jsoncompat 0.5.0

//! Compatibility reporting over lowered OpenAPI request/response contracts.

use crate::{
    CompatibilityError, CompatibilityResult, Role, analyze_compat, explain_compat_failure,
    validate_compatibility_input,
};
use jsoncompat_openapi::{
    LoweredOperation, OpenApiDocument, OpenApiLoweringError, OperationKey, lower_operations,
};
use std::collections::BTreeMap;

#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum OpenApiCompatibilityError {
    #[error(transparent)]
    Lowering(#[from] OpenApiLoweringError),
    #[error(transparent)]
    Compatibility(#[from] CompatibilityError),
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize)]
#[serde(rename_all = "snake_case")]
pub enum OpenApiCompatibilitySurface {
    Operation,
    Request,
    Response,
}

#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize)]
pub struct OpenApiCompatibilityIssue {
    pub method: String,
    pub path: String,
    pub surface: OpenApiCompatibilitySurface,
    pub message: String,
    pub kind: OpenApiCompatibilityIssueKind,
}

/// Removed operations are structural breaks; schema breaks carry a validated
/// value. An unsuccessful inclusion proof alone is explicitly unknown.
#[derive(Debug, Clone, PartialEq, Eq, serde::Serialize)]
#[serde(tag = "status", rename_all = "snake_case")]
pub enum OpenApiCompatibilityIssueKind {
    OperationRemoved,
    Incompatible {
        direction: Role,
        counterexample: serde_json::Value,
    },
    Unknown {
        reason: String,
    },
}

#[derive(Debug, Clone, Default, PartialEq, Eq, serde::Serialize)]
pub struct OpenApiCompatibilityReport {
    issues: Vec<OpenApiCompatibilityIssue>,
}

impl OpenApiCompatibilityReport {
    #[must_use]
    pub fn is_compatible(&self) -> bool {
        self.issues.is_empty()
    }

    /// True only when at least one break was established.
    #[must_use]
    pub fn is_incompatible(&self) -> bool {
        self.issues
            .iter()
            .any(|issue| !matches!(issue.kind, OpenApiCompatibilityIssueKind::Unknown { .. }))
    }
    #[must_use]
    pub fn is_unknown(&self) -> bool {
        !self.is_compatible() && !self.is_incompatible()
    }

    #[must_use]
    pub fn issues(&self) -> &[OpenApiCompatibilityIssue] {
        &self.issues
    }

    fn push(
        &mut self,
        operation: &OperationKey,
        surface: OpenApiCompatibilitySurface,
        message: impl Into<String>,
        kind: OpenApiCompatibilityIssueKind,
    ) {
        self.issues.push(OpenApiCompatibilityIssue {
            method: operation.method.clone(),
            path: operation.path.clone(),
            surface,
            message: message.into(),
            kind,
        });
    }
}

struct OpenApiCompatibilityInput<'a> {
    document: &'a OpenApiDocument,
    operations: BTreeMap<OperationKey, PreparedOperation>,
}

struct PreparedOperation {
    lowered: LoweredOperation,
    request: crate::SchemaDocument,
    response: crate::SchemaDocument,
}

struct OperationSurface<'a> {
    old: &'a crate::SchemaDocument,
    new: &'a crate::SchemaDocument,
    changed: bool,
    surface: OpenApiCompatibilitySurface,
    role: Role,
    fallback_message: &'static str,
}

impl<'a> OpenApiCompatibilityInput<'a> {
    fn new(document: &'a OpenApiDocument) -> Result<Self, OpenApiCompatibilityError> {
        let mut operations = BTreeMap::new();
        for (key, lowered) in lower_operations(document)? {
            let request = prepare_lowered_contract(document, &lowered.request)?;
            let response = prepare_lowered_contract(document, &lowered.response)?;
            operations.insert(
                key,
                PreparedOperation {
                    lowered,
                    request,
                    response,
                },
            );
        }

        Ok(Self {
            document,
            operations,
        })
    }
}

/// Return whether an OpenAPI document is fully supported by the compatibility layer.
///
/// [`OpenApiDocument::from_json`] validates OpenAPI document shape. This helper
/// finishes the compatibility-specific validation pass: it resolves and lowers
/// every operation contract, then verifies that the generated request and
/// response schemas stay inside the raw JSON Schema compatibility subset.
pub fn validate_openapi_compatibility_input(
    document: &OpenApiDocument,
) -> Result<(), OpenApiCompatibilityError> {
    OpenApiCompatibilityInput::new(document).map(|_| ())
}

pub fn check_openapi_compat(
    old: &OpenApiDocument,
    new: &OpenApiDocument,
) -> Result<OpenApiCompatibilityReport, OpenApiCompatibilityError> {
    let old = OpenApiCompatibilityInput::new(old)?;
    let new = OpenApiCompatibilityInput::new(new)?;
    let mut report = OpenApiCompatibilityReport::default();
    let dialects_differ = !old.document.uses_same_schema_dialect_as(new.document)?;

    for (key, old_operation) in &old.operations {
        let Some(new_operation) = new.operations.get(key) else {
            report.push(
                key,
                OpenApiCompatibilitySurface::Operation,
                "operation was removed",
                OpenApiCompatibilityIssueKind::OperationRemoved,
            );
            continue;
        };
        for surface in [
            OperationSurface {
                old: &old_operation.request,
                new: &new_operation.request,
                changed: old_operation.lowered.request != new_operation.lowered.request
                    || dialects_differ,
                surface: OpenApiCompatibilitySurface::Request,
                role: Role::Deserializer,
                fallback_message: "request contract became incompatible",
            },
            OperationSurface {
                old: &old_operation.response,
                new: &new_operation.response,
                changed: old_operation.lowered.response != new_operation.lowered.response
                    || dialects_differ,
                surface: OpenApiCompatibilitySurface::Response,
                role: Role::Serializer,
                fallback_message: "response contract became incompatible",
            },
        ] {
            surface.report_if_incompatible(&mut report, key)?;
        }
    }

    Ok(report)
}

impl OperationSurface<'_> {
    fn report_if_incompatible(
        self,
        report: &mut OpenApiCompatibilityReport,
        operation: &OperationKey,
    ) -> Result<(), OpenApiCompatibilityError> {
        if !self.changed {
            return Ok(());
        }
        let (message, kind) = match analyze_compat(self.old, self.new, self.role)? {
            CompatibilityResult::Compatible => return Ok(()),
            CompatibilityResult::Incompatible {
                direction,
                counterexample,
            } => (
                explain_compat_failure(self.old, self.new, self.role)?
                    .unwrap_or_else(|| self.fallback_message.to_owned()),
                OpenApiCompatibilityIssueKind::Incompatible {
                    direction,
                    counterexample,
                },
            ),
            CompatibilityResult::Unknown { reason } => (
                reason.clone(),
                OpenApiCompatibilityIssueKind::Unknown { reason },
            ),
        };
        report.push(operation, self.surface, message, kind);
        Ok(())
    }
}

fn prepare_lowered_contract(
    document: &OpenApiDocument,
    schema: &serde_json::Value,
) -> Result<crate::SchemaDocument, OpenApiCompatibilityError> {
    let schema = document.lowered_contract_document(schema)?;
    validate_compatibility_input(&schema)?;
    Ok(schema)
}