';
 import {AnkiNoteBuilder} from '../data/anki-note-builder.js';
 import {getDynamicTemplates} from '../data/anki-template-util.js';
-import {invalidNoteId, isNoteDataValid} from '../data/anki-util.js';
+import {INVALID_NOTE_ID, isNoteDataValid} from '../data/anki-util.js';
 import {PopupMenu} from '../dom/popup-menu.js';
 import {querySelectorNotNull} from '../dom/query-selector.js';
 import {TemplateRendererProxy} from '../templates/template-renderer-proxy.js';
@@ -50,7 +50,7 @@ export class DisplayAnki {
         /** @type {?import('./display-notification.js').DisplayNotification} */
         this._tagsNotification = null;
         /** @type {?Promise<void>} */
-        this._updateAdderButtonsPromise = null;
+        this._updateSaveButtonsPromise = null;
         /** @type {?import('core').TokenObject} */
         this._updateDictionaryEntryDetailsToken = null;
         /** @type {EventListenerCollection} */
@@ -101,7 +101,7 @@ export class DisplayAnki {
         /** @type {(event: MouseEvent) => void} */
         this._onShowTagsBind = this._onShowTags.bind(this);
         /** @type {(event: MouseEvent) => void} */
-        this._onNoteAddBind = this._onNoteAdd.bind(this);
+        this._onNoteSaveBind = this._onNoteSave.bind(this);
         /** @type {(event: MouseEvent) => void} */
         this._onViewNotesButtonClickBind = this._onViewNotesButtonClick.bind(this);
         /** @type {(event: MouseEvent) => void} */
@@ -115,9 +115,9 @@ export class DisplayAnki {
         this._noteContext = this._getNoteContext();
         /* eslint-disable @stylistic/no-multi-spaces */
         this._display.hotkeyHandler.registerActions([
-            ['addNoteKanji',      () => { this._tryAddAnkiNoteForSelectedEntry('kanji'); }],
-            ['addNoteTermKanji',  () => { this._tryAddAnkiNoteForSelectedEntry('term-kanji'); }],
-            ['addNoteTermKana',   () => { this._tryAddAnkiNoteForSelectedEntry('term-kana'); }],
+            ['addNoteKanji',      () => { this._hotkeySaveAnkiNoteForSelectedEntry('kanji'); }],
+            ['addNoteTermKanji',  () => { this._hotkeySaveAnkiNoteForSelectedEntry('term-kanji'); }],
+            ['addNoteTermKana',   () => { this._hotkeySaveAnkiNoteForSelectedEntry('term-kana'); }],
             ['viewNotes',         this._viewNotesForSelectedEntry.bind(this)]
         ]);
         /* eslint-enable @stylistic/no-multi-spaces */
@@ -251,8 +251,8 @@ export class DisplayAnki {
         for (const node of element.querySelectorAll('.action-button[data-action=view-tags]')) {
             eventListeners.addEventListener(node, 'click', this._onShowTagsBind);
         }
-        for (const node of element.querySelectorAll('.action-button[data-action=add-note]')) {
-            eventListeners.addEventListener(node, 'click', this._onNoteAddBind);
+        for (const node of element.querySelectorAll('.action-button[data-action=save-note]')) {
+            eventListeners.addEventListener(node, 'click', this._onNoteSaveBind);
         }
         for (const node of element.querySelectorAll('.action-button[data-action=view-note]')) {
             eventListeners.addEventListener(node, 'click', this._onViewNotesButtonClickBind);
@@ -276,13 +276,13 @@ export class DisplayAnki {
     /**
      * @param {MouseEvent} e
      */
-    _onNoteAdd(e) {
+    _onNoteSave(e) {
         e.preventDefault();
         const element = /** @type {HTMLElement} */ (e.currentTarget);
         const mode = this._getValidCreateMode(element.dataset.mode);
         if (mode === null) { return; }
         const index = this._display.getElementDictionaryEntryIndex(element);
-        void this._addAnkiNote(index, mode);
+        void this._saveAnkiNote(index, mode);
     }
 
     /**
@@ -300,9 +300,9 @@ export class DisplayAnki {
      * @param {import('display-anki').CreateMode} mode
      * @returns {?HTMLButtonElement}
      */
-    _adderButtonFind(index, mode) {
+    _saveButtonFind(index, mode) {
         const entry = this._getEntry(index);
-        return entry !== null ? entry.querySelector(`.action-button[data-action=add-note][data-mode="${mode}"]`) : null;
+        return entry !== null ? entry.querySelector(`.action-button[data-action=save-note][data-mode="${mode}"]`) : null;
     }
 
     /**
@@ -356,66 +356,76 @@ export class DisplayAnki {
         /** @type {?import('core').TokenObject} */
         const token = {};
         this._updateDictionaryEntryDetailsToken = token;
-        if (this._updateAdderButtonsPromise !== null) {
-            await this._updateAdderButtonsPromise;
+        if (this._updateSaveButtonsPromise !== null) {
+            await this._updateSaveButtonsPromise;
         }
         if (this._updateDictionaryEntryDetailsToken !== token) { return; }
 
         const {promise, resolve} = /** @type {import('core').DeferredPromiseDetails<void>} */ (deferPromise());
         try {
-            this._updateAdderButtonsPromise = promise;
+            this._updateSaveButtonsPromise = promise;
             const dictionaryEntryDetails = await this._getDictionaryEntryDetails(dictionaryEntries);
             if (this._updateDictionaryEntryDetailsToken !== token) { return; }
             this._dictionaryEntryDetails = dictionaryEntryDetails;
-            this._updateAdderButtons(dictionaryEntryDetails);
+            this._updateSaveButtons(dictionaryEntryDetails);
         } finally {
             resolve();
-            if (this._updateAdderButtonsPromise === promise) {
-                this._updateAdderButtonsPromise = null;
+            if (this._updateSaveButtonsPromise === promise) {
+                this._updateSaveButtonsPromise = null;
             }
         }
     }
 
     /**
      * @param {HTMLButtonElement} button
+     * @param {number[]} noteIds
      */
-    _showDuplicateAddButton(button) {
-        const isKanjiAdd = button.dataset.mode === 'term-kanji';
+    _updateSaveButtonForDuplicateBehavior(button, noteIds) {
+        const behavior = this._duplicateBehavior;
+        if (behavior === 'prevent') {
+            button.disabled = true;
+            return;
+        }
 
-        const title = button.getAttribute('title');
-        if (title) {
-            button.setAttribute('title', title.replace(/Add (?!duplicate)/, 'Add duplicate '));
+        const mode = button.dataset.mode;
+        const verb = behavior === 'overwrite' ? 'Overwrite' : 'Add duplicate';
+        const iconPrefix = behavior === 'overwrite' ? 'overwrite' : 'add-duplicate';
+        const target = mode === 'term-kanji' ? 'expression' : 'reading';
+
+        if (behavior === 'overwrite') {
+            button.dataset.overwrite = 'true';
+            if (!noteIds.some((id) => id !== INVALID_NOTE_ID)) {
+                button.disabled = true;
+            }
+        } else {
+            delete button.dataset.overwrite;
         }
 
+        button.setAttribute('title', `${verb} ${target}`);
+
         // eslint-disable-next-line no-underscore-dangle
         const hotkeyLabel = this._display._hotkeyHelpController.getHotkeyLabel(button);
-
         if (hotkeyLabel) {
-            if (hotkeyLabel === 'Add expression ({0})') {
-                // eslint-disable-next-line no-underscore-dangle
-                this._display._hotkeyHelpController.setHotkeyLabel(button, 'Add duplicate expression ({0})');
-            } else if (hotkeyLabel === 'Add reading ({0})') {
-                // eslint-disable-next-line no-underscore-dangle
-                this._display._hotkeyHelpController.setHotkeyLabel(button, 'Add duplicate reading ({0})');
-            }
+            // eslint-disable-next-line no-underscore-dangle
+            this._display._hotkeyHelpController.setHotkeyLabel(button, `${verb} ${target} ({0})`);
         }
 
         const actionIcon = button.querySelector('.action-icon');
         if (actionIcon instanceof HTMLElement) {
-            actionIcon.dataset.icon = isKanjiAdd ? 'add-duplicate-term-kanji' : 'add-duplicate-term-kana';
+            actionIcon.dataset.icon = `${iconPrefix}-${mode}`;
         }
     }
 
     /**
      * @param {import('display-anki').DictionaryEntryDetails[]} dictionaryEntryDetails
      */
-    _updateAdderButtons(dictionaryEntryDetails) {
+    _updateSaveButtons(dictionaryEntryDetails) {
         const displayTags = this._displayTags;
         for (let i = 0, ii = dictionaryEntryDetails.length; i < ii; ++i) {
             /** @type {?Set<number>} */
             let allNoteIds = null;
             for (const {mode, canAdd, noteIds, noteInfos, ankiError} of dictionaryEntryDetails[i].modeMap.values()) {
-                const button = this._adderButtonFind(i, mode);
+                const button = this._saveButtonFind(i, mode);
                 if (button !== null) {
                     button.disabled = !canAdd;
                     button.hidden = (ankiError !== null);
@@ -425,14 +435,14 @@ export class DisplayAnki {
 
                     // If entry has noteIds, show the "add duplicate" button.
                     if (Array.isArray(noteIds) && noteIds.length > 0) {
-                        this._updateButtonForDuplicate(button);
+                        this._updateSaveButtonForDuplicateBehavior(button, noteIds);
                     }
                 }
 
                 if (Array.isArray(noteIds) && noteIds.length > 0) {
                     if (allNoteIds === null) { allNoteIds = new Set(); }
                     for (const noteId of noteIds) {
-                        if (noteId !== invalidNoteId) {
+                        if (noteId !== INVALID_NOTE_ID) {
                             allNoteIds.add(noteId);
                         }
                     }
@@ -448,17 +458,6 @@ export class DisplayAnki {
     }
 
     /**
-     * @param {HTMLButtonElement} button
-     */
-    _updateButtonForDuplicate(button) {
-        if (this._duplicateBehavior === 'prevent') {
-            button.disabled = true;
-        } else {
-            this._showDuplicateAddButton(button);
-        }
-    }
-
-    /**
      * @param {number} i
      * @param {(?import('anki').NoteInfo)[]} noteInfos
      */
@@ -503,16 +502,16 @@ export class DisplayAnki {
     /**
      * @param {import('display-anki').CreateMode} mode
      */
-    _tryAddAnkiNoteForSelectedEntry(mode) {
+    _hotkeySaveAnkiNoteForSelectedEntry(mode) {
         const index = this._display.selectedIndex;
-        void this._addAnkiNote(index, mode);
+        void this._saveAnkiNote(index, mode);
     }
 
     /**
      * @param {number} dictionaryEntryIndex
      * @param {import('display-anki').CreateMode} mode
      */
-    async _addAnkiNote(dictionaryEntryIndex, mode) {
+    async _saveAnkiNote(dictionaryEntryIndex, mode) {
         const dictionaryEntries = this._display.dictionaryEntries;
         const dictionaryEntryDetails = this._dictionaryEntryDetails;
         if (!(
@@ -529,7 +528,7 @@ export class DisplayAnki {
 
         const {requirements} = details;
 
-        const button = this._adderButtonFind(dictionaryEntryIndex, mode);
+        const button = this._saveButtonFind(dictionaryEntryIndex, mode);
         if (button === null || button.disabled) { return; }
 
         this._hideErrorNotification(true);
@@ -544,34 +543,9 @@ export class DisplayAnki {
 
             const error = this._getAddNoteRequirementsError(requirements, outputRequirements);
             if (error !== null) { allErrors.push(error); }
-
-            let noteId = null;
-            let addNoteOkay = false;
-            try {
-                noteId = await this._display.application.api.addAnkiNote(note);
-                addNoteOkay = true;
-            } catch (e) {
-                allErrors.length = 0;
-                allErrors.push(toError(e));
-            }
-
-            if (addNoteOkay) {
-                if (noteId === null) {
-                    allErrors.push(new Error('Note could not be added'));
-                } else {
-                    if (this._suspendNewCards) {
-                        try {
-                            await this._display.application.api.suspendAnkiCardsForNote(noteId);
-                        } catch (e) {
-                            allErrors.push(toError(e));
-                        }
-                    }
-                    // Now that this dictionary entry has a duplicate in Anki, show the "add duplicate" buttons.
-                    this._updateButtonForDuplicate(button);
-
-                    this._updateViewNoteButton(dictionaryEntryIndex, [noteId], true);
-                }
-            }
+            await (button.dataset.overwrite ?
+                this._updateAnkiNote(note, allErrors, button, dictionaryEntryIndex) :
+                this._addNewAnkiNote(note, allErrors, button, dictionaryEntryIndex));
         } catch (e) {
             allErrors.push(toError(e));
         } finally {
@@ -586,6 +560,69 @@ export class DisplayAnki {
     }
 
     /**
+     * @param {import('anki').Note} note
+     * @param {Error[]} allErrors
+     * @param {HTMLButtonElement} button
+     * @param {number} dictionaryEntryIndex
+     */
+    async _addNewAnkiNote(note, allErrors, button, dictionaryEntryIndex) {
+        let noteId = null;
+        let addNoteOkay = false;
+        try {
+            noteId = await this._display.application.api.addAnkiNote(note);
+            addNoteOkay = true;
+        } catch (e) {
+            allErrors.length = 0;
+            allErrors.push(toError(e));
+        }
+
+        if (addNoteOkay) {
+            if (noteId === null) {
+                allErrors.push(new Error('Note could not be added'));
+            } else {
+                if (this._suspendNewCards) {
+                    try {
+                        await this._display.application.api.suspendAnkiCardsForNote(noteId);
+                    } catch (e) {
+                        allErrors.push(toError(e));
+                    }
+                }
+                this._updateSaveButtonForDuplicateBehavior(button, [noteId]);
+
+                this._updateViewNoteButton(dictionaryEntryIndex, [noteId], true);
+            }
+        }
+    }
+
+    /**
+     * @param {import('anki').Note} note
+     * @param {Error[]} allErrors
+     * @param {HTMLButtonElement} button
+     * @param {number} dictionaryEntryIndex
+     */
+    async _updateAnkiNote(note, allErrors, button, dictionaryEntryIndex) {
+        const dictionaryEntries = this._display.dictionaryEntries;
+        const allEntryDetails = await this._getDictionaryEntryDetails(dictionaryEntries);
+        const relevantEntryDetails = allEntryDetails[dictionaryEntryIndex];
+        const mode = this._getValidCreateMode(button.dataset.mode);
+        if (mode === null) { return; }
+        const relevantModeDetails = relevantEntryDetails.modeMap.get(mode);
+        if (typeof relevantModeDetails === 'undefined') { return; }
+        const {noteIds} = relevantModeDetails;
+        if (noteIds === null) { return; }
+        const overwriteTarget = noteIds.find((id) => id !== INVALID_NOTE_ID);
+        if (typeof overwriteTarget === 'undefined') { return; }
+
+        try {
+            const noteWithId = {...note, id: overwriteTarget};
+            await this._display.application.api.updateAnkiNote(noteWithId);
+        } catch (e) {
+            allErrors.length = 0;
+            allErrors.push(toError(e));
+        }
+    }
+
+    /**
      * @param {import('anki-note-builder').Requirement[]} requirements
      * @param {import('anki-note-builder').Requirement[]} outputRequirements
      * @returns {?DisplayAnkiError}
diff --git a/ext/js/pages/settings/anki-controller.js b/ext/js/pages/settings/anki-controller.js
index 2d461336..de8b2c39 100644
--- a/ext/js/pages/settings/anki-controller.js
+++ b/ext/js/pages/settings/anki-controller.js
@@ -63,6 +63,10 @@ export class AnkiController {
         /** @type {HTMLElement} */
         this._ankiErrorInvalidResponseInfo = querySelectorNotNull(document, '#anki-error-invalid-response-info');
         /** @type {HTMLElement} */
+        this._duplicateBehaviorSelect = querySelectorNotNull(document, '[data-setting="anki.duplicateBehavior"]');
+        /** @type {HTMLElement} */
+        this._duplicateOverwriteWarning = querySelectorNotNull(document, '#anki-overwrite-warning');
+        /** @type {HTMLElement} */
         this._ankiCardPrimary = querySelectorNotNull(document, '#anki-card-primary');
         /** @type {?Error} */
         this._ankiError = null;
@@ -109,6 +113,8 @@ export class AnkiController {
         ankiApiKeyInput.addEventListener('focus', this._onApiKeyInputFocus.bind(this));
         ankiApiKeyInput.addEventListener('blur', this._onApiKeyInputBlur.bind(this));
 
+        this._duplicateBehaviorSelect.addEventListener('change', this._onDuplicateBehaviorSelectChange.bind(this));
+
         await this._updateOptions();
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
 
@@ -171,6 +177,8 @@ export class AnkiController {
         this._selectorObserver.disconnect();
         this._selectorObserver.observe(document.documentElement, true);
 
+        this._updateDuplicateOverwriteWarning(anki.duplicateBehavior);
+
         this._setupFieldMenus(dictionaries);
     }
 
@@ -240,6 +248,22 @@ export class AnkiController {
     }
 
     /**
+     * @param {Event} e
+     */
+    _onDuplicateBehaviorSelectChange(e) {
+        const node = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const behavior = node.value;
+        this._updateDuplicateOverwriteWarning(behavior);
+    }
+
+    /**
+     * @param {string} behavior
+     */
+    _updateDuplicateOverwriteWarning(behavior) {
+        this._duplicateOverwriteWarning.hidden = behavior !== 'overwrite';
+    }
+
+    /**
      * @param {string} ankiCardType
      * @param {string} [ankiCardMenu]
      */
diff --git a/ext/settings.html b/ext/settings.html
index 525e99b1..12281764 100644
--- a/ext/settings.html
+++ b/ext/settings.html
@@ -1709,10 +1709,20 @@
                         <div class="settings-item-right">
                             <select data-setting="anki.duplicateBehavior">
                                 <option value="prevent">Prevent adding</option>
+                                <option value="overwrite">Allow overwriting</option>
                                 <option value="new">Allow adding</option>
                             </select>
                         </div>
                     </div>
+                    <div class="settings-item-children" id="anki-overwrite-warning" hidden>
+                        <p class="danger-text">
+                            Overwriting a card can result in the loss of data.
+                        </p>
+                        <p class="warning-text">
+                            Duplicate cards of a different note type cannot be overwritten.
+                            If there are multiple duplicate cards, the first card found will be overwritten.
+                        </p>
+                    </div>
                 </div>
             </div>
         </div>
diff --git a/ext/templates-display.html b/ext/templates-display.html
index 944a10ab..a948d4c3 100644
--- a/ext/templates-display.html
+++ b/ext/templates-display.html
@@ -12,10 +12,10 @@
                 <span class="action-icon icon color-icon" data-icon="view-note"></span>
                 <span class="action-button-badge icon" hidden></span>
             </button>
-            <button type="button" class="action-button" data-action="add-note" hidden disabled data-mode="term-kanji" title="Add expression" data-hotkey='["addNoteTermKanji","title","Add expression ({0})"]'>
+            <button type="button" class="action-button" data-action="save-note" hidden disabled data-mode="term-kanji" title="Add expression" data-hotkey='["addNoteTermKanji","title","Add expression ({0})"]'>
                 <span class="action-icon icon color-icon" data-icon="add-term-kanji"></span>
             </button>
-            <button type="button" class="action-button" data-action="add-note" hidden disabled data-mode="term-kana" title="Add reading" data-hotkey='["addNoteTermKana","title","Add reading ({0})"]'>
+            <button type="button" class="action-button" data-action="save-note" hidden disabled data-mode="term-kana" title="Add reading" data-hotkey='["addNoteTermKana","title","Add reading ({0})"]'>
                 <span class="action-icon icon color-icon" data-icon="add-term-kana"></span>
             </button>
             <button type="button" class="action-button" data-action="play-audio" title="Play audio" data-title-default="Play audio" data-hotkey='["playAudio",["title","data-title-default"],"Play audio ({0})"]' data-menu-position="left below h-cover v-cover">
@@ -114,8 +114,8 @@
             <button type="button" class="action-button" data-action="view-note" hidden disabled title="View added note" data-hotkey='["viewNotes","title","View added note ({0})"]'>
                 <span class="action-icon icon color-icon" data-icon="view-note"></span>
             </button>
-            <button type="button" class="action-button" data-action="add-note" hidden disabled data-mode="kanji" title="Add kanji" data-hotkey='["addNoteKanji","title","Add kanji ({0})"]'>
-                <span class="action-icon icon color-icon" data-icon="add-term-kanji"></span>
+            <button type="button" class="action-button" data-action="save-note" hidden disabled data-mode="kanji" title="Add kanji" data-hotkey='["addNoteKanji","title","Add kanji ({0})"]'>
+                <span class="action-icon icon color-icon" data-icon="add-kanji"></span>
             </button>
             <span class="entry-current-indicator-icon" title="Current entry">
                 <span class="icon color-icon" data-icon="entry-current"></span>
diff --git a/types/ext/anki.d.ts b/types/ext/anki.d.ts
index 4a903c52..8ad0890f 100644
--- a/types/ext/anki.d.ts
+++ b/types/ext/anki.d.ts
@@ -22,6 +22,8 @@ export type NoteId = number;
 
 export type CardId = number;
 
+export type NoteWithId = Note & {id: NoteId};
+
 export type Note = {
     fields: NoteFields;
     tags: string[];
diff --git a/types/ext/api.d.ts b/types/ext/api.d.ts
index 9a922fb0..3a2fc0b8 100644
--- a/types/ext/api.d.ts
+++ b/types/ext/api.d.ts
@@ -169,6 +169,12 @@ type ApiSurface = {
         };
         return: Anki.NoteId | null;
     };
+    updateAnkiNote: {
+        params: {
+            noteWithId: Anki.NoteWithId;
+        };
+        return: null;
+    };
     getAnkiNoteInfo: {
         params: {
             notes: Anki.Note[];
diff --git a/types/ext/display-anki.d.ts b/types/ext/display-anki.d.ts
index 1b0dd4ff..4b6c6e37 100644
--- a/types/ext/display-anki.d.ts
+++ b/types/ext/display-anki.d.ts
@@ -46,6 +46,9 @@ export type DictionaryEntryModeDetails = {
     requirements: AnkiNoteBuilder.Requirement[];
     canAdd: boolean;
     valid: boolean;
+    /**
+     * Anki IDs of duplicate notes. May contain INVALID_NOTE_ID for notes whose ID could not be found.
+     */
     noteIds: Anki.NoteId[] | null;
     noteInfos?: (Anki.NoteInfo | null)[];
     ankiError: Error | null;
diff --git a/types/ext/settings.d.ts b/types/ext/settings.d.ts
index 1fce0f59..48a66728 100644
--- a/types/ext/settings.d.ts
+++ b/types/ext/settings.d.ts
@@ -395,7 +395,7 @@ export type AnkiScreenshotFormat = 'png' | 'jpeg';
 
 export type AnkiDuplicateScope = 'collection' | 'deck' | 'deck-root';
 
-export type AnkiDuplicateBehavior = 'prevent' | 'new';
+export type AnkiDuplicateBehavior = 'prevent' | 'overwrite' | 'new';
 
 export type AnkiDisplayTags = 'never' | 'always' | 'non-standard';