use crate::{
    backend::Backend,
    buffer::{Buffer, Cell},
    layout::Rect,
};
use std::{fmt::Write, io};
use unicode_width::UnicodeWidthStr;

/// A backend used for the integration tests.
#[derive(Debug)]
pub struct TestBackend {
    width: u16,
    buffer: Buffer,
    height: u16,
    cursor: bool,
    pos: (u16, u16),
}

/// Returns a string representation of the given buffer for debugging purpose.
fn buffer_view(buffer: &Buffer) -> String {
    let mut view = String::with_capacity(buffer.content.len() + buffer.area.height as usize * 3);
    for cells in buffer.content.chunks(buffer.area.width as usize) {
        let mut overwritten = vec![];
        let mut skip: usize = 0;
        view.push('"');
        for (x, c) in cells.iter().enumerate() {
            if skip == 0 {
                view.push_str(&c.symbol);
            } else {
                overwritten.push((x, &c.symbol))
            }
            skip = std::cmp::max(skip, c.symbol.width()).saturating_sub(1);
        }
        view.push('"');
        if !overwritten.is_empty() {
            write!(
                &mut view,
                " Hidden by multi-width symbols: {:?}",
                overwritten
            )
            .unwrap();
        }
        view.push_str("\n");
    }
    view
}

impl TestBackend {
    pub fn new(width: u16, height: u16) -> TestBackend {
        TestBackend {
            width,
            height,
            buffer: Buffer::empty(Rect::new(0, 0, width, height)),
            cursor: false,
            pos: (0, 0),
        }
    }

    pub fn buffer(&self) -> &Buffer {
        &self.buffer
    }

    pub fn assert_buffer(&self, expected: &Buffer) {
        assert_eq!(expected.area, self.buffer.area);
        let diff = expected.diff(&self.buffer);
        if diff.is_empty() {
            return;
        }

        let mut debug_info = String::from("Buffers are not equal");
        debug_info.push_str("\n");
        debug_info.push_str("Expected:");
        debug_info.push_str("\n");
        let expected_view = buffer_view(expected);
        debug_info.push_str(&expected_view);
        debug_info.push_str("\n");
        debug_info.push_str("Got:");
        debug_info.push_str("\n");
        let view = buffer_view(&self.buffer);
        debug_info.push_str(&view);
        debug_info.push_str("\n");

        debug_info.push_str("Diff:");
        debug_info.push_str("\n");
        let nice_diff = diff
            .iter()
            .enumerate()
            .map(|(i, (x, y, cell))| {
                let expected_cell = expected.get(*x, *y);
                format!(
                    "{}: at ({}, {}) expected {:?} got {:?}",
                    i, x, y, expected_cell, cell
                )
            })
            .collect::<Vec<String>>()
            .join("\n");
        debug_info.push_str(&nice_diff);
        panic!(debug_info);
    }
}

impl Backend for TestBackend {
    fn draw<'a, I>(&mut self, content: I) -> Result<(), io::Error>
    where
        I: Iterator<Item = (u16, u16, &'a Cell)>,
    {
        for (x, y, c) in content {
            let cell = self.buffer.get_mut(x, y);
            cell.symbol = c.symbol.clone();
            cell.style = c.style;
        }
        Ok(())
    }

    fn hide_cursor(&mut self) -> Result<(), io::Error> {
        self.cursor = false;
        Ok(())
    }

    fn show_cursor(&mut self) -> Result<(), io::Error> {
        self.cursor = true;
        Ok(())
    }

    fn get_cursor(&mut self) -> Result<(u16, u16), io::Error> {
        Ok(self.pos)
    }

    fn set_cursor(&mut self, x: u16, y: u16) -> Result<(), io::Error> {
        self.pos = (x, y);
        Ok(())
    }

    fn clear(&mut self) -> Result<(), io::Error> {
        Ok(())
    }

    fn size(&self) -> Result<Rect, io::Error> {
        Ok(Rect::new(0, 0, self.width, self.height))
    }

    fn flush(&mut self) -> Result<(), io::Error> {
        Ok(())
    }
}