use std::sync::atomic::AtomicU32;

#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct FileId {
    id: u32,
}

impl FileId {
    pub fn new() -> Self {
        static GEN: AtomicU32 = AtomicU32::new(0);
        Self {
            id: GEN.fetch_add(1, std::sync::atomic::Ordering::SeqCst),
        }
    }

    pub fn from(self, start: u32) -> SpanFrom {
        SpanFrom::new(self, start)
    }

    pub fn span(self, start: u32, end: u32) -> Span {
        Span::new(self, start, end)
    }
}

#[derive(Copy, Clone)]
pub struct SpanFrom {
    pub file: FileId,
    pub start: u32,
}

impl SpanFrom {
    pub fn new(file: FileId, start: u32) -> Self {
        Self { file, start }
    }

    pub fn to(self, end: u32) -> Span {
        Span::new(self.file, self.start, end)
    }

    pub fn with_len(self, len: u32) -> Span {
        self.to(self.start + len)
    }
}

#[derive(Copy, Clone, PartialEq, Eq)]
pub struct Span {
    pub file: FileId,
    pub start: u32,
    pub end: u32,
}

/// manual implementation of PartialOrd to ensure shorter Spans are first
impl PartialOrd for Span {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        match self.file.partial_cmp(&other.file) {
            Some(core::cmp::Ordering::Equal) => {}
            ord => return ord,
        }
        match self.start.partial_cmp(&other.start) {
            Some(core::cmp::Ordering::Equal) => {}
            ord => return ord,
        }
        other.end.partial_cmp(&self.end)
    }
}

/// manual implementation of Ord to ensure shorter Spans are first
impl Ord for Span {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        match self.file.cmp(&other.file) {
            core::cmp::Ordering::Equal => {}
            ord => return ord,
        }
        match self.start.cmp(&other.start) {
            core::cmp::Ordering::Equal => {}
            ord => return ord,
        }
        other.end.cmp(&self.end)
    }
}

impl Span {
    pub fn new(file: FileId, start: u32, end: u32) -> Self {
        Self { file, start, end }
    }
}