// Copyright (c) 2016-2021 Fabian Schuiki

//! A global source file table that assigns an opaque ID to each processed
//! source file. This helps keeping the source location lean and allow for
//! simple querying of information.

use crate::name::RcStr;
use memmap::Mmap;
use once_cell::sync::OnceCell;
use std;
use std::borrow::Borrow;
use std::cell::RefCell;
use std::cmp::{max, min};
use std::collections::HashMap;
use std::fmt;
use std::fs::File;
use std::hash::{Hash, Hasher};
use std::path::Path;
use std::rc::Rc;

pub const INVALID_SOURCE: Source = Source(0);
pub const INVALID_LOCATION: Location = Location {
    source: INVALID_SOURCE,
    offset: 0,
};
pub const INVALID_SPAN: Span = Span {
    source: INVALID_SOURCE,
    begin: 0,
    end: 0,
};

#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Source(pub u32);

impl Source {
    /// Return the path of this source file.
    pub fn get_path(self) -> RcStr {
        get_source_manager().with(self, |x| x.get_path())
    }

    /// Access the contents of this source file.
    pub fn get_content(self) -> Rc<dyn SourceContent> {
        get_source_manager().with(self, |x| x.get_content())
    }

    /// Copy a range of the source content into a String instance owned by the
    /// caller, possibly converting the encoding such that the result is in
    /// UTF-8.
    pub fn extract(self, begin: usize, end: usize) -> String {
        get_source_manager().with(self, |x| x.extract(begin, end))
    }
}

impl fmt::Debug for Source {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        if self.0 > 0 {
            write!(f, "Source({}; \"{}\")", self.0, self.get_path())
        } else {
            write!(f, "Source(INVALID)")
        }
    }
}

impl fmt::Display for Source {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.get_path(), f)
    }
}

// impl Encodable for Source {
//     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
//         s.emit_bool(self.0 == 0)?;
//         if self.0 > 0 {
//             s.emit_str(self.get_path().borrow())?
//         }
//         Ok(())
//     }
// }

// impl Decodable for Source {
//     fn decode<S: Decoder>(s: &mut S) -> Result<Source, S::Error> {
//         let invalid = s.read_bool()?;
//         if !invalid {
//             let path = s.read_str()?;
//             match get_source_manager().open(&path) {
//                 Some(x) => Ok(x),
//                 None => panic!("trying to decode invalid source `{}`", path),
//             }
//         } else {
//             Ok(INVALID_SOURCE)
//         }
//     }
// }

pub trait SourceFile {
    fn get_id(&self) -> Source;
    fn get_path(&self) -> RcStr;
    // TODO: getter for character iterator
    // TODO: getter for source file extracts

    /// Obtain the content of this source file. The returned object may be used
    /// to iterate over the characters in the file or extract portions of it.
    fn get_content(&self) -> Rc<dyn SourceContent>;

    /// Copy a range of the source content into a String instance owned by the
    /// caller, possibly converting the encoding such that the result is in
    /// UTF-8.
    fn extract(&self, begin: usize, end: usize) -> String {
        self.get_content().extract(begin, end)
    }
}

pub trait SourceContent {
    /// Obtain an iterator over the characters within the source file, together
    /// with their respective byte positions.
    fn iter(&self) -> Box<CharIter>;

    /// Obtain an iterator over the characters within the source file, starting
    /// at the provided location `offset`, together with their respective byte
    /// positions.
    fn iter_from(&self, offset: usize) -> Box<CharIter>;

    /// Copy a range of the source content into a String instance owned by the
    /// caller, possibly converting the encoding such that the result is in
    /// UTF-8.
    fn extract(&self, begin: usize, end: usize) -> String;

    /// Obtain an iterator over an extract of the source content. This might be
    /// more efficient than copying the extract into a String.
    fn extract_iter(&self, begin: usize, end: usize) -> Box<CharIter>;

    /// Obtain a slice voer all bytes within the source file. This is the
    /// fastest way of getting at the file's contents, since no parsing or
    /// character encoding is performed or assumed.
    fn bytes(&self) -> &[u8];

    /// Return a list of byte offsets indicating the start of lines.
    fn lines(&self) -> &[usize];
}

/// A manager for source files and their assigned IDs.
pub struct SourceManager {
    map: RefCell<HashMap<RcStr, Source>>,
    vect: RefCell<Vec<Box<dyn SourceFile>>>,
}

impl SourceManager {
    fn new() -> SourceManager {
        SourceManager {
            map: RefCell::new(HashMap::new()),
            vect: RefCell::new(Vec::new()),
        }
    }

    /// Obtain the source file for a given source ID.
    pub fn with<F, R>(&self, id: Source, f: F) -> R
    where
        F: FnOnce(&dyn SourceFile) -> R,
    {
        let ref vect = *self.vect.borrow();
        assert!(id.0 > 0, "invalid source");
        assert!(
            (id.0 as usize - 1) < vect.len(),
            "unknown source file: Source({}) >= {}",
            id.0,
            vect.len()
        );
        f(&*vect[id.0 as usize - 1])
    }

    pub fn find<Q: ?Sized>(&self, filename: &Q) -> Option<Source>
    where
        RcStr: Borrow<Q>,
        Q: Eq + Hash,
    {
        (*self.map.borrow()).get(filename).map(|v| *v)
    }

    pub fn open(&self, filename: &str) -> Option<Source> {
        // Check if the file has already been opened and return its pointer.
        let mut map = self.map.borrow_mut();
        if let Some(&id) = map.get(filename) {
            return Some(id);
        }

        // Check whether the file exists and allocate a new index for it.
        if Path::new(filename).exists() {
            let mut vect = self.vect.borrow_mut();
            let new_id = Source(vect.len() as u32 + 1);
            let v = RcStr::new(filename);
            map.insert(v.clone(), new_id);
            vect.push(Box::new(DiskSourceFile {
                id: new_id,
                filename: v,
                content: RefCell::new(None),
            }));
            Some(new_id)
        } else {
            None
        }
    }

    /// Create a virtual file from the contents of a string and add it to the
    /// source manager. Future calls to `open()` with the given filename will
    /// yield the provided contents.
    pub fn add(&self, filename: &str, content: &str) -> Source {
        let mut map = self.map.borrow_mut();
        assert!(
            !map.contains_key(filename),
            "add failed: source \"{}\" already exists",
            filename
        );
        let mut vect = self.vect.borrow_mut();
        let new_id = Source(vect.len() as u32 + 1);
        let v = RcStr::new(filename);
        map.insert(v.clone(), new_id);
        vect.push(Box::new(VirtualSourceFile {
            id: new_id,
            filename: v,
            content: Rc::new(VirtualSourceContent(content.to_string(), OnceCell::new())),
        }));
        new_id
    }

    /// Create a virtual file from the contents of a string and add it to the
    /// source manager. The file can only be used with the returned `Source`,
    /// since there is no name associated with it by which it could be referred
    /// to.
    pub fn add_anonymous<S>(&self, content: S) -> Source
    where
        S: Into<String>,
    {
        let mut vect = self.vect.borrow_mut();
        let new_id = Source(vect.len() as u32 + 1);
        vect.push(Box::new(VirtualSourceFile {
            id: new_id,
            filename: RcStr::new("<anonymous>"),
            content: Rc::new(VirtualSourceContent(content.into(), OnceCell::new())),
        }));
        new_id
    }
}

/// Get the global source manager.
pub fn get_source_manager() -> Rc<SourceManager> {
    thread_local!(static MNGR: Rc<SourceManager> = {
        Rc::new(SourceManager::new())
    });
    MNGR.with(|x| x.clone())
}

fn line_starts(iter: impl Iterator<Item = (usize, char)>) -> impl Iterator<Item = usize> {
    Some(0)
        .into_iter()
        .chain(iter.filter(|(_i, c)| *c == '\n').map(|(i, _c)| i + 1))
}

/// A virtual source file that has no correspondence in the file system. Useful
/// for unit tests.
struct VirtualSourceFile {
    id: Source,
    filename: RcStr,
    content: Rc<VirtualSourceContent>,
}

struct VirtualSourceContent(pub String, OnceCell<Vec<usize>>);

impl SourceFile for VirtualSourceFile {
    fn get_id(&self) -> Source {
        self.id
    }

    fn get_path(&self) -> RcStr {
        self.filename.clone()
    }

    fn get_content(&self) -> Rc<dyn SourceContent> {
        self.content.clone()
    }
}

impl SourceContent for VirtualSourceContent {
    fn iter(&self) -> Box<CharIter> {
        Box::new(self.0.char_indices())
    }

    fn iter_from(&self, offset: usize) -> Box<CharIter> {
        Box::new(self.0[offset..].char_indices())
    }

    fn extract(&self, begin: usize, end: usize) -> String {
        self.0[begin..end].to_string()
    }

    fn extract_iter(&self, begin: usize, end: usize) -> Box<CharIter> {
        Box::new(self.0[begin..end].char_indices())
    }

    fn bytes(&self) -> &[u8] {
        self.0.as_bytes()
    }

    fn lines(&self) -> &[usize] {
        self.1.get_or_init(|| line_starts(self.iter()).collect())
    }
}

/// A source file on disk.
struct DiskSourceFile {
    id: Source,
    filename: RcStr,
    content: RefCell<Option<Rc<DiskSourceContent>>>,
}

#[derive(Debug)]
struct DiskSourceContent(pub Mmap, OnceCell<Vec<usize>>);

impl SourceFile for DiskSourceFile {
    fn get_id(&self) -> Source {
        self.id
    }

    fn get_path(&self) -> RcStr {
        self.filename.clone()
    }

    fn get_content(&self) -> Rc<dyn SourceContent> {
        let is_none = self.content.borrow().is_none();
        if is_none {
            let c = Rc::new(DiskSourceContent(
                unsafe { Mmap::map(&File::open(&*self.filename).unwrap()).unwrap() },
                OnceCell::new(),
            ));
            *self.content.borrow_mut() = Some(c.clone());
            c
        } else {
            self.content.borrow().clone().unwrap()
        }
    }
}

impl SourceContent for DiskSourceContent {
    fn iter(&self) -> Box<CharIter> {
        use std::str;
        Box::new(str::from_utf8(&self.0[..]).unwrap().char_indices())
    }

    fn iter_from(&self, offset: usize) -> Box<CharIter> {
        use std::str;
        Box::new(str::from_utf8(&self.0[offset..]).unwrap().char_indices())
    }

    fn extract(&self, begin: usize, end: usize) -> String {
        use std::str;
        str::from_utf8(&self.0[begin..end]).unwrap().to_string()
    }

    fn extract_iter(&self, begin: usize, end: usize) -> Box<CharIter> {
        use std::str;
        Box::new(str::from_utf8(&self.0[begin..end]).unwrap().char_indices())
    }

    fn bytes(&self) -> &[u8] {
        &self.0[..]
    }

    fn lines(&self) -> &[usize] {
        self.1.get_or_init(|| line_starts(self.iter()).collect())
    }
}

/// An iterator that yields the characters from an input file together with the
/// byte positions within the stream.
pub type CharIter<'a> = dyn DoubleEndedIterator<Item = (usize, char)> + 'a;

/// A single location within a source file, expressed as a byte offset.
#[derive(Copy, Clone, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct Location {
    pub source: Source,
    pub offset: usize,
}

impl Location {
    /// Create a new location.
    pub fn new(source: Source, offset: usize) -> Location {
        Location {
            source: source,
            offset: offset,
        }
    }

    /// Create a new location given a human-readable line and column.
    pub fn with_line_and_column(source: Source, line: usize, column: usize) -> Location {
        let c = source.get_content();
        let lines = c.lines();
        if line > 0 && line <= lines.len() {
            Location::new(source, lines[line - 1] + column - 1)
        } else {
            Location::new(source, 0)
        }
    }

    /// Obtain an iterator into the source file at this location.
    pub fn iter<'a>(self, content: &'a Rc<dyn SourceContent>) -> Box<CharIter<'a>> {
        content.iter_from(self.offset)
    }

    /// Determine the line and column information at this location.
    ///
    /// Returns a tuple `(line, column, line_offset)`.
    pub fn human(self) -> (usize, usize, usize) {
        let c = self.source.get_content();
        let lines = c.lines();
        let index = lines.partition_point(|&x| x <= self.offset) - 1;
        let line = index + 1;
        let line_offset = lines[index];
        assert!(line_offset <= self.offset);
        let col = self.offset - line_offset + 1;
        (line, col, line_offset)
    }

    /// Determine the line at this location.
    pub fn human_line(self) -> usize {
        self.human().0
    }

    /// Determine the column at this location.
    pub fn human_column(self) -> usize {
        self.human().1
    }

    /// Determine the line offset at this location.
    pub fn human_line_offset(self) -> usize {
        self.human().2
    }
}

impl fmt::Debug for Location {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{:?}:{}", self.source, self.offset)
    }
}

impl From<Location> for Span {
    fn from(l: Location) -> Span {
        Span::new(l.source, l.offset, l.offset)
    }
}

/// A span of locations within a source file, expressed as a half-open interval
/// of bytes `[begin,end)`.
#[derive(Copy, Clone, PartialOrd, Ord, PartialEq, Eq, Hash)]
pub struct Span {
    pub source: Source,
    pub begin: usize,
    pub end: usize,
}

impl Span {
    /// Create a new span from two byte offsets.
    pub fn new(source: Source, begin: usize, end: usize) -> Span {
        Span {
            source: source,
            begin: begin,
            end: end,
        }
    }

    /// Create a new span that covers two spans, i.e. represents the smallest
    /// possible span that fully contains both input spans `a` and `b`.
    pub fn union<S: Into<Span>>(a: S, b: S) -> Span {
        let sa = a.into();
        let sb = b.into();
        // assert_eq!(sa.source, sb.source);
        if sa.source != sb.source {
            return sa;
        }
        Span {
            source: sa.source,
            begin: min(sa.begin, sb.begin),
            end: max(sa.end, sb.end),
        }
    }

    /// Modify this range to also cover the entirety of the `other` range. The
    /// `other` range must lie in the same source as `self`.
    pub fn expand<S: Into<Span>>(&mut self, other: S) -> &mut Self {
        let o = other.into();
        // assert_eq!(self.source, o.source);
        if self.source == o.source {
            self.begin = min(self.begin, o.begin);
            self.end = max(self.end, o.end);
        }
        self
    }

    /// Return the location just before the first character in this span.
    pub fn begin(&self) -> Location {
        Location::new(self.source, self.begin)
    }

    /// Return the location just after the last character in this span.
    pub fn end(&self) -> Location {
        Location::new(self.source, self.end)
    }

    /// Copy the portion of the source file in this span into an owned string.
    pub fn extract(&self) -> String {
        self.source.get_content().extract(self.begin, self.end)
    }

    /// Obtain an iterator over the extract of the source file describe by this
    /// span.
    pub fn iter<'a>(self, content: &'a Rc<dyn SourceContent>) -> Box<CharIter<'a>> {
        content.extract_iter(self.begin, self.end)
    }
}

impl fmt::Debug for Span {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{:?}:{}-{}", self.source, self.begin, self.end)
    }
}

/// A wrapper that associates a span with a value.
#[derive(PartialOrd, Ord, PartialEq, Eq)]
pub struct Spanned<T> {
    pub value: T,
    pub span: Span,
}

impl<T> Spanned<T> {
    /// Wrap a given value together with the span it covers.
    pub fn new(value: T, span: Span) -> Spanned<T> {
        Spanned {
            value: value,
            span: span,
        }
    }

    /// Map the spanned value, preserving the span.
    pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Spanned<U> {
        Spanned::new(f(self.value), self.span)
    }

    pub fn map_into<U>(self) -> Spanned<U>
    where
        T: Into<U>,
    {
        Spanned::new(self.value.into(), self.span)
    }

    pub fn as_ref(&self) -> Spanned<&T> {
        Spanned::new(&self.value, self.span)
    }
}

impl<T> std::fmt::Debug for Spanned<T>
where
    T: std::fmt::Debug,
{
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        self.value.fmt(f)
    }
}

impl<T> std::fmt::Display for Spanned<T>
where
    T: std::fmt::Display,
{
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        self.value.fmt(f)
    }
}

impl<T> Copy for Spanned<T> where T: Copy {}

impl<T> Clone for Spanned<T>
where
    T: Clone,
{
    fn clone(&self) -> Self {
        Spanned {
            value: self.value.clone(),
            span: self.span,
        }
    }
}

impl<T> Hash for Spanned<T>
where
    T: Hash,
{
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher,
    {
        self.value.hash(state)
    }
}

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

    #[test]
    #[should_panic(expected = "invalid source")]
    fn invalid_source_id() {
        get_source_manager().with(Source(0), |_| ());
    }

    #[test]
    #[should_panic(expected = "unknown source file")]
    fn unknown_source_id() {
        get_source_manager().with(Source(1), |_| ());
    }

    #[test]
    fn inject_file() {
        let sm = get_source_manager();
        let id = sm.add("flabberghasted.txt", "Hello\nWorld\n");
        let source = sm.open("flabberghasted.txt").expect("file should exist");
        assert_eq!(source, id);
    }

    #[test]
    fn inexistent_file() {
        let sm = get_source_manager();
        assert_eq!(sm.open("/this/path/points/nowhere"), None);
    }

    #[test]
    fn chars() {
        let sm = get_source_manager();
        let source = sm.add("test.txt", "老虎.");
        let content = source.get_content();
        let elements: Vec<(usize, char)> = content.iter().collect();
        assert_eq!(elements, vec![(0, '老'), (3, '虎'), (6, '.')]);
    }

    #[test]
    fn file() {
        use std::fs::File;
        use std::io::Write;
        use std::path::Path;

        let path = Path::new("/tmp/moore-test");
        let data = "Löwe 老虎 Léopard\n";
        File::create(path)
            .unwrap()
            .write_all(data.as_bytes())
            .unwrap();

        let sm = get_source_manager();
        let source = sm.open(path.to_str().unwrap()).expect("file should exist");
        let content = source.get_content();
        let expected: Vec<_> = data.char_indices().collect();
        let actual: Vec<_> = content.iter().collect();

        assert_eq!(expected, actual);
    }
}