forma_json 0.1.0

use crate::error::Error;
use forma_core::ser::*;
use std::io;

pub struct Serializer<W: io::Write> {
    writer: W,
    first: Vec<bool>,
    indent: Option<&'static str>,
    current_indent: usize,
}

impl<W: io::Write> Serializer<W> {
    pub fn new(writer: W) -> Self {
        Serializer {
            writer,
            first: Vec::new(),
            indent: None,
            current_indent: 0,
        }
    }

    pub fn pretty(writer: W, indent: &'static str) -> Self {
        Serializer {
            writer,
            first: Vec::new(),
            indent: Some(indent),
            current_indent: 0,
        }
    }

    pub fn into_inner(self) -> W {
        self.writer
    }

    fn is_pretty(&self) -> bool {
        self.indent.is_some()
    }

    fn push_scope(&mut self) {
        self.first.push(true);
        self.current_indent += 1;
    }

    fn write_comma(&mut self) -> Result<(), Error> {
        match self.first.last_mut() {
            Some(first) if *first => {
                *first = false;
                if self.is_pretty() {
                    self.write_newline_indent()?;
                }
                Ok(())
            }
            Some(_) => {
                self.writer.write_all(b",")?;
                if self.is_pretty() {
                    self.write_newline_indent()?;
                }
                Ok(())
            }
            None => Ok(()),
        }
    }

    fn pop_scope(&mut self) {
        self.first.pop();
        self.current_indent -= 1;
    }

    fn write_newline_indent(&mut self) -> Result<(), Error> {
        if let Some(indent) = self.indent {
            self.writer.write_all(b"\n")?;
            for _ in 0..self.current_indent {
                self.writer.write_all(indent.as_bytes())?;
            }
        }
        Ok(())
    }
}

impl<'a, W: io::Write> forma_core::ser::Serializer for &'a mut Serializer<W> {
    type Ok = ();
    type Error = Error;
    type SerializeSeq = Compound<'a, W>;
    type SerializeTuple = Compound<'a, W>;
    type SerializeTupleStruct = Compound<'a, W>;
    type SerializeTupleVariant = Compound<'a, W>;
    type SerializeMap = Compound<'a, W>;
    type SerializeStruct = Compound<'a, W>;
    type SerializeStructVariant = Compound<'a, W>;

    fn serialize_bool(self, v: bool) -> Result<(), Error> {
        self.writer
            .write_all(if v { b"true" } else { b"false" })?;
        Ok(())
    }

    fn serialize_i8(self, v: i8) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }
    fn serialize_i16(self, v: i16) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }
    fn serialize_i32(self, v: i32) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }
    fn serialize_i64(self, v: i64) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }
    fn serialize_i128(self, v: i128) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }

    fn serialize_u8(self, v: u8) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }
    fn serialize_u16(self, v: u16) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }
    fn serialize_u32(self, v: u32) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }
    fn serialize_u64(self, v: u64) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }
    fn serialize_u128(self, v: u128) -> Result<(), Error> {
        write!(self.writer, "{v}")?;
        Ok(())
    }

    fn serialize_f32(self, v: f32) -> Result<(), Error> {
        if v.is_finite() {
            write!(self.writer, "{v}")?;
        } else {
            return Err(Error::Message(format!(
                "JSON does not support {v}"
            )));
        }
        Ok(())
    }
    fn serialize_f64(self, v: f64) -> Result<(), Error> {
        if v.is_finite() {
            write!(self.writer, "{v}")?;
        } else {
            return Err(Error::Message(format!(
                "JSON does not support {v}"
            )));
        }
        Ok(())
    }

    fn serialize_char(self, v: char) -> Result<(), Error> {
        let mut buf = [0u8; 4];
        self.serialize_str(v.encode_utf8(&mut buf))
    }

    fn serialize_str(self, v: &str) -> Result<(), Error> {
        write_escaped_str(&mut self.writer, v)
    }

    fn serialize_bytes(self, v: &[u8]) -> Result<(), Error> {
        self.writer.write_all(b"[")?;
        self.current_indent += 1;
        for (i, byte) in v.iter().enumerate() {
            if i > 0 {
                self.writer.write_all(b",")?;
            }
            if self.is_pretty() {
                self.write_newline_indent()?;
            }
            write!(self.writer, "{byte}")?;
        }
        self.current_indent -= 1;
        if self.is_pretty() && !v.is_empty() {
            self.write_newline_indent()?;
        }
        self.writer.write_all(b"]")?;
        Ok(())
    }

    fn serialize_none(self) -> Result<(), Error> {
        self.writer.write_all(b"null")?;
        Ok(())
    }

    fn serialize_some<T: Serialize + ?Sized>(self, value: &T) -> Result<(), Error> {
        value.serialize(self)
    }

    fn serialize_unit(self) -> Result<(), Error> {
        self.writer.write_all(b"null")?;
        Ok(())
    }

    fn serialize_unit_struct(self, _name: &'static str) -> Result<(), Error> {
        self.writer.write_all(b"null")?;
        Ok(())
    }

    fn serialize_unit_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
    ) -> Result<(), Error> {
        self.serialize_str(variant)
    }

    fn serialize_newtype_struct<T: Serialize + ?Sized>(
        self,
        _name: &'static str,
        value: &T,
    ) -> Result<(), Error> {
        value.serialize(self)
    }

    fn serialize_newtype_variant<T: Serialize + ?Sized>(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
        value: &T,
    ) -> Result<(), Error> {
        self.writer.write_all(b"{")?;
        self.current_indent += 1;
        if self.is_pretty() {
            self.write_newline_indent()?;
        }
        write_escaped_str(&mut self.writer, variant)?;
        self.writer.write_all(if self.is_pretty() { b": " } else { b":" })?;
        value.serialize(&mut *self)?;
        self.current_indent -= 1;
        if self.is_pretty() {
            self.write_newline_indent()?;
        }
        self.writer.write_all(b"}")?;
        Ok(())
    }

    fn serialize_seq(self, _len: Option<usize>) -> Result<Compound<'a, W>, Error> {
        self.writer.write_all(b"[")?;
        self.push_scope();
        Ok(Compound { ser: self, kind: CompoundKind::Array })
    }

    fn serialize_tuple(self, _len: usize) -> Result<Compound<'a, W>, Error> {
        self.serialize_seq(None)
    }

    fn serialize_tuple_struct(
        self,
        _name: &'static str,
        _len: usize,
    ) -> Result<Compound<'a, W>, Error> {
        self.serialize_seq(None)
    }

    fn serialize_tuple_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
        _len: usize,
    ) -> Result<Compound<'a, W>, Error> {
        self.writer.write_all(b"{")?;
        self.current_indent += 1;
        if self.is_pretty() {
            self.write_newline_indent()?;
        }
        write_escaped_str(&mut self.writer, variant)?;
        self.writer.write_all(if self.is_pretty() { b": [" } else { b":[" })?;
        self.push_scope();
        Ok(Compound { ser: self, kind: CompoundKind::WrappedArray })
    }

    fn serialize_map(self, _len: Option<usize>) -> Result<Compound<'a, W>, Error> {
        self.writer.write_all(b"{")?;
        self.push_scope();
        Ok(Compound { ser: self, kind: CompoundKind::Object })
    }

    fn serialize_struct(
        self,
        _name: &'static str,
        _len: usize,
    ) -> Result<Compound<'a, W>, Error> {
        self.serialize_map(None)
    }

    fn serialize_struct_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
        _len: usize,
    ) -> Result<Compound<'a, W>, Error> {
        self.writer.write_all(b"{")?;
        self.current_indent += 1;
        if self.is_pretty() {
            self.write_newline_indent()?;
        }
        write_escaped_str(&mut self.writer, variant)?;
        self.writer.write_all(if self.is_pretty() { b": {" } else { b":{" })?;
        self.push_scope();
        Ok(Compound { ser: self, kind: CompoundKind::WrappedObject })
    }
}

#[derive(Clone, Copy)]
enum CompoundKind {
    Array,
    Object,
    WrappedArray,
    WrappedObject,
}

pub struct Compound<'a, W: io::Write> {
    ser: &'a mut Serializer<W>,
    kind: CompoundKind,
}

impl<W: io::Write> SerializeSeq for Compound<'_, W> {
    type Ok = ();
    type Error = Error;

    fn serialize_element<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), Error> {
        self.ser.write_comma()?;
        value.serialize(&mut *self.ser)
    }

    fn end(self) -> Result<(), Error> {
        let had_elements = !self.ser.first.last().copied().unwrap_or(true);
        self.ser.pop_scope();
        match self.kind {
            CompoundKind::Array => {
                if self.ser.is_pretty() && had_elements {
                    self.ser.write_newline_indent()?;
                }
                self.ser.writer.write_all(b"]")?;
            }
            CompoundKind::WrappedArray => {
                if self.ser.is_pretty() && had_elements {
                    self.ser.write_newline_indent()?;
                }
                self.ser.writer.write_all(b"]")?;
                self.ser.current_indent -= 1;
                if self.ser.is_pretty() {
                    self.ser.write_newline_indent()?;
                }
                self.ser.writer.write_all(b"}")?;
            }
            _ => unreachable!(),
        }
        Ok(())
    }
}

impl<W: io::Write> SerializeTuple for Compound<'_, W> {
    type Ok = ();
    type Error = Error;

    fn serialize_element<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), Error> {
        SerializeSeq::serialize_element(self, value)
    }

    fn end(self) -> Result<(), Error> {
        SerializeSeq::end(self)
    }
}

impl<W: io::Write> SerializeTupleStruct for Compound<'_, W> {
    type Ok = ();
    type Error = Error;

    fn serialize_field<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), Error> {
        SerializeSeq::serialize_element(self, value)
    }

    fn end(self) -> Result<(), Error> {
        SerializeSeq::end(self)
    }
}

impl<W: io::Write> SerializeTupleVariant for Compound<'_, W> {
    type Ok = ();
    type Error = Error;

    fn serialize_field<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), Error> {
        SerializeSeq::serialize_element(self, value)
    }

    fn end(self) -> Result<(), Error> {
        SerializeSeq::end(self)
    }
}

impl<W: io::Write> SerializeMap for Compound<'_, W> {
    type Ok = ();
    type Error = Error;

    fn serialize_key<T: Serialize + ?Sized>(&mut self, key: &T) -> Result<(), Error> {
        self.ser.write_comma()?;
        key.serialize(MapKeySerializer(&mut *self.ser))
    }

    fn serialize_value<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<(), Error> {
        self.ser.writer.write_all(if self.ser.is_pretty() { b": " } else { b":" })?;
        value.serialize(&mut *self.ser)
    }

    fn end(self) -> Result<(), Error> {
        let had_entries = !self.ser.first.last().copied().unwrap_or(true);
        self.ser.pop_scope();
        match self.kind {
            CompoundKind::Object => {
                if self.ser.is_pretty() && had_entries {
                    self.ser.write_newline_indent()?;
                }
                self.ser.writer.write_all(b"}")?;
            }
            CompoundKind::WrappedObject => {
                if self.ser.is_pretty() && had_entries {
                    self.ser.write_newline_indent()?;
                }
                self.ser.writer.write_all(b"}")?;
                self.ser.current_indent -= 1;
                if self.ser.is_pretty() {
                    self.ser.write_newline_indent()?;
                }
                self.ser.writer.write_all(b"}")?;
            }
            _ => unreachable!(),
        }
        Ok(())
    }
}

impl<W: io::Write> SerializeStruct for Compound<'_, W> {
    type Ok = ();
    type Error = Error;

    fn serialize_field<T: Serialize + ?Sized>(
        &mut self,
        key: &'static str,
        value: &T,
    ) -> Result<(), Error> {
        SerializeMap::serialize_key(self, key)?;
        SerializeMap::serialize_value(self, value)
    }

    fn end(self) -> Result<(), Error> {
        SerializeMap::end(self)
    }
}

impl<W: io::Write> SerializeStructVariant for Compound<'_, W> {
    type Ok = ();
    type Error = Error;

    fn serialize_field<T: Serialize + ?Sized>(
        &mut self,
        key: &'static str,
        value: &T,
    ) -> Result<(), Error> {
        SerializeMap::serialize_key(self, key)?;
        SerializeMap::serialize_value(self, value)
    }

    fn end(self) -> Result<(), Error> {
        SerializeMap::end(self)
    }
}

// Map keys must serialize as strings in JSON.
struct MapKeySerializer<'a, W: io::Write>(&'a mut Serializer<W>);

impl<W: io::Write> forma_core::ser::Serializer for MapKeySerializer<'_, W> {
    type Ok = ();
    type Error = Error;
    type SerializeSeq = Impossible<(), Error>;
    type SerializeTuple = Impossible<(), Error>;
    type SerializeTupleStruct = Impossible<(), Error>;
    type SerializeTupleVariant = Impossible<(), Error>;
    type SerializeMap = Impossible<(), Error>;
    type SerializeStruct = Impossible<(), Error>;
    type SerializeStructVariant = Impossible<(), Error>;

    fn serialize_bool(self, v: bool) -> Result<(), Error> {
        self.0.serialize_str(if v { "true" } else { "false" })
    }

    fn serialize_i8(self, v: i8) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }
    fn serialize_i16(self, v: i16) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }
    fn serialize_i32(self, v: i32) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }
    fn serialize_i64(self, v: i64) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }
    fn serialize_i128(self, v: i128) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }

    fn serialize_u8(self, v: u8) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }
    fn serialize_u16(self, v: u16) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }
    fn serialize_u32(self, v: u32) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }
    fn serialize_u64(self, v: u64) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }
    fn serialize_u128(self, v: u128) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, &v.to_string())
    }

    fn serialize_f32(self, _v: f32) -> Result<(), Error> {
        Err(Error::Message("float keys are not supported in JSON".into()))
    }
    fn serialize_f64(self, _v: f64) -> Result<(), Error> {
        Err(Error::Message("float keys are not supported in JSON".into()))
    }

    fn serialize_char(self, v: char) -> Result<(), Error> {
        let mut buf = [0u8; 4];
        self.serialize_str(v.encode_utf8(&mut buf))
    }
    fn serialize_str(self, v: &str) -> Result<(), Error> {
        write_escaped_str(&mut self.0.writer, v)
    }
    fn serialize_bytes(self, _v: &[u8]) -> Result<(), Error> {
        Err(Error::Message("bytes keys are not supported in JSON".into()))
    }
    fn serialize_none(self) -> Result<(), Error> {
        Err(Error::Message("null keys are not supported in JSON".into()))
    }
    fn serialize_some<T: Serialize + ?Sized>(self, _value: &T) -> Result<(), Error> {
        Err(Error::Message("option keys are not supported in JSON".into()))
    }
    fn serialize_unit(self) -> Result<(), Error> {
        Err(Error::Message("unit keys are not supported in JSON".into()))
    }
    fn serialize_unit_struct(self, _name: &'static str) -> Result<(), Error> {
        Err(Error::Message("unit struct keys are not supported in JSON".into()))
    }
    fn serialize_unit_variant(self, _name: &'static str, _idx: u32, variant: &'static str) -> Result<(), Error> {
        self.serialize_str(variant)
    }
    fn serialize_newtype_struct<T: Serialize + ?Sized>(self, _name: &'static str, value: &T) -> Result<(), Error> {
        value.serialize(self)
    }
    fn serialize_newtype_variant<T: Serialize + ?Sized>(self, _name: &'static str, _idx: u32, _variant: &'static str, _value: &T) -> Result<(), Error> {
        Err(Error::Message("newtype variant keys are not supported in JSON".into()))
    }
    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, Error> {
        Err(Error::Message("seq keys are not supported in JSON".into()))
    }
    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, Error> {
        Err(Error::Message("tuple keys are not supported in JSON".into()))
    }
    fn serialize_tuple_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeTupleStruct, Error> {
        Err(Error::Message("tuple struct keys are not supported in JSON".into()))
    }
    fn serialize_tuple_variant(self, _name: &'static str, _idx: u32, _variant: &'static str, _len: usize) -> Result<Self::SerializeTupleVariant, Error> {
        Err(Error::Message("tuple variant keys are not supported in JSON".into()))
    }
    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Error> {
        Err(Error::Message("map keys are not supported in JSON".into()))
    }
    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct, Error> {
        Err(Error::Message("struct keys are not supported in JSON".into()))
    }
    fn serialize_struct_variant(self, _name: &'static str, _idx: u32, _variant: &'static str, _len: usize) -> Result<Self::SerializeStructVariant, Error> {
        Err(Error::Message("struct variant keys are not supported in JSON".into()))
    }
}

fn write_escaped_str(writer: &mut impl io::Write, s: &str) -> Result<(), Error> {
    writer.write_all(b"\"")?;

    let bytes = s.as_bytes();
    let mut start = 0; // start of current unescaped run

    for (i, &b) in bytes.iter().enumerate() {
        let escape = match b {
            b'"' => Some(b"\\\"" as &[u8]),
            b'\\' => Some(b"\\\\" as &[u8]),
            b'\n' => Some(b"\\n" as &[u8]),
            b'\r' => Some(b"\\r" as &[u8]),
            b'\t' => Some(b"\\t" as &[u8]),
            0x00..=0x1F => {
                // Flush the clean run, then write \uXXXX.
                if start < i {
                    writer.write_all(&bytes[start..i])?;
                }
                write!(writer, "\\u{:04x}", b)?;
                start = i + 1;
                None
            }
            _ => None, // safe byte (including multi-byte UTF-8 continuations)
        };

        if let Some(esc) = escape {
            // Flush the clean run before this escape.
            if start < i {
                writer.write_all(&bytes[start..i])?;
            }
            writer.write_all(esc)?;
            start = i + 1;
        }
    }

    // Flush any remaining clean bytes.
    if start < bytes.len() {
        writer.write_all(&bytes[start..])?;
    }

    writer.write_all(b"\"")?;
    Ok(())
}