use std::borrow::Cow;
use std::convert::TryFrom;

use sexp::{Atom, Sexp};

use crate::asm::data::{DataDisp, Rd, RdData, reg, Wr, WrData};
use crate::asm::data::literal::{ConstantName, Label, RegisterAlias, Value};
use crate::asm::error::CrsnError;
use crate::asm::parse::ParserContext;
use crate::asm::parse::sexp_expect::expect_string_atom;

fn is_valid_identifier(name: &str) -> bool {
    name.starts_with(|c: char| c.is_ascii_alphabetic() || c == '_')
        && name.chars().find(|c| !c.is_ascii_alphanumeric() && *c != '_').is_none()
}

/// Parse register alias
pub fn parse_reg_alias(name: Option<Sexp>) -> Result<RegisterAlias, CrsnError> {
    // trace!("parse reg alias: {:?}", name);

    let name = expect_string_atom(name)?;

    if !is_valid_identifier(&name) {
        return Err(CrsnError::Parse(format!("\"{}\" is not an allowed register alias.", name).into()));
    }

    Ok(name)
}

/// Parse constant name
pub fn parse_constant_name(name: Option<Sexp>) -> Result<ConstantName, CrsnError> {
    // trace!("parse const name: {:?}", name);

    let name = expect_string_atom(name)?;

    if !is_valid_identifier(&name) {
        return Err(CrsnError::Parse(format!("\"{}\" is not an allowed constant name.", name).into()));
    }

    Ok(name)
}

/// Parse a label
pub fn parse_label(name: Option<Sexp>) -> Result<Label, CrsnError> {
    // trace!("parse label: {:?}", name);

    let name = expect_string_atom(name)?;
    Ok(Label::Named(name.trim_start_matches(':').into()))
}

/// Parse data disposition (address/value, without the read/write restriction)
pub fn parse_data_disp(tok: Option<Sexp>, pcx: &ParserContext) -> Result<DataDisp, CrsnError> {
    // trace!("parse data: {:?}", tok);

    let tok = if let Some(tok) = tok {
        tok
    } else {
        return Err(CrsnError::Parse("Expected data disposition token".into()));
    };

    // TODO implement masks

    match &tok {
        Sexp::Atom(Atom::I(val)) => {
            Ok(DataDisp::Immediate(unsafe { std::mem::transmute(*val) }))
        }
        Sexp::Atom(Atom::S(s)) => {
            if s == "_" {
                return Ok(DataDisp::Discard);
            }

            // check if we have an alias defined
            {
                let pstate = pcx.state.borrow();
                if let Some(val) = pstate.constants.get(s) {
                    return Ok(DataDisp::Immediate(*val));
                }

                if let Some(val) = pstate.reg_aliases.get(s) {
                    return Ok(DataDisp::Register(*val));
                }
            }

            if let Some(reference) = s.strip_prefix('@') {
                Ok(DataDisp::ObjectPtr(reg::parse_reg(reference)?))
            } else if s.starts_with(|c: char| c.is_ascii_digit()) {
                Ok(DataDisp::Immediate(unsafe { std::mem::transmute(parse_i64(s)?) }))
            } else {
                Ok(DataDisp::Register(reg::parse_reg(s)?))
            }
        }
        _ => {
            Err(CrsnError::Parse(format!("bad data disp: {:?}", tok).into()))
        }
    }
}

/// Parse immediate value
pub fn parse_value(tok: Option<Sexp>) -> Result<Value, CrsnError> {
    let tok = if let Some(tok) = tok {
        tok
    } else {
        return Err(CrsnError::Parse("Expected value token".into()));
    };

    // trace!("parse value: {:?}", tok);

    match &tok {
        Sexp::Atom(Atom::I(val)) => {
            Ok(unsafe { std::mem::transmute(*val) })
        }
        Sexp::Atom(Atom::S(s)) => {
            Ok(unsafe { std::mem::transmute(parse_i64(s)?) })
        }
        _ => {
            Err(CrsnError::Parse(format!("bad value format: {:?}", tok).into()))
        }
    }
}


pub fn parse_u64(literal: &str) -> anyhow::Result<u64> {
    // trace!("parse u64 from {}", literal);
    let mut without_underscores = Cow::Borrowed(literal);
    if without_underscores.contains('_') {
        without_underscores = without_underscores.replace('_', "").into();
    }

    if let Some(hex) = without_underscores.strip_prefix("0x") {
        Ok(u64::from_str_radix(hex, 16)?)
    } else if let Some(hex) = without_underscores.strip_prefix("0b") {
        Ok(u64::from_str_radix(hex, 2)?)
    } else {
        Ok(u64::from_str_radix(&without_underscores, 10)?)
    }
}

pub fn parse_i64(literal: &str) -> anyhow::Result<i64> {
    // trace!("parse i64 from {}", literal);
    if let Some(_value) = literal.strip_prefix("-") {
        Ok(-1 * i64::try_from(parse_u64(literal)?)?)
    } else {
        Ok(i64::try_from(parse_u64(literal)?)?)
    }
}

pub fn parse_rd(tok: Option<Sexp>, pcx: &ParserContext) -> anyhow::Result<Rd> {
    Ok(Rd::new(RdData::try_from(parse_data_disp(tok, pcx)?)?))
}

pub fn parse_wr(tok: Option<Sexp>, pcx: &ParserContext) -> anyhow::Result<Wr> {
    Ok(Wr::new(WrData::try_from(parse_data_disp(tok, pcx)?)?))
}