//! Whole-ship assembly from XBG7 part families.
//!
//! Project Sylpheed's capital ships are never stored as a single mesh. A ship is
//! modelled, then **split into destructible parts** — hull segments, bridge,
//! engines, integral turrets — each shipped as its own XBG7 resource inside a
//! `hidden/resource3d/Stage_SNN.xpr` container. The split lets the game hide a
//! part when the player destroys it (bridge, shield generator, thruster) and swap
//! in a `_break` variant.
//!
//! Each part's vertices are authored around the origin; the world placement lives
//! in the **primary composite scene graph** `e_rou_<id>` (see [`assemble_ship`]).
//! Its node hierarchy (`rou_<id>_root`→`…_front`/`…_rear`→`rou_<id>_bdy_NN`) names
//! the separate hull resources and carries their world TRS — the cross-resource
//! analogue of how [`mesh::node_transforms`] poses one model's sub-parts. The
//! `GN_*` nodes in the same composite are the Vessel hardpoint frames (bridge /
//! shield / engine / turret mounts, matching the IDXD recipe `Frame` names).
//!
//! Resource naming (learned from the retail stage containers):
//! - `<id>` is `[a-z]NNN` (`e106`, `f105`, `n050`). The leading letter is the
//!   faction: `e` = ADAN (enemy), `f` = TCAF (player side), `n` = neutral /
//!   structures / debris.
//! - A base part is `<id>_<name>` (`e106_bdy_01`, `e106_brg_01`, `f105_sld_02`).
//! - `_l` / `_m` / `_d`(`NN`) suffixes are lower level-of-detail copies; `_bNN` /
//!   `_dead` / `_break` are destruction geometry; `_joint` / `_open` / `_Near` are
//!   logic/animation nodes. All are skipped.
//! - `e_rou_<id>` is the primary composite; `e_rou_<id>_eng` / `_wep_*` are LOCAL
//!   detail rigs (their nodes are in their own frame, not ship-space) and are NOT
//!   used for placement.

use crate::mesh::{scene_world_nodes, xbg7_resource_names, ScenePart};
use std::collections::HashSet;

/// Which side a ship belongs to, from the first letter of its resource id.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Faction {
    /// `e…` — ADAN (the enemy).
    Adan,
    /// `f…` — TCAF (the player's coalition).
    Tcaf,
    /// `n…` — neutral: stations, structures, asteroids, debris.
    Neutral,
    /// Anything else (`j…`, `s…`, …).
    Other,
}

impl Faction {
    fn from_id(id: &str) -> Faction {
        match id.as_bytes().first() {
            Some(b'e') => Faction::Adan,
            Some(b'f') => Faction::Tcaf,
            Some(b'n') => Faction::Neutral,
            _ => Faction::Other,
        }
    }

    /// Short human label.
    pub fn label(self) -> &'static str {
        match self {
            Faction::Adan => "ADAN",
            Faction::Tcaf => "TCAF",
            Faction::Neutral => "Neutral",
            Faction::Other => "Other",
        }
    }
}

/// A ship reconstructed from one XBG7 part family in a stage container.
#[derive(Debug, Clone)]
pub struct ShipModel {
    /// The family id, e.g. `e106` — matches a [`crate::game_data::Vessel`] whose
    /// `model` is `rou_e106`.
    pub id: String,
    /// Faction inferred from the id's leading letter.
    pub faction: Faction,
    /// Base geometry resource names to draw together, in directory order.
    pub parts: Vec<String>,
}

/// The `[a-z]NNN` id prefix of a resource name, if it has one (`e106_bdy_01`
/// → `e106`). Returns `None` for scene/logic resources (`e_rou_e106`) and
/// anything not starting with a letter + three digits.
pub fn ship_id_of(resource: &str) -> Option<&str> {
    let b = resource.as_bytes();
    if b.len() >= 4
        && b[0].is_ascii_lowercase()
        && b[1].is_ascii_digit()
        && b[2].is_ascii_digit()
        && b[3].is_ascii_digit()
    {
        // Reject a longer alnum run (`e1234…`): the id is exactly letter+3 digits,
        // followed by end-of-string or a non-alphanumeric (`_`).
        if b.get(4).is_none_or(|c| !c.is_ascii_alphanumeric()) {
            return Some(&resource[..4]);
        }
    }
    None
}

/// Whether a resource is a base geometry part (not a LOD copy, destruction
/// variant, or scene/logic node) that should be drawn in a whole-ship render.
pub fn is_base_part(resource: &str) -> bool {
    if ship_id_of(resource).is_none() {
        return false;
    }
    // Level-of-detail copies of a base part: a trailing `_l`/`_m`/`_d` token,
    // optionally with a number (`_d01`, `_l02`).
    if let Some(last) = resource.rsplit('_').next() {
        let mut cs = last.chars();
        if matches!(cs.next(), Some('l' | 'm' | 'd')) && cs.all(|c| c.is_ascii_digit()) {
            return false;
        }
    }
    // Destruction / logic geometry.
    if resource.contains("break")
        || resource.contains("dead")
        || resource.contains("_joint")
        || resource.contains("_open")
        || resource.contains("_Near")
    {
        return false;
    }
    // Break-piece geometry carries a bare `b` / `bNN` token (`e106_brg_01_b_02`,
    // `e108_eng_01_b01`). `bdy` etc. are safe — only an exact `b`-then-digits token
    // counts.
    if resource.split('_').skip(1).any(|t| {
        t == "b" || (t.starts_with('b') && t.len() >= 2 && t[1..].bytes().all(|c| c.is_ascii_digit()))
    }) {
        return false;
    }
    true
}

/// Group every base part in an XPR2 container into whole ships, keyed by id.
///
/// Ships are returned sorted by id. A stage container also holds shared turret /
/// prop models as their own ids — every group with at least one base part is
/// returned; the caller can filter by [`ShipModel::parts`] length or faction.
pub fn ships_in_container(bytes: &[u8]) -> Vec<ShipModel> {
    let names = xbg7_resource_names(bytes);
    let mut ids: Vec<String> = Vec::new();
    let mut ships: std::collections::HashMap<String, ShipModel> = std::collections::HashMap::new();
    for n in &names {
        if !is_base_part(n) {
            continue;
        }
        let id = ship_id_of(n).unwrap().to_string();
        let entry = ships.entry(id.clone()).or_insert_with(|| {
            ids.push(id.clone());
            ShipModel { id: id.clone(), faction: Faction::from_id(&id), parts: Vec::new() }
        });
        entry.parts.push(n.clone());
    }
    ids.sort();
    ids.into_iter().map(|id| ships.remove(&id).unwrap()).collect()
}

/// Map a composite scene-graph node name to the geometry resource it draws.
/// Hull nodes are `rou_<id>_<part>[_root|_mov|_NN]`; the geometry resource is the
/// `<id>_<part>` stem. Structural nodes (`rou_e106_front`, `…_root`) resolve to
/// nothing and only pose their children.
fn resolve_hull_resource(node: &str, resources: &HashSet<String>) -> Option<String> {
    let stem = node.rsplit_once("rou_").map(|(_, s)| s).unwrap_or(node);
    if resources.contains(stem) {
        return Some(stem.to_string());
    }
    for suf in ["_root", "_mov"] {
        if let Some(s) = stem.strip_suffix(suf) {
            if resources.contains(s) {
                return Some(s.to_string());
            }
        }
    }
    // Trailing `_NN` instance index (`eng_01_1` → `eng_01`).
    if let Some(pos) = stem.rfind('_') {
        if !stem[pos + 1..].is_empty() && stem[pos + 1..].bytes().all(|c| c.is_ascii_digit()) {
            let s = &stem[..pos];
            if resources.contains(s) {
                return Some(s.to_string());
            }
        }
    }
    None
}

/// The trailing digit run of a name (`GN_Bridge_01` → `01`, `sld_02` → `02`).
fn trailing_index(name: &str) -> &str {
    let bytes = name.as_bytes();
    let mut start = bytes.len();
    while start > 0 && bytes[start - 1].is_ascii_digit() {
        start -= 1;
    }
    &name[start..]
}

/// Which stage-container resources are the composite scene graphs for ship `id`
/// (`e_rou_e106`, `e_rou_e106_eng`, …). Excludes destruction (`_break`) scenes.
fn composites_for<'a>(names: &'a [String], id: &str) -> Vec<&'a String> {
    let needle = format!("rou_{id}");
    names
        .iter()
        .filter(|n| {
            n.contains(&needle)
                && ship_id_of(n).is_none()
                && !n.contains("break")
                && !n.contains("dead")
        })
        .collect()
}

/// Reconstruct a whole ship as a list of geometry-resource placements in a shared
/// ship-local frame — the placement the game builds at runtime.
///
/// Two tiers, matching how the game splits a ship:
/// 1. **Hull** — `rou_<id>_*` nodes in the primary composite scene graph name the
///    hull body resources and carry their world transform. This tier is exact: the
///    bodies (and any engine posed by a `rou_` node) land where the game puts them.
/// 2. **External hardpoints** — `GN_*` frame nodes are the Vessel mounts; each
///    unplaced bridge / shield-generator / engine part (`<id>_brg_*`, `_sld_*`,
///    `_eng_*`) is placed at its matching frame by category + index. This tier is
///    APPROXIMATE: a `GN_*` frame is the mount *pivot* (often on the centreline),
///    while the part's outboard/rotational offset lives in a detail sub-rig or in
///    runtime code that this static pass does not recover — so external parts land
///    near, not exactly, where they belong. Gated by `include_external`.
///
/// Turret placement (shared `e3NN`/`e4NN` gun models mounted at many `GN_*Gun*`
/// frames) needs the per-mount Vessel recipe and is not resolved at all.
pub fn assemble_ship(bytes: &[u8], id: &str, include_external: bool) -> Vec<ScenePart> {
    let names = xbg7_resource_names(bytes);
    let resources: HashSet<String> = names.iter().cloned().collect();

    // The PRIMARY composite carries the real ship-space layout (hull bodies +
    // every `GN_*` hardpoint frame). Sibling composites (`e_rou_<id>_eng`,
    // `_wep_*`) are LOCAL detail rigs — their nodes are in their own frame, not
    // ship-space, so folding them in floats parts mid-ship. Pick the composite
    // with the most nodes; that is the assembled hull.
    let scenes: Vec<(String, Vec<ScenePart>)> = composites_for(&names, id)
        .into_iter()
        .map(|c| (c.clone(), scene_world_nodes(bytes, c)))
        .collect();
    let Some((_, nodes)) = scenes.iter().max_by_key(|(_, n)| n.len()) else {
        // No composite at all → raw fallback below.
        let mut placed = Vec::new();
        const ID: [[f32; 3]; 3] = [[1.0, 0.0, 0.0], [0.0, 1.0, 0.0], [0.0, 0.0, 1.0]];
        for part in names.iter().filter(|n| is_base_part(n) && ship_id_of(n) == Some(id)) {
            placed.push(ScenePart { resource: part.clone(), m: ID, t: [0.0; 3], s: [1.0; 3] });
        }
        return placed;
    };

    let mut placed: Vec<ScenePart> = Vec::new();
    let mut placed_res: HashSet<String> = HashSet::new();
    // GN hardpoint frames, world-space, from the primary composite.
    let mut frames: Vec<ScenePart> = Vec::new();

    for node in nodes {
        if node.resource.starts_with("GN_") {
            frames.push(node.clone());
        } else if let Some(res) = resolve_hull_resource(&node.resource, &resources) {
            // Only the ship's own parts. A composite also mounts shared, cross-id
            // turret models (`e303_wep_*` on an `e106` hull); those need the
            // per-mount Vessel recipe and are placed separately.
            if ship_id_of(&res) != Some(id) {
                continue;
            }
            if placed_res.insert(res.clone()) {
                placed.push(ScenePart { resource: res, m: node.m, t: node.t, s: node.s });
            }
        }
    }

    // Place unplaced external parts at their Vessel hardpoint frame (APPROXIMATE —
    // see the doc comment). Skipped for a clean, exact hull-only render.
    const CATS: [(&str, &str); 3] = [("brg", "Bridge"), ("sld", "ShieldG"), ("eng", "Engine")];
    for part in names
        .iter()
        .filter(|_| include_external)
        .filter(|n| is_base_part(n) && ship_id_of(n) == Some(id))
    {
        if placed_res.contains(part) {
            continue;
        }
        let rest = &part[(id.len() + 1).min(part.len())..]; // "brg_01"
        let mut toks = rest.split('_');
        let cat = toks.next().unwrap_or("");
        let idx = toks.next().unwrap_or("");
        let Some((_, gncat)) = CATS.iter().find(|(c, _)| *c == cat) else {
            continue;
        };
        if let Some(frame) =
            frames.iter().find(|f| f.resource.contains(gncat) && trailing_index(&f.resource) == idx)
        {
            placed.push(ScenePart { resource: part.clone(), m: frame.m, t: frame.t, s: frame.s });
            placed_res.insert(part.clone());
        }
    }

    // Fallback for a ship with no composite scene graph (a simple prop): draw its
    // base parts untransformed rather than nothing.
    if placed.is_empty() {
        const ID: [[f32; 3]; 3] = [[1.0, 0.0, 0.0], [0.0, 1.0, 0.0], [0.0, 0.0, 1.0]];
        for part in names.iter().filter(|n| is_base_part(n) && ship_id_of(n) == Some(id)) {
            placed.push(ScenePart { resource: part.clone(), m: ID, t: [0.0; 3], s: [1.0; 3] });
        }
    }

    placed
}

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

    #[test]
    fn id_extraction() {
        assert_eq!(ship_id_of("e106_bdy_01"), Some("e106"));
        assert_eq!(ship_id_of("f105_sld_02_l"), Some("f105"));
        assert_eq!(ship_id_of("e_rou_e106"), None);
        assert_eq!(ship_id_of("_rou_e106_break"), None);
        assert_eq!(ship_id_of("Base"), None);
    }

    #[test]
    fn base_part_filter() {
        assert!(is_base_part("e106_bdy_01"));
        assert!(is_base_part("e106_brg_01"));
        assert!(is_base_part("f105_wep_02_01"));
        assert!(!is_base_part("e106_bdy_01_l")); // LOD
        assert!(!is_base_part("e106_bdy_01_m")); // LOD
        assert!(!is_base_part("e106_brg_01_b_02")); // break piece
        assert!(!is_base_part("_rou_e106_break")); // logic
        assert!(!is_base_part("e_rou_e106")); // scene node
    }

    #[test]
    fn faction_from_id() {
        assert_eq!(Faction::from_id("e106"), Faction::Adan);
        assert_eq!(Faction::from_id("f105"), Faction::Tcaf);
        assert_eq!(Faction::from_id("n050"), Faction::Neutral);
        assert_eq!(Faction::from_id("j004"), Faction::Other);
    }

    // Disc-gated: reconstruct the ADAN cruiser family from a real stage container.
    #[test]
    fn ships_from_real_stage() {
        let Ok(iso) = std::env::var("SYLPHEED_ISO") else {
            eprintln!("SYLPHEED_ISO unset — skipping");
            return;
        };
        let bytes = {
            use crate::xiso::open_iso;
            let rt = tokio::runtime::Builder::new_current_thread().build().unwrap();
            rt.block_on(async {
                let mut r = open_iso(std::path::Path::new(&iso)).await.unwrap();
                r.read_file("hidden/resource3d/Stage_S02.xpr").await.unwrap()
            })
        };
        let ships = ships_in_container(&bytes);
        assert!(!ships.is_empty(), "stage should hold ships");
        // The ADAN frigate e108 appears in S02 with hull + engine + weapon parts.
        let e108 = ships.iter().find(|s| s.id == "e108").expect("e108 present");
        assert_eq!(e108.faction, Faction::Adan);
        assert!(e108.parts.iter().any(|p| p.contains("_bdy_")));
        assert!(e108.parts.iter().all(|p| is_base_part(p)));
    }

    // Disc-gated: the scene graph must SPREAD a ship's parts, not stack them at
    // the origin. Reconstruct the ADAN frigate e106 and assert its bridge sits
    // clearly aft of its forward hull body (a real ship layout, not a pile).
    #[test]
    fn assemble_spreads_parts() {
        let Ok(iso) = std::env::var("SYLPHEED_ISO") else {
            eprintln!("SYLPHEED_ISO unset — skipping");
            return;
        };
        let bytes = {
            use crate::xiso::open_iso;
            let rt = tokio::runtime::Builder::new_current_thread().build().unwrap();
            rt.block_on(async {
                let mut r = open_iso(std::path::Path::new(&iso)).await.unwrap();
                r.read_file("hidden/resource3d/Stage_S02.xpr").await.unwrap()
            })
        };
        let placed = assemble_ship(&bytes, "e106", true);
        assert!(placed.len() >= 5, "e106 should place its hull + external parts");
        // The forward hull body and the bridge must land at distinct fore/aft Z.
        let z = |res: &str| placed.iter().find(|p| p.resource == res).map(|p| p.t[2]);
        let bdy = z("e106_bdy_01").expect("bdy_01 placed");
        let brg = z("e106_brg_01").expect("brg_01 placed at its GN_Bridge frame");
        assert!(
            (bdy - brg).abs() > 200.0,
            "bridge ({brg}) and forward body ({bdy}) must be far apart, not stacked"
        );
    }
}