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

#[derive(Debug)]
pub enum NormalizeError {
    EmptyInput,
    CwdNotAbsolute,
}

pub fn normalize_path(root: &Path, origin: &Path, input: &Path) -> Result<PathBuf, NormalizeError> {
    let cwd = env::current_dir().map_err(|_| NormalizeError::CwdNotAbsolute)?;
    normalize_path_with_preset_cwd(root, origin, input, &cwd)
}

fn normalize_path_with_preset_cwd(
    root: &Path,
    origin: &Path,
    input: &Path,
    cwd: &Path,
) -> Result<PathBuf, NormalizeError> {
    if input.as_os_str().is_empty() {
        return Err(NormalizeError::EmptyInput);
    }
    if !cwd.is_absolute() {
        return Err(NormalizeError::CwdNotAbsolute);
    }
    let input = if input.is_absolute() {
        input.to_path_buf()
    } else if origin.is_absolute() {
        origin.join(input)
    } else {
        cwd.join(origin).join(input)
    };
    let root = if root.is_absolute() {
        root.to_path_buf()
    } else {
        cwd.join(root)
    };
    let mut stack = Vec::new();
    for component in input.components() {
        match component {
            Component::CurDir => (),
            Component::ParentDir => {
                stack.pop();
            }
            Component::Prefix(_) => stack.push(component),
            Component::Normal(_) => stack.push(component),
            Component::RootDir => stack.push(component),
        }
    }
    let normalized_input = PathBuf::from_iter(stack);
    Ok(normalize_to_root(normalized_input, &root))
}

fn normalize_to_root(target: PathBuf, mut root: &Path) -> PathBuf {
    let mut prefix = PathBuf::new();
    loop {
        if let Ok(suffix) = target.strip_prefix(root) {
            return prefix.join(suffix);
        }
        if let Some(new_root) = root.parent() {
            prefix.push("..");
            root = new_root;
        } else {
            return target;
        }
    }
}

#[cfg(test)]
mod tests {
    use std::path::Path;

    use super::{NormalizeError, normalize_path_with_preset_cwd};

    #[test]
    fn empty_path_returns_error() {
        let fake_cwd = Path::new("/sandbox");
        let root = Path::new("");
        let origin_dir = Path::new("");
        let input = Path::new("");
        let result = normalize_path_with_preset_cwd(root, origin_dir, input, fake_cwd);
        assert!(matches!(result, Err(NormalizeError::EmptyInput)));
    }

    #[test]
    fn plain_filename_with_root_at_cwd_returns_filename() {
        let fake_cwd = Path::new("/sandbox");
        let root = Path::new("");
        let origin_dir = Path::new("");
        let input = Path::new("main.rs");
        let result = normalize_path_with_preset_cwd(root, origin_dir, input, fake_cwd);
        assert!(result.is_ok());
        assert_eq!(result.unwrap(), Path::new("main.rs"));
    }

    #[test]
    fn relative_path_from_origin_is_resolved() {
        let fake_cwd = Path::new("/sandbox");
        let root = Path::new("");
        let origin_dir = Path::new("src");
        let input = Path::new("../main.rs");
        let result = normalize_path_with_preset_cwd(root, origin_dir, input, fake_cwd);
        assert!(result.is_ok());
        assert_eq!(result.unwrap(), Path::new("main.rs"));
    }

    #[test]
    fn path_is_made_relative_to_root() {
        let fake_cwd = Path::new("/sandbox");
        let root = Path::new("/project");
        let origin_dir = Path::new("/project/src");
        let input = Path::new("main.rs");
        let result = normalize_path_with_preset_cwd(root, origin_dir, input, fake_cwd);
        assert_eq!(result.unwrap(), Path::new("src/main.rs"));
    }

    #[test]
    fn path_is_made_relative_to_root_from_outside() {
        let fake_cwd = Path::new("/sandbox");
        let root = Path::new("/project");
        let origin_dir = Path::new("/outside");
        let input = Path::new("main.rs");
        let result = normalize_path_with_preset_cwd(root, origin_dir, input, fake_cwd);
        assert_eq!(result.unwrap(), Path::new("../outside/main.rs"));
    }

    #[test]
    fn path_is_made_relative_to_root_even_if_root_dir_is_relative() {
        let fake_cwd = Path::new("/sandbox");
        let root = Path::new("project");
        let origin_dir = Path::new("/sandbox/outside");
        let input = Path::new("main.rs");
        let result = normalize_path_with_preset_cwd(root, origin_dir, input, fake_cwd);
        assert_eq!(result.unwrap(), Path::new("../outside/main.rs"));
    }

    #[test]
    fn absolute_inputs_work() {
        let fake_cwd = Path::new("/sandbox");
        let root = Path::new("project");
        let origin_dir = Path::new("/sandbox/outside");
        let input = Path::new("/sandbox/main.rs");
        let result = normalize_path_with_preset_cwd(root, origin_dir, input, fake_cwd);
        assert_eq!(result.unwrap(), Path::new("../main.rs"));
    }

    #[test]
    fn path_is_made_relative_to_root_even_if_origin_dir_is_relative() {
        let fake_cwd = Path::new("/sandbox");
        let root = Path::new("/sandbox/project");
        let origin_dir = Path::new("outside");
        let input = Path::new("main.rs");
        let result = normalize_path_with_preset_cwd(root, origin_dir, input, fake_cwd);
        assert_eq!(result.unwrap(), Path::new("../outside/main.rs"));
    }
}