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//! Serializing `indextree` structure.
//!
//! ## Version support
//!
//! | `indextree` version | `serde_indextree` version |
//! |---------------------|---------------------------|
//! | 3.3.x               | 0.1.x                     |
//! | 4.0.x               | 0.2.x                     |
//!
//! ## Usage
//!
//! `serde_indextree` provides two struct: `Node` for serializing
//! a node and its descendants, `SiblingNodes` for serializing a
//! node and its siblings in sequence.
//!
//! ```rust
//! use indextree::Arena;
//! use serde::Serialize;
//! use serde_indextree::Node;
//! use serde_json::to_string_pretty;
//!
//! #[derive(Serialize)]
//! struct HtmlElement {
//!     tag: &'static str
//! }
//!
//! // <html>
//! // <head>
//! //     <title></title>
//! // <head>
//! // <body>
//! //     <h1></h1>
//! //     <h2></h2>
//! // </body>
//! // </html>
//! let arena = &mut Arena::new();
//! let a = arena.new_node(HtmlElement { tag: "html" });
//! let b = arena.new_node(HtmlElement { tag: "head" });
//! a.append(b, arena);
//! let c = arena.new_node(HtmlElement { tag: "title" });
//! b.append(c, arena);
//! let d = arena.new_node(HtmlElement { tag: "body" });
//! a.append(d, arena);
//! let e = arena.new_node(HtmlElement { tag: "h1" });
//! d.append(e, arena);
//! let f = arena.new_node(HtmlElement { tag: "h2" });
//! d.append(f, arena);
//!
//! println!("{}", to_string_pretty(&Node::new(a, arena)).unwrap());
//! // {
//! //   "tag": "html",
//! //   "children": [
//! //     {
//! //       "tag": "head",
//! //       "children": [
//! //         {
//! //           "tag": "title"
//! //         }
//! //       ]
//! //     },
//! //     {
//! //       "tag": "body",
//! //       "children": [
//! //         {
//! //           "tag": "h1"
//! //         },
//! //         {
//! //           "tag": "h2"
//! //         }
//! //       ]
//! //     }
//! //   ]
//! // }
//! ```
//!
//! ## Customization
//!
//! Unfortunately, `serde_indextree` doesn't come up with any customization.
//!
//! If you want to rename field names or anything, just copy the entire code
//! (only 40+ lines) and modify it at your wish.
//!
//! ## License
//!
//! MIT

use indextree::{Arena, NodeId};
use serde::ser::{SerializeSeq, Serializer};
use serde::Serialize;

/// Convenience wrapper struct for serializing a node and its descendants.
#[derive(Serialize)]
pub struct Node<'a, T: Serialize> {
    #[serde(flatten)]
    data: &'a T,
    #[serde(skip_serializing_if = "Option::is_none")]
    children: Option<SiblingNodes<'a, T>>,
}

impl<'a, T: Serialize> Node<'a, T> {
    pub fn new(id: NodeId, arena: &'a Arena<T>) -> Self {
        let node = &arena[id];
        Node {
            data: &node.get(),
            children: node
                .first_child()
                .map(|first| SiblingNodes::new(first, arena)),
        }
    }
}

/// Convenience wrapper struct for serializing a node and its siblings.
pub struct SiblingNodes<'a, T: Serialize> {
    first: NodeId,
    arena: &'a Arena<T>,
}

impl<'a, T: Serialize> SiblingNodes<'a, T> {
    pub fn new(id: NodeId, arena: &'a Arena<T>) -> Self {
        SiblingNodes { first: id, arena }
    }
}

impl<T: Serialize> Serialize for SiblingNodes<'_, T> {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        let mut seq = serializer.serialize_seq(None)?;
        for node in self.first.following_siblings(&self.arena) {
            seq.serialize_element(&Node::new(node, &self.arena))?;
        }
        seq.end()
    }
}