//! Content scaling test (#500, D-026).
//!
//! Verifies that adding extra NPCs doesn't degrade tick timing beyond
//! acceptable bounds. Runs the Gauntlet baseline, then adds additional
//! NPCs and compares:
//!   1. Tick timing stays within D-026 budget (100ms)
//!   2. Baseline entities still behave identically (deterministic)
//!
//! Run with: cargo test --test content_scaling -- --nocapture

use bevy_app::prelude::*;
use std::time::Instant;

use settled_reach_server::bridge::types::*;
use settled_reach_server::bridge::BridgePlugin;
use settled_reach_server::knowledge::registry::{EntityRegistry, StableEntityId};
use settled_reach_server::knowledge::KnowledgePlugin;
use settled_reach_server::npc::{Contentment, Npc, NpcPlugin, ToleranceThreshold, Want, WantKind};
use settled_reach_server::simulation::interaction::Interactable;
use settled_reach_server::simulation::movement::TilePosition;
use settled_reach_server::simulation::path_follow::MovementSpeed;
use settled_reach_server::simulation::SimulationPlugin;

/// Number of ticks to run for timing measurements.
const TIMING_TICKS: usize = 50;

/// D-026 budget: 100ms per tick maximum.
const MAX_TICK_MS: f64 = 100.0;

/// Extra NPC counts for scaling tiers.
const EXTRA_NPC_COUNTS: &[usize] = &[0, 15, 50];

/// Set up a Gauntlet world and return the app.
fn setup_baseline() -> App {
    let mut app = App::new();
    app.add_plugins(SimulationPlugin);
    app.add_plugins(BridgePlugin);
    app.add_plugins(KnowledgePlugin);
    app.add_plugins(NpcPlugin);

    #[cfg(feature = "gauntlet")]
    settled_reach_server::test_world::setup_gauntlet(&mut app);

    app
}

/// Spawn N extra NPCs spread across the Gauntlet hub area.
/// NPCs are placed in a grid starting at (40, 48) to stay within walkable space.
fn spawn_extra_npcs(app: &mut App, count: usize) {
    // Remove registry from world so we can mutate it while also spawning entities.
    let mut registry = app
        .world_mut()
        .remove_resource::<EntityRegistry>()
        .expect("EntityRegistry should exist after setup_gauntlet");
    let cols = 10;

    for i in 0..count {
        let x = 40 + (i % cols) as i32;
        let y = 48 + (i / cols) as i32;
        let pos = TilePosition::new(x, y, 0);

        let entity = app
            .world_mut()
            .spawn((
                Npc,
                Interactable,
                pos,
                Want {
                    primary: WantKind::Safety,
                    intensity: 5,
                    description: format!("extra_npc_{}", i),
                },
                Contentment { level: 0 },
                ToleranceThreshold {
                    current_stress: 0,
                    threshold: 50,
                },
                MovementSpeed::default(),
            ))
            .id();
        let sid = registry.register(entity);
        app.world_mut()
            .entity_mut(entity)
            .insert(StableEntityId(sid));
    }

    app.insert_resource(registry);
}

/// Tick the app N times and return average milliseconds per tick.
fn measure_tick_timing(app: &mut App, ticks: usize) -> f64 {
    // Warm-up tick (first tick has startup overhead)
    app.update();

    let start = Instant::now();
    for _ in 0..ticks {
        app.update();
    }
    let elapsed = start.elapsed();
    elapsed.as_secs_f64() * 1000.0 / ticks as f64
}

/// Collect snapshot entity IDs from the VisibilityGeometry and entity count.
fn count_entities(app: &App) -> usize {
    let registry = app.world().resource::<EntityRegistry>();
    registry.len() as usize
}

/// Baseline tick timing: Gauntlet with default entities stays within D-026 budget.
#[test]
#[cfg(feature = "gauntlet")]
fn baseline_tick_timing_within_budget() {
    let mut app = setup_baseline();
    let entity_count = count_entities(&app);
    let avg_ms = measure_tick_timing(&mut app, TIMING_TICKS);

    eprintln!(
        "Baseline: {} entities, avg {:.3}ms/tick over {} ticks",
        entity_count, avg_ms, TIMING_TICKS
    );

    assert!(
        avg_ms < MAX_TICK_MS,
        "Baseline tick timing ({:.3}ms) exceeds D-026 budget ({}ms)",
        avg_ms,
        MAX_TICK_MS
    );
}

/// Scaling test: adding NPCs keeps tick timing within D-026 budget.
/// Tests 0 (baseline), 15, and 50 extra NPCs.
#[test]
#[cfg(feature = "gauntlet")]
fn scaling_tick_timing_within_budget() {
    let mut results: Vec<(usize, usize, f64)> = Vec::new();

    for &extra_count in EXTRA_NPC_COUNTS {
        let mut app = setup_baseline();
        if extra_count > 0 {
            spawn_extra_npcs(&mut app, extra_count);
        }
        let total_entities = count_entities(&app);
        let avg_ms = measure_tick_timing(&mut app, TIMING_TICKS);
        results.push((extra_count, total_entities, avg_ms));
    }

    eprintln!("\n=== Content Scaling Results (D-026: {}ms budget) ===", MAX_TICK_MS);
    eprintln!("{:<12} {:<10} {:<15}", "Extra NPCs", "Total", "Avg ms/tick");
    eprintln!("{:-<37}", "");
    for &(extra, total, avg_ms) in &results {
        let status = if avg_ms < MAX_TICK_MS { "OK" } else { "OVER" };
        eprintln!("{:<12} {:<10} {:<15.3} {}", extra, total, avg_ms, status);
    }

    // Assert all tiers stay within budget
    for &(extra, _total, avg_ms) in &results {
        assert!(
            avg_ms < MAX_TICK_MS,
            "Tick timing with +{} NPCs ({:.3}ms) exceeds D-026 budget ({}ms)",
            extra,
            avg_ms,
            MAX_TICK_MS
        );
    }

    // Assert scaling is reasonable: +50 NPCs shouldn't more than 5x the baseline
    if results.len() >= 2 {
        let baseline_ms = results[0].2;
        let max_extra_ms = results.last().unwrap().2;
        let scaling_factor = max_extra_ms / baseline_ms;
        eprintln!(
            "\nScaling factor (baseline → +{} NPCs): {:.2}x",
            results.last().unwrap().0,
            scaling_factor
        );
        assert!(
            scaling_factor < 5.0,
            "Scaling factor {:.2}x exceeds 5x threshold — possible O(n^2) regression",
            scaling_factor
        );
    }
}

/// Determinism test: baseline entities produce identical snapshots regardless
/// of extra NPCs being present. The original Gauntlet entities (StableId 0
/// through RESET_PLATE_STABLE_IDS.1) should have the same positions and
/// visibility after the same number of ticks.
#[test]
#[cfg(feature = "gauntlet")]
fn extra_npcs_dont_affect_baseline_behavior() {
    // Run baseline
    let mut baseline_app = setup_baseline();
    for _ in 0..10 {
        baseline_app.update();
    }
    let baseline_buffer = baseline_app
        .world()
        .resource::<SnapshotBuffer>()
        .snapshot
        .clone();

    // Run with extra NPCs
    let mut scaled_app = setup_baseline();
    spawn_extra_npcs(&mut scaled_app, 15);
    for _ in 0..10 {
        scaled_app.update();
    }
    let scaled_buffer = scaled_app
        .world()
        .resource::<SnapshotBuffer>()
        .snapshot
        .clone();

    let baseline_snap = baseline_buffer.expect("baseline should produce a snapshot");
    let scaled_snap = scaled_buffer.expect("scaled should produce a snapshot");

    // Same tick
    assert_eq!(baseline_snap.tick, scaled_snap.tick, "tick count should match");

    // Same game time
    assert_eq!(
        baseline_snap.game_time.time_of_day, scaled_snap.game_time.time_of_day,
        "game time should match"
    );

    // Player position should be identical
    let baseline_player = baseline_snap.entities.iter().find(|e| e.kind == EntityKind::Player);
    let scaled_player = scaled_snap.entities.iter().find(|e| e.kind == EntityKind::Player);
    assert!(baseline_player.is_some(), "baseline should have player");
    assert!(scaled_player.is_some(), "scaled should have player");

    let bp = baseline_player.unwrap();
    let sp = scaled_player.unwrap();
    assert_eq!(bp.x, sp.x, "player x should match");
    assert_eq!(bp.y, sp.y, "player y should match");

    // Original entities (entity_id <= max Gauntlet StableId) visible in baseline
    // should still be visible in scaled run. Extra NPCs may add to the visible
    // set, but shouldn't remove baseline visibility.
    let max_baseline_id = settled_reach_server::test_world::constants::RESET_PLATE_STABLE_IDS.1;
    let baseline_original_ids: Vec<u64> = baseline_snap
        .entities
        .iter()
        .filter(|e| e.entity_id <= max_baseline_id)
        .map(|e| e.entity_id)
        .collect();

    let scaled_original_ids: Vec<u64> = scaled_snap
        .entities
        .iter()
        .filter(|e| e.entity_id <= max_baseline_id)
        .map(|e| e.entity_id)
        .collect();

    assert_eq!(
        baseline_original_ids, scaled_original_ids,
        "Original Gauntlet entities (id <= max_baseline_id) should be identical in both runs"
    );
}