// Copyright 2017 Mozilla
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
// this file except in compliance with the License. You may obtain a copy of the
// License at http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software distributed
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied. See the License for the
// specific language governing permissions and limitations under the License.

use std::io::stdin;

use linefeed::{
    DefaultTerminal,
    Reader,
    ReadResult,
    Signal,
};

use termion::{
    color,
};

use self::InputResult::*;

use command_parser::{
    Command,
    command,
};

use failure::Error;

/// Starting prompt
const DEFAULT_PROMPT: &'static str = "mentat=> ";
/// Prompt when further input is being read
// TODO: Should this actually reflect the current open brace?
const MORE_PROMPT: &'static str = "mentat.> ";

/// Possible results from reading input from `InputReader`
#[derive(Clone, Debug)]
pub enum InputResult {
    /// mentat command as input; (name, rest of line)
    MetaCommand(Command),
    /// An empty line
    Empty,
    /// Needs more input
    More,
    /// End of file reached
    Eof,
}

/// Reads input from `stdin`
pub struct InputReader {
    buffer: String,
    reader: Option<Reader<DefaultTerminal>>,
    in_process_cmd: Option<Command>,
}

enum UserAction {
    // We've received some text that we should interpret as a new command, or
    // as part of the current command.
    TextInput(String),
    // We were interrupted, if we have a current command we should clear it,
    // otherwise we should exit. Currently can only be generated by reading from
    // a terminal (and not by reading from stdin).
    Interrupt,
    // We hit the end of the file, there was an error getting user input, or
    // something else happened that means we should exit.
    Quit,
}

impl InputReader {
    /// Constructs a new `InputReader` reading from `stdin`.
    pub fn new() -> InputReader {
        let r = match Reader::new("mentat") {
            Ok(mut r) => {
                // Handle SIGINT (Ctrl-C)
                r.set_report_signal(Signal::Interrupt, true);
                r.set_word_break_chars(" \t\n!\"#$%&'(){}*+,-./:;<=>?@[\\]^`");
                Some(r)
            },
            Err(_) => None,
        };

        InputReader{
            buffer: String::new(),
            reader: r,
            in_process_cmd: None,
        }
    }

    /// Returns whether the `InputReader` is reading from a TTY.
    pub fn is_tty(&self) -> bool {
        self.reader.is_some()
    }

    /// Reads a single command, item, or statement from `stdin`.
    /// Returns `More` if further input is required for a complete result.
    /// In this case, the input received so far is buffered internally.
    pub fn read_input(&mut self) -> Result<InputResult, Error> {
        let prompt = if self.in_process_cmd.is_some() { MORE_PROMPT } else { DEFAULT_PROMPT };
        let prompt = format!("{blue}{prompt}{reset}",
                             blue = color::Fg(::BLUE),
                             prompt = prompt,
                             reset = color::Fg(color::Reset));
        let line = match self.read_line(prompt.as_str()) {
            UserAction::TextInput(s) => s,
            UserAction::Interrupt if self.in_process_cmd.is_some() => {
                self.in_process_cmd = None;
                self.buffer.clear();
                // Move to the next line, so that our next prompt isn't on top
                // of the previous.
                println!();
                String::new()
            },
            _ => return Ok(Eof),
        };

        if !self.buffer.is_empty() {
            self.buffer.push('\n');
        }

        self.buffer.push_str(&line);

        if self.buffer.is_empty() {
            return Ok(Empty);
        }

        // if we have a command in process (i.e. an incomplete query or transaction),
        // then we already know which type of command it is and so we don't need to parse the
        // command again, only the content, which we do later.
        // Therefore, we add the newly read in line to the existing command args.
        // If there is no in process command, we parse the read in line as a new command.
        let cmd = match &self.in_process_cmd {
            &Some(Command::QueryPrepared(ref args)) => {
                Ok(Command::QueryPrepared(args.clone() + " " + &line))
            },
            &Some(Command::Query(ref args)) => {
                Ok(Command::Query(args.clone() + " " + &line))
            },
            &Some(Command::Transact(ref args)) => {
                Ok(Command::Transact(args.clone() + " " + &line))
            },
            _ => {
                command(&self.buffer)
            },
        };

        match cmd {
            Ok(cmd) => {
                match cmd {
                    Command::Query(_) |
                    Command::QueryPrepared(_) |
                    Command::Transact(_) |
                    Command::QueryExplain(_) if !cmd.is_complete() => {
                        // A query or transact is complete if it contains a valid EDN.
                        // if the command is not complete, ask for more from the REPL and remember
                        // which type of command we've found here.
                        self.in_process_cmd = Some(cmd);
                        Ok(More)
                    },
                    _ => {
                        let entry = self.buffer.clone();
                        self.buffer.clear();
                        self.add_history(entry);
                        self.in_process_cmd = None;
                        Ok(InputResult::MetaCommand(cmd))
                    }
                }
            },
            Err(e) => {
                let entry = self.buffer.clone();
                self.buffer.clear();
                self.add_history(entry);
                self.in_process_cmd = None;
                Err(e)
            },
        }
    }

    fn read_line(&mut self, prompt: &str) -> UserAction {
        match self.reader {
            Some(ref mut r) => {
                r.set_prompt(prompt);
                r.read_line().ok().map_or(UserAction::Quit, |line|
                    match line {
                        ReadResult::Input(s) => UserAction::TextInput(s),
                        ReadResult::Signal(Signal::Interrupt) =>
                            UserAction::Interrupt,
                        _ => UserAction::Quit,
                    })

            },
            None => self.read_stdin()
        }
    }

    fn read_stdin(&self) -> UserAction {
        let mut s = String::new();

        match stdin().read_line(&mut s) {
            Ok(0) | Err(_) => UserAction::Quit,
            Ok(_) => UserAction::TextInput(s)
        }
    }

    fn add_history(&mut self, line: String) {
        if let Some(ref mut r) = self.reader {
            r.add_history(line);
        }
    }
}