qubit-json 0.9.0

// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
//! Incremental external writer for budget-aware JSON encoding.

use std::cell::RefCell;
use std::io;
use std::io::Write;

use qubit_budget::ResourceQuantity;

use super::json_output_accounting::JsonOutputAccounting;
use crate::encode::JsonEncodeError;

/// Writes accepted JSON bytes directly to an external destination.
pub(in crate::encode) struct JsonOutputWriter<'a, W, R, Q>
where
    Q: ResourceQuantity,
{
    /// Destination receiving each accepted byte slice.
    writer: W,

    /// Shared output budget and first-failure state.
    accounting: &'a RefCell<JsonOutputAccounting<'a, R, Q>>,

    /// Whether accepted writes must charge an output-byte budget.
    has_output_budget: bool,

    /// A copy of the first destination error for typed conversion after
    /// serde_json has erased it.
    io_error: Option<io::Error>,
}

impl<'a, W, R, Q> JsonOutputWriter<'a, W, R, Q>
where
    Q: ResourceQuantity,
{
    /// Creates an incremental writer over shared output accounting.
    #[inline]
    pub(in crate::encode) fn new(writer: W, accounting: &'a RefCell<JsonOutputAccounting<'a, R, Q>>) -> Self {
        Self {
            writer,
            accounting,
            has_output_budget: accounting.borrow().has_output_budget(),
            io_error: None,
        }
    }

    /// Converts the serializer result while preserving typed failures.
    pub(in crate::encode) fn into_result(
        self,
        result: Result<(), serde_json::Error>,
    ) -> Result<(), JsonEncodeError<R, Q>> {
        let violation = self.accounting.borrow_mut().take_violation();
        if let Some(error) = violation {
            return Err(JsonEncodeError::<R, Q>::budget(error));
        }
        let syntax_error = self.accounting.borrow_mut().take_syntax_error();
        if let Some(error) = syntax_error {
            return Err(JsonEncodeError::<R, Q>::invalid_raw_json(error));
        }
        if let Some(error) = self.io_error {
            return Err(JsonEncodeError::<R, Q>::write(error));
        }
        if result.is_err() {
            let error = self.accounting.borrow_mut().take_serialization_error_or_custom();
            return Err(JsonEncodeError::<R, Q>::serialization(error));
        }
        Ok(())
    }
}

impl<W, R, Q> Write for JsonOutputWriter<'_, W, R, Q>
where
    W: Write,
    R: Clone,
    Q: ResourceQuantity,
{
    /// Checks capacity, writes one slice, and charges only bytes accepted by
    /// the destination.
    fn write(&mut self, input: &[u8]) -> io::Result<usize> {
        if self.has_output_budget {
            let accounting = self.accounting.borrow();
            if let Err(error) = accounting.check_available(input.len()) {
                drop(accounting);
                self.accounting.borrow_mut().record_violation(error);
                return Err(io::Error::other("JSON output budget exceeded"));
            }
        }

        match self.writer.write(input) {
            Ok(written) => {
                if written == 0 && !input.is_empty() {
                    let error = io::Error::new(io::ErrorKind::WriteZero, "JSON output writer accepted no bytes");
                    self.io_error = Some(io::Error::new(error.kind(), error.to_string()));
                    return Err(error);
                }
                if self.has_output_budget {
                    let mut accounting = self.accounting.borrow_mut();
                    if let Err(error) = accounting.consume(written) {
                        accounting.record_violation(error);
                        return Err(io::Error::other("JSON output budget exceeded"));
                    }
                }
                Ok(written)
            }
            Err(error) => {
                self.io_error = Some(io::Error::new(error.kind(), error.to_string()));
                Err(error)
            }
        }
    }

    /// Flushes the destination and preserves any resulting I/O error.
    fn flush(&mut self) -> io::Result<()> {
        match self.writer.flush() {
            Ok(()) => Ok(()),
            Err(error) => {
                self.io_error = Some(io::Error::new(error.kind(), error.to_string()));
                Err(error)
            }
        }
    }
}