cqlib-core 0.1.0-beta.5

// This code is part of Cqlib.
//
// (C) Copyright China Telecom Quantum Group 2026
//
// This code is licensed under the Apache License, Version 2.0.
// You may obtain a copy of this license in the LICENSE.txt file in
// the root directory of this source tree or at
// http://www.apache.org/licenses/LICENSE-2.0.
//
// Any modifications or derivative works of this code must retain this
// copyright notice, and modified files need to carry a notice indicating
// that they have been altered from the originals.

//! Shared operation, output, and traversal support for circuit lowering passes.

use crate::circuit::{Instruction, Operation, Parameter, ParameterValue, Qubit, ValueOperation};
use crate::compile::CompilerError;
use crate::compile::transform::rebuild::ClassicalRemap;
use smallvec::SmallVec;

/// A gate-like operation with resolved parameters awaiting lowering.
#[derive(Debug, Clone)]
pub(super) struct LowerableOperation {
    pub(super) instruction: Instruction,
    pub(super) qubits: SmallVec<[Qubit; 3]>,
    pub(super) params: SmallVec<[ParameterValue; 1]>,
    pub(super) label: Option<Box<str>>,
}

impl LowerableOperation {
    /// Reads the first parameter as an exact global-phase contribution.
    ///
    /// The caller must have identified this operation as `GPhase`. This checks
    /// for a missing parameter; instruction and parameter arity validation
    /// remain the responsibility of the caller's input pipeline.
    pub(super) fn gphase_param(&self) -> Result<Parameter, CompilerError> {
        self.params.first().map(Parameter::from).ok_or_else(|| {
            CompilerError::InvariantViolation(
                "GPhase operation must contain one parameter".to_string(),
            )
        })
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum LoweringScope {
    TopLevel,
    ControlFlowBody,
}

/// Mutable output state for one independently lowered operation sequence.
///
/// The target only owns common emission state. Pass-specific finalization,
/// such as flushing delayed device leaves or materializing a body-local
/// `GPhase`, remains the responsibility of the lowering pass.
pub(crate) struct LoweringTarget<'a> {
    output: &'a mut Vec<ValueOperation>,
    phase_delta: &'a mut Parameter,
    scope: LoweringScope,
}

impl<'a> LoweringTarget<'a> {
    /// Creates a target for a circuit's root operation sequence.
    pub(crate) fn top_level(
        output: &'a mut Vec<ValueOperation>,
        phase_delta: &'a mut Parameter,
    ) -> Self {
        Self {
            output,
            phase_delta,
            scope: LoweringScope::TopLevel,
        }
    }

    /// Creates a target for one structured-control body.
    pub(crate) fn control_flow_body(
        output: &'a mut Vec<ValueOperation>,
        phase_delta: &'a mut Parameter,
    ) -> Self {
        Self {
            output,
            phase_delta,
            scope: LoweringScope::ControlFlowBody,
        }
    }

    /// Returns whether this target emits the circuit's root sequence.
    pub(crate) const fn is_top_level(&self) -> bool {
        matches!(self.scope, LoweringScope::TopLevel)
    }

    /// Appends one value-level operation to this sequence.
    pub(crate) fn push(&mut self, operation: ValueOperation) {
        self.output.push(operation);
    }

    /// Adds an exact global-phase contribution to this sequence.
    pub(crate) fn accumulate_phase(&mut self, phase: Parameter) {
        *self.phase_delta = &*self.phase_delta + &phase;
    }
}

/// Common linear sequence driver for lowering passes whose unit of work is one
/// source operation.
pub(crate) trait OperationSequenceLowerer {
    /// Lowers one operation into `target`.
    fn lower_one_operation(
        &mut self,
        operation: &Operation,
        classical_remap: &ClassicalRemap,
        target: &mut LoweringTarget<'_>,
    ) -> Result<(), CompilerError>;

    /// Lowers one operation sequence in source order.
    fn lower_sequence(
        &mut self,
        operations: &[Operation],
        classical_remap: &ClassicalRemap,
        mut target: LoweringTarget<'_>,
    ) -> Result<(), CompilerError> {
        for operation in operations {
            self.lower_one_operation(operation, classical_remap, &mut target)?;
        }
        Ok(())
    }
}