use ratatui::{
    buffer::Buffer,
    layout::Rect,
    style::{Color, Modifier, Style},
    widgets::{Block, Borders, Widget},
};

use crate::model::Model;
use crate::ui::app::AppMode;

pub struct FormulaPanel<'a> {
    pub model: &'a Model,
    pub mode: &'a AppMode,
    pub cursor: usize,
}

impl<'a> FormulaPanel<'a> {
    pub fn new(model: &'a Model, mode: &'a AppMode, cursor: usize) -> Self {
        Self {
            model,
            mode,
            cursor,
        }
    }
}

impl<'a> Widget for FormulaPanel<'a> {
    fn render(self, area: Rect, buf: &mut Buffer) {
        let is_active = matches!(
            self.mode,
            AppMode::FormulaPanel | AppMode::FormulaEdit { .. }
        );
        let border_style = if is_active {
            Style::default().fg(Color::Yellow)
        } else {
            Style::default().fg(Color::DarkGray)
        };

        let block = Block::default()
            .borders(Borders::ALL)
            .border_style(border_style)
            .title(" Formulas [n]ew [d]elete ");
        let inner = block.inner(area);
        block.render(area, buf);

        let formulas = self.model.formulas();

        if formulas.is_empty() {
            buf.set_string(
                inner.x,
                inner.y,
                "(no formulas — press 'n' to add)",
                Style::default().fg(Color::DarkGray),
            );
            return;
        }

        for (i, formula) in formulas.iter().enumerate() {
            if inner.y + i as u16 >= inner.y + inner.height {
                break;
            }
            let is_selected = i == self.cursor && is_active;
            let style = if is_selected {
                Style::default()
                    .fg(Color::Black)
                    .bg(Color::Yellow)
                    .add_modifier(Modifier::BOLD)
            } else {
                Style::default().fg(Color::Green)
            };
            let text = format!("  {} = {:?}", formula.target, formula.raw);
            let truncated = if text.len() > inner.width as usize {
                format!("{}…", &text[..inner.width as usize - 1])
            } else {
                text
            };
            buf.set_string(inner.x, inner.y + i as u16, &truncated, style);
        }

        // Formula edit mode
        if let AppMode::FormulaEdit { buffer } = self.mode {
            let y = inner.y + inner.height.saturating_sub(2);
            buf.set_string(
                inner.x,
                y,
                "┄ Enter formula (Name = expr): ",
                Style::default().fg(Color::Yellow),
            );
            let y = y + 1;
            let prompt = format!("> {buffer}█");
            buf.set_string(inner.x, y, &prompt, Style::default().fg(Color::Green));
        }
    }
}