use core::cmp;

use cast::u32;
use stm32::rcc::cfgr::{SWW, USBPREW};
use stm32::{rcc, RCC};

use flash::ACR;
use time::Hertz;

/// Extension trait that constrains the `RCC` peripheral
pub trait RccExt {
    /// Constrains the `RCC` peripheral so it plays nicely with the other abstractions
    fn constrain(self) -> Rcc;
}

impl RccExt for RCC {
    fn constrain(self) -> Rcc {
        Rcc {
            ahb: AHB { _0: () },
            apb1: APB1 { _0: () },
            apb2: APB2 { _0: () },
            cfgr: CFGR {
                hse: None,
                hclk: None,
                pclk1: None,
                pclk2: None,
                sysclk: None,
            },
        }
    }
}

/// Constrained RCC peripheral
pub struct Rcc {
    /// AMBA High-performance Bus (AHB) registers
    pub ahb: AHB,
    /// Advanced Peripheral Bus 1 (APB1) registers
    pub apb1: APB1,
    /// Advanced Peripheral Bus 2 (APB2) registers
    pub apb2: APB2,
    pub cfgr: CFGR,
}

/// AMBA High-performance Bus (AHB) registers
pub struct AHB {
    _0: (),
}

impl AHB {
    pub(crate) fn enr(&mut self) -> &rcc::AHBENR {
        // NOTE(unsafe) this proxy grants exclusive access to this register
        unsafe { &(*RCC::ptr()).ahbenr }
    }
}

/// Advanced Peripheral Bus 1 (APB1) registers
pub struct APB1 {
    _0: (),
}

impl APB1 {
    pub(crate) fn enr(&mut self) -> &rcc::APB1ENR {
        // NOTE(unsafe) this proxy grants exclusive access to this register
        unsafe { &(*RCC::ptr()).apb1enr }
    }

    pub(crate) fn rstr(&mut self) -> &rcc::APB1RSTR {
        // NOTE(unsafe) this proxy grants exclusive access to this register
        unsafe { &(*RCC::ptr()).apb1rstr }
    }
}

/// Advanced Peripheral Bus 2 (APB2) registers
pub struct APB2 {
    _0: (),
}

impl APB2 {
    pub(crate) fn enr(&mut self) -> &rcc::APB2ENR {
        // NOTE(unsafe) this proxy grants exclusive access to this register
        unsafe { &(*RCC::ptr()).apb2enr }
    }

    pub(crate) fn rstr(&mut self) -> &rcc::APB2RSTR {
        // NOTE(unsafe) this proxy grants exclusive access to this register
        unsafe { &(*RCC::ptr()).apb2rstr }
    }
}

const HSI: u32 = 8_000_000; // Hz

pub struct CFGR {
    hse: Option<u32>,
    hclk: Option<u32>,
    pclk1: Option<u32>,
    pclk2: Option<u32>,
    sysclk: Option<u32>,
}

impl CFGR {
    /// Uses HSE (external oscillator) instead of HSI (internal RC oscillator) as the clock source.
    /// Will result in a hang if an external oscillator is not connected or it fails to start.
    pub fn use_hse<F>(mut self, freq: F) -> Self
    where
        F: Into<Hertz>,
    {
        self.hse = Some(freq.into().0);
        self
    }

    /// Sets the desired frequency for the HCLK clock
    pub fn hclk<F>(mut self, freq: F) -> Self
    where
        F: Into<Hertz>,
    {
        self.hclk = Some(freq.into().0);
        self
    }

    /// Sets the desired frequency for the PCKL1 clock
    pub fn pclk1<F>(mut self, freq: F) -> Self
    where
        F: Into<Hertz>,
    {
        self.pclk1 = Some(freq.into().0);
        self
    }

    /// Sets the desired frequency for the PCLK2 clock
    pub fn pclk2<F>(mut self, freq: F) -> Self
    where
        F: Into<Hertz>,
    {
        self.pclk2 = Some(freq.into().0);
        self
    }

    /// Sets the desired frequency for the SYSCLK clock
    pub fn sysclk<F>(mut self, freq: F) -> Self
    where
        F: Into<Hertz>,
    {
        self.sysclk = Some(freq.into().0);
        self
    }

    pub fn freeze(self, acr: &mut ACR) -> Clocks {
        // TODO ADC clock

        let pllsrcclk = self.hse.unwrap_or(HSI / 2);

        let pllmul = self.sysclk.unwrap_or(pllsrcclk) / pllsrcclk;
        let pllmul = cmp::min(cmp::max(pllmul, 1), 16);

        let (pllmul_bits, sysclk) = if pllmul == 1 {
            (None, self.hse.unwrap_or(HSI))
        } else {
            (Some(pllmul as u8 - 2), pllsrcclk * pllmul)
        };

        assert!(sysclk <= 72_000_000);

        let hpre_bits = self.hclk
            .map(|hclk| match sysclk / hclk {
                0 => unreachable!(),
                1 => 0b0111,
                2 => 0b1000,
                3...5 => 0b1001,
                6...11 => 0b1010,
                12...39 => 0b1011,
                40...95 => 0b1100,
                96...191 => 0b1101,
                192...383 => 0b1110,
                _ => 0b1111,
            })
            .unwrap_or(0b0111);

        let hclk = sysclk / (1 << (hpre_bits - 0b0111));

        assert!(hclk <= 72_000_000);

        let ppre1_bits = self.pclk1
            .map(|pclk1| match hclk / pclk1 {
                0 => unreachable!(),
                1 => 0b011,
                2 => 0b100,
                3...5 => 0b101,
                6...11 => 0b110,
                _ => 0b111,
            })
            .unwrap_or(0b011);

        let ppre1 = 1 << (ppre1_bits - 0b011);
        let pclk1 = hclk / u32(ppre1);

        assert!(pclk1 <= 36_000_000);

        let ppre2_bits = self.pclk2
            .map(|pclk2| match hclk / pclk2 {
                0 => unreachable!(),
                1 => 0b011,
                2 => 0b100,
                3...5 => 0b101,
                6...11 => 0b110,
                _ => 0b111,
            })
            .unwrap_or(0b011);

        let ppre2 = 1 << (ppre2_bits - 0b011);
        let pclk2 = hclk / u32(ppre2);

        assert!(pclk2 <= 72_000_000);

        // adjust flash wait states
        unsafe {
            acr.acr().write(|w| {
                w.latency().bits(if sysclk <= 24_000_000 {
                    0b000
                } else if sysclk <= 48_000_000 {
                    0b001
                } else {
                    0b010
                })
            })
        }

        // the USB clock is only valid if an external crystal is used, the PLL is enabled, and the
        // PLL output frequency is a supported one.
        let (usbpre, usbclk_valid) = match (self.hse, pllmul_bits, sysclk) {
            (Some(_), Some(_), 72_000_000) => (USBPREW::DIV15, true),
            (Some(_), Some(_), 48_000_000) => (USBPREW::NODIV, true),
            _ => (USBPREW::NODIV, false),
        };

        let rcc = unsafe { &*RCC::ptr() };

        if self.hse.is_some() {
            // enable HSE and wait for it to be ready

            rcc.cr.modify(|_, w| w.hseon().set_bit());

            while rcc.cr.read().hserdy().bit_is_clear() {}
        }

        if let Some(pllmul_bits) = pllmul_bits {
            // enable PLL and wait for it to be ready

            rcc.cfgr.modify(|_, w| unsafe {
                w.pllmul()
                    .bits(pllmul_bits)
                    .pllsrc()
                    .bit(if self.hse.is_some() {
                        true
                    } else {
                        false
                    })
            });

            rcc.cr.modify(|_, w| w.pllon().set_bit());

            while rcc.cr.read().pllrdy().bit_is_clear() {}
        }

        // set prescalers and clock source
        rcc.cfgr.modify(|_, w| unsafe {
            w.ppre2()
                .bits(ppre2_bits)
                .ppre1()
                .bits(ppre1_bits)
                .hpre()
                .bits(hpre_bits)
                .usbpre()
                .variant(usbpre)
                .sw()
                .variant(if pllmul_bits.is_some() {
                    SWW::PLL
                } else if self.hse.is_some() {
                    SWW::HSE
                } else {
                    SWW::HSI
                })
        });

        Clocks {
            hclk: Hertz(hclk),
            pclk1: Hertz(pclk1),
            pclk2: Hertz(pclk2),
            ppre1,
            ppre2,
            sysclk: Hertz(sysclk),
            usbclk_valid,
        }
    }
}

/// Frozen clock frequencies
///
/// The existence of this value indicates that the clock configuration can no longer be changed
#[derive(Clone, Copy)]
pub struct Clocks {
    hclk: Hertz,
    pclk1: Hertz,
    pclk2: Hertz,
    ppre1: u8,
    ppre2: u8,
    sysclk: Hertz,
    usbclk_valid: bool,
}

impl Clocks {
    /// Returns the frequency of the AHB
    pub fn hclk(&self) -> Hertz {
        self.hclk
    }

    /// Returns the frequency of the APB1
    pub fn pclk1(&self) -> Hertz {
        self.pclk1
    }

    /// Returns the frequency of the APB2
    pub fn pclk2(&self) -> Hertz {
        self.pclk2
    }

    pub(crate) fn ppre1(&self) -> u8 {
        self.ppre1
    }

    // TODO remove `allow`
    #[allow(dead_code)]
    pub(crate) fn ppre2(&self) -> u8 {
        self.ppre2
    }

    /// Returns the system (core) frequency
    pub fn sysclk(&self) -> Hertz {
        self.sysclk
    }

    /// Returns whether the USBCLK clock frequency is valid for the USB peripheral
    pub fn usbclk_valid(&self) -> bool {
        self.usbclk_valid
    }
}