use std::{
    error::Error,
    fmt::{self, Debug, Display},
    fs::{File, OpenOptions},
    io::{Read, Seek, SeekFrom, Write},
    path::Path,
};

use eframe::egui::{self, Key, TextEdit, ViewportBuilder};

enum RunError {
    HomeDir(homedir::GetHomeError),
    NoHome,
    OpenFile(std::io::Error),
    EFrame(eframe::Error),
}

impl Debug for RunError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        Display::fmt(self, f)
    }
}
impl Display for RunError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::HomeDir(e) => f.write_fmt(format_args!("homedir error: {e}")),
            Self::NoHome => f.write_fmt(format_args!("failed to find home directory")),
            Self::OpenFile(e) => f.write_fmt(format_args!("error while opening todo.txt: {e}")),
            Self::EFrame(e) => f.write_fmt(format_args!("eframe error: {e}")),
        }
    }
}
impl Error for RunError {}

fn main() -> Result<(), RunError> {
    std::env::set_var("WINIT_UNIX_BACKEND", "wayland");
    let home_dir = homedir::get_my_home()
        .map_err(RunError::HomeDir)?
        .ok_or(RunError::NoHome)?;
    let todo_file = OpenOptions::new()
        .create(true)
        .read(true)
        .write(true)
        .append(false)
        .open(Path::join(&home_dir, "todo.txt"))
        .map_err(RunError::OpenFile)?;

    let native_options = eframe::NativeOptions {
        viewport: ViewportBuilder::default().with_app_id("todoodoo"),
        ..Default::default()
    };
    eframe::run_native(
        "To-DooDoo",
        native_options,
        Box::new(|_cc| Box::new(ToDooDooApp::new(todo_file))),
    )
    .map_err(RunError::EFrame)?;
    Ok(())
}

struct ToDooDooApp {
    notes: String,
    file: File,
}

impl ToDooDooApp {
    fn new(mut file: File) -> Self {
        let mut notes = String::with_capacity(
            file.metadata()
                .expect("file metadata")
                .len()
                .try_into()
                .expect("file too big"),
        );
        file.read_to_string(&mut notes)
            .expect("failed to read file");
        Self { file, notes }
    }

    fn save(&mut self) {
        self.file.set_len(0).expect("failed to truncate file");
        self.file.seek(SeekFrom::Start(0)).expect("failed to seek");
        self.file
            .write_all(self.notes.as_bytes())
            .expect("failed to write file");
        self.file.flush().expect("failed to flush");
    }
}

impl eframe::App for ToDooDooApp {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        egui::CentralPanel::default().show(ctx, |ui| {
            if ctx.input(|i| i.key_pressed(Key::S) && i.modifiers.command) {
                self.save();
            }
            ui.add_sized(ui.available_size(), TextEdit::multiline(&mut self.notes));
        });
    }
}