/// Implementation of Value serialisation *to* JSON.
///
/// This can not be implemented through standard serde-derive methods,
/// as there is internal Nix logic that must happen within the
/// serialisation methods.
use super::{CoercionKind, Value};
use crate::errors::ErrorKind;
use crate::generators::{self, GenCo};
use crate::NixContext;

use bstr::ByteSlice;
use serde_json::value::to_value;
use serde_json::Value as Json; // name clash with *our* `Value`
use serde_json::{Map, Number};

impl Value {
    /// Transforms the structure into a JSON
    /// and accumulate all encountered context in the second's element
    /// of the return type.
    pub async fn into_contextful_json(self, co: &GenCo) -> Result<(Json, NixContext), ErrorKind> {
        let self_forced = generators::request_force(co, self).await;
        let mut context = NixContext::new();

        let value = match self_forced {
            Value::Null => Json::Null,
            Value::Bool(b) => Json::Bool(b),
            Value::Integer(i) => Json::Number(Number::from(i)),
            Value::Float(f) => to_value(f)?,
            Value::String(s) => {
                context.mimic(&s);

                Json::String(s.to_str()?.to_owned())
            }

            Value::Path(p) => {
                let imported = generators::request_path_import(co, *p).await;
                let path = imported.to_string_lossy().to_string();
                context = context.append(crate::NixContextElement::Plain(path.clone()));
                Json::String(path)
            }

            Value::List(l) => {
                let mut out = Vec::with_capacity(l.len());

                for val in l.into_iter() {
                    let (json_item, ctx) = Box::pin(val.into_contextful_json(co)).await?;
                    context.extend(ctx.into_iter());
                    out.push(json_item);
                }

                Json::Array(out)
            }

            Value::Attrs(attrs) => {
                // Attribute sets with a callable `__toString` attribute
                // serialise to the string-coerced version of the result of
                // calling that.
                if attrs.select("__toString").is_some() {
                    let span = generators::request_span(co).await;
                    match Value::Attrs(attrs)
                        .coerce_to_string_(
                            co,
                            CoercionKind {
                                strong: false,
                                import_paths: false,
                            },
                            span,
                        )
                        .await?
                    {
                        Value::Catchable(cek) => return Err(ErrorKind::CatchableError(*cek)),
                        Value::String(s) => {
                            // We need a fresh context here because `__toString` will discard
                            // everything.
                            let mut fresh = NixContext::new();
                            fresh.mimic(&s);
                            return Ok((Json::String(s.to_str()?.to_owned()), fresh));
                        }
                        _ => panic!("Value::coerce_to_string_() returned a non-string!"),
                    }
                }

                // Attribute sets with an `outPath` attribute
                // serialise to a JSON serialisation of that inner
                // value (regardless of what it is!).
                if let Some(out_path) = attrs.select("outPath") {
                    let (json_out_path, ctx) =
                        Box::pin(out_path.clone().into_contextful_json(co)).await?;
                    context.extend(ctx.into_iter());
                    return Ok((json_out_path, context));
                }

                let mut out = Map::with_capacity(attrs.len());
                for (name, value) in attrs.into_iter_sorted() {
                    let (json_value, ctx) = Box::pin(value.into_contextful_json(co)).await?;
                    context.extend(ctx.into_iter());
                    out.insert(name.to_str()?.to_owned(), json_value);
                }

                Json::Object(out)
            }

            Value::Catchable(c) => return Err(ErrorKind::CatchableError(*c)),

            val @ Value::Closure(_)
            | val @ Value::Thunk(_)
            | val @ Value::Builtin(_)
            | val @ Value::AttrNotFound
            | val @ Value::Blueprint(_)
            | val @ Value::DeferredUpvalue(_)
            | val @ Value::UnresolvedPath(_)
            | val @ Value::FinaliseRequest(_) => {
                return Err(ErrorKind::NotSerialisableToJson(val.type_of()))
            }
        };
        Ok((value, context))
    }
}