// Copyright (c) 2024 RustyTorch++ Team
// Licensed under the Apache License, Version 2.0

//! Utility functions and helpers for finite element analysis.

pub mod io;
pub mod math;
pub mod profiling;
pub mod visualization;

#[cfg(test)]
mod math_tests;

use nalgebra::Vector3;
use std::time::{Duration, Instant};

pub use io::*;
pub use math::*;
pub use profiling::*;
pub use visualization::*;

/// Coordinate system transformations.
pub struct CoordinateTransforms;

impl CoordinateTransforms {
    /// Convert Cartesian to cylindrical coordinates.
    pub fn cartesian_to_cylindrical(point: &Vector3<f64>) -> Vector3<f64> {
        let r = (point.x * point.x + point.y * point.y).sqrt();
        let theta = point.y.atan2(point.x);
        let z = point.z;
        Vector3::new(r, theta, z)
    }

    /// Convert cylindrical to Cartesian coordinates.
    pub fn cylindrical_to_cartesian(point: &Vector3<f64>) -> Vector3<f64> {
        let x = point.x * point.y.cos();
        let y = point.x * point.y.sin();
        let z = point.z;
        Vector3::new(x, y, z)
    }

    /// Convert Cartesian to spherical coordinates.
    pub fn cartesian_to_spherical(point: &Vector3<f64>) -> Vector3<f64> {
        let r = point.norm();
        let theta = (point.z / r).acos();
        let phi = point.y.atan2(point.x);
        Vector3::new(r, theta, phi)
    }

    /// Convert spherical to Cartesian coordinates.
    pub fn spherical_to_cartesian(point: &Vector3<f64>) -> Vector3<f64> {
        let x = point.x * point.y.sin() * point.z.cos();
        let y = point.x * point.y.sin() * point.z.sin();
        let z = point.x * point.y.cos();
        Vector3::new(x, y, z)
    }
}

/// Memory usage utilities.
pub struct MemoryUtils;

impl MemoryUtils {
    /// Get current memory usage in bytes.
    pub fn current_usage() -> usize {
        // Simplified implementation - would use proper memory tracking
        0
    }

    /// Get peak memory usage in bytes.
    pub fn peak_usage() -> usize {
        // Simplified implementation
        0
    }

    /// Format memory size in human-readable format.
    pub fn format_bytes(bytes: usize) -> String {
        const UNITS: &[&str] = &["B", "KB", "MB", "GB", "TB"];
        let mut size = bytes as f64;
        let mut unit_index = 0;

        while size >= 1024.0 && unit_index < UNITS.len() - 1 {
            size /= 1024.0;
            unit_index += 1;
        }

        format!("{:.2} {}", size, UNITS[unit_index])
    }

    /// Estimate memory requirement for sparse matrix.
    pub fn estimate_sparse_matrix_memory(
        nnz: usize,
        index_size: usize,
        value_size: usize,
    ) -> usize {
        nnz * (index_size + value_size) + index_size * 2 // Row pointers
    }

    /// Estimate memory requirement for dense matrix.
    pub fn estimate_dense_matrix_memory(rows: usize, cols: usize, element_size: usize) -> usize {
        rows * cols * element_size
    }
}

/// Performance benchmarking utilities.
pub struct BenchmarkUtils;

impl BenchmarkUtils {
    /// Measure execution time of a function.
    pub fn time_function<F, R>(f: F) -> (R, Duration)
    where
        F: FnOnce() -> R,
    {
        let start = Instant::now();
        let result = f();
        let duration = start.elapsed();
        (result, duration)
    }

    /// Run benchmark multiple times and get statistics.
    pub fn benchmark_function<F>(f: F, iterations: usize) -> BenchmarkStats
    where
        F: Fn(),
    {
        let mut times = Vec::with_capacity(iterations);

        for _ in 0..iterations {
            let ((), duration) = Self::time_function(&f);
            times.push(duration);
        }

        BenchmarkStats::from_times(times)
    }

    /// Create a simple progress bar.
    pub fn create_progress_bar(total: usize) -> ProgressBar {
        ProgressBar::new(total)
    }
}

/// Benchmark statistics.
#[derive(Debug, Clone)]
pub struct BenchmarkStats {
    pub mean: Duration,
    pub std_dev: Duration,
    pub min: Duration,
    pub max: Duration,
    pub iterations: usize,
}

impl BenchmarkStats {
    /// Create statistics from timing measurements.
    pub fn from_times(times: Vec<Duration>) -> Self {
        if times.is_empty() {
            return Self {
                mean: Duration::new(0, 0),
                std_dev: Duration::new(0, 0),
                min: Duration::new(0, 0),
                max: Duration::new(0, 0),
                iterations: 0,
            };
        }

        let iterations = times.len();
        let total_nanos: u64 = times.iter().map(|d| d.as_nanos() as u64).sum();
        let mean_nanos = total_nanos / iterations as u64;
        let mean = Duration::from_nanos(mean_nanos);

        let min = times.iter().min().copied().unwrap_or_default();
        let max = times.iter().max().copied().unwrap_or_default();

        // Calculate standard deviation
        let variance: f64 = times
            .iter()
            .map(|d| {
                let diff = d.as_nanos() as f64 - mean_nanos as f64;
                diff * diff
            })
            .sum::<f64>()
            / iterations as f64;

        let std_dev = Duration::from_nanos(variance.sqrt() as u64);

        Self {
            mean,
            std_dev,
            min,
            max,
            iterations,
        }
    }
}

impl std::fmt::Display for BenchmarkStats {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        writeln!(f, "Benchmark Statistics ({} iterations):", self.iterations)?;
        writeln!(f, "  Mean:    {:.3} ms", self.mean.as_secs_f64() * 1000.0)?;
        writeln!(
            f,
            "  Std Dev: {:.3} ms",
            self.std_dev.as_secs_f64() * 1000.0
        )?;
        writeln!(f, "  Min:     {:.3} ms", self.min.as_secs_f64() * 1000.0)?;
        writeln!(f, "  Max:     {:.3} ms", self.max.as_secs_f64() * 1000.0)?;
        Ok(())
    }
}

/// Simple progress bar for console output.
#[derive(Debug)]
pub struct ProgressBar {
    total: usize,
    current: usize,
    width: usize,
    start_time: Instant,
}

impl ProgressBar {
    /// Create a new progress bar.
    pub fn new(total: usize) -> Self {
        Self {
            total,
            current: 0,
            width: 50,
            start_time: Instant::now(),
        }
    }

    /// Set the width of the progress bar.
    pub fn set_width(&mut self, width: usize) {
        self.width = width;
    }

    /// Update progress and display.
    pub fn update(&mut self, current: usize) {
        self.current = current;
        self.display();
    }

    /// Increment progress by one.
    pub fn increment(&mut self) {
        self.current += 1;
        self.display();
    }

    /// Display the progress bar.
    fn display(&self) {
        let percentage = if self.total > 0 {
            (self.current as f64 / self.total as f64 * 100.0).min(100.0)
        } else {
            0.0
        };

        let filled = (percentage / 100.0 * self.width as f64) as usize;
        let empty = self.width - filled;

        let elapsed = self.start_time.elapsed();
        let rate = if elapsed.as_secs() > 0 {
            self.current as f64 / elapsed.as_secs_f64()
        } else {
            0.0
        };

        let eta = if rate > 0.0 && self.current < self.total {
            Duration::from_secs_f64((self.total - self.current) as f64 / rate)
        } else {
            Duration::new(0, 0)
        };

        print!(
            "\r[{}{}] {:.1}% ({}/{}) Rate: {:.1}/s ETA: {:.0}s",
            "█".repeat(filled),
            "░".repeat(empty),
            percentage,
            self.current,
            self.total,
            rate,
            eta.as_secs_f64()
        );

        use std::io::{self, Write};
        io::stdout().flush().unwrap();

        if self.current >= self.total {
            println!(); // New line when complete
        }
    }

    /// Mark as complete.
    pub fn finish(&mut self) {
        self.current = self.total;
        self.display();
    }
}

/// String utilities for FEA.
pub struct StringUtils;

impl StringUtils {
    /// Convert scientific notation to readable format.
    pub fn format_scientific(value: f64, precision: usize) -> String {
        if value.abs() < 1e-15 {
            "0".to_string()
        } else if value.abs() >= 1e6 || value.abs() < 1e-3 {
            format!("{value:.precision$e}")
        } else {
            format!("{value:.precision$}")
        }
    }

    /// Format duration in human-readable format.
    pub fn format_duration(duration: Duration) -> String {
        let total_secs = duration.as_secs_f64();

        if total_secs < 1.0 {
            format!("{:.1} ms", total_secs * 1000.0)
        } else if total_secs < 60.0 {
            format!("{total_secs:.2} s")
        } else if total_secs < 3600.0 {
            let minutes = (total_secs / 60.0) as u32;
            let seconds = total_secs % 60.0;
            format!("{minutes}m {seconds:.1}s")
        } else {
            let hours = (total_secs / 3600.0) as u32;
            let minutes = ((total_secs % 3600.0) / 60.0) as u32;
            format!("{hours}h {minutes}m")
        }
    }

    /// Generate unique identifier.
    pub fn generate_id() -> String {
        use std::time::{SystemTime, UNIX_EPOCH};
        let timestamp = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_nanos();
        format!("fea_{timestamp}")
    }
}

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

    #[test]
    fn test_coordinate_transforms() {
        let cartesian = Vector3::new(1.0, 1.0, 1.0);
        let cylindrical = CoordinateTransforms::cartesian_to_cylindrical(&cartesian);
        let back_to_cartesian = CoordinateTransforms::cylindrical_to_cartesian(&cylindrical);

        assert!((cartesian - back_to_cartesian).norm() < 1e-10);
    }

    #[test]
    fn test_memory_utils() {
        let formatted = MemoryUtils::format_bytes(1024 * 1024);
        assert_eq!(formatted, "1.00 MB");

        let formatted = MemoryUtils::format_bytes(1536);
        assert_eq!(formatted, "1.50 KB");
    }

    #[test]
    fn test_benchmark_stats() {
        let times = vec![
            Duration::from_millis(10),
            Duration::from_millis(12),
            Duration::from_millis(11),
            Duration::from_millis(13),
            Duration::from_millis(9),
        ];

        let stats = BenchmarkStats::from_times(times);
        assert_eq!(stats.iterations, 5);
        assert!(stats.mean.as_millis() > 0);
        assert!(stats.min <= stats.mean);
        assert!(stats.max >= stats.mean);
    }

    #[test]
    fn test_progress_bar() {
        let mut progress = ProgressBar::new(100);
        progress.set_width(10);
        progress.update(50);
        assert_eq!(progress.current, 50);
        assert_eq!(progress.total, 100);
    }

    #[test]
    fn test_string_utils() {
        let scientific = StringUtils::format_scientific(1.23e-6, 2);
        assert!(scientific.contains("e"));

        let duration = StringUtils::format_duration(Duration::from_secs(65));
        assert!(duration.contains("m"));

        let id = StringUtils::generate_id();
        assert!(id.starts_with("fea_"));
    }

    #[test]
    fn test_benchmark_function() {
        let stats = BenchmarkUtils::benchmark_function(
            || {
                std::thread::sleep(Duration::from_millis(1));
            },
            3,
        );

        assert_eq!(stats.iterations, 3);
        assert!(stats.mean.as_millis() >= 1);
    }
}