//! This module contains utilities that work with the `SourceMap` from `libsyntax`/`syntex_syntax`.
//! This includes extension traits and methods for looking up spans and line ranges for AST nodes.

use syntax::source_map::{BytePos, SourceMap, Span};

use crate::comment::FindUncommented;
use crate::config::file_lines::LineRange;
use crate::visitor::SnippetProvider;

pub(crate) trait SpanUtils {
    fn span_after(&self, original: Span, needle: &str) -> BytePos;
    fn span_after_last(&self, original: Span, needle: &str) -> BytePos;
    fn span_before(&self, original: Span, needle: &str) -> BytePos;
    fn span_before_last(&self, original: Span, needle: &str) -> BytePos;
    fn opt_span_after(&self, original: Span, needle: &str) -> Option<BytePos>;
    fn opt_span_before(&self, original: Span, needle: &str) -> Option<BytePos>;
}

pub(crate) trait LineRangeUtils {
    /// Returns the `LineRange` that corresponds to `span` in `self`.
    ///
    /// # Panics
    ///
    /// Panics if `span` crosses a file boundary, which shouldn't happen.
    fn lookup_line_range(&self, span: Span) -> LineRange;
}

impl<'a> SpanUtils for SnippetProvider<'a> {
    fn span_after(&self, original: Span, needle: &str) -> BytePos {
        self.opt_span_after(original, needle).unwrap_or_else(|| {
            panic!(
                "bad span: `{}`: `{}`",
                needle,
                self.span_to_snippet(original).unwrap()
            )
        })
    }

    fn span_after_last(&self, original: Span, needle: &str) -> BytePos {
        let snippet = self.span_to_snippet(original).unwrap();
        let mut offset = 0;

        while let Some(additional_offset) = snippet[offset..].find_uncommented(needle) {
            offset += additional_offset + needle.len();
        }

        original.lo() + BytePos(offset as u32)
    }

    fn span_before(&self, original: Span, needle: &str) -> BytePos {
        self.opt_span_before(original, needle).unwrap_or_else(|| {
            panic!(
                "bad span: `{}`: `{}`",
                needle,
                self.span_to_snippet(original).unwrap()
            )
        })
    }

    fn span_before_last(&self, original: Span, needle: &str) -> BytePos {
        let snippet = self.span_to_snippet(original).unwrap();
        let mut offset = 0;

        while let Some(additional_offset) = snippet[offset..].find_uncommented(needle) {
            offset += additional_offset + needle.len();
        }

        original.lo() + BytePos(offset as u32 - 1)
    }

    fn opt_span_after(&self, original: Span, needle: &str) -> Option<BytePos> {
        self.opt_span_before(original, needle)
            .map(|bytepos| bytepos + BytePos(needle.len() as u32))
    }

    fn opt_span_before(&self, original: Span, needle: &str) -> Option<BytePos> {
        let snippet = self.span_to_snippet(original)?;
        let offset = snippet.find_uncommented(needle)?;

        Some(original.lo() + BytePos(offset as u32))
    }
}

impl LineRangeUtils for SourceMap {
    fn lookup_line_range(&self, span: Span) -> LineRange {
        let snippet = self.span_to_snippet(span).unwrap_or_default();
        let lo = self.lookup_line(span.lo()).unwrap();
        let hi = self.lookup_line(span.hi()).unwrap();

        debug_assert_eq!(
            lo.sf.name, hi.sf.name,
            "span crossed file boundary: lo: {:?}, hi: {:?}",
            lo, hi
        );

        // in case the span starts with a newline, the line range is off by 1 without the
        // adjustment below
        let offset = 1 + if snippet.starts_with('\n') { 1 } else { 0 };
        // Line numbers start at 1
        LineRange {
            file: lo.sf.clone(),
            lo: lo.line + offset,
            hi: hi.line + offset,
        }
    }
}