use crate::checker::CompositeChecker;
use crate::error::*;
#[cfg(windows)]
use crate::helper::has_executable_extension;
use either::Either;
#[cfg(feature = "regex")]
use regex::Regex;
#[cfg(feature = "regex")]
use std::borrow::Borrow;
use std::borrow::Cow;
use std::env;
use std::ffi::OsStr;
#[cfg(any(feature = "regex", target_os = "windows"))]
use std::fs;
use std::iter;
use std::path::{Component, Path, PathBuf};

// Home dir shim, use home crate when possible. Otherwise, return None
#[cfg(any(windows, unix, target_os = "redox"))]
use home::home_dir;

#[cfg(not(any(windows, unix, target_os = "redox")))]
fn home_dir() -> Option<std::path::PathBuf> {
    None
}

pub trait Checker {
    fn is_valid(&self, path: &Path) -> bool;
}

trait PathExt {
    fn has_separator(&self) -> bool;

    fn to_absolute<P>(self, cwd: P) -> PathBuf
    where
        P: AsRef<Path>;
}

impl PathExt for PathBuf {
    fn has_separator(&self) -> bool {
        self.components().count() > 1
    }

    fn to_absolute<P>(self, cwd: P) -> PathBuf
    where
        P: AsRef<Path>,
    {
        if self.is_absolute() {
            self
        } else {
            let mut new_path = PathBuf::from(cwd.as_ref());
            new_path.push(self);
            new_path
        }
    }
}

pub struct Finder;

impl Finder {
    pub fn new() -> Finder {
        Finder
    }

    pub fn find<T, U, V>(
        &self,
        binary_name: T,
        paths: Option<U>,
        cwd: Option<V>,
        binary_checker: CompositeChecker,
    ) -> Result<impl Iterator<Item = PathBuf>>
    where
        T: AsRef<OsStr>,
        U: AsRef<OsStr>,
        V: AsRef<Path>,
    {
        let path = PathBuf::from(&binary_name);

        #[cfg(feature = "tracing")]
        tracing::debug!(
            "query binary_name = {:?}, paths = {:?}, cwd = {:?}",
            binary_name.as_ref().to_string_lossy(),
            paths.as_ref().map(|p| p.as_ref().to_string_lossy()),
            cwd.as_ref().map(|p| p.as_ref().display())
        );

        let binary_path_candidates = match cwd {
            Some(cwd) if path.has_separator() => {
                #[cfg(feature = "tracing")]
                tracing::trace!(
                    "{} has a path seperator, so only CWD will be searched.",
                    path.display()
                );
                // Search binary in cwd if the path have a path separator.
                Either::Left(Self::cwd_search_candidates(path, cwd).into_iter())
            }
            _ => {
                #[cfg(feature = "tracing")]
                tracing::trace!("{} has no path seperators, so only paths in PATH environment variable will be searched.", path.display());
                // Search binary in PATHs(defined in environment variable).
                let paths =
                    env::split_paths(&paths.ok_or(Error::CannotGetCurrentDirAndPathListEmpty)?)
                        .collect::<Vec<_>>();
                if paths.is_empty() {
                    return Err(Error::CannotGetCurrentDirAndPathListEmpty);
                }

                Either::Right(Self::path_search_candidates(path, paths).into_iter())
            }
        };
        let ret = binary_path_candidates
            .filter(move |p| binary_checker.is_valid(p))
            .map(correct_casing);
        #[cfg(feature = "tracing")]
        let ret = ret.map(|p| {
            tracing::debug!("found path {}", p.display());
            p
        });
        Ok(ret)
    }

    #[cfg(feature = "regex")]
    pub fn find_re<T>(
        &self,
        binary_regex: impl Borrow<Regex>,
        paths: Option<T>,
        binary_checker: CompositeChecker,
    ) -> Result<impl Iterator<Item = PathBuf>>
    where
        T: AsRef<OsStr>,
    {
        let p = paths.ok_or(Error::CannotGetCurrentDirAndPathListEmpty)?;
        // Collect needs to happen in order to not have to
        // change the API to borrow on `paths`.
        #[allow(clippy::needless_collect)]
        let paths: Vec<_> = env::split_paths(&p).collect();

        let matching_re = paths
            .into_iter()
            .flat_map(fs::read_dir)
            .flatten()
            .flatten()
            .map(|e| e.path())
            .filter(move |p| {
                if let Some(unicode_file_name) = p.file_name().unwrap().to_str() {
                    binary_regex.borrow().is_match(unicode_file_name)
                } else {
                    false
                }
            })
            .filter(move |p| binary_checker.is_valid(p));

        Ok(matching_re)
    }

    fn cwd_search_candidates<C>(binary_name: PathBuf, cwd: C) -> impl IntoIterator<Item = PathBuf>
    where
        C: AsRef<Path>,
    {
        let path = binary_name.to_absolute(cwd);

        Self::append_extension(iter::once(path))
    }

    fn path_search_candidates<P>(
        binary_name: PathBuf,
        paths: P,
    ) -> impl IntoIterator<Item = PathBuf>
    where
        P: IntoIterator<Item = PathBuf>,
    {
        let new_paths = paths
            .into_iter()
            .map(move |p| tilde_expansion(&p).join(binary_name.clone()));

        Self::append_extension(new_paths)
    }

    #[cfg(not(windows))]
    fn append_extension<P>(paths: P) -> impl IntoIterator<Item = PathBuf>
    where
        P: IntoIterator<Item = PathBuf>,
    {
        paths
    }

    #[cfg(windows)]
    fn append_extension<P>(paths: P) -> impl IntoIterator<Item = PathBuf>
    where
        P: IntoIterator<Item = PathBuf>,
    {
        use std::sync::OnceLock;

        // Sample %PATHEXT%: .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC
        // PATH_EXTENSIONS is then [".COM", ".EXE", ".BAT", …].
        // (In one use of PATH_EXTENSIONS we skip the dot, but in the other we need it;
        // hence its retention.)
        static PATH_EXTENSIONS: OnceLock<Vec<String>> = OnceLock::new();

        paths
            .into_iter()
            .flat_map(move |p| -> Box<dyn Iterator<Item = _>> {
                let path_extensions = PATH_EXTENSIONS.get_or_init(|| {
                    env::var("PATHEXT")
                        .map(|pathext| {
                            pathext
                                .split(';')
                                .filter_map(|s| {
                                    if s.as_bytes().first() == Some(&b'.') {
                                        Some(s.to_owned())
                                    } else {
                                        // Invalid segment; just ignore it.
                                        None
                                    }
                                })
                                .collect()
                        })
                        // PATHEXT not being set or not being a proper Unicode string is exceedingly
                        // improbable and would probably break Windows badly. Still, don't crash:
                        .unwrap_or_default()
                });
                // Check if path already have executable extension
                if has_executable_extension(&p, path_extensions) {
                    #[cfg(feature = "tracing")]
                    tracing::trace!(
                        "{} already has an executable extension, not modifying it further",
                        p.display()
                    );
                    Box::new(iter::once(p))
                } else {
                    #[cfg(feature = "tracing")]
                    tracing::trace!(
                        "{} has no extension, using PATHEXT environment variable to infer one",
                        p.display()
                    );
                    // Appended paths with windows executable extensions.
                    // e.g. path `c:/windows/bin[.ext]` will expand to:
                    // [c:/windows/bin.ext]
                    // c:/windows/bin[.ext].COM
                    // c:/windows/bin[.ext].EXE
                    // c:/windows/bin[.ext].CMD
                    // ...
                    Box::new(
                        iter::once(p.clone()).chain(path_extensions.iter().map(move |e| {
                            // Append the extension.
                            let mut p = p.clone().into_os_string();
                            p.push(e);
                            let ret = PathBuf::from(p);
                            #[cfg(feature = "tracing")]
                            tracing::trace!("possible extension: {}", ret.display());
                            ret
                        })),
                    )
                }
            })
    }
}

fn tilde_expansion(p: &PathBuf) -> Cow<'_, PathBuf> {
    let mut component_iter = p.components();
    if let Some(Component::Normal(o)) = component_iter.next() {
        if o == "~" {
            let mut new_path = home_dir().unwrap_or_default();
            new_path.extend(component_iter);
            #[cfg(feature = "tracing")]
            tracing::trace!(
                "found tilde, substituting in user's home directory to get {}",
                new_path.display()
            );
            Cow::Owned(new_path)
        } else {
            Cow::Borrowed(p)
        }
    } else {
        Cow::Borrowed(p)
    }
}

#[cfg(target_os = "windows")]
fn correct_casing(mut p: PathBuf) -> PathBuf {
    if let (Some(parent), Some(file_name)) = (p.parent(), p.file_name()) {
        if let Ok(iter) = fs::read_dir(parent) {
            for e in iter.filter_map(std::result::Result::ok) {
                if e.file_name().eq_ignore_ascii_case(file_name) {
                    p.pop();
                    p.push(e.file_name());
                    break;
                }
            }
        }
    }
    p
}

#[cfg(not(target_os = "windows"))]
fn correct_casing(p: PathBuf) -> PathBuf {
    p
}
