#![allow(non_snake_case)]

use std::ffi::{CStr, CString};
use std::fmt;
use std::ptr;

use libc::{c_char, c_int, c_void};
use libpcre_sys::{
    pcre, pcre_compile, pcre_exec, pcre_extra, pcre_free, pcre_free_study,
    pcre_study, PCRE_ERROR_NOMATCH, PCRE_NO_UTF8_CHECK, PCRE_UTF8,
};

const PCRE_UCP: c_int = 0x20000000;
const PCRE_STUDY_JIT_COMPLETE: c_int = 0x0001;

// We use libpcre-sys directly because the pcre crate has unavoidable
// performance problems in its core matching routines. (e.g., It always
// allocates an ovector.)
pub struct Regex {
    code: *mut pcre,
    extra: *mut pcre_extra,
}

unsafe impl Send for Regex {}

impl Drop for Regex {
    fn drop(&mut self) {
        unsafe {
            pcre_free_study(self.extra);
            pcre_free(self.code as *mut c_void);
        }
    }
}

pub struct Error {
    msg: String,
    offset: c_int,
}

impl Regex {
    pub fn new(pattern: &str) -> Result<Regex, Error> {
        let pattern = CString::new(pattern.to_owned()).unwrap();
        let mut errptr: *const c_char = ptr::null();
        let mut erroffset: c_int = 0;
        let code = unsafe {
            pcre_compile(
                pattern.as_ptr(),
                PCRE_UCP | PCRE_UTF8,
                &mut errptr,
                &mut erroffset,
                ptr::null(),
            )
        };
        if code.is_null() {
            let msg =
                unsafe { CStr::from_ptr(errptr).to_str().unwrap().to_owned() };
            return Err(Error { msg: msg, offset: erroffset });
        }

        let extra =
            unsafe { pcre_study(code, PCRE_STUDY_JIT_COMPLETE, &mut errptr) };
        if extra.is_null() {
            if errptr.is_null() {
                panic!("unexpected error. Maybe JIT support isn't enabled?");
            }
            let msg =
                unsafe { CStr::from_ptr(errptr).to_str().unwrap().to_owned() };
            return Err(Error { msg: msg, offset: 0 });
        }
        Ok(Regex { code: code, extra: extra })
    }

    pub fn is_match(&self, text: &str) -> bool {
        self.find_at(text, 0).is_some()
    }

    pub fn find_iter<'r, 't>(&'r self, text: &'t str) -> FindMatches<'r, 't> {
        FindMatches { re: self, text: text, last_match_end: 0 }
    }

    fn find_at(&self, text: &str, start: usize) -> Option<(usize, usize)> {
        const OVEC_SIZE: usize = 15 * 3; // hopefully enough for benchmarks?
        let mut ovec: [c_int; OVEC_SIZE] = [0; OVEC_SIZE];
        let err = unsafe {
            pcre_exec(
                self.code,
                self.extra,
                text.as_ptr() as *const i8,
                text.len() as c_int,
                start as c_int,
                PCRE_NO_UTF8_CHECK,
                ovec.as_mut_ptr(),
                OVEC_SIZE as c_int,
            )
        };
        if err == PCRE_ERROR_NOMATCH {
            None
        } else if err < 0 {
            panic!("unknown error code: {:?}", err)
        } else {
            Some((ovec[0] as usize, ovec[1] as usize))
        }
    }
}

pub struct FindMatches<'r, 't> {
    re: &'r Regex,
    text: &'t str,
    last_match_end: usize,
}

impl<'r, 't> Iterator for FindMatches<'r, 't> {
    type Item = (usize, usize);

    fn next(&mut self) -> Option<(usize, usize)> {
        match self.re.find_at(self.text, self.last_match_end) {
            None => None,
            Some((s, e)) => {
                self.last_match_end = e;
                Some((s, e))
            }
        }
    }
}

impl fmt::Debug for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "PCRE error at {:?}: {}", self.offset, self.msg)
    }
}