//! The tokenizer glues states from the state machine together.
//!
//! It facilitates everything needed to turn codes into tokens and events with
//! a state machine.
//! It also enables logic needed for parsing markdown, such as an [`attempt`][]
//! to parse something, which can succeed or, when unsuccessful, revert the
//! attempt.
//! Similarly, a [`check`][] exists, which does the same as an `attempt` but
//! reverts even if successful.
//!
//! [`attempt`]: Tokenizer::attempt
//! [`check`]: Tokenizer::check

use crate::parser::ParseState;
use crate::token::Token;
use std::collections::HashMap;

/// Embedded content type.
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum ContentType {
    /// Represents [flow content][crate::content::flow].
    Flow,
    /// Represents [text content][crate::content::text].
    Text,
    /// Represents [string content][crate::content::string].
    String,
}

/// Enum representing a character code.
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum Code {
    /// End of the input stream (called eof).
    None,
    /// Used to make parsing line endings easier as it represents both
    /// `Code::Char('\r')` and `Code::Char('\n')` combined.
    CarriageReturnLineFeed,
    /// the expansion of a tab (`Code::Char('\t')`), depending on where the tab
    /// ocurred, it’s followed by 0 to 3 (both inclusive) `Code::VirtualSpace`s.
    VirtualSpace,
    /// The most frequent variant of this enum is `Code::Char(char)`, which just
    /// represents a char, but micromark adds meaning to certain other values.
    Char(char),
}

/// A location in the document (`line`/`column`/`offset`).
///
/// The interface for the location in the document comes from unist `Point`:
/// <https://github.com/syntax-tree/unist#point>.
#[derive(Debug, Clone, PartialEq)]
pub struct Point {
    /// 1-indexed line number.
    pub line: usize,
    /// 1-indexed column number.
    /// This is increases up to a tab stop for tabs.
    /// Some editors count tabs as 1 character, so this position is not always
    /// the same as editors.
    pub column: usize,
    /// 0-indexed position in the document.
    pub offset: usize,
}

/// Possible event types.
#[derive(Debug, PartialEq, Clone)]
pub enum EventType {
    /// The start of something.
    Enter,
    /// The end of something.
    Exit,
}

/// Something semantic happening somewhere.
#[derive(Debug, Clone)]
pub struct Event {
    pub event_type: EventType,
    pub token_type: Token,
    pub point: Point,
    pub index: usize,
    pub previous: Option<usize>,
    pub next: Option<usize>,
    pub content_type: Option<ContentType>,
}

/// The essence of the state machine are functions: `StateFn`.
/// It’s responsible for dealing with that single passed [`Code`][].
/// It yields a [`StateFnResult`][].
pub type StateFn = dyn FnOnce(&mut Tokenizer, Code) -> StateFnResult;

/// Each [`StateFn`][] yields something back: primarily the state.
/// In certain cases, it can also yield back up parsed codes that were passed down.
pub type StateFnResult = (State, Option<Vec<Code>>);

/// Callback that can be registered and is called when the tokenizer is done.
///
/// Resolvers are supposed to change the list of events, because parsing is
/// sometimes messy, and they help expose a cleaner interface of events to
/// the compiler and other users.
pub type Resolver = dyn FnOnce(&mut Tokenizer) -> Vec<Event>;

/// The result of a state.
pub enum State {
    /// There is a future state: a boxed [`StateFn`][] to pass the next code to.
    Fn(Box<StateFn>),
    /// The state is successful.
    Ok,
    /// The state is not successful.
    Nok,
}

/// Loose label starts we found.
#[derive(Debug)]
pub struct LabelStart {
    /// Indices of where the label starts and ends in `events`.
    pub start: (usize, usize),
    /// A boolean used internally to figure out if a label start link can’t be
    /// used (because links in links are incorrect).
    pub inactive: bool,
    /// A boolean used internally to figure out if a label is balanced: they’re
    /// not media, it’s just balanced braces.
    pub balanced: bool,
}

/// Media we found.
#[derive(Debug)]
pub struct Media {
    /// Indices of where the media’s label start starts and ends in `events`.
    pub start: (usize, usize),
    /// Indices of where the media’s label end starts and ends in `events`.
    pub end: (usize, usize),
    /// Identifier
    pub id: String,
}

/// To do.
#[derive(Default, Debug)]
pub struct ContainerState {
    pub blank_initial: bool,
    pub size: usize,
}

/// The internal state of a tokenizer, not to be confused with states from the
/// state machine, this instead is all the information about where we currently
/// are and what’s going on.
#[derive(Debug, Clone)]
struct InternalState {
    /// Length of `events`. We only add to events, so reverting will just pop stuff off.
    events_len: usize,
    /// Length of the stack. It’s not allowed to decrease the stack in a check or an attempt.
    stack_len: usize,
    /// Previous code.
    previous: Code,
    /// Current code.
    current: Code,
    /// `index` in codes of the current code.
    index: usize,
    /// Current relative and absolute position in the file.
    point: Point,
}

// #[derive(Debug)]

/// A tokenizer itself.
#[allow(clippy::struct_excessive_bools)]
pub struct Tokenizer<'a> {
    column_start: HashMap<usize, usize>,
    /// Track whether a character is expected to be consumed, and whether it’s
    /// actually consumed
    ///
    /// Tracked to make sure everything’s valid.
    consumed: bool,
    /// Track whether this tokenizer is done.
    drained: bool,
    /// Semantic labels of one or more codes in `codes`.
    pub events: Vec<Event>,
    /// Hierarchy of semantic labels.
    ///
    /// Tracked to make sure everything’s valid.
    pub stack: Vec<Token>,
    /// Previous character code.
    pub previous: Code,
    /// Current character code.
    current: Code,
    /// `index` in codes of the current code.
    pub index: usize,
    /// Current relative and absolute place in the file.
    pub point: Point,
    /// List of attached resolvers, which will be called when done feeding,
    /// to clean events.
    resolvers: Vec<Box<Resolver>>,
    /// List of names associated with attached resolvers.
    resolver_ids: Vec<String>,
    /// Shared parsing state across tokenizers.
    pub parse_state: &'a ParseState,
    /// Stack of label (start) that could form images and links.
    ///
    /// Used when tokenizing [text content][crate::content::text].
    pub label_start_stack: Vec<LabelStart>,
    /// Stack of label (start) that cannot form images and links.
    ///
    /// Used when tokenizing [text content][crate::content::text].
    pub label_start_list_loose: Vec<LabelStart>,
    /// Stack of images and links.
    ///
    /// Used when tokenizing [text content][crate::content::text].
    pub media_list: Vec<Media>,
    /// Whether we would be interrupting something.
    ///
    /// Used when tokenizing [flow content][crate::content::flow].
    pub interrupt: bool,
    /// To do.
    pub concrete: bool,
    /// To do.
    pub lazy: bool,
    /// To do.
    pub container: Option<ContainerState>,
}

impl<'a> Tokenizer<'a> {
    /// Create a new tokenizer.
    pub fn new(point: Point, index: usize, parse_state: &'a ParseState) -> Tokenizer {
        Tokenizer {
            previous: Code::None,
            current: Code::None,
            column_start: HashMap::new(),
            index,
            consumed: true,
            drained: false,
            point,
            stack: vec![],
            events: vec![],
            parse_state,
            label_start_stack: vec![],
            label_start_list_loose: vec![],
            media_list: vec![],
            interrupt: false,
            concrete: false,
            lazy: false,
            container: None,
            resolvers: vec![],
            resolver_ids: vec![],
        }
    }

    /// Register a resolver.
    pub fn register_resolver(&mut self, id: String, resolver: Box<Resolver>) {
        if !self.resolver_ids.contains(&id) {
            self.resolver_ids.push(id);
            self.resolvers.push(resolver);
        }
    }

    /// Register a resolver, before others.
    pub fn register_resolver_before(&mut self, id: String, resolver: Box<Resolver>) {
        if !self.resolver_ids.contains(&id) {
            self.resolver_ids.push(id);
            self.resolvers.insert(0, resolver);
        }
    }

    /// Prepare for a next code to get consumed.
    pub fn expect(&mut self, code: Code, force: bool) {
        if !force {
            assert!(self.consumed, "expected previous character to be consumed");
        }
        self.consumed = false;
        self.current = code;
    }

    /// Define a jump between two places.
    ///
    /// This defines how much columns are increased when consuming a line
    /// ending.
    pub fn define_skip(&mut self, point: &Point) {
        self.column_start.insert(point.line, point.column);
        self.account_for_potential_skip();
        log::debug!("position: define skip: `{:?}`", point);
    }

    /// Increment the current positional info if we’re right after a line
    /// ending, which has a skip defined.
    fn account_for_potential_skip(&mut self) {
        if self.point.column == 1 {
            match self.column_start.get(&self.point.line) {
                None => {}
                Some(next_column) => {
                    let col = *next_column;
                    self.point.column = col;
                    self.point.offset += col - 1;
                    self.index += col - 1;
                }
            };
        }
    }

    /// Consume the current character.
    /// Each [`StateFn`][] is expected to call this to signal that this code is
    /// used, or call a next `StateFn`.
    pub fn consume(&mut self, code: Code) {
        assert_eq!(
            code, self.current,
            "expected given code to equal expected code"
        );
        log::debug!("consume: `{:?}` ({:?})", code, self.point);
        assert!(!self.consumed, "expected code to not have been consumed: this might be because `x(code)` instead of `x` was returned");

        match code {
            Code::CarriageReturnLineFeed | Code::Char('\n' | '\r') => {
                self.point.line += 1;
                self.point.column = 1;
                self.point.offset += if code == Code::CarriageReturnLineFeed {
                    2
                } else {
                    1
                };
                self.account_for_potential_skip();
                log::debug!("position: after eol: `{:?}`", self.point);
            }
            Code::VirtualSpace => {
                // Empty.
            }
            _ => {
                self.point.column += 1;
                self.point.offset += 1;
            }
        }

        self.index += 1;
        self.previous = code;
        // Mark as consumed.
        self.consumed = true;
    }

    /// Mark the start of a semantic label.
    pub fn enter(&mut self, token_type: Token) {
        self.enter_with_content(token_type, None);
    }

    pub fn enter_with_content(&mut self, token_type: Token, content_type: Option<ContentType>) {
        log::debug!("enter `{:?}` ({:?})", token_type, self.point);
        self.events.push(Event {
            event_type: EventType::Enter,
            token_type: token_type.clone(),
            point: self.point.clone(),
            index: self.index,
            previous: None,
            next: None,
            content_type,
        });
        self.stack.push(token_type);
    }

    /// Mark the end of a semantic label.
    pub fn exit(&mut self, token_type: Token) {
        let current_token = self.stack.pop().expect("cannot close w/o open tokens");

        assert_eq!(
            current_token, token_type,
            "expected exit token to match current token"
        );

        let previous = self.events.last().expect("cannot close w/o open event");
        let mut index = self.index;
        let mut point = self.point.clone();

        assert!(
            current_token != previous.token_type || previous.index != index,
            "expected non-empty token"
        );

        // A bit weird, but if we exit right after a line ending, we *don’t* want to consider\
        // potential skips.
        if matches!(
            self.previous,
            Code::CarriageReturnLineFeed | Code::Char('\n' | '\r')
        ) {
            let shift = point.column - 1;
            point.column -= shift;
            point.offset -= shift;
            index -= shift;
        }

        log::debug!("exit `{:?}` ({:?})", token_type, point);
        self.events.push(Event {
            event_type: EventType::Exit,
            token_type,
            point,
            index,
            previous: None,
            next: None,
            content_type: None,
        });
    }

    /// Capture the internal state.
    fn capture(&mut self) -> InternalState {
        InternalState {
            index: self.index,
            previous: self.previous,
            current: self.current,
            point: self.point.clone(),
            events_len: self.events.len(),
            stack_len: self.stack.len(),
        }
    }

    /// Apply the internal state.
    fn free(&mut self, previous: InternalState) {
        self.index = previous.index;
        self.previous = previous.previous;
        self.current = previous.current;
        self.point = previous.point;
        assert!(
            self.events.len() >= previous.events_len,
            "expected to restore less events than before"
        );
        self.events.truncate(previous.events_len);
        assert!(
            self.stack.len() >= previous.stack_len,
            "expected to restore less stack items than before"
        );
        self.stack.truncate(previous.stack_len);
    }

    /// Parse with `state_fn` and its future states, switching to `ok` when
    /// successful, and passing [`State::Nok`][] back up if it occurs.
    ///
    /// This function does not capture the current state, in case of
    /// `State::Nok`, as it is assumed that this `go` is itself wrapped in
    /// another `attempt`.
    #[allow(clippy::unused_self)]
    pub fn go(
        &mut self,
        state_fn: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
        after: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
    ) -> Box<StateFn> {
        attempt_impl(
            state_fn,
            |_code| false,
            vec![],
            |result: (Vec<Code>, Vec<Code>), ok, tokenizer: &mut Tokenizer, _state| {
                if ok {
                    feed_impl(tokenizer, &if ok { result.1 } else { result.0 }, after)
                } else {
                    (State::Nok, None)
                }
            },
        )
    }

    /// Like `go`, but this lets you *hijack* back to some other state after a
    /// certain code.
    #[allow(clippy::unused_self)]
    pub fn go_until(
        &mut self,
        state_fn: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
        until: impl FnMut(Code) -> bool + 'static,
        done: impl FnOnce(StateFnResult) -> StateFnResult + 'static,
    ) -> Box<StateFn> {
        attempt_impl(
            state_fn,
            until,
            vec![],
            |result: (Vec<Code>, Vec<Code>), _ok, tokenizer: &mut Tokenizer, state| {
                tokenizer.consumed = true;
                done(check_statefn_result((state, Some(result.1))))
            },
        )
    }

    /// Parse with `state_fn` and its future states, to check if it result in
    /// [`State::Ok`][] or [`State::Nok`][], revert on both cases, and then
    /// call `done` with whether it was successful or not.
    ///
    /// This captures the current state of the tokenizer, returns a wrapped
    /// state that captures all codes and feeds them to `state_fn` and its
    /// future states until it yields `State::Ok` or `State::Nok`.
    /// It then applies the captured state, calls `done`, and feeds all
    /// captured codes to its future states.
    pub fn check(
        &mut self,
        state_fn: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
        done: impl FnOnce(bool) -> Box<StateFn> + 'static,
    ) -> Box<StateFn> {
        let previous = self.capture();

        attempt_impl(
            state_fn,
            |_code| false,
            vec![],
            |result: (Vec<Code>, Vec<Code>), ok, tokenizer: &mut Tokenizer, _state| {
                tokenizer.free(previous);
                feed_impl(tokenizer, &result.0, done(ok))
            },
        )
    }

    /// Parse with `state_fn` and its future states, to check if it results in
    /// [`State::Ok`][] or [`State::Nok`][], revert on the case of
    /// `State::Nok`, and then call `done` with whether it was successful or
    /// not.
    ///
    /// This captures the current state of the tokenizer, returns a wrapped
    /// state that captures all codes and feeds them to `state_fn` and its
    /// future states until it yields `State::Ok`, at which point it calls
    /// `done` and yields its result.
    /// If instead `State::Nok` was yielded, the captured state is applied,
    /// `done` is called, and all captured codes are fed to its future states.
    pub fn attempt(
        &mut self,
        state_fn: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
        done: impl FnOnce(bool) -> Box<StateFn> + 'static,
    ) -> Box<StateFn> {
        let previous = self.capture();

        attempt_impl(
            state_fn,
            |_code| false,
            vec![],
            |result: (Vec<Code>, Vec<Code>), ok, tokenizer: &mut Tokenizer, _state| {
                if !ok {
                    tokenizer.free(previous);
                }

                let codes = if ok { result.1 } else { result.0 };

                log::debug!(
                    "attempt: {:?}, codes: {:?}, at {:?}",
                    ok,
                    codes,
                    tokenizer.point
                );
                feed_impl(tokenizer, &codes, done(ok))
            },
        )
    }

    /// Just like [`attempt`][Tokenizer::attempt], but many.
    pub fn attempt_n(
        &mut self,
        mut state_fns: Vec<Box<StateFn>>,
        done: impl FnOnce(bool) -> Box<StateFn> + 'static,
    ) -> Box<StateFn> {
        if state_fns.is_empty() {
            done(false)
        } else {
            let state_fn = state_fns.remove(0);
            self.attempt(state_fn, move |ok| {
                if ok {
                    done(ok)
                } else {
                    Box::new(|t, code| t.attempt_n(state_fns, done)(t, code))
                }
            })
        }
    }

    /// Just like [`attempt`][Tokenizer::attempt], but for when you don’t care
    /// about `ok`.
    pub fn attempt_opt(
        &mut self,
        state_fn: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
        after: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
    ) -> Box<StateFn> {
        self.attempt(state_fn, |_ok| Box::new(after))
    }

    /// Feed a list of `codes` into `start`.
    ///
    /// This is set up to support repeatedly calling `feed`, and thus streaming
    /// markdown into the state machine, and normally pauses after feeding.
    /// When `done: true` is passed, the EOF is fed.
    pub fn push(
        &mut self,
        codes: &[Code],
        start: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
        drain: bool,
    ) -> StateFnResult {
        assert!(!self.drained, "cannot feed after drain");

        let mut result = feed_impl(self, codes, start);

        if drain {
            let func = match result.0 {
                State::Fn(func) => func,
                _ => unreachable!("expected next state"),
            };

            result = flush_impl(self, func);

            self.drained = true;

            while !self.resolvers.is_empty() {
                let resolver = self.resolvers.remove(0);
                self.events = resolver(self);
            }
        }

        result
    }

    /// To do.
    pub fn flush(
        &mut self,
        start: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
    ) -> StateFnResult {
        flush_impl(self, start)
    }
}

/// Internal utility to wrap states to also capture codes.
///
/// Recurses into itself.
/// Used in [`Tokenizer::attempt`][Tokenizer::attempt] and  [`Tokenizer::check`][Tokenizer::check].
fn attempt_impl(
    state: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
    mut pause: impl FnMut(Code) -> bool + 'static,
    mut codes: Vec<Code>,
    done: impl FnOnce((Vec<Code>, Vec<Code>), bool, &mut Tokenizer, State) -> StateFnResult + 'static,
) -> Box<StateFn> {
    Box::new(|tokenizer, code| {
        // To do: `pause` is currently used after the code.
        // Should it be before?
        // How to match `eof`?
        if !codes.is_empty() && pause(tokenizer.previous) {
            return done(
                (codes, vec![code]),
                false,
                tokenizer,
                State::Fn(Box::new(state)),
            );
        }

        let (next, remainder) = check_statefn_result(state(tokenizer, code));

        match code {
            Code::None => {}
            _ => {
                codes.push(code);
            }
        }

        if let Some(ref list) = remainder {
            assert!(
                list.len() <= codes.len(),
                "`remainder` must be less than or equal to `codes`"
            );
        }

        match next {
            State::Ok => {
                let remaining = if let Some(x) = remainder { x } else { vec![] };
                check_statefn_result(done((codes, remaining), true, tokenizer, next))
            }
            State::Nok => check_statefn_result(done((codes, vec![]), false, tokenizer, next)),
            State::Fn(func) => {
                assert!(remainder.is_none(), "expected no remainder");
                check_statefn_result((State::Fn(attempt_impl(func, pause, codes, done)), None))
            }
        }
    })
}

/// Feed a list of `codes` into `start`.
///
/// This is set up to support repeatedly calling `feed`, and thus streaming
/// markdown into the state machine, and normally pauses after feeding.
/// When `done: true` is passed, the EOF is fed.
fn feed_impl(
    tokenizer: &mut Tokenizer,
    codes: &[Code],
    start: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
) -> StateFnResult {
    let codes = codes;
    let mut state = State::Fn(Box::new(start));
    let mut index = 0;

    tokenizer.consumed = true;

    while index < codes.len() {
        let code = codes[index];

        match state {
            State::Nok | State::Ok => {
                break;
            }
            State::Fn(func) => {
                log::debug!("main: passing `{:?}`", code);
                tokenizer.expect(code, false);
                let (next, remainder) = check_statefn_result(func(tokenizer, code));
                state = next;
                index = index + 1
                    - (if let Some(ref x) = remainder {
                        x.len()
                    } else {
                        0
                    });
            }
        }
    }

    // Yield to a higher loop.
    check_statefn_result((state, Some(codes[index..].to_vec())))
}

/// To do.
fn flush_impl(
    tokenizer: &mut Tokenizer,
    start: impl FnOnce(&mut Tokenizer, Code) -> StateFnResult + 'static,
) -> StateFnResult {
    let mut state = State::Fn(Box::new(start));
    tokenizer.consumed = true;

    loop {
        // Feed EOF.
        match state {
            State::Ok | State::Nok => break,
            State::Fn(func) => {
                let code = Code::None;
                log::debug!("main: passing eof");
                tokenizer.expect(code, false);
                let (next, remainder) = check_statefn_result(func(tokenizer, code));
                assert!(remainder.is_none(), "expected no remainder");
                state = next;
            }
        }
    }

    match state {
        State::Ok => {}
        _ => unreachable!("expected final state to be `State::Ok`"),
    }

    check_statefn_result((state, None))
}

/// Check a [`StateFnResult`][], make sure its valid (that there are no bugs),
/// and clean a final eof passed back in `remainder`.
fn check_statefn_result(result: StateFnResult) -> StateFnResult {
    let (state, mut remainder) = result;

    // Remove an eof.
    // For convencience, feeding back an eof is allowed, but cleaned here.
    // Most states handle eof and eol in the same branch, and hence pass
    // all back.
    // This might not be needed, because if EOF is passed back, we’re at the EOF.
    // But they’re not supposed to be in codes, so here we remove them.
    if let Some(ref mut list) = remainder {
        if Some(&Code::None) == list.last() {
            list.pop();
        }

        if list.is_empty() {
            return (state, None);
        }
    }

    (state, remainder)
}