use anyhow::Result;
use ratatui::crossterm::{
    style::{style, Stylize},
    terminal,
};
use std::io::{self, StdoutLock, Write};

use crate::{
    app_state::{AppState, ExercisesProgress},
    clear_terminal,
    exercise::{RunnableExercise, OUTPUT_CAPACITY},
    progress_bar::progress_bar,
    terminal_link::TerminalFileLink,
};

#[derive(PartialEq, Eq)]
enum DoneStatus {
    DoneWithSolution(String),
    DoneWithoutSolution,
    Pending,
}

pub struct WatchState<'a> {
    writer: StdoutLock<'a>,
    app_state: &'a mut AppState,
    output: Vec<u8>,
    show_hint: bool,
    done_status: DoneStatus,
    manual_run: bool,
}

impl<'a> WatchState<'a> {
    pub fn new(app_state: &'a mut AppState, manual_run: bool) -> Self {
        let writer = io::stdout().lock();

        Self {
            writer,
            app_state,
            output: Vec::with_capacity(OUTPUT_CAPACITY),
            show_hint: false,
            done_status: DoneStatus::Pending,
            manual_run,
        }
    }

    #[inline]
    pub fn into_writer(self) -> StdoutLock<'a> {
        self.writer
    }

    pub fn run_current_exercise(&mut self) -> Result<()> {
        self.show_hint = false;

        let success = self
            .app_state
            .current_exercise()
            .run_exercise(&mut self.output, self.app_state.target_dir())?;
        if success {
            self.done_status =
                if let Some(solution_path) = self.app_state.current_solution_path()? {
                    DoneStatus::DoneWithSolution(solution_path)
                } else {
                    DoneStatus::DoneWithoutSolution
                };
        } else {
            self.app_state
                .set_pending(self.app_state.current_exercise_ind())?;

            self.done_status = DoneStatus::Pending;
        }

        self.render()
    }

    pub fn handle_file_change(&mut self, exercise_ind: usize) -> Result<()> {
        // Don't skip exercises on file changes to avoid confusion from missing exercises.
        // Skipping exercises must be explicit in the interactive list.
        // But going back to an earlier exercise on file change is fine.
        if self.app_state.current_exercise_ind() < exercise_ind {
            return Ok(());
        }

        self.app_state.set_current_exercise_ind(exercise_ind)?;
        self.run_current_exercise()
    }

    /// Move on to the next exercise if the current one is done.
    pub fn next_exercise(&mut self) -> Result<ExercisesProgress> {
        if self.done_status == DoneStatus::Pending {
            return Ok(ExercisesProgress::CurrentPending);
        }

        self.app_state.done_current_exercise(&mut self.writer)
    }

    fn show_prompt(&mut self) -> io::Result<()> {
        self.writer.write_all(b"\n")?;

        if self.manual_run {
            write!(self.writer, "{}:run / ", 'r'.bold())?;
        }

        if self.done_status != DoneStatus::Pending {
            write!(self.writer, "{}:{} / ", 'n'.bold(), "next".underlined())?;
        }

        if !self.show_hint {
            write!(self.writer, "{}:hint / ", 'h'.bold())?;
        }

        write!(self.writer, "{}:list / {}:quit ? ", 'l'.bold(), 'q'.bold())?;

        self.writer.flush()
    }

    pub fn render(&mut self) -> Result<()> {
        // Prevent having the first line shifted if clearing wasn't successful.
        self.writer.write_all(b"\n")?;

        clear_terminal(&mut self.writer)?;

        self.writer.write_all(&self.output)?;
        self.writer.write_all(b"\n")?;

        if self.show_hint {
            writeln!(
                self.writer,
                "{}\n{}\n",
                "Hint".bold().cyan().underlined(),
                self.app_state.current_exercise().hint,
            )?;
        }

        if self.done_status != DoneStatus::Pending {
            writeln!(
                self.writer,
                "{}\n",
                "Exercise done ✓
When you are done experimenting, enter `n` to move on to the next exercise 🦀"
                    .bold()
                    .green(),
            )?;
        }

        if let DoneStatus::DoneWithSolution(solution_path) = &self.done_status {
            writeln!(
                self.writer,
                "A solution file can be found at {}\n",
                style(TerminalFileLink(solution_path)).underlined().green(),
            )?;
        }

        let line_width = terminal::size()?.0;
        let progress_bar = progress_bar(
            self.app_state.n_done(),
            self.app_state.exercises().len() as u16,
            line_width,
        )?;
        writeln!(
            self.writer,
            "{progress_bar}Current exercise: {}",
            self.app_state.current_exercise().terminal_link(),
        )?;

        self.show_prompt()?;

        Ok(())
    }

    pub fn show_hint(&mut self) -> Result<()> {
        self.show_hint = true;
        self.render()
    }
}