use crate::c;
use crate::btree::bkey::AsBkeyI;
use crate::errcode::{bch_err_throw, bch_errcode, ret_to_result_void as ret_to_result, BchError};
use crate::alloc::buckets::DiskReservation;
use crate::btree::iter::{BtreeIterFlags, CommitOpts, UpdateTriggerFlags};
use core::ops::ControlFlow;

/// RAII guard for a device reference. Calls bch2_dev_put on drop.
///
/// Obtained via `Fs::dev_get()`. Derefs to `&bch_dev` for read access.
pub struct DevRef(*mut c::bch_dev);

impl DevRef {
    /// Get a raw mutable pointer to the device. Needed for C functions
    /// that take `*mut bch_dev`.
    pub fn as_mut_ptr(&self) -> *mut c::bch_dev {
        self.0
    }
}

impl core::ops::Deref for DevRef {
    type Target = c::bch_dev;
    fn deref(&self) -> &c::bch_dev {
        unsafe { &*self.0 }
    }
}

impl Drop for DevRef {
    fn drop(&mut self) {
        unsafe { c::bch2_dev_put(self.0) };
    }
}

/// RAII guard for bch_fs::sb_lock. Unlocks on drop.
pub struct SbLockGuard<'a> {
    fs: &'a Fs,
}

impl Drop for SbLockGuard<'_> {
    fn drop(&mut self) {
        unsafe { c::mutex_unlock(&mut (*self.fs.raw).sb_lock ); }
    }
}

pub struct Fs {
    pub raw: *mut c::bch_fs,
}

#[derive(Copy, Clone)]
pub struct BorrowedFs(*mut c::bch_fs);

// SAFETY: BorrowedFs is a non-owning pointer to a live filesystem supplied by
// C. Users must ensure the borrowed bch_fs outlives all cross-thread users.
unsafe impl Send for BorrowedFs {}
// SAFETY: bch_fs internal synchronization is handled by the filesystem code.
unsafe impl Sync for BorrowedFs {}

impl BorrowedFs {
    /// Create a cross-thread non-owning `Fs` handle.
    ///
    /// Callers must ensure the underlying bch_fs remains live while any
    /// resulting borrowed Fs views are in use.
    pub fn new(fs: &Fs) -> Self {
        Self(fs.raw)
    }

    pub fn get(&self) -> core::mem::ManuallyDrop<Fs> {
        unsafe { Fs::borrow_raw(self.0) }
    }
}

impl Fs {
    /// Create a non-owning `Fs` view from a raw pointer.
    ///
    /// Returns `ManuallyDrop<Fs>` to prevent `Fs::drop` from calling
    /// `bch2_fs_exit`. Deref gives `&Fs` for all methods.
    ///
    /// # Safety
    /// `raw` must point to a valid, live `bch_fs`.
    pub unsafe fn borrow_raw(raw: *mut c::bch_fs) -> core::mem::ManuallyDrop<Fs> {
        core::mem::ManuallyDrop::new(Fs { raw })
    }

    /// Access the superblock handle.
    pub fn sb_handle(&self) -> &c::bch_sb_handle {
        unsafe { &(*self.raw).disk_sb }
    }

    /// Access the superblock.
    pub fn sb(&self) -> &c::bch_sb {
        self.sb_handle().sb()
    }

    /// Acquire the superblock lock, returning a guard that releases it on drop.
    pub fn sb_lock(&self) -> SbLockGuard<'_> {
        unsafe { c::mutex_lock(&mut (*self.raw).sb_lock); }
        SbLockGuard { fs: self }
    }

    /// Write superblock to disk. Caller must hold sb_lock.
    pub fn write_super(&self) {
        unsafe { c::bch2_write_super(self.raw) };
    }

    pub fn throw<T>(&self, error: bch_errcode) -> Result<T, BchError> {
        Err(bch_err_throw(error))
    }

    pub fn require<T>(&self, value: Option<T>, error: bch_errcode) -> Result<T, BchError> {
        match value {
            Some(v) => Ok(v),
            None    => self.throw(error),
        }
    }

    pub fn ensure(&self, condition: bool, error: bch_errcode) -> Result<(), BchError> {
        if condition {
            Ok(())
        } else {
            self.throw(error)
        }
    }

    /// Get a mutable reference to a member entry in the superblock.
    /// Caller must hold sb_lock.
    ///
    /// # Safety
    /// Caller must hold sb_lock for mutation safety.
    #[allow(clippy::mut_from_ref)] // interior mutability guarded by sb_lock
    pub unsafe fn member_mut(&self, dev_idx: u32) -> &mut c::bch_member {
        unsafe { &mut *c::bch2_members_v2_get_mut((*self.raw).disk_sb.sb, dev_idx as i32) }
    }

    /// Shut down the filesystem, returning the error code from bch2_fs_exit.
    /// Consumes self so the caller can't use it afterward; forget prevents
    /// Drop from double-freeing.
    pub fn exit(self) -> i32 {
        let ret = unsafe { c::bch2_fs_exit(self.raw) };
        core::mem::forget(self);
        ret
    }

    /// Iterate over all online member devices.
    ///
    /// Equivalent to the C `for_each_online_member` macro. Ref counting
    /// is handled automatically, including on early break.
    pub fn for_each_online_member<F>(&self, mut f: F) -> ControlFlow<()>
    where
        F: FnMut(&c::bch_dev) -> ControlFlow<()>,
    {
        let mut ca: *mut c::bch_dev = core::ptr::null_mut();
        loop {
            // any device state, READ ref-class, ref_idx 0.
            ca = unsafe { c::bch2_get_next_online_dev(self.raw, ca, !0u32, 0 /* READ */, 0) };
            if ca.is_null() {
                return ControlFlow::Continue(());
            }
            if f(unsafe { &*ca }).is_break() {
                unsafe { c::enumerated_ref_put(&mut (*ca).io_ref[0 /* READ */], 0) };
                return ControlFlow::Break(());
            }
        }
    }

    /// Get the root btree node for a btree ID.
    pub fn btree_id_root(&self, id: u32) -> Option<&c::btree> {
        unsafe {
            let c = &*self.raw;
            let nr_known = u32::from(c::btree_id::nr);

            let r = if id < nr_known {
                &c.btree.cache.roots_known[id as usize]
            } else {
                let idx = (id - nr_known) as usize;
                if idx >= c.btree.cache.roots_extra.nr {
                    return None;
                }
                &*c.btree.cache.roots_extra.data.add(idx)
            };

            let b = r.b;
            if b.is_null() { None } else { Some(&*b) }
        }
    }

    /// Total number of btree IDs (known + dynamic) on this filesystem.
    pub fn btree_id_nr_alive(&self) -> u32 {
        unsafe {
            let c = &*self.raw;
            u32::from(c::btree_id::nr) + c.btree.cache.roots_extra.nr as u32
        }
    }

    /// Number of devices in the filesystem superblock.
    pub fn nr_devices(&self) -> u32 {
        unsafe { (*self.raw).sb.nr_devices as u32 }
    }

    /// Get a reference to a device by index. Returns None if the device
    /// doesn't exist or can't be referenced.
    pub fn dev_get(&self, dev: u32) -> Option<DevRef> {
        let ca = unsafe { c::bch2_dev_tryget_noerror(self.raw, dev) };
        if ca.is_null() { None } else { Some(DevRef(ca)) }
    }

    /// Start the filesystem (recovery, journal replay, etc).
    pub fn start(&self) -> Result<(), BchError> {
        ret_to_result(unsafe { c::bch2_fs_start(self.raw) })
    }

    /// Allocate the buckets_nouse bitmaps for all devices.
    pub fn buckets_nouse_alloc(&self) -> Result<(), BchError> {
        ret_to_result(unsafe { c::bch2_buckets_nouse_alloc(self.raw) })
    }

    /// Mark device superblock buckets in btree metadata.
    pub fn trans_mark_dev_sb(&self, ca: &DevRef, flags: UpdateTriggerFlags) -> Result<(), BchError> {
        ret_to_result(unsafe { c::bch2_trans_mark_dev_sb(self.raw, ca.as_mut_ptr(), c::btree_iter_update_trigger_flags(flags.bits())) })
    }

    /// Write superblock to disk (locked version). Caller must hold sb_lock.
    /// Returns Ok(()) on success or the error code on failure.
    pub fn write_super_ret(&self) -> Result<(), BchError> {
        ret_to_result(unsafe { c::bch2_write_super(self.raw) })
    }

    /// Check if a device index exists and has a device pointer.
    pub fn dev_exists(&self, dev: u32) -> bool {
        unsafe {
            let c = &*self.raw;
            (dev as usize) < c.sb.nr_devices as usize
                && !c.devs[dev as usize].is_null()
        }
    }

    /// Transition filesystem to read-only mode.
    pub fn read_only(&self) {
        unsafe { c::bch2_fs_read_only(self.raw) };
    }

    /// Set a device's allocator to RW or RO.
    pub fn dev_allocator_set_rw(&self, dev: u32, rw: bool) {
        unsafe {
            let ca = (*self.raw).devs[dev as usize];
            if !ca.is_null() {
                c::bch2_dev_allocator_set_rw(self.raw, ca, rw);
            }
        }
    }

    /// Flush all journal pins (equivalent to bch2_journal_flush_all_pins).
    pub fn journal_flush_all_pins(&self) {
        unsafe {
            c::bch2_journal_flush_pins(
                &mut (*self.raw).journal,
                u64::MAX,
            );
        }
    }

    /// Flush pins up to the current journal sequence.
    pub fn journal_flush_outstanding_pins(&self) -> bool {
        unsafe { c::bch2_journal_flush_outstanding_pins(&mut (*self.raw).journal) }
    }

    /// Delete a range of keys in a btree.
    pub fn btree_delete_range(
        &self,
        btree_id: c::btree_id,
        start: c::bpos,
        end: c::bpos,
        flags: BtreeIterFlags,
    ) -> Result<(), BchError> {
        ret_to_result(unsafe {
            c::bch2_btree_delete_range(self.raw, btree_id, start, end, c::btree_iter_update_trigger_flags(flags.bits()))
        })
    }

    pub fn btree_insert(
        &self,
        btree_id:     c::btree_id,
        key:          &mut impl AsBkeyI,
        disk_res:     Option<&DiskReservation<'_>>,
        commit_flags: CommitOpts,
        iter_flags:   BtreeIterFlags,
    ) -> Result<(), BchError> {
        let disk_res = disk_res
            .map(|r| r.as_mut_ptr())
            .unwrap_or(core::ptr::null_mut());

        ret_to_result(unsafe {
            c::bch2_btree_insert(
                self.raw,
                btree_id,
                key.as_bkey_i_mut(),
                disk_res,
                commit_flags.to_c(),
                c::btree_iter_update_trigger_flags(iter_flags.bits()),
            )
        })
    }

    /// Read full device usage stats.
    pub fn dev_usage_full_read(&self, dev: u32) -> c::bch_dev_usage_full {
        unsafe {
            let ca = (*self.raw).devs[dev as usize];
            let mut usage: c::bch_dev_usage_full = core::mem::zeroed();
            c::bch2_dev_usage_full_read_fast(ca, &mut usage);
            usage
        }
    }

    /// Get the raw device pointer by index.
    ///
    /// # Safety
    /// Caller must ensure the device exists and the pointer is valid.
    pub unsafe fn dev_raw(&self, dev: u32) -> *mut c::bch_dev {
        (*self.raw).devs[dev as usize]
    }

    /// Access the mutable superblock handle for resize operations.
    ///
    /// # Safety
    /// Caller must hold sb_lock.
    #[allow(clippy::mut_from_ref)] // interior mutability guarded by sb_lock
    pub unsafe fn disk_sb_mut(&self) -> &mut c::bch_sb_handle {
        &mut (*self.raw).disk_sb
    }

    /// Filesystem block size in bytes.
    pub fn block_bytes(&self) -> u64 {
        unsafe { c::block_bytes(self.raw) as u64 }
    }

    /// Look up an inode by (subvol, inum).
    pub fn inode_find_by_inum(&self, inum: c::subvol_inum) -> Result<c::bch_inode_unpacked, BchError> {
        let mut bi: c::bch_inode_unpacked = Default::default();
        ret_to_result(unsafe { c::bch2_inode_find_by_inum(self.raw, inum, &mut bi) })?;
        Ok(bi)
    }

    /// Convert a bcachefs internal time to a timespec.
    pub fn time_to_timespec(&self, time: i64) -> c::timespec64 {
        unsafe { c::bch2_time_to_timespec(self.raw, time) }
    }

    /// Convert a timespec to a bcachefs internal time.
    pub fn timespec_to_time(&self, ts: c::timespec64) -> i64 {
        unsafe { c::timespec_to_bch2_time(self.raw, ts) }
    }

    /// Current time in bcachefs internal time format.
    pub fn current_time(&self) -> u64 {
        unsafe { c::bch2_current_time(self.raw) as u64 }
    }

    /// Short filesystem usage summary.
    pub fn usage_read_short(&self) -> c::bch_fs_usage_short {
        unsafe { c::bch2_fs_usage_read_short(self.raw) }
    }

    /// Get the link count for an inode.
    pub fn inode_nlink_get(bi: &c::bch_inode_unpacked) -> u32 {
        unsafe { c::bch2_inode_nlink_get(bi as *const _ as *mut _) }
    }

    /// Set the filesystem log level.
    pub fn set_loglevel(&self, level: u32) {
        unsafe { (*self.raw).loglevel = level; }
    }
}

impl Drop for Fs {
    fn drop(&mut self) {
        unsafe { c::bch2_fs_exit(self.raw); }
    }
}

// Standalone helpers — pure Rust reimplementations of C static inlines.

/// Sector offset of bucket `b` on device `ca`.
pub fn bucket_to_sector(ca: &c::bch_dev, b: u64) -> u64 {
    b * ca.mi.bucket_size as u64
}

/// Size of one bucket in bytes.
pub fn bucket_bytes(ca: &c::bch_dev) -> u64 {
    ca.mi.bucket_size as u64 * 512
}

/// Build a hashed writepoint specifier (sets low bit to mark as hashed).
pub fn writepoint_hashed(v: usize) -> c::write_point_specifier {
    c::write_point_specifier { v: (v | 1) as _ }
}

/// Convert a device index to a target (TARGET_DEV_START = 1).
pub fn dev_to_target(dev: u32) -> u16 {
    1 + dev as u16
}

/// Check if a btree ID is an allocator btree.
pub fn btree_id_is_alloc(id: u32) -> bool {
    matches!(
        c::btree_id::from_raw(id),
        Some(c::btree_id::alloc
            | c::btree_id::backpointers
            | c::btree_id::stripe_backpointers
            | c::btree_id::need_discard
            | c::btree_id::freespace
            | c::btree_id::bucket_gens
            | c::btree_id::lru
            | c::btree_id::accounting
            | c::btree_id::reconcile_work
            | c::btree_id::reconcile_hipri
            | c::btree_id::reconcile_pending
            | c::btree_id::reconcile_scan)
    )
}
