use bytes_cast::BytesCast;

use std::path::PathBuf;

use std::{collections::BTreeMap, convert::TryInto};

use super::path_with_basename::WithBasename;

use crate::dirstate::parsers::clear_ambiguous_mtime;

use crate::dirstate::parsers::pack_entry;

use crate::dirstate::parsers::packed_entry_size;

use crate::dirstate::parsers::parse_dirstate_entries;

use crate::dirstate::parsers::parse_dirstate_parents;

use crate::dirstate::parsers::Timestamp;

use crate::matchers::Matcher;

use crate::revlog::node::NULL_NODE;

use crate::utils::hg_path::{HgPath, HgPathBuf};

use crate::CopyMapIter;

use crate::DirstateEntry;

use crate::DirstateError;

use crate::DirstateMapError;

use crate::DirstateParents;

use crate::DirstateStatus;

use crate::EntryState;

use crate::PatternFileWarning;

use crate::StateMapIter;

use crate::StatusError;

use crate::StatusOptions;

pub struct DirstateMap {

    parents: Option<DirstateParents>,

    dirty_parents: bool,

    root: ChildNodes,

    /// Number of nodes anywhere in the tree that have `.entry.is_some()`.

    nodes_with_entry_count: usize,

    /// Number of nodes anywhere in the tree that have

    /// `.copy_source.is_some()`.

    nodes_with_copy_source_count: usize,

}

/// Using a plain `HgPathBuf` of the full path from the repository root as a

/// map key would also work: all paths in a given map have the same parent

/// path, so comparing full paths gives the same result as comparing base

/// names. However `BTreeMap` would waste time always re-comparing the same

/// string prefix.

type ChildNodes = BTreeMap<WithBasename<HgPathBuf>, Node>;

/// Represents a file or a directory

#[derive(Default)]

struct Node {

    /// `None` for directories

    entry: Option<DirstateEntry>,

    copy_source: Option<HgPathBuf>,

    children: ChildNodes,

    /// How many (non-inclusive) descendants of this node are tracked files

    tracked_descendants_count: usize,

}

impl Node {

    /// Whether this node has a `DirstateEntry` with `.state.is_tracked()`

    fn is_tracked_file(&self) -> bool {

        if let Some(entry) = &self.entry {

            entry.state.is_tracked()

        } else {

            false

        }

    }

}

/// `(full_path, entry, copy_source)`

type NodeDataMut<'a> = (

    &'a WithBasename<HgPathBuf>,

    &'a mut Option<DirstateEntry>,

    &'a mut Option<HgPathBuf>,

);

impl DirstateMap {

    pub fn new() -> Self {

        Self {

            parents: None,

            dirty_parents: false,

            root: ChildNodes::new(),

            nodes_with_entry_count: 0,

            nodes_with_copy_source_count: 0,

        }

    }

    fn get_node(&self, path: &HgPath) -> Option<&Node> {

        let mut children = &self.root;

        let mut components = path.components();

        let mut component =

            components.next().expect("expected at least one components");

        loop {

            let child = children.get(component)?;

            if let Some(next_component) = components.next() {

                component = next_component;

                children = &child.children;

            } else {

                return Some(child);

            }

        }

    }

    /// Returns a mutable reference to the node at `path` if it exists

    ///

    /// This takes `root` instead of `&mut self` so that callers can mutate

    /// other fields while the returned borrow is still valid

    fn get_node_mut<'tree>(

        root: &'tree mut ChildNodes,

        path: &HgPath,

    ) -> Option<&'tree mut Node> {

        Self::each_and_get(root, path, |_| {})

    }

    /// Call `each` for each ancestor node of the one at `path` (not including

    /// that node itself), starting from nearest the root.

    ///

    /// Panics (possibly after some calls to `each`) if there is no node at

    /// `path`.

    fn for_each_ancestor_node<'tree>(

        &mut self,

        path: &HgPath,

        each: impl FnMut(&mut Node),

    ) {

        let parent = path.parent();

        if !parent.is_empty() {

            Self::each_and_get(&mut self.root, parent, each)

                .expect("missing dirstate node");

        }

    }

    /// Common implementation detail of `get_node_mut` and

    /// `for_each_ancestor_node`

    fn each_and_get<'tree>(

        root: &'tree mut ChildNodes,

        path: &HgPath,

        mut each: impl FnMut(&mut Node),

    ) -> Option<&'tree mut Node> {

        let mut children = root;

        let mut components = path.components();

        let mut component =

            components.next().expect("expected at least one components");

        loop {

            let child = children.get_mut(component)?;

            each(child);

            if let Some(next_component) = components.next() {

                component = next_component;

                children = &mut child.children;

            } else {

                return Some(child);

            }

        }

    }

    fn get_or_insert_node<'tree>(

        root: &'tree mut ChildNodes,

        path: &HgPath,

    ) -> &'tree mut Node {

        let mut child_nodes = root;

        let mut inclusive_ancestor_paths =

            WithBasename::inclusive_ancestors_of(path);

        let mut ancestor_path = inclusive_ancestor_paths

            .next()

            .expect("expected at least one inclusive ancestor");

        loop {

            // TODO: can we avoid double lookup in all cases without allocating

            // an owned key in cases where the map already contains that key?

            let child_node =

                if child_nodes.contains_key(ancestor_path.base_name()) {

                    child_nodes.get_mut(ancestor_path.base_name()).unwrap()

                } else {

                    // This is always a vacant entry, using `.entry()` lets us

                    // return a `&mut Node` of the newly-inserted node without

                    // yet another lookup. `BTreeMap::insert` doesn’t do this.

                    child_nodes.entry(ancestor_path.to_owned()).or_default()

                };

            if let Some(next) = inclusive_ancestor_paths.next() {

                ancestor_path = next;

                child_nodes = &mut child_node.children;

            } else {

                return child_node;

            }

        }

    }

    /// The meaning of `new_copy_source` is:

    ///

    /// * `Some(Some(x))`: set `Node::copy_source` to `Some(x)`

    /// * `Some(None)`: set `Node::copy_source` to `None`

    /// * `None`: leave `Node::copy_source` unchanged

    fn add_file_node(

        &mut self,

        path: &HgPath,

        new_entry: DirstateEntry,

        new_copy_source: Option<Option<HgPathBuf>>,

    ) {

        let node = Self::get_or_insert_node(&mut self.root, path);

        if node.entry.is_none() {

            self.nodes_with_entry_count += 1

        }

        if let Some(source) = &new_copy_source {

            if node.copy_source.is_none() && source.is_some() {

                self.nodes_with_copy_source_count += 1

            }

            if node.copy_source.is_some() && source.is_none() {

                self.nodes_with_copy_source_count -= 1

            }

        }

        let tracked_count_increment =

            match (node.is_tracked_file(), new_entry.state.is_tracked()) {

                (false, true) => 1,

                (true, false) => -1,

                _ => 0,

            };

        node.entry = Some(new_entry);

        if let Some(source) = new_copy_source {

            node.copy_source = source

        }

        // Borrow of `self.root` through `node` ends here

        match tracked_count_increment {

            1 => self.for_each_ancestor_node(path, |node| {

                node.tracked_descendants_count += 1

            }),

            // We can’t use `+= -1` because the counter is unsigned

            -1 => self.for_each_ancestor_node(path, |node| {

                node.tracked_descendants_count -= 1

            }),

            _ => {}

        }

    }

    fn iter_nodes<'a>(

        &'a self,

    ) -> impl Iterator<Item = (&'a WithBasename<HgPathBuf>, &'a Node)> + 'a

    {

        // Depth first tree traversal.

        //

        // If we could afford internal iteration and recursion,

        // this would look like:

        //

        // ```

        // fn traverse_children(

        //     children: &ChildNodes,

        //     each: &mut impl FnMut(&Node),

        // ) {

        //     for child in children.values() {

        //         traverse_children(&child.children, each);

        //         each(child);

        //     }

        // }

        // ```

        //

        // However we want an external iterator and therefore can’t use the

        // call stack. Use an explicit stack instead:

        let mut stack = Vec::new();

        let mut iter = self.root.iter();

        std::iter::from_fn(move || {

            while let Some((key, child_node)) = iter.next() {

                // Pseudo-recursion

                let new_iter = child_node.children.iter();

                let old_iter = std::mem::replace(&mut iter, new_iter);

                stack.push((key, child_node, old_iter));

            }

            // Found the end of a `children.iter()` iterator.

            if let Some((key, child_node, next_iter)) = stack.pop() {

                // "Return" from pseudo-recursion by restoring state from the

                // explicit stack

                iter = next_iter;

                Some((key, child_node))

            } else {

                // Reached the bottom of the stack, we’re done

                None

            }

        })

    }

    /// Mutable iterator for the `(entry, copy source)` of each node.

    ///

    /// It would not be safe to yield mutable references to nodes themeselves

    /// with `-> impl Iterator<Item = &mut Node>` since child nodes are

    /// reachable from their ancestor nodes, potentially creating multiple

    /// `&mut` references to a given node.

    fn iter_node_data_mut<'a>(

        &'a mut self,

    ) -> impl Iterator<Item = NodeDataMut<'a>> + 'a {

        // Explict stack for pseudo-recursion, see `iter_nodes` above.

        let mut stack = Vec::new();

        let mut iter = self.root.iter_mut();

        std::iter::from_fn(move || {

            while let Some((key, child_node)) = iter.next() {

                // Pseudo-recursion

                let data =

                    (key, &mut child_node.entry, &mut child_node.copy_source);

                let new_iter = child_node.children.iter_mut();

                let old_iter = std::mem::replace(&mut iter, new_iter);

                stack.push((data, old_iter));

            }

            // Found the end of a `children.values_mut()` iterator.

            if let Some((data, next_iter)) = stack.pop() {

                // "Return" from pseudo-recursion by restoring state from the

                // explicit stack

                iter = next_iter;

                Some(data)

            } else {

                // Reached the bottom of the stack, we’re done

                None

            }

        })

    }

}

impl super::dispatch::DirstateMapMethods for DirstateMap {

    fn clear(&mut self) {

        self.set_parents(&DirstateParents {

            p1: NULL_NODE,

            p2: NULL_NODE,

        });

        self.root.clear();

        self.nodes_with_entry_count = 0;

        self.nodes_with_copy_source_count = 0;

    }

    fn add_file(

        &mut self,

        filename: &HgPath,

        _old_state: EntryState,

        entry: DirstateEntry,

    ) -> Result<(), DirstateMapError> {

        self.add_file_node(filename, entry, None);

        Ok(())

    }

    fn remove_file(

        &mut self,

        filename: &HgPath,

        _old_state: EntryState,

        size: i32,

    ) -> Result<(), DirstateMapError> {

        let entry = DirstateEntry {

            state: EntryState::Removed,

            mode: 0,

            size,

            mtime: 0,

        };

        self.add_file_node(filename, entry, None);