//! SystemNameIndex — Aho-Corasick automaton for event-driven pre-generation (D-206).
//!
//! Loaded once at startup from `systems.db`. Scans NPC dialogue and news ticker
//! text; any match names a body_id to enqueue for background generation at Low
//! priority (D-206 §event-driven pre-generation).
//!
//! The automaton is case-insensitive and matches overlapping patterns so that
//! "New Chengdu" and "Chengdu" both fire independently when present.

use std::path::Path;

use aho_corasick::{AhoCorasick, AhoCorasickBuilder, MatchKind};
use bevy_ecs::prelude::*;
use rusqlite::{Connection, OpenFlags};

// ---------------------------------------------------------------------------
// Public types
// ---------------------------------------------------------------------------

/// A single match returned by [`SystemNameIndex::scan`].
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct NameMatch {
    /// The `body_id` (or `system_id`) that was matched.
    pub id: String,
    /// The matched text span (byte offsets into the input string).
    pub start: usize,
    pub end: usize,
}

// ---------------------------------------------------------------------------
// Resource
// ---------------------------------------------------------------------------

/// Aho-Corasick automaton over all body/system/station proper names in systems.db.
///
/// Built once from the DB at startup; immutable thereafter.
/// All queries are `O(n)` in the length of the scanned text regardless of
/// how many names the automaton holds.
///
/// Returned IDs are body_ids for bodies/stations, or system_ids for star systems
/// that have no body entries. The caller (background generation queue, D-206)
/// decides which IDs are actionable.
#[derive(Resource)]
pub struct SystemNameIndex {
    automaton: AhoCorasick,
    /// Maps automaton pattern index → the body_id / system_id it represents.
    ids: Vec<String>,
}

impl SystemNameIndex {
    /// Build the index from `systems.db` at `path`.
    ///
    /// Loads proper names from `bodies`, `stations`, and `star_systems`.
    /// Returns `None` on DB open failure (logged at warn level; the game
    /// runs without the index, just without event-driven pre-generation).
    pub fn load(path: &Path) -> Option<Self> {
        let conn = match Connection::open_with_flags(path, OpenFlags::SQLITE_OPEN_READ_ONLY) {
            Ok(c) => c,
            Err(e) => {
                tracing::warn!(path = %path.display(), error = %e, "SystemNameIndex: failed to open systems.db");
                return None;
            }
        };

        let entries = match collect_names(&conn) {
            Ok(e) => e,
            Err(e) => {
                tracing::warn!(error = %e, "SystemNameIndex: failed to collect names");
                return None;
            }
        };

        if entries.is_empty() {
            tracing::warn!("SystemNameIndex: no names found in systems.db — index empty");
        }

        let (patterns, ids): (Vec<String>, Vec<String>) = entries.into_iter().unzip();

        let automaton = match AhoCorasickBuilder::new()
            .ascii_case_insensitive(true)
            .match_kind(MatchKind::LeftmostFirst)
            .build(&patterns)
        {
            Ok(a) => a,
            Err(e) => {
                tracing::error!(error = %e, "SystemNameIndex: automaton build failed — index unavailable");
                return None;
            }
        };

        tracing::info!(pattern_count = ids.len(), "SystemNameIndex built");
        Some(Self { automaton, ids })
    }

    /// Scan `text` and return all name matches.
    ///
    /// Each match carries the body_id / system_id and the byte span.
    /// Overlapping matches are not reported (leftmost-first wins per AhoCorasick
    /// `MatchKind::LeftmostFirst`).
    pub fn scan(&self, text: &str) -> Vec<NameMatch> {
        self.automaton
            .find_iter(text)
            .map(|m| NameMatch {
                id: self.ids[m.pattern().as_usize()].clone(),
                start: m.start(),
                end: m.end(),
            })
            .collect()
    }

    /// How many patterns the automaton holds (for diagnostics).
    pub fn pattern_count(&self) -> usize {
        self.ids.len()
    }
}

// ---------------------------------------------------------------------------
// DB helpers
// ---------------------------------------------------------------------------

fn collect_names(conn: &Connection) -> rusqlite::Result<Vec<(String, String)>> {
    let mut entries: Vec<(String, String)> = Vec::new();

    // Bodies — use proper_name only (body_id like "GJ-15Ab" is not natural language)
    {
        let mut stmt = conn.prepare(
            "SELECT body_id, proper_name FROM bodies WHERE proper_name IS NOT NULL AND proper_name != ''",
        )?;
        let rows = stmt.query_map([], |row| {
            Ok((row.get::<_, String>(1)?, row.get::<_, String>(0)?))
        })?;
        for row in rows {
            entries.push(row?);
        }
    }

    // Stations
    {
        let mut stmt = conn.prepare(
            "SELECT station_id, proper_name FROM stations WHERE proper_name IS NOT NULL AND proper_name != ''",
        )?;
        let rows = stmt.query_map([], |row| {
            Ok((row.get::<_, String>(1)?, row.get::<_, String>(0)?))
        })?;
        for row in rows {
            entries.push(row?);
        }
    }

    // Star systems — include both system_name and proper_name as separate patterns
    // so "Van Maanen's Star" and "GJ 35" both trigger if used in dialogue.
    {
        let mut stmt =
            conn.prepare("SELECT system_id, system_name, proper_name FROM star_systems")?;
        let rows = stmt.query_map([], |row| {
            Ok((
                row.get::<_, String>(0)?,
                row.get::<_, Option<String>>(1)?,
                row.get::<_, Option<String>>(2)?,
            ))
        })?;
        for row in rows {
            let (system_id, system_name, proper_name) = row?;
            if let Some(name) = system_name {
                if !name.is_empty() {
                    entries.push((name, system_id.clone()));
                }
            }
            if let Some(name) = proper_name {
                if !name.is_empty() {
                    entries.push((name, system_id.clone()));
                }
            }
        }
    }

    Ok(entries)
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;
    use aho_corasick::{AhoCorasick, AhoCorasickBuilder, MatchKind};

    /// Build a minimal index directly (no DB) for unit testing.
    fn make_index(pairs: &[(&str, &str)]) -> SystemNameIndex {
        let (patterns, ids): (Vec<&str>, Vec<String>) =
            pairs.iter().map(|(p, id)| (*p, id.to_string())).unzip();
        let automaton = AhoCorasickBuilder::new()
            .ascii_case_insensitive(true)
            .match_kind(MatchKind::LeftmostFirst)
            .build(&patterns)
            .unwrap();
        SystemNameIndex { automaton, ids }
    }

    #[test]
    fn scan_finds_exact_match() {
        let idx = make_index(&[("Xin Chengdu", "GJ-380c")]);
        let matches = idx.scan("The freighter docked at Xin Chengdu yesterday.");
        assert_eq!(matches.len(), 1);
        assert_eq!(matches[0].id, "GJ-380c");
    }

    #[test]
    fn scan_is_case_insensitive() {
        let idx = make_index(&[("Horizon Station", "GJ-380-oort-S1")]);
        let matches = idx.scan("HORIZON STATION cargo rates up 12%.");
        assert_eq!(matches.len(), 1);
        assert_eq!(matches[0].id, "GJ-380-oort-S1");
    }

    #[test]
    fn scan_returns_empty_on_no_match() {
        let idx = make_index(&[("Xin Chengdu", "GJ-380c")]);
        let matches = idx.scan("Nothing here matches.");
        assert!(matches.is_empty());
    }

    #[test]
    fn scan_returns_multiple_distinct_matches() {
        let idx = make_index(&[
            ("Xin Chengdu", "GJ-380c"),
            ("Horizon Station", "GJ-380-oort-S1"),
        ]);
        let text = "Xin Chengdu imports from Horizon Station.";
        let matches = idx.scan(text);
        assert_eq!(matches.len(), 2);
        let ids: Vec<&str> = matches.iter().map(|m| m.id.as_str()).collect();
        assert!(ids.contains(&"GJ-380c"));
        assert!(ids.contains(&"GJ-380-oort-S1"));
    }

    #[test]
    fn scan_span_is_correct() {
        let idx = make_index(&[("Chengdu", "GJ-380c")]);
        let text = "0123456Chengdu rest";
        let matches = idx.scan(text);
        assert_eq!(matches.len(), 1);
        assert_eq!(matches[0].start, 7);
        assert_eq!(matches[0].end, 14);
        assert_eq!(&text[matches[0].start..matches[0].end], "Chengdu");
    }

    #[test]
    fn empty_index_scans_without_panic() {
        let idx = make_index(&[]);
        let matches = idx.scan("Any text at all.");
        assert!(matches.is_empty());
    }

    #[test]
    fn pattern_count_matches_entries() {
        let idx = make_index(&[("Alpha", "sys-1"), ("Beta", "sys-2"), ("Gamma", "sys-3")]);
        assert_eq!(idx.pattern_count(), 3);
    }
}