use crate::dirstate_tree::on_disk::DirstateV2ParseError;

use crate::errors::HgError;

use bitflags::bitflags;

use std::convert::{TryFrom, TryInto};

use std::fs;

use std::io;

use std::time::{SystemTime, UNIX_EPOCH};

#[derive(Copy, Clone, Debug, Eq, PartialEq)]

pub enum EntryState {

    Normal,

    Added,

    Removed,

    Merged,

}

/// `size` and `mtime.seconds` are truncated to 31 bits.

///

/// TODO: double-check status algorithm correctness for files

/// larger than 2 GiB or modified after 2038.

#[derive(Debug, Copy, Clone)]

pub struct DirstateEntry {

    pub(crate) flags: Flags,

    mode_size: Option<(u32, u32)>,

    mtime: Option<TruncatedTimestamp>,

}

bitflags! {

    pub(crate) struct Flags: u8 {

        const WDIR_TRACKED = 1 << 0;

        const P1_TRACKED = 1 << 1;

        const P2_INFO = 1 << 2;

        const HAS_FALLBACK_EXEC = 1 << 3;

        const FALLBACK_EXEC = 1 << 4;

        const HAS_FALLBACK_SYMLINK = 1 << 5;

        const FALLBACK_SYMLINK = 1 << 6;

    }

}

/// A Unix timestamp with nanoseconds precision

#[derive(Debug, Copy, Clone)]

pub struct TruncatedTimestamp {

    truncated_seconds: u32,

    /// Always in the `0 .. 1_000_000_000` range.

    nanoseconds: u32,

}

impl TruncatedTimestamp {

    /// Constructs from a timestamp potentially outside of the supported range,

    /// and truncate the seconds components to its lower 31 bits.

    ///

    /// Panics if the nanoseconds components is not in the expected range.

    pub fn new_truncate(seconds: i64, nanoseconds: u32) -> Self {

        assert!(nanoseconds < NSEC_PER_SEC);

        Self {

            truncated_seconds: seconds as u32 & RANGE_MASK_31BIT,

            nanoseconds,

        }

    }

    /// Construct from components. Returns an error if they are not in the

    /// expcted range.

    pub fn from_already_truncated(

        truncated_seconds: u32,

        nanoseconds: u32,

    ) -> Result<Self, DirstateV2ParseError> {

        if truncated_seconds & !RANGE_MASK_31BIT == 0

            && nanoseconds < NSEC_PER_SEC

        {

            Ok(Self {

                truncated_seconds,

                nanoseconds,

            })

        } else {

            Err(DirstateV2ParseError)

        }

    }

    pub fn for_mtime_of(metadata: &fs::Metadata) -> io::Result<Self> {

        #[cfg(unix)]

        {

            use std::os::unix::fs::MetadataExt;

            let seconds = metadata.mtime();

            // i64 -> u32 with value always in the `0 .. NSEC_PER_SEC` range

            let nanoseconds = metadata.mtime_nsec().try_into().unwrap();

            Ok(Self::new_truncate(seconds, nanoseconds))

        }

        #[cfg(not(unix))]

        {

            metadata.modified().map(Self::from)

        }

    }

    pub fn to_integer_second(mut self) -> Self {

        self.nanoseconds = 0;

        self

    }

    /// The lower 31 bits of the number of seconds since the epoch.

    pub fn truncated_seconds(&self) -> u32 {

        self.truncated_seconds

    }

    /// The sub-second component of this timestamp, in nanoseconds.

    /// Always in the `0 .. 1_000_000_000` range.

    ///

    /// This timestamp is after `(seconds, 0)` by this many nanoseconds.

    pub fn nanoseconds(&self) -> u32 {

        self.nanoseconds

    }

    /// Returns whether two timestamps are equal modulo 2**31 seconds.

    ///

    /// If this returns `true`, the original values converted from `SystemTime`

    /// or given to `new_truncate` were very likely equal. A false positive is

    /// possible if they were exactly a multiple of 2**31 seconds apart (around

    /// 68 years). This is deemed very unlikely to happen by chance, especially

    /// on filesystems that support sub-second precision.

    ///

    /// If someone is manipulating the modification times of some files to

    /// intentionally make `hg status` return incorrect results, not truncating

    /// wouldn’t help much since they can set exactly the expected timestamp.

    pub fn likely_equal(self, other: Self) -> bool {

        self.truncated_seconds == other.truncated_seconds

    }

    pub fn likely_equal_to_mtime_of(

        self,

        metadata: &fs::Metadata,

    ) -> io::Result<bool> {

        Ok(self.likely_equal(Self::for_mtime_of(metadata)?))

    }

}

impl From<SystemTime> for TruncatedTimestamp {

    fn from(system_time: SystemTime) -> Self {

        // On Unix, `SystemTime` is a wrapper for the `timespec` C struct:

        // https://www.gnu.org/software/libc/manual/html_node/Time-Types.html#index-struct-timespec

        // We want to effectively access its fields, but the Rust standard

        // library does not expose them. The best we can do is:

        let seconds;

        let nanoseconds;

        match system_time.duration_since(UNIX_EPOCH) {

            Ok(duration) => {

                seconds = duration.as_secs() as i64;

                nanoseconds = duration.subsec_nanos();

            }

            Err(error) => {

                // `system_time` is before `UNIX_EPOCH`.

                // We need to undo this algorithm:

                // https://github.com/rust-lang/rust/blob/6bed1f0bc3cc50c10aab26d5f94b16a00776b8a5/library/std/src/sys/unix/time.rs#L40-L41

                let negative = error.duration();

                let negative_secs = negative.as_secs() as i64;

                let negative_nanos = negative.subsec_nanos();

                if negative_nanos == 0 {

                    seconds = -negative_secs;

                    nanoseconds = 0;

                } else {

                    // For example if `system_time` was 4.3 seconds before

                    // the Unix epoch we get a Duration that represents

                    // `(-4, -0.3)` but we want `(-5, +0.7)`:

                    seconds = -1 - negative_secs;

                    nanoseconds = NSEC_PER_SEC - negative_nanos;

                }

            }

        };

        Self::new_truncate(seconds, nanoseconds)

    }

}

const NSEC_PER_SEC: u32 = 1_000_000_000;

const RANGE_MASK_31BIT: u32 = 0x7FFF_FFFF;

pub const MTIME_UNSET: i32 = -1;

/// A `DirstateEntry` with a size of `-2` means that it was merged from the

/// other parent. This allows revert to pick the right status back during a

/// merge.

pub const SIZE_FROM_OTHER_PARENT: i32 = -2;

/// A special value used for internal representation of special case in

/// dirstate v1 format.

pub const SIZE_NON_NORMAL: i32 = -1;

impl DirstateEntry {

    pub fn from_v2_data(

        wdir_tracked: bool,

        p1_tracked: bool,

        p2_info: bool,

        mode_size: Option<(u32, u32)>,

        mtime: Option<TruncatedTimestamp>,

        fallback_exec: Option<bool>,

        fallback_symlink: Option<bool>,

    ) -> Self {

        if let Some((mode, size)) = mode_size {

            // TODO: return an error for out of range values?

            assert!(mode & !RANGE_MASK_31BIT == 0);

            assert!(size & !RANGE_MASK_31BIT == 0);

        }

        let mut flags = Flags::empty();

        flags.set(Flags::WDIR_TRACKED, wdir_tracked);

        flags.set(Flags::P1_TRACKED, p1_tracked);

        flags.set(Flags::P2_INFO, p2_info);

        if let Some(exec) = fallback_exec {

            flags.insert(Flags::HAS_FALLBACK_EXEC);

            if exec {

                flags.insert(Flags::FALLBACK_EXEC);

            }

        }

        if let Some(exec) = fallback_symlink {

            flags.insert(Flags::HAS_FALLBACK_SYMLINK);

            if exec {

                flags.insert(Flags::FALLBACK_SYMLINK);

            }

        }

        Self {

            flags,

            mode_size,

            mtime,

        }

    }

    pub fn from_v1_data(

        state: EntryState,

        mode: i32,

        size: i32,

        mtime: i32,

    ) -> Self {

        match state {

            EntryState::Normal => {

                if size == SIZE_FROM_OTHER_PARENT {

                    Self {

                        // might be missing P1_TRACKED

                        flags: Flags::WDIR_TRACKED | Flags::P2_INFO,

                        mode_size: None,

                        mtime: None,

                    }

                } else if size == SIZE_NON_NORMAL {

                    Self {

                        flags: Flags::WDIR_TRACKED | Flags::P1_TRACKED,

                        mode_size: None,

                        mtime: None,

                    }

                } else if mtime == MTIME_UNSET {

                    // TODO: return an error for negative values?

                    let mode = u32::try_from(mode).unwrap();

                    let size = u32::try_from(size).unwrap();

                    Self {

                        flags: Flags::WDIR_TRACKED | Flags::P1_TRACKED,

                        mode_size: Some((mode, size)),

                        mtime: None,

                    }

                } else {

                    // TODO: return an error for negative values?

                    let mode = u32::try_from(mode).unwrap();

                    let size = u32::try_from(size).unwrap();

                    let mtime = u32::try_from(mtime).unwrap();

                    let mtime =

                        TruncatedTimestamp::from_already_truncated(mtime, 0)

                            .unwrap();

                    Self {

                        flags: Flags::WDIR_TRACKED | Flags::P1_TRACKED,

                        mode_size: Some((mode, size)),

                        mtime: Some(mtime),

                    }

                }

            }

            EntryState::Added => Self {

                flags: Flags::WDIR_TRACKED,

                mode_size: None,

                mtime: None,

            },

            EntryState::Removed => Self {

                flags: if size == SIZE_NON_NORMAL {

                    Flags::P1_TRACKED | Flags::P2_INFO

                } else if size == SIZE_FROM_OTHER_PARENT {

                    // We don’t know if P1_TRACKED should be set (file history)

                    Flags::P2_INFO

                } else {

                    Flags::P1_TRACKED

                },

                mode_size: None,

                mtime: None,

            },

            EntryState::Merged => Self {

                flags: Flags::WDIR_TRACKED

                    | Flags::P1_TRACKED // might not be true because of rename ?

                    | Flags::P2_INFO, // might not be true because of rename ?

                mode_size: None,

                mtime: None,

            },

        }

    }

    /// Creates a new entry in "removed" state.

    ///

    /// `size` is expected to be zero, `SIZE_NON_NORMAL`, or

    /// `SIZE_FROM_OTHER_PARENT`

    pub fn new_removed(size: i32) -> Self {

        Self::from_v1_data(EntryState::Removed, 0, size, 0)

    }

    pub fn tracked(&self) -> bool {

        self.flags.contains(Flags::WDIR_TRACKED)

    }

    pub fn p1_tracked(&self) -> bool {

        self.flags.contains(Flags::P1_TRACKED)

    }

    fn in_either_parent(&self) -> bool {

        self.flags.intersects(Flags::P1_TRACKED | Flags::P2_INFO)

    }

    pub fn removed(&self) -> bool {

        self.in_either_parent() && !self.flags.contains(Flags::WDIR_TRACKED)

    }

    pub fn p2_info(&self) -> bool {

        self.flags.contains(Flags::WDIR_TRACKED | Flags::P2_INFO)

    }

    pub fn added(&self) -> bool {

        self.flags.contains(Flags::WDIR_TRACKED) && !self.in_either_parent()

    }

    pub fn maybe_clean(&self) -> bool {

        if !self.flags.contains(Flags::WDIR_TRACKED) {

            false

        } else if !self.flags.contains(Flags::P1_TRACKED) {

            false

        } else if self.flags.contains(Flags::P2_INFO) {

            false

        } else {

            true

        }

    }

    pub fn any_tracked(&self) -> bool {

        self.flags.intersects(

            Flags::WDIR_TRACKED | Flags::P1_TRACKED | Flags::P2_INFO,

        )

    }