datatransfer object, drag_and_drop example, fix drag-and-drop (#4789)

* wip: implement datatransfer

* Editable kanban contents

* desktop sorta works without crashing

* lint

packages/html/src/data_transfer.rs

@@ -0,0 +1,180 @@
+pub struct DataTransfer {
+    inner: Box<dyn NativeDataTransfer>,
+}
+
+impl DataTransfer {
+    pub fn new(inner: impl NativeDataTransfer + 'static) -> Self {
+        Self {
+            inner: Box::new(inner),
+        }
+    }
+
+    #[cfg(feature = "serialize")]
+    pub fn store(&self, item: impl Serialize) -> Result<(), String> {
+        let serialized = serde_json::to_string(&item).map_err(|e| e.to_string())?;
+        self.set_data("application/json", &serialized)
+    }
+
+    #[cfg(feature = "serialize")]
+    pub fn retrieve<T: for<'de> serde::Deserialize<'de>>(&self) -> Result<Option<T>, String> {
+        if let Some(data) = self.get_data("application/json") {
+            let deserialized = serde_json::from_str(&data).map_err(|e| e.to_string())?;
+            Ok(Some(deserialized))
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn get_data(&self, format: &str) -> Option<String> {
+        self.inner.get_data(format)
+    }
+
+    pub fn get_as_text(&self) -> Option<String> {
+        self.get_data("text/plain")
+    }
+
+    pub fn set_data(&self, format: &str, data: &str) -> Result<(), String> {
+        self.inner.set_data(format, data)
+    }
+
+    pub fn clear_data(&self, format: Option<&str>) -> Result<(), String> {
+        self.inner.clear_data(format)
+    }
+
+    pub fn effect_allowed(&self) -> String {
+        self.inner.effect_allowed()
+    }
+
+    pub fn set_effect_allowed(&self, effect: &str) {
+        self.inner.set_effect_allowed(effect)
+    }
+
+    pub fn drop_effect(&self) -> String {
+        self.inner.drop_effect()
+    }
+
+    pub fn set_drop_effect(&self, effect: &str) {
+        self.inner.set_drop_effect(effect)
+    }
+
+    pub fn files(&self) -> Vec<crate::file_data::FileData> {
+        self.inner.files()
+    }
+}
+
+pub trait NativeDataTransfer: Send + Sync {
+    fn get_data(&self, format: &str) -> Option<String>;
+    fn set_data(&self, format: &str, data: &str) -> Result<(), String>;
+    fn clear_data(&self, format: Option<&str>) -> Result<(), String>;
+    fn effect_allowed(&self) -> String;
+    fn set_effect_allowed(&self, effect: &str);
+    fn drop_effect(&self) -> String;
+    fn set_drop_effect(&self, effect: &str);
+    fn files(&self) -> Vec<crate::file_data::FileData>;
+}
+
+pub trait HasDataTransferData {
+    fn data_transfer(&self) -> DataTransfer;
+}
+
+#[cfg(feature = "serialize")]
+pub use ser::*;
+#[cfg(feature = "serialize")]
+use serde::Serialize;
+
+#[cfg(feature = "serialize")]
+mod ser {
+    use crate::DragData;
+
+    use super::*;
+    use serde::{Deserialize, Serialize};
+
+    /// A serialized version of DataTransfer
+    #[derive(Serialize, Deserialize, Debug, PartialEq, Clone)]
+    pub struct SerializedDataTransfer {
+        pub items: Vec<SerializedDataTransferItem>,
+        pub files: Vec<crate::file_data::SerializedFileData>,
+        pub effect_allowed: String,
+        pub drop_effect: String,
+    }
+
+    #[derive(Serialize, Deserialize, Debug, PartialEq, Clone)]
+    pub struct SerializedDataTransferItem {
+        pub kind: String,
+        pub type_: String,
+        pub data: String,
+    }
+
+    impl NativeDataTransfer for SerializedDataTransfer {
+        fn get_data(&self, format: &str) -> Option<String> {
+            self.items
+                .iter()
+                .find(|item| item.type_ == format)
+                .map(|item| item.data.clone())
+        }
+
+        fn set_data(&self, _format: &str, _data: &str) -> Result<(), String> {
+            // todo!()
+            // Err("Cannot set data on serialized DataTransfer".into())
+            Ok(())
+        }
+
+        fn clear_data(&self, _format: Option<&str>) -> Result<(), String> {
+            // todo!()
+            // Err("Cannot clear data on serialized DataTransfer".into())
+            Ok(())
+        }
+
+        fn effect_allowed(&self) -> String {
+            self.effect_allowed.clone()
+        }
+
+        fn set_effect_allowed(&self, _effect: &str) {
+            // No-op
+        }
+
+        fn drop_effect(&self) -> String {
+            self.drop_effect.clone()
+        }
+
+        fn set_drop_effect(&self, _effect: &str) {
+            // No-op
+        }
+
+        fn files(&self) -> Vec<crate::file_data::FileData> {
+            self.files
+                .iter()
+                .map(|f| crate::file_data::FileData::new(f.clone()))
+                .collect()
+        }
+    }
+
+    impl From<&DragData> for SerializedDataTransfer {
+        fn from(_drag: &DragData) -> Self {
+            todo!()
+            //     let items = vec![]; // drag.data_transfer().items().iter().map(|item| SerializedDataTransferItem {
+            //                         //     kind: item.kind().to_string(),
+            //                         //     type_: item.type_().to_string(),
+            //                         //     data: item.data().unwrap_or_default(),
+            //                         // }).collect();
+
+            //     let files = drag
+            //         .files()
+            //         .iter()
+            //         .map(|f| crate::file_data::SerializedFileData {
+            //             name: f.name().to_string(),
+            //             size: f.size(),
+            //             type_: f.type_().to_string(),
+            //         })
+            //         .collect();
+
+            //     Self {
+            //         items,
+            //         files,
+            //         effect_allowed: drag.effect_allowed().to_string(),
+            //         drop_effect: drag.drop_effect().to_string(),
+            //     }
+            // }
+        }
+    }
+}