// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2025 Lennard Kittner <lennard@kittner.dev>

//! CPU Frequency scaling.
//!
//! C header: [`include/linux/cpufreq.h`](srctree/include/linux/cpufreq.h)

use core::marker::PhantomData;
use crate::bindings;


//TODO: policy also contains a cpufreq_governor 
// we probably have to register our own governor or find a governor that will do what we tell it to do.
// We could also try to unregister the governor and see what happens without a governor

/// Returns the current CPU frequency (in kHz)
/// cpufreq_get wrapper
pub fn get_current_frequency(cpu: u32) -> u32 {
    unsafe { bindings::cpufreq_get(cpu) }
}

/// Gets the CPU frequency (in kHz) from policy->cur
/// This is the last known freq, without actually getting it from the driver.
/// Return value will be same as what is shown in scaling_cur_freq in sysfs
/// cpufreq_quick_get wrapper
pub fn get_current_frequency_from_policy(cpu: u32) -> u32 {
    unsafe { bindings::cpufreq_quick_get(cpu) }
}

/// Relations between frequencies
#[derive(Debug, Clone, Copy)]
#[repr(u32)]
pub enum FrequencyRelation {
    /// Lowest frequency at or above target
    Lowest = 0,
    /// Highest frequency below or at target
    Highest = 1,
    /// Closest frequency to target
    Closest = 2,
    /// Get if possible an efficient frequency
    /// Efficient = 1 << 2
    /// Lowest + Efficient
    LowestEfficient = 0 | 1 << 2,
    /// Highest + Efficient
    HighestEfficient = 1 | 1 << 2,
    /// Closest + Efficient
    ClosestEfficient = 2 | 1 << 2,
}

/// cpufreq_cpuinfo wrapper
#[repr(transparent)]
pub struct CpufreqCpuinfo {
    inner: bindings::cpufreq_cpuinfo,
}

impl CpufreqCpuinfo {
    /// Creates CpufreqCpuinfo from raw cpufreq_cpuinfo
    pub fn new(info: bindings::cpufreq_cpuinfo) -> CpufreqCpuinfo {
        CpufreqCpuinfo {
            inner: info,
        }
    }

    /// The raw cpufreq_cpuinfo
    pub fn get_raw(&self) -> bindings::cpufreq_cpuinfo {
        self.inner
    }

    /// The maximum frequency in kHz
    pub fn get_max_frequency(&self) -> u32 {
        self.inner.max_freq
    }

    /// The minimum frequency in kHz
    pub fn get_min_frequency(&self) -> u32 {
        self.inner.min_freq
    }

    /// The transition latency in nanoseconds
    /// TODO: can I return Duration
    pub fn get_transition_latency(&self) -> u32 {
        self.inner.transition_latency
    }
}


/// Marker type for read only access
pub struct ReadOnly;
/// Marker type for read and write access
pub struct ReadWrite;

/// cpufreq_policy wrapper
#[repr(transparent)]
pub struct CpufreqPolicy<AccessType: 'static> {
    inner: *mut bindings::cpufreq_policy,
    _access_type: PhantomData<AccessType>
}

impl CpufreqPolicy<ReadOnly> {
    /// Returns the frequency policy of a specific CPU and mark it as busy.
    pub fn get_policy_from_cpu(cpu: u32) -> Option<CpufreqPolicy<ReadOnly
>> {
        let ptr = unsafe { bindings::cpufreq_cpu_get(cpu) };
        if ptr == core::ptr::null_mut() {
            None
        } else {
            Some(CpufreqPolicy {
                inner: ptr,
                _access_type: PhantomData,
            })
        }
    }

    /// Puts this policy on the cpu it belongs to
    pub fn put_on_cpu(self) {
        // drop will call cpufreq_cpu_put
    }
}

impl CpufreqPolicy<ReadWrite> {
   /// Returns the frequency policy of a specific CPU and mark it as busy and lock it.
   pub fn acquire_policy_from_cpu(cpu: u32) -> Option<CpufreqPolicy<ReadWrite>> {
        let ptr = unsafe { bindings::cpufreq_cpu_acquire(cpu) };
        if ptr == core::ptr::null_mut() {
            None
        } else {
            Some(CpufreqPolicy {
                inner: ptr,
                _access_type: PhantomData,
            })
        }
    }

    /// Releases the lock on this policy and puts it on the cpu it belongs to
    pub fn release(self) {
        // drop will call cpufreq_cpu_release
    }

    /// Reevaluates the policy on the CPU
    pub fn update(&self) {
        let cpu = unsafe { *self.inner }.cpu;
        unsafe { bindings::cpufreq_update_policy(cpu) };
    }

    /// Enable fast frequency switching for the policy.
    /// The attempt will fail if there is at least one transition notifier registered
    /// at this point, as fast frequency switching is quite fundamentally at odds
    /// with transition notifiers. Thus if successful, it will make registration of
    /// transition notifiers fail going forward.
    pub fn enable_fast_switching(&mut self) {
        unsafe { bindings::cpufreq_enable_fast_switch(self.as_ptr()) };
    }

    /// Disables fast frequency switching for the policy.
    pub fn disable_fast_switch(&mut self) {
        unsafe { bindings::cpufreq_disable_fast_switch(self.as_ptr()) };
    }

    /// Sets the maximum frequency of the policy
    pub fn set_max_frequency(&mut self, max: u32) {
        unsafe { *self.inner }.max = max;
    }

    /// Sets the minimum frequency of the policy
    pub fn set_min_frequency(&mut self, min: u32) {
        unsafe { *self.inner }.min = min;
    }

    /// Pass a target frequency to the cpufreq driver
    pub fn set_driver_target(&mut self, target_freq: u32, relation: FrequencyRelation) -> Result<(), i32> {
        let err = unsafe { bindings::cpufreq_driver_target(self.as_ptr(), target_freq, relation as u32) };
        if err == 0 {
            Ok(())
        } else {
            Err(err)
        }
    }

}

impl<AccessType> CpufreqPolicy<AccessType> {
    /// Returns a raw pointer to the inner C struct.
    #[inline]
    pub fn as_ptr(&self) -> *mut bindings::cpufreq_policy {
        self.inner
    }

    /// Whether the policy is inactive
    /// TODO: doc and inline static
    pub fn is_inactive(&self) -> bool {
        //bindings::policy_is_inactive(self.as_ptr())
        todo!()
    }

    /// Whether the policy is shared
    /// TODO: doc and inline static
    pub fn is_shared(&self) -> bool {
        //bindings::policy_is_shared(self.as_ptr())
        todo!()
    }

    /// Returns the cpu frequency info
    pub fn get_cpu_frequency_info(&self) -> CpufreqCpuinfo {
        CpufreqCpuinfo::new(unsafe {*self.inner}.cpuinfo)
    }

    /// Returns the minimum frequency of the policy in kHz
    pub fn get_min_frequency(&self) -> u32 {
        unsafe { *self.inner }.min
    }

    /// Returns the maximum frequency of the policy in kHz
    pub fn get_max_frequency(&self) -> u32 {
        unsafe { *self.inner }.max
    }

    /// Returns the current frequency targeted by the policy in kHz
    /// only needed if cpufreq governors are used
    pub fn get_current_frequency(&self) -> u32 {
        unsafe { *self.inner }.cur
    }
}

impl<AccessType: 'static> Drop for CpufreqPolicy<AccessType> {
    fn drop(&mut self) {
        if core::any::TypeId::of::<AccessType>() == core::any::TypeId::of::<ReadOnly>() {
            unsafe { bindings::cpufreq_cpu_put(self.as_ptr()) }
        }
        if core::any::TypeId::of::<AccessType>() == core::any::TypeId::of::<ReadWrite>() {
            unsafe { bindings::cpufreq_cpu_release(self.as_ptr()) };
        }
    }
}