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// Small functions of utility

use core::SearchType::{self, ExactMatch, StartsWith};
use core::Session;
use std;
use std::cmp;
use std::fs::File;
use std::io::{BufRead, BufReader};
use std::path::Path;

pub fn getline(filepath: &Path, linenum: usize, session: &Session) -> String {
    let reader = BufReader::new(session.open_file(filepath).unwrap());
    reader.lines().nth(linenum - 1).unwrap_or(Ok("not found".into())).unwrap()
}

pub fn is_pattern_char(c: char) -> bool {
    c.is_alphanumeric() || c.is_whitespace() || (c == '_') || (c == ':') || (c == '.')
}

pub fn is_search_expr_char(c: char) -> bool {
    c.is_alphanumeric() || (c == '_') || (c == ':') || (c == '.')
}

pub fn is_ident_char(c: char) -> bool {
    c.is_alphanumeric() || (c == '_')
}

pub fn txt_matches(stype: SearchType, needle: &str, haystack: &str) -> bool {
    match stype {
        ExactMatch => {
            let nlen = needle.len();
            let hlen = haystack.len();

            if nlen == 0 {
                return true;
            }

            // PD: switch to use .match_indices() when that stabilizes
            let mut n=0;
            while let Some(n1) = haystack[n..].find(needle) {
                n += n1;
                if (n == 0  || !is_ident_char(char_at(haystack, n-1))) &&
                    (n+nlen == hlen || !is_ident_char(char_at(haystack, n+nlen))) {
                    return true;
                }
                n += 1;
            }
            false
        },
        StartsWith => {
            if needle.is_empty() {
                return true;
            }

            // PD: switch to use .match_indices() when that stabilizes
            let mut n=0;
            while let Some(n1) = haystack[n..].find(needle) {
                n += n1;
                if n == 0  || !is_ident_char(char_at(haystack, n-1)) {
                    return true;
                }
                n += 1;
            }
            false
        }
    }
}

pub fn symbol_matches(stype: SearchType, searchstr: &str, candidate: &str) -> bool {
   match stype {
        ExactMatch => searchstr == candidate,
        StartsWith => candidate.starts_with(searchstr)
    }
}

// pub fn get_backtrace() -> String {
//     let mut m = std::old_io::MemWriter::new();
//     let s = std::rt::backtrace::write(&mut m)
//         .ok().map_or("NO backtrace".to_string(),
//                      |_| String::from_utf8_lossy(m.get_ref()).to_string());
//     return s;
// }

pub fn is_double_dot(msrc: &str, i: usize) -> bool {
    (i > 1) && &msrc[i-1..i+1] == ".."
}

#[test]
fn txt_matches_matches_stuff() {
    assert_eq!(true, txt_matches(ExactMatch, "Vec","Vec"));
    assert_eq!(true, txt_matches(StartsWith, "Vec","Vector"));
    assert_eq!(false, txt_matches(ExactMatch, "Vec","use Vector"));
    assert_eq!(true, txt_matches(StartsWith, "Vec","use Vector"));
    assert_eq!(false, txt_matches(StartsWith, "Vec","use aVector"));
    assert_eq!(true, txt_matches(ExactMatch, "Vec","use Vec"));
}


pub fn expand_ident(s: &str, pos: usize) -> (usize, usize) {
    // TODO: Would this better be an assertion ? Why are out-of-bound values getting here ?
    // They are coming from the command-line, question is, if they should be handled beforehand
    // clamp pos into allowed range
    let pos = cmp::min(s.len(), pos);
    let sb = &s[..pos];
    let mut start = pos;

    // backtrack to find start of word
    for (i, c) in sb.char_indices().rev() {
        if !is_ident_char(c) {
            break;
        }
        start = i;
    }
    (start, pos)
}

pub fn find_ident_end(s: &str, pos: usize) -> usize {
    // find end of word
    let sa = &s[pos..];
    for (i, c) in sa.char_indices() {
        if !is_ident_char(c) {
            return pos + i;
        }
    }
    s.len()
}

#[test]
fn find_ident_end_ascii() {
    assert_eq!(5, find_ident_end("ident", 0));
    assert_eq!(6, find_ident_end("(ident)", 1));
    assert_eq!(17, find_ident_end("let an_identifier = 100;", 4));
}

#[test]
fn find_ident_end_unicode() {
    assert_eq!(7, find_ident_end("num_µs", 0));
    assert_eq!(10, find_ident_end("ends_in_µ", 0));
}

// PD: short term replacement for .char_at() function. Should be replaced once
// that stabilizes
pub fn char_at(src: &str, i: usize) -> char {
    src[i..].chars().next().unwrap()
}

// PD: short term replacement for path.exists() (PathExt trait). Replace once
// that stabilizes
pub fn path_exists<P: AsRef<Path>>(path: P) -> bool {
    is_dir(&path) || File::open(path).is_ok()
}

// PD: short term replacement for path.is_dir() (PathExt trait). Replace once
// that stabilizes
pub fn is_dir<P: AsRef<Path>>(path: P) -> bool {
    std::fs::metadata(path).map(|info| info.is_dir()).unwrap_or(false)
}