cadmpeg-ir 0.6.1

// SPDX-License-Identifier: Apache-2.0
//! The sealed encoder contract and its blanket implementation.
//!
//! A backend declares the domain its targets come from, receives only a
//! request resolved through that domain, and returns a bare [`ExportBody`].
//! The sealed [`Encoder::plan`] wrapper is the single author of the export's
//! identity and fidelity resolution: a backend cannot report a format, a
//! target, or a fidelity state other than the one it was given.

use std::io::Write;

use crate::codec::FormatId;
use crate::document::CadIr;
use crate::report::{
    export::{
        CensusBasis, EntityCensus, ExportReport, FidelityResolution, ReplayFidelity,
        SynthesisFidelity, WritePath as ReportWritePath,
    },
    loss::LossNote,
};
use crate::source_fidelity::SourceFidelity;
use cadmpeg_core::target::TargetCatalog;
use cadmpeg_core::CodecError;

mod coverage;
mod loss;
pub mod target;

pub use coverage::{ArenaCoverage, ArenaDisposition, ArenaDispositions};
use target::{DialectFree, TargetDomain, TargetRequest, TargetResolution};

/// Implementation surface for one output format.
///
/// Backends declare one target domain and receive only a request already
/// resolved through that domain. Callers use the sealed [`Encoder`] wrapper.
pub trait EncoderBackend {
    /// Stable output format id, taken from the codec that reads the format.
    const FORMAT: FormatId;

    /// The domain this backend's targets come from.
    type Target: TargetDomain;

    /// The domain value: [`DialectFree`] or a [`target::Catalog`] of this format's
    /// output flavors.
    const TARGET: Self::Target;

    /// Plans a write from the request resolved by [`Encoder::plan`].
    fn plan_resolved(
        &self,
        input: EncodeInput<'_>,
        target: <Self::Target as TargetDomain>::Resolved<'_>,
    ) -> Result<ExportBody, CodecError>;
}

mod encoder_sealed {
    pub trait Sealed {}
    impl<E: super::EncoderBackend> Sealed for E {}
}

/// Public planning interface for an output format.
pub trait Encoder: encoder_sealed::Sealed {
    /// Stable output format id.
    fn id(&self) -> FormatId;

    /// The static catalog of output flavors this encoder can produce.
    ///
    /// Whether a given input reaches one is resolution's answer, not the
    /// catalog's: a patch-only writer's row is reachable only from a retained
    /// source of that flavor, and `plan` refuses by name where it cannot
    /// deliver. Preservation of dialects outside the catalog is not listed
    /// here; [`TargetRequest::Inherit`] asks for it. Ids come from this
    /// encoder's own format namespace only.
    fn targets(&self) -> TargetCatalog;

    /// Plans one export without writing to the destination.
    fn plan(
        &self,
        input: EncodeInput<'_>,
        request: TargetRequest<'_>,
    ) -> Result<ExportPlan, CodecError>;
}

impl<E: EncoderBackend> Encoder for E {
    fn id(&self) -> FormatId {
        E::FORMAT
    }

    fn targets(&self) -> TargetCatalog {
        E::TARGET.targets(E::FORMAT)
    }

    fn plan(
        &self,
        input: EncodeInput<'_>,
        request: TargetRequest<'_>,
    ) -> Result<ExportPlan, CodecError> {
        let target = E::TARGET.resolve(input.ir, request, E::FORMAT)?;
        let identity = target.export_target().cloned();
        let body = self.plan_resolved(input, target)?;
        let ExportBody {
            bytes,
            census,
            write_path,
            coverage,
            mut losses,
            notes,
        } = body;
        losses.extend(coverage.omission_losses(&input.ir.model, E::FORMAT.as_str()));
        let write_path = write_path.into_report(input.fidelity.is_some());
        let report = match identity {
            None => ExportReport::cadir(census, write_path, losses, notes),
            Some(target) => ExportReport::native(target, census, write_path, losses, notes),
        };
        Ok(ExportPlan { report, bytes })
    }
}

/// Borrowed inputs used to plan an export.
#[derive(Debug, Clone, Copy)]
pub struct EncodeInput<'a> {
    /// Neutral document to export.
    pub ir: &'a CadIr,
    /// Decode-time fidelity state, when available.
    pub fidelity: Option<&'a SourceFidelity>,
}

impl<'a> EncodeInput<'a> {
    /// Borrows a document and its decode-time fidelity for one export.
    #[must_use]
    pub const fn new(ir: &'a CadIr, fidelity: Option<&'a SourceFidelity>) -> Self {
        Self { ir, fidelity }
    }
}

/// What a backend did with the source fidelity it was given.
///
/// Carried only by synthesized writes and patches that did not replay source
/// content. The wrapper maps it onto [`FidelityResolution`] and discards it
/// when the input carried no fidelity.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Consumption {
    /// This backend does not consume source fidelity.
    NotConsumed,
    /// Fidelity was available but could not be consumed.
    Degraded {
        /// Explanation of the degradation.
        reason: String,
    },
}

impl From<Consumption> for FidelityResolution {
    fn from(consumption: Consumption) -> Self {
        match consumption {
            Consumption::NotConsumed => Self::NotConsumed {},
            Consumption::Degraded { reason } => Self::Degraded { reason },
        }
    }
}

impl From<Consumption> for SynthesisFidelity {
    fn from(consumption: Consumption) -> Self {
        match consumption {
            Consumption::NotConsumed => Self::NotConsumed {},
            Consumption::Degraded { reason } => Self::Degraded { reason },
        }
    }
}

/// How a patched write handled the source fidelity supplied to it.
///
/// Some patchers edit retained sidecar bytes. Others patch native records
/// already stored in the IR and either do not consume the sidecar or report
/// why an eligible sidecar path was unavailable.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum PatchConsumption {
    /// Retained source content was consumed successfully.
    Replayed,
    /// The patch did not replay retained source content.
    Independent(Consumption),
}

/// Structurally valid backend write paths and their fidelity consumption.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum WritePath {
    /// The writer authored every output byte from neutral IR.
    Synthesized {
        /// How the synthesized write handled available source fidelity.
        consumption: Consumption,
    },
    /// The writer rewrote part of a container it did not author in full.
    Patched {
        /// How the patch handled available source fidelity.
        consumption: PatchConsumption,
    },
    /// Retained source bytes were copied unchanged.
    VerbatimReplay,
}

impl WritePath {
    fn into_report(self, fidelity_provided: bool) -> ReportWritePath {
        match self {
            Self::Synthesized { consumption } => ReportWritePath::Synthesized {
                fidelity: if fidelity_provided {
                    consumption.into()
                } else {
                    SynthesisFidelity::NotProvided {}
                },
            },
            Self::Patched {
                consumption: PatchConsumption::Replayed,
            } => ReportWritePath::Patched {
                fidelity: if fidelity_provided {
                    FidelityResolution::Replayed {}
                } else {
                    FidelityResolution::NotProvided {}
                },
            },
            Self::Patched {
                consumption: PatchConsumption::Independent(consumption),
            } => ReportWritePath::Patched {
                fidelity: if fidelity_provided {
                    consumption.into()
                } else {
                    FidelityResolution::NotProvided {}
                },
            },
            Self::VerbatimReplay => ReportWritePath::VerbatimReplay {
                fidelity: if fidelity_provided {
                    ReplayFidelity::Replayed {}
                } else {
                    ReplayFidelity::NotProvided {}
                },
            },
        }
    }
}

/// What a backend returns from `plan_resolved`.
///
/// Identity is not here: the wrapper stamps the resolved target, and the
/// fidelity resolution, onto the report it builds from this body.
#[derive(Debug, Clone, PartialEq)]
pub struct ExportBody {
    /// The complete materialized payload.
    pub bytes: Vec<u8>,
    /// Entity counts and the semantic basis on which they were measured.
    pub census: EntityCensus,
    /// How the payload was produced.
    pub write_path: WritePath,
    /// Which model arenas the payload carries. The wrapper charges a loss for
    /// every non-empty arena this coverage omits.
    pub coverage: ArenaCoverage,
    /// Losses charged while planning.
    pub losses: Vec<LossNote>,
    /// Free-form notes.
    pub notes: Vec<String>,
}

impl ExportBody {
    /// A synthesized payload counted on IR arenas that consumes no fidelity.
    #[must_use]
    pub fn synthesized(bytes: Vec<u8>, ir: &CadIr, coverage: ArenaCoverage) -> Self {
        Self {
            bytes,
            census: EntityCensus {
                basis: CensusBasis::IrArenas,
                counts: ir.census(),
            },
            write_path: WritePath::Synthesized {
                consumption: Consumption::NotConsumed,
            },
            coverage,
            losses: Vec::new(),
            notes: Vec::new(),
        }
    }
}

/// A fully reported export awaiting its destination write.
///
/// The plan owns the complete payload. Atomic file staging belongs to the
/// artifact store; [`Self::write_to`] also supports non-file sinks.
#[derive(Debug)]
pub struct ExportPlan {
    report: ExportReport,
    bytes: Vec<u8>,
}

impl ExportPlan {
    /// Returns the complete plan-time export report.
    pub fn report(&self) -> &ExportReport {
        &self.report
    }

    /// Writes the planned payload and returns the unchanged plan-time report.
    pub fn write_to(self, writer: &mut dyn Write) -> Result<ExportReport, CodecError> {
        writer.write_all(&self.bytes)?;
        Ok(self.report)
    }
}

/// Encoder for canonical versioned CADIR JSON.
#[derive(Debug, Clone, Copy, Default)]
pub struct CadirEncoder;

impl EncoderBackend for CadirEncoder {
    const FORMAT: FormatId = FormatId::new("cadir");

    /// CADIR writes the neutral document. Its version identifies the CADIR
    /// schema. The serialized export report uses the `cadir` identity variant,
    /// which has no native dialect target.
    type Target = DialectFree;
    const TARGET: DialectFree = DialectFree;

    fn plan_resolved(&self, input: EncodeInput<'_>, (): ()) -> Result<ExportBody, CodecError> {
        let mut bytes = crate::hash::finite_json::to_canonical_json_string(input.ir)
            .map_err(|error| CodecError::Malformed(error.to_string()))?
            .into_bytes();
        bytes.push(b'\n');
        // CADIR is the neutral document itself: there is no container to
        // replay or patch, so this encoder has one path and states it. The
        // serialization carries every arena.
        Ok(ExportBody::synthesized(
            bytes,
            input.ir,
            ArenaCoverage::Complete,
        ))
    }
}

#[cfg(test)]
mod tests;

#[cfg(test)]
mod test_support;