use std::borrow::Cow;

#[derive(Clone, Debug)]
/// The data structure that describes about pretty printing.
///
/// You should avoid using variants on this enum;
/// instead, use helper functions on this enum.
pub enum Doc<'a> {
    #[doc(hidden)]
    Nil,

    #[doc(hidden)]
    /// The first component is for "flat" mode;
    /// the second component is for "break" mode.
    Alt(Box<Doc<'a>>, Box<Doc<'a>>),

    #[doc(hidden)]
    /// Try printing the first doc.
    /// If it exceeds the width limitation, print the second doc.
    Union(Box<Doc<'a>>, Box<Doc<'a>>),

    #[doc(hidden)]
    Nest(usize, Nest<'a>),

    #[doc(hidden)]
    Text(Cow<'a, str>),

    #[doc(hidden)]
    NewLine,

    #[doc(hidden)]
    EmptyLine,

    #[doc(hidden)]
    /// The first component is the number of spaces if it can be put on a single line;
    /// the second component is the number of offset if it will be broken into different lines.
    Break(usize, usize),

    #[doc(hidden)]
    Group(Cow<'a, [Doc<'a>]>),

    #[doc(hidden)]
    List(Vec<Doc<'a>>),

    #[doc(hidden)]
    Slice(&'a [Doc<'a>]),
}

impl<'a> Doc<'a> {
    #[inline]
    /// Insert a piece of text. It **must not** contain line breaks.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let doc = Doc::text("code");
    /// assert_eq!("code", &print(&doc, &Default::default()));
    ///
    /// let doc = Doc::text(String::from("code"));
    /// assert_eq!("code", &print(&doc, &Default::default()));
    /// ```
    pub fn text(s: impl Into<Cow<'a, str>>) -> Doc<'a> {
        Doc::Text(s.into())
    }

    #[inline]
    /// Empty doc, which does nothing.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let doc = Doc::nil();
    /// assert!(print(&doc, &Default::default()).is_empty());
    /// ```
    pub fn nil() -> Doc<'a> {
        Doc::Nil
    }

    #[inline]
    /// Just a space. This is just short for calling [`text`](Doc::text) with a space.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let doc = Doc::space();
    /// assert_eq!(" ", &print(&doc, &Default::default()));
    /// ```
    pub fn space() -> Doc<'a> {
        Doc::Text(" ".into())
    }

    #[inline]
    /// Force to print a line break.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc, LineBreak, PrintOptions};
    ///
    /// let doc = Doc::hard_line();
    /// let options = Default::default();
    /// assert_eq!("\n", &print(&doc, &options));
    /// let options = PrintOptions {
    ///     line_break: LineBreak::Crlf,
    ///     ..Default::default()
    /// };
    /// assert_eq!("\r\n", &print(&doc, &options));
    ///
    /// // There's a `hard_line` call inside a group,
    /// // so the group always breaks even it doesn't exceed the width limitation.
    /// let doc = Doc::text("fn(")
    ///     .append(Doc::line_or_space())
    ///     .append(Doc::hard_line())
    ///     .group();
    /// assert_eq!("fn(\n\n", &print(&doc, &Default::default()));
    /// ```
    pub fn hard_line() -> Doc<'a> {
        Doc::NewLine
    }

    #[inline]
    /// "Soft line" allows you to put docs on a single line as many as possible.
    /// Once it's going to exceed the width limitation, it will insert a line break,
    /// but before that it will insert spaces instead of line break.
    ///
    /// This is different from [`line_or_space`](Doc::line_or_space). See the examples below.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc, PrintOptions};
    ///
    /// let options = PrintOptions { width: 10, ..Default::default() };
    /// assert_eq!(
    ///     "aaaa bbbb\ncccc",
    ///     &print(
    ///         &Doc::list(vec![
    ///             Doc::text("aaaa"),
    ///             Doc::soft_line(),
    ///             Doc::text("bbbb"),
    ///             Doc::soft_line(),
    ///             Doc::text("cccc"),
    ///         ]).group(),
    ///         &options,
    ///     ),
    /// );
    /// assert_eq!(
    ///     "aaaa\nbbbb\ncccc",
    ///     &print(
    ///         &Doc::list(vec![
    ///             Doc::text("aaaa"),
    ///             Doc::line_or_space(),
    ///             Doc::text("bbbb"),
    ///             Doc::line_or_space(),
    ///             Doc::text("cccc"),
    ///         ]).group(),
    ///         &options,
    ///     ),
    /// );
    /// ```
    pub fn soft_line() -> Doc<'a> {
        Doc::Group((&[Doc::Break(1, 0)]).into())
    }

    #[inline]
    /// "Empty line" is similar to [`hard_line`](Doc::hard_line) but it won't be
    /// affected by indentation. That is, it always prints an empty line without
    /// spaces or tabs indented.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc, PrintOptions};
    ///
    /// assert_eq!(
    ///     "\n",
    ///     &print(
    ///         &Doc::empty_line().nest(1),
    ///         &Default::default(),
    ///     ),
    /// );
    /// assert_eq!(
    ///     "\n ",
    ///     &print(
    ///         &Doc::hard_line().nest(1),
    ///         &Default::default(),
    ///     ),
    /// );
    /// ```
    pub fn empty_line() -> Doc<'a> {
        Doc::EmptyLine
    }

    #[inline]
    /// Create a list of docs.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let doc = Doc::list(vec![Doc::text("a"), Doc::text("b"), Doc::text("c")]);
    /// assert_eq!("abc", &print(&doc, &Default::default()));
    /// ```
    pub fn list(docs: Vec<Doc<'a>>) -> Doc<'a> {
        Doc::List(docs)
    }

    #[inline]
    /// Create a slice of docs, similar to [`list`](Doc::list).
    ///
    /// This won't create a [`Vec`] with allocation, but calling [`append`](Doc::append) or [`concat`](Doc::concat) on it will create a [`Vec`].
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let docs = [Doc::text("a"), Doc::text("b"), Doc::text("c")];
    /// assert_eq!("abc", &print(&Doc::slice(&docs), &Default::default()));
    /// ```
    pub fn slice(docs: &'a [Doc<'a>]) -> Doc<'a> {
        Doc::Slice(docs)
    }

    #[inline]
    /// Print a space if doc can be put on a single line, otherwise print a line break.
    ///
    /// *This won't take any effects if used outside a group: it will just print a line break.*
    ///
    /// ```
    /// use tiny_pretty::{print, Doc, PrintOptions};
    ///
    /// let options = PrintOptions { width: 10, ..Default::default() };
    /// assert_eq!(
    ///     "aaaa\nbbbb\ncccc",
    ///     &print(
    ///         &Doc::list(vec![
    ///             Doc::text("aaaa"),
    ///             Doc::line_or_space(),
    ///             Doc::text("bbbb"),
    ///             Doc::line_or_space(),
    ///             Doc::text("cccc"),
    ///         ]).group(),
    ///         &options,
    ///     ),
    /// );
    /// assert_eq!(
    ///     "a b",
    ///     &print(
    ///         &Doc::list(vec![
    ///             Doc::text("a"),
    ///             Doc::line_or_space(),
    ///             Doc::text("b"),
    ///         ]).group(),
    ///         &options,
    ///     ),
    /// );
    ///
    /// assert_eq!(
    ///     "a\nb",
    ///     &print(
    ///         &Doc::list(vec![
    ///             Doc::text("a"),
    ///             Doc::line_or_space(),
    ///             Doc::text("b"),
    ///         ]), // <-- no grouping here
    ///         &options,
    ///     ),
    /// );
    /// ```
    pub fn line_or_space() -> Doc<'a> {
        Doc::Break(1, 0)
    }

    #[inline]
    /// Print nothing if doc can be put on a single line, otherwise print a line break.
    ///
    /// *This won't take any effects if used outside a group: it will just print a line break.*
    ///
    /// ```
    /// use tiny_pretty::{print, Doc, PrintOptions};
    ///
    /// let options = PrintOptions { width: 5, ..Default::default() };
    /// assert_eq!(
    ///     "func(\narg",
    ///     &print(
    ///         &Doc::list(vec![
    ///             Doc::text("func("),
    ///             Doc::line_or_nil(),
    ///             Doc::text("arg"),
    ///         ]).group(),
    ///         &options,
    ///     ),
    /// );
    /// assert_eq!(
    ///     "f(arg",
    ///     &print(
    ///         &Doc::list(vec![
    ///             Doc::text("f("),
    ///             Doc::line_or_nil(),
    ///             Doc::text("arg"),
    ///         ]).group(),
    ///         &options,
    ///     ),
    /// );
    ///
    /// assert_eq!(
    ///     "f(\narg",
    ///     &print(
    ///         &Doc::list(vec![
    ///             Doc::text("f("),
    ///             Doc::line_or_nil(),
    ///             Doc::text("arg"),
    ///         ]), // <-- no grouping here
    ///         &options,
    ///     ),
    /// );
    /// ```
    pub fn line_or_nil() -> Doc<'a> {
        Doc::Break(0, 0)
    }

    #[inline]
    /// Apply `doc_flat` when it can be put on a single line,
    /// otherwise apply `doc_break`.
    ///
    /// *This won't take any effects if used outside a group: it will just apply `doc_break`.*
    ///
    /// ```
    /// use tiny_pretty::{print, Doc, PrintOptions};
    ///
    /// let doc = Doc::list(vec![
    ///     Doc::text("function("),
    ///     Doc::line_or_nil(),
    ///     Doc::text("arg"),
    ///     Doc::flat_or_break(Doc::nil(), Doc::text(",")),
    ///     Doc::line_or_nil(),
    ///     Doc::text(")"),
    /// ]).group();
    ///
    /// let options = PrintOptions {
    ///     width: 10,
    ///     ..Default::default()
    /// };
    /// assert_eq!("function(\narg,\n)", &print(&doc, &options));
    ///
    /// let options = PrintOptions {
    ///     width: 20,
    ///     ..Default::default()
    /// };
    /// assert_eq!("function(arg)", &print(&doc, &options));
    ///
    ///
    ///
    /// let doc = Doc::list(vec![
    ///     Doc::text("function("),
    ///     Doc::line_or_nil(),
    ///     Doc::text("arg"),
    ///     Doc::flat_or_break(Doc::nil(), Doc::text(",")),
    ///     Doc::line_or_nil(),
    ///     Doc::text(")"),
    /// ]); // <-- no grouping here
    ///
    /// let options = PrintOptions {
    ///     width: 20,
    ///     ..Default::default()
    /// };
    /// assert_eq!("function(\narg,\n)", &print(&doc, &options));
    /// ```
    pub fn flat_or_break(doc_flat: Doc<'a>, doc_break: Doc<'a>) -> Doc<'a> {
        Doc::Alt(Box::new(doc_flat), Box::new(doc_break))
    }

    #[inline]
    /// Try applying the current doc. If it exceeds the width limitation, apply the `alternate` doc.
    ///
    /// This looks similar to [`flat_or_break`](Doc::flat_or_break),
    /// but you should use [`flat_or_break`](Doc::flat_or_break) with [`group`](Doc::group) as possible.
    ///
    /// Only consider using this if there're some [`hard_line`](Doc::hard_line) calls in your doc,
    /// since [`hard_line`](Doc::hard_line) will always break in a group.
    /// ```
    /// use tiny_pretty::{print, Doc, PrintOptions};
    ///
    /// let closure = Doc::list(vec![
    ///     Doc::text("|| {"),
    ///     Doc::hard_line()
    ///         .append(
    ///             Doc::text("call2(|| {")
    ///                 .append(Doc::hard_line().append(Doc::text("value")).nest(4))
    ///                 .append(Doc::hard_line())
    ///                 .append(Doc::text("})"))
    ///         )
    ///         .nest(4),
    ///     Doc::hard_line(),
    ///     Doc::text("}"),
    /// ]);
    ///
    /// let doc = Doc::text("fn main() {")
    ///     .append(
    ///         Doc::hard_line()
    ///             .append(
    ///                 Doc::list(vec![
    ///                     Doc::text("call1("),
    ///                     Doc::nil()
    ///                         .append(Doc::text("very_long_arg"))
    ///                         .append(Doc::text(","))
    ///                         .append(Doc::space())
    ///                         .append(closure.clone())
    ///                         .nest(0),
    ///                     Doc::text(")"),
    ///                 ]).union(Doc::list(vec![
    ///                     Doc::text("call1("),
    ///                         Doc::hard_line()
    ///                             .append(Doc::text("very_long_arg"))
    ///                             .append(Doc::text(","))
    ///                             .append(Doc::hard_line())
    ///                             .append(closure)
    ///                             .nest(4),
    ///                         Doc::hard_line(),
    ///                         Doc::text(")"),
    ///                 ])),
    ///             )
    ///             .nest(4)
    ///     )
    ///     .append(Doc::hard_line())
    ///     .append(Doc::text("}"));
    ///
    /// let options = PrintOptions {
    ///     width: 10,
    ///     ..Default::default()
    /// };
    /// assert_eq!("fn main() {
    ///     call1(
    ///         very_long_arg,
    ///         || {
    ///             call2(|| {
    ///                 value
    ///             })
    ///         }
    ///     )
    /// }", &print(&doc, &options));
    ///
    /// let options = PrintOptions {
    ///     width: 30,
    ///     ..Default::default()
    /// };
    /// assert_eq!("fn main() {
    ///     call1(very_long_arg, || {
    ///         call2(|| {
    ///             value
    ///         })
    ///     })
    /// }", &print(&doc, &options));
    /// ```
    pub fn union(self, alternate: Doc<'a>) -> Doc<'a> {
        Doc::Union(Box::new(self), Box::new(alternate))
    }

    #[inline]
    /// Mark the docs as a group.
    ///
    /// For a group of docs, when printing,
    /// they will be checked if those docs can be put on a single line.
    /// If they can't, it may insert line breaks according to the
    /// [`line_or_space`](Doc::line_or_space), [`line_or_nil`](Doc::line_or_nil)
    /// or [`soft_line`](Doc::soft_line) calls in the group.
    /// (Also, please read examples of those functions for usage of `group`.)
    ///
    /// Calling this on text won’t take any effects.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let doc = Doc::text("code").group();
    /// assert_eq!("code", &print(&doc, &Default::default()));
    /// ```
    pub fn group(self) -> Doc<'a> {
        match self {
            Doc::List(list) => Doc::Group(list.into()),
            Doc::Slice(slice) => Doc::Group(slice.into()),
            Doc::Group(..) => self,
            doc => Doc::Group(vec![doc].into()),
        }
    }

    #[inline]
    /// Join two docs.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let doc = Doc::text("a").append(Doc::text("b")).append(Doc::text("c"));
    /// assert_eq!("abc", &print(&doc, &Default::default()));
    /// ```
    pub fn append(self, other: Doc<'a>) -> Doc<'a> {
        let mut current = if let Doc::List(docs) = self {
            docs
        } else {
            vec![self]
        };
        match other {
            Doc::List(mut docs) => current.append(&mut docs),
            _ => current.push(other),
        }
        Doc::List(current)
    }

    #[inline]
    /// Concatenate an iterator whose items are docs.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let doc = Doc::text("a").concat(vec![Doc::text("b"), Doc::text("c")].into_iter());
    /// assert_eq!("abc", &print(&doc, &Default::default()));
    /// ```
    pub fn concat(self, iter: impl Iterator<Item = Doc<'a>>) -> Doc<'a> {
        let mut current = if let Doc::List(docs) = self {
            docs
        } else {
            vec![self]
        };
        current.extend(iter);
        Doc::List(current)
    }

    #[inline]
    /// Increase indentation level. Usually this method should be called on group
    /// or line break. Calling this on text won't take any effects.
    ///
    /// ```
    /// use tiny_pretty::{print, Doc};
    ///
    /// let doc = Doc::hard_line().nest(2);
    /// assert_eq!("\n  ", &print(&doc, &Default::default()));
    ///
    /// let doc = Doc::text("code").nest(2);
    /// assert_eq!("code", &print(&doc, &Default::default()));
    /// ```
    pub fn nest(self, size: usize) -> Doc<'a> {
        match self {
            Doc::Break(a, b) => Doc::Break(a, b + size),
            Doc::List(list) => Doc::Nest(size, Nest::Vec(list)),
            Doc::Slice(slice) => Doc::Nest(size, Nest::Slice(slice)),
            doc => Doc::Nest(size, Nest::Box(Box::new(doc))),
        }
    }
}

#[derive(Clone, Debug)]
/// Wrapper type to avoid creating redundant `Box` on `Vec<Doc>` or `&[Doc]`.
pub enum Nest<'a> {
    Vec(Vec<Doc<'a>>),
    Slice(&'a [Doc<'a>]),
    Box(Box<Doc<'a>>),
}
