// Copyright 2018 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#![warn(missing_docs)]

//! pbrt is a rust implementation of http://www.pbr-book.org/3ed-2018/contents.html

pub mod core;
pub mod filters;
pub mod textures;

#[cfg(feature = "float-as-double")]
/// submodule to defined types, constants and methods when `Float` is defined as a `f64` using the
/// "float-as-double" cargo feature.
pub mod float {
    pub use std::f64::*;
    /// Alias of the `f64` type, to be used through out the codebase anywhere a default sized
    /// `Float` is necessary.
    pub type Float = f64;
}

#[cfg(not(feature = "float-as-double"))]
/// submodule to defined types, constants and methods when `Float` is defined as a `f32` when not using the
/// "float-as-double" cargo feature.
pub mod float {
    pub use std::f32::*;
    /// Alias of the `f32` type, to be used through out the codebase anywhere a default sized
    /// `Float` is necessary.
    pub type Float = f32;
}

pub use float::Float;

/// Wrapper type for `Float` to ensure degree vs radian is clear.
#[derive(Copy, Clone)]
pub struct Degree(pub(crate) Float);

impl From<Float> for Degree {
    fn from(f: Float) -> Degree {
        Degree(f)
    }
}

/// Options for the renderer.  These are mostly passed through from commandline flags or from the
/// configuration file parsed.
#[derive(Clone, Debug)]
pub struct Options {
    /// number of threads to use when rendering.
    pub num_threads: u32,
    /// Not implemented: enable some options for quick draft quality rendering.
    pub quick_render: bool,
    /// Squelch all non-error output.
    pub quiet: bool,
    /// Enable extra logging output.
    pub verbose: bool,
    /// Path to stored rendered output.
    pub image_file: String,
}

impl Default for Options {
    fn default() -> Options {
        Options {
            num_threads: 1,
            quick_render: false,
            quiet: false,
            verbose: true,
            image_file: "".to_owned(),
        }
    }
}

//const PI: Float = 3.14159265358979323846;
//const INV_PI: Float = 0.31830988618379067154;
//const INV2_PI: Float = 0.15915494309189533577;
//const INV4_PI: Float = 0.07957747154594766788;
//const PI_OVER2: Float = 1.57079632679489661923;
//const PI_OVER4: Float = 0.78539816339744830961;
//const SQRT2: Float = 1.41421356237309504880;

/// Convert `value` into sRGB gamma-corrected value.
pub fn gamma_correct(value: Float) -> Float {
    if value <= 0.0031308 {
        12.92 * value
    } else {
        1.055 * value.powf(1. / 2.4) - 0.055
    }
}

/// Clamp `val` between `low` and `high`.
///
/// # Examples
/// ```
/// use pbrt::clamp;
///
/// assert_eq!(clamp(-1., 0., 1.), 0.);
/// assert_eq!(clamp(0.5, 0., 1.), 0.5);
/// assert_eq!(clamp(2., 0., 1.), 1.0);
///
/// assert_eq!(clamp(-1, 0, 2), 0);
/// assert_eq!(clamp(1, 0, 2), 1);
/// assert_eq!(clamp(3, 0, 2), 2);
/// ```
pub fn clamp<T>(val: T, low: T, high: T) -> T
where
    T: PartialOrd,
{
    if val < low {
        low
    } else if val > high {
        high
    } else {
        val
    }
}

/// Linear interpolate `t` between `v1` and `v2`.
///
/// # Examples
/// ```
/// use pbrt::lerp;
///
/// assert_eq!(lerp(0., 0., 1.), 0.);
/// assert_eq!(lerp(0.5, 0., 1.), 0.5);
/// assert_eq!(lerp(1., 0., 1.), 1.);
/// assert_eq!(lerp(0.75, 0., 2.), 1.5);
/// ```
pub fn lerp(t: Float, v1: Float, v2: Float) -> Float {
    (1. - t) * v1 + t * v2
}

/// Note: assert_almost_equal_options exists only for doc tests, it is not part of the pbrt API.
pub fn assert_almost_equal_options(l: Option<(Float, Float)>, r: Option<(Float, Float)>) {
    if l.is_none() && r.is_none() {
        return;
    }
    assert!(l.is_some());
    assert!(r.is_some());
    let l = l.unwrap();
    let r = r.unwrap();
    assert_almost_equal(l.0, r.0);
    assert_almost_equal(l.1, r.1);
}

fn assert_almost_equal(f1: Float, f2: Float) {
    let diff = (f1 - f2).abs();
    assert!(diff < float::EPSILON, "{} != {}, diff of {}", f1, f2, diff);
}

/// Find roots of quadratic equation, if they exist.
///
/// # Examples
/// From
/// https://www.cliffsnotes.com/study-guides/algebra/algebra-i/quadratic-equations/solving-quadratic-equations
/// ```
/// use pbrt::Float;
/// use pbrt::quadratic;
/// use pbrt::assert_almost_equal_options;
///
/// assert_eq!(quadratic(1., 1., 1.), None);
/// assert_eq!(quadratic(1., -6., -16.), Some((-2., 8.)));
/// assert_eq!(quadratic(1., 6., 5.), Some((-5., -1.)));
/// assert_eq!(quadratic(1., 0., -16.), Some((-4. ,4.)));
/// assert_eq!(quadratic(1., 6., 0.), Some((-6. ,0.)));
/// // This quadratic returns irrational numbers, so some care is taken to ensure the equality
/// // tests work out.
/// let three: Float = 3.;
/// assert_almost_equal_options(quadratic(1., 2., -2.),
///     Some(((-1.-three.sqrt()), (-1.+three.sqrt()))));
pub fn quadratic(a: Float, b: Float, c: Float) -> Option<(Float, Float)> {
    let a = a as f64;
    let b = b as f64;
    let c = c as f64;
    // Find quadratic discriminant
    let discrim = b * b - 4. * a * c;
    if discrim < 0. {
        return None;
    }
    let root_discrim = discrim.sqrt();
    let q = if b < 0. {
        -0.5 * (b - root_discrim)
    } else {
        -0.5 * (b + root_discrim)
    };
    let t0 = (q / a) as Float;
    let t1 = (c / q) as Float;
    if t0 > t1 {
        Some((t1, t0))
    } else {
        Some((t0, t1))
    }
}