use aho_corasick::{AhoCorasickBuilder, MatchKind};
use lazy_static::lazy_static;

use crate::gen::codepoints::DIGIT;
use crate::pattern::Replacer;

fn build_double_quoted_replacer() -> Replacer {
    let mut patterns = Vec::<Vec<u8>>::new();
    let mut replacements = Vec::<Vec<u8>>::new();

    // Replace all `"` with `&#34`, unless the quote is followed by a digit or semicolon,
    // in which case add a semicolon to the encoded entity.
    for c in "0123456789;".bytes() {
        patterns.push(vec![b'"', c]);
        replacements.push(vec![b'&', b'#', b'3', b'4', b';', c]);
    };
    patterns.push(b"\"".to_vec());
    replacements.push(b"&#34".to_vec());

    Replacer::new(
        AhoCorasickBuilder::new()
            .dfa(true)
            .match_kind(MatchKind::LeftmostLongest)
            .build(patterns),
        replacements,
    )
}

fn build_single_quoted_replacer() -> Replacer {
    let mut patterns = Vec::<Vec<u8>>::new();
    let mut replacements = Vec::<Vec<u8>>::new();

    // Replace all `'` with `&#39`, unless the quote is followed by a digit or semicolon,
    // in which case add a semicolon to the encoded entity.
    for c in "0123456789;".bytes() {
        patterns.push(vec![b'\'', c]);
        replacements.push(vec![b'&', b'#', b'3', b'9', b';', c]);
    };
    patterns.push(b"'".to_vec());
    replacements.push(b"&#39".to_vec());

    Replacer::new(
        AhoCorasickBuilder::new()
            .dfa(true)
            .match_kind(MatchKind::LeftmostLongest)
            .build(patterns),
        replacements,
    )
}

static WS: &[(u8, &[u8])] = &[
    (b'\x09', b"&#9"),
    (b'\x0a', b"&#10"),
    (b'\x0c', b"&#12"),
    (b'\x0d', b"&#13"),
    (b'\x20', b"&#32"),
];

fn build_unquoted_replacer() -> Replacer {
    let mut patterns = Vec::<Vec<u8>>::new();
    let mut replacements = Vec::<Vec<u8>>::new();

    // Replace all whitespace with a numeric entity, unless the whitespace is followed by a digit or semicolon,
    // in which case add a semicolon to the encoded entity.
    for c in "0123456789;".bytes() {
        for &(ws, rep) in WS {
            patterns.push(vec![ws, c]);
            replacements.push({
                let mut ent = rep.to_vec();
                ent.push(b';');
                ent.push(c);
                ent
            });
        };
    };
    for &(ws, rep) in WS {
        patterns.push(vec![ws]);
        replacements.push(rep.to_vec());
    };

    // Replace all `>` with `&GT`, unless the chevron is followed by a semicolon,
    // in which case add a semicolon to the encoded entity.
    // Use `&GT` instead of `&gt` as `&gt` has more conflicting entities e.g. `&gtcc;`, `&gtdot;`.
    patterns.push(b">;".to_vec());
    replacements.push(b"&GT;;".to_vec());
    patterns.push(b">".to_vec());
    replacements.push(b"&GT".to_vec());

    Replacer::new(
        AhoCorasickBuilder::new()
            .dfa(true)
            .match_kind(MatchKind::LeftmostLongest)
            .build(patterns),
        replacements,
    )
}

lazy_static! {
    static ref DOUBLE_QUOTED_REPLACER: Replacer = build_double_quoted_replacer();
    static ref SINGLE_QUOTED_REPLACER: Replacer = build_single_quoted_replacer();
    static ref UNQUOTED_QUOTED_REPLACER: Replacer = build_unquoted_replacer();
}

struct MinifiedVal {
    prefix: &'static [u8],
    data: Vec<u8>,
    start: usize,
    suffix: &'static [u8],
}

impl MinifiedVal {
    pub fn len(&self) -> usize {
        self.prefix.len() + (self.data.len() - self.start) + self.suffix.len()
    }

    pub fn res(&self) -> Vec<u8> {
        let mut res = Vec::<u8>::with_capacity(self.len());
        res.extend_from_slice(self.prefix);
        res.extend_from_slice(&self.data[self.start..]);
        res.extend_from_slice(self.suffix);
        res
    }
}

pub fn minify_attr_val(val: &[u8]) -> Vec<u8> {
    let double_quoted = MinifiedVal {
        prefix: b"\"",
        data: DOUBLE_QUOTED_REPLACER.replace_all(val),
        start: 0,
        suffix: b"\"",
    };
    let single_quoted = MinifiedVal {
        prefix: b"'",
        data: SINGLE_QUOTED_REPLACER.replace_all(val),
        start: 0,
        suffix: b"'",
    };
    let unquoted = {
        let mut res = UNQUOTED_QUOTED_REPLACER.replace_all(val);
        let first_char_encoded: &'static [u8] = match res.get(0) {
            Some(b'"') => match res.get(1) {
                Some(&s) if DIGIT[s] || s == b';' => b"&#34;",
                _ => b"&#34",
            },
            Some(b'\'') => match res.get(1) {
                Some(&s) if DIGIT[s] || s == b';' => b"&#39;",
                _ => b"&#39",
            },
            _ => b"",
        };
        let start = if !first_char_encoded.is_empty() {
            1
        } else {
            0
        };
        MinifiedVal {
            prefix: b"",
            data: res,
            start,
            suffix: b"",
        }
    };

    // When lengths are equal, prefer double quotes to all and single quotes to unquoted.
    let mut min = double_quoted;
    if single_quoted.len() < min.len() {
        min = single_quoted;
    };
    if unquoted.len() < min.len() {
        min = unquoted;
    };
    min.res()
}