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use rustc::lint::*;
use rustc_front::hir::*;
use syntax::codemap::Span;

use syntax::ast::Lit_::*;

use unicode_normalization::UnicodeNormalization;

use utils::{snippet, span_help_and_lint};

declare_lint!{ pub ZERO_WIDTH_SPACE, Deny,
               "using a zero-width space in a string literal, which is confusing" }
declare_lint!{ pub NON_ASCII_LITERAL, Allow,
               "using any literal non-ASCII chars in a string literal; suggests \
                using the \\u escape instead" }
declare_lint!{ pub UNICODE_NOT_NFC, Allow,
               "using a unicode literal not in NFC normal form (see \
               http://www.unicode.org/reports/tr15/ for further information)" }


#[derive(Copy, Clone)]
pub struct Unicode;

impl LintPass for Unicode {
    fn get_lints(&self) -> LintArray {
        lint_array!(ZERO_WIDTH_SPACE, NON_ASCII_LITERAL, UNICODE_NOT_NFC)
    }
}

impl LateLintPass for Unicode {
    fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
        if let ExprLit(ref lit) = expr.node {
            if let LitStr(_, _) = lit.node {
                check_str(cx, lit.span)
            }
        }
    }
}

fn escape<T: Iterator<Item=char>>(s: T) -> String {
    let mut result = String::new();
    for c in s {
        if c as u32 > 0x7F {
            for d in c.escape_unicode() { result.push(d) };
        } else {
            result.push(c);
        }
    }
    result
}

fn check_str(cx: &LateContext, span: Span) {
    let string = snippet(cx, span, "");
    if string.contains('\u{200B}') {
        span_help_and_lint(cx, ZERO_WIDTH_SPACE, span,
            "zero-width space detected",
            &format!("Consider replacing the string with:\n\"{}\"",
                string.replace("\u{200B}", "\\u{200B}")));
    }
    if string.chars().any(|c| c as u32 > 0x7F) {
        span_help_and_lint(cx, NON_ASCII_LITERAL, span,
            "literal non-ASCII character detected",
            &format!("Consider replacing the string with:\n\"{}\"",
                if cx.current_level(UNICODE_NOT_NFC) == Level::Allow {
                    escape(string.chars())
                } else {
                    escape(string.nfc())
                }));
    }
    if cx.current_level(NON_ASCII_LITERAL) == Level::Allow &&
            string.chars().zip(string.nfc()).any(|(a, b)| a != b) {
        span_help_and_lint(cx, UNICODE_NOT_NFC, span,
            "non-nfc unicode sequence detected",
            &format!("Consider replacing the string with:\n\"{}\"",
                string.nfc().collect::<String>()));
    }
}