use std::rc::Rc;

use super::{
    TextBuffer,
    rope::{NodeIterator, Rope},
};

pub struct TextBufferReader {
    node_iterator: NodeIterator,
    current_node: Option<Rc<Rope>>,
    cursor: usize,
}

impl TextBufferReader {
    pub fn new(text_buffer: &TextBuffer) -> Self {
        let mut node_iterator = Rc::clone(&text_buffer.contents).iter_nodes();
        let current_node = node_iterator.next();
        Self {
            node_iterator,
            current_node,
            cursor: 0,
        }
    }
}

impl std::io::Read for TextBufferReader {
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        let mut bytes_written = 0;
        while let Some(rope) = self.current_node.clone() {
            if let Rope::Leaf { text, .. } = rope.as_ref() {
                let bytes = text.as_bytes();
                let length = bytes
                    .len()
                    .min(buf.len() - bytes_written)
                    .min(bytes.len() - self.cursor);
                buf[bytes_written..bytes_written + length]
                    .copy_from_slice(&bytes[self.cursor..self.cursor + length]);
                bytes_written += length;
                self.cursor += length;
                if self.cursor == bytes.len() {
                    self.current_node = self.node_iterator.next();
                    self.cursor = 0;
                }
            } else {
                // Should always be leaf node
                panic!();
            }
            if bytes_written == buf.len() {
                break;
            }
        }
        Ok(bytes_written)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::text_buffer::Point;
    use std::io::Read;

    #[test]
    fn test_read_string() {
        let text_fragments = [
            "Sed ut perspiciatis unde omnis iste natus error sit voluptatem ",
            "accusantium doloremque laudantium, totam rem aperiam, eaque ",
            "ipsa quae ab illo inventore veritatis et quasi architecto beatae ",
            "vitae dicta sunt explicabo. Nemo enim ipsam voluptatem quia ",
            "voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur ",
            "magni dolores eos qui ratione voluptatem sequi nesciunt. Neque ",
            "porro quisquam est, qui dolorem ipsum quia dolor sit amet, ",
            "consectetur, adipisci velit, sed quia non numquam eius modi tempora ",
            "incidunt ut labore et dolore magnam aliquam quaerat voluptatem. Ut ",
            "enim ad minima veniam, quis nostrum exercitationem ullam ",
            "corporis suscipit laboriosam, nisi ut aliquid ex ea commodi ",
            "consequatur? Quis autem vel eum iure reprehenderit qui in ea voluptate ",
            "velit esse quam nihil molestiae consequatur, vel illum qui dolorem ",
            "eum fugiat quo voluptas nulla pariatur?",
        ];
        let mut text_buffer = TextBuffer::new();
        for fragment in text_fragments {
            text_buffer.insert_text(fragment, Point::End);
        }
        let mut target = TextBufferReader::new(&text_buffer);
        let mut bytes_buffer = Vec::new();
        target.read_to_end(&mut bytes_buffer).unwrap();
        let target_string = String::from_utf8(bytes_buffer).unwrap();
        let expected_string: String = text_fragments.iter().flat_map(|s| s.chars()).collect();
        assert_eq!(target_string, expected_string);
    }
}