use std::collections::HashMap;
use std::iter::IntoIterator;
use std::str::FromStr;

use aho_corasick::{AhoCorasick, AhoCorasickBuilder, MatchKind};
use once_cell::unsync::Lazy;
use regex::Regex;

use crate::{
    pagerules::PageRules,
    rule::{Conv, ConvAction, ConvRule},
    variant::Variant,
};

// Ref: https://github.com/wikimedia/mediawiki/blob/7bf779524ab1fd8e1d74f79ea4840564d48eea4d/includes/language/LanguageConverter.php#L76
const NESTED_RULE_MAX_DEPTH: usize = 10;

/// A ZhConverter. See also [`ZhConverterBuilder`].
pub struct ZhConverter {
    variant: Variant,
    automaton: AhoCorasick,
    mapping: HashMap<String, String>,
}

impl ZhConverter {
    /// Create a new converter from a automaton and a mapping.
    ///
    /// It is provided for convenience and not expected to be called directly.
    /// [`ZhConverterBuilder`] would take care of these
    /// details.
    pub fn new(automaton: AhoCorasick, mapping: HashMap<String, String>) -> ZhConverter {
        ZhConverter {
            variant: Variant::Zh,
            automaton,
            mapping,
        }
    }

    /// Create a new converter of a sequence of `(from, to)` pairs.
    ///
    /// It use [`ZhConverterBuilder`] internally.
    #[inline(always)]
    pub fn from_pairs(pairs: &[(impl AsRef<str>, impl AsRef<str>)]) -> ZhConverter {
        let mut builder = ZhConverterBuilder::new();
        for (from, to) in pairs {
            builder = builder.add_conv_pair(from, to);
        }
        builder.build()
    }

    /// Convert a text.
    pub fn convert(&self, text: &str) -> String {
        let mut output = String::with_capacity(text.len());
        self.converted(text, &mut output);
        output
    }

    /// Same as `convert`, except that it takes a `&mut String` as dest instead of returning a `String`.
    pub fn converted(&self, text: &str, output: &mut String) {
        // Ref: https://github.dev/rust-lang/regex/blob/5197f21287344d2994f9cf06758a3ea30f5a26c3/src/re_trait.rs#L192
        let mut last = 0;
        // let mut cnt = HashMap::<usize, usize>::new();
        // leftmost-longest matching
        for (s, e) in self.automaton.find_iter(text).map(|m| (m.start(), m.end())) {
            if s > last {
                output.push_str(&text[last..s]);
            }
            // *cnt.entry(text[s..e].chars().count()).or_insert(0) += 1;
            output.push_str(self.mapping.get(&text[s..e]).unwrap());
            last = e;
        }
        output.push_str(&text[last..]);
    }

    /// Convert a text with inline conv rules applied.
    ///
    /// It only processes the display output of inline rules. Mutations to global rules specified
    /// via inline rules are just ignored. To activate global rules, build a [`ZhConverterBuilder`]
    /// with [`PageRules`](crate::pagerules::PageRules).
    ///
    /// The internal implementation are intendedly replicating the behavior of
    /// [LanguageConverter.php](https://github.com/wikimedia/mediawiki/blob/7bf779524ab1fd8e1d74f79ea4840564d48eea4d/includes/language/LanguageConverter.php#L855)
    /// in MediaWiki. But it is not fully compliant with MediaWiki and providing NO PROTECTION over
    /// XSS attack.
    ///
    /// Compared to the plain `convert`, this is known to be much slower due to the inevitable
    /// nature of the implementation decision made by MediaWiki.
    pub fn convert_allowing_inline_rules(&self, text: &str) -> String {
        // Ref: https://github.com/wikimedia/mediawiki/blob/7bf779524ab1fd8e1d74f79ea4840564d48eea4d/includes/language/LanguageConverter.php#L855
        //  and https://github.com/wikimedia/mediawiki/blob/7bf779524ab1fd8e1d74f79ea4840564d48eea4d/includes/language/LanguageConverter.php#L910
        //  and https://github.com/wikimedia/mediawiki/blob/7bf779524ab1fd8e1d74f79ea4840564d48eea4d/includes/language/LanguageConverter.php#L532
        // TODO: this may degrade to O(n^2)
        let p1 = Lazy::new(|| {
            // start of rule | noHtml | noStyle | no code | no pre
            Regex::new(r#"-\{|<script.*?>.*?</script>|<style.*?>.*?</style>|<code>.*?</code>|<pre.*?>.*?</pre>"#).unwrap()
        });
        // TODO: we need to understand what the hell it is so that to adapt it to compatible syntax
        // 		$noHtml = '<(?:[^>=]*+(?>[^>=]*+=\s*+(?:"[^"]*"|\'[^\']*\'|[^\'">\s]*+))*+[^>=]*+>|.*+)(*SKIP)(*FAIL)';
        let p2 = Lazy::new(|| Regex::new(r#"-\{|\}-"#).unwrap());
        let mut pos = 0;
        let mut converted = String::with_capacity(text.len());
        let mut pieces = vec![];
        while let Some(m1) = p1.find_at(text, pos) {
            // convert anything before (possible) the toplevel -{
            self.converted(&text[pos..m1.start()], &mut converted);
            if m1.as_str() != "-{" {
                // not start of rule, just <foobar></foobar> to exclude
                converted.push_str(&text[m1.start()..m1.end()]); // kept as-is
                pos = m1.end();
                continue; // i.e. <SKIP><FAIL>
            }
            // found toplevel -{
            pos = m1.start() + 2;
            pieces.push(String::new());
            while let Some(m2) = p2.find_at(text, pos) {
                // let mut piece = String::from(&text[pos..m2.start()]);
                if m2.as_str() == "-{" {
                    // if there are two many open start tag, ignore the new nested rule
                    if pieces.len() >= NESTED_RULE_MAX_DEPTH {
                        pos += 2;
                        continue;
                    }
                    // start tag
                    pieces.last_mut().unwrap().push_str(&text[pos..m2.start()]);
                    pieces.push(String::new()); // e.g. -{ zh: AAA -{
                    pos = m2.end();
                } else {
                    // end tag
                    let mut piece = pieces.pop().unwrap();
                    piece.push_str(&text[pos..m2.start()]);
                    let upper = if let Some(upper) = pieces.last_mut() {
                        upper
                    } else {
                        &mut converted
                    };
                    // only take it output; mutations to global rules are ignored
                    ConvRule::from_str_infallible(&piece)
                        .write_output(upper, self.variant)
                        .unwrap();
                    // if let Ok(rule) = dbg!(ConvRule::from_str(&piece)) {
                    //     rule.write_output(upper, self.variant).unwrap();
                    // } else {
                    //     // rule is invalid
                    //     // TODO: what should we do actually? for now, we just do nothing to it
                    //     upper.push_str(&piece);
                    // }
                    pos = m2.end();
                    if pieces.is_empty() {
                        // return to toplevel
                        break;
                    }
                }
            }
            while let Some(piece) = pieces.pop() {
                converted.push_str("-{");
                converted.push_str(&piece);
            }
            // TODO: produce convert(&text[pos..])
        }
        if pos < text.len() {
            // no more conv rules, just convert and append
            converted.push_str(&self.convert(&text[pos..]));
        }
        converted
    }

    // TODO: inplace? we need to maintain a stack which could be at most O(n)
    //       and it requires access to underlying bytes for subtle mutations
    // pub fn convert_inplace(&self, text: &mut String) {
    //     let tbp = VecDeque::<&str>::new(); // to be pushed
    //     let mut wi = 0; // writing index
    //     let mut ri = 0; // reading index
    //     while let Some((s, e)) = self.regex.find_at(text, ri).map(|m| (m.start(), m.end())) {
    //         while !tbp.is_empty() && s - wi >= tbp[0].len() {
    //             let raw = unsafe { text.as_bytes_mut() };
    //             raw[wi..wi + tbp[0].len()].clone_from_slice(tbp[0].as_bytes());
    //             tbp.pop_front();
    //         }
    //     }
    // }
}

/// A builder that helps build a `ZhConverter`.
///
/// # Example
/// Build a Zh2CN converter with some additional rules.
/// ```
/// use zhconv::{zhconv, ZhConverterBuilder, Variant, tables::ZH_HANS_CN_TABLE};
/// // extracted from https://zh.wikipedia.org/wiki/Template:CGroup/Template:CGroup/文學.
/// let conv_lines = r"zh-hans:三个火枪手;zh-hant:三劍客;zh-tw:三劍客;
///                    zh-cn:雾都孤儿;zh-tw:孤雛淚;zh-hk:苦海孤雛;zh-sg:雾都孤儿;zh-mo:苦海孤雛;";
/// let converter = ZhConverterBuilder::new()
///                     .target(Variant::ZhCN)
///                     .table(*ZH_HANS_CN_TABLE)
///                     .dfa(true) // dfa enabled: slower build, faster conversion
///                     .conv_lines(conv_lines)
///                     .build();
/// let original = "《三劍客》是亞歷山大·仲馬的作品。《孤雛淚》是查爾斯·狄更斯的作品。";
/// assert_eq!(converter.convert(original), "《三个火枪手》是亚历山大·仲马的作品。《雾都孤儿》是查尔斯·狄更斯的作品。");
/// assert_eq!(zhconv(original, Variant::ZhCN), "《三剑客》是亚历山大·仲马的作品。《孤雏泪》是查尔斯·狄更斯的作品。")
#[derive(Debug, Clone, Default)]
pub struct ZhConverterBuilder<'t> {
    target: Variant,
    /// The base conversion table
    tables: Vec<(&'t str, &'t str)>,
    /// Rules to be added, from page rules or cgroups
    adds: HashMap<String, String>,
    /// Rules to be removed, from page rules or cgroups
    removes: HashMap<String, String>, // TODO: unnecessary owned type
    dfa: bool,
}

impl<'t> ZhConverterBuilder<'t> {
    pub fn new() -> Self {
        Default::default()
    }

    /// Set the target Chinese variant to convert to.
    ///
    /// The target variant is only useful to get proper conv pairs from
    /// [`ConvRule`](crate::rule::ConvRule)s. That is, if only tables are specified, the target
    /// variant would be useless.
    pub fn target(mut self, variant: Variant) -> Self {
        self.target = variant;
        self
    }

    /// Add a conversion table, which is typically those in [`tables`](crate::tables).
    pub fn table(mut self, table: (&'t str, &'t str)) -> Self {
        self.tables.push(table);
        self
    }

    //  [CGroup](https://zh.wikipedia.org/wiki/Module:CGroup) (a.k.a 公共轉換組)

    /// Add a set of rules extracted from a page.
    ///
    /// This is a helper wrapper around `page_rules`.
    #[inline(always)]
    pub fn rules_from_page(self, text: &str) -> Self {
        self.page_rules(
            &PageRules::from_str(text).expect("Page rules parsing is infallible for now"),
        )
    }

    /// Add a set of rules from `PageRules`.
    #[inline(always)]
    pub fn page_rules(self, page_rules: &PageRules) -> Self {
        self.conv_actions(page_rules.as_conv_actions())
    }

    /// Add a set of rules.
    ///
    /// These rules take the higher precedence over those specified via `table`.
    fn conv_actions<'i>(mut self, conv_actions: impl IntoIterator<Item = &'i ConvAction>) -> Self {
        for conv_action in conv_actions {
            let pairs = conv_action.as_conv().get_conv_pairs(self.target);
            if conv_action.adds() {
                self.adds
                    .extend(pairs.iter().map(|&(f, t)| (f.to_owned(), t.to_owned())));
            } else {
                self.removes
                    .extend(pairs.iter().map(|&(f, t)| (f.to_owned(), t.to_owned())));
            }
        }
        self
    }

    /// Add a [`Conv`].
    ///
    /// For general cases, check [`add_conv_pair`](#method.add_conv_pair) which takes a plain
    /// `from -> to` pair.
    pub fn add_conv(mut self, conv: Conv) -> Self {
        let pairs = conv.get_conv_pairs(self.target);
        self.adds
            .extend(pairs.iter().map(|&(f, t)| (f.to_owned(), t.to_owned())));
        self
    }

    /// Mark a conv as removed.
    pub fn remove_conv(mut self, conv: Conv) -> Self {
        let pairs = conv.get_conv_pairs(self.target);
        self.removes
            .extend(pairs.iter().map(|&(f, t)| (f.to_owned(), t.to_owned())));
        self
    }

    /// Add a single `from -> to` conversion pair.
    ///
    /// It takes the precedence over those specified via `table`. It shares the same precedence level with those specified via `cgroup`.
    pub fn add_conv_pair(mut self, from: impl AsRef<str>, to: impl AsRef<str>) -> Self {
        let (from, to): (&str, &str) = (from.as_ref(), to.as_ref());
        if from.is_empty() {
            panic!("Conv pair should have non-empty from.")
        }
        self.adds.insert(from.to_owned(), to.to_owned());
        self
    }

    /// Mark a single conversion pair as removed.
    ///
    /// Any rule with the same `from`, whether specified via `add_conv_pair`, `conv_lines` or `table`, is removed.
    pub fn remove_conv_pair(mut self, from: impl AsRef<str>, to: impl AsRef<str>) -> Self {
        self.removes
            .insert(from.as_ref().to_owned(), to.as_ref().to_owned());
        self
    }

    /// Add a text of conv lines.
    ///
    /// e.g.
    /// ```text
    /// zh-cn:天堂执法者; zh-hk:夏威夷探案; zh-tw:檀島警騎2.0;
    /// zh-cn:史蒂芬·'史蒂夫'·麦格瑞特; zh-tw:史提夫·麥加雷; zh-hk:麥星帆;
    /// zh-cn:丹尼尔·'丹尼/丹诺'·威廉姆斯; zh-tw:丹尼·威廉斯; zh-hk:韋丹尼;
    /// ```
    pub fn conv_lines(mut self, lines: &str) -> Self {
        for line in lines.lines().map(str::trim).filter(|s| !s.is_empty()) {
            if let Ok(conv) = Conv::from_str(line.trim()) {
                self.adds
                    .extend(conv.get_conv_pairs(self.target).iter().map(|&(f, t)| {
                        if f.is_empty() {
                            panic!("Conv pair should have non-empty from.")
                        }
                        (f.to_owned(), t.to_owned())
                    }));
            }
        }
        self
    }

    /// Set whether to activate the feature DFA of Aho-Corasick.
    ///
    /// With DFA enabled, it takes rougly 5x time to build the converter while the conversion
    /// speed is < 2x faster. All built-in converters have this feature enabled for better
    /// conversion performance.
    pub fn dfa(mut self, enabled: bool) -> Self {
        self.dfa = enabled;
        self
    }

    /// Do the build.
    ///
    /// It internally aggregate previously specified tables, rules and pairs, from where an
    /// automaton and a mapping are built, which are then feed into the new converter.
    pub fn build(&self) -> ZhConverter {
        let Self {
            target,
            tables,
            dfa,
            adds,
            removes,
        } = self;
        let mut mapping = HashMap::with_capacity(
            (tables.iter().map(|(fs, _ts)| fs.len()).sum::<usize>() + adds.len())
                .saturating_sub(removes.len()),
        );
        mapping.extend(
            tables
                .iter()
                .flat_map(|(froms, tos)| {
                    itertools::zip(froms.trim().split('|'), tos.trim().split('|'))
                })
                .filter(|&(from, to)| !(from.is_empty() && to.is_empty())) // empty str will trouble AC
                .filter(|&(from, _to)| !removes.contains_key(from))
                .map(|(from, to)| (from.to_owned(), to.to_owned())),
        );
        mapping.extend(
            adds.iter()
                .filter(|(from, _to)| !removes.contains_key(from.as_str()))
                .map(|(from, to)| (from.to_owned(), to.to_owned())),
        );
        let sequence = mapping.keys();
        let automaton = AhoCorasickBuilder::new()
            .match_kind(MatchKind::LeftmostLongest)
            .dfa(*dfa)
            .build(sequence);
        ZhConverter {
            variant: *target,
            mapping,
            automaton,
        }
    }
}