/*!
Parsing flags from text.

Format and parse a flags value as text using the following grammar:

- _Flags:_ (_Whitespace_ _Flag_ _Whitespace_)`|`*
- _Flag:_ _Name_ | _Hex Number_
- _Name:_ The name of any defined flag
- _Hex Number_: `0x`([0-9a-fA-F])*
- _Whitespace_: (\s)*

As an example, this is how `Flags::A | Flags::B | 0x0c` can be represented as text:

```text
A | B | 0x0c
```

Alternatively, it could be represented without whitespace:

```text
A|B|0x0C
```

Note that identifiers are *case-sensitive*, so the following is *not equivalent*:

```text
a|b|0x0C
```
*/

#![allow(clippy::let_unit_value)]

use core::fmt::{self, Write};

use crate::{Bits, Flags};

/**
Write a flags value as text.

Any bits that aren't part of a contained flag will be formatted as a hex number.
*/
pub fn to_writer<B: Flags>(flags: &B, mut writer: impl Write) -> Result<(), fmt::Error>
where
 B::Bits: WriteHex,
{
 // A formatter for bitflags that produces text output like:
 //
 // A | B | 0xf6
 //
 // The names of set flags are written in a bar-separated-format,
 // followed by a hex number of any remaining bits that are set
 // but don't correspond to any flags.

 // Iterate over known flag values
 let mut first = true;
 let mut iter = flags.iter_names();
 for (name, _) in &mut iter {
 if !first {
 writer.write_str(" | ")?;
 }

 first = false;
 writer.write_str(name)?;
 }

 // Append any extra bits that correspond to flags to the end of the format
 let remaining = iter.remaining().bits();
 if remaining != B::Bits::EMPTY {
 if !first {
 writer.write_str(" | ")?;
 }

 writer.write_str("0x")?;
 remaining.write_hex(writer)?;
 }

 fmt::Result::Ok(())
}

#[cfg(feature = "serde")]
pub(crate) struct AsDisplay<'a, B>(pub(crate) &'a B);

#[cfg(feature = "serde")]
impl<'a, B: Flags> fmt::Display for AsDisplay<'a, B>
where
 B::Bits: WriteHex,
{
 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 to_writer(self.0, f)
 }
}

/**
Parse a flags value from text.

This function will fail on any names that don't correspond to defined flags.
Unknown bits will be retained.
*/
pub fn from_str<B: Flags>(input: &str) -> Result<B, ParseError>
where
 B::Bits: ParseHex,
{
 let mut parsed_flags = B::empty();

 // If the input is empty then return an empty set of flags
 if input.trim().is_empty() {
 return Ok(parsed_flags);
 }

 for flag in input.split('|') {
 let flag = flag.trim();

 // If the flag is empty then we've got missing input
 if flag.is_empty() {
 return Err(ParseError::empty_flag());
 }

 // If the flag starts with `0x` then it's a hex number
 // Parse it directly to the underlying bits type
 let parsed_flag = if let Some(flag) = flag.strip_prefix("0x") {
 let bits =
 <B::Bits>::parse_hex(flag).map_err(|_| ParseError::invalid_hex_flag(flag))?;

 B::from_bits_retain(bits)
 }
 // Otherwise the flag is a name
 // The generated flags type will determine whether
 // or not it's a valid identifier
 else {
 B::from_name(flag).ok_or_else(|| ParseError::invalid_named_flag(flag))?
 };

 parsed_flags.insert(parsed_flag);
 }

 Ok(parsed_flags)
}

/**
Write a flags value as text, ignoring any unknown bits.
*/
pub fn to_writer_truncate<B: Flags>(flags: &B, writer: impl Write) -> Result<(), fmt::Error>
where
 B::Bits: WriteHex,
{
 to_writer(&B::from_bits_truncate(flags.bits()), writer)
}

/**
Parse a flags value from text.

This function will fail on any names that don't correspond to defined flags.
Unknown bits will be ignored.
*/
pub fn from_str_truncate<B: Flags>(input: &str) -> Result<B, ParseError>
where
 B::Bits: ParseHex,
{
 Ok(B::from_bits_truncate(from_str::<B>(input)?.bits()))
}

/**
Write only the contained, defined, named flags in a flags value as text.
*/
pub fn to_writer_strict<B: Flags>(flags: &B, mut writer: impl Write) -> Result<(), fmt::Error> {
 // This is a simplified version of `to_writer` that ignores
 // any bits not corresponding to a named flag

 let mut first = true;
 let mut iter = flags.iter_names();
 for (name, _) in &mut iter {
 if !first {
 writer.write_str(" | ")?;
 }

 first = false;
 writer.write_str(name)?;
 }

 fmt::Result::Ok(())
}

/**
Parse a flags value from text.

This function will fail on any names that don't correspond to defined flags.
This function will fail to parse hex values.
*/
pub fn from_str_strict<B: Flags>(input: &str) -> Result<B, ParseError> {
 // This is a simplified version of `from_str` that ignores
 // any bits not corresponding to a named flag

 let mut parsed_flags = B::empty();

 // If the input is empty then return an empty set of flags
 if input.trim().is_empty() {
 return Ok(parsed_flags);
 }

 for flag in input.split('|') {
 let flag = flag.trim();

 // If the flag is empty then we've got missing input
 if flag.is_empty() {
 return Err(ParseError::empty_flag());
 }

 // If the flag starts with `0x` then it's a hex number
 // These aren't supported in the strict parser
 if flag.starts_with("0x") {
 return Err(ParseError::invalid_hex_flag("unsupported hex flag value"));
 }

 let parsed_flag = B::from_name(flag).ok_or_else(|| ParseError::invalid_named_flag(flag))?;

 parsed_flags.insert(parsed_flag);
 }

 Ok(parsed_flags)
}

/**
Encode a value as a hex string.

Implementors of this trait should not write the `0x` prefix.
*/
pub trait WriteHex {
 /// Write the value as hex.
 fn write_hex<W: fmt::Write>(&self, writer: W) -> fmt::Result;
}

/**
Parse a value from a hex string.
*/
pub trait ParseHex {
 /// Parse the value from hex.
 fn parse_hex(input: &str) -> Result<Self, ParseError>
 where
 Self: Sized;
}

/// An error encountered while parsing flags from text.
#[derive(Debug)]
pub struct ParseError(ParseErrorKind);

#[derive(Debug)]
#[allow(clippy::enum_variant_names)]
enum ParseErrorKind {
 EmptyFlag,
 InvalidNamedFlag {
 #[cfg(not(feature = "std"))]
 got: (),
 #[cfg(feature = "std")]
 got: String,
 },
 InvalidHexFlag {
 #[cfg(not(feature = "std"))]
 got: (),
 #[cfg(feature = "std")]
 got: String,
 },
}

impl ParseError {
 /// An invalid hex flag was encountered.
 pub fn invalid_hex_flag(flag: impl fmt::Display) -> Self {
 let _flag = flag;

 let got = {
 #[cfg(feature = "std")]
 {
 _flag.to_string()
 }
 };

 ParseError(ParseErrorKind::InvalidHexFlag { got })
 }

 /// A named flag that doesn't correspond to any on the flags type was encountered.
 pub fn invalid_named_flag(flag: impl fmt::Display) -> Self {
 let _flag = flag;

 let got = {
 #[cfg(feature = "std")]
 {
 _flag.to_string()
 }
 };

 ParseError(ParseErrorKind::InvalidNamedFlag { got })
 }

 /// A hex or named flag wasn't found between separators.
 pub const fn empty_flag() -> Self {
 ParseError(ParseErrorKind::EmptyFlag)
 }
}

impl fmt::Display for ParseError {
 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 match &self.0 {
 ParseErrorKind::InvalidNamedFlag { got } => {
 let _got = got;

 write!(f, "unrecognized named flag")?;

 #[cfg(feature = "std")]
 {
 write!(f, " `{}`", _got)?;
 }
 }
 ParseErrorKind::InvalidHexFlag { got } => {
 let _got = got;

 write!(f, "invalid hex flag")?;

 #[cfg(feature = "std")]
 {
 write!(f, " `{}`", _got)?;
 }
 }
 ParseErrorKind::EmptyFlag => {
 write!(f, "encountered empty flag")?;
 }
 }

 Ok(())
 }
}

#[cfg(feature = "std")]
impl std::error::Error for ParseError {}