/* relish: versatile lisp shell
 * Copyright (C) 2021 Aidan Hahn
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

use crate::eval::eval;
use crate::lex::lex;
use crate::segment::{Ctr, Seg};
use crate::sym::{Args, SymTable, Symbol, ValueType};
use std::path::Path;
use std::fs;
use std::iter::FromIterator;
use std::env::{vars, var, current_dir};
use std::rc::Rc;

fn prompt_default_callback(_: &Seg, _: &mut SymTable) -> Result<Ctr, String> {
    Ok(Ctr::Symbol("λ".to_string()))
}

fn get_paths() -> Vec<String> {
    Vec::from_iter(var("PATH")
                   .unwrap_or("".to_string().into())
                   .split(':')
                   .map(String::from))
}

pub fn load_defaults(syms: &mut SymTable) {
    syms.insert(
        "CFG_RELISH_POSIX".to_string(),
        Symbol {
            name: String::from("CFG_RELISH_POSIX"),
            args: Args::None,
            conditional_branches: false,
            docs: "variable holding whether or not POSIX job control functions are to be loaded.
    checked at shell startup by configuration daemon. not used afterwards.

    default value: false".to_string(),
            value: ValueType::VarForm(Box::new(Ctr::Bool(false))),
            ..Default::default()
        },
    );

    syms.insert(
        "CFG_RELISH_ENV".to_string(),
        Symbol {
            name: String::from("CFG_RELISH_ENV"),
            args: Args::None,
            conditional_branches: false,
            docs: "variable holding whether or not vars and other symbols should be linked to process environment variables.
If set/defined all calls to def will result in additions or subtractions from user environment variables.
checked at shell startup by configuration daemon. not used afterwards.

default value: 1 (set)
".to_string(),
            value: ValueType::VarForm(Box::new(Ctr::Bool(true))),
            ..Default::default()
        },
    );

    syms.insert(
        "CFG_RELISH_PROMPT".to_string(),
        Symbol {
            name: String::from("default relish prompt"),
            args: Args::None,
            conditional_branches: false,
            docs: "function called to output prompt. this function is called with no arguments.
default value (<lambda>)"
                .to_string(),
            value: ValueType::Internal(Rc::new(prompt_default_callback)),
            ..Default::default()
        },
    );
}

pub fn load_environment(syms: &mut SymTable) {
    for (key, value) in vars() {
        syms.insert(
            key.clone(),
            Symbol{
                name: key,
                args: Args::None,
                conditional_branches: false,
                docs: String::from("from env vars at time of load"),
                value: ValueType::VarForm(Box::new(Ctr::String(value))),
                ..Default::default()
            }
        );
    }
}

pub fn run(filename: String, syms: &mut SymTable) -> Result<(), String> {
    let script_read_res = fs::read_to_string(filename);
    if script_read_res.is_err() {
        Err(format!("Couldnt read script: {}", script_read_res.err().unwrap()))
    } else {
        let script_read = script_read_res.unwrap() + ")";
        let script = "(".to_string() + &script_read;
        eval(&*lex(&script)?, syms)?;
        Ok(())
    }
}

pub const RUN_DOCSTRING: &str = "Takes one string argument.
Attempts to find argument in PATH and attempts to call argument";

pub fn run_callback(ast: &Seg, syms: &mut SymTable) ->  Result<Ctr, String> {
    let mut prefixes = get_paths();
    if let Ok(s) = current_dir() {
        prefixes.push(String::from(s.to_str().unwrap()));
    }
    prefixes.push(String::from("/"));
    if let Ctr::String(ref filename) = *ast.car {
        for prefix in prefixes {
            let candidate = Path::new(&prefix.clone()).join(filename);
            if candidate.exists() {
                if filename.ends_with(".rls") {
                    return run(String::from(candidate.to_str().unwrap()), syms)
                        .and(Ok(Ctr::None))
                } else {
                    return Err("binary called, unimplemented!".to_string())
                }
            }
        }

        Err(format!("file {} not found", filename))
    } else {
        Err("impossible: not a string".to_string())
    }
}