/*!
A simple [CSS 2.1](https://www.w3.org/TR/CSS21/) parser and selector.

This is not a browser-grade CSS parser. If you need one,
use [cssparser](https://crates.io/crates/cssparser) +
[selectors](https://crates.io/crates/selectors).

Since it's very simple we will start with limitations:

## Limitations

- [At-rules](https://www.w3.org/TR/CSS21/syndata.html#at-rules) are not supported.
  They will be skipped during parsing.
- Property values are not parsed.
  In CSS like `* { width: 5px }` you will get a `width` property with a `5px` value as a string.
- CDO/CDC comments are not supported.
- Parser is case sensitive. All keywords must be lowercase.
- Unicode escape, like `\26`, is not supported.

## Features

- Selector matching support.
- The rules are sorted by specificity.
- `!import` parsing support.
- Has a high-level parsers and low-level, zero-allocation tokenizers.
- No unsafe.
*/

#![doc(html_root_url = "https://docs.rs/simplecss/0.2.1")]

#![forbid(unsafe_code)]
#![warn(missing_docs)]

use std::fmt;

use log::warn;

mod selector;
mod stream;

pub use selector::*;
use stream::Stream;


/// A list of possible errors.
#[derive(Clone, Copy, PartialEq, Debug)]
pub enum Error {
    /// The steam ended earlier than we expected.
    ///
    /// Should only appear on invalid input data.
    UnexpectedEndOfStream,

    /// An invalid ident.
    InvalidIdent(TextPos),

    /// An unclosed comment.
    InvalidComment(TextPos),

    /// An invalid declaration value.
    InvalidValue(TextPos),

    /// An invalid byte.
    #[allow(missing_docs)]
    InvalidByte { expected: u8, actual: u8, pos: TextPos },

    /// A missing selector.
    SelectorMissing,

    /// An unexpected selector.
    UnexpectedSelector,

    /// An unexpected combinator.
    UnexpectedCombinator,

    /// An invalid or unsupported attribute selector.
    InvalidAttributeSelector,

    /// An invalid language pseudo-class.
    InvalidLanguagePseudoClass,
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            Error::UnexpectedEndOfStream => {
                write!(f, "unexpected end of stream")
            }
            Error::InvalidIdent(pos) => {
                write!(f, "invalid ident at {}", pos)
            }
            Error::InvalidComment(pos) => {
                write!(f, "invalid comment at {}", pos)
            }
            Error::InvalidValue(pos) => {
                write!(f, "invalid value at {}", pos)
            }
            Error::InvalidByte { expected, actual, pos } => {
                write!(f, "expected '{}' not '{}' at {}",
                       expected as char, actual as char, pos)
            }
            Error::SelectorMissing => {
                write!(f, "selector missing")
            }
            Error::UnexpectedSelector => {
                write!(f, "unexpected selector")
            }
            Error::UnexpectedCombinator => {
                write!(f, "unexpected combinator")
            }
            Error::InvalidAttributeSelector => {
                write!(f, "invalid or unsupported attribute selector")
            }
            Error::InvalidLanguagePseudoClass => {
                write!(f, "invalid language pseudo-class")
            }
        }
    }
}

impl std::error::Error for Error {}


/// A position in text.
///
/// Position indicates a row/line and a column in the original text. Starting from 1:1.
#[derive(Clone, Copy, PartialEq, Debug)]
#[allow(missing_docs)]
pub struct TextPos {
    pub row: u32,
    pub col: u32,
}

impl TextPos {
    /// Constructs a new `TextPos`.
    ///
    /// Should not be invoked manually, but rather via `Stream::gen_text_pos`.
    pub fn new(row: u32, col: u32) -> TextPos {
        TextPos { row, col }
    }
}

impl fmt::Display for TextPos {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}:{}", self.row, self.col)
    }
}


/// A declaration.
#[derive(Clone, Copy, PartialEq, Debug)]
#[allow(missing_docs)]
pub struct Declaration<'a> {
    pub name: &'a str,
    pub value: &'a str,
    pub important: bool,
}

/// A rule.
#[derive(Clone, Debug)]
pub struct Rule<'a> {
    /// A rule selector.
    pub selector: Selector<'a>,
    /// A rule declarations.
    pub declarations: Vec<Declaration<'a>>,
}

/// A style sheet.
#[derive(Clone, Debug)]
pub struct StyleSheet<'a> {
    /// A list of rules.
    pub rules: Vec<Rule<'a>>,
}

impl<'a> StyleSheet<'a> {
    /// Creates an empty style sheet.
    pub fn new() -> Self {
        StyleSheet { rules: Vec::new() }
    }

    /// Parses a style sheet from text.
    ///
    /// At-rules are not supported and will be skipped.
    ///
    /// # Errors
    ///
    /// Doesn't produce any errors. In worst case scenario will return an empty stylesheet.
    ///
    /// All warnings will be logged.
    pub fn parse(text: &'a str) -> Self {
        let mut sheet = StyleSheet::new();
        sheet.parse_more(text);
        sheet
    }

    /// Parses a style sheet from a text to the current style sheet.
    pub fn parse_more(&mut self, text: &'a str) {
        let mut s = Stream::from(text);

        if s.skip_spaces_and_comments().is_err() {
            return;
        }

        while !s.at_end() {
            if s.skip_spaces_and_comments().is_err() {
                break;
            }

            let _ = consume_statement(&mut s, &mut self.rules);
        }

        if !s.at_end() {
            warn!("{} bytes were left.", s.slice_tail().len());
        }

        // Remove empty rules.
        self.rules.retain(|rule| !rule.declarations.is_empty());

        // Sort the rules by specificity.
        self.rules.sort_by_cached_key(|rule| rule.selector.specificity());
    }
}

impl fmt::Display for StyleSheet<'_> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        for (i, rule) in self.rules.iter().enumerate() {
            write!(f, "{} {{ ", rule.selector)?;
            for dec in &rule.declarations {
                write!(f, "{}:{}", dec.name, dec.value)?;
                if dec.important {
                    write!(f, " !important")?;
                }
                write!(f, ";")?;
            }
            write!(f, " }}")?;

            if i != self.rules.len() - 1 {
                writeln!(f)?;
            }
        }

        Ok(())
    }
}

fn consume_statement<'a>(s: &mut Stream<'a>, rules: &mut Vec<Rule<'a>>) -> Result<(), Error> {
    if s.curr_byte() == Ok(b'@') {
        s.advance(1);
        consume_at_rule(s)
    } else {
        consume_rule_set(s, rules)
    }
}

fn consume_at_rule(s: &mut Stream) -> Result<(), Error> {
    let ident = s.consume_ident()?;
    warn!("The @{} rule is not supported. Skipped.", ident);

    s.skip_bytes(|c| c != b';' && c != b'{');

    match s.curr_byte()? {
        b';' => s.advance(1),
        b'{' => consume_block(s),
        _ => {}
    }

    Ok(())
}

fn consume_rule_set<'a>(s: &mut Stream<'a>, rules: &mut Vec<Rule<'a>>) -> Result<(), Error> {
    let start_rule_idx = rules.len();

    while s.curr_byte()? == b',' || start_rule_idx == rules.len() {
        if s.curr_byte()? == b',' {
            s.advance(1);
        }

        let (selector, offset) = crate::selector::parse(s.slice_tail());
        s.advance(offset);
        s.skip_spaces();

        if let Some(selector) = selector {
            rules.push(Rule { selector, declarations: Vec::new() });
        }

        match s.curr_byte()? {
            b'{' => break,
            b',' => {}
            _ => {
                s.skip_bytes(|c| c != b'{');
                break;
            }
        }
    }

    s.try_consume_byte(b'{');

    let declarations = consume_declarations(s)?;
    for i in start_rule_idx..rules.len() {
        rules[i].declarations = declarations.clone();
    }

    s.try_consume_byte(b'}');

    Ok(())
}

fn consume_block(s: &mut Stream) {
    s.try_consume_byte(b'{');
    consume_until_block_end(s);
}

fn consume_until_block_end(s: &mut Stream) {
    // Block can have nested blocks, so we have to check for matching braces.
    // We simply counting the number of opening braces, which is incorrect,
    // since `{` can be inside a string, but it's fine for majority of the cases.

    let mut braces = 0;
    while !s.at_end() {
        match s.curr_byte_unchecked() {
            b'{' => {
                braces += 1;
            }
            b'}' => {
                if braces == 0 {
                    break;
                } else {
                    braces -= 1;
                }
            }
            _ => {}
        }

        s.advance(1);
    }

    s.try_consume_byte(b'}');
}

fn consume_declarations<'a>(s: &mut Stream<'a>) -> Result<Vec<Declaration<'a>>, Error> {
    let mut declarations = Vec::new();

    while !s.at_end() && s.curr_byte() != Ok(b'}') {
        match consume_declaration(s) {
            Ok(declaration) => declarations.push(declaration),
            Err(_) => {
                consume_until_block_end(s);
                break;
            }
        }
    }

    Ok(declarations)
}


/// A declaration tokenizer.
///
/// Tokenizer will stop at the first invalid token.
///
/// # Example
///
/// ```
/// use simplecss::{DeclarationTokenizer, Declaration};
///
/// let mut t = DeclarationTokenizer::from("background: url(\"img.png\"); color:red !important");
/// assert_eq!(t.next().unwrap(), Declaration { name: "background", value: "url(\"img.png\")", important: false });
/// assert_eq!(t.next().unwrap(), Declaration { name: "color", value: "red", important: true });
/// ```
pub struct DeclarationTokenizer<'a> {
    stream: Stream<'a>,
}

impl<'a> From<&'a str> for DeclarationTokenizer<'a> {
    fn from(text: &'a str) -> Self {
        DeclarationTokenizer {
            stream: Stream::from(text),
        }
    }
}

impl<'a> Iterator for DeclarationTokenizer<'a> {
    type Item = Declaration<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        let _ = self.stream.skip_spaces_and_comments();

        if self.stream.at_end() {
            return None;
        }

        match consume_declaration(&mut self.stream) {
            Ok(v) => Some(v),
            Err(_) => {
                self.stream.jump_to_end();
                None
            }
        }
    }
}

fn consume_declaration<'a>(s: &mut Stream<'a>) -> Result<Declaration<'a>, Error> {
    s.skip_spaces_and_comments()?;

    // Parse name.

    // https://snook.ca/archives/html_and_css/targetting_ie7
    if s.curr_byte() == Ok(b'*') {
        s.advance(1);
    }

    let name = s.consume_ident()?;

    s.skip_spaces_and_comments()?;
    s.consume_byte(b':')?;
    s.skip_spaces_and_comments()?;

    // Parse value.
    let start = s.pos();
    let mut end = s.pos();
    while consume_term(s).is_ok() {
        end = s.pos();
        s.skip_spaces_and_comments()?;
    }
    let value = s.slice_range(start, end).trim();

    s.skip_spaces_and_comments()?;

    // Check for `important`.
    let mut important = false;
    if s.curr_byte() == Ok(b'!') {
        s.advance(1);
        s.skip_spaces_and_comments()?;
        if s.slice_tail().starts_with("important") {
            s.advance(9);
            important = true;
        }
    }

    s.skip_spaces_and_comments()?;

    while s.curr_byte() == Ok(b';') {
        s.advance(1);
        s.skip_spaces_and_comments()?;
    }

    s.skip_spaces_and_comments()?;

    if value.is_empty() {
        return Err(Error::InvalidValue(s.gen_text_pos_from(start)));
    }

    Ok(Declaration { name, value, important })
}

fn consume_term(s: &mut Stream) -> Result<(), Error> {
    fn consume_digits(s: &mut Stream) {
        while let Ok(c) = s.curr_byte() {
            match c {
                b'0'..=b'9' => s.advance(1),
                _ => break,
            }
        }
    }

    match s.curr_byte()? {
        b'#' => {
            s.advance(1);
            match s.consume_ident() {
                Ok(_) => {}
                Err(_) => {
                    // Try consume as a hex color.
                    while let Ok(c) = s.curr_byte() {
                        match c {
                            b'0'..=b'9' | b'a'..=b'f' | b'A'..=b'F' => s.advance(1),
                            _ => break,
                        }
                    }
                }
            }
        }
        b'+' | b'-' | b'0'..=b'9' | b'.' => {
            // Consume number.

            s.advance(1);
            consume_digits(s);
            if s.curr_byte() == Ok(b'.') {
                s.advance(1);
                consume_digits(s);
            }

            if s.curr_byte() == Ok(b'%') {
                s.advance(1);
            } else {
                // Consume suffix if any.
                let _ = s.consume_ident();
            }
        }
        b'\'' | b'"' => {
            s.consume_string()?;
        }
        b',' => {
            s.advance(1);
        }
        _ => {
            let _ = s.consume_ident()?;

            // Consume function.
            if s.curr_byte() == Ok(b'(') {
                s.skip_bytes(|c| c != b')');
                s.consume_byte(b')')?;
            }
        }
    }

    Ok(())
}