Implement AI

API/ROLAC.API/Controllers/ExpenseAiController.cs

@@ -0,0 +1,26 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using ROLAC.API.DTOs.Expense;
+using ROLAC.API.Services.Ai;
+
+namespace ROLAC.API.Controllers;
+
+[ApiController]
+[Route("api/expense-ai")]
+[Authorize]   // Open to any authenticated user — same audience as the expense-entry form, which any
+              // member filing a reimbursement can reach. The endpoint only reads the category catalog.
+public class ExpenseAiController : ControllerBase
+{
+    private readonly IExpenseAiService _svc;
+    public ExpenseAiController(IExpenseAiService svc) => _svc = svc;
+
+    [HttpPost("assist")]
+    public async Task<IActionResult> Assist([FromBody] ExpenseAiAssistRequest request, CancellationToken ct)
+    {
+        if (string.IsNullOrWhiteSpace(request.Text))
+            return BadRequest("Text is required.");
+
+        var suggestion = await _svc.SuggestAsync(request.Text, request.Amount, ct);
+        return Ok(suggestion);
+    }
+}

API/ROLAC.API/DTOs/Expense/ExpenseAiDtos.cs

@@ -0,0 +1,29 @@
+using System.ComponentModel.DataAnnotations;
+namespace ROLAC.API.DTOs.Expense;
+
+/// <summary>Request body for the expense AI assist endpoint.</summary>
+public class ExpenseAiAssistRequest
+{
+    /// <summary>The user's free-text expense description (typically Chinese).</summary>
+    [Required] public string Text { get; set; } = "";
+    /// <summary>The expense amount, used as a hint when classifying the category.</summary>
+    public decimal Amount { get; set; }
+}
+
+/// <summary>
+/// AI suggestion for an expense: an English translation of the description plus a proposed
+/// major category (大項) and sub-category (系項). Category ids are null when the model could
+/// not confidently classify or returned an id outside the live catalog.
+/// </summary>
+public class ExpenseAiSuggestion
+{
+    public string? EnglishDescription { get; set; }
+    public int?    GroupId            { get; set; }
+    public int?    SubCategoryId      { get; set; }
+    /// <summary>Bilingual label of the suggested group, e.g. "Consumables / 消耗品".</summary>
+    public string? GroupLabel         { get; set; }
+    /// <summary>Bilingual label of the suggested sub-category, e.g. "Batteries / 電池".</summary>
+    public string? SubLabel           { get; set; }
+    /// <summary>Model self-reported confidence in the classification, 0..1.</summary>
+    public double  Confidence         { get; set; }
+}

API/ROLAC.API/Program.cs

@@ -179,6 +179,12 @@ builder.Services.AddScoped<ROLAC.API.Services.Notifications.ILineNotificationSer
 builder.Services.AddHttpClient<ROLAC.API.Services.Notifications.IMessageChannel,
                                ROLAC.API.Services.Notifications.LineMessageChannel>();
 
+// ── AI assist (Google Gemini) ──────────────────────────────────────────────
+// Backend proxy for expense translation + category suggestion; the API key stays server-side.
+builder.Services.Configure<ROLAC.API.Services.Ai.GeminiOptions>(config.GetSection("Gemini"));
+builder.Services.AddHttpClient<ROLAC.API.Services.Ai.IExpenseAiService,
+                               ROLAC.API.Services.Ai.GeminiExpenseAiService>();
+
 // ---------------------------------------------------------------------------
 // Configurable role-based permissions (RBAC matrix)
 // ---------------------------------------------------------------------------

API/ROLAC.API/Services/Ai/GeminiExpenseAiService.cs

@@ -0,0 +1,181 @@
+using System.Net.Http.Json;
+using System.Text.Json;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Options;
+using ROLAC.API.Data;
+using ROLAC.API.DTOs.Expense;
+
+namespace ROLAC.API.Services.Ai;
+
+/// <summary>
+/// Calls the Google Gemini <c>generateContent</c> API to translate an expense description and
+/// classify it into the church's existing expense category catalog (大項 / 系項). The full active
+/// catalog is sent in the prompt so the model can only choose from real ids; any id it returns is
+/// re-validated against the catalog before being surfaced, so a hallucinated id is dropped, not echoed.
+/// </summary>
+public sealed class GeminiExpenseAiService : IExpenseAiService
+{
+    private readonly HttpClient _http;
+    private readonly GeminiOptions _options;
+    private readonly AppDbContext _db;
+    private readonly ILogger<GeminiExpenseAiService> _logger;
+
+    public GeminiExpenseAiService(
+        HttpClient http,
+        IOptions<GeminiOptions> options,
+        AppDbContext db,
+        ILogger<GeminiExpenseAiService> logger)
+    {
+        _http = http;
+        _options = options.Value;
+        _db = db;
+        _logger = logger;
+    }
+
+    public async Task<ExpenseAiSuggestion> SuggestAsync(string chineseText, decimal amount, CancellationToken ct = default)
+    {
+        // Load the active catalog: the allow-list the model must classify into.
+        var groups = await _db.ExpenseCategoryGroups
+            .AsNoTracking()
+            .Where(group => group.IsActive)
+            .OrderBy(group => group.SortOrder)
+            .Select(group => new
+            {
+                group.Id,
+                group.Name_en,
+                group.Name_zh,
+                Subs = group.SubCategories
+                    .Where(sub => sub.IsActive)
+                    .OrderBy(sub => sub.SortOrder)
+                    .Select(sub => new { sub.Id, sub.Name_en, sub.Name_zh })
+                    .ToList(),
+            })
+            .ToListAsync(ct);
+
+        if (string.IsNullOrWhiteSpace(_options.ApiKey))
+        {
+            _logger.LogWarning("Gemini API key is not configured; expense AI assist is disabled.");
+            return new ExpenseAiSuggestion();
+        }
+
+        try
+        {
+            var catalogJson = JsonSerializer.Serialize(groups);
+            var prompt =
+                "You are a bookkeeping assistant for a church. Given an expense description (often in " +
+                "Traditional Chinese) and its amount, do two things:\n" +
+                "1. Translate the description into concise, natural accounting English (a short noun phrase, " +
+                "not a full sentence).\n" +
+                "2. Choose the single best matching major category (group) and sub-category from the catalog " +
+                "below. You MUST pick a groupId and subCategoryId that appear in the catalog, and the " +
+                "subCategoryId must belong to that groupId. If nothing fits well, choose the closest " +
+                "\"Other / 其他\" option and lower your confidence.\n\n" +
+                $"Expense description: {chineseText}\n" +
+                $"Amount: {amount}\n\n" +
+                $"Category catalog (JSON; each group has an id, English/Chinese names, and its sub-categories):\n{catalogJson}\n\n" +
+                "Respond with JSON: englishDescription (string), groupId (integer), subCategoryId (integer), " +
+                "confidence (number 0..1).";
+
+            var payload = new
+            {
+                contents = new[]
+                {
+                    new { parts = new[] { new { text = prompt } } },
+                },
+                generationConfig = new
+                {
+                    responseMimeType = "application/json",
+                    responseSchema = new
+                    {
+                        type = "object",
+                        properties = new
+                        {
+                            englishDescription = new { type = "string" },
+                            groupId = new { type = "integer" },
+                            subCategoryId = new { type = "integer" },
+                            confidence = new { type = "number" },
+                        },
+                        required = new[] { "englishDescription", "groupId", "subCategoryId", "confidence" },
+                    },
+                },
+            };
+
+            var url = $"{_options.BaseUrl}/models/{_options.Model}:generateContent";
+            using var request = new HttpRequestMessage(HttpMethod.Post, url)
+            {
+                Content = JsonContent.Create(payload),
+            };
+            request.Headers.Add("X-goog-api-key", _options.ApiKey);
+
+            using var response = await _http.SendAsync(request, ct);
+            if (!response.IsSuccessStatusCode)
+            {
+                var body = await response.Content.ReadAsStringAsync(ct);
+                _logger.LogWarning("Gemini returned {Status}: {Body}", (int)response.StatusCode, body);
+                return new ExpenseAiSuggestion();
+            }
+
+            // Navigate candidates[0].content.parts[0].text — the model's JSON answer as a string.
+            using var doc = JsonDocument.Parse(await response.Content.ReadAsStreamAsync(ct));
+            var text = doc.RootElement
+                .GetProperty("candidates")[0]
+                .GetProperty("content")
+                .GetProperty("parts")[0]
+                .GetProperty("text")
+                .GetString();
+
+            if (string.IsNullOrWhiteSpace(text))
+            {
+                _logger.LogWarning("Gemini response contained no text part.");
+                return new ExpenseAiSuggestion();
+            }
+
+            var parsed = JsonSerializer.Deserialize<GeminiAnswer>(
+                text, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
+            if (parsed is null) return new ExpenseAiSuggestion();
+
+            var suggestion = new ExpenseAiSuggestion
+            {
+                EnglishDescription = string.IsNullOrWhiteSpace(parsed.EnglishDescription)
+                    ? null
+                    : parsed.EnglishDescription.Trim(),
+                Confidence = parsed.Confidence,
+            };
+
+            // Re-validate the returned ids against the catalog; drop anything that doesn't line up.
+            var group = groups.FirstOrDefault(candidate => candidate.Id == parsed.GroupId);
+            if (group is not null)
+            {
+                suggestion.GroupId = group.Id;
+                suggestion.GroupLabel = Label(group.Name_en, group.Name_zh);
+
+                var sub = group.Subs.FirstOrDefault(candidate => candidate.Id == parsed.SubCategoryId);
+                if (sub is not null)
+                {
+                    suggestion.SubCategoryId = sub.Id;
+                    suggestion.SubLabel = Label(sub.Name_en, sub.Name_zh);
+                }
+            }
+
+            return suggestion;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Expense AI assist failed.");
+            return new ExpenseAiSuggestion();
+        }
+    }
+
+    /// <summary>Mirror the frontend's bilingual() convention: "English / 中文" (or just English).</summary>
+    private static string Label(string nameEn, string? nameZh)
+        => string.IsNullOrWhiteSpace(nameZh) ? nameEn : $"{nameEn} / {nameZh}";
+
+    /// <summary>Shape of the model's JSON answer (constrained by responseSchema).</summary>
+    private sealed class GeminiAnswer
+    {
+        public string? EnglishDescription { get; set; }
+        public int     GroupId            { get; set; }
+        public int     SubCategoryId      { get; set; }
+        public double  Confidence         { get; set; }
+    }
+}

API/ROLAC.API/Services/Ai/GeminiOptions.cs

@@ -0,0 +1,10 @@
+namespace ROLAC.API.Services.Ai;
+
+/// <summary>Google Gemini API settings (bound from the "Gemini" config section).</summary>
+public sealed class GeminiOptions
+{
+    /// <summary>API key sent as the <c>X-goog-api-key</c> header. Keep out of source control.</summary>
+    public string ApiKey  { get; set; } = "";
+    public string Model   { get; set; } = "gemini-2.5-flash";
+    public string BaseUrl { get; set; } = "https://generativelanguage.googleapis.com/v1beta";
+}

API/ROLAC.API/Services/Ai/IExpenseAiService.cs

@@ -0,0 +1,14 @@
+using ROLAC.API.DTOs.Expense;
+
+namespace ROLAC.API.Services.Ai;
+
+/// <summary>AI assistance for expense entry: translate a description and suggest a category.</summary>
+public interface IExpenseAiService
+{
+    /// <summary>
+    /// Translate <paramref name="chineseText"/> to concise accounting English and suggest the best
+    /// major/sub category from the live catalog, using <paramref name="amount"/> as a hint.
+    /// Never throws on an upstream/AI failure — returns a suggestion with null fields instead.
+    /// </summary>
+    Task<ExpenseAiSuggestion> SuggestAsync(string chineseText, decimal amount, CancellationToken ct = default);
+}

API/ROLAC.API/appsettings.json

@@ -41,5 +41,10 @@
   "Line": {
     "ChannelAccessToken": "",
     "ChannelSecret": ""
+  },
+  "Gemini": {
+    "ApiKey": "",
+    "Model": "gemini-flash-latest",
+    "BaseUrl": "https://generativelanguage.googleapis.com/v1beta"
   }
 }

APP/src/app/features/expense/components/expense-form-dialog/expense-form-dialog.component.html

@@ -10,10 +10,37 @@
         <span>連續登打 / Continuous Entry</span>
       </label>
 
-      <!-- Description -->
-      <label class="flex flex-col gap-1 md:col-span-2">Description
-        <kendo-textbox [(ngModel)]="form.description" placeholder="Brief description of expense"></kendo-textbox>
+      <!-- Description (with AI assist: translate to English + suggest a category) -->
+      <div class="flex flex-col gap-1 md:col-span-2">
+        <div class="flex items-end justify-between gap-2">
+          <label class="flex flex-1 flex-col gap-1">Description
+            <kendo-textbox [(ngModel)]="form.description" placeholder="Brief description of expense / 費用說明（可輸入中文）"></kendo-textbox>
           </label>
+          <button kendoButton fillMode="outline" themeColor="primary" type="button"
+            [disabled]="!form.description.trim() || aiLoading" (click)="requestAiAssist()"
+            title="Translate to English and suggest a category / 翻譯並建議分類">
+            {{ aiLoading ? '思考中… / Thinking…' : '✨ AI 建議' }}
+          </button>
+        </div>
+
+        <!-- Suggestion card: the "suggest & confirm" step — user applies or dismisses -->
+        <div *ngIf="hasAiSuggestion" class="rounded border border-blue-200 bg-blue-50 p-3 flex flex-col gap-2 text-sm">
+          <div class="font-semibold text-blue-800">AI 建議 / Suggestion</div>
+          <div *ngIf="aiSuggestion?.englishDescription" class="flex gap-2">
+            <span class="text-gray-500 shrink-0">English:</span>
+            <span class="font-medium">{{ aiSuggestion?.englishDescription }}</span>
+          </div>
+          <div *ngIf="aiSuggestion?.groupLabel" class="flex gap-2">
+            <span class="text-gray-500 shrink-0">分類 / Category:</span>
+            <span class="font-medium">{{ aiSuggestion?.groupLabel }}<span *ngIf="aiSuggestion?.subLabel"> → {{ aiSuggestion?.subLabel }}</span></span>
+          </div>
+          <div class="text-xs text-gray-500">信心 / Confidence: {{ (aiSuggestion?.confidence ?? 0) * 100 | number:'1.0-0' }}%</div>
+          <div class="flex gap-2">
+            <button kendoButton themeColor="primary" size="small" type="button" (click)="applyAiSuggestion()">套用 / Apply</button>
+            <button kendoButton fillMode="flat" size="small" type="button" (click)="dismissAiSuggestion()">忽略 / Dismiss</button>
+          </div>
+        </div>
+      </div>
       <!-- Member picker (finance creating on behalf of a member) -->
       <label *ngIf="allowMemberPick" class="flex flex-col gap-1 md:col-span-2">Member
         <kendo-dropdownlist [data]="memberResults" textField="displayName" valueField="id" [valuePrimitive]="true"

APP/src/app/features/expense/components/expense-form-dialog/expense-form-dialog.component.ts

@@ -10,11 +10,12 @@ import { DateInputsModule } from '@progress/kendo-angular-dateinputs';
 import { MinistryApiService } from '../../services/ministry-api.service';
 import { ExpenseCategoryApiService } from '../../services/expense-category-api.service';
 import { ExpenseApiService } from '../../services/expense-api.service';
+import { ExpenseAiService } from '../../services/expense-ai.service';
 import { MemberApiService } from '../../../members/services/member-api.service';
 import { MemberListItemDto, memberDisplayName } from '../../../members/models/member.model';
 import {
   MinistryDto, ExpenseCategoryGroupDto, ExpenseSubCategoryDto, ExpenseType, CreateExpenseRequest,
-  ExpenseDto, FunctionalClass,
+  ExpenseDto, FunctionalClass, ExpenseAiSuggestion,
 } from '../../models/expense.model';
 
 export interface ExpenseFormResult {
@@ -101,11 +102,18 @@ export class ExpenseFormDialogComponent implements OnInit, OnDestroy {
   zoomOut(): void { this.receiptZoom = Math.max(this.minZoom, +(this.receiptZoom - 0.25).toFixed(2)); }
   resetZoom(): void { this.receiptZoom = 1; }
 
+  // ── AI assist (translate description + suggest category) ────────────────────
+  /** True while an assist request is in flight (disables the button, shows a spinner label). */
+  aiLoading = false;
+  /** The latest suggestion awaiting the user's Apply/Dismiss decision; null when none is shown. */
+  aiSuggestion: ExpenseAiSuggestion | null = null;
+
   constructor(
     private ministryApi: MinistryApiService,
     private catApi: ExpenseCategoryApiService,
     private memberApi: MemberApiService,
     private expenseApi: ExpenseApiService,
+    private aiApi: ExpenseAiService,
     private sanitizer: DomSanitizer,
   ) {}
 
@@ -166,6 +174,44 @@ export class ExpenseFormDialogComponent implements OnInit, OnDestroy {
     line.subs = this.groups.find(g => g.id === groupId)?.subCategories ?? [];
   }
 
+  /** Ask the backend AI to translate the description and suggest a category; show it for confirmation. */
+  requestAiAssist(): void {
+    const text = this.form.description.trim();
+    if (!text || this.aiLoading) return;
+    this.aiLoading = true;
+    this.aiSuggestion = null;
+    this.aiApi.assist(text, this.totalAmount).subscribe({
+      next: suggestion => { this.aiSuggestion = suggestion; this.aiLoading = false; },
+      error: () => { this.aiLoading = false; },
+    });
+  }
+
+  /** True once a suggestion offers at least a translation or a category to apply. */
+  get hasAiSuggestion(): boolean {
+    const s = this.aiSuggestion;
+    return !!s && (!!s.englishDescription || s.groupId != null);
+  }
+
+  /**
+   * Apply the suggestion: replace the description with the English translation and set the first
+   * line's category/sub. Most expenses are single-line; multi-line users adjust the rest by hand.
+   */
+  applyAiSuggestion(): void {
+    const suggestion = this.aiSuggestion;
+    if (!suggestion) return;
+    if (suggestion.englishDescription) this.form.description = suggestion.englishDescription;
+    if (suggestion.groupId != null) {
+      const firstLine = this.lines[0];
+      firstLine.categoryGroupId = suggestion.groupId;
+      // Populate the sub-category list for the chosen group, then select the suggested sub.
+      this.onLineGroupChange(firstLine, suggestion.groupId);
+      if (suggestion.subCategoryId != null) firstLine.subCategoryId = suggestion.subCategoryId;
+    }
+    this.aiSuggestion = null;
+  }
+
+  dismissAiSuggestion(): void { this.aiSuggestion = null; }
+
   addLine(): void { this.lines.push(this.emptyLine()); }
 
   removeLine(index: number): void {

APP/src/app/features/expense/models/expense.model.ts

@@ -33,6 +33,16 @@ export interface ExpenseDto extends ExpenseListItemDto {
   submittedBy: string | null; submittedAt: string | null; paidAt: string | null;
   lines: ExpenseLineItemDto[];
 }
+/** AI assist suggestion: English translation + a proposed major/sub category (null when unclassified). */
+export interface ExpenseAiSuggestion {
+  englishDescription: string | null;
+  groupId: number | null;
+  subCategoryId: number | null;
+  groupLabel: string | null;
+  subLabel: string | null;
+  confidence: number;
+}
+
 export interface ExpenseLineInput {
   categoryGroupId: number; subCategoryId: number; amount: number;
   functionalClass: FunctionalClass | null; description: string | null;

APP/src/app/features/expense/services/expense-ai.service.ts

@@ -0,0 +1,18 @@
+import { Injectable } from '@angular/core';
+import { HttpClient } from '@angular/common/http';
+import { Observable } from 'rxjs';
+import { ApiConfigService } from '../../../core/services/api-config.service';
+import { ExpenseAiSuggestion } from '../models/expense.model';
+
+@Injectable({ providedIn: 'root' })
+export class ExpenseAiService {
+  private readonly endpoint: string;
+  constructor(private http: HttpClient, private apiConfig: ApiConfigService) {
+    this.endpoint = apiConfig.getApiUrl('expense-ai');
+  }
+
+  /** Ask the backend (which proxies Gemini) to translate the text and suggest a category. */
+  assist(text: string, amount: number): Observable<ExpenseAiSuggestion> {
+    return this.http.post<ExpenseAiSuggestion>(`${this.endpoint}/assist`, { text, amount });
+  }
+}