use regex::bytes::Regex;

use std::collections::HashMap;

use std::fs::File;

use std::io::Read;

use std::vec::Vec;

lazy_static! {

    static ref RE_ESCAPE: Vec<Vec<u8>> = {

        let mut v: Vec<Vec<u8>> = (0..=255).map(|byte| vec![byte]).collect();

        let to_escape = b"()[]{}?*+-|^$\\.&~# \t\n\r\x0b\x0c";

        for byte in to_escape {

            v[*byte as usize].insert(0, b'\\');

        }

        v

    };

}

/// These are matched in order

const GLOB_REPLACEMENTS: &[(&[u8], &[u8])] =

    &[(b"*/", b"(?:.*/)?"), (b"*", b".*"), (b"", b"[^/]*")];

#[derive(Debug, Copy, Clone, PartialEq, Eq)]

pub enum PatternSyntax {

    Regexp,

    /// Glob that matches at the front of the path

    RootGlob,

    /// Glob that matches at any suffix of the path (still anchored at slashes)

    Glob,

    Path,

    RelPath,

    RelGlob,

    RelRegexp,

    RootFiles,

}

/// Transforms a glob pattern into a regex

fn glob_to_re(pat: &[u8]) -> Vec<u8> {

    let mut input = pat;

    let mut res: Vec<u8> = vec![];

    let mut group_depth = 0;

    while let Some((c, rest)) = input.split_first() {

        input = rest;

        match c {

            b'*' => {

                for (source, repl) in GLOB_REPLACEMENTS {

                    if input.starts_with(source) {

                        input = &input[source.len()..];

                        res.extend(*repl);

                        break;

                    }

                }

            }

            b'?' => res.extend(b"."),

            b'[' => {

                match input.iter().skip(1).position(|b| *b == b']') {

                    None => res.extend(b"\\["),

                    Some(end) => {

                        // Account for the one we skipped

                        let end = end + 1;

                        res.extend(b"[");

                        for (i, b) in input[..end].iter().enumerate() {

                            if *b == b'!' && i == 0 {

                                res.extend(b"^")

                            } else if *b == b'^' && i == 0 {

                                res.extend(b"\\^")

                            } else if *b == b'\\' {

                                res.extend(b"\\\\")

                            } else {

                                res.push(*b)

                            }

                        }

                        res.extend(b"]");

                        input = &input[end + 1..];

                    }

                }

            }

            b'{' => {

                group_depth += 1;

                res.extend(b"(?:")

            }

            b'}' if group_depth > 0 => {

                group_depth -= 1;

                res.extend(b")");

            }

            b',' if group_depth > 0 => res.extend(b"|"),

            b'\\' => {

                let c = {

                    if let Some((c, rest)) = input.split_first() {

                        input = rest;

                        c

                    } else {

                        c

                    }

                };

                res.extend(&RE_ESCAPE[*c as usize])

            }

            _ => res.extend(&RE_ESCAPE[*c as usize]),

        }

    }

    res

}

fn escape_pattern(pattern: &[u8]) -> Vec<u8> {

    pattern

        .iter()

        .flat_map(|c| RE_ESCAPE[*c as usize].clone())

        .collect()

}

fn parse_pattern_syntax(kind: &[u8]) -> Result<PatternSyntax, PatternError> {

    match kind {

        b"re" => Ok(PatternSyntax::Regexp),

        b"path" => Ok(PatternSyntax::Path),

        b"relpath" => Ok(PatternSyntax::RelPath),

        b"rootfilesin" => Ok(PatternSyntax::RootFiles),

        b"relglob" => Ok(PatternSyntax::RelGlob),

        b"relre" => Ok(PatternSyntax::RelRegexp),

        b"glob" => Ok(PatternSyntax::Glob),

        b"rootglob" => Ok(PatternSyntax::RootGlob),

        _ => Err(PatternError::UnsupportedSyntax(

            String::from_utf8_lossy(kind).to_string(),

        )),

    }

}

/// Builds the regex that corresponds to the given pattern.

/// If within a `syntax: regexp` context, returns the pattern,

/// otherwise, returns the corresponding regex.

fn _build_single_regex(

    syntax: PatternSyntax,

    pattern: &[u8],

    globsuffix: &[u8],

) -> Vec<u8> {

    if pattern.is_empty() {

        return vec![];

    }

    match syntax {

        PatternSyntax::Regexp => pattern.to_owned(),

        PatternSyntax::RelRegexp => {

            if pattern[0] == b'^' {

                return pattern.to_owned();

            }

            let mut res = b".*".to_vec();

            res.extend(pattern);

            res

        }

        PatternSyntax::Path | PatternSyntax::RelPath => {

            if pattern == b"." {

                return vec![];

            }

            let mut pattern = escape_pattern(pattern);

            pattern.extend(b"(?:/|$)");

            pattern

        }

        PatternSyntax::RootFiles => {

            let mut res = if pattern == b"." {

                vec![]

            } else {

                // Pattern is a directory name.

                let mut as_vec: Vec<u8> = escape_pattern(pattern);

                as_vec.push(b'/');

                as_vec

            };

            // Anything after the pattern must be a non-directory.

            res.extend(b"[^/]+$");

            res

        }

        PatternSyntax::Glob

        | PatternSyntax::RelGlob

        | PatternSyntax::RootGlob => {

            let mut res: Vec<u8> = vec![];

            if syntax == PatternSyntax::RelGlob {

                res.extend(b"(?:|.*/)");

            }

            res.extend(glob_to_re(pattern));

            res.extend(globsuffix.iter());

            res

        }

    }

}

const GLOB_SPECIAL_CHARACTERS: [u8; 7] =

    [b'*', b'?', b'[', b']', b'{', b'}', b'\\'];

/// Wrapper function to `_build_single_regex` that short-circuits 'exact' globs

/// that don't need to be transformed into a regex.

pub fn build_single_regex(

    kind: &[u8],

    pat: &[u8],

    globsuffix: &[u8],

) -> Result<Vec<u8>, PatternError> {

    let enum_kind = parse_pattern_syntax(kind)?;

    if enum_kind == PatternSyntax::RootGlob

        && !pat.iter().any(|b| GLOB_SPECIAL_CHARACTERS.contains(b))

    {

        let mut escaped = escape_pattern(pat);

        escaped.extend(b"(?:/|$)");

        Ok(escaped)

    } else {

        Ok(_build_single_regex(enum_kind, pat, globsuffix))

    }

}

lazy_static! {

    static ref SYNTAXES: HashMap<&'static [u8], &'static [u8]> = {

        let mut m = HashMap::new();

        m.insert(b"re".as_ref(), b"relre:".as_ref());

        m.insert(b"regexp".as_ref(), b"relre:".as_ref());

        m.insert(b"glob".as_ref(), b"relglob:".as_ref());

        m.insert(b"rootglob".as_ref(), b"rootglob:".as_ref());

        m.insert(b"include".as_ref(), b"include".as_ref());

        m.insert(b"subinclude".as_ref(), b"subinclude".as_ref());

        m

    };

}

pub type PatternTuple = (Vec<u8>, LineNumber, Vec<u8>);

type WarningTuple = (String, String);

pub fn parse_pattern_file_contents(

    lines: &[u8],

    file_path: &[u8],

    warn: bool,

) -> (Vec<PatternTuple>, Vec<WarningTuple>) {

    let comment_regex = Regex::new(r"((?:^|[^\\])(?:\\\\)*)#.*").unwrap();

    let mut inputs: Vec<PatternTuple> = vec![];

    let mut warnings: Vec<WarningTuple> = vec![];

    let mut current_syntax = b"relre:".as_ref();

    for (line_number, mut line) in lines.split(|c| *c == b'\n').enumerate() {

        let line_number = line_number + 1;

        if line.contains(&('#' as u8)) {

            if let Some(cap) = comment_regex.captures(line) {

                line = &line[..cap.get(1).unwrap().end()]

            }

            let mut line = line.to_owned();

            replace_slice(&mut line, br"\#", b"#");

        }

        let mut line = line.trim_end();

        if line.is_empty() {

            continue;

        }

        if line.starts_with(b"syntax:") {

            let syntax = line[b"syntax:".len()..].trim();

            if let Some(rel_syntax) = SYNTAXES.get(syntax) {

                current_syntax = rel_syntax;

            } else if warn {

                warnings.push((

                    String::from_utf8_lossy(file_path).to_string(),

                    String::from_utf8_lossy(syntax).to_string(),

                ));

            }

            continue;

        }

        let mut line_syntax: &[u8] = &current_syntax;

        for (s, rels) in SYNTAXES.iter() {

            if line.starts_with(rels) {

                line_syntax = rels;

                line = &line[rels.len()..];

                break;

            } else if line.starts_with(&[s, b":".as_ref()].concat()) {

                line_syntax = rels;

                line = &line[s.len() + 1..];

                break;

            }

        }

        inputs.push((

            [line_syntax, line].concat(),

            line_number,

            line.to_owned(),

        ));

    }

    (inputs, warnings)

}

pub fn read_pattern_file(

    file_path: &[u8],

    warn: bool,

) -> Result<(Vec<PatternTuple>, Vec<WarningTuple>), PatternFileError> {

    let mut f = File::open(get_path_from_bytes(file_path))?;

    let mut contents = Vec::new();

    f.read_to_end(&mut contents)?;

    Ok(parse_pattern_file_contents(&contents, file_path, warn))

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn escape_pattern_test() {

        let untouched = br#"!"%',/0123456789:;<=>@ABCDEFGHIJKLMNOPQRSTUVWXYZ_`abcdefghijklmnopqrstuvwxyz"#;

        assert_eq!(escape_pattern(untouched), untouched.to_vec());

        // All escape codes

        assert_eq!(

            escape_pattern(br#"()[]{}?*+-|^$\\.&~# \t\n\r\v\f"#),

            br#"\(\)\[\]\{\}\?\*\+\-\|\^\$\\\\\.\&\~\#\ \\t\\n\\r\\v\\f"#

                .to_vec()

        );

    }

    #[test]

    fn glob_test() {

        assert_eq!(glob_to_re(br#"?"#), br#"."#);

        assert_eq!(glob_to_re(br#"*"#), br#"[^/]*"#);

        assert_eq!(glob_to_re(br#"**"#), br#".*"#);

        assert_eq!(glob_to_re(br#"**/a"#), br#"(?:.*/)?a"#);

        assert_eq!(glob_to_re(br#"a/**/b"#), br#"a/(?:.*/)?b"#);

        assert_eq!(glob_to_re(br#"[a*?!^][^b][!c]"#), br#"[a*?!^][\^b][^c]"#);

        assert_eq!(glob_to_re(br#"{a,b}"#), br#"(?:a|b)"#);

        assert_eq!(glob_to_re(br#".\*\?"#), br#"\.\*\?"#);

    }

    #[test]

    fn test_parse_pattern_file_contents() {

        let lines = b"syntax: glob\n*.elc";

        assert_eq!(

            vec![(b"relglob:*.elc".to_vec(), 2, b"*.elc".to_vec())],