use std::collections::{HashMap, HashSet};

use crate::api::AssetMeta;
use crate::util;
use chrono::DateTime;

/// Unique identifier for a node in the virtual tree.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct NodeId(pub usize);

/// A node is either a directory or a file reference.
#[derive(Debug, Clone)]
pub enum NodeKind {
    Directory,
    /// Points to an index in the flat asset list.
    File { asset_index: usize },
}

/// A node in the virtual directory tree.
#[derive(Debug, Clone)]
pub struct VNode {
    pub name: String,
    pub kind: NodeKind,
    pub children: Vec<NodeId>,
    #[allow(dead_code)]
    pub parent: Option<NodeId>,
}

impl VNode {
    pub fn is_directory(&self) -> bool {
        matches!(self.kind, NodeKind::Directory)
    }
}

/// The complete virtual directory tree built from a list of assets.
pub struct VirtualTree {
    nodes: Vec<VNode>,
    /// Normalized path -> NodeId lookup.
    path_index: HashMap<String, NodeId>,
}

impl VirtualTree {
    /// Build the virtual tree from a flat list of assets.
    pub fn build(assets: &[AssetMeta]) -> Self {
        let mut tree = TreeBuilder::new();

        // Create top-level directories
        let root = tree.root();
        let can_dir = tree.add_dir("CAN", root);
        let app_dir = tree.add_dir("APPLICATION", root);
        let dates_dir = tree.add_dir("DATES", root);
        let tags_dir = tree.add_dir("TAGS", root);

        for (i, asset) in assets.iter().enumerate() {
            let ext = util::mime_to_ext(&asset.mime_type);
            let hash8 = &asset.hash[..asset.hash.len().min(8)];

            // 1) CAN/ — always: {timestamp}_{hash8}.ext
            let can_name = format!("{}_{}.{}", asset.timestamp, hash8, ext);
            let can_name = util::sanitize_filename(&can_name);
            tree.add_file(&can_name, can_dir, i);

            // Display name for other folders: human_filename if available, else hash8.ext
            let display_name = if let Some(ref hf) = asset.human_filename {
                util::sanitize_filename(hf)
            } else {
                format!("{}.{}", hash8, ext)
            };

            // 2) APPLICATION/{app}/ — if application is set
            if let Some(ref app) = asset.application {
                let app_name = util::sanitize_filename(app);
                let app_sub = tree.ensure_dir(&app_name, app_dir);
                tree.add_file(&display_name, app_sub, i);
            }

            // 3) DATES/{year}/{month:02}/
            if let Some(dt) = DateTime::from_timestamp_millis(asset.timestamp) {
                let year_str = dt.format("%Y").to_string();
                let month_str = dt.format("%m").to_string();
                let year_dir = tree.ensure_dir(&year_str, dates_dir);
                let month_dir = tree.ensure_dir(&month_str, year_dir);
                tree.add_file(&display_name, month_dir, i);
            }

            // 4) TAGS/{tag}/
            for tag in &asset.tags {
                let tag_name = util::sanitize_filename(tag);
                if tag_name.is_empty() {
                    continue;
                }
                let tag_sub = tree.ensure_dir(&tag_name, tags_dir);
                tree.add_file(&display_name, tag_sub, i);
            }
        }

        // Sort children and build path index
        tree.finalize()
    }

    /// Look up a node by its normalized path (e.g., `\can\file.txt`).
    pub fn lookup(&self, path: &str) -> Option<NodeId> {
        let normalized = path.to_lowercase().replace('/', "\\");
        let normalized = if normalized.len() > 1 && normalized.ends_with('\\') {
            &normalized[..normalized.len() - 1]
        } else {
            &normalized
        };
        self.path_index.get(normalized).copied()
    }

    /// Get a node by ID.
    pub fn get(&self, id: NodeId) -> &VNode {
        &self.nodes[id.0]
    }

    /// Get the root node ID.
    #[allow(dead_code)]
    pub fn root(&self) -> NodeId {
        NodeId(0)
    }
}

/// Builder helper for constructing the virtual tree.
struct TreeBuilder {
    nodes: Vec<VNode>,
    /// Track names used per directory to resolve collisions.
    dir_names: HashMap<usize, HashSet<String>>,
    /// Cache for ensure_dir: (parent_id, name) -> NodeId
    dir_cache: HashMap<(usize, String), NodeId>,
}

impl TreeBuilder {
    fn new() -> Self {
        let root = VNode {
            name: String::new(),
            kind: NodeKind::Directory,
            children: Vec::new(),
            parent: None,
        };
        let mut dir_names = HashMap::new();
        dir_names.insert(0, HashSet::new());
        Self {
            nodes: vec![root],
            dir_names,
            dir_cache: HashMap::new(),
        }
    }

    fn root(&self) -> NodeId {
        NodeId(0)
    }

    /// Add a directory as a child of `parent`. Returns its NodeId.
    fn add_dir(&mut self, name: &str, parent: NodeId) -> NodeId {
        let id = NodeId(self.nodes.len());
        self.nodes.push(VNode {
            name: name.to_string(),
            kind: NodeKind::Directory,
            children: Vec::new(),
            parent: Some(parent),
        });
        self.nodes[parent.0].children.push(id);
        self.dir_names.insert(id.0, HashSet::new());
        self.dir_names
            .entry(parent.0)
            .or_default()
            .insert(name.to_lowercase());
        self.dir_cache
            .insert((parent.0, name.to_lowercase()), id);
        id
    }

    /// Get or create a subdirectory by name under `parent`.
    fn ensure_dir(&mut self, name: &str, parent: NodeId) -> NodeId {
        let key = (parent.0, name.to_lowercase());
        if let Some(&id) = self.dir_cache.get(&key) {
            return id;
        }
        self.add_dir(name, parent)
    }

    /// Add a file node as a child of `parent`, deduplicating names.
    fn add_file(&mut self, name: &str, parent: NodeId, asset_index: usize) {
        let used = self.dir_names.entry(parent.0).or_default();
        let lower = name.to_lowercase();

        let final_name = if !used.contains(&lower) {
            used.insert(lower);
            name.to_string()
        } else {
            // Deduplicate: try _2, _3, etc.
            let (stem, ext) = if let Some(dot_pos) = name.rfind('.') {
                (&name[..dot_pos], &name[dot_pos..])
            } else {
                (name, "")
            };
            let mut n = 2;
            loop {
                let candidate = format!("{}_{}{}", stem, n, ext);
                let cand_lower = candidate.to_lowercase();
                if !used.contains(&cand_lower) {
                    used.insert(cand_lower);
                    break candidate;
                }
                n += 1;
            }
        };

        let id = NodeId(self.nodes.len());
        self.nodes.push(VNode {
            name: final_name,
            kind: NodeKind::File { asset_index },
            children: Vec::new(),
            parent: Some(parent),
        });
        self.nodes[parent.0].children.push(id);
    }

    /// Sort children and build the path index.
    fn finalize(mut self) -> VirtualTree {
        // Sort children by name (case-insensitive)
        let names: Vec<String> = self.nodes.iter().map(|n| n.name.to_lowercase()).collect();
        for node in &mut self.nodes {
            node.children.sort_by(|a, b| names[a.0].cmp(&names[b.0]));
        }

        // Build path index by walking the tree
        let mut path_index = HashMap::new();
        path_index.insert("\\".to_string(), NodeId(0));

        fn walk(
            nodes: &[VNode],
            id: NodeId,
            prefix: &str,
            index: &mut HashMap<String, NodeId>,
        ) {
            for &child_id in &nodes[id.0].children {
                let child = &nodes[child_id.0];
                let path = if prefix == "\\" {
                    format!("\\{}", child.name.to_lowercase())
                } else {
                    format!("{}\\{}", prefix, child.name.to_lowercase())
                };
                index.insert(path.clone(), child_id);
                if child.is_directory() {
                    walk(nodes, child_id, &path, index);
                }
            }
        }

        walk(&self.nodes, NodeId(0), "\\", &mut path_index);

        VirtualTree {
            nodes: self.nodes,
            path_index,
        }
    }
}