#![forbid(unsafe_code)]
use crate::types::*;
use smol::prelude::*;

use smol::fs::File;
use smol::lock::RwLock;
use std::path::PathBuf;
use std::process::ExitCode;
use std::ops::Range;

mod encoding;
mod terminal;
mod types;


struct Ivy {
  terminal: RwLock<Terminal>,
  buffer: RwLock<Buffer>,
  window: RwLock<Window>,
  argument_files: Vec<PathBuf>,
}

struct Buffer {
  path: Option<PathBuf>,
  contents: RwLock<Vec<u8>>,
  lines: RwLock<Vec<usize>>,
  has_end_newline: RwLock<bool>,
}

struct Window {
  /* The traditional order of writing "row, column" is the opposite of the
   * traditional order of writing "x, y"; be mindful. An alternate approach
   * would use "x" and "y" for all the names, which might arguably reduce
   * confusion, but personally we find the ordering concern to be
   * aesthetically pleasing, a quiet reminder of how much humans care about
   * everything.
   */
  cursor_row: RwLock<usize>,
  cursor_column: RwLock<usize>,
  /* The neutral column is the one that vertical movement will attempt to
   * land in, if it exists in the target row.
   */
  cursor_neutral_column: RwLock<usize>,
  scroll_top: RwLock<usize>,
}


fn main() -> ExitCode {
  smol::block_on(async {
    if let Err(e) = Ivy::new().await.run().await {
      println!("{:?}", e);
      ExitCode::FAILURE
    } else {
      ExitCode::SUCCESS
    }
  })
}


impl Ivy {
  async fn new() -> Self {
    Ivy {
      terminal: RwLock::new(Terminal::new().await),
      buffer: RwLock::new(Buffer::new().await),
      window: RwLock::new(Window::new().await),
      argument_files: Vec::new(),
    }
  }

  async fn run(mut self) -> Result<()> {
    /* The awkward structure here is because it's important that cleanup still
     * happen even if something fails in the middle.
     */
    let mut error = None;

    error = error.or(self.init().await.err());
    error = error.or(self.interact().await.err());
    error = error.or(self.zap().await.err());

    if let Some(error) = error {
      Err(error)
    } else {
      Ok(())
    }
  }

  async fn init(&mut self) -> Result<()> {
    self.init_arguments().await?;
    self.init_editor().await?;

    self.terminal.write().await.init_termios().await?;
    self.terminal.write().await.init_full_screen().await?;

    Ok(())
  }

  async fn zap(&mut self) -> Result<()> {
    let mut error = None;

    error = error.or(
        self.terminal.write().await.zap_full_screen().await.err());
    error = error.or(
        self.terminal.write().await.zap_termios().await.err());

    if let Some(error) = error {
      Err(error)
    } else {
      Ok(())
    }
  }

  async fn init_arguments(&mut self) -> Result<()> {
    self.argument_files.clear();

    let mut args = std::env::args();

    let _ = args.next();

    for argument in args {
      self.argument_files.push(argument.into());
    }

    Ok(())
  }

  async fn init_editor(&mut self) -> Result<()> {
    if !self.argument_files.is_empty() {
      let path = self.argument_files.remove(0);
      let new_buffer = Buffer::from_file(path).await?;
      *self.buffer.write().await = new_buffer;
    }

    Ok(())
  }

  async fn draw(&mut self) -> Result<()> {
    let mut terminal = self.terminal.write().await;
    let buffer = self.buffer.read().await;

    let height = *terminal.height.read().await;

    let window = self.window.read().await;
    let scroll_top = *window.scroll_top.read().await;

    let mut screen_y = 0;
    for i in 0 .. height - 1 {
      if let Some(span) = buffer.line_span(i + scroll_top).await {
        if i > 0 {
          terminal.stdout.write_all("\n".as_bytes()).await?;
        }

        terminal.stdout.write_all(&buffer.contents.read().await[span]).await?;

        screen_y += 1;
      } else {
        break;
      }
    }

    for _ in screen_y .. height - 1 {
      terminal.stdout.write_all("\n~".as_bytes()).await?;
    }

    terminal.stdout.write_all("\n        status goes here".as_bytes()).await?;

    let window = self.window.read().await;
    terminal.do_cursor_position(*window.cursor_column.read().await,
                                *window.cursor_row.read().await
                                - *window.scroll_top.read().await).await?;
    terminal.stdout.flush().await?;

    Ok(())
  }

  async fn interact(&mut self) -> Result<()> {
    self.draw().await?;

    loop {
      let c = self.terminal.write().await.read_char().await?;

      match c {
        'h' => {
          self.handle_movement(async |ivy: &mut Ivy| {
            let window = ivy.window.write().await;

            let mut column = window.cursor_column.write().await;
            if *column > 0 {
              *column -= 1;

              /* The neutral column only changes if the horizontal part of
               * the movement actually moves. Tentatively, it doesn't look
               * like POSIX has an opinion on this, but it matches Vim.
               */
              *window.cursor_neutral_column.write().await = *column;
            }

            Ok(())
          }).await?;
        },

        'j' => {
          self.handle_movement(async |ivy: &mut Ivy| {
            let buffer = ivy.buffer.read().await;
            let window = ivy.window.write().await;

            let mut row = window.cursor_row.write().await;
            if *row + 1 < buffer.lines.read().await.len() {
              *row += 1;
            };

            Ok(())
          }).await?;
        },

        'k' => {
          self.handle_movement(async |ivy: &mut Ivy| {
            let window = ivy.window.write().await;

            let mut row = window.cursor_row.write().await;
            if *row > 0 {
              *row -= 1;
            }

            Ok(())
          }).await?;
        },

        'l' => {
          self.handle_movement(async |ivy: &mut Ivy| {
            let buffer = ivy.buffer.read().await;
            let window = ivy.window.write().await;

            let row = *window.cursor_row.read().await;
            if let Some(span) = buffer.line_span(row).await {
              let width = span.end - span.start;

              let mut column = window.cursor_column.write().await;
              if *column + 1 < width {
                *column += 1;

                /* The neutral column only changes if the horizontal part of
                 * the movement actually moves. Tentatively, it doesn't look
                 * like POSIX has an opinion on this, but it matches Vim.
                 */
                *window.cursor_neutral_column.write().await = *column;
              }
            }

            Ok(())
          }).await?;
        },

        '0' => {
          self.handle_movement(async |ivy: &mut Ivy| {
            let window = ivy.window.write().await;

            let mut column = window.cursor_column.write().await;
            *column = 0;

            /* For this one, the neutral column changes regardless of
             * whether the column does.
             */
            *window.cursor_neutral_column.write().await = *column;

            Ok(())
          }).await?;
        },

        '$' => {
          self.handle_movement(async |ivy: &mut Ivy| {
            let buffer = ivy.buffer.read().await;
            let window = ivy.window.write().await;

            let row = *window.cursor_row.read().await;
            if let Some(span) = buffer.line_span(row).await {
              let width = span.end - span.start;

              let mut column = window.cursor_column.write().await;
              if width > 0 {
                *column = width - 1;
              } else {
                *column = 0;
              }

              /* For this one, the neutral column changes regardless of
               * whether the column does.
               */
              *window.cursor_neutral_column.write().await = *column;
            }

            Ok(())
          }).await?;
        },

        _ => {
          return Ok(());
        },
      }
    }
  }

  /* A movement is an arbitrarily complicated action that will not change the
   * contents of the buffer, but may change other things, including the cursor
   * position.
   */
  async fn handle_movement(&mut self,
                           movement: impl AsyncFn(&mut Ivy) -> Result<()>)
      -> Result<()>
  {
    let (old_row, old_column) = {
      let window = self.window.read().await;

      (*window.cursor_row.read().await,
       *window.cursor_column.read().await)
    };

    movement(self).await?;

    /* We clamp the column to the line width unconditionally, regardless of
     * what kind of movement we did. This is always correct, because no
     * intended behavior ever places the cursor beyond the end of the line.
     * It does require taking a couple of locks that we might always need, but
     * there's no strong reason to avoid that.
     */
    self.clamp_cursor_column().await?;

    self.scroll_to_cursor().await?;

    {
      let window = self.window.read().await;
      let row = *window.cursor_row.read().await;
      let column = *window.cursor_column.read().await;

      if old_row != row || old_column != column {
        let mut terminal = self.terminal.write().await;
        let scroll_top = *window.scroll_top.read().await;

        terminal.do_cursor_position(column, row - scroll_top).await?;
        terminal.stdout.flush().await?;
      }
    }

    Ok(())
  }

  async fn clamp_cursor_column(&mut self) -> Result<()> {
    let window = self.window.write().await;
    let row = window.cursor_row.read().await;
    let mut column = window.cursor_column.write().await;
    let buffer = self.buffer.read().await;

    if let Some(span) = buffer.line_span(*row).await {
      let width = span.end - span.start;
      let neutral_column = *window.cursor_neutral_column.read().await;

      if neutral_column < width {
        *column = neutral_column;
      } else if width > 0 {
        *column = width - 1;
      } else {
        *column = 0;
      }
    }

    Ok(())
  }

  async fn scroll_to_cursor(&mut self) -> Result<()> {
    let old_scroll_top = *self.window.read().await.scroll_top.read().await;

    {
      let terminal = self.terminal.read().await;
      let window = self.window.write().await;

      let mut scroll_top = window.scroll_top.write().await;
      let row = *window.cursor_row.read().await;
      let height = *terminal.height.read().await;
      let last_visible = *scroll_top + height - 2;

      if row < *scroll_top {
        *scroll_top -= *scroll_top - row;
      } else if row > last_visible {
        *scroll_top += row - last_visible;
      }
    }

    let new_scroll_top = *self.window.read().await.scroll_top.read().await;
    if old_scroll_top != new_scroll_top {
      self.terminal.write().await.clear().await?;
      self.draw().await?;
    }

    Ok(())
  }
}


impl Buffer {
  pub async fn new() -> Self {
    Buffer {
      path: None,
      contents: RwLock::new("\n".to_string().into_bytes()),
      lines: RwLock::new(vec![0]),
      has_end_newline: RwLock::new(true),
    }
  }

  pub async fn from_file(path: PathBuf) -> Result<Self> {
    let mut file = File::open(&path).await?;

    let mut contents = Vec::new();
    let _ = file.read_to_end(&mut contents).await?;

    let mut result = Buffer {
      path: Some(path),
      contents: RwLock::new(contents),
      lines: RwLock::new(vec![0]),
      has_end_newline: RwLock::new(true),
    };

    result.count_lines().await;

    Ok(result)
  }

  pub async fn count_lines(&mut self) {
    let contents = self.contents.read().await;

    *self.lines.write().await = vec![0];

    if contents.len() == 0 {
      *self.has_end_newline.write().await = false;
    } else {
      let mut offset = 0;

      while offset < contents.len() {
        let c = contents[offset];

        offset += 1;

        if c == b'\n' {
          if offset < contents.len() {
            self.lines.write().await.push(offset);
          } else {
            *self.has_end_newline.write().await = true;
          }
        } else if offset == contents.len() {
          *self.has_end_newline.write().await = false;
        }
      }
    }
  }

  pub async fn line_span(&self, index: usize) -> Option<Range<usize>> {
    let lines = self.lines.read().await;

    if index < lines.len() {
      let start = lines[index];

      if index + 1 < lines.len() {
        let end = lines[index + 1] - 1;

        Some(start .. end)
      } else {
        let end = if *self.has_end_newline.read().await {
          self.contents.read().await.len() - 1
        } else {
          self.contents.read().await.len()
        };

        Some(start .. end)
      }
    } else {
      None
    }
  }
}


impl Window {
  pub async fn new() -> Self {
    Window {
      cursor_row: RwLock::new(0),
      cursor_column: RwLock::new(0),
      cursor_neutral_column: RwLock::new(0),
      scroll_top: RwLock::new(0),
    }
  }
}