use std::fmt;
use std::io;
use std::io::Write;

use crate::tui;
use crate::wrapping::word_wrap_lines_borrowed;
use crossterm::Command;
use crossterm::cursor::MoveTo;
use crossterm::queue;
use crossterm::style::Color as CColor;
use crossterm::style::Colors;
use crossterm::style::Print;
use crossterm::style::SetAttribute;
use crossterm::style::SetBackgroundColor;
use crossterm::style::SetColors;
use crossterm::style::SetForegroundColor;
use ratatui::layout::Size;
use ratatui::style::Color;
use ratatui::style::Modifier;
use ratatui::text::Line;
use ratatui::text::Span;

/// Insert `lines` above the viewport using the terminal's backend writer
/// (avoids direct stdout references).
pub(crate) fn insert_history_lines(terminal: &mut tui::Terminal, lines: Vec<Line>) {
    let mut out = std::io::stdout();
    insert_history_lines_to_writer(terminal, &mut out, lines);
}

/// Like `insert_history_lines`, but writes ANSI to the provided writer. This
/// is intended for testing where a capture buffer is used instead of stdout.
pub fn insert_history_lines_to_writer<B, W>(
    terminal: &mut crate::custom_terminal::Terminal<B>,
    writer: &mut W,
    lines: Vec<Line>,
) where
    B: ratatui::backend::Backend,
    W: Write,
{
    let screen_size = terminal.backend().size().unwrap_or(Size::new(0, 0));

    let mut area = terminal.viewport_area;

    // Pre-wrap lines using word-aware wrapping so terminal scrollback sees the same
    // formatting as the TUI. This avoids character-level hard wrapping by the terminal.
    let wrapped = word_wrap_lines_borrowed(&lines, area.width.max(1) as usize);
    let wrapped_lines = wrapped.len() as u16;
    let cursor_top = if area.bottom() < screen_size.height {
        // If the viewport is not at the bottom of the screen, scroll it down to make room.
        // Don't scroll it past the bottom of the screen.
        let scroll_amount = wrapped_lines.min(screen_size.height - area.bottom());

        // Emit ANSI to scroll the lower region (from the top of the viewport to the bottom
        // of the screen) downward by `scroll_amount` lines. We do this by:
        //   1) Limiting the scroll region to [area.top()+1 .. screen_height] (1-based bounds)
        //   2) Placing the cursor at the top margin of that region
        //   3) Emitting Reverse Index (RI, ESC M) `scroll_amount` times
        //   4) Resetting the scroll region back to full screen
        let top_1based = area.top() + 1; // Convert 0-based row to 1-based for DECSTBM
        queue!(writer, SetScrollRegion(top_1based..screen_size.height)).ok();
        queue!(writer, MoveTo(0, area.top())).ok();
        for _ in 0..scroll_amount {
            // Reverse Index (RI): ESC M
            queue!(writer, Print("\x1bM")).ok();
        }
        queue!(writer, ResetScrollRegion).ok();

        let cursor_top = area.top().saturating_sub(1);
        area.y += scroll_amount;
        terminal.set_viewport_area(area);
        cursor_top
    } else {
        area.top().saturating_sub(1)
    };

    // Limit the scroll region to the lines from the top of the screen to the
    // top of the viewport. With this in place, when we add lines inside this
    // area, only the lines in this area will be scrolled. We place the cursor
    // at the end of the scroll region, and add lines starting there.
    //
    // ┌─Screen───────────────────────┐
    // │┌╌Scroll region╌╌╌╌╌╌╌╌╌╌╌╌╌╌┐│
    // │┆                            ┆│
    // │┆                            ┆│
    // │┆                            ┆│
    // │█╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┘│
    // │╭─Viewport───────────────────╮│
    // ││                            ││
    // │╰────────────────────────────╯│
    // └──────────────────────────────┘
    queue!(writer, SetScrollRegion(1..area.top())).ok();

    // NB: we are using MoveTo instead of set_cursor_position here to avoid messing with the
    // terminal's last_known_cursor_position, which hopefully will still be accurate after we
    // fetch/restore the cursor position. insert_history_lines should be cursor-position-neutral :)
    queue!(writer, MoveTo(0, cursor_top)).ok();

    for line in wrapped {
        queue!(writer, Print("\r\n")).ok();
        write_spans(writer, &line).ok();
    }

    queue!(writer, ResetScrollRegion).ok();

    // Restore the cursor position to where it was before we started.
    queue!(
        writer,
        MoveTo(
            terminal.last_known_cursor_pos.x,
            terminal.last_known_cursor_pos.y
        )
    )
    .ok();
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SetScrollRegion(pub std::ops::Range<u16>);

impl Command for SetScrollRegion {
    fn write_ansi(&self, f: &mut impl fmt::Write) -> fmt::Result {
        write!(f, "\x1b[{};{}r", self.0.start, self.0.end)
    }

    #[cfg(windows)]
    fn execute_winapi(&self) -> std::io::Result<()> {
        panic!("tried to execute SetScrollRegion command using WinAPI, use ANSI instead");
    }

    #[cfg(windows)]
    fn is_ansi_code_supported(&self) -> bool {
        // TODO(nornagon): is this supported on Windows?
        true
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ResetScrollRegion;

impl Command for ResetScrollRegion {
    fn write_ansi(&self, f: &mut impl fmt::Write) -> fmt::Result {
        write!(f, "\x1b[r")
    }

    #[cfg(windows)]
    fn execute_winapi(&self) -> std::io::Result<()> {
        panic!("tried to execute ResetScrollRegion command using WinAPI, use ANSI instead");
    }

    #[cfg(windows)]
    fn is_ansi_code_supported(&self) -> bool {
        // TODO(nornagon): is this supported on Windows?
        true
    }
}

struct ModifierDiff {
    pub from: Modifier,
    pub to: Modifier,
}

impl ModifierDiff {
    fn queue<W>(self, mut w: W) -> io::Result<()>
    where
        W: io::Write,
    {
        use crossterm::style::Attribute as CAttribute;
        let removed = self.from - self.to;
        if removed.contains(Modifier::REVERSED) {
            queue!(w, SetAttribute(CAttribute::NoReverse))?;
        }
        if removed.contains(Modifier::BOLD) {
            queue!(w, SetAttribute(CAttribute::NormalIntensity))?;
            if self.to.contains(Modifier::DIM) {
                queue!(w, SetAttribute(CAttribute::Dim))?;
            }
        }
        if removed.contains(Modifier::ITALIC) {
            queue!(w, SetAttribute(CAttribute::NoItalic))?;
        }
        if removed.contains(Modifier::UNDERLINED) {
            queue!(w, SetAttribute(CAttribute::NoUnderline))?;
        }
        if removed.contains(Modifier::DIM) {
            queue!(w, SetAttribute(CAttribute::NormalIntensity))?;
        }
        if removed.contains(Modifier::CROSSED_OUT) {
            queue!(w, SetAttribute(CAttribute::NotCrossedOut))?;
        }
        if removed.contains(Modifier::SLOW_BLINK) || removed.contains(Modifier::RAPID_BLINK) {
            queue!(w, SetAttribute(CAttribute::NoBlink))?;
        }

        let added = self.to - self.from;
        if added.contains(Modifier::REVERSED) {
            queue!(w, SetAttribute(CAttribute::Reverse))?;
        }
        if added.contains(Modifier::BOLD) {
            queue!(w, SetAttribute(CAttribute::Bold))?;
        }
        if added.contains(Modifier::ITALIC) {
            queue!(w, SetAttribute(CAttribute::Italic))?;
        }
        if added.contains(Modifier::UNDERLINED) {
            queue!(w, SetAttribute(CAttribute::Underlined))?;
        }
        if added.contains(Modifier::DIM) {
            queue!(w, SetAttribute(CAttribute::Dim))?;
        }
        if added.contains(Modifier::CROSSED_OUT) {
            queue!(w, SetAttribute(CAttribute::CrossedOut))?;
        }
        if added.contains(Modifier::SLOW_BLINK) {
            queue!(w, SetAttribute(CAttribute::SlowBlink))?;
        }
        if added.contains(Modifier::RAPID_BLINK) {
            queue!(w, SetAttribute(CAttribute::RapidBlink))?;
        }

        Ok(())
    }
}

fn write_spans<'a, I>(mut writer: &mut impl Write, content: I) -> io::Result<()>
where
    I: IntoIterator<Item = &'a Span<'a>>,
{
    let mut fg = Color::Reset;
    let mut bg = Color::Reset;
    let mut last_modifier = Modifier::empty();
    for span in content {
        let mut modifier = Modifier::empty();
        modifier.insert(span.style.add_modifier);
        modifier.remove(span.style.sub_modifier);
        if modifier != last_modifier {
            let diff = ModifierDiff {
                from: last_modifier,
                to: modifier,
            };
            diff.queue(&mut writer)?;
            last_modifier = modifier;
        }
        let next_fg = span.style.fg.unwrap_or(Color::Reset);
        let next_bg = span.style.bg.unwrap_or(Color::Reset);
        if next_fg != fg || next_bg != bg {
            queue!(
                writer,
                SetColors(Colors::new(next_fg.into(), next_bg.into()))
            )?;
            fg = next_fg;
            bg = next_bg;
        }

        queue!(writer, Print(span.content.clone()))?;
    }

    queue!(
        writer,
        SetForegroundColor(CColor::Reset),
        SetBackgroundColor(CColor::Reset),
        SetAttribute(crossterm::style::Attribute::Reset),
    )
}

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

    #[test]
    fn writes_bold_then_regular_spans() {
        use ratatui::style::Stylize;

        let spans = ["A".bold(), "B".into()];

        let mut actual: Vec<u8> = Vec::new();
        write_spans(&mut actual, spans.iter()).unwrap();

        let mut expected: Vec<u8> = Vec::new();
        queue!(
            expected,
            SetAttribute(crossterm::style::Attribute::Bold),
            Print("A"),
            SetAttribute(crossterm::style::Attribute::NormalIntensity),
            Print("B"),
            SetForegroundColor(CColor::Reset),
            SetBackgroundColor(CColor::Reset),
            SetAttribute(crossterm::style::Attribute::Reset),
        )
        .unwrap();

        assert_eq!(
            String::from_utf8(actual).unwrap(),
            String::from_utf8(expected).unwrap()
        );
    }
}