//! FIXME: write short doc here

use crate::TextUnit;
use rustc_hash::FxHashMap;
use superslice::Ext;

#[derive(Clone, Debug, PartialEq, Eq)]
pub struct LineIndex {
    pub(crate) newlines: Vec<TextUnit>,
    pub(crate) utf16_lines: FxHashMap<u32, Vec<Utf16Char>>,
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct LineCol {
    /// Zero-based
    pub line: u32,
    /// Zero-based
    pub col_utf16: u32,
}

#[derive(Clone, Debug, Hash, PartialEq, Eq)]
pub(crate) struct Utf16Char {
    pub(crate) start: TextUnit,
    pub(crate) end: TextUnit,
}

impl Utf16Char {
    fn len(&self) -> TextUnit {
        self.end - self.start
    }
}

impl LineIndex {
    pub fn new(text: &str) -> LineIndex {
        let mut utf16_lines = FxHashMap::default();
        let mut utf16_chars = Vec::new();

        let mut newlines = vec![0.into()];
        let mut curr_row = 0.into();
        let mut curr_col = 0.into();
        let mut line = 0;
        for c in text.chars() {
            curr_row += TextUnit::of_char(c);
            if c == '\n' {
                newlines.push(curr_row);

                // Save any utf-16 characters seen in the previous line
                if !utf16_chars.is_empty() {
                    utf16_lines.insert(line, utf16_chars);
                    utf16_chars = Vec::new();
                }

                // Prepare for processing the next line
                curr_col = 0.into();
                line += 1;
                continue;
            }

            let char_len = TextUnit::of_char(c);
            if char_len.to_usize() > 1 {
                utf16_chars.push(Utf16Char { start: curr_col, end: curr_col + char_len });
            }

            curr_col += char_len;
        }

        // Save any utf-16 characters seen in the last line
        if !utf16_chars.is_empty() {
            utf16_lines.insert(line, utf16_chars);
        }

        LineIndex { newlines, utf16_lines }
    }

    pub fn line_col(&self, offset: TextUnit) -> LineCol {
        let line = self.newlines.upper_bound(&offset) - 1;
        let line_start_offset = self.newlines[line];
        let col = offset - line_start_offset;

        LineCol { line: line as u32, col_utf16: self.utf8_to_utf16_col(line as u32, col) as u32 }
    }

    pub fn offset(&self, line_col: LineCol) -> TextUnit {
        //FIXME: return Result
        let col = self.utf16_to_utf8_col(line_col.line, line_col.col_utf16);
        self.newlines[line_col.line as usize] + col
    }

    fn utf8_to_utf16_col(&self, line: u32, mut col: TextUnit) -> usize {
        if let Some(utf16_chars) = self.utf16_lines.get(&line) {
            let mut correction = TextUnit::from_usize(0);
            for c in utf16_chars {
                if col >= c.end {
                    correction += c.len() - TextUnit::from_usize(1);
                } else {
                    // From here on, all utf16 characters come *after* the character we are mapping,
                    // so we don't need to take them into account
                    break;
                }
            }

            col -= correction;
        }

        col.to_usize()
    }

    fn utf16_to_utf8_col(&self, line: u32, col: u32) -> TextUnit {
        let mut col: TextUnit = col.into();
        if let Some(utf16_chars) = self.utf16_lines.get(&line) {
            for c in utf16_chars {
                if col >= c.start {
                    col += c.len() - TextUnit::from_usize(1);
                } else {
                    // From here on, all utf16 characters come *after* the character we are mapping,
                    // so we don't need to take them into account
                    break;
                }
            }
        }

        col
    }
}

#[cfg(test)]
/// Simple reference implementation to use in proptests
pub fn to_line_col(text: &str, offset: TextUnit) -> LineCol {
    let mut res = LineCol { line: 0, col_utf16: 0 };
    for (i, c) in text.char_indices() {
        if i + c.len_utf8() > offset.to_usize() {
            // if it's an invalid offset, inside a multibyte char
            // return as if it was at the start of the char
            break;
        }
        if c == '\n' {
            res.line += 1;
            res.col_utf16 = 0;
        } else {
            res.col_utf16 += 1;
        }
    }
    res
}

#[cfg(test)]
mod test_line_index {
    use super::*;
    use proptest::{prelude::*, proptest};
    use ra_text_edit::test_utils::{arb_offset, arb_text};

    #[test]
    fn test_line_index() {
        let text = "hello\nworld";
        let index = LineIndex::new(text);
        assert_eq!(index.line_col(0.into()), LineCol { line: 0, col_utf16: 0 });
        assert_eq!(index.line_col(1.into()), LineCol { line: 0, col_utf16: 1 });
        assert_eq!(index.line_col(5.into()), LineCol { line: 0, col_utf16: 5 });
        assert_eq!(index.line_col(6.into()), LineCol { line: 1, col_utf16: 0 });
        assert_eq!(index.line_col(7.into()), LineCol { line: 1, col_utf16: 1 });
        assert_eq!(index.line_col(8.into()), LineCol { line: 1, col_utf16: 2 });
        assert_eq!(index.line_col(10.into()), LineCol { line: 1, col_utf16: 4 });
        assert_eq!(index.line_col(11.into()), LineCol { line: 1, col_utf16: 5 });
        assert_eq!(index.line_col(12.into()), LineCol { line: 1, col_utf16: 6 });

        let text = "\nhello\nworld";
        let index = LineIndex::new(text);
        assert_eq!(index.line_col(0.into()), LineCol { line: 0, col_utf16: 0 });
        assert_eq!(index.line_col(1.into()), LineCol { line: 1, col_utf16: 0 });
        assert_eq!(index.line_col(2.into()), LineCol { line: 1, col_utf16: 1 });
        assert_eq!(index.line_col(6.into()), LineCol { line: 1, col_utf16: 5 });
        assert_eq!(index.line_col(7.into()), LineCol { line: 2, col_utf16: 0 });
    }

    fn arb_text_with_offset() -> BoxedStrategy<(TextUnit, String)> {
        arb_text().prop_flat_map(|text| (arb_offset(&text), Just(text))).boxed()
    }

    fn to_line_col(text: &str, offset: TextUnit) -> LineCol {
        let mut res = LineCol { line: 0, col_utf16: 0 };
        for (i, c) in text.char_indices() {
            if i + c.len_utf8() > offset.to_usize() {
                // if it's an invalid offset, inside a multibyte char
                // return as if it was at the start of the char
                break;
            }
            if c == '\n' {
                res.line += 1;
                res.col_utf16 = 0;
            } else {
                res.col_utf16 += 1;
            }
        }
        res
    }

    proptest! {
        #[test]
        fn test_line_index_proptest((offset, text) in arb_text_with_offset()) {
            let expected = to_line_col(&text, offset);
            let line_index = LineIndex::new(&text);
            let actual = line_index.line_col(offset);

            assert_eq!(actual, expected);
        }
    }
}

#[cfg(test)]
mod test_utf8_utf16_conv {
    use super::*;

    #[test]
    fn test_char_len() {
        assert_eq!('メ'.len_utf8(), 3);
        assert_eq!('メ'.len_utf16(), 1);
    }

    #[test]
    fn test_empty_index() {
        let col_index = LineIndex::new(
            "
const C: char = 'x';
",
        );
        assert_eq!(col_index.utf16_lines.len(), 0);
    }

    #[test]
    fn test_single_char() {
        let col_index = LineIndex::new(
            "
const C: char = 'メ';
",
        );

        assert_eq!(col_index.utf16_lines.len(), 1);
        assert_eq!(col_index.utf16_lines[&1].len(), 1);
        assert_eq!(col_index.utf16_lines[&1][0], Utf16Char { start: 17.into(), end: 20.into() });

        // UTF-8 to UTF-16, no changes
        assert_eq!(col_index.utf8_to_utf16_col(1, 15.into()), 15);

        // UTF-8 to UTF-16
        assert_eq!(col_index.utf8_to_utf16_col(1, 22.into()), 20);

        // UTF-16 to UTF-8, no changes
        assert_eq!(col_index.utf16_to_utf8_col(1, 15), TextUnit::from(15));

        // UTF-16 to UTF-8
        assert_eq!(col_index.utf16_to_utf8_col(1, 19), TextUnit::from(21));
    }

    #[test]
    fn test_string() {
        let col_index = LineIndex::new(
            "
const C: char = \"メ メ\";
",
        );

        assert_eq!(col_index.utf16_lines.len(), 1);
        assert_eq!(col_index.utf16_lines[&1].len(), 2);
        assert_eq!(col_index.utf16_lines[&1][0], Utf16Char { start: 17.into(), end: 20.into() });
        assert_eq!(col_index.utf16_lines[&1][1], Utf16Char { start: 21.into(), end: 24.into() });

        // UTF-8 to UTF-16
        assert_eq!(col_index.utf8_to_utf16_col(1, 15.into()), 15);

        assert_eq!(col_index.utf8_to_utf16_col(1, 21.into()), 19);
        assert_eq!(col_index.utf8_to_utf16_col(1, 25.into()), 21);

        assert!(col_index.utf8_to_utf16_col(2, 15.into()) == 15);

        // UTF-16 to UTF-8
        assert_eq!(col_index.utf16_to_utf8_col(1, 15), TextUnit::from_usize(15));

        assert_eq!(col_index.utf16_to_utf8_col(1, 18), TextUnit::from_usize(20));
        assert_eq!(col_index.utf16_to_utf8_col(1, 19), TextUnit::from_usize(23));

        assert_eq!(col_index.utf16_to_utf8_col(2, 15), TextUnit::from_usize(15));
    }
}