//! Search index with frecency-based ranking.
//!
//! This module provides a deduplicated search index where each unique command
//! is stored once, with metadata about all its invocations. This enables:
//!
//! - Efficient fuzzy matching (fewer items to match)
//! - Frecency-based ranking (frequency + recency)
//! - Dynamic filtering by directory, host, session, etc.

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

use atuin_client::history::{History, is_known_agent};
use atuin_client::settings::Search;
use atuin_nucleo::{Injector, Nucleo, pattern};
use dashmap::DashMap;
use lasso::{Spur, ThreadedRodeo};
use time::OffsetDateTime;
use tokio::sync::RwLock;
use tracing::{Level, instrument};
use uuid::Uuid;

use crate::components::search::with_trailing_slash;

/// Parse a UUID string into a 16-byte array.
/// Returns None if the string is not a valid UUID.
fn parse_uuid_bytes(s: &str) -> Option<[u8; 16]> {
    Uuid::parse_str(s).ok().map(|u| *u.as_bytes())
}

/// Format a 16-byte array as a UUID string.
fn format_uuid_bytes(bytes: &[u8; 16]) -> String {
    Uuid::from_bytes(*bytes).to_string()
}

/// Pre-computed frecency data for O(1) lookup.
#[derive(Debug, Clone, Default)]
pub struct FrecencyData {
    /// Total number of times this command was used.
    pub count: u32,
    /// Most recent usage timestamp (unix seconds).
    pub last_used: i64,
}

impl FrecencyData {
    /// Record a new usage of this command.
    pub fn record_use(&mut self, timestamp: i64) {
        self.count += 1;
        if timestamp > self.last_used {
            self.last_used = timestamp;
        }
    }

    /// Compute frecency score based on count and recency.
    ///
    /// Uses a decay function where more recent commands score higher.
    /// The formula balances frequency (how often) with recency (how recent).
    ///
    /// Multipliers allow tuning the relative weights:
    /// - `recency_mul`: Multiplier for recency score (default: 1.0)
    /// - `frequency_mul`: Multiplier for frequency score (default: 1.0)
    ///
    /// A multiplier of 0.0 disables that component, 1.0 is unchanged, 2.0 doubles weight.
    /// Values like 0.5 reduce weight by half, 1.5 increases by 50%, etc.
    #[instrument(level = tracing::Level::TRACE, name = "index_frecency_compute")]
    pub fn compute(&self, now: i64, recency_mul: f64, frequency_mul: f64) -> u32 {
        if self.count == 0 {
            return 0;
        }

        // Time-based decay: score decreases as time passes
        let age_seconds = (now - self.last_used).max(0) as u64;
        let age_hours = age_seconds / 3600;

        // Decay factor: recent commands get higher scores
        // - Last hour: multiplier ~1.0
        // - Last day: multiplier ~0.5
        // - Last week: multiplier ~0.1
        // - Older: multiplier approaches 0
        let recency_score: f64 = match age_hours {
            0 => 100.0,
            1..=6 => 90.0,
            7..=24 => 70.0,
            25..=72 => 50.0,
            73..=168 => 30.0,
            169..=720 => 15.0,
            _ => 5.0,
        };

        // Frequency boost: more uses = higher score (with diminishing returns)
        let frequency_score = ((self.count as f64).ln() * 20.0).min(100.0);

        // Apply multipliers and combine scores, then round to u32
        ((recency_score * recency_mul) + (frequency_score * frequency_mul)).round() as u32
    }
}

/// Data for a unique command.
pub struct CommandData {
    /// History ID of the most recent invocation (16-byte UUID).
    most_recent_id: [u8; 16],
    /// Timestamp of the most recent invocation.
    most_recent_timestamp: i64,
    /// Pre-computed global frecency.
    pub global_frecency: FrecencyData,

    // Pre-computed indexes for O(1) filter lookups
    // Using HashSet instead of DashSet since CommandData lives inside DashMap (already synchronized)
    /// All directories where this command has been run (interned keys).
    directories: HashSet<Spur>,
    /// All hostnames where this command has been run (interned keys).
    hosts: HashSet<Spur>,
    /// All sessions where this command has been run (as 16-byte UUIDs).
    sessions: HashSet<[u8; 16]>,
}

impl CommandData {
    /// Create a new CommandData from a history entry.
    /// Returns None if the history entry has invalid UUIDs.
    pub fn new(history: &History, interner: &ThreadedRodeo) -> Option<Self> {
        let history_id = parse_uuid_bytes(&history.id.0)?;
        let session = parse_uuid_bytes(&history.session)?;
        let timestamp = history.timestamp.unix_timestamp();

        let dir_key = interner.get_or_intern(with_trailing_slash(&history.cwd));
        let host_key = interner.get_or_intern(&history.hostname);

        let mut directories = HashSet::new();
        directories.insert(dir_key);

        let mut hosts = HashSet::new();
        hosts.insert(host_key);

        let mut sessions = HashSet::new();
        sessions.insert(session);

        let mut global_frecency = FrecencyData::default();
        global_frecency.record_use(timestamp);

        Some(Self {
            most_recent_id: history_id,
            most_recent_timestamp: timestamp,
            global_frecency,
            directories,
            hosts,
            sessions,
        })
    }

    /// Add an invocation from a history entry.
    /// Returns false if the history entry has invalid UUIDs.
    pub fn add_invocation(&mut self, history: &History, interner: &ThreadedRodeo) -> bool {
        let Some(history_id) = parse_uuid_bytes(&history.id.0) else {
            return false;
        };
        let Some(session) = parse_uuid_bytes(&history.session) else {
            return false;
        };

        let timestamp = history.timestamp.unix_timestamp();

        // Update global frecency
        self.global_frecency.record_use(timestamp);

        // Update pre-computed indexes for O(1) filter lookups
        let dir_key = interner.get_or_intern(with_trailing_slash(&history.cwd));
        self.directories.insert(dir_key);
        self.hosts.insert(interner.get_or_intern(&history.hostname));
        self.sessions.insert(session);

        // Update most recent if this invocation is newer
        if timestamp > self.most_recent_timestamp {
            self.most_recent_id = history_id;
            self.most_recent_timestamp = timestamp;
        }

        true
    }

    /// Get the most recent history ID for this command.
    pub fn most_recent_id(&self) -> String {
        format_uuid_bytes(&self.most_recent_id)
    }

    /// Check if any invocation matches a directory filter (exact match).
    /// O(1) lookup using pre-computed index.
    pub fn has_invocation_in_dir(&self, dir: &str, interner: &ThreadedRodeo) -> bool {
        interner
            .get(dir)
            .is_some_and(|spur| self.directories.contains(&spur))
    }

    /// Check if any invocation matches a directory prefix (workspace/git root).
    /// O(n) where n = number of unique directories for this command.
    pub fn has_invocation_in_workspace(&self, prefix: &str, interner: &ThreadedRodeo) -> bool {
        self.directories
            .iter()
            .any(|&spur| interner.resolve(&spur).starts_with(prefix))
    }

    /// Check if any invocation matches a hostname.
    /// O(1) lookup using pre-computed index.
    pub fn has_invocation_on_host(&self, hostname: &str, interner: &ThreadedRodeo) -> bool {
        interner
            .get(hostname)
            .is_some_and(|spur| self.hosts.contains(&spur))
    }

    /// Check if any invocation matches a session.
    /// O(1) lookup using pre-computed index.
    pub fn has_invocation_in_session(&self, session: &str) -> bool {
        parse_uuid_bytes(session).is_some_and(|bytes| self.sessions.contains(&bytes))
    }
}

/// Filter mode for search queries.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum IndexFilterMode {
    /// No filtering - search all commands.
    Global,
    /// Filter to commands run in a specific directory.
    Directory(String),
    /// Filter to commands run in a workspace (directory prefix).
    Workspace(String),
    /// Filter to commands run on a specific host.
    Host(String),
    /// Filter to commands run in a specific session.
    Session(String),
}

/// Context for search queries.
#[derive(Debug, Clone, Default)]
pub struct QueryContext {
    pub cwd: Option<String>,
    pub git_root: Option<String>,
    pub hostname: Option<String>,
    pub session_id: Option<String>,
}

/// Shareable frecency map: command -> frecency score.
/// Wrapped in Arc for zero-copy sharing with scorer callbacks.
type FrecencyMap = Arc<HashMap<Arc<str>, u32>>;

/// A deduplicated search index with frecency-based ranking.
///
/// Commands are stored by their text, with metadata about all invocations.
/// Nucleo handles fuzzy matching, while frecency is computed via scorer callback.
///
/// Global frecency is precomputed by a background task and used for scoring.
/// If frecency data is not available, search still works but without frecency ranking;
/// although this should never happen due to precomputing the frecency map.
pub struct SearchIndex {
    /// Map from command text to command data.
    ///
    /// Using `DashMap` for concurrent read/write access, wrapped in `Arc` for sharing with scorer.
    /// Keys are `Arc<str>` to enable zero-copy sharing with frecency_map.
    commands: Arc<DashMap<Arc<str>, CommandData>>,
    /// Nucleo fuzzy matcher - items are command strings.
    nucleo: RwLock<Nucleo<String>>,
    /// Injector for adding new commands to Nucleo.
    injector: Injector<String>,
    /// Precomputed global frecency map. Updated by background task.
    frecency_map: RwLock<Option<FrecencyMap>>,
    /// String interner for deduplicating cwd, hostname, and directory paths.
    interner: Arc<ThreadedRodeo>,
}

impl SearchIndex {
    /// Create a new empty search index.
    pub fn new() -> Self {
        let nucleo_config = atuin_nucleo::Config::DEFAULT;
        // Single column for command text
        let nucleo = Nucleo::<String>::new(nucleo_config, Arc::new(|| {}), None, 1);
        let injector = nucleo.injector();

        Self {
            commands: Arc::new(DashMap::new()),
            nucleo: RwLock::new(nucleo),
            injector,
            frecency_map: RwLock::new(None),
            interner: Arc::new(ThreadedRodeo::new()),
        }
    }

    /// Add a history entry to the index.
    ///
    /// If the command already exists, updates its invocation data.
    /// If it's a new command, adds it to both the map and Nucleo.
    pub fn add_history(&self, history: &History) {
        if is_known_agent(&history.author) {
            return;
        }

        let command = history.command.as_str();

        // DashMap with Arc<str> keys can be looked up with &str via Borrow trait
        if let Some(mut entry) = self.commands.get_mut(command) {
            // Existing command - just update invocations
            entry.add_invocation(history, &self.interner);
        } else {
            // New command - create Arc<str> once and share it
            let Some(data) = CommandData::new(history, &self.interner) else {
                return; // Invalid UUIDs, skip this entry
            };
            let command_arc: Arc<str> = command.into();
            self.commands.insert(Arc::clone(&command_arc), data);
            // Nucleo still needs String (unavoidable copy for fuzzy matching)
            self.injector.push(command_arc.to_string(), |cmd, cols| {
                cols[0] = cmd.clone().into();
            });
        }
        // Note: frecency_map is rebuilt by background task, not invalidated here
    }

    /// Add multiple history entries to the index.
    pub fn add_histories(&self, histories: &[History]) {
        for history in histories {
            self.add_history(history);
        }
    }

    /// Get the number of unique commands in the index.
    pub fn command_count(&self) -> usize {
        self.commands.len()
    }

    /// Get the number of items in Nucleo (should match command_count).
    pub async fn nucleo_item_count(&self) -> u32 {
        self.nucleo.read().await.snapshot().item_count()
    }

    /// Search for commands matching a query.
    ///
    /// Returns a list of history IDs (most recent invocation per command).
    /// Uses precomputed global frecency for scoring if available.
    #[instrument(skip_all, level = tracing::Level::TRACE, name = "index_search", fields(query = %query))]
    pub async fn search(
        &self,
        query: &str,
        filter_mode: IndexFilterMode,
        _context: &QueryContext,
        limit: u32,
    ) -> Vec<String> {
        let mut nucleo = self.nucleo.write().await;

        // Get precomputed frecency map (may be None if not yet computed)
        let frecency_map = self.frecency_map.read().await.clone();

        // Build filter based on mode
        let filter = self.build_filter(&filter_mode);
        nucleo.set_filter(filter);

        // Build scorer from precomputed frecency (or None if not available)
        let scorer = Self::build_scorer(frecency_map);
        nucleo.set_scorer(scorer);

        // Update pattern
        nucleo.pattern.reparse(
            0,
            query,
            pattern::CaseMatching::Smart,
            pattern::Normalization::Smart,
            false,
        );

        tracing::span!(Level::TRACE, "index_search_tick").in_scope(|| {
            // Tick until complete
            while nucleo.tick(10).running {}
        });

        // Collect results
        let snapshot = nucleo.snapshot();
        let matched_count = snapshot.matched_item_count().min(limit);

        tracing::span!(Level::TRACE, "index_search_results").in_scope(|| {
            snapshot
                .matched_items(..matched_count)
                .filter_map(|item| {
                    let cmd = item.data;
                    // DashMap<Arc<str>, _>::get accepts &str via Borrow trait
                    self.commands
                        .get(cmd.as_str())
                        .map(|data| data.most_recent_id())
                })
                .collect()
        })
    }

    /// Rebuild the global frecency map.
    ///
    /// This should be called by a background task periodically.
    /// The map is used for scoring search results.
    ///
    /// Uses multipliers from search settings:
    /// - `recency_score_multiplier`: Weight for recency component
    /// - `frequency_score_multiplier`: Weight for frequency component
    /// - `frecency_score_multiplier`: Overall multiplier for final score
    #[instrument(skip_all, level = tracing::Level::DEBUG, name = "rebuild_frecency")]
    pub async fn rebuild_frecency(&self, search_settings: &Search) {
        let now = OffsetDateTime::now_utc().unix_timestamp();
        let mut frecency_map: HashMap<Arc<str>, u32> = HashMap::new();

        // Clamp multipliers to non-negative values to prevent broken frecency ranking
        // (negative values would produce unexpected results when cast to u32)
        let recency_mul = search_settings.recency_score_multiplier.max(0.0);
        let frequency_mul = search_settings.frequency_score_multiplier.max(0.0);
        let frecency_mul = search_settings.frecency_score_multiplier.max(0.0);

        for entry in self.commands.iter() {
            let frecency = entry
                .global_frecency
                .compute(now, recency_mul, frequency_mul);
            // Apply overall frecency multiplier and round to u32
            let frecency = (frecency as f64 * frecency_mul).round() as u32;
            // Arc::clone is cheap - just increments reference count
            frecency_map.insert(Arc::clone(entry.key()), frecency);
        }

        *self.frecency_map.write().await = Some(Arc::new(frecency_map));
    }

    /// Build filter predicate for the given mode.
    fn build_filter(&self, mode: &IndexFilterMode) -> Option<atuin_nucleo::Filter<String>> {
        // For Global mode, no filter needed
        if matches!(mode, IndexFilterMode::Global) {
            return None;
        }

        // Pre-compute which commands pass the filter
        // Use HashSet<String> for the short-lived filter (simpler than Arc lookup)
        let passing_commands: Arc<HashSet<String>> = {
            let mut set = HashSet::new();
            for entry in self.commands.iter() {
                let passes = match mode {
                    IndexFilterMode::Global => unreachable!(),
                    IndexFilterMode::Directory(dir) => {
                        entry.has_invocation_in_dir(dir, &self.interner)
                    }
                    IndexFilterMode::Workspace(prefix) => {
                        entry.has_invocation_in_workspace(prefix, &self.interner)
                    }
                    IndexFilterMode::Host(hostname) => {
                        entry.has_invocation_on_host(hostname, &self.interner)
                    }
                    IndexFilterMode::Session(session) => entry.has_invocation_in_session(session),
                };
                if passes {
                    // Convert Arc<str> to String for filter lookup
                    set.insert(entry.key().to_string());
                }
            }
            Arc::new(set)
        };

        Some(Arc::new(move |cmd: &String| passing_commands.contains(cmd)))
    }

    /// Build scorer from precomputed frecency map.
    ///
    /// Returns None if frecency map is not available (search still works, just without frecency ranking).
    fn build_scorer(frecency_map: Option<FrecencyMap>) -> Option<atuin_nucleo::Scorer<String>> {
        let map = frecency_map?;
        Some(Arc::new(move |cmd: &String, fuzzy_score: u32| {
            // HashMap<Arc<str>, _>::get accepts &str via Borrow trait
            let frecency = map.get(cmd.as_str()).copied().unwrap_or(0);
            fuzzy_score + frecency
        }))
    }
}

impl Default for SearchIndex {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use time::macros::datetime;

    fn make_history(command: &str, cwd: &str, timestamp: OffsetDateTime) -> History {
        History::import()
            .timestamp(timestamp)
            .command(command)
            .cwd(cwd)
            .build()
            .into()
    }

    #[test]
    fn frecency_data_compute() {
        let now = 1000000i64;

        // Recent command (with default multipliers of 1.0)
        let recent = FrecencyData {
            count: 5,
            last_used: now - 60, // 1 minute ago
        };
        assert!(recent.compute(now, 1.0, 1.0) > 100); // High score

        // Old command
        let old = FrecencyData {
            count: 5,
            last_used: now - 86400 * 30, // 30 days ago
        };
        assert!(old.compute(now, 1.0, 1.0) < recent.compute(now, 1.0, 1.0));

        // Frequently used old command
        let frequent_old = FrecencyData {
            count: 100,
            last_used: now - 86400 * 7, // 1 week ago
        };
        // Should still have decent score due to frequency
        assert!(frequent_old.compute(now, 1.0, 1.0) > 50);
    }

    #[test]
    fn frecency_data_compute_with_multipliers() {
        let now = 1000000i64;

        let data = FrecencyData {
            count: 5,
            last_used: now - 60, // 1 minute ago (recency_score = 100)
        };

        // Default multipliers (1.0, 1.0)
        let default_score = data.compute(now, 1.0, 1.0);

        // Double recency weight
        let double_recency = data.compute(now, 2.0, 1.0);
        assert!(double_recency > default_score);

        // Double frequency weight
        let double_frequency = data.compute(now, 1.0, 2.0);
        assert!(double_frequency > default_score);

        // Zero out recency (only frequency counts)
        let no_recency = data.compute(now, 0.0, 1.0);
        assert!(no_recency < default_score);

        // Zero out frequency (only recency counts)
        let no_frequency = data.compute(now, 1.0, 0.0);
        assert!(no_frequency < default_score);

        // Zero both (should be zero)
        let no_score = data.compute(now, 0.0, 0.0);
        assert_eq!(no_score, 0);

        // Fractional multipliers
        let half_recency = data.compute(now, 0.5, 1.0);
        assert!(half_recency < default_score);
        assert!(half_recency > no_recency);

        // 1.5x multiplier
        let boost_recency = data.compute(now, 1.5, 1.0);
        assert!(boost_recency > default_score);
        assert!(boost_recency < double_recency);
    }

    #[test]
    fn command_data_add_invocation() {
        let interner = ThreadedRodeo::new();

        let (dir1, dir2) = if cfg!(windows) {
            ("C:\\Users\\User\\project", "C:\\Users\\User\\other")
        } else {
            ("/home/user/project", "/home/user/other")
        };

        let history1 = make_history("git status", dir1, datetime!(2024-01-01 10:00 UTC));
        let history2 = make_history("git status", dir2, datetime!(2024-01-01 12:00 UTC));

        let mut data = CommandData::new(&history1, &interner).unwrap();
        assert_eq!(data.global_frecency.count, 1);
        let id1 = data.most_recent_id();

        data.add_invocation(&history2, &interner);
        assert_eq!(data.global_frecency.count, 2);

        // Most recent ID should update to history2 (newer timestamp)
        let id2 = data.most_recent_id();
        assert_ne!(id1, id2);
    }

    #[test]
    fn command_data_filters() {
        let interner = ThreadedRodeo::new();

        let (dir1, dir2) = if cfg!(windows) {
            ("C:\\Users\\User\\project", "C:\\Users\\User\\other")
        } else {
            ("/home/user/project", "/home/user/other")
        };

        let h1 = make_history("git status", dir1, datetime!(2024-01-01 10:00 UTC));
        let h2 = make_history("git status", dir2, datetime!(2024-01-01 12:00 UTC));

        let mut data = CommandData::new(&h1, &interner).unwrap();
        data.add_invocation(&h2, &interner);

        let (check1, check2, check3) = if cfg!(windows) {
            (
                with_trailing_slash("C:\\Users\\User\\project"),
                with_trailing_slash("C:\\Users\\User\\other"),
                with_trailing_slash("C:\\Users\\User\\missing"),
            )
        } else {
            (
                with_trailing_slash("/home/user/project"),
                with_trailing_slash("/home/user/other"),
                with_trailing_slash("/home/user/missing"),
            )
        };

        assert!(data.has_invocation_in_dir(&check1, &interner));
        assert!(data.has_invocation_in_dir(&check2, &interner));
        assert!(!data.has_invocation_in_dir(&check3, &interner));

        let (check1, check2, check3) = if cfg!(windows) {
            (
                with_trailing_slash("C:\\Users\\User"),
                with_trailing_slash("C:\\Users"),
                with_trailing_slash("C:\\Users\\User\\var"),
            )
        } else {
            (
                with_trailing_slash("/home/user"),
                with_trailing_slash("/home"),
                with_trailing_slash("/var"),
            )
        };

        assert!(data.has_invocation_in_workspace(&check1, &interner));
        assert!(data.has_invocation_in_workspace(&check2, &interner));
        assert!(!data.has_invocation_in_workspace(&check3, &interner));
    }

    #[tokio::test]
    async fn search_index_add_and_search() {
        let index = SearchIndex::new();

        let h1 = make_history(
            "git status",
            "/home/user/project",
            datetime!(2024-01-01 10:00 UTC),
        );
        let h2 = make_history(
            "git commit -m 'test'",
            "/home/user/project",
            datetime!(2024-01-01 10:05 UTC),
        );
        let h3 = make_history(
            "ls -la",
            "/home/user/other",
            datetime!(2024-01-01 10:10 UTC),
        );

        index.add_history(&h1);
        index.add_history(&h2);
        index.add_history(&h3);

        assert_eq!(index.command_count(), 3);

        // Search for "git" - should match 2 commands
        let results = index
            .search("git", IndexFilterMode::Global, &QueryContext::default(), 10)
            .await;
        assert_eq!(results.len(), 2);

        // Search with directory filter
        let results = index
            .search(
                "",
                IndexFilterMode::Directory(with_trailing_slash("/home/user/project")),
                &QueryContext::default(),
                10,
            )
            .await;
        assert_eq!(results.len(), 2); // git status and git commit
    }
}
