//! WorldGen - Video Diffusion World Simulator.
//!
//! This demo showcases DiT-based video generation with physics grounding,
//! enabling generation of physically plausible video from text prompts.

pub mod diffusion;
pub mod physics;
pub mod sample_data;
pub mod scheduler;

use thiserror::Error;
use worldgen_shared::{
    GenerationRequest, GenerationResult, ModelConfig, SchedulerConfig, TrainingConfig,
    TrainingProgress, VideoClip,
};

/// Errors that can occur in WorldGen.
#[derive(Debug, Error)]
pub enum WorldGenError {
    /// Invalid generation request.
    #[error("Invalid generation request: {0}")]
    InvalidRequest(String),

    /// Generation failed.
    #[error("Generation failed: {0}")]
    GenerationFailed(String),

    /// Model not initialized.
    #[error("Model not initialized")]
    ModelNotInitialized,

    /// Physics simulation failed.
    #[error("Physics simulation failed: {0}")]
    PhysicsFailed(String),
}

/// Main WorldGen system.
#[derive(Debug)]
pub struct WorldGen {
    /// Model configuration.
    model_config: ModelConfig,
    /// Scheduler configuration.
    scheduler_config: SchedulerConfig,
    /// Diffusion model.
    diffusion_model: diffusion::DiffusionTransformer,
    /// Physics engine.
    physics_engine: physics::PhysicsEngine,
    /// Is initialized.
    initialized: bool,
}

impl Default for WorldGen {
    fn default() -> Self {
        Self::new(ModelConfig::default(), SchedulerConfig::default())
    }
}

impl WorldGen {
    /// Create a new WorldGen instance.
    #[must_use]
    pub fn new(model_config: ModelConfig, scheduler_config: SchedulerConfig) -> Self {
        Self {
            diffusion_model: diffusion::DiffusionTransformer::new(&model_config),
            physics_engine: physics::PhysicsEngine::new(),
            model_config,
            scheduler_config,
            initialized: true,
        }
    }

    /// Generate a video from a text prompt.
    pub fn generate(
        &mut self,
        request: &GenerationRequest,
    ) -> Result<GenerationResult, WorldGenError> {
        if !self.initialized {
            return Err(WorldGenError::ModelNotInitialized);
        }

        if request.prompt.is_empty() {
            return Err(WorldGenError::InvalidRequest("Prompt is empty".to_string()));
        }

        if request.num_frames == 0 {
            return Err(WorldGenError::InvalidRequest(
                "num_frames must be > 0".to_string(),
            ));
        }

        let start_time = std::time::Instant::now();

        // Create scheduler
        let scheduler = scheduler::NoiseScheduler::new(&self.scheduler_config);

        // Encode text prompt
        let text_embedding = self.encode_prompt(&request.prompt);

        // Initialize latent noise
        let seed = request.seed.unwrap_or(42);
        let latent_shape = (
            request.num_frames,
            self.model_config.latent_channels,
            request.height / 8,
            request.width / 8,
        );
        let mut latents = self.initialize_latents(latent_shape, seed);

        // Denoising loop
        let timesteps = scheduler.get_timesteps(request.num_inference_steps);
        for &t in &timesteps {
            // Predict noise
            let noise_pred = self.diffusion_model.forward(&latents, t, &text_embedding);

            // Apply physics constraints
            let physics_guidance = if !request.physics_constraints.is_empty() {
                Some(
                    self.physics_engine
                        .compute_guidance(&latents, &request.physics_constraints),
                )
            } else {
                None
            };

            // Update latents
            latents = scheduler.step(&latents, &noise_pred, t, physics_guidance.as_deref());
        }

        // Decode latents to video frames
        let video = self.decode_latents(&latents, request);

        // Calculate physics score
        let physics_score = if !request.physics_constraints.is_empty() {
            Some(
                self.physics_engine
                    .evaluate_physics(&video, &request.physics_constraints),
            )
        } else {
            None
        };

        Ok(GenerationResult {
            video,
            generation_time: start_time.elapsed().as_secs_f64(),
            physics_score,
            prompt: request.prompt.clone(),
        })
    }

    /// Train the model.
    pub fn train(
        &mut self,
        _config: &TrainingConfig,
        progress_callback: Option<Box<dyn Fn(TrainingProgress) + Send>>,
    ) -> Result<(), WorldGenError> {
        let start_time = std::time::Instant::now();
        let total_steps = 100; // Demo steps

        for step in 0..total_steps {
            // Simulate training step
            let loss = 0.5 * (-0.01 * step as f64).exp();

            if let Some(ref callback) = progress_callback {
                callback(TrainingProgress {
                    epoch: step / 10 + 1,
                    total_epochs: 10,
                    step: step + 1,
                    total_steps,
                    diffusion_loss: loss,
                    physics_loss: Some(loss * 0.1),
                    total_loss: loss * 1.1,
                    learning_rate: 1e-4,
                    elapsed_seconds: start_time.elapsed().as_secs_f64(),
                });
            }
        }

        Ok(())
    }

    /// Encode text prompt to embedding.
    fn encode_prompt(&self, prompt: &str) -> Vec<f64> {
        // Simplified text encoding (in reality, would use CLIP or similar)
        let mut embedding = vec![0.0; self.model_config.hidden_dim];

        // Simple hash-based encoding for demo
        for (i, c) in prompt.chars().enumerate() {
            let idx = i % embedding.len();
            embedding[idx] += (c as u32) as f64 / 1000.0;
        }

        // Normalize
        let norm: f64 = embedding.iter().map(|x| x * x).sum::<f64>().sqrt();
        if norm > 1e-10 {
            for e in &mut embedding {
                *e /= norm;
            }
        }

        embedding
    }

    /// Initialize random latent noise.
    fn initialize_latents(&self, shape: (usize, usize, usize, usize), seed: u64) -> Vec<f64> {
        let size = shape.0 * shape.1 * shape.2 * shape.3;
        let mut latents = vec![0.0; size];
        let mut rng_state = seed;

        for latent in &mut latents {
            // LCG random
            rng_state = rng_state
                .wrapping_mul(6364136223846793005)
                .wrapping_add(1442695040888963407);
            let u1 = (rng_state >> 11) as f64 / (1u64 << 53) as f64 + 1e-10;

            rng_state = rng_state
                .wrapping_mul(6364136223846793005)
                .wrapping_add(1442695040888963407);
            let u2 = (rng_state >> 11) as f64 / (1u64 << 53) as f64;

            // Box-Muller
            *latent = (-2.0 * u1.ln()).sqrt() * (2.0 * std::f64::consts::PI * u2).cos();
        }

        latents
    }

    /// Decode latents to video frames.
    fn decode_latents(&self, latents: &[f64], request: &GenerationRequest) -> VideoClip {
        use worldgen_shared::VideoFrame;

        let latent_h = request.height / 8;
        let latent_w = request.width / 8;
        let latent_c = self.model_config.latent_channels;
        let frame_size = latent_c * latent_h * latent_w;

        let frames: Vec<VideoFrame> = (0..request.num_frames)
            .map(|frame_idx| {
                let frame_latent_start = frame_idx * frame_size;
                let frame_latent = &latents[frame_latent_start
                    ..frame_latent_start + frame_size.min(latents.len() - frame_latent_start)];

                // Decode latent to pixels (simplified upsampling)
                let mut pixels = vec![0u8; request.width * request.height * 3];

                for y in 0..request.height {
                    for x in 0..request.width {
                        let latent_x = x / 8;
                        let latent_y = y / 8;

                        for c in 0..3 {
                            let latent_idx = (c % latent_c) * latent_h * latent_w
                                + latent_y * latent_w
                                + latent_x;
                            let value = if latent_idx < frame_latent.len() {
                                frame_latent[latent_idx]
                            } else {
                                0.0
                            };

                            // Map to [0, 255]
                            let pixel_value =
                                ((value.tanh() + 1.0) * 127.5).clamp(0.0, 255.0) as u8;
                            pixels[(y * request.width + x) * 3 + c] = pixel_value;
                        }
                    }
                }

                VideoFrame {
                    index: frame_idx,
                    width: request.width,
                    height: request.height,
                    data: pixels,
                    timestamp: frame_idx as f64 / request.fps as f64,
                }
            })
            .collect();

        VideoClip {
            frames,
            fps: request.fps,
            duration: request.num_frames as f32 / request.fps,
            width: request.width,
            height: request.height,
        }
    }

    /// Get model config.
    #[must_use]
    pub fn model_config(&self) -> &ModelConfig {
        &self.model_config
    }

    /// Get scheduler config.
    #[must_use]
    pub fn scheduler_config(&self) -> &SchedulerConfig {
        &self.scheduler_config
    }
}

/// Run the demo.
pub fn run_demo() -> Result<GenerationResult, WorldGenError> {
    let mut worldgen = WorldGen::default();

    let request = worldgen_shared::sample_generation_request();
    worldgen.generate(&request)
}

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

    #[test]
    fn test_worldgen_creation() {
        let worldgen = WorldGen::default();
        assert!(worldgen.initialized);
    }

    #[test]
    fn test_generate_video() {
        let mut worldgen = WorldGen::default();
        let mut request = worldgen_shared::sample_generation_request();
        request.num_frames = 4;
        request.width = 64;
        request.height = 64;
        request.num_inference_steps = 5;

        let result = worldgen.generate(&request);
        assert!(result.is_ok());

        let result = result.unwrap();
        assert_eq!(result.video.frames.len(), 4);
        assert!(!result.prompt.is_empty());
    }

    #[test]
    fn test_empty_prompt() {
        let mut worldgen = WorldGen::default();
        let mut request = worldgen_shared::sample_generation_request();
        request.prompt = String::new();

        let result = worldgen.generate(&request);
        assert!(matches!(result, Err(WorldGenError::InvalidRequest(_))));
    }

    #[test]
    fn test_physics_constraints() {
        let mut worldgen = WorldGen::default();
        let mut request = worldgen_shared::sample_generation_request();
        request.num_frames = 4;
        request.width = 64;
        request.height = 64;
        request.num_inference_steps = 3;

        let result = worldgen.generate(&request).unwrap();
        assert!(result.physics_score.is_some());
    }

    #[test]
    fn test_encode_prompt() {
        let worldgen = WorldGen::default();
        let embedding = worldgen.encode_prompt("test prompt");

        assert_eq!(embedding.len(), worldgen.model_config.hidden_dim);

        // Check normalization
        let norm: f64 = embedding.iter().map(|x| x * x).sum::<f64>().sqrt();
        assert!((norm - 1.0).abs() < 0.01);
    }

    #[test]
    fn test_run_demo() {
        let result = run_demo();
        assert!(result.is_ok());
    }
}