// Copyright (c) 2019-2023 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module builtin

// IError holds information about an error instance
pub interface IError {
    // >> Hack to allow old style custom error implementations
    // TODO: remove once deprecation period for `IError` methods has ended
    msg string
    code int // <<
    msg() string
    code() int
}

// str returns the message of IError
pub fn (err IError) str() string {
    return match err {
        None__ {
            'none'
        }
        Error {
            err.msg()
        }
        MessageError {
            err.msg()
        }
        else {
            // >> Hack to allow old style custom error implementations
            // TODO: remove once deprecation period for `IError` methods has ended
            // old_error_style := unsafe { voidptr(&err.msg) != voidptr(&err.code) } // if fields are not defined (new style) they don't have an offset between
            // <<
            '${err.type_name()}: ${err.msg()}'
        }
    }
}

// Error is the empty default implementation of `IError`.
pub struct Error {}

pub fn (err Error) msg() string {
    return ''
}

pub fn (err Error) code() int {
    return 0
}

// MessageError is the default implementation of the `IError` interface that is returned by the `error()` function
struct MessageError {
pub:
    msg  string
    code int
}

// msg returns the message of MessageError
pub fn (err MessageError) msg() string {
    if err.code > 0 {
        return '${err.msg}; code: ${err.code}'
    }
    return err.msg
}

// code returns the code of MessageError
pub fn (err MessageError) code() int {
    return err.code
}

[unsafe]
pub fn (err &MessageError) free() {
    unsafe { err.msg.free() }
}

const none__ = IError(&None__{})

struct None__ {
    Error
}

fn (_ None__) str() string {
    return 'none'
}

[if trace_error ?]
fn trace_error(x string) {
    eprintln('> ${@FN} | ${x}')
}

// error returns a default error instance containing the error given in `message`.
// Example: if ouch { return error('an error occurred') }
[inline]
pub fn error(message string) IError {
    trace_error(message)
    return &MessageError{
        msg: message
    }
}

// error_with_code returns a default error instance containing the given `message` and error `code`.
// Example: if ouch { return error_with_code('an error occurred', 1) }
[inline]
pub fn error_with_code(message string, code int) IError {
    trace_error('${message} | code: ${code}')
    return &MessageError{
        msg: message
        code: code
    }
}

// Option is the base of V's internal option return system.
struct Option {
    state u8
    err   IError = none__
    // Data is trailing after err
    // and is not included in here but in the
    // derived Option_xxx types
}

// option is the base of V's internal option return system.
struct _option {
    state u8
    err   IError = none__
    // Data is trailing after err
    // and is not included in here but in the
    // derived _option_xxx types
}

fn _option_none(data voidptr, mut option _option, size int) {
    unsafe {
        *option = _option{
            state: 2
        }
        // use err to get the end of OptionBase and then memcpy into it
        vmemcpy(&u8(&option.err) + sizeof(IError), data, size)
    }
}

fn _option_ok(data voidptr, mut option _option, size int) {
    unsafe {
        *option = _option{}
        // use err to get the end of OptionBase and then memcpy into it
        vmemcpy(&u8(&option.err) + sizeof(IError), data, size)
    }
}

struct _result {
    is_error bool
    err      IError = none__
    // Data is trailing after err
    // and is not included in here but in the
    // derived Result_xxx types
}

fn _result_ok(data voidptr, mut res _result, size int) {
    unsafe {
        *res = _result{}
        // use err to get the end of ResultBase and then memcpy into it
        vmemcpy(&u8(&res.err) + sizeof(IError), data, size)
    }
}

pub fn (_ none) str() string {
    return 'none'
}