feat: define account binding match priority

src/WxAgent.Core/AccountBindingMatcher.cs

@@ -0,0 +1,33 @@
+namespace WxAgent.Core;
+
+public sealed record UiAccountIdentity(string? WechatId, string? Nickname);
+public sealed record DatabaseAccountIdentity(string AccountId, string? WechatId, string? Nickname);
+public sealed record AccountMatch(string? AccountId, string Strategy, bool IsUnique)
+{
+    public bool IsMatched => AccountId is not null && IsUnique;
+}
+
+public static class AccountBindingMatcher
+{
+    public static AccountMatch Match(UiAccountIdentity ui, IReadOnlyList<DatabaseAccountIdentity> accounts)
+    {
+        ArgumentNullException.ThrowIfNull(ui);
+        ArgumentNullException.ThrowIfNull(accounts);
+        var wechatId = Normalize(ui.WechatId);
+        if (wechatId is not null)
+        {
+            var matches = accounts.Where(a => string.Equals(Normalize(a.WechatId), wechatId, StringComparison.OrdinalIgnoreCase)).ToArray();
+            if (matches.Length == 1) return new AccountMatch(matches[0].AccountId, "wechatId", true);
+            if (matches.Length > 1) return new AccountMatch(null, "wechatId", false);
+        }
+
+        var nickname = Normalize(ui.Nickname);
+        if (nickname is null) return new AccountMatch(null, "none", false);
+        var nicknameMatches = accounts.Where(a => string.Equals(Normalize(a.Nickname), nickname, StringComparison.Ordinal)).ToArray();
+        return nicknameMatches.Length == 1
+            ? new AccountMatch(nicknameMatches[0].AccountId, "nickname", true)
+            : new AccountMatch(null, nicknameMatches.Length == 0 ? "none" : "nickname", false);
+    }
+
+    private static string? Normalize(string? value) => string.IsNullOrWhiteSpace(value) ? null : value.Trim();
+}

tests/WxAgent.Core.Tests/AccountBindingMatcherTests.cs

@@ -0,0 +1,33 @@
+using WxAgent.Core;
+using Xunit;
+
+namespace WxAgent.Core.Tests;
+
+public sealed class AccountBindingMatcherTests
+{
+    [Fact]
+    public void PrefersExactWechatIdOverNickname()
+    {
+        var result = AccountBindingMatcher.Match(new UiAccountIdentity("wxid-a", "Same"),
+        [new("db-1", "wxid-a", "Other"), new("db-2", "wxid-b", "Same")]);
+        Assert.True(result.IsMatched); Assert.Equal("db-1", result.AccountId); Assert.Equal("wechatId", result.Strategy);
+    }
+
+    [Fact]
+    public void UsesUniqueNicknameOnlyWhenWechatIdIsUnavailable()
+    {
+        var result = AccountBindingMatcher.Match(new UiAccountIdentity(null, " Alice "),
+        [new("db-1", null, "Alice"), new("db-2", null, "Bob")]);
+        Assert.True(result.IsMatched); Assert.Equal("db-1", result.AccountId); Assert.Equal("nickname", result.Strategy);
+    }
+
+    [Fact]
+    public void RejectsDuplicateNicknameAndConflictingDuplicateWechatId()
+    {
+        var duplicateName = AccountBindingMatcher.Match(new UiAccountIdentity(null, "Alice"),
+        [new("db-1", null, "Alice"), new("db-2", null, "Alice")]);
+        var duplicateId = AccountBindingMatcher.Match(new UiAccountIdentity("wxid-a", "Alice"),
+        [new("db-1", "wxid-a", "One"), new("db-2", "wxid-a", "Two")]);
+        Assert.False(duplicateName.IsMatched); Assert.False(duplicateId.IsMatched);
+    }
+}