use crate::time::Duration;

const SECS_IN_MINUTE: u64 = 60;
const SECS_IN_HOUR: u64 = SECS_IN_MINUTE * 60;
const SECS_IN_DAY: u64 = SECS_IN_HOUR * 24;

#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
pub struct Instant(Duration);

#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
pub struct SystemTime(Duration);

pub const UNIX_EPOCH: SystemTime = SystemTime(Duration::from_secs(0));

impl Instant {
    pub fn now() -> Instant {
        // If we have a timestamp protocol, use it.
        if let Some(x) = instant_internal::timestamp_protocol() {
            return x;
        }

        if let Some(x) = instant_internal::platform_specific() {
            return x;
        }

        panic!("time not implemented on this platform")
    }

    pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
        self.0.checked_sub(other.0)
    }

    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
        Some(Instant(self.0.checked_add(*other)?))
    }

    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
        Some(Instant(self.0.checked_sub(*other)?))
    }
}

impl SystemTime {
    pub fn now() -> SystemTime {
        system_time_internal::now()
            .unwrap_or_else(|| panic!("time not implemented on this platform"))
    }

    pub fn sub_time(&self, other: &SystemTime) -> Result<Duration, Duration> {
        self.0.checked_sub(other.0).ok_or_else(|| other.0 - self.0)
    }

    pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
        Some(SystemTime(self.0.checked_add(*other)?))
    }

    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
        Some(SystemTime(self.0.checked_sub(*other)?))
    }
}

pub(crate) mod system_time_internal {
    use super::super::helpers;
    use super::*;
    use crate::mem::MaybeUninit;
    use crate::ptr::NonNull;
    use r_efi::efi::{RuntimeServices, Time};

    pub fn now() -> Option<SystemTime> {
        let runtime_services: NonNull<RuntimeServices> = helpers::runtime_services()?;
        let mut t: MaybeUninit<Time> = MaybeUninit::uninit();
        let r = unsafe {
            ((*runtime_services.as_ptr()).get_time)(t.as_mut_ptr(), crate::ptr::null_mut())
        };

        if r.is_error() {
            return None;
        }

        let t = unsafe { t.assume_init() };

        Some(SystemTime(uefi_time_to_duration(t)))
    }

    // This algorithm is based on the one described in the post
    // https://blog.reverberate.org/2020/05/12/optimizing-date-algorithms.html
    pub const fn uefi_time_to_duration(t: r_efi::system::Time) -> Duration {
        assert!(t.month <= 12);
        assert!(t.month != 0);

        const YEAR_BASE: u32 = 4800; /* Before min year, multiple of 400. */

        // Calculate the number of days since 1/1/1970
        // Use 1 March as the start
        let (m_adj, overflow): (u32, bool) = (t.month as u32).overflowing_sub(3);
        let (carry, adjust): (u32, u32) = if overflow { (1, 12) } else { (0, 0) };
        let y_adj: u32 = (t.year as u32) + YEAR_BASE - carry;
        let month_days: u32 = (m_adj.wrapping_add(adjust) * 62719 + 769) / 2048;
        let leap_days: u32 = y_adj / 4 - y_adj / 100 + y_adj / 400;
        let days: u32 = y_adj * 365 + leap_days + month_days + (t.day as u32 - 1) - 2472632;

        let localtime_epoch: u64 = (days as u64) * SECS_IN_DAY
            + (t.second as u64)
            + (t.minute as u64) * SECS_IN_MINUTE
            + (t.hour as u64) * SECS_IN_HOUR;

        let utc_epoch: u64 = if t.timezone == r_efi::efi::UNSPECIFIED_TIMEZONE {
            localtime_epoch
        } else {
            (localtime_epoch as i64 + (t.timezone as i64) * SECS_IN_MINUTE as i64) as u64
        };

        Duration::new(utc_epoch, t.nanosecond)
    }
}

pub(crate) mod instant_internal {
    use super::super::helpers;
    use super::*;
    use crate::mem::MaybeUninit;
    use crate::ptr::NonNull;
    use crate::sync::atomic::{AtomicPtr, Ordering};
    use crate::sys_common::mul_div_u64;
    use r_efi::protocols::timestamp;

    const NS_PER_SEC: u64 = 1_000_000_000;

    pub fn timestamp_protocol() -> Option<Instant> {
        fn try_handle(handle: NonNull<crate::ffi::c_void>) -> Option<u64> {
            let protocol: NonNull<timestamp::Protocol> =
                helpers::open_protocol(handle, timestamp::PROTOCOL_GUID).ok()?;
            let mut properties: MaybeUninit<timestamp::Properties> = MaybeUninit::uninit();

            let r = unsafe { ((*protocol.as_ptr()).get_properties)(properties.as_mut_ptr()) };
            if r.is_error() {
                return None;
            }

            let freq = unsafe { properties.assume_init().frequency };
            let ts = unsafe { ((*protocol.as_ptr()).get_timestamp)() };
            Some(mul_div_u64(ts, NS_PER_SEC, freq))
        }

        static LAST_VALID_HANDLE: AtomicPtr<crate::ffi::c_void> =
            AtomicPtr::new(crate::ptr::null_mut());

        if let Some(handle) = NonNull::new(LAST_VALID_HANDLE.load(Ordering::Acquire)) {
            if let Some(ns) = try_handle(handle) {
                return Some(Instant(Duration::from_nanos(ns)));
            }
        }

        if let Ok(handles) = helpers::locate_handles(timestamp::PROTOCOL_GUID) {
            for handle in handles {
                if let Some(ns) = try_handle(handle) {
                    LAST_VALID_HANDLE.store(handle.as_ptr(), Ordering::Release);
                    return Some(Instant(Duration::from_nanos(ns)));
                }
            }
        }

        None
    }

    pub fn platform_specific() -> Option<Instant> {
        cfg_if::cfg_if! {
            if #[cfg(any(target_arch = "x86_64", target_arch = "x86"))] {
                timestamp_rdtsc().map(Instant)
            } else {
                None
            }
        }
    }

    #[cfg(target_arch = "x86_64")]
    fn timestamp_rdtsc() -> Option<Duration> {
        if !crate::arch::x86_64::has_cpuid() {
            return None;
        }

        static FREQUENCY: crate::sync::OnceLock<u64> = crate::sync::OnceLock::new();

        // Get Frequency in Mhz
        // Inspired by [`edk2/UefiCpuPkg/Library/CpuTimerLib/CpuTimerLib.c`](https://github.com/tianocore/edk2/blob/master/UefiCpuPkg/Library/CpuTimerLib/CpuTimerLib.c)
        let freq = FREQUENCY
            .get_or_try_init(|| {
                let cpuid = unsafe { crate::arch::x86_64::__cpuid(0x15) };
                if cpuid.eax == 0 || cpuid.ebx == 0 || cpuid.ecx == 0 {
                    return Err(());
                }
                Ok(mul_div_u64(cpuid.ecx as u64, cpuid.ebx as u64, cpuid.eax as u64))
            })
            .ok()?;

        let ts = unsafe { crate::arch::x86_64::_rdtsc() };
        let ns = mul_div_u64(ts, 1000, *freq);
        Some(Duration::from_nanos(ns))
    }

    #[cfg(target_arch = "x86")]
    fn timestamp_rdtsc() -> Option<Duration> {
        if !crate::arch::x86::has_cpuid() {
            return None;
        }

        static FREQUENCY: crate::sync::OnceLock<u64> = crate::sync::OnceLock::new();

        let freq = FREQUENCY
            .get_or_try_init(|| {
                let cpuid = unsafe { crate::arch::x86::__cpuid(0x15) };
                if cpuid.eax == 0 || cpuid.ebx == 0 || cpuid.ecx == 0 {
                    return Err(());
                }
                Ok(mul_div_u64(cpuid.ecx as u64, cpuid.ebx as u64, cpuid.eax as u64))
            })
            .ok()?;

        let ts = unsafe { crate::arch::x86::_rdtsc() };
        let ns = mul_div_u64(ts, 1000, *freq);
        Some(Duration::from_nanos(ns))
    }
}
