qubit-metadata 0.6.2

// =============================================================================
//    Copyright (c) 2025 - 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
//! Seed decoder for the strict metadata v1 wire envelope.

use std::fmt;

use serde::de::DeserializeSeed;
use serde::de::Deserializer;
use serde::de::Error as DeError;
use serde::de::MapAccess;
use serde::de::Visitor;

use super::metadata_wire_v1::MetadataWireV1;

/// Deserializes a metadata envelope with a bounded values seed.
pub(crate) struct MetadataWireV1Seed<S> {
    /// Seed used to decode the values map.
    values: S,
}

impl<S> MetadataWireV1Seed<S> {
    /// Creates a metadata-envelope seed.
    pub(crate) const fn new(values: S) -> Self {
        Self { values }
    }
}

impl<'de, S> DeserializeSeed<'de> for MetadataWireV1Seed<S>
where
    S: DeserializeSeed<'de>,
{
    type Value = MetadataWireV1<S::Value>;

    /// Deserializes the strict envelope and delegates values to its seed.
    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
    where
        D: Deserializer<'de>,
    {
        struct MetadataWireVisitor<S> {
            /// Decoded values-map seed, if the envelope supplied it.
            values: Option<S>,
        }

        impl<'de, S> Visitor<'de> for MetadataWireVisitor<S>
        where
            S: DeserializeSeed<'de>,
        {
            type Value = MetadataWireV1<S::Value>;

            /// Describes the strict metadata envelope.
            fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
                formatter.write_str("a strict metadata V1 envelope")
            }

            /// Decodes each envelope field and rejects duplicates or unknowns.
            fn visit_map<A>(mut self, mut map: A) -> Result<Self::Value, A::Error>
            where
                A: MapAccess<'de>,
            {
                let mut version = None;
                let mut values = None;
                while let Some(key) = map.next_key::<String>()? {
                    match key.as_str() {
                        "version" => {
                            if version.is_some() {
                                return Err(DeError::duplicate_field("version"));
                            }
                            version = Some(map.next_value::<u8>()?);
                        }
                        "values" => {
                            if values.is_some() {
                                return Err(DeError::duplicate_field("values"));
                            }
                            let seed = self.values.take().expect("metadata values seed is consumed once");
                            values = Some(map.next_value_seed(seed)?);
                        }
                        _ => {
                            return Err(DeError::unknown_field(&key, &["version", "values"]));
                        }
                    }
                }
                Ok(MetadataWireV1 {
                    version: version.ok_or_else(|| DeError::missing_field("version"))?,
                    values: values.ok_or_else(|| DeError::missing_field("values"))?,
                })
            }
        }

        deserializer.deserialize_struct(
            "MetadataWireV1",
            &["version", "values"],
            MetadataWireVisitor {
                values: Some(self.values),
            },
        )
    }
}