use super::*;
use std::marker::PhantomData;
use std::{fmt,error};
use std::ops::Deref;
use std::borrow::{Borrow, ToOwned};

/// A spec to validate the formatting of a string for.
pub trait FormatSpec
{
    type Error: Into<eyre::Report>;
    fn validate(s: &str) -> Result<(), Self::Error>;
}


/// A strongly validated string slice
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct FormattedStr<F: FormatSpec + ?Sized>(PhantomData<*const F>, str);

impl<F: FormatSpec + ?Sized> std::marker::Unpin for FormattedStr<F>{}
unsafe impl<F: FormatSpec + ?Sized> std::marker::Send for FormattedStr<F>{}
unsafe impl<F: FormatSpec + ?Sized> std::marker::Sync for FormattedStr<F>{}

/// A strongly validated string
// TODO: How to perform validation on deserialise? Custom `Deserialize` impl? might have to.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct  FormattedString<F: FormatSpec + ?Sized>(String, PhantomData<F>);

// Deserialising
const _:() = {
    use serde::{
	de::Visitor,
	de::Error,
	de,
	Serialize,
	ser::Serializer,
    };

    impl<F: FormatSpec + ?Sized> Serialize for FormattedStr<F>
    {
	fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
	where
            S: Serializer,
	{
            serializer.serialize_str(&self.1)
	}
    }
    impl<F: FormatSpec + ?Sized> Serialize for FormattedString<F>
    {
	fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
	where
            S: Serializer,
	{
            serializer.serialize_str(&self.0)
	}
    }

    #[derive(Debug, Clone, Copy)]
    struct FormattedStringVisitor<F: FormatSpec + ?Sized>(PhantomData<F>);

    impl<'de, F: FormatSpec + ?Sized> Visitor<'de> for FormattedStringVisitor<F>
    {
	type Value = FormattedString<F>;
	fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
	{
	    write!(f, "a string satisfying the requirements of {}", std::any::type_name::<F>())
	}
	fn visit_str<E: Error>(self, s: &str) -> Result<Self::Value, E>
	{
	    FormattedStr::<F>::new(s).map_err(|x| E::custom(x.into())).map(ToOwned::to_owned)
	}
	fn visit_string<E: Error>(self, s: String) -> Result<Self::Value, E>
	{
	    FormattedString::<F>::new(s).map_err(|x| E::custom(x.into()))
	}
    }
    
    impl<'de, F: FormatSpec + ?Sized> de::Deserialize<'de> for FormattedString<F> {
	fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
	where
            D: de::Deserializer<'de>,
	{
	    let vis = FormattedStringVisitor::<F>(PhantomData);
            deserializer.deserialize_string(vis)
	}
    }
};

impl<F: FormatSpec + ?Sized> FormattedStr<F>
{
    /// Create a new instance without validating the input.
    ///
    /// # Safety
    /// You must be sure the input is of a valid state to `F`.
    #[inline(always)] pub unsafe fn new_unchecked<'a>(s: &'a str) -> &'a Self
    {
	std::mem::transmute(s)
    }

    /// Create and validate a the format of a new instance.
    pub fn new<'a>(s: &'a str) -> Result<&'a Self, F::Error>
    {
	F::validate(s).map(move |_| unsafe {Self::new_unchecked(s)})
    }

    /// Get the inner str
    #[inline] pub fn as_str<'a>(&'a self) -> &'a str
    {
	&self.1
    }
}

impl<F: FormatSpec + ?Sized> FormattedString<F>
{
    /// Create a new instance without validating the input.
    ///
    /// # Safety
    /// You must be sure the input is of a valid state to `F`.
    #[inline(always)] pub unsafe fn new_unchecked(s: String) -> Self
    {
	std::mem::transmute(s)
    }
    
    /// Create and validate a the format of a new instance.
    pub fn new(s: String) -> Result<Self, F::Error>
    {
	F::validate(&s)
	    .map(move |_| unsafe {Self::new_unchecked(s)})
    }

}

impl<F: FormatSpec + ?Sized> FormattedString<F>
{
    /// As a formatted str
    #[inline] pub fn as_ref<'a>(&'a self) -> &'a FormattedStr<F>
    {
	unsafe { FormattedStr::new_unchecked(&self.0) }
    }
}

impl<F: FormatSpec + ?Sized> AsRef<str> for FormattedStr<F>
{
    #[inline] fn as_ref(&self) -> &str
    {
	self.as_str()
    }
}

impl<F: FormatSpec + ?Sized> Borrow<FormattedStr<F>> for FormattedString<F>
{
    #[inline] fn borrow(&self) -> &FormattedStr<F> {
	self.as_ref()
    }
}

impl<F: FormatSpec + ?Sized> ToOwned for FormattedStr<F>
{
    type Owned = FormattedString<F>;
    #[inline] fn to_owned(&self) -> Self::Owned {
	FormattedString(String::from(&self.1), PhantomData)
    }
}

impl<F: FormatSpec + ?Sized> AsRef<FormattedStr<F>> for FormattedString<F>
{
    #[inline] fn as_ref(&self) -> &FormattedStr<F> {
	self.as_ref()
    }
}

impl<F: FormatSpec + ?Sized> Deref for FormattedString<F>
{
    type Target = FormattedStr<F>;
    #[inline] fn deref(&self) -> &Self::Target {
	self.as_ref()
    }
}

impl<'a,F: FormatSpec + ?Sized> From<&'a FormattedStr<F>> for &'a str
{
    #[inline] fn from(from: &'a FormattedStr<F>) -> Self
    {
	&from.1
    }
}
impl<'a,F: FormatSpec + ?Sized> TryFrom<&'a str> for &'a FormattedStr<F>
{
    type Error = F::Error;

    #[inline] fn try_from(from: &'a str) -> Result<Self, Self::Error>
    {
	FormattedStr::new(from)
    }
}

impl<'a, F: FormatSpec + ?Sized> From<FormattedString<F>> for String
{
    #[inline] fn from(from: FormattedString<F>) -> Self
    {
	from.0
    }
}

impl<'a, F: FormatSpec + ?Sized> TryFrom<String> for FormattedString<F>
{
    type Error = F::Error;

    fn try_from(from: String) -> Result<Self, Self::Error>
    {
	Self::new(from)
    }
}



pub mod formats
{    
    use super::*;
    /// A hex string format specifier
    #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub enum HexFormat{}
    #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub enum MaxLenFormat<const MAX: usize>{}

    impl<const MAX: usize> FormatSpec for MaxLenFormat<MAX>
    {
	type Error = MaxLenExceededError<MAX>;

	#[inline] fn validate(s: &str) -> Result<(), Self::Error> {
	    if s.len() > MAX {
		Err(MaxLenExceededError)
	    } else {
		Ok(())
	    }
	}
    }

    #[derive(Debug)]
    pub struct MaxLenExceededError<const MAX: usize>;

    impl<const MAX: usize> error::Error for MaxLenExceededError<MAX>{}
    impl<const MAX: usize> fmt::Display for MaxLenExceededError<MAX>
    {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
	{
	    write!(f, "string length exceeds {}", MAX)
	}
    }

    
    impl HexFormat
    {
	const HEX_MAP: &'static [u8] = b"1234567890abcdefABCDEF";
    }

    impl FormatSpec for HexFormat
    {
	type Error = HexFormatError;
	fn validate(s: &str) -> Result<(), Self::Error> {
	    
	    for (i, chr) in s.char_indices()
	    {
		if !chr.is_ascii_alphanumeric() || !Self::HEX_MAP.contains(&(chr as u8)) {
		    return Err(HexFormatError(chr, i));
		}
	    }
	    Ok(())
	}
    }

    /// Error for an invalid hex string.
    #[derive(Debug)]
    pub struct HexFormatError(char, usize);

    impl error::Error for HexFormatError{}
    impl fmt::Display for HexFormatError
    {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
	{
	    write!(f, "invalid hex char {:?} at index {}", self.0, self.1)
	}
    }

    
    /// A PEM formatted string.
    #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub enum PEMFormat{}

    #[derive(Debug)]
    pub struct PEMFormatError;

    impl error::Error for PEMFormatError{}
    impl fmt::Display for PEMFormatError
    {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
	{
	    write!(f, "invalid PEM format")
	}
    }

    impl FormatSpec for PEMFormat
    {
	type Error = PEMFormatError;
	fn validate(_s: &str) -> Result<(), Self::Error> {
	    Ok(())
	}
    }
    
    pub type MaxLenStr<const MAX: usize> = FormattedStr<MaxLenFormat<MAX>>;
    pub type MaxLenString<const MAX: usize> = FormattedString<MaxLenFormat<MAX>>;
    
    pub type HexFormattedStr = FormattedStr<HexFormat>;
    pub type HexFormattedString = FormattedString<HexFormat>;
    
    pub type PEMFormattedStr = FormattedStr<PEMFormat>;
    pub type PEMFormattedString = FormattedString<PEMFormat>;

    #[cfg(test)]
    mod tests
    {
	use super::*;
	#[test]
	fn hex_format()
	{
	    let _invalid = HexFormattedStr::new("ab120982039840i ").expect_err("Invalidation");
	    let _valid = HexFormattedStr::new("abc123982095830495adcfDD").expect("Validation");
	}
    }

}