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use std::io;
use std::path::{Component, Path, PathBuf};

pub fn absolutize<P, Q>(relative_to: P, path: Q) -> PathBuf
where
    P: AsRef<Path>,
    Q: AsRef<Path>,
{
    let path = if path.as_ref() == Path::new(".") {
        // Joining a Path with '.' appends a '.' at the end, making the prompt
        // more ugly - so we don't do anything, which should result in an equal
        // path on all supported systems.
        relative_to.as_ref().to_owned()
    } else if path.as_ref().starts_with("~") {
        #[cfg(feature = "dirs")]
        {
            let expanded_path = expand_tilde(path.as_ref());
            match expanded_path {
                Some(p) => p,
                _ => path.as_ref().to_owned(),
            }
        }
        #[cfg(not(feature = "dirs"))]
        relative_to.as_ref().join(path)
    } else {
        relative_to.as_ref().join(path)
    };

    let (relative_to, path) = {
        let components: Vec<_> = path.components().collect();
        let separator = components
            .iter()
            .enumerate()
            .find(|(_, c)| c == &&Component::CurDir || c == &&Component::ParentDir);

        if let Some((index, _)) = separator {
            let (absolute, relative) = components.split_at(index);
            let absolute: PathBuf = absolute.iter().collect();
            let relative: PathBuf = relative.iter().collect();

            (absolute, relative)
        } else {
            (
                relative_to.as_ref().to_path_buf(),
                components.iter().collect::<PathBuf>(),
            )
        }
    };

    let path = if path.is_relative() {
        let mut result = relative_to;
        path.components().for_each(|component| match component {
            Component::ParentDir => {
                result.pop();
            }
            Component::Normal(normal) => result.push(normal),
            _ => {}
        });

        result
    } else {
        path
    };

    dunce::simplified(&path).to_path_buf()
}

// borrowed from here https://stackoverflow.com/questions/54267608/expand-tilde-in-rust-path-idiomatically
#[cfg(feature = "dirs")]
fn expand_tilde<P: AsRef<Path>>(path_user_input: P) -> Option<PathBuf> {
    let p = path_user_input.as_ref();
    if !p.starts_with("~") {
        return Some(p.to_path_buf());
    }

    if p == Path::new("~") {
        return dirs_next::home_dir();
    }

    dirs_next::home_dir().map(|mut h| {
        if h == Path::new("/") {
            // Corner case: `h` root directory;
            // don't prepend extra `/`, just drop the tilde.
            p.strip_prefix("~")
                .expect("cannot strip ~ prefix")
                .to_path_buf()
        } else {
            h.push(p.strip_prefix("~/").expect("cannot strip ~/ prefix"));
            h
        }
    })
}

pub fn canonicalize<P, Q>(relative_to: P, path: Q) -> io::Result<PathBuf>
where
    P: AsRef<Path>,
    Q: AsRef<Path>,
{
    let absolutized = absolutize(&relative_to, path);
    let path = match std::fs::read_link(&absolutized) {
        Ok(resolved) => {
            let parent = absolutized.parent().unwrap_or(&absolutized);
            absolutize(parent, resolved)
        }

        Err(e) => {
            if absolutized.exists() {
                absolutized
            } else {
                return Err(e);
            }
        }
    };

    Ok(dunce::simplified(&path).to_path_buf())
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io;

    #[test]
    fn absolutize_two_dots() {
        let relative_to = Path::new("/foo/bar");
        let path = Path::new("..");

        assert_eq!(
            PathBuf::from("/foo"), // missing path
            absolutize(relative_to, path)
        );
    }

    #[test]
    fn absolutize_with_curdir() {
        let relative_to = Path::new("/foo");
        let path = Path::new("./bar/./baz");

        assert!(!absolutize(relative_to, path)
            .to_str()
            .unwrap()
            .contains('.'));
    }

    #[test]
    fn canonicalize_should_succeed() -> io::Result<()> {
        let relative_to = Path::new("/foo/bar");
        let path = Path::new("../..");

        assert_eq!(
            PathBuf::from("/"), // existing path
            canonicalize(relative_to, path)?,
        );

        Ok(())
    }

    #[test]
    fn canonicalize_should_fail() {
        let relative_to = Path::new("/foo/bar/baz"); // '/foo' is missing
        let path = Path::new("../..");

        assert!(canonicalize(relative_to, path).is_err());
    }
}