//! Transformation module
//!
//! Useful to turn on-screen coordinates into the measurements in the "real" world the map
//! describes and the other way around.

use piston_window::math;

const STANDARD_PIXELS_PER_M: f64 = 64.;
const MIN_PIXELS_PER_M: f64 = 0.5;
const MAX_PIXELS_PER_M: f64 = 10_000.;

pub struct Transform {
    /// The (not necessarily natural) number of pixels per m, i.e. the current scale of the map
    pixels_per_m: f64,
    /// The vector the entire on-screen map is moved by in pixels
    translation_px: [f64; 2],
}

impl Transform {
    /// Create a new standard transformation for the map.
    pub fn new() -> Self {
        Self {
            pixels_per_m: STANDARD_PIXELS_PER_M,
            translation_px: [0., 0.],
        }
    }

    /// Convert a point that is given in meters into the corresponding point in pixels.
    #[inline]
    pub fn point_m_to_px(&self, point: [f64; 2]) -> [f64; 2] {
        // Start by converting the absolute position in meters into the absolute position in
        // pixels, then add the translation of the screen.
        math::add(
            math::mul_scalar(point, self.pixels_per_m),
            self.translation_px,
        )
    }

    /// Convert an on-screen point into an absolute point with values in meters.
    #[inline]
    pub fn point_px_to_m(&self, point: [f64; 2]) -> [f64; 2] {
        // Start by subtracting the pixel translation and afterwards convert these absolute pixel
        // measurements into meters.
        math::mul_scalar(
            math::sub(point, self.translation_px),
            1. / self.pixels_per_m,
        )
    }

    /// Convert a length given in meters into a length in pixels
    #[inline]
    pub fn length_m_to_px(&self, length: f64) -> f64 {
        length * self.pixels_per_m
    }

    /// Convert a length given in pixels into a length in meters
    #[inline]
    pub fn length_px_to_m(&self, length: f64) -> f64 {
        length / self.pixels_per_m
    }

    /// Convert a rectangle which has measurements in meters into one of pixels
    #[inline]
    pub fn rect_m_to_px(&self, rect: [f64; 4]) -> [f64; 4] {
        let left_upper = self.point_m_to_px([rect[0], rect[1]]);
        [
            left_upper[0],
            left_upper[1],
            self.length_m_to_px(rect[2]),
            self.length_m_to_px(rect[3]),
        ]
    }

    /// Convert a rectangle which has measurements in pixels into one of meters
    #[inline]
    pub fn rect_px_to_m(&self, rect: [f64; 4]) -> [f64; 4] {
        let left_upper = self.point_px_to_m([rect[0], rect[1]]);
        [
            left_upper[0],
            left_upper[1],
            self.length_px_to_m(rect[2]),
            self.length_px_to_m(rect[3]),
        ]
    }

    /* Helper function to make sure the standard zoom factor is always exact. This helps
     * normalising zoom levels even when the user zooms in and out extremely often, assuming they
     * pass the standard zoom factor.
     */
    fn normalise_zoom(&mut self) {
        if self.pixels_per_m > STANDARD_PIXELS_PER_M - 5.
            && self.pixels_per_m < STANDARD_PIXELS_PER_M + 5.
        {
            self.pixels_per_m = STANDARD_PIXELS_PER_M;
        }
    }

    /// Attempts to zoom in a step and return true.
    /// If the maximum zoom is reached, this function changes nothing and returns false.
    pub fn try_zoom_in(&mut self) -> bool {
        // TODO: Zoom in on mouse pointer position
        if self.pixels_per_m < MAX_PIXELS_PER_M {
            self.pixels_per_m *= 1.2;
            self.normalise_zoom();
            true
        } else {
            false
        }
    }

    /// Attempts to zoom out a step and return true.
    /// If the minimum zoom is reached, this function changes nothing and returns false.
    pub fn try_zoom_out(&mut self) -> bool {
        // TODO: Zoom out at mouse pointer position
        if self.pixels_per_m > MIN_PIXELS_PER_M {
            self.pixels_per_m /= 1.2;
            self.normalise_zoom();
            true
        } else {
            false
        }
    }

    /// Move the canvas by the vector in pixels.
    pub fn move_by_px(&mut self, by: [f64; 2]) {
        self.translation_px = math::add(self.translation_px, by);
    }

    pub fn pixels_per_m(&self) -> f64 {
        self.pixels_per_m
    }
    pub fn translation_px(&self) -> [f64; 2] {
        self.translation_px
    }
}