// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use self::WhichLine::*;

use std::fs::File;
use std::io::BufReader;
use std::io::prelude::*;
use std::path::Path;

pub struct ExpectedError {
    pub line_num: usize,
    pub kind: String,
    pub msg: String,
}

#[derive(PartialEq, Debug)]
enum WhichLine { ThisLine, FollowPrevious(usize), AdjustBackward(usize) }

/// Looks for either "//~| KIND MESSAGE" or "//~^^... KIND MESSAGE"
/// The former is a "follow" that inherits its target from the preceding line;
/// the latter is an "adjusts" that goes that many lines up.
///
/// Goal is to enable tests both like: //~^^^ ERROR go up three
/// and also //~^ ERROR message one for the preceding line, and
///          //~| ERROR message two for that same line.
///
/// If cfg is not None (i.e., in an incremental test), then we look
/// for `//[X]~` instead, where `X` is the current `cfg`.
pub fn load_errors(testfile: &Path, cfg: Option<&str>) -> Vec<ExpectedError> {
    let rdr = BufReader::new(File::open(testfile).unwrap());

    // `last_nonfollow_error` tracks the most recently seen
    // line with an error template that did not use the
    // follow-syntax, "//~| ...".
    //
    // (pnkfelix could not find an easy way to compose Iterator::scan
    // and Iterator::filter_map to pass along this information into
    // `parse_expected`. So instead I am storing that state here and
    // updating it in the map callback below.)
    let mut last_nonfollow_error = None;

    let tag = match cfg {
        Some(rev) => format!("//[{}]~", rev),
        None => format!("//~")
    };

    rdr.lines()
       .enumerate()
       .filter_map(|(line_num, line)| {
           parse_expected(last_nonfollow_error,
                          line_num + 1,
                          &line.unwrap(),
                          &tag)
               .map(|(which, error)| {
                   match which {
                       FollowPrevious(_) => {}
                       _ => last_nonfollow_error = Some(error.line_num),
                   }
                   error
               })
       })
       .collect()
}

fn parse_expected(last_nonfollow_error: Option<usize>,
                  line_num: usize,
                  line: &str,
                  tag: &str)
                  -> Option<(WhichLine, ExpectedError)> {
    let start = match line.find(tag) { Some(i) => i, None => return None };
    let (follow, adjusts) = if line.char_at(start + tag.len()) == '|' {
        (true, 0)
    } else {
        (false, line[start + tag.len()..].chars().take_while(|c| *c == '^').count())
    };
    let kind_start = start + tag.len() + adjusts + (follow as usize);
    let letters = line[kind_start..].chars();
    let kind = letters.skip_while(|c| c.is_whitespace())
                      .take_while(|c| !c.is_whitespace())
                      .flat_map(|c| c.to_lowercase())
                      .collect::<String>();
    let letters = line[kind_start..].chars();
    let msg = letters.skip_while(|c| c.is_whitespace())
                     .skip_while(|c| !c.is_whitespace())
                     .collect::<String>().trim().to_owned();

    let (which, line_num) = if follow {
        assert!(adjusts == 0, "use either //~| or //~^, not both.");
        let line_num = last_nonfollow_error.expect("encountered //~| without \
                                                    preceding //~^ line.");
        (FollowPrevious(line_num), line_num)
    } else {
        let which =
            if adjusts > 0 { AdjustBackward(adjusts) } else { ThisLine };
        let line_num = line_num - adjusts;
        (which, line_num)
    };

    debug!("line={} tag={:?} which={:?} kind={:?} msg={:?}",
           line_num, tag, which, kind, msg);
    Some((which, ExpectedError { line_num: line_num,
                                 kind: kind,
                                 msg: msg, }))
}