use crate::errors::{HgError, HgResultExt};

use crate::repo::{Repo, Vfs};

use std::collections::HashSet;

fn parse(bytes: &[u8]) -> Result<HashSet<String>, HgError> {

    // The Python code reading this file uses `str.splitlines`

    // which looks for a number of line separators (even including a couple of

    // non-ASCII ones), but Python code writing it always uses `\n`.

    let lines = bytes.split(|&byte| byte == b'\n');

    lines

        .filter(|line| !line.is_empty())

        .map(|line| {

            // Python uses Unicode `str.isalnum` but feature names are all

            // ASCII

            if line[0].is_ascii_alphanumeric() && line.is_ascii() {

                Ok(String::from_utf8(line.into()).unwrap())

            } else {

                Err(HgError::corrupted("parse error in 'requires' file"))

            }

        })

        .collect()

}

pub(crate) fn load_if_exists(hg_vfs: Vfs) -> Result<HashSet<String>, HgError> {

    if let Some(bytes) = hg_vfs.read("requires").io_not_found_as_none()? {

        parse(&bytes)

    } else {

        // Treat a missing file the same as an empty file.

        // From `mercurial/localrepo.py`:

        // > requires file contains a newline-delimited list of

        // > features/capabilities the opener (us) must have in order to use

        // > the repository. This file was introduced in Mercurial 0.9.2,

        // > which means very old repositories may not have one. We assume

        // > a missing file translates to no requirements.

        Ok(HashSet::new())

    }

}

pub(crate) fn check(repo: &Repo) -> Result<(), HgError> {

    for feature in repo.requirements() {

        if !SUPPORTED.contains(&feature.as_str()) {

            // TODO: collect and all unknown features and include them in the

            // error message?

            return Err(HgError::UnsupportedFeature(format!(

                "repository requires feature unknown to this Mercurial: {}",

                feature

            )));

        }

    }

    Ok(())

}

// TODO: set this to actually-supported features

const SUPPORTED: &[&str] = &[

    "dotencode",

    "fncache",

    "generaldelta",

    "revlogv1",

    SHARED_REQUIREMENT,

    SPARSEREVLOG_REQUIREMENT,

    RELATIVE_SHARED_REQUIREMENT,

    "store",

    // As of this writing everything rhg does is read-only.

    // When it starts writing to the repository, it’ll need to either keep the

    // persistent nodemap up to date or remove this entry:

    "persistent-nodemap",

];

// Copied from mercurial/requirements.py:

/// When narrowing is finalized and no longer subject to format changes,

/// we should move this to just "narrow" or similar.

#[allow(unused)]

pub(crate) const NARROW_REQUIREMENT: &str = "narrowhg-experimental";

/// Enables sparse working directory usage

#[allow(unused)]

pub(crate) const SPARSE_REQUIREMENT: &str = "exp-sparse";

/// Enables the internal phase which is used to hide changesets instead

/// of stripping them

#[allow(unused)]

pub(crate) const INTERNAL_PHASE_REQUIREMENT: &str = "internal-phase";

/// Stores manifest in Tree structure

#[allow(unused)]

pub(crate) const TREEMANIFEST_REQUIREMENT: &str = "treemanifest";

/// Increment the sub-version when the revlog v2 format changes to lock out old

/// clients.

#[allow(unused)]

pub(crate) const REVLOGV2_REQUIREMENT: &str = "exp-revlogv2.1";

/// A repository with the sparserevlog feature will have delta chains that

/// can spread over a larger span. Sparse reading cuts these large spans into

/// pieces, so that each piece isn't too big.

/// Without the sparserevlog capability, reading from the repository could use

/// huge amounts of memory, because the whole span would be read at once,

/// including all the intermediate revisions that aren't pertinent for the

/// chain. This is why once a repository has enabled sparse-read, it becomes

/// required.

#[allow(unused)]

pub(crate) const SPARSEREVLOG_REQUIREMENT: &str = "sparserevlog";

/// A repository with the sidedataflag requirement will allow to store extra

/// information for revision without altering their original hashes.

#[allow(unused)]

pub(crate) const SIDEDATA_REQUIREMENT: &str = "exp-sidedata-flag";

/// A repository with the the copies-sidedata-changeset requirement will store

/// copies related information in changeset's sidedata.

#[allow(unused)]

pub(crate) const COPIESSDC_REQUIREMENT: &str = "exp-copies-sidedata-changeset";

/// The repository use persistent nodemap for the changelog and the manifest.

#[allow(unused)]

pub(crate) const NODEMAP_REQUIREMENT: &str = "persistent-nodemap";

/// Denotes that the current repository is a share

#[allow(unused)]

pub(crate) const SHARED_REQUIREMENT: &str = "shared";

/// Denotes that current repository is a share and the shared source path is

/// relative to the current repository root path

#[allow(unused)]

pub(crate) const RELATIVE_SHARED_REQUIREMENT: &str = "relshared";

/// A repository with share implemented safely. The repository has different

/// store and working copy requirements i.e. both `.hg/requires` and

/// `.hg/store/requires` are present.

#[allow(unused)]