//! Full bridge scene compositor — Sprint 4.
//!
//! Builds a single merged mesh for a simple 40 m single-span PSC-I girder bridge:
//! - 5 × PSC-I Girder (2500 mm c/c)
//! - 1 × Deck Slab (12000 mm wide)
//! - 10 × Elastomeric Bearing (5 per abutment)
//! - 2 × Abutment (start & end)
//!
//! Positions are in the same coordinate space as the girder mesh:
//!   X = transverse (right = +), Y = vertical (up = +), Z = along span.

use cimery_core::{AbutmentType, BearingType, MaterialGrade, SectionType};
use cimery_ir::{
    AbutmentIR, BearingIR, DeckSlabIR, FeatureId, GirderIR,
    PscISectionParams, SectionParams, WingWallIR,
};
use cimery_kernel::{GeomKernel, KernelError, Mesh};

// ── Part colours (linear sRGB) ──────────────────────────────────────────────
pub const COL_GIRDER:   [f32; 3] = [0.85, 0.82, 0.72]; // light concrete
pub const COL_DECK:     [f32; 3] = [0.72, 0.70, 0.62]; // slightly darker slab
pub const COL_BEARING:  [f32; 3] = [0.30, 0.30, 0.35]; // dark rubber/steel
pub const COL_ABUTMENT: [f32; 3] = [0.65, 0.60, 0.50]; // brown concrete

// ─── Helpers ─────────────────────────────────────────────────────────────────

fn translate(mut mesh: Mesh, dx: f32, dy: f32, dz: f32) -> Mesh {
    for v in &mut mesh.vertices {
        v[0] += dx;
        v[1] += dy;
        v[2] += dz;
    }
    mesh
}

fn merge(meshes: Vec<Mesh>) -> Mesh {
    cimery_kernel::sweep::merge_meshes(meshes)
}

// ─── Scene builder ────────────────────────────────────────────────────────────

/// Build a complete bridge scene mesh using the provided kernel.
pub fn build_bridge_scene<K: GeomKernel>(kernel: &K) -> Result<Mesh, KernelError> {
    const SPAN_M:       f64 = 40.0;
    const SPAN_MM:      f32 = 40_000.0;
    const N_GIRDERS:    usize = 5;
    const SPACING:      f32 = 2_500.0;   // mm c/c
    const GIRDER_H:     f32 = 1_800.0;   // mm
    const BEARING_H:    f32 = 60.0;      // mm

    let mut parts: Vec<Mesh> = Vec::new();

    // ── Girders ────────────────────────────────────────────────────────────────
    for i in 0..N_GIRDERS {
        let x = (i as f32 - (N_GIRDERS as f32 - 1.0) * 0.5) * SPACING;
        let ir = GirderIR {
            id:                    FeatureId::new(),
            station_start:         0.0,
            station_end:           SPAN_M,
            offset_from_alignment: x as f64,
            section_type:          SectionType::PscI,
            section: SectionParams::PscI(PscISectionParams::kds_standard()),
            count:    1,
            spacing:  0.0,
            material: MaterialGrade::C50,
        };
        let mut mesh = kernel.girder_mesh(&ir)?;
        mesh.recolor(COL_GIRDER);
        parts.push(translate(mesh, x, 0.0, 0.0));
    }

    // ── Deck Slab ──────────────────────────────────────────────────────────────
    // KDS: min 220 mm, width = (N-1)*spacing + 2 × cantilever
    let half_width = ((N_GIRDERS as f32 - 1.0) * SPACING) * 0.5 + 1_000.0; // 1 m cantilever
    let deck_ir = DeckSlabIR {
        id:            FeatureId::new(),
        station_start: 0.0,
        station_end:   SPAN_M,
        width_left:    half_width as f64,
        width_right:   half_width as f64,
        thickness:     220.0,
        haunch_depth:  0.0,
        cross_slope:   2.0,
        material:      MaterialGrade::C40,
    };
    let mut deck_mesh = kernel.deck_slab_mesh(&deck_ir)?;
    deck_mesh.recolor(COL_DECK);
    parts.push(translate(deck_mesh, 0.0, GIRDER_H + 220.0, 0.0));

    // ── Bearings ───────────────────────────────────────────────────────────────
    // 5 per abutment, one under each girder
    for &z in &[0.0_f32, SPAN_MM] {
        for i in 0..N_GIRDERS {
            let x = (i as f32 - (N_GIRDERS as f32 - 1.0) * 0.5) * SPACING;
            let bearing_ir = BearingIR {
                id:                FeatureId::new(),
                station:           if z < 1.0 { 0.0 } else { SPAN_M },
                bearing_type:      BearingType::Elastomeric,
                plan_length:       350.0,
                plan_width:        450.0,
                total_height:      BEARING_H as f64,
                capacity_vertical: 1_500.0,
            };
            let mut mesh = kernel.bearing_mesh(&bearing_ir)?;
            mesh.recolor(COL_BEARING);
            parts.push(translate(mesh, x, 0.0, z - 225.0));
        }
    }

    // ── Abutments ──────────────────────────────────────────────────────────────
    let wing = WingWallIR { length: 5_000.0, height: 2_500.0, thickness: 500.0 };
    let total_w = (N_GIRDERS as f64 - 1.0) * SPACING as f64 + 3_000.0; // incl. overhangs

    for &(station, z) in &[(0.0f64, -800.0_f32), (SPAN_M, SPAN_MM)] {
        let abut_ir = AbutmentIR {
            id:                      FeatureId::new(),
            station,
            skew_angle:              0.0,
            abutment_type:           AbutmentType::ReverseT,
            breast_wall_height:      (GIRDER_H + BEARING_H) as f64,
            breast_wall_thickness:   800.0,
            breast_wall_width:       total_w,
            footing_length:          4_000.0,
            footing_width:           total_w + 1_000.0,
            footing_thickness:       1_000.0,
            wing_wall_left:          wing.clone(),
            wing_wall_right:         wing.clone(),
            material:                MaterialGrade::C40,
        };
        let mut mesh = kernel.abutment_mesh(&abut_ir)?;
        mesh.recolor(COL_ABUTMENT);
        let y = -(BEARING_H + abut_ir.breast_wall_height as f32);
        parts.push(translate(mesh, 0.0, y, z));
    }

    Ok(merge(parts))
}

/// Bounding box of the full bridge scene (for camera setup).
pub fn scene_extents() -> ([f32; 3], [f32; 3]) {
    const SPAN_MM: f32 = 40_000.0;
    const HALF_W:  f32 = 6_500.0;
    const TOP_Y:   f32 = 2_020.0;  // top of slab
    const BOT_Y:   f32 = -3_000.0; // footing bottom approx
    ([-HALF_W, BOT_Y, -2_000.0], [HALF_W, TOP_Y, SPAN_MM + 2_000.0])
}