use crate::errors::HgError;

use crate::repo::Repo;

use crate::revlog::path_encode::path_encode;

use crate::revlog::revlog::RevlogEntry;

use crate::revlog::revlog::{Revlog, RevlogError};

use crate::revlog::NodePrefix;

use crate::revlog::Revision;

use crate::utils::files::get_path_from_bytes;

use crate::utils::hg_path::HgPath;

use crate::utils::SliceExt;

use std::path::PathBuf;

/// A specialized `Revlog` to work with file data logs.

pub struct Filelog {

    /// The generic `revlog` format.

    revlog: Revlog,

}

impl Filelog {

    pub fn open_vfs(

        store_vfs: &crate::vfs::Vfs<'_>,

        file_path: &HgPath,

    ) -> Result<Self, HgError> {

        let index_path = store_path(file_path, b".i");

        let data_path = store_path(file_path, b".d");

        let revlog =

            Revlog::open(store_vfs, index_path, Some(&data_path), false)?;

        Ok(Self { revlog })

    }

    pub fn open(repo: &Repo, file_path: &HgPath) -> Result<Self, HgError> {

        Self::open_vfs(&repo.store_vfs(), file_path)

    }

    /// The given node ID is that of the file as found in a filelog, not of a

    /// changeset.

    pub fn data_for_node(

        &self,

        file_node: impl Into<NodePrefix>,

    ) -> Result<FilelogRevisionData, RevlogError> {

        let file_rev = self.revlog.rev_from_node(file_node.into())?;

        self.data_for_rev(file_rev)

    }

    /// The given revision is that of the file as found in a filelog, not of a

    /// changeset.

    pub fn data_for_rev(

        &self,

        file_rev: Revision,

    ) -> Result<FilelogRevisionData, RevlogError> {

        let data: Vec<u8> = self.revlog.get_rev_data(file_rev)?.into_owned();

    }

    /// The given node ID is that of the file as found in a filelog, not of a

    /// changeset.

    pub fn entry_for_node(

        &self,

        file_node: impl Into<NodePrefix>,

    ) -> Result<FilelogEntry, RevlogError> {

        let file_rev = self.revlog.rev_from_node(file_node.into())?;

        self.entry_for_rev(file_rev)

    }

    /// The given revision is that of the file as found in a filelog, not of a

    /// changeset.

    pub fn entry_for_rev(

        &self,

        file_rev: Revision,

    ) -> Result<FilelogEntry, RevlogError> {

        Ok(FilelogEntry(self.revlog.get_entry(file_rev)?))

    }

}

fn store_path(hg_path: &HgPath, suffix: &[u8]) -> PathBuf {

    let encoded_bytes =

        path_encode(&[b"data/", hg_path.as_bytes(), suffix].concat());

    get_path_from_bytes(&encoded_bytes).into()

}

pub struct FilelogEntry<'a>(RevlogEntry<'a>);

impl FilelogEntry<'_> {

    /// `self.data()` can be expensive, with decompression and delta

    /// resolution.

    ///

    /// *Without* paying this cost, based on revlog index information

    /// including `RevlogEntry::uncompressed_len`:

    ///

    /// * Returns `true` if the length that `self.data().file_data().len()`

    ///   would return is definitely **not equal** to `other_len`.

    /// * Returns `false` if available information is inconclusive.

    pub fn file_data_len_not_equal_to(&self, other_len: u64) -> bool {

        // Relevant code that implement this behavior in Python code:

        // basefilectx.cmp, filelog.size, storageutil.filerevisioncopied,

        // revlog.size, revlog.rawsize

        // Let’s call `file_data_len` what would be returned by

        // `self.data().file_data().len()`.

        if self.0.is_censored() {

            let file_data_len = 0;

            return other_len != file_data_len;

        }

        if self.0.has_length_affecting_flag_processor() {

            // We can’t conclude anything about `file_data_len`.

            return false;

        }

        // Revlog revisions (usually) have metadata for the size of

        // their data after decompression and delta resolution

        // as would be returned by `Revlog::get_rev_data`.

        //

        // For filelogs this is the file’s contents preceded by an optional

        // metadata block.

        let uncompressed_len = if let Some(l) = self.0.uncompressed_len() {

            l as u64

        } else {

            // The field was set to -1, the actual uncompressed len is unknown.

            // We need to decompress to say more.

            return false;

        };

        // `uncompressed_len = file_data_len + optional_metadata_len`,

        // so `file_data_len <= uncompressed_len`.

        if uncompressed_len < other_len {

            // Transitively, `file_data_len < other_len`.

            // So `other_len != file_data_len` definitely.

            return true;

        }

        if uncompressed_len == other_len + 4 {

            // It’s possible that `file_data_len == other_len` with an empty

            // metadata block (2 start marker bytes + 2 end marker bytes).

            // This happens when there wouldn’t otherwise be metadata, but

            // the first 2 bytes of file data happen to match a start marker

            // and would be ambiguous.

            return false;

        }

        if !self.0.has_p1() {

            // There may or may not be copy metadata, so we can’t deduce more

            // about `file_data_len` without computing file data.

            return false;

        }

        // Filelog ancestry is not meaningful in the way changelog ancestry is.

        // It only provides hints to delta generation.

        // p1 and p2 are set to null when making a copy or rename since

        // contents are likely unrelatedto what might have previously existed

        // at the destination path.

        //

        // Conversely, since here p1 is non-null, there is no copy metadata.

        // Note that this reasoning may be invalidated in the presence of

        // merges made by some previous versions of Mercurial that

        // swapped p1 and p2. See <https://bz.mercurial-scm.org/show_bug.cgi?id=6528>

        // and `tests/test-issue6528.t`.

        //

        // Since copy metadata is currently the only kind of metadata

        // kept in revlog data of filelogs,

        // this `FilelogEntry` does not have such metadata:

        let file_data_len = uncompressed_len;

    }

    pub fn data(&self) -> Result<FilelogRevisionData, HgError> {

        Ok(FilelogRevisionData(self.0.data()?.into_owned()))

    }

}

/// The data for one revision in a filelog, uncompressed and delta-resolved.

pub struct FilelogRevisionData(Vec<u8>);

impl FilelogRevisionData {

    /// Split into metadata and data

    pub fn split(&self) -> Result<(Option<&[u8]>, &[u8]), HgError> {

        const DELIMITER: &[u8; 2] = &[b'\x01', b'\n'];

        if let Some(rest) = self.0.drop_prefix(DELIMITER) {

            if let Some((metadata, data)) = rest.split_2_by_slice(DELIMITER) {

                Ok((Some(metadata), data))

            } else {

                Err(HgError::corrupted(

                    "Missing metadata end delimiter in filelog entry",

                ))

            }

        } else {

            Ok((None, &self.0))

        }

    }

    /// Returns the file contents at this revision, stripped of any metadata

    pub fn file_data(&self) -> Result<&[u8], HgError> {

        let (_metadata, data) = self.split()?;

        Ok(data)

    }

    /// Consume the entry, and convert it into data, discarding any metadata,

    /// if present.

    pub fn into_file_data(self) -> Result<Vec<u8>, HgError> {

        if let (Some(_metadata), data) = self.split()? {

            Ok(data.to_owned())

        } else {

            Ok(self.0)

        }

    }

}