//! This module implements the serialisation of derivations into the
//! [ATerm][] format used by C++ Nix.
//!
//! [ATerm]: http://program-transformation.org/Tools/ATermFormat.html

use crate::aterm::escape_bytes;
use crate::derivation::{ca_kind_prefix, output::Output};
use crate::nixbase32;
use crate::store_path::{StorePath, StorePathRef, STORE_DIR_WITH_SLASH};
use bstr::BString;
use std::fmt::Display;
use std::{
    collections::{BTreeMap, BTreeSet},
    io,
    io::Error,
    io::Write,
};

use super::NixHash;

pub const DERIVATION_PREFIX: &str = "Derive";
pub const PAREN_OPEN: char = '(';
pub const PAREN_CLOSE: char = ')';
pub const BRACKET_OPEN: char = '[';
pub const BRACKET_CLOSE: char = ']';
pub const COMMA: char = ',';
pub const QUOTE: char = '"';

/// Something that can be written as ATerm.
///
/// Note that we mostly use explicit `write_*` calls
/// instead since the serialization of the items depends on
/// the context a lot.
pub(crate) trait AtermWriteable: Display {
    fn aterm_write(&self, writer: &mut impl Write) -> std::io::Result<()>;

    fn aterm_bytes(&self) -> Vec<u8> {
        let mut bytes = Vec::new();
        self.aterm_write(&mut bytes)
            .expect("unexpected write errors to Vec");
        bytes
    }
}

impl AtermWriteable for StorePathRef<'_> {
    fn aterm_write(&self, writer: &mut impl Write) -> std::io::Result<()> {
        write_char(writer, QUOTE)?;
        writer.write_all(STORE_DIR_WITH_SLASH.as_bytes())?;
        writer.write_all(nixbase32::encode(self.digest()).as_bytes())?;
        write_char(writer, '-')?;
        writer.write_all(self.name().as_bytes())?;
        write_char(writer, QUOTE)?;
        Ok(())
    }
}

impl AtermWriteable for StorePath {
    fn aterm_write(&self, writer: &mut impl Write) -> std::io::Result<()> {
        let r: StorePathRef = self.into();
        r.aterm_write(writer)
    }
}

impl AtermWriteable for String {
    fn aterm_write(&self, writer: &mut impl Write) -> std::io::Result<()> {
        write_field(writer, self, true)
    }
}

impl AtermWriteable for NixHash {
    fn aterm_write(&self, writer: &mut impl Write) -> std::io::Result<()> {
        // When we serialize the placeholder hashes,
        // they need to be SHA256.
        debug_assert!(matches!(self, NixHash::Sha256(_)));
        write_field(writer, self.to_plain_hex_string(), false)
    }
}

// Writes a character to the writer.
pub(crate) fn write_char(writer: &mut impl Write, c: char) -> io::Result<()> {
    let mut buf = [0; 4];
    let b = c.encode_utf8(&mut buf).as_bytes();
    writer.write_all(b)
}

// Write a string `s` as a quoted field to the writer.
// The `escape` argument controls whether escaping will be skipped.
// This is the case if `s` is known to only contain characters that need no
// escaping.
pub(crate) fn write_field<S: AsRef<[u8]>>(
    writer: &mut impl Write,
    s: S,
    escape: bool,
) -> io::Result<()> {
    write_char(writer, QUOTE)?;

    if !escape {
        writer.write_all(s.as_ref())?;
    } else {
        writer.write_all(&escape_bytes(s.as_ref()))?;
    }

    write_char(writer, QUOTE)?;

    Ok(())
}

fn write_array_elements<S: AsRef<[u8]>>(
    writer: &mut impl Write,
    elements: &[S],
) -> Result<(), io::Error> {
    for (index, element) in elements.iter().enumerate() {
        if index > 0 {
            write_char(writer, COMMA)?;
        }

        write_field(writer, element, true)?;
    }

    Ok(())
}

pub(crate) fn write_outputs(
    writer: &mut impl Write,
    outputs: &BTreeMap<String, Output>,
) -> Result<(), io::Error> {
    write_char(writer, BRACKET_OPEN)?;
    for (ii, (output_name, output)) in outputs.iter().enumerate() {
        if ii > 0 {
            write_char(writer, COMMA)?;
        }

        write_char(writer, PAREN_OPEN)?;

        let path_str = output.path_str();
        let mut elements: Vec<&str> = vec![output_name, &path_str];

        let (mode_and_algo, digest) = match &output.ca_hash {
            Some(ca_hash) => (
                format!("{}{}", ca_kind_prefix(ca_hash), ca_hash.digest().algo()),
                data_encoding::HEXLOWER.encode(ca_hash.digest().digest_as_bytes()),
            ),
            None => ("".to_string(), "".to_string()),
        };

        elements.push(&mode_and_algo);
        elements.push(&digest);

        write_array_elements(writer, &elements)?;

        write_char(writer, PAREN_CLOSE)?;
    }
    write_char(writer, BRACKET_CLOSE)?;

    Ok(())
}

pub(crate) fn write_input_derivations(
    writer: &mut impl Write,
    input_derivations: &BTreeMap<impl AtermWriteable, BTreeSet<String>>,
) -> Result<(), io::Error> {
    write_char(writer, BRACKET_OPEN)?;

    for (ii, (input_derivation_aterm, output_names)) in input_derivations.iter().enumerate() {
        if ii > 0 {
            write_char(writer, COMMA)?;
        }

        write_char(writer, PAREN_OPEN)?;
        input_derivation_aterm.aterm_write(writer)?;
        write_char(writer, COMMA)?;

        write_char(writer, BRACKET_OPEN)?;
        write_array_elements(
            writer,
            &output_names
                .iter()
                .map(String::as_bytes)
                .collect::<Vec<_>>(),
        )?;
        write_char(writer, BRACKET_CLOSE)?;

        write_char(writer, PAREN_CLOSE)?;
    }

    write_char(writer, BRACKET_CLOSE)?;

    Ok(())
}

pub(crate) fn write_input_sources(
    writer: &mut impl Write,
    input_sources: &BTreeSet<StorePath>,
) -> Result<(), io::Error> {
    write_char(writer, BRACKET_OPEN)?;
    write_array_elements(
        writer,
        &input_sources
            .iter()
            .map(StorePath::to_absolute_path)
            .collect::<Vec<_>>(),
    )?;
    write_char(writer, BRACKET_CLOSE)?;

    Ok(())
}

pub(crate) fn write_system(writer: &mut impl Write, platform: &str) -> Result<(), Error> {
    write_field(writer, platform, true)?;
    Ok(())
}

pub(crate) fn write_builder(writer: &mut impl Write, builder: &str) -> Result<(), Error> {
    write_field(writer, builder, true)?;
    Ok(())
}

pub(crate) fn write_arguments(
    writer: &mut impl Write,
    arguments: &[String],
) -> Result<(), io::Error> {
    write_char(writer, BRACKET_OPEN)?;
    write_array_elements(
        writer,
        &arguments
            .iter()
            .map(|s| s.as_bytes().to_vec().into())
            .collect::<Vec<BString>>(),
    )?;
    write_char(writer, BRACKET_CLOSE)?;

    Ok(())
}

pub(crate) fn write_environment<E, K, V>(
    writer: &mut impl Write,
    environment: E,
) -> Result<(), io::Error>
where
    E: IntoIterator<Item = (K, V)>,
    K: AsRef<[u8]>,
    V: AsRef<[u8]>,
{
    write_char(writer, BRACKET_OPEN)?;

    for (i, (k, v)) in environment.into_iter().enumerate() {
        if i > 0 {
            write_char(writer, COMMA)?;
        }

        write_char(writer, PAREN_OPEN)?;
        write_field(writer, k, false)?;
        write_char(writer, COMMA)?;
        write_field(writer, v, true)?;
        write_char(writer, PAREN_CLOSE)?;
    }

    write_char(writer, BRACKET_CLOSE)?;

    Ok(())
}