// app/build.gradle
apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
 
android {
  compileSdkVersion 34
  defaultConfig {
    applicationId "com.example.drawingboard"
    minSdkVersion 21
    targetSdkVersion 34
  }
  buildFeatures { viewBinding true }
  kotlinOptions { jvmTarget = "1.8" }
}
 
dependencies {
  implementation 'androidx.appcompat:appcompat:1.6.1'
  implementation 'androidx.core:core-ktx:1.10.1'
  implementation 'com.google.android.material:material:1.9.0'
  implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.6.1'
}

// =======================================================
// 文件: res/layout/activity_main.xml
// 描述: 主界面布局，包含工具欄、DrawingBoardView、顏色/筆寬工具
// =======================================================
<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent" android:layout_height="match_parent">
 
  <!-- 頂部操作欄 -->
  <com.google.android.material.appbar.MaterialToolbar
      android:id="@+id/toolbar"
      android:layout_width="match_parent"
      android:layout_height="?attr/actionBarSize"
      android:theme="@style/ThemeOverlay.MaterialComponents.Dark.ActionBar"
      app:title="寫字板"/>
 
  <!-- 繪制面板 -->
  <com.example.drawingboard.DrawingBoardView
      android:id="@+id/drawingBoard"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_marginTop="?attr/actionBarSize"
      android:background="#FFFFFF"/>
 
  <!-- 底部工具欄 -->
  <LinearLayout
      android:id="@+id/bottomTools"
      android:orientation="horizontal"
      android:gravity="center_vertical"
      android:padding="8dp"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_gravity="bottom"
      android:background="#CCFFFFFF">
 
    <!-- 顏色面板 -->
    <HorizontalScrollView
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="wrap_content">
      <LinearLayout
          android:id="@+id/colorPalette"
          android:orientation="horizontal"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"/>
    </HorizontalScrollView>
 
    <!-- 筆寬滑動條 -->
    <SeekBar
        android:id="@+id/seekStroke"
        android:layout_width="120dp"
        android:layout_height="wrap_content"
        android:max="50"
        android:progress="10"
        android:layout_marginStart="16dp"/>
  </LinearLayout>
 
  <!-- 懸浮操作按鈕 -->
  <com.google.android.material.floatingactionbutton.FloatingActionButton
      android:id="@+id/btnClear"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_margin="16dp"
      android:src="@drawable/ic_baseline_clear_24"
      app:layout_anchorGravity="bottom|end"
      app:layout_anchor="@id/drawingBoard"/>
 
  <com.google.android.material.floatingactionbutton.FloatingActionButton
      android:id="@+id/btnUndo"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_margin="16dp"
      android:src="@drawable/ic_baseline_undo_24"
      app:layout_anchorGravity="bottom|start"
      app:layout_anchor="@id/drawingBoard"/>
 
  <com.google.android.material.floatingactionbutton.FloatingActionButton
      android:id="@+id/btnRedo"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_margin="16dp"
      android:src="@drawable/ic_baseline_redo_24"
      app:layout_anchorGravity="bottom|start"
      app:layout_anchor="@id/btnUndo"/>
 
  <com.google.android.material.floatingactionbutton.FloatingActionButton
      android:id="@+id/btnSave"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_margin="16dp"
      android:src="@drawable/ic_baseline_save_24"
      app:layout_anchorGravity="bottom|end"
      app:layout_anchor="@id/btnClear"/>
 
</androidx.coordinatorlayout.widget.CoordinatorLayout>
 
// =======================================================
// 文件: DrawingBoardView.kt
// 描述: 自定義繪制板，支持繪制、撤銷、重做、清空、導出
// =======================================================
package com.example.drawingboard
 
import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import java.util.*
 
class DrawingBoardView @JvmOverloads constructor(
  context: Context, attrs: AttributeSet? = null
) : View(context, attrs) {
 
  // 畫筆與路徑集合
  private var paint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
    color = Color.BLACK; strokeWidth = 10f
    style = Paint.Style.STROKE; strokeCap = Paint.Cap.ROUND
    strokeJoin = Paint.Join.ROUND
  }
  private var currentPath = Path()
  private val paths = mutableListOf<Pair<Path, Paint>>()
  private val redoStack = Stack<Pair<Path, Paint>>()
 
  // 觸摸上一個點
  private var prevX = 0f; private var prevY = 0f
 
  /** 設置畫筆顏色 */
  fun setStrokeColor(color: Int) { paint.color = color }
 
  /** 設置畫筆粗細 */
  fun setStrokeWidth(width: Float) { paint.strokeWidth = width }
 
  /** 撤銷 */
  fun undo() {
    if (paths.isNotEmpty()) redoStack.push(paths.removeAt(paths.lastIndex))
    invalidate()
  }
 
  /** 重做 */
  fun redo() {
    if (redoStack.isNotEmpty()) paths += redoStack.pop()
    invalidate()
  }
 
  /** 清空 */
  fun clear() {
    paths.clear(); redoStack.clear()
    invalidate()
  }
 
  /** 導出 Bitmap */
  fun exportBitmap(): Bitmap {
    val bmp = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
    val canvas = Canvas(bmp)
    canvas.drawColor(Color.WHITE)
    for ((p, paint) in paths) canvas.drawPath(p, paint)
    return bmp
  }
 
  override fun onTouchEvent(e: MotionEvent): Boolean {
    val x = e.x; val y = e.y
    when (e.action) {
      MotionEvent.ACTION_DOWN -> {
        currentPath = Path().apply { moveTo(x, y) }
        prevX = x; prevY = y
        // 新操作清空 redo 棧
        redoStack.clear()
      }
      MotionEvent.ACTION_MOVE -> {
        val mx = (x + prevX) / 2
        val my = (y + prevY) / 2
        currentPath.quadTo(prevX, prevY, mx, my)
        prevX = x; prevY = y
      }
      MotionEvent.ACTION_UP -> {
        // 完成一筆，將路徑及其畫筆屬性存儲
        val p = Path(currentPath)
        val paintCopy = Paint(paint)
        paths += Pair(p, paintCopy)
      }
    }
    invalidate()
    return true
  }
 
  override fun onDraw(canvas: Canvas) {
    super.onDraw(canvas)
    // 依次繪制歷史路徑
    for ((p, paint) in paths) canvas.drawPath(p, paint)
    // 繪制當前路徑
    canvas.drawPath(currentPath, paint)
  }
}
 
// =======================================================
// 文件: ImageUtil.kt
// 描述: 圖片保存與分享工具
// =======================================================
package com.example.drawingboard
 
import android.content.Context
import android.graphics.Bitmap
import android.net.Uri
import android.os.Build
import android.provider.MediaStore
import java.io.*
 
object ImageUtil {
  /** 保存到相冊并返回 Uri */
  fun saveBitmapToGallery(ctx: Context, bmp: Bitmap, name: String = "draw_${System.currentTimeMillis()}"): Uri? {
    return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
      val values = ContentValues().apply {
        put(MediaStore.Images.Media.DISPLAY_NAME, "$name.png")
        put(MediaStore.Images.Media.MIME_TYPE, "image/png")
        put(MediaStore.Images.Media.RELATIVE_PATH, "Pictures/DrawingBoard")
        put(MediaStore.Images.Media.IS_PENDING, 1)
      }
      val uri = ctx.contentResolver.insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values)
      uri?.let {
        ctx.contentResolver.openOutputStream(it)?.use { os -> bmp.compress(Bitmap.CompressFormat.PNG, 100, os) }
        values.clear(); values.put(MediaStore.Images.Media.IS_PENDING, 0)
        ctx.contentResolver.update(it, values, null, null)
      }
      uri
    } else {
      val dir = File(ctx.getExternalFilesDir(null), "DrawingBoard")
      if (!dir.exists()) dir.mkdirs()
      val file = File(dir, "$name.png")
      FileOutputStream(file).use { fos -> bmp.compress(Bitmap.CompressFormat.PNG, 100, fos) }
      Uri.fromFile(file)
    }
  }
}
 
// =======================================================
// 文件: MainActivity.kt
// 描述: 主界面邏輯：初始化畫板、工具綁定、保存與分享
// =======================================================
package com.example.drawingboard
 
import android.content.Intent
import android.graphics.Color
import android.net.Uri
import android.os.Bundle
import android.widget.ImageButton
import android.widget.Toast
import androidx.activity.result.contract.ActivityResultContracts
import androidx.appcompat.app.AppCompatActivity
import androidx.core.content.FileProvider
import com.example.drawingboard.databinding.ActivityMainBinding
import kotlinx.coroutines.*
 
class MainActivity : AppCompatActivity() {
  private lateinit var binding: ActivityMainBinding
  private val scope = CoroutineScope(Dispatchers.Main + Job())
 
  // 分享后臨時 Uri
  private var savedImageUri: Uri? = null
 
  // 分享授權
  private val shareLauncher = registerForActivityResult(
    ActivityResultContracts.StartActivityForResult()
  ) { /* nothing */ }
 
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    binding = ActivityMainBinding.inflate(layoutInflater)
    setContentView(binding.root)
 
    // 初始化顏色面板
    initColorPalette()
 
    // 筆寬控制
    binding.seekStroke.setOnSeekBarChangeListener(object: SimpleSeekListener(){
      override fun onProgressChanged(sb: androidx.appcompat.widget.AppCompatSeekBar, p: Int, u: Boolean) {
        binding.drawingBoard.setStrokeWidth(p.toFloat())
      }
    })
 
    // 頂部按鈕綁定
    binding.btnClear.setOnClickListener { binding.drawingBoard.clear() }
    binding.btnUndo.setOnClickListener  { binding.drawingBoard.undo() }
    binding.btnRedo.setOnClickListener  { binding.drawingBoard.redo() }
    binding.btnSave.setOnClickListener  { saveDrawing() }
  }
 
  private fun initColorPalette() {
    val colors = listOf(Color.BLACK, Color.RED, Color.BLUE, Color.GREEN, Color.MAGENTA)
    for (c in colors) {
      val btn = ImageButton(this).apply {
        val size = resources.getDimensionPixelSize(R.dimen.color_btn_size)
        layoutParams = androidx.appcompat.widget.LinearLayoutCompat.LayoutParams(size, size).apply {
          marginEnd = 16
        }
        setBackgroundColor(c)
        setOnClickListener { binding.drawingBoard.setStrokeColor(c) }
      }
      binding.colorPalette.addView(btn)
    }
  }
 
  private fun saveDrawing() {
    // 異步保存并分享
    scope.launch {
      val bmp = withContext(Dispatchers.Default) { binding.drawingBoard.exportBitmap() }
      savedImageUri = ImageUtil.saveBitmapToGallery(this@MainActivity, bmp)
      if (savedImageUri != null) {
        shareImage(savedImageUri!!)
      } else {
        Toast.makeText(this@MainActivity, "保存失敗", Toast.LENGTH_SHORT).show()
      }
    }
  }
 
  private fun shareImage(uri: Uri) {
    val contentUri = if (uri.scheme == "file") {
      FileProvider.getUriForFile(this, "$packageName.fileprovider", Uri.parse(uri.path!!).toFile())
    } else uri
    val intent = Intent(Intent.ACTION_SEND).apply {
      type = "image/png"
      putExtra(Intent.EXTRA_STREAM, contentUri)
      addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
    }
    shareLauncher.launch(Intent.createChooser(intent, "分享繪圖"))
  }
 
  override fun onDestroy() {
    super.onDestroy()
    scope.cancel()
  }
}
 
// =======================================================
// 文件: SimpleSeekListener.kt
// 描述: 簡易 SeekBar 監(jiān)聽，省略回調(diào)實現(xiàn)
// =======================================================
package com.example.drawingboard
 
import android.widget.SeekBar
 
abstract class SimpleSeekListener: SeekBar.OnSeekBarChangeListener {
  override fun onStartTrackingTouch(p0: SeekBar?) {}
  override fun onStopTrackingTouch(p0: SeekBar?) {}
}