/// PDF points per inch constant
const PDF_POINTS_PER_INCH: f64 = 72.0;

/// Calculate smart DPI based on page dimensions, memory constraints, and target DPI
#[allow(clippy::cast_possible_truncation)]
pub(crate) fn calculate_smart_dpi(
    page_width: f64,
    page_height: f64,
    target_dpi: i32,
    max_dimension: i32,
    max_memory_mb: f64,
) -> i32 {
    let width_inches = page_width / PDF_POINTS_PER_INCH;
    let height_inches = page_height / PDF_POINTS_PER_INCH;

    let max_pixels = (max_memory_mb * 1024.0 * 1024.0 / 3.0).sqrt().round() as i32;

    let max_dpi_for_memory_width = if width_inches > 0.0 {
        (f64::from(max_pixels) / width_inches).round() as i32
    } else {
        target_dpi
    };

    let max_dpi_for_memory_height = if height_inches > 0.0 {
        (f64::from(max_pixels) / height_inches).round() as i32
    } else {
        target_dpi
    };

    let memory_constrained_dpi = max_dpi_for_memory_width.min(max_dpi_for_memory_height);

    let dimension_constrained_dpi =
        calculate_dimension_constrained_dpi(width_inches, height_inches, target_dpi, max_dimension);

    let final_dpi = target_dpi.min(memory_constrained_dpi).min(dimension_constrained_dpi);

    final_dpi.max(72)
}

/// Calculate DPI constrained by maximum dimension
#[allow(clippy::cast_possible_truncation)]
fn calculate_dimension_constrained_dpi(
    width_inches: f64,
    height_inches: f64,
    target_dpi: i32,
    max_dimension: i32,
) -> i32 {
    let target_width_pixels = (width_inches * f64::from(target_dpi)).round() as i32;
    let target_height_pixels = (height_inches * f64::from(target_dpi)).round() as i32;
    let max_pixel_dimension = target_width_pixels.max(target_height_pixels);

    if max_pixel_dimension > max_dimension {
        let max_dpi_for_width = if width_inches > 0.0 {
            (f64::from(max_dimension) / width_inches).round() as i32
        } else {
            target_dpi
        };

        let max_dpi_for_height = if height_inches > 0.0 {
            (f64::from(max_dimension) / height_inches).round() as i32
        } else {
            target_dpi
        };

        max_dpi_for_width.min(max_dpi_for_height)
    } else {
        target_dpi
    }
}

/// Calculate optimal DPI with min/max constraints
#[cfg(test)]
pub(crate) fn calculate_optimal_dpi(
    page_width: f64,
    page_height: f64,
    target_dpi: i32,
    max_dimension: i32,
    min_dpi: i32,
    max_dpi: i32,
) -> i32 {
    let smart_dpi = calculate_smart_dpi(page_width, page_height, target_dpi, max_dimension, 2048.0);

    min_dpi.max(smart_dpi.min(max_dpi))
}

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

    #[test]
    fn test_calculate_smart_dpi_basic() {
        let dpi = calculate_smart_dpi(612.0, 792.0, 300, 4096, 2048.0);
        assert!(dpi >= 72);
        assert!(dpi <= 300);
    }

    #[test]
    fn test_calculate_smart_dpi_memory_constrained() {
        let dpi = calculate_smart_dpi(1224.0, 1584.0, 300, 8192, 10.0);
        assert!(dpi < 300);
        assert!(dpi >= 72);
    }

    #[test]
    fn test_calculate_smart_dpi_dimension_constrained() {
        let dpi = calculate_smart_dpi(612.0, 792.0, 300, 1000, 2048.0);
        assert!(dpi < 300);
    }

    #[test]
    fn test_calculate_smart_dpi_minimum_dpi() {
        let dpi = calculate_smart_dpi(10000.0, 10000.0, 300, 100, 1.0);
        assert_eq!(dpi, 72);
    }

    #[test]
    fn test_calculate_smart_dpi_zero_dimensions() {
        let dpi = calculate_smart_dpi(0.0, 792.0, 300, 4096, 2048.0);
        assert!(dpi >= 72);

        let dpi = calculate_smart_dpi(612.0, 0.0, 300, 4096, 2048.0);
        assert!(dpi >= 72);

        let dpi = calculate_smart_dpi(0.0, 0.0, 300, 4096, 2048.0);
        assert_eq!(dpi, 300);
    }

    #[test]
    fn test_calculate_dimension_constrained_dpi() {
        let dpi = calculate_dimension_constrained_dpi(8.5, 11.0, 300, 4096);
        assert!(dpi <= 300);

        let dpi = calculate_dimension_constrained_dpi(8.5, 11.0, 600, 2000);
        assert!(dpi < 600);
    }

    #[test]
    fn test_calculate_optimal_dpi() {
        let dpi = calculate_optimal_dpi(612.0, 792.0, 300, 4096, 72, 600);
        assert!(dpi >= 72);
        assert!(dpi <= 600);

        let dpi = calculate_optimal_dpi(10000.0, 10000.0, 300, 100, 100, 600);
        assert_eq!(dpi, 100);

        let dpi = calculate_optimal_dpi(72.0, 72.0, 1000, 10000, 72, 600);
        assert_eq!(dpi, 600);
    }

    #[test]
    fn test_memory_calculation() {
        let dpi = calculate_smart_dpi(612.0, 792.0, 10000, 100000, 2048.0);
        assert!(dpi < 10000);
        assert!(dpi >= 72);
    }

    #[test]
    fn test_aspect_ratio_preservation() {
        let wide_dpi = calculate_smart_dpi(1224.0, 396.0, 300, 4096, 2048.0);
        let tall_dpi = calculate_smart_dpi(396.0, 1224.0, 300, 4096, 2048.0);

        assert!(wide_dpi >= 72);
        assert!(tall_dpi >= 72);
    }
}