From ee17b238a20876a5e590233ad4d667f55c7ba93a Mon Sep 17 00:00:00 2001
From: Miwa / Ensan <ensan.hcl.dev@gmail.com>
Date: Sat, 12 Jul 2025 01:52:59 +0900
Subject: [PATCH] =?UTF-8?q?feat:=20=E3=82=A4=E3=83=B3=E3=83=87=E3=83=83?=
 =?UTF-8?q?=E3=82=AF=E3=82=B9=E3=81=AE=E6=95=B4=E5=90=88=E6=80=A7=E3=82=92?=
 =?UTF-8?q?=E5=8F=96=E3=82=8B=E3=81=9F=E3=82=81=E3=81=AEAPI=E3=82=92?=
 =?UTF-8?q?=E8=BF=BD=E5=8A=A0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../InputManagement/ComposingText.swift       | 34 +++++++++++++++++++
 .../ComposingTextTests.swift                  | 26 ++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/Sources/KanaKanjiConverterModule/InputManagement/ComposingText.swift b/Sources/KanaKanjiConverterModule/InputManagement/ComposingText.swift
index e185097..4b5d051 100644
--- a/Sources/KanaKanjiConverterModule/InputManagement/ComposingText.swift
+++ b/Sources/KanaKanjiConverterModule/InputManagement/ComposingText.swift
@@ -384,6 +384,40 @@ public struct ComposingText: Sendable {
         return text
     }
 
+    public func inputIndexToSurfaceIndexMap() -> [Int: Int] {
+        // i2c: input indexからconvert target indexへのmap
+        // c2i: convert target indexからinput indexへのmap
+
+        // 例1.
+        // [k, y, o, u, h, a, i, i, t, e, n, k, i, d, a]
+        // [き, ょ, う, は, い, い, て, ん, き, だ]
+        // i2c: [0: 0, 3: 2(きょ), 4: 3(う), 6: 4(は), 7: 5(い), 8: 6(い), 10: 7(て), 13: 9(んき), 15: 10(だ)]
+
+        var map: [Int: (surfaceIndex: Int, surface: String)] = [0: (0, "")]
+
+        // 逐次更新用のバッファ
+        var convertTargetElements: [ConvertTargetElement] = []
+
+        for (idx, element) in self.input.enumerated() {
+            // 要素を追加して表層文字列を更新
+            Self.updateConvertTargetElements(currentElements: &convertTargetElements, newElement: element)
+            // 表層側の長さを再計算
+            let currentSurface = convertTargetElements.reduce(into: "") { $0 += $1.string }
+            // idx 個の要素を処理し終えた直後（= 次の要素を処理する前）の
+            // カーソル位置は idx + 1
+            map[idx + 1] = (currentSurface.count, currentSurface)
+        }
+        // 最終的なサーフェスと一致したものだけ残す
+        let finalSurface = convertTargetElements.reduce(into: "") { $0 += $1.string }
+        return map
+            .filter {
+                finalSurface.hasPrefix($0.value.surface)
+            }
+            .mapValues {
+                $0.surfaceIndex
+            }
+    }
+
     public mutating func stopComposition() {
         self.input = []
         self.convertTarget = ""
diff --git a/Tests/KanaKanjiConverterModuleTests/ComposingTextTests.swift b/Tests/KanaKanjiConverterModuleTests/ComposingTextTests.swift
index da96691..3082036 100644
--- a/Tests/KanaKanjiConverterModuleTests/ComposingTextTests.swift
+++ b/Tests/KanaKanjiConverterModuleTests/ComposingTextTests.swift
@@ -216,4 +216,30 @@ final class ComposingTextTests: XCTestCase {
             XCTAssertEqual(c2.differenceSuffix(to: c1).addedInput, 1)
         }
     }
+
+    func testIndexMap() throws {
+        var c = ComposingText()
+        sequentialInput(&c, sequence: "kyouhaiitenkida", inputStyle: .roman2kana)
+        let map = c.inputIndexToSurfaceIndexMap()
+
+        // Note: 現在の実装では、アドホックな対処によってnが"ん"に切り替わる
+        XCTAssertEqual(c.input[10], .init(character: "ん", inputStyle: .direct))
+
+        XCTAssertEqual(map[0], 0)     // ""
+        XCTAssertEqual(map[1], nil)   // k
+        XCTAssertEqual(map[2], nil)   // y
+        XCTAssertEqual(map[3], 2)     // o
+        XCTAssertEqual(map[4], 3)     // u
+        XCTAssertEqual(map[5], nil)   // h
+        XCTAssertEqual(map[6], 4)     // a
+        XCTAssertEqual(map[7], 5)     // i
+        XCTAssertEqual(map[8], 6)     // i
+        XCTAssertEqual(map[9], nil)   // t
+        XCTAssertEqual(map[10], 7)    // e
+        XCTAssertEqual(map[11], 8)    // n   // アドホックな対処の影響。nの場合はnilであるべき。
+        XCTAssertEqual(map[12], nil)  // k
+        XCTAssertEqual(map[13], 9)    // i
+        XCTAssertEqual(map[14], nil)  // d
+        XCTAssertEqual(map[15], 10)   // a
+    }
 }