// Copyright 2020 Brian J. Tarricone <brian@tarricone.org>
// 
// 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
// 
//     http://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.

//! The `aqi` crate provides functions for calculating the Air Quality
//! Index based on concentrations of particuate matter.
//!
//! The AQI is defined for ozone (O₃), 1.0-2.5 micron particulate matter
//! (PM2.5), 2.5-10 micron particulate matter (PM10), carbon monoxide
//! (CO), sulfur dioxide (SO₂), and nitrogen dioxide (NO₂).
//!
//! The AQI helps make air quality more understandable to laypersons,
//! normalizing air quality on a scale from 0 to 500, with round-number
//! ranges that indicate qualities such as "Good", "Unhealthy", and
//! "Hazardous".
//!
//! Further details about AQI in general can be found at
//! [https://www.airnow.gov/aqi/aqi-basics/](https://www.airnow.gov/aqi/aqi-basics/).
//!
//! Further details about the AQI equation can be found at 
//! [https://www.airnow.gov/publications/air-quality-index/technical-assistance-document-for-reporting-the-daily-aqi/](https://www.airnow.gov/publications/air-quality-index/technical-assistance-document-for-reporting-the-daily-aqi/).
//!
//! Additionally, this library supports "adjusted" PM2.5 AQI values, using
//! the LRAPA and AQandU conversion formulas.

use core::convert::TryFrom;

/// Represents the human-friendly interpretation of the AQI
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub enum AirQualityLevel {
    /// The air quality is good and safe for everyone
    Good,
    /// The air quality is moderate, but unusually sensitive people should avoid heavy outdoor
    /// exertion
    Moderate,
    /// The air quality is unhealthy for those with respiratory issues or other health problems
    UnhealthySensitive,
    /// The air quality is unhealthy for everyone
    Unhealthy,
    /// The air quality is very unhealthy for everyone
    VeryUnhealthy,
    /// The air quality is hazardous and everyone should avoid outdoor exertion
    Hazardous,
}

macro_rules! def_try_from_aq {
    ($tpe:ty) => {
        impl TryFrom<$tpe> for AirQualityLevel {
            type Error = &'static str;
            fn try_from(v: $tpe) -> Result<Self, Self::Error> {
                use AirQualityLevel::*;
                match v {
                    0..=50 => Ok(Good),
                    51..=100 => Ok(Moderate),
                    101..=150 => Ok(UnhealthySensitive),
                    151..=200 => Ok(Unhealthy),
                    201..=300 => Ok(VeryUnhealthy),
                    301..=500 => Ok(Hazardous),
                    _ => Err("Value is out of range for AQI"),
                }
            }
        }
    }
}

def_try_from_aq!{u16}
def_try_from_aq!{i16}
def_try_from_aq!{u32}
def_try_from_aq!{i32}
def_try_from_aq!{u64}
def_try_from_aq!{i64}

/// Result type for AQI calculations
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub struct AirQuality {
    /// The numerical AQI value, in a range between 0 and 500
    pub aqi: u32,
    /// The human-friendly interpretation of the numeric AQI value
    pub level: AirQualityLevel,
}

struct Breakpoint {
    conc_low: f64,
    conc_high: f64,
    aqi_low: u32,
    aqi_high: u32,
    level: AirQualityLevel,
}

const OZONE8_BREAKPOINTS: [Breakpoint; 5] = [
    Breakpoint { conc_low: 0.000, conc_high: 0.054, aqi_low:   0, aqi_high:  50, level: AirQualityLevel::Good, },
    Breakpoint { conc_low: 0.055, conc_high: 0.070, aqi_low:  51, aqi_high: 100, level: AirQualityLevel::Moderate, },
    Breakpoint { conc_low: 0.071, conc_high: 0.085, aqi_low: 101, aqi_high: 150, level: AirQualityLevel::UnhealthySensitive, },
    Breakpoint { conc_low: 0.086, conc_high: 0.105, aqi_low: 151, aqi_high: 200, level: AirQualityLevel::Unhealthy, },
    Breakpoint { conc_low: 0.106, conc_high: 0.200, aqi_low: 201, aqi_high: 300, level: AirQualityLevel::VeryUnhealthy, },
];
const OZONE1_BREAKPOINTS: [Breakpoint; 5] = [
    Breakpoint { conc_low: 0.125, conc_high: 0.164, aqi_low: 101, aqi_high: 150, level: AirQualityLevel::UnhealthySensitive, },
    Breakpoint { conc_low: 0.165, conc_high: 0.204, aqi_low: 151, aqi_high: 200, level: AirQualityLevel::Unhealthy, },
    Breakpoint { conc_low: 0.205, conc_high: 0.404, aqi_low: 201, aqi_high: 300, level: AirQualityLevel::VeryUnhealthy, },
    Breakpoint { conc_low: 0.405, conc_high: 0.504, aqi_low: 301, aqi_high: 400, level: AirQualityLevel::Hazardous, },
    Breakpoint { conc_low: 0.505, conc_high: 0.604, aqi_low: 401, aqi_high: 500, level: AirQualityLevel::Hazardous, },
];
const PM25_BREAKPOINTS: [Breakpoint; 7] = [
    Breakpoint { conc_low:   0.0, conc_high:  12.0, aqi_low:   0, aqi_high:  50, level: AirQualityLevel::Good, },
    Breakpoint { conc_low:  12.1, conc_high:  35.4, aqi_low:  51, aqi_high: 100, level: AirQualityLevel::Moderate, },
    Breakpoint { conc_low:  35.5, conc_high:  55.4, aqi_low: 101, aqi_high: 150, level: AirQualityLevel::UnhealthySensitive, },
    Breakpoint { conc_low:  55.5, conc_high: 150.4, aqi_low: 151, aqi_high: 200, level: AirQualityLevel::Unhealthy, },
    Breakpoint { conc_low: 150.5, conc_high: 250.4, aqi_low: 201, aqi_high: 300, level: AirQualityLevel::VeryUnhealthy, },
    Breakpoint { conc_low: 250.5, conc_high: 350.4, aqi_low: 301, aqi_high: 400, level: AirQualityLevel::Hazardous, },
    Breakpoint { conc_low: 350.5, conc_high: 500.4, aqi_low: 401, aqi_high: 500, level: AirQualityLevel::Hazardous, },
];
const PM10_BREAKPOINTS: [Breakpoint; 7] = [
    Breakpoint { conc_low:   0.0, conc_high:  54.0, aqi_low:   0, aqi_high:  50, level: AirQualityLevel::Good, },
    Breakpoint { conc_low:  55.0, conc_high: 154.0, aqi_low:  51, aqi_high: 100, level: AirQualityLevel::Moderate, },
    Breakpoint { conc_low: 155.0, conc_high: 254.0, aqi_low: 101, aqi_high: 150, level: AirQualityLevel::UnhealthySensitive, },
    Breakpoint { conc_low: 255.0, conc_high: 354.0, aqi_low: 151, aqi_high: 200, level: AirQualityLevel::Unhealthy, },
    Breakpoint { conc_low: 355.0, conc_high: 424.0, aqi_low: 201, aqi_high: 300, level: AirQualityLevel::VeryUnhealthy, },
    Breakpoint { conc_low: 425.0, conc_high: 504.0, aqi_low: 301, aqi_high: 400, level: AirQualityLevel::Hazardous, },
    Breakpoint { conc_low: 505.0, conc_high: 604.0, aqi_low: 401, aqi_high: 500, level: AirQualityLevel::Hazardous, },
];
const CO_BREAKPOINTS: [Breakpoint; 7] = [
    Breakpoint { conc_low:   0.0, conc_high:   4.4, aqi_low:   0, aqi_high:  50, level: AirQualityLevel::Good, },
    Breakpoint { conc_low:   4.5, conc_high:   9.4, aqi_low:  51, aqi_high: 100, level: AirQualityLevel::Moderate, },
    Breakpoint { conc_low:   9.5, conc_high:  12.4, aqi_low: 101, aqi_high: 150, level: AirQualityLevel::UnhealthySensitive, },
    Breakpoint { conc_low:  12.5, conc_high:  15.4, aqi_low: 151, aqi_high: 200, level: AirQualityLevel::Unhealthy, },
    Breakpoint { conc_low:  15.5, conc_high:  30.4, aqi_low: 201, aqi_high: 300, level: AirQualityLevel::VeryUnhealthy, },
    Breakpoint { conc_low:  30.5, conc_high:  40.4, aqi_low: 301, aqi_high: 400, level: AirQualityLevel::Hazardous, },
    Breakpoint { conc_low:  40.5, conc_high:  50.4, aqi_low: 401, aqi_high: 500, level: AirQualityLevel::Hazardous, },
];
const SO2_1_BREAKPOINTS: [Breakpoint; 3] = [
    Breakpoint { conc_low:   0.0, conc_high:  35.0, aqi_low:   0, aqi_high:  50, level: AirQualityLevel::Good, },
    Breakpoint { conc_low:  36.0, conc_high:  75.0, aqi_low:  51, aqi_high: 100, level: AirQualityLevel::Moderate, },
    Breakpoint { conc_low:  76.0, conc_high: 185.0, aqi_low: 101, aqi_high: 150, level: AirQualityLevel::UnhealthySensitive, },
];
const SO2_24_BREAKPOINTS: [Breakpoint; 7] = [
    Breakpoint { conc_low:   0.0, conc_high:  35.0, aqi_low:   0, aqi_high:  50, level: AirQualityLevel::Good, },
    Breakpoint { conc_low:  36.0, conc_high:  75.0, aqi_low:  51, aqi_high: 100, level: AirQualityLevel::Moderate, },
    Breakpoint { conc_low:  76.0, conc_high: 185.0, aqi_low: 101, aqi_high: 150, level: AirQualityLevel::UnhealthySensitive, },
    Breakpoint { conc_low: 186.0, conc_high: 304.0, aqi_low: 151, aqi_high: 200, level: AirQualityLevel::Unhealthy, },
    Breakpoint { conc_low: 305.0, conc_high: 604.0, aqi_low: 201, aqi_high: 300, level: AirQualityLevel::VeryUnhealthy, },
    Breakpoint { conc_low: 605.0, conc_high: 804.0, aqi_low: 301, aqi_high: 400, level: AirQualityLevel::Hazardous, },
    Breakpoint { conc_low: 805.0, conc_high:1004.0, aqi_low: 401, aqi_high: 500, level: AirQualityLevel::Hazardous, },
];
const NO2_BREAKPOINTS: [Breakpoint; 7] = [
    Breakpoint { conc_low:   0.0, conc_high:  53.0, aqi_low:   0, aqi_high:  50, level: AirQualityLevel::Good, },
    Breakpoint { conc_low:  54.0, conc_high: 100.0, aqi_low:  51, aqi_high: 100, level: AirQualityLevel::Moderate, },
    Breakpoint { conc_low: 101.0, conc_high: 360.0, aqi_low: 101, aqi_high: 150, level: AirQualityLevel::UnhealthySensitive, },
    Breakpoint { conc_low: 361.0, conc_high: 649.0, aqi_low: 151, aqi_high: 200, level: AirQualityLevel::Unhealthy, },
    Breakpoint { conc_low: 650.0, conc_high:1249.0, aqi_low: 201, aqi_high: 300, level: AirQualityLevel::VeryUnhealthy, },
    Breakpoint { conc_low:1250.0, conc_high:1649.0, aqi_low: 301, aqi_high: 400, level: AirQualityLevel::Hazardous, },
    Breakpoint { conc_low:1650.0, conc_high:2049.0, aqi_low: 401, aqi_high: 500, level: AirQualityLevel::Hazardous, },
];

fn find_breakpoint(breakpoints: &[Breakpoint], concentration: f64) -> Option<&Breakpoint> {
    breakpoints.iter().find(|breakpoint| breakpoint.conc_low <= concentration && concentration <= breakpoint.conc_high)
}

fn calc_aqi(breakpoints: &[Breakpoint], concentration: f64) -> Option<AirQuality> {
    find_breakpoint(breakpoints, concentration).map(|breakpoint| {
        let aqi = (
            (
                (breakpoint.aqi_high as f64 - breakpoint.aqi_low as f64) /
                (breakpoint.conc_high - breakpoint.conc_low)
            ) *
            (concentration - breakpoint.conc_low) +
            (breakpoint.aqi_low as f64)
        ).round() as u32;
        AirQuality {
            aqi,
            level: breakpoint.level,
        }
    })
}

fn trunc(value: f64, nplaces: u32) -> f64 {
    let truncator = 10_u32.pow(nplaces) as f64;
    ((value * truncator) as u64) as f64 / truncator
}

/// Calculates the Ozone Air Quality Index from the provided 8-hour concentration
///
/// The AQI is defined for concentrations between 0.000 and 0.200 ppm.  For
/// values between 0.201 and 0.604 ppm, a 1-hour concentration should be used if
/// available.
///
/// # Arguments
///
/// * `concentration` - The 8-hour ozone concentration in ppm
pub fn ozone8(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&OZONE8_BREAKPOINTS, trunc(concentration, 3))
}

/// Calculates the ozone Air Quality Index from the provided 1-hour concentration
///
/// The AQI is defined for concentrations between 0.125 and 0.604 ppm.  For
/// values between 0.000 and 0.124 ppm, an 8-hour concentration should be used if
/// available.
///
/// # Arguments
///
/// * `concentration` - The 1-hour ozone concentration in ppm
pub fn ozone1(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&OZONE1_BREAKPOINTS, trunc(concentration, 3))
}

/// Calculates the PM2.5 Air Quality Index from the provided 24-hour concentration
///
/// The AQI is defined for concentrations between 0.0 and 500.4 µg/m³.
///
/// # Arguments
///
/// * `concentration` - The 24-hour PM2.5 concentration in µg/m³
pub fn pm2_5(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&PM25_BREAKPOINTS, trunc(concentration, 1))
}

/// Calcuates the LRAPA-adjusted PM2.5 Air Quality Index for the provided 24-hour concentration
///
/// See
/// [https://www.lrapa.org/DocumentCenter/View/4147/PurpleAir-Correction-Summary](https://www.lrapa.org/DocumentCenter/View/4147/PurpleAir-Correction-Summary)
/// for more information.
///
/// The LRAPA-adjusted AQI is defined for concentrations between 0.66 and
/// 1002.12 µg/m³.
///
///
/// # Arguments
///
/// * `concentration` - The 24-hour PM2.5 concentration in µg/m³
pub fn pm2_5_lrapa(concentration: f64) -> Option<AirQuality> {
    if concentration <= 65.0 {
        calc_aqi(&PM25_BREAKPOINTS, trunc(0.5 * concentration - 0.66, 1))
    } else {
        None
    }
}

/// Calcuates the AQandU-adjusted PM2.5 Air Quality Index for the provided 24-hour concentration
///
/// See
/// [https://www.aqandu.org/airu_sensor#calibrationSection](https://www.aqandu.org/airu_sensor#calibrationSection)
/// for more information.
///
/// The AQandU-adjusted AQI is defined for concentrations between 0.0 and
/// 639.78 µg/m³.
///
/// # Arguments
///
/// * `concentration` - The 24-hour PM2.5 concentration in µg/m³
pub fn pm2_5_aqandu(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&PM25_BREAKPOINTS, trunc(0.778 * concentration + 2.65, 1))
}

/// Calculates the PM10 Air Quality Index from the provided 24-hour concentration
///
/// The AQI is defined for concentrations between 0.0 and 604.0 µg/m³.
///
/// # Arguments
///
/// * `concentration` - The 24-hour PM10 concentration in µg/m³
pub fn pm10(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&PM10_BREAKPOINTS, concentration as u32 as f64)
}

/// Calculates the carbon monoxide Air Quality Index from the provided 8-hour concentration
///
/// The AQI is defined for concentrations between 0.0 and 50.4 ppm.
///
/// # Arguments
///
/// * `concentration` - The 8-hour CO concentration in ppm
pub fn co(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&CO_BREAKPOINTS, trunc(concentration, 1))
}

/// Calculates the sulfur dioxide Air Quality Index from the provided 1-hour concentration
///
/// The AQI is  defined for concentrations between 0 and 185 ppb.  For
/// values between 186 and 1004 ppb, a 24-hour concentration should be used if
/// available.
///
/// # Arguments
///
/// * `concentration` - The 1-hour SO₂ concentration in ppb
pub fn so2_1(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&SO2_1_BREAKPOINTS, trunc(concentration, 0))
}

/// Calculates the sulfur dioxide Air Quality Index from the provided 24-hour concentration
///
/// The AQI is defined for concentrations between 0 and 1004 ppb.
///
/// # Arguments
///
/// * `concentration` - The 24-hour SO₂ concentration in ppb
pub fn so2_24(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&SO2_24_BREAKPOINTS, trunc(concentration, 0))
}

/// Calculates the nitrogen dioxide Air Quality Index from the provided 1-hour concentration
///
/// The AQI is defined for concentrations between 0 and 2049 ppb.
///
/// # Arguments
///
/// * `concentration` - The 1-hour NO₂ concentration in ppb
pub fn no2(concentration: f64) -> Option<AirQuality> {
    calc_aqi(&NO2_BREAKPOINTS, trunc(concentration, 0))
}

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

    #[test]
    fn test_pm2_5() {
        let test_data: [(f64, u32); 22] = [
            (0.0, 0),
            (12.0, 50),
            (12.1, 51),
            (16.0, 59),
            (35.4, 100),
            (35.5, 101),
            (55.4, 150),
            (55.5, 151),
            (85.0, 166),
            (94.0, 171),
            (138.0, 194),
            (150.4, 200),
            (150.5, 201),
            (158.0, 208),
            (175.0, 225),
            (192.0, 242),
            (200.0, 250),
            (250.4, 300),
            (250.5, 301),
            (350.4, 400),
            (350.5, 401),
            (500.4, 500),
        ];

        for (conc, aqi) in test_data.iter() {
            assert_eq!(Some(*aqi), pm2_5(*conc).map(|aq| aq.aqi));
        }
    }
}