//! An in-memory index of the files we share with other peers.
//!
//! Scanning a directory produces a read-only [`Shares`] snapshot keyed by the
//! peer-facing *virtual path* (the shared directory's own name followed by the
//! backslash-separated relative path, matching the Soulseek wire convention).

use std::collections::{HashMap, HashSet};
use std::io;
use std::path::{Path, PathBuf};

/// One shared file: its peer-facing virtual path and where it lives on disk.
#[derive(Debug, Clone)]
pub struct SharedFile {
    /// Backslash-separated path exposed to peers, e.g. `music\album\song.mp3`.
    pub virtual_path: String,
    /// `virtual_path` lowercased once at scan time, so answering a search does
    /// not lowercase every shared path again.
    search_key: String,
    /// The real filesystem path used to serve the bytes.
    pub real_path: PathBuf,
    pub size: u64,
    /// Optional `(code, value)` audio attributes (empty for now).
    pub attributes: Vec<(u32, u32)>,
}

/// A read-only snapshot of the shared files, cheap to clone behind an `Arc`.
#[derive(Debug, Default)]
pub struct Shares {
    files: Vec<SharedFile>,
    by_virtual: HashMap<String, usize>,
    folder_count: usize,
}

impl Shares {
    /// An empty share set (nothing shared).
    #[must_use]
    pub fn empty() -> Self {
        Self::default()
    }

    /// Scan `root` recursively into a share index. Symlinks and unreadable
    /// entries are skipped so a single bad entry never aborts the scan.
    ///
    /// # Errors
    /// Returns an error only if `root` itself cannot be read.
    pub fn scan(root: &Path) -> io::Result<Self> {
        // Fail fast if the root is unreadable; deeper failures are skipped.
        let _ = std::fs::read_dir(root)?;

        Ok(Self::scan_many(&[root.to_path_buf()]))
    }

    /// Scan several roots into one merged index. Unreadable roots are
    /// skipped (with a log line) instead of failing the whole scan, and
    /// roots that share a directory name get a ` (2)`, ` (3)`… suffix so
    /// their virtual paths cannot collide.
    #[must_use]
    pub fn scan_many(roots: &[PathBuf]) -> Self {
        let mut files = Vec::new();
        let mut folder_count = 0;
        let mut name_uses: HashMap<String, u32> = HashMap::new();

        for root in roots {
            if std::fs::read_dir(root).is_err() {
                crate::warn!(
                    "Skipping unreadable shared directory {}",
                    root.display()
                );
                continue;
            }
            let base = root_display_name(root);
            let uses = name_uses.entry(base.clone()).or_insert(0);
            *uses += 1;
            let name = if *uses == 1 {
                base
            } else {
                format!("{base} ({uses})")
            };
            scan_root(root, &name, &mut files, &mut folder_count);
        }

        Self::from_files(files, folder_count)
    }

    fn from_files(files: Vec<SharedFile>, folder_count: usize) -> Self {
        let by_virtual = files
            .iter()
            .enumerate()
            .map(|(i, f)| (f.virtual_path.clone(), i))
            .collect();
        Self {
            files,
            by_virtual,
            folder_count,
        }
    }

    /// Files whose virtual path contains *every* whitespace-separated term of
    /// `query` (case-insensitive). An empty query matches nothing.
    #[must_use]
    pub fn search(&self, query: &str) -> Vec<&SharedFile> {
        let terms: Vec<String> = query
            .to_lowercase()
            .split_whitespace()
            .map(String::from)
            .collect();
        if terms.is_empty() {
            return Vec::new();
        }
        self.files
            .iter()
            .filter(|f| terms.iter().all(|t| f.search_key.contains(t.as_str())))
            .collect()
    }

    /// Look up a shared file by its exact virtual path.
    #[must_use]
    pub fn get(&self, virtual_path: &str) -> Option<&SharedFile> {
        self.by_virtual.get(virtual_path).map(|&i| &self.files[i])
    }

    /// All shared files, in scan order.
    #[must_use]
    pub fn files(&self) -> &[SharedFile] {
        &self.files
    }

    /// Files grouped by their virtual directory (everything before the final
    /// backslash), as `(directory, [(basename, size)])`. Used to build a
    /// SharedFileListResponse.
    #[must_use]
    pub fn directories(&self) -> Vec<(String, Vec<(String, u64)>)> {
        let mut by_dir: std::collections::BTreeMap<String, Vec<(String, u64)>> =
            std::collections::BTreeMap::new();
        for file in &self.files {
            let (dir, base) = file
                .virtual_path
                .rsplit_once('\\')
                .unwrap_or(("", file.virtual_path.as_str()));
            by_dir
                .entry(dir.to_string())
                .or_default()
                .push((base.to_string(), file.size));
        }
        by_dir.into_iter().collect()
    }

    #[must_use]
    pub const fn file_count(&self) -> u32 {
        self.files.len() as u32
    }

    #[must_use]
    pub const fn folder_count(&self) -> u32 {
        self.folder_count as u32
    }
}

fn root_display_name(root: &Path) -> String {
    root.file_name().map_or_else(
        || "shared".to_string(),
        |n| n.to_string_lossy().into_owned(),
    )
}

/// Recursively walk `root`, appending its files (under the virtual root name
/// `root_name`) to `files` and counting folders that contain files.
fn scan_root(
    root: &Path,
    root_name: &str,
    files: &mut Vec<SharedFile>,
    folder_count: &mut usize,
) {
    let mut folders_with_files: HashSet<PathBuf> = HashSet::new();
    let mut stack = vec![root.to_path_buf()];

    while let Some(dir) = stack.pop() {
        let Ok(entries) = std::fs::read_dir(&dir) else {
            continue;
        };
        for entry in entries.flatten() {
            let Ok(meta) = entry.metadata() else {
                continue;
            };
            // `entry.metadata()` does not traverse the symlink itself.
            if meta.file_type().is_symlink() {
                continue;
            }
            let path = entry.path();
            if meta.is_dir() {
                stack.push(path);
            } else if meta.is_file() {
                // The download directory is usually shared too; an in-progress
                // `.part` file is not something to offer other peers.
                if path
                    .to_string_lossy()
                    .ends_with(crate::utils::path::PART_SUFFIX)
                {
                    continue;
                }
                let virtual_path = virtual_path_for(root_name, root, &path);
                files.push(SharedFile {
                    search_key: virtual_path.to_lowercase(),
                    virtual_path,
                    real_path: path,
                    size: meta.len(),
                    attributes: Vec::new(),
                });
                folders_with_files.insert(dir.clone());
            }
        }
    }
    *folder_count += folders_with_files.len();
}

/// Build the peer-facing virtual path for `path` under `root`: the root's own
/// name followed by the backslash-separated components relative to it.
fn virtual_path_for(root_name: &str, root: &Path, path: &Path) -> String {
    let rel = path.strip_prefix(root).unwrap_or(path);
    let mut parts = vec![root_name.to_string()];
    for component in rel.components() {
        parts.push(component.as_os_str().to_string_lossy().into_owned());
    }
    parts.join("\\")
}

#[cfg(test)]
mod tests {
    use super::Shares;

    fn temp_tree() -> std::path::PathBuf {
        use std::sync::atomic::{AtomicU32, Ordering};
        static COUNTER: AtomicU32 = AtomicU32::new(0);
        let n = COUNTER.fetch_add(1, Ordering::Relaxed);
        let root = std::env::temp_dir()
            .join(format!("soulseek-shares-{}-{n}", std::process::id()));
        let _ = std::fs::remove_dir_all(&root);
        std::fs::create_dir_all(root.join("album")).unwrap();
        std::fs::write(root.join("top.mp3"), b"aaaa").unwrap();
        std::fs::write(root.join("album").join("song one.flac"), b"bbbbbb")
            .unwrap();
        std::fs::write(root.join("album").join("song two.flac"), b"cc")
            .unwrap();
        root
    }

    #[test]
    fn scan_counts_files_and_folders() {
        let root = temp_tree();
        let shares = Shares::scan(&root).unwrap();
        assert_eq!(shares.file_count(), 3);
        // Two folders contain files: the root and `album`.
        assert_eq!(shares.folder_count(), 2);
        let _ = std::fs::remove_dir_all(root);
    }

    #[test]
    fn in_progress_downloads_are_not_shared() {
        let root = temp_tree();
        std::fs::write(root.join("half.mp3.part"), b"dd").unwrap();

        let shares = Shares::scan(&root).unwrap();
        assert_eq!(shares.file_count(), 3, ".part files stay out of the index");
        let base = root.file_name().unwrap().to_string_lossy().into_owned();
        assert!(shares.get(&format!("{base}\\half.mp3.part")).is_none());
        let _ = std::fs::remove_dir_all(root);
    }

    #[test]
    fn nested_files_use_backslash_virtual_paths() {
        let root = temp_tree();
        let base = root.file_name().unwrap().to_string_lossy().into_owned();
        let shares = Shares::scan(&root).unwrap();

        let vpath = format!("{base}\\album\\song one.flac");
        let file = shares.get(&vpath).expect("nested file indexed");
        assert_eq!(file.size, 6);
        assert!(shares.get("does\\not\\exist").is_none());
        let _ = std::fs::remove_dir_all(root);
    }

    #[test]
    fn a_mixed_case_path_matches_a_lowercase_query() {
        let root = std::env::temp_dir()
            .join(format!("soulseek-shares-case-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&root);
        std::fs::create_dir_all(root.join("Live Set")).unwrap();
        std::fs::write(root.join("Live Set").join("Opening TRACK.flac"), b"x")
            .unwrap();
        let shares = Shares::scan(&root).unwrap();

        assert_eq!(shares.search("live opening track").len(), 1);
        let _ = std::fs::remove_dir_all(root);
    }

    #[test]
    fn search_is_case_insensitive_and_multi_term_and() {
        let root = temp_tree();
        let shares = Shares::scan(&root).unwrap();

        // Both album files match "SONG"; "song one" narrows to one.
        assert_eq!(shares.search("SONG").len(), 2);
        assert_eq!(shares.search("song ONE").len(), 1);
        assert!(shares.search("nonexistent").is_empty());
        assert!(shares.search("").is_empty());
        let _ = std::fs::remove_dir_all(root);
    }

    #[test]
    fn scan_many_merges_roots() {
        let root_a = temp_tree();
        let root_b = temp_tree();
        let shares = Shares::scan_many(&[root_a.clone(), root_b.clone()]);
        assert_eq!(shares.file_count(), 6);
        assert_eq!(shares.folder_count(), 4);
        // Files from both roots are reachable under their root's name.
        let name_a = root_a.file_name().unwrap().to_string_lossy();
        let name_b = root_b.file_name().unwrap().to_string_lossy();
        assert!(shares.get(&format!("{name_a}\\top.mp3")).is_some());
        assert!(shares.get(&format!("{name_b}\\top.mp3")).is_some());
        let _ = std::fs::remove_dir_all(root_a);
        let _ = std::fs::remove_dir_all(root_b);
    }

    #[test]
    fn scan_many_disambiguates_equal_root_names() {
        // Two different directories both named "music".
        let parent_a = temp_tree();
        let parent_b = temp_tree();
        let music_a = parent_a.join("music");
        let music_b = parent_b.join("music");
        std::fs::create_dir_all(&music_a).unwrap();
        std::fs::create_dir_all(&music_b).unwrap();
        std::fs::write(music_a.join("a.mp3"), b"a").unwrap();
        std::fs::write(music_b.join("b.mp3"), b"b").unwrap();

        let shares = Shares::scan_many(&[music_a, music_b]);
        assert!(shares.get("music\\a.mp3").is_some());
        assert!(
            shares.get("music (2)\\b.mp3").is_some(),
            "second root with the same name gets a numbered suffix"
        );
        let _ = std::fs::remove_dir_all(parent_a);
        let _ = std::fs::remove_dir_all(parent_b);
    }

    #[test]
    fn scan_many_skips_unreadable_roots() {
        let root = temp_tree();
        let shares = Shares::scan_many(&[
            std::path::PathBuf::from("/does/not/exist"),
            root.clone(),
        ]);
        assert_eq!(shares.file_count(), 3);
        let _ = std::fs::remove_dir_all(root);
    }

    #[test]
    fn empty_shares_have_no_files_or_folders() {
        let shares = Shares::empty();
        assert_eq!(shares.file_count(), 0);
        assert_eq!(shares.folder_count(), 0);
        assert!(shares.search("anything").is_empty());
    }
}