use std::collections::HashSet;
use std::fmt::Display;
use std::hash::{DefaultHasher, Hash, Hasher};
use ratatui::text::ToText;

/// One item inside a [`Tree`](crate::Tree).
///
/// Can have zero or more `children`.
///
/// # identifier
///
/// The `identifier` is used to keep the state like the currently selected or opened [`TreeItem`]s in the [`TreeState`](crate::TreeState).
///
/// It needs to be unique among its siblings but can be used again on parent or child [`TreeItem`]s.
/// A common example would be a filename which has to be unique in its directory while it can exist in another.
///
/// The `text` can be different from its `identifier`.
/// To repeat the filename analogy: File browsers sometimes hide file extensions.
/// The filename `main.rs` is the identifier while it's shown as `main`.
/// Two files `main.rs` and `main.toml` can exist in the same directory and can both be displayed as `main` but their identifier is different.
///
/// Just like every file in a file system can be uniquely identified with its file and directory names each [`TreeItem`] in a [`Tree`](crate::Tree) can be with these identifiers.
/// As an example the following two identifiers describe the main file in a Rust cargo project: `vec!["src", "main.rs"]`.
///
/// The identifier does not need to be a `String` and is therefore generic.
/// Until version 0.14 this crate used `usize` and indices.
/// This might still be perfect for your use case.
///
/// # Example
///
/// ```
/// # use managarr_tree_widget::TreeItem;
/// let a = TreeItem::new_leaf("Leaf");
/// let b = TreeItem::new("Root", vec![a])?;
/// # Ok::<(), std::io::Error>(())
/// ```
#[derive(Debug, Clone)]
pub struct TreeItem<T>
where
    T: ToText + Clone + Default + Display + Hash,
{
    pub(super) identifier: u64,
    pub(super) content: T,
    pub(super) children: Vec<Self>,
}

impl<T> TreeItem<T>
where
    T: ToText + Clone + Default + Display + Hash,
{
    /// Create a new `TreeItem` with children.
    ///
    /// # Errors
    ///
    /// Errors when there are duplicate identifiers in the children.
    pub fn new(content: T, children: Vec<Self>) -> std::io::Result<Self> {
        let identifiers = children
            .iter()
            .map(|item| &item.identifier)
            .collect::<HashSet<_>>();
        if identifiers.len() != children.len() {
            return Err(std::io::Error::new(
                std::io::ErrorKind::AlreadyExists,
                "The children contain duplicate identifiers",
            ));
        }

        let mut hasher = DefaultHasher::new();
        content.hash(&mut hasher);

        Ok(Self {
            identifier: hasher.finish(),
            content,
            children,
        })
    }

    /// Create a new `TreeItem` without children.
    #[must_use]
    pub fn new_leaf(content: T) -> Self {
        let mut hasher = DefaultHasher::new();
        content.hash(&mut hasher);
        
        Self {
            identifier: hasher.finish(),
            content,
            children: Vec::new(),
        }
    }

    /// Get a reference to the identifier.
    #[must_use]
    pub const fn identifier(&self) -> u64 {
        self.identifier
    }

    /// Get a reference to the text.
    #[must_use]
    pub const fn content(&self) -> &T {
        &self.content
    }

    #[must_use]
    pub fn children(&self) -> &[Self] {
        &self.children
    }

    /// Get a reference to a child by index.
    #[must_use]
    pub fn child(&self, index: usize) -> Option<&Self> {
        self.children.get(index)
    }

    /// Get a mutable reference to a child by index.
    ///
    /// When you choose to change the `identifier` the [`TreeState`](crate::TreeState) might not work as expected afterward.
    #[must_use]
    pub fn child_mut(&mut self, index: usize) -> Option<&mut Self> {
        self.children.get_mut(index)
    }

    #[must_use]
    pub fn height(&self) -> usize {
        self.content.clone().to_text().height()
    }

    /// Add a child to the `TreeItem`.
    ///
    /// # Errors
    ///
    /// Errors when the `identifier` of the `child` already exists in the children.
    pub fn add_child(&mut self, child: Self) -> std::io::Result<()> {
        let existing = self
            .children
            .iter()
            .map(|item| &item.identifier)
            .collect::<HashSet<_>>();
        if existing.contains(&child.identifier) {
            return Err(std::io::Error::new(
                std::io::ErrorKind::AlreadyExists,
                "identifier already exists in the children",
            ));
        }

        self.children.push(child);
        Ok(())
    }
}

impl TreeItem<&'static str> {
    #[cfg(test)]
    #[must_use]
    pub(crate) fn example() -> Vec<Self> {
        vec![
            Self::new_leaf("Alfa"),
            Self::new(
                "Bravo",
                vec![
                    Self::new_leaf("Charlie"),
                    Self::new(
                        "Delta",
                        vec![
                            Self::new_leaf("Echo"),
                            Self::new_leaf( "Foxtrot"),
                        ],
                    )
                    .expect("all item identifiers are unique"),
                    Self::new_leaf("Golf"),
                ],
            )
            .expect("all item identifiers are unique"),
            Self::new_leaf( "Hotel"),
        ]
    }
}

#[test]
#[should_panic = "duplicate identifiers"]
fn tree_item_new_errors_with_duplicate_identifiers() {
    let item = TreeItem::new_leaf( "text");
    let another = item.clone();
    TreeItem::new("Root", vec![item, another]).unwrap();
}

#[test]
#[should_panic = "identifier already exists"]
fn tree_item_add_child_errors_with_duplicate_identifiers() {
    let item = TreeItem::new_leaf("text");
    let another = item.clone();
    let mut root = TreeItem::new( "Root", vec![item]).unwrap();
    root.add_child(another).unwrap();
}