use super::super::format::{FormatParseError, FormatPart, FormatString};
use super::super::pyobject::{
    PyContext, PyFuncArgs, PyObject, PyObjectPayload, PyObjectRef, PyResult, TypeProtocol,
};
use super::super::vm::VirtualMachine;
use super::objint;
use super::objsequence::PySliceableSequence;
use super::objtype;
use num_traits::ToPrimitive;
use std::hash::{Hash, Hasher};
// rust's builtin to_lowercase isn't sufficient for casefold
extern crate caseless;
extern crate unicode_segmentation;

use self::unicode_segmentation::UnicodeSegmentation;

pub fn init(context: &PyContext) {
    let str_type = &context.str_type;
    context.set_attr(&str_type, "__add__", context.new_rustfunc(str_add));
    context.set_attr(&str_type, "__eq__", context.new_rustfunc(str_eq));
    context.set_attr(
        &str_type,
        "__contains__",
        context.new_rustfunc(str_contains),
    );
    context.set_attr(&str_type, "__getitem__", context.new_rustfunc(str_getitem));
    context.set_attr(&str_type, "__gt__", context.new_rustfunc(str_gt));
    context.set_attr(&str_type, "__lt__", context.new_rustfunc(str_lt));
    context.set_attr(&str_type, "__hash__", context.new_rustfunc(str_hash));
    context.set_attr(&str_type, "__len__", context.new_rustfunc(str_len));
    context.set_attr(&str_type, "__mul__", context.new_rustfunc(str_mul));
    context.set_attr(&str_type, "__new__", context.new_rustfunc(str_new));
    context.set_attr(&str_type, "__str__", context.new_rustfunc(str_str));
    context.set_attr(&str_type, "__repr__", context.new_rustfunc(str_repr));
    context.set_attr(&str_type, "format", context.new_rustfunc(str_format));
    context.set_attr(&str_type, "lower", context.new_rustfunc(str_lower));
    context.set_attr(&str_type, "casefold", context.new_rustfunc(str_casefold));
    context.set_attr(&str_type, "upper", context.new_rustfunc(str_upper));
    context.set_attr(
        &str_type,
        "capitalize",
        context.new_rustfunc(str_capitalize),
    );
    context.set_attr(&str_type, "split", context.new_rustfunc(str_split));
    context.set_attr(&str_type, "rsplit", context.new_rustfunc(str_rsplit));
    context.set_attr(&str_type, "strip", context.new_rustfunc(str_strip));
    context.set_attr(&str_type, "lstrip", context.new_rustfunc(str_lstrip));
    context.set_attr(&str_type, "rstrip", context.new_rustfunc(str_rstrip));
    context.set_attr(&str_type, "endswith", context.new_rustfunc(str_endswith));
    context.set_attr(
        &str_type,
        "startswith",
        context.new_rustfunc(str_startswith),
    );
    context.set_attr(&str_type, "isalnum", context.new_rustfunc(str_isalnum));
    context.set_attr(&str_type, "isnumeric", context.new_rustfunc(str_isnumeric));
    context.set_attr(&str_type, "isdigit", context.new_rustfunc(str_isdigit));
    context.set_attr(&str_type, "isdecimal", context.new_rustfunc(str_isdecimal));
    context.set_attr(&str_type, "title", context.new_rustfunc(str_title));
    context.set_attr(&str_type, "swapcase", context.new_rustfunc(str_swapcase));
    context.set_attr(&str_type, "isalpha", context.new_rustfunc(str_isalpha));
    context.set_attr(&str_type, "replace", context.new_rustfunc(str_replace));
    context.set_attr(&str_type, "center", context.new_rustfunc(str_center));
    context.set_attr(&str_type, "isspace", context.new_rustfunc(str_isspace));
    context.set_attr(&str_type, "isupper", context.new_rustfunc(str_isupper));
    context.set_attr(&str_type, "islower", context.new_rustfunc(str_islower));
    context.set_attr(&str_type, "isascii", context.new_rustfunc(str_isascii));
    context.set_attr(
        &str_type,
        "splitlines",
        context.new_rustfunc(str_splitlines),
    );
    context.set_attr(&str_type, "join", context.new_rustfunc(str_join));
    context.set_attr(&str_type, "find", context.new_rustfunc(str_find));
    context.set_attr(&str_type, "rfind", context.new_rustfunc(str_rfind));
    context.set_attr(&str_type, "index", context.new_rustfunc(str_index));
    context.set_attr(&str_type, "rindex", context.new_rustfunc(str_rindex));
    context.set_attr(&str_type, "partition", context.new_rustfunc(str_partition));
    context.set_attr(
        &str_type,
        "rpartition",
        context.new_rustfunc(str_rpartition),
    );
    context.set_attr(&str_type, "istitle", context.new_rustfunc(str_istitle));
    context.set_attr(&str_type, "count", context.new_rustfunc(str_count));
    context.set_attr(&str_type, "zfill", context.new_rustfunc(str_zfill));
    context.set_attr(&str_type, "ljust", context.new_rustfunc(str_ljust));
    context.set_attr(&str_type, "rjust", context.new_rustfunc(str_rjust));
    context.set_attr(
        &str_type,
        "expandtabs",
        context.new_rustfunc(str_expandtabs),
    );
    context.set_attr(
        &str_type,
        "isidentifier",
        context.new_rustfunc(str_isidentifier),
    );
}

pub fn get_value(obj: &PyObjectRef) -> String {
    if let PyObjectPayload::String { value } = &obj.borrow().payload {
        value.to_string()
    } else {
        panic!("Inner error getting str");
    }
}

fn str_eq(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(a, Some(vm.ctx.str_type())), (b, None)]
    );

    let result = if objtype::isinstance(b, &vm.ctx.str_type()) {
        get_value(a) == get_value(b)
    } else {
        false
    };
    Ok(vm.ctx.new_bool(result))
}

fn str_gt(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [
            (zelf, Some(vm.ctx.str_type())),
            (other, Some(vm.ctx.str_type()))
        ]
    );
    let zelf = get_value(zelf);
    let other = get_value(other);
    let result = zelf > other;
    Ok(vm.ctx.new_bool(result))
}

fn str_lt(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [
            (zelf, Some(vm.ctx.str_type())),
            (other, Some(vm.ctx.str_type()))
        ]
    );
    let zelf = get_value(zelf);
    let other = get_value(other);
    let result = zelf < other;
    Ok(vm.ctx.new_bool(result))
}

fn str_str(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    Ok(s.clone())
}

fn count_char(s: &str, c: char) -> usize {
    s.chars().filter(|x| *x == c).count()
}

fn str_repr(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(s);
    let quote_char = if count_char(&value, '\'') > count_char(&value, '"') {
        '"'
    } else {
        '\''
    };
    let mut formatted = String::new();
    formatted.push(quote_char);
    for c in value.chars() {
        if c == quote_char || c == '\\' {
            formatted.push('\\');
            formatted.push(c);
        } else if c == '\n' {
            formatted.push('\\');
            formatted.push('n');
        } else if c == '\t' {
            formatted.push('\\');
            formatted.push('t');
        } else if c == '\r' {
            formatted.push('\\');
            formatted.push('r');
        } else {
            formatted.push(c);
        }
    }
    formatted.push(quote_char);
    Ok(vm.ctx.new_str(formatted))
}

fn str_add(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (s2, None)]
    );
    if objtype::isinstance(s2, &vm.ctx.str_type()) {
        Ok(vm
            .ctx
            .new_str(format!("{}{}", get_value(&s), get_value(&s2))))
    } else {
        Err(vm.new_type_error(format!("Cannot add {} and {}", s.borrow(), s2.borrow())))
    }
}

fn str_format(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    if args.args.is_empty() {
        return Err(
            vm.new_type_error("descriptor 'format' of 'str' object needs an argument".to_string())
        );
    }

    let zelf = &args.args[0];
    if !objtype::isinstance(&zelf, &vm.ctx.str_type()) {
        let zelf_typ = zelf.typ();
        let actual_type = vm.to_pystr(&zelf_typ)?;
        return Err(vm.new_type_error(format!(
            "descriptor 'format' requires a 'str' object but received a '{}'",
            actual_type
        )));
    }
    let format_string_text = get_value(zelf);
    match FormatString::from_str(format_string_text.as_str()) {
        Ok(format_string) => perform_format(vm, &format_string, &args),
        Err(err) => match err {
            FormatParseError::UnmatchedBracket => {
                Err(vm.new_value_error("expected '}' before end of string".to_string()))
            }
            _ => Err(vm.new_value_error("Unexpected error parsing format string".to_string())),
        },
    }
}

fn call_object_format(
    vm: &mut VirtualMachine,
    argument: PyObjectRef,
    format_spec: &str,
) -> PyResult {
    let returned_type = vm.ctx.new_str(format_spec.to_string());
    let result = vm.call_method(&argument, "__format__", vec![returned_type])?;
    if !objtype::isinstance(&result, &vm.ctx.str_type()) {
        let result_type = result.typ();
        let actual_type = vm.to_pystr(&result_type)?;
        return Err(vm.new_type_error(format!("__format__ must return a str, not {}", actual_type)));
    }
    Ok(result)
}

fn perform_format(
    vm: &mut VirtualMachine,
    format_string: &FormatString,
    arguments: &PyFuncArgs,
) -> PyResult {
    let mut final_string = String::new();
    if format_string.format_parts.iter().any(FormatPart::is_auto)
        && format_string.format_parts.iter().any(FormatPart::is_index)
    {
        return Err(vm.new_value_error(
            "cannot switch from automatic field numbering to manual field specification"
                .to_string(),
        ));
    }
    let mut auto_argument_index: usize = 1;
    for part in &format_string.format_parts {
        let result_string: String = match part {
            FormatPart::AutoSpec(format_spec) => {
                let result = match arguments.args.get(auto_argument_index) {
                    Some(argument) => call_object_format(vm, argument.clone(), &format_spec)?,
                    None => {
                        return Err(vm.new_index_error("tuple index out of range".to_string()));
                    }
                };
                auto_argument_index += 1;
                get_value(&result)
            }
            FormatPart::IndexSpec(index, format_spec) => {
                let result = match arguments.args.get(*index + 1) {
                    Some(argument) => call_object_format(vm, argument.clone(), &format_spec)?,
                    None => {
                        return Err(vm.new_index_error("tuple index out of range".to_string()));
                    }
                };
                get_value(&result)
            }
            FormatPart::KeywordSpec(keyword, format_spec) => {
                let result = match arguments.get_optional_kwarg(&keyword) {
                    Some(argument) => call_object_format(vm, argument.clone(), &format_spec)?,
                    None => {
                        return Err(vm.new_key_error(format!("'{}'", keyword)));
                    }
                };
                get_value(&result)
            }
            FormatPart::Literal(literal) => literal.clone(),
        };
        final_string.push_str(&result_string);
    }
    Ok(vm.ctx.new_str(final_string))
}

fn str_hash(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(zelf, Some(vm.ctx.str_type()))]);
    let value = get_value(zelf);
    let mut hasher = std::collections::hash_map::DefaultHasher::new();
    value.hash(&mut hasher);
    let hash = hasher.finish();
    Ok(vm.ctx.new_int(hash))
}

fn str_len(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let sv = get_value(s);
    Ok(vm.ctx.new_int(sv.chars().count()))
}

fn str_mul(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (s2, None)]
    );
    if objtype::isinstance(s2, &vm.ctx.int_type()) {
        let value1 = get_value(&s);
        let value2 = objint::get_value(s2).to_i32().unwrap();
        let mut result = String::new();
        for _x in 0..value2 {
            result.push_str(value1.as_str());
        }
        Ok(vm.ctx.new_str(result))
    } else {
        Err(vm.new_type_error(format!(
            "Cannot multiply {} and {}",
            s.borrow(),
            s2.borrow()
        )))
    }
}

fn str_upper(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s).to_uppercase();
    Ok(vm.ctx.new_str(value))
}

fn str_lower(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s).to_lowercase();
    Ok(vm.ctx.new_str(value))
}

fn str_capitalize(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    let (first_part, lower_str) = value.split_at(1);
    let capitalized = format!("{}{}", first_part.to_uppercase(), lower_str);
    Ok(vm.ctx.new_str(capitalized))
}

fn str_rsplit(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type()))],
        optional = [
            (pat, Some(vm.ctx.str_type())),
            (num, Some(vm.ctx.int_type()))
        ]
    );
    let value = get_value(&s);
    let pat = match pat {
        Some(s) => get_value(&s),
        None => " ".to_string(),
    };
    let num_splits = match num {
        Some(n) => objint::get_value(&n).to_usize().unwrap(),
        None => value.split(&pat).count(),
    };
    let elements = value
        .rsplitn(num_splits + 1, &pat)
        .map(|o| vm.ctx.new_str(o.to_string()))
        .collect();
    Ok(vm.ctx.new_list(elements))
}

fn str_split(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type()))],
        optional = [
            (pat, Some(vm.ctx.str_type())),
            (num, Some(vm.ctx.int_type()))
        ]
    );
    let value = get_value(&s);
    let pat = match pat {
        Some(s) => get_value(&s),
        None => " ".to_string(),
    };
    let num_splits = match num {
        Some(n) => objint::get_value(&n).to_usize().unwrap(),
        None => value.split(&pat).count(),
    };
    let elements = value
        .splitn(num_splits + 1, &pat)
        .map(|o| vm.ctx.new_str(o.to_string()))
        .collect();
    Ok(vm.ctx.new_list(elements))
}

fn str_strip(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s).trim().to_string();
    Ok(vm.ctx.new_str(value))
}

fn str_lstrip(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s).trim_start().to_string();
    Ok(vm.ctx.new_str(value))
}

fn str_rstrip(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s).trim_end().to_string();
    Ok(vm.ctx.new_str(value))
}

fn str_endswith(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (pat, Some(vm.ctx.str_type()))]
    );
    let value = get_value(&s);
    let pat = get_value(&pat);
    Ok(vm.ctx.new_bool(value.ends_with(pat.as_str())))
}

fn str_isidentifier(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    let mut is_identifier: bool = true;
    // a string is not an identifier if it has whitespace or starts with a number
    if !value.chars().any(|c| c.is_ascii_whitespace())
        && !value.chars().nth(0).unwrap().is_digit(10)
    {
        for c in value.chars() {
            if c != "_".chars().nth(0).unwrap() && !c.is_digit(10) && !c.is_alphabetic() {
                is_identifier = false;
            }
        }
    } else {
        is_identifier = false;
    }
    Ok(vm.ctx.new_bool(is_identifier))
}

// cpython's isspace ignores whitespace, including \t and \n, etc, unless the whole string is empty
// which is why isspace is using is_ascii_whitespace. Same for isupper & islower
fn str_isspace(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    Ok(vm
        .ctx
        .new_bool(!value.is_empty() && value.chars().all(|c| c.is_ascii_whitespace())))
}

fn str_isupper(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    Ok(vm.ctx.new_bool(
        !value.is_empty()
            && value
                .chars()
                .filter(|x| !x.is_ascii_whitespace())
                .all(|c| c.is_uppercase()),
    ))
}

fn str_islower(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    Ok(vm.ctx.new_bool(
        !value.is_empty()
            && value
                .chars()
                .filter(|x| !x.is_ascii_whitespace())
                .all(|c| c.is_lowercase()),
    ))
}

// doesn't implement keep new line delimeter just yet
fn str_splitlines(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let elements = get_value(&s)
        .split('\n')
        .map(|e| vm.ctx.new_str(e.to_string()))
        .collect();
    Ok(vm.ctx.new_list(elements))
}

fn str_zfill(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (len, Some(vm.ctx.int_type()))]
    );
    let value = get_value(&s);
    let len = objint::get_value(&len).to_usize().unwrap();
    let new_str = if len <= value.len() {
        value
    } else {
        format!("{}{}", "0".repeat(len - value.len()), value)
    };
    Ok(vm.ctx.new_str(new_str))
}

fn str_join(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (iterable, None)]
    );
    let value = get_value(&s);
    let elements: Vec<String> = vm
        .extract_elements(iterable)?
        .iter()
        .map(|w| get_value(&w))
        .collect();
    let joined = elements.join(&value);
    Ok(vm.ctx.new_str(joined))
}

fn str_count(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (sub, Some(vm.ctx.str_type()))],
        optional = [
            (start, Some(vm.ctx.int_type())),
            (end, Some(vm.ctx.int_type()))
        ]
    );
    let value = get_value(&s);
    let sub = get_value(&sub);
    let (start, end) = match get_slice(start, end, value.len()) {
        Ok((start, end)) => (start, end),
        Err(e) => return Err(vm.new_index_error(e)),
    };
    let num_occur: usize = value[start..end].matches(&sub).count();
    Ok(vm.ctx.new_int(num_occur))
}

fn str_index(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (sub, Some(vm.ctx.str_type()))],
        optional = [
            (start, Some(vm.ctx.int_type())),
            (end, Some(vm.ctx.int_type()))
        ]
    );
    let value = get_value(&s);
    let sub = get_value(&sub);
    let (start, end) = match get_slice(start, end, value.len()) {
        Ok((start, end)) => (start, end),
        Err(e) => return Err(vm.new_index_error(e)),
    };
    let ind: usize = match value[start..=end].find(&sub) {
        Some(num) => num,
        None => {
            return Err(vm.new_value_error("substring not found".to_string()));
        }
    };
    Ok(vm.ctx.new_int(ind))
}

fn str_find(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (sub, Some(vm.ctx.str_type()))],
        optional = [
            (start, Some(vm.ctx.int_type())),
            (end, Some(vm.ctx.int_type()))
        ]
    );
    let value = get_value(&s);
    let sub = get_value(&sub);
    let (start, end) = match get_slice(start, end, value.len()) {
        Ok((start, end)) => (start, end),
        Err(e) => return Err(vm.new_index_error(e)),
    };
    let ind: i128 = match value[start..=end].find(&sub) {
        Some(num) => num as i128,
        None => -1 as i128,
    };
    Ok(vm.ctx.new_int(ind))
}

// casefold is much more aggresive than lower
fn str_casefold(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    let folded_str: String = caseless::default_case_fold_str(&value);
    Ok(vm.ctx.new_str(folded_str))
}

fn str_swapcase(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    let mut swapped_str = String::with_capacity(value.len());
    for c in value.chars() {
        // to_uppercase returns an iterator, to_ascii_uppercase returns the char
        if c.is_lowercase() {
            swapped_str.push(c.to_ascii_uppercase());
        } else if c.is_uppercase() {
            swapped_str.push(c.to_ascii_lowercase());
        } else {
            swapped_str.push(c);
        }
    }
    Ok(vm.ctx.new_str(swapped_str))
}

fn str_replace(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [
            (s, Some(vm.ctx.str_type())),
            (old, Some(vm.ctx.str_type())),
            (rep, Some(vm.ctx.str_type()))
        ],
        optional = [(n, Some(vm.ctx.int_type()))]
    );
    let s = get_value(&s);
    let old_str = get_value(&old);
    let rep_str = get_value(&rep);
    let num_rep: usize = match n {
        Some(num) => objint::get_value(&num).to_usize().unwrap(),
        None => 1,
    };
    let new_str = s.replacen(&old_str, &rep_str, num_rep);
    Ok(vm.ctx.new_str(new_str))
}

fn str_expandtabs(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type()))],
        optional = [(size, Some(vm.ctx.int_type()))]
    );
    let value = get_value(&s);
    let tab_stop = match size {
        Some(num) => objint::get_value(&num).to_usize().unwrap(),
        None => 8 as usize,
    };
    let mut expanded_str = String::new();
    let mut tab_size = tab_stop;
    let mut col_count = 0 as usize;
    for ch in value.chars() {
        // 0x0009 is tab
        if ch == 0x0009 as char {
            let num_spaces = tab_size - col_count;
            col_count += num_spaces;
            let expand = " ".repeat(num_spaces);
            expanded_str.push_str(&expand);
        } else {
            expanded_str.push(ch);
            col_count += 1;
        }
        if col_count >= tab_size {
            tab_size += tab_stop;
        }
    }
    Ok(vm.ctx.new_str(expanded_str))
}

fn str_rpartition(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (sub, Some(vm.ctx.str_type()))]
    );
    let value = get_value(&s);
    let sub = get_value(&sub);
    let mut new_tup = Vec::new();
    if value.contains(&sub) {
        new_tup = value
            .rsplitn(2, &sub)
            .map(|s| vm.ctx.new_str(s.to_string()))
            .collect();
        new_tup.swap(0, 1); // so it's in the right order
        new_tup.insert(1, vm.ctx.new_str(sub));
    } else {
        new_tup.push(vm.ctx.new_str(value));
        new_tup.push(vm.ctx.new_str("".to_string()));
        new_tup.push(vm.ctx.new_str("".to_string()));
    }
    Ok(vm.ctx.new_tuple(new_tup))
}

fn str_partition(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (sub, Some(vm.ctx.str_type()))]
    );
    let value = get_value(&s);
    let sub = get_value(&sub);
    let mut new_tup = Vec::new();
    if value.contains(&sub) {
        new_tup = value
            .splitn(2, &sub)
            .map(|s| vm.ctx.new_str(s.to_string()))
            .collect();
        new_tup.insert(1, vm.ctx.new_str(sub));
    } else {
        new_tup.push(vm.ctx.new_str(value));
        new_tup.push(vm.ctx.new_str("".to_string()));
        new_tup.push(vm.ctx.new_str("".to_string()));
    }
    Ok(vm.ctx.new_tuple(new_tup))
}

fn str_title(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    Ok(vm.ctx.new_str(make_title(&get_value(&s))))
}

fn str_rjust(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (num, Some(vm.ctx.int_type()))],
        optional = [(rep, Some(vm.ctx.str_type()))]
    );
    let value = get_value(&s);
    let num = objint::get_value(&num).to_usize().unwrap();
    let rep = match rep {
        Some(st) => {
            let rep_str = get_value(&st);
            if rep_str.len() == 1 {
                rep_str
            } else {
                return Err(vm.new_type_error(
                    "The fill character must be exactly one character long".to_string(),
                ));
            }
        }
        None => " ".to_string(),
    };
    let new_str = format!("{}{}", rep.repeat(num), value);
    Ok(vm.ctx.new_str(new_str))
}

fn str_ljust(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (num, Some(vm.ctx.int_type()))],
        optional = [(rep, Some(vm.ctx.str_type()))]
    );
    let value = get_value(&s);
    let num = objint::get_value(&num).to_usize().unwrap();
    let rep = match rep {
        Some(st) => {
            let rep_str = get_value(&st);
            if rep_str.len() == 1 {
                rep_str
            } else {
                return Err(vm.new_type_error(
                    "The fill character must be exactly one character long".to_string(),
                ));
            }
        }
        None => " ".to_string(),
    };
    let new_str = format!("{}{}", value, rep.repeat(num));
    Ok(vm.ctx.new_str(new_str))
}

fn str_istitle(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    let mut is_titled = true;

    if value.is_empty() {
        is_titled = false;
    } else {
        for word in value.split(' ') {
            if word != make_title(&word) {
                is_titled = false;
                break;
            }
        }
    }
    Ok(vm.ctx.new_bool(is_titled))
}

fn str_center(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (len, Some(vm.ctx.int_type()))],
        optional = [(chars, Some(vm.ctx.str_type()))]
    );
    let value = get_value(&s);
    let len = objint::get_value(&len).to_usize().unwrap();
    let rep_char = match chars {
        Some(c) => get_value(&c),
        None => " ".to_string(),
    };
    let left_buff: usize = (len - value.len()) / 2;
    let right_buff = len - value.len() - left_buff;
    let new_str = format!(
        "{}{}{}",
        rep_char.repeat(left_buff),
        value,
        rep_char.repeat(right_buff)
    );
    Ok(vm.ctx.new_str(new_str))
}

fn str_startswith(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (pat, Some(vm.ctx.str_type()))]
    );
    let value = get_value(&s);
    let pat = get_value(&pat);
    Ok(vm.ctx.new_bool(value.starts_with(pat.as_str())))
}

fn str_contains(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [
            (s, Some(vm.ctx.str_type())),
            (needle, Some(vm.ctx.str_type()))
        ]
    );
    let value = get_value(&s);
    let needle = get_value(&needle);
    Ok(vm.ctx.new_bool(value.contains(needle.as_str())))
}

fn str_isalnum(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    Ok(vm
        .ctx
        .new_bool(!value.is_empty() && value.chars().all(|c| c.is_alphanumeric())))
}

fn str_isascii(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    Ok(vm
        .ctx
        .new_bool(!value.is_empty() && value.chars().all(|c| c.is_ascii())))
}

fn str_rindex(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (sub, Some(vm.ctx.str_type()))],
        optional = [
            (start, Some(vm.ctx.int_type())),
            (end, Some(vm.ctx.int_type()))
        ]
    );
    let value = get_value(&s);
    let sub = get_value(&sub);
    let (start, end) = match get_slice(start, end, value.len()) {
        Ok((start, end)) => (start, end),
        Err(e) => return Err(vm.new_index_error(e)),
    };
    let ind: i64 = match value[start..=end].rfind(&sub) {
        Some(num) => num as i64,
        None => {
            return Err(vm.new_value_error("substring not found".to_string()));
        }
    };
    Ok(vm.ctx.new_int(ind))
}

fn str_rfind(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (sub, Some(vm.ctx.str_type()))],
        optional = [
            (start, Some(vm.ctx.int_type())),
            (end, Some(vm.ctx.int_type()))
        ]
    );
    let value = get_value(&s);
    let sub = get_value(&sub);
    let (start, end) = match get_slice(start, end, value.len()) {
        Ok((start, end)) => (start, end),
        Err(e) => return Err(vm.new_index_error(e)),
    };
    let ind = match value[start..=end].rfind(&sub) {
        Some(num) => num as i128,
        None => -1 as i128,
    };
    Ok(vm.ctx.new_int(ind))
}

fn str_isnumeric(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    Ok(vm
        .ctx
        .new_bool(!value.is_empty() && value.chars().all(|c| c.is_numeric())))
}

fn str_isalpha(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    Ok(vm
        .ctx
        .new_bool(!value.is_empty() && value.chars().all(|c| c.is_alphanumeric())))
}

fn str_isdigit(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);
    let value = get_value(&s);
    // python's isdigit also checks if exponents are digits, these are the unicodes for exponents
    let valid_unicodes: [u16; 10] = [
        0x2070, 0x00B9, 0x00B2, 0x00B3, 0x2074, 0x2075, 0x2076, 0x2077, 0x2078, 0x2079,
    ];
    let mut is_digit: bool = true;

    if value.is_empty() {
        is_digit = false;
    } else {
        for c in value.chars() {
            if !c.is_digit(10) {
                // checking if char is exponent
                let char_as_uni: u16 = c as u16;
                if valid_unicodes.contains(&char_as_uni) {
                    continue;
                } else {
                    is_digit = false;
                    break;
                }
            }
        }
    }

    Ok(vm.ctx.new_bool(is_digit))
}

fn str_isdecimal(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(vm, args, required = [(s, Some(vm.ctx.str_type()))]);

    let value = get_value(&s);

    let is_decimal = if !value.is_empty() {
        value.chars().all(|c| c.is_ascii_digit())
    } else {
        false
    };

    Ok(vm.ctx.new_bool(is_decimal))
}

fn str_getitem(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    arg_check!(
        vm,
        args,
        required = [(s, Some(vm.ctx.str_type())), (needle, None)]
    );
    let value = get_value(&s);
    subscript(vm, &value, needle.clone())
}

// TODO: should with following format
// class str(object='')
// class str(object=b'', encoding='utf-8', errors='strict')
fn str_new(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
    if args.args.len() == 1 {
        return Ok(vm.new_str("".to_string()));
    }

    if args.args.len() > 2 {
        panic!("str expects exactly one parameter");
    };

    vm.to_str(&args.args[1])
}

impl PySliceableSequence for String {
    fn do_slice(&self, start: usize, stop: usize) -> Self {
        to_graphemes(self)
            .get(start..stop)
            .map_or(String::default(), |c| c.join(""))
    }

    fn do_stepped_slice(&self, start: usize, stop: usize, step: usize) -> Self {
        if let Some(s) = to_graphemes(self).get(start..stop) {
            return s
                .iter()
                .cloned()
                .step_by(step)
                .collect::<Vec<String>>()
                .join("");
        }
        String::default()
    }

    fn len(&self) -> usize {
        to_graphemes(self).len()
    }
}

/// Convert a string-able `value` to a vec of graphemes
/// represents the string according to user perceived characters
fn to_graphemes<S: AsRef<str>>(value: S) -> Vec<String> {
    UnicodeSegmentation::graphemes(value.as_ref(), true)
        .map(String::from)
        .collect()
}

pub fn subscript(vm: &mut VirtualMachine, value: &str, b: PyObjectRef) -> PyResult {
    if objtype::isinstance(&b, &vm.ctx.int_type()) {
        match objint::get_value(&b).to_i32() {
            Some(pos) => {
                let graphemes = to_graphemes(value);
                let idx = graphemes.get_pos(pos);
                graphemes
                    .get(idx)
                    .map(|c| vm.new_str(c.to_string()))
                    .ok_or(vm.new_index_error("string index out of range".to_string()))
            }
            None => {
                Err(vm.new_index_error("cannot fit 'int' into an index-sized integer".to_string()))
            }
        }
    } else {
        match (*b.borrow()).payload {
            PyObjectPayload::Slice { .. } => {
                Ok(vm.new_str(value.to_string().get_slice_items(&b).to_string()))
            }
            _ => panic!(
                "TypeError: indexing type {:?} with index {:?} is not supported (yet?)",
                value, b
            ),
        }
    }
}

// help get optional string indices
fn get_slice(
    start: Option<&std::rc::Rc<std::cell::RefCell<PyObject>>>,
    end: Option<&std::rc::Rc<std::cell::RefCell<PyObject>>>,
    len: usize,
) -> Result<(usize, usize), String> {
    let start_idx = match start {
        Some(int) => objint::get_value(&int).to_usize().unwrap(),
        None => 0 as usize,
    };
    let end_idx = match end {
        Some(int) => objint::get_value(&int).to_usize().unwrap(),
        None => len - 1,
    };
    if start_idx >= usize::min_value() && start_idx < end_idx && end_idx < len {
        Ok((start_idx, end_idx))
    } else {
        Err("provided index is not valid".to_string())
    }
}

// helper function to title strings
fn make_title(s: &str) -> String {
    let mut titled_str = String::new();
    let mut capitalize_char: bool = true;
    for c in s.chars() {
        if c.is_alphabetic() {
            if !capitalize_char {
                titled_str.push(c);
            } else if capitalize_char {
                titled_str.push(c.to_ascii_uppercase());
                capitalize_char = false;
            }
        } else {
            titled_str.push(c);
            capitalize_char = true;
        }
    }
    titled_str
}