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#![no_std]
#![feature(array_value_iter)]

pub struct JsonCompound {
    data: [u8; 4096],
    index: usize
}
impl JsonCompound {
    pub fn new() -> Self {
        let mut this = JsonCompound {
            data: [0; 4096],
            index: 1
        };
        this.data[0] = b'{';
        this
    }
    #[inline]
    fn write_str(&mut self, s: &str) {
        self.write_bytes(s.as_bytes());
    }
    #[inline]
    fn write_bytes(&mut self, b: &[u8]) {
        self.data[self.index..][..b.len()].copy_from_slice(b);
        self.index += b.len();
    }
    #[inline]
    fn write_char(&mut self, c: u8) {
        self.data[self.index] = c;
        self.index += 1;
    }
    fn key(&mut self, key: &str) {
        if self.index > 1 {self.write_char(b',')}
        self.write_char(b'"');
        self.write_str(key);
        self.write_bytes(b"\":");
    }
    pub fn literal(mut self, key: impl AsRef<str>, value: impl AsRef<str>) -> Self {
        self.key(key.as_ref());
        self.write_str(value.as_ref());
        self
    }
    pub fn string(mut self, key: impl AsRef<str>, value: impl AsRef<str>) -> Self {
        self.key(key.as_ref());
        self.write_char(b'"');
        self.write_str(value.as_ref());
        self.write_char(b'"');
        self
    }
    pub fn json(mut self, key: impl AsRef<str>, json: JsonResult) -> Self {
        self.key(key.as_ref());
        self.write_bytes(json.as_bytes());
        self
    }
    pub fn build(mut self) -> JsonResult {
        self.write_char(b'}');
        JsonResult {
            data: self.data,
            len: self.index
        }
    }
}

pub struct JsonList {
    data: [u8; 4096],
    index: usize
}
impl JsonList {
    pub fn new() -> Self {
        let mut this = JsonList {
            data: [0; 4096],
            index: 1
        };
        this.data[0] = b'[';
        this
    }
    #[inline]
    fn write_str(&mut self, s: &str) {
        self.write_bytes(s.as_bytes());
    }
    #[inline]
    fn write_bytes(&mut self, b: &[u8]) {
        self.data[self.index..][..b.len()].copy_from_slice(b);
        self.index += b.len();
    }
    #[inline]
    fn write_char(&mut self, c: u8) {
        self.data[self.index] = c;
        self.index += 1;
    }
    #[inline]
    fn item(&mut self) {
        if self.index > 1 {self.write_char(b',')}
    }
    pub fn literal<S: AsRef<str>>(mut self, values: impl IntoIterator<Item=S>) -> Self {
        for value in values {
            self.item();
            self.write_str(value.as_ref());
        }
        self
    }
    pub fn string<S: AsRef<str>>(mut self, values: impl IntoIterator<Item=S>) -> Self {
        for value in values {
            self.item();
            self.write_char(b'"');
            self.write_str(value.as_ref());
            self.write_char(b'"');
        }
        self
    }
    pub fn json(mut self, json: impl IntoIterator<Item=JsonResult>) -> Self {
        for j in json {
            self.item();
            self.write_bytes(j.as_bytes());
        }
        self
    }
    pub fn build(mut self) -> JsonResult {
        self.write_char(b']');
        JsonResult {
            data: self.data,
            len: self.index
        }
    }
}

pub struct JsonResult {
    data: [u8; 4096],
    len: usize
}
impl JsonResult {
    pub fn as_bytes(&self) -> &[u8] {
        &self.data[..self.len]
    }
}

#[cfg(test)]
mod tests {
    use crate::{JsonCompound, JsonList};

    #[test]
    fn test() {
        let json = JsonCompound::new()
            .literal("foo", "3")
            .string("bar", "bart")
            .json(
                "object",
                JsonCompound::new()
                    .literal("quux", "5")
                    .build()
            )
            .json(
                "list",
                JsonList::new().json(
                    core::array::IntoIter::new([
                        JsonCompound::new()
                            .literal("hello", "5")
                            .string("world", "!")
                            .build(),
                        JsonCompound::new()
                            .literal("world", "5")
                            .string("hello", "!")
                            .build()
                    ])
                ).build()
            )
            .build();
        assert_eq!(core::str::from_utf8(json.as_bytes()).unwrap(),
r#"{"foo":3,"bar":"bart","object":{"quux":5},"list":[{"hello":5,"world":"!"},{"world":5,"hello":"!"}]}"#);
    }
}