sbom-model 0.8.0

#![doc = include_str!("../readme.md")]

pub mod versions;

use indexmap::IndexMap;
use packageurl::PackageUrl;
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::collections::{BTreeMap, BTreeSet};
use std::fmt;
use std::str::FromStr;

/// format-agnostic SBOM (Software Bill of Materials) representation.
///
/// this is the central type that holds all components and their relationships.
/// it abstracts over format-specific details from CycloneDX, SPDX, and other formats.
///
/// # Example
///
/// ```
/// use sbom_model::{Sbom, Component};
///
/// let mut sbom = Sbom::default();
/// let component = Component::new("serde".into(), Some("1.0.0".into()));
/// sbom.components.insert(component.id.clone(), component);
/// ```
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Sbom {
    /// document-level metadata (creation time, tools, authors).
    pub metadata: Metadata,
    /// all components indexed by their stable identifier.
    pub components: IndexMap<ComponentId, Component>,
    /// dependency graph as adjacency list: parent -> (child -> kind).
    pub dependencies: BTreeMap<ComponentId, BTreeMap<ComponentId, DependencyKind>>,
    /// reverse dependency index: child -> set of parents.
    ///
    /// derived from `dependencies`; call [`rebuild_reverse_deps`](Sbom::rebuild_reverse_deps)
    /// after modifying `dependencies` to keep it in sync.
    #[serde(skip)]
    pub reverse_deps: BTreeMap<ComponentId, BTreeSet<ComponentId>>,
    /// non-fatal warnings produced during parsing (e.g. orphaned dependency refs).
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub warnings: Vec<String>,
}

impl PartialEq for Sbom {
    fn eq(&self, other: &Self) -> bool {
        self.metadata == other.metadata
            && self.components == other.components
            && self.dependencies == other.dependencies
            && self.warnings == other.warnings
    }
}

impl Eq for Sbom {}

impl Default for Sbom {
    fn default() -> Self {
        Self {
            metadata: Metadata::default(),
            components: IndexMap::new(),
            dependencies: BTreeMap::new(),
            reverse_deps: BTreeMap::new(),
            warnings: Vec::new(),
        }
    }
}

/// SBOM document metadata.
///
/// contains information about when and how the SBOM was created.
/// this data is stripped during normalization since it varies between
/// tool runs and shouldn't affect diff comparisons.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, Default)]
pub struct Metadata {
    /// ISO 8601 timestamp of document creation.
    pub timestamp: Option<String>,
    /// tools used to generate the SBOM (e.g., "syft", "trivy").
    pub tools: Vec<String>,
    /// document authors or organizations.
    pub authors: Vec<String>,
}

/// the semantic type of a dependency relationship.
///
/// SPDX distinguishes between runtime, dev, build, test, optional, and
/// provided dependencies via typed relationship names. CycloneDX encodes
/// scope on the component itself (`required` / `optional` / `excluded`),
/// which is mapped to the appropriate variant when constructing edges.
///
/// the default is `Runtime`, which also covers generic relationships
/// like `DEPENDS_ON` or `CONTAINS` that don't specify a scope.
#[derive(
    Debug, Clone, Copy, Default, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize,
)]
#[serde(rename_all = "lowercase")]
pub enum DependencyKind {
    /// runtime or unspecified dependency (the default).
    #[default]
    Runtime,
    /// development-only dependency.
    Dev,
    /// build-time dependency.
    Build,
    /// test-only dependency.
    Test,
    /// optional dependency.
    Optional,
    /// provided by the runtime environment.
    Provided,
}

impl fmt::Display for DependencyKind {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Runtime => write!(f, "runtime"),
            Self::Dev => write!(f, "dev"),
            Self::Build => write!(f, "build"),
            Self::Test => write!(f, "test"),
            Self::Optional => write!(f, "optional"),
            Self::Provided => write!(f, "provided"),
        }
    }
}

/// stable identifier for a component.
///
/// used as a key in the component map and dependency graph. prefers package URLs
/// (purls) when available since they provide globally unique identifiers. falls
/// back to a deterministic SHA-256 hash of component properties when no purl exists.
///
/// # Example
///
/// ```
/// use sbom_model::ComponentId;
///
/// // with a purl (preferred)
/// let id = ComponentId::new(Some("pkg:npm/lodash@4.17.21"), &[]);
/// assert_eq!(id.as_str(), "pkg:npm/lodash@4.17.21");
///
/// // without a purl (hash fallback)
/// let id = ComponentId::new(None, &[("name", "foo"), ("version", "1.0")]);
/// assert!(id.as_str().starts_with("h:"));
/// ```
#[derive(Debug, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
pub struct ComponentId(String);

impl ComponentId {
    /// creates a new identifier from a purl or property hash.
    ///
    /// if a purl is provided, it will be canonicalized. otherwise, a deterministic
    /// SHA-256 hash is computed from the provided key-value properties.
    pub fn new(purl: Option<&str>, properties: &[(&str, &str)]) -> Self {
        if let Some(purl) = purl {
            if let Ok(parsed) = PackageUrl::from_str(purl) {
                return ComponentId(parsed.to_string());
            }
            return ComponentId(purl.to_string());
        }

        // deterministic hash fallback
        let mut hasher = Sha256::new();
        for (k, v) in properties {
            hasher.update(k.as_bytes());
            hasher.update(b":");
            hasher.update(v.as_bytes());
            hasher.update(b"|");
        }
        let hash = hex::encode(hasher.finalize());
        ComponentId(format!("h:{}", hash))
    }

    /// returns the identifier as a string slice.
    pub fn as_str(&self) -> &str {
        &self.0
    }
}

impl std::fmt::Display for ComponentId {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

/// a software component (package, library, or application).
///
/// represents a single entry in the SBOM with all its metadata.
/// components are identified by their [`ComponentId`] and can have
/// relationships to other components via the dependency graph.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Component {
    /// stable identifier for this component.
    pub id: ComponentId,
    /// package name (e.g., "serde", "lodash").
    pub name: String,
    /// package version (e.g., "1.0.0", "4.17.21").
    pub version: Option<String>,
    /// package ecosystem (e.g., "cargo", "npm", "pypi").
    pub ecosystem: Option<String>,
    /// package supplier or publisher.
    pub supplier: Option<String>,
    /// human-readable description.
    pub description: Option<String>,
    /// package URL per the [purl spec](https://github.com/package-url/purl-spec).
    pub purl: Option<String>,
    /// SPDX license identifiers (e.g., "MIT", "Apache-2.0").
    pub licenses: BTreeSet<String>,
    /// the SPDX license expression the source document declared, when it
    /// declared one (e.g., "MIT OR Apache-2.0").
    ///
    /// [`licenses`](Self::licenses) is the flattened identifier set of this
    /// expression and stays populated either way; policy decisions should go
    /// through [`licensing`](Self::licensing), which keeps the operators.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub license_expression: Option<String>,
    /// checksums keyed by algorithm (e.g., "sha256" -> "abc123...").
    pub hashes: BTreeMap<String, String>,
    /// original identifiers from the source document (e.g., SPDX SPDXRef, CycloneDX bom-ref).
    pub source_ids: Vec<String>,
}

impl Component {
    /// creates a new component with the given name and optional version.
    ///
    /// the component ID is generated from a hash of the name and version.
    /// use this for simple cases; for full control, construct the struct directly.
    pub fn new(name: String, version: Option<String>) -> Self {
        let mut props = vec![("name", name.as_str())];
        if let Some(v) = &version {
            props.push(("version", v));
        }
        let id = ComponentId::new(None, &props);

        Self {
            id,
            name,
            version,
            ecosystem: None,
            supplier: None,
            description: None,
            purl: None,
            licenses: BTreeSet::new(),
            license_expression: None,
            hashes: BTreeMap::new(),
            source_ids: Vec::new(),
        }
    }

    /// returns the licensing this component declares, for policy evaluation.
    pub fn licensing(&self) -> Licensing<'_> {
        Licensing {
            expression: self.license_expression.as_deref(),
            ids: &self.licenses,
        }
    }
}

impl Sbom {
    /// normalizes the SBOM for deterministic comparison.
    ///
    /// this method:
    /// - sorts components by ID
    /// - deduplicates and sorts licenses within each component
    /// - lowercases hash algorithms and values
    /// - clears volatile metadata (timestamps, tools, authors)
    ///
    /// call this before comparing two SBOMs to ignore irrelevant differences.
    pub fn normalize(&mut self) {
        // sort components by ID for deterministic output
        self.components.sort_keys();

        // normalize components
        for component in self.components.values_mut() {
            component.normalize();
        }

        // strip volatile metadata
        self.metadata.timestamp = None;
        self.metadata.tools.clear();
        self.metadata.authors.clear();

        self.rebuild_reverse_deps();
    }

    /// rebuilds the reverse dependency index from the forward `dependencies` map.
    ///
    /// must be called after modifying `dependencies` for `rdeps()` and `roots()`
    /// to return correct results. Parsers call this automatically; call it
    /// explicitly when constructing an `Sbom` by hand.
    pub fn rebuild_reverse_deps(&mut self) {
        self.reverse_deps.clear();
        for (parent, children) in &self.dependencies {
            for child in children.keys() {
                self.reverse_deps
                    .entry(child.clone())
                    .or_default()
                    .insert(parent.clone());
            }
        }
    }

    /// returns root components (those not depended on by any other component).
    ///
    /// these are typically the top-level packages or applications in the SBOM.
    /// uses the precomputed `reverse_deps` index.
    pub fn roots(&self) -> Vec<ComponentId> {
        self.components
            .keys()
            .filter(|id| self.reverse_deps.get(*id).is_none_or(BTreeSet::is_empty))
            .cloned()
            .collect()
    }

    /// returns direct dependencies of the given component.
    pub fn deps(&self, id: &ComponentId) -> Vec<ComponentId> {
        self.dependencies
            .get(id)
            .map(|d| d.keys().cloned().collect())
            .unwrap_or_default()
    }

    /// returns reverse dependencies (components that depend on the given component).
    /// uses the precomputed `reverse_deps` index.
    pub fn rdeps(&self, id: &ComponentId) -> Vec<ComponentId> {
        self.reverse_deps
            .get(id)
            .map(|parents| parents.iter().cloned().collect())
            .unwrap_or_default()
    }

    /// returns all transitive dependencies of the given component.
    ///
    /// traverses the dependency graph depth-first and returns all reachable components.
    pub fn transitive_deps(&self, id: &ComponentId) -> BTreeSet<ComponentId> {
        let mut visited = BTreeSet::new();
        let mut stack = vec![id.clone()];
        while let Some(current) = stack.pop() {
            if let Some(children) = self.dependencies.get(&current) {
                for child in children.keys() {
                    if visited.insert(child.clone()) {
                        stack.push(child.clone());
                    }
                }
            }
        }
        visited
    }

    /// returns all unique ecosystems present in the SBOM.
    pub fn ecosystems(&self) -> BTreeSet<String> {
        self.components
            .values()
            .filter_map(|c| c.ecosystem.clone())
            .collect()
    }

    /// returns all unique licenses present across all components.
    pub fn licenses(&self) -> BTreeSet<String> {
        self.components
            .values()
            .flat_map(|c| c.licenses.iter().cloned())
            .collect()
    }

    /// returns components that have no checksums/hashes.
    ///
    /// useful for identifying components that may need integrity verification.
    pub fn missing_hashes(&self) -> Vec<ComponentId> {
        self.components
            .iter()
            .filter(|(_, c)| c.hashes.is_empty())
            .map(|(id, _)| id.clone())
            .collect()
    }

    /// finds a component by its package URL.
    pub fn by_purl(&self, purl: &str) -> Option<&Component> {
        let id = ComponentId::new(Some(purl), &[]);
        self.components.get(&id)
    }

    /// detects dependency cycles in the SBOM's dependency graph.
    ///
    /// uses iterative stack-based depth-first search with three-color marking
    /// (white/gray/black) to find all distinct cycles. each returned vector
    /// contains the component IDs forming a cycle, starting and ending with
    /// the same ID.
    ///
    /// returns an empty vector if the graph is acyclic.
    pub fn detect_cycles(&self) -> Vec<Vec<ComponentId>> {
        enum Frame {
            Enter(ComponentId),
            Exit(ComponentId),
        }

        let mut visited = BTreeSet::new();
        let mut on_stack = BTreeSet::new();
        let mut path = Vec::new();
        let mut cycles = Vec::new();

        let mut stack: Vec<Frame> = self
            .dependencies
            .keys()
            .rev()
            .map(|k| Frame::Enter(k.clone()))
            .collect();

        while let Some(frame) = stack.pop() {
            match frame {
                Frame::Enter(node) => {
                    if visited.contains(&node) {
                        continue;
                    }
                    visited.insert(node.clone());
                    on_stack.insert(node.clone());
                    path.push(node.clone());
                    stack.push(Frame::Exit(node.clone()));

                    if let Some(children) = self.dependencies.get(&node) {
                        for child in children.keys().rev() {
                            if !visited.contains(child) {
                                stack.push(Frame::Enter(child.clone()));
                            } else if on_stack.contains(child) {
                                if let Some(start) = path.iter().position(|n| n == child) {
                                    let mut cycle: Vec<_> = path[start..].to_vec();
                                    cycle.push(child.clone());
                                    cycles.push(cycle);
                                }
                            }
                        }
                    }
                }
                Frame::Exit(node) => {
                    path.pop();
                    on_stack.remove(&node);
                }
            }
        }

        cycles
    }
}

impl Component {
    /// normalizes the component for deterministic comparison.
    ///
    /// lowercases hash keys and values. licenses are stored as a BTreeSet
    /// so they're already sorted and deduplicated.
    pub fn normalize(&mut self) {
        let normalized_hashes: BTreeMap<String, String> = self
            .hashes
            .iter()
            .map(|(k, v)| (k.to_lowercase(), v.to_lowercase()))
            .collect();
        self.hashes = normalized_hashes;
    }
}

/// extracts the ecosystem (package type) from a purl string.
///
/// returns `None` if the purl is invalid or cannot be parsed.
///
/// # Example
///
/// ```
/// use sbom_model::ecosystem_from_purl;
///
/// assert_eq!(ecosystem_from_purl("pkg:npm/lodash@4.17.21"), Some("npm".to_string()));
/// assert_eq!(ecosystem_from_purl("pkg:cargo/serde@1.0.0"), Some("cargo".to_string()));
/// assert_eq!(ecosystem_from_purl("invalid"), None);
/// ```
pub fn ecosystem_from_purl(purl: &str) -> Option<String> {
    PackageUrl::from_str(purl).ok().map(|p| p.ty().to_string())
}

/// extracts individual license IDs from an SPDX expression.
///
/// parses the expression and returns all license IDs found, including
/// `LicenseRef-` identifiers. if parsing fails, returns the original
/// string as a single-element set.
///
/// # Example
///
/// ```
/// use sbom_model::parse_license_expression;
///
/// let ids = parse_license_expression("MIT OR Apache-2.0");
/// assert!(ids.contains("MIT"));
/// assert!(ids.contains("Apache-2.0"));
///
/// let ids = parse_license_expression("LicenseRef-proprietary AND Apache-2.0");
/// assert!(ids.contains("LicenseRef-proprietary"));
/// assert!(ids.contains("Apache-2.0"));
/// ```
pub fn parse_license_expression(license: &str) -> BTreeSet<String> {
    match spdx::Expression::parse(license) {
        Ok(expr) => {
            let ids: BTreeSet<String> = expr
                .requirements()
                .map(|r| match &r.req.license {
                    spdx::LicenseItem::Spdx { id, .. } => id.name.to_string(),
                    other => other.to_string(),
                })
                .collect();
            if ids.is_empty() {
                // expression parsed but no IDs found, keep original
                BTreeSet::from([license.to_string()])
            } else {
                ids
            }
        }
        Err(_) => {
            // not a valid SPDX expression, keep original
            BTreeSet::from([license.to_string()])
        }
    }
}

/// a single license requirement: one identifier plus the `WITH` exception
/// bound to it, if any.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct LicenseRequirement {
    /// the license identifier, e.g. `GPL-2.0-only` or `LicenseRef-proprietary`.
    pub license: String,
    /// whether the identifier carried a `+` suffix.
    pub or_later: bool,
    /// the exception identifier following `WITH`.
    pub exception: Option<String>,
}

impl LicenseRequirement {
    /// builds a bare requirement from a license identifier.
    pub fn new(license: impl Into<String>) -> Self {
        Self {
            license: license.into(),
            or_later: false,
            exception: None,
        }
    }
}

impl std::fmt::Display for LicenseRequirement {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.license)?;
        if self.or_later {
            f.write_str("+")?;
        }
        if let Some(exception) = &self.exception {
            write!(f, " WITH {exception}")?;
        }
        Ok(())
    }
}

fn to_requirement(req: &spdx::LicenseReq) -> LicenseRequirement {
    let (license, or_later) = match &req.license {
        spdx::LicenseItem::Spdx { id, or_later } => (id.name.to_string(), *or_later),
        other => (other.to_string(), false),
    };
    LicenseRequirement {
        license,
        or_later,
        exception: req.addition.as_ref().map(|a| a.to_string()),
    }
}

/// the licensing a component declares.
///
/// carries the SPDX expression when the source document had one, so `AND`/`OR`
/// and `WITH` survive; otherwise it falls back to the flattened identifier set,
/// which is read as a conjunction (every identifier applies).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Licensing<'a> {
    /// the declared SPDX expression, if any.
    pub expression: Option<&'a str>,
    /// the flattened license identifiers.
    pub ids: &'a BTreeSet<String>,
}

impl<'a> Licensing<'a> {
    /// builds a licensing view from a flat identifier set.
    pub fn from_ids(ids: &'a BTreeSet<String>) -> Self {
        Self {
            expression: None,
            ids,
        }
    }

    /// reports whether the licensing can be satisfied by taking on only
    /// requirements `acceptable` approves of.
    ///
    /// `OR` lets the consumer pick one side, `AND` demands both. an expression
    /// that fails to parse, or an absent expression, falls back to requiring
    /// every identifier in the flat set.
    ///
    /// # Example
    ///
    /// ```
    /// use sbom_model::Licensing;
    /// use std::collections::BTreeSet;
    ///
    /// let ids: BTreeSet<String> = ["Apache-2.0".into(), "MIT".into()].into();
    /// let choice = Licensing { expression: Some("MIT OR Apache-2.0"), ids: &ids };
    /// assert!(choice.satisfiable(|r| r.license == "MIT"));
    ///
    /// let both = Licensing { expression: Some("MIT AND Apache-2.0"), ids: &ids };
    /// assert!(!both.satisfiable(|r| r.license == "MIT"));
    /// ```
    pub fn satisfiable<F>(&self, mut acceptable: F) -> bool
    where
        F: FnMut(&LicenseRequirement) -> bool,
    {
        if let Some(expression) = self.expression {
            if let Ok(expr) = spdx::Expression::parse(expression) {
                return expr.evaluate(|req| acceptable(&to_requirement(req)));
            }
        }
        self.ids
            .iter()
            .all(|id| acceptable(&LicenseRequirement::new(id)))
    }

    /// returns every requirement the licensing mentions, whether or not a
    /// consumer must accept it.
    pub fn requirements(&self) -> BTreeSet<LicenseRequirement> {
        if let Some(expression) = self.expression {
            if let Ok(expr) = spdx::Expression::parse(expression) {
                let reqs: BTreeSet<LicenseRequirement> = expr
                    .requirements()
                    .map(|r| to_requirement(&r.req))
                    .collect();
                if !reqs.is_empty() {
                    return reqs;
                }
            }
        }
        self.ids.iter().map(LicenseRequirement::new).collect()
    }

    /// returns the minimal requirement sets that satisfy the licensing, or
    /// `None` when the expression expands past `MAX_CHOICES`.
    fn choices(&self) -> Option<Choices> {
        if let Some(expression) = self.expression {
            if let Ok(expr) = spdx::Expression::parse(expression) {
                return expression_choices(&expr);
            }
        }
        Some(BTreeSet::from([self
            .ids
            .iter()
            .map(LicenseRequirement::new)
            .collect()]))
    }

    /// returns the copyleft identifiers no satisfying choice can avoid.
    fn mandatory_copyleft(&self) -> BTreeSet<String> {
        self.requirements()
            .into_iter()
            .filter(|r| is_copyleft_license(&r.license))
            .filter(|r| !self.satisfiable(|other| other.license != r.license))
            .map(|r| r.license)
            .collect()
    }

    /// returns the minimal copyleft burdens the licensing's satisfying choices
    /// carry, or `None` when the expression expands past `MAX_CHOICES`.
    fn copyleft_burdens(&self) -> Option<Burdens> {
        let burdens = self
            .choices()?
            .into_iter()
            .map(|choice| {
                choice
                    .into_iter()
                    .filter(|r| is_copyleft_license(&r.license))
                    .map(|r| r.license)
                    .collect()
            })
            .collect();
        Some(minimal_sets(burdens))
    }
}

/// the alternative requirement sets an expression offers a consumer.
type Choices = BTreeSet<BTreeSet<LicenseRequirement>>;

/// the copyleft identifiers each alternative an expression offers carries.
type Burdens = BTreeSet<BTreeSet<String>>;

/// the largest number of alternatives an expression is expanded into before it
/// is compared by spelling instead.
const MAX_CHOICES: usize = 64;

/// drops every set that another set in the collection is a strict subset of.
fn minimal_sets<T: Ord + Clone>(sets: BTreeSet<BTreeSet<T>>) -> BTreeSet<BTreeSet<T>> {
    sets.iter()
        .filter(|set| {
            sets.iter()
                .all(|other| other == *set || !other.is_subset(set))
        })
        .cloned()
        .collect()
}

/// expands a parsed expression into its minimal satisfying requirement sets.
fn expression_choices(expr: &spdx::Expression) -> Option<Choices> {
    let mut stack: Vec<Choices> = Vec::new();

    for node in expr.iter() {
        match node {
            spdx::expression::ExprNode::Req(req) => {
                stack.push(BTreeSet::from([BTreeSet::from([to_requirement(&req.req)])]));
            }
            spdx::expression::ExprNode::Op(op) => {
                let rhs = stack.pop()?;
                let lhs = stack.pop()?;
                let combined: Choices = match op {
                    spdx::expression::Operator::Or => lhs.union(&rhs).cloned().collect(),
                    spdx::expression::Operator::And => lhs
                        .iter()
                        .flat_map(|l| rhs.iter().map(|r| l.union(r).cloned().collect()))
                        .collect(),
                };
                if combined.len() > MAX_CHOICES {
                    return None;
                }
                stack.push(minimal_sets(combined));
            }
        }
    }

    let choices = stack.pop()?;
    stack.is_empty().then_some(choices)
}

/// reports whether two licensings impose the same obligations.
///
/// a licensing without a declared expression is read as a conjunction of its
/// identifiers, so it differs from one with an expression only when that
/// expression means something a bare identifier set cannot. an expression too
/// wide to expand is compared by spelling and never matches a bare set.
///
/// # Example
///
/// ```
/// use sbom_model::{licensings_equivalent, Licensing};
/// use std::collections::BTreeSet;
///
/// let ids: BTreeSet<String> = ["GPL-3.0-only".into(), "MIT".into()].into();
/// let flat = Licensing::from_ids(&ids);
///
/// let both = Licensing { expression: Some("MIT AND GPL-3.0-only"), ids: &ids };
/// assert!(licensings_equivalent(both, flat));
///
/// let choice = Licensing { expression: Some("MIT OR GPL-3.0-only"), ids: &ids };
/// assert!(!licensings_equivalent(choice, flat));
/// ```
pub fn licensings_equivalent(a: Licensing<'_>, b: Licensing<'_>) -> bool {
    match (a.choices(), b.choices()) {
        (Some(x), Some(y)) => x == y,
        _ => match (a.expression, b.expression) {
            (Some(x), Some(y)) => license_expressions_equivalent(x, y),
            _ => false,
        },
    }
}

/// returns the copyleft licenses `new` can put a consumer under that `old`
/// could not.
///
/// empty when `new` offers a way to satisfy it whose copyleft obligations `old`
/// already offered — so a dual license like `MIT OR GPL-3.0-only` is not an
/// introduction, while `MIT AND GPL-3.0-only` is, and an unchanged
/// `GPL-2.0-only OR GPL-3.0-only` choice is neither. otherwise it is the
/// copyleft carried by `new`'s minimal satisfying choices, minus the copyleft
/// every choice of `old` already carried; those choices need not be comparable,
/// so a consumer may end up under only some of the returned licenses. an
/// expression too wide to expand is measured against the copyleft `old` made
/// individually unavoidable.
///
/// # Example
///
/// ```
/// use sbom_model::{copyleft_obligations_added, Licensing};
/// use std::collections::BTreeSet;
///
/// let old_ids: BTreeSet<String> = ["MIT".into()].into();
/// let new_ids: BTreeSet<String> = ["GPL-3.0-only".into(), "MIT".into()].into();
/// let old = Licensing { expression: Some("MIT"), ids: &old_ids };
///
/// let choice = Licensing { expression: Some("MIT OR GPL-3.0-only"), ids: &new_ids };
/// assert!(copyleft_obligations_added(old, choice).is_empty());
///
/// let both = Licensing { expression: Some("MIT AND GPL-3.0-only"), ids: &new_ids };
/// assert!(copyleft_obligations_added(old, both).contains("GPL-3.0-only"));
/// ```
pub fn copyleft_obligations_added(old: Licensing<'_>, new: Licensing<'_>) -> BTreeSet<String> {
    match (old.copyleft_burdens(), new.copyleft_burdens()) {
        (Some(offered), Some(demanded)) => {
            if demanded
                .iter()
                .any(|burden| offered.iter().any(|had| burden.is_subset(had)))
            {
                return BTreeSet::new();
            }
            let unavoidable = offered
                .into_iter()
                .reduce(|acc, had| acc.intersection(&had).cloned().collect())
                .unwrap_or_default();
            demanded
                .into_iter()
                .flatten()
                .filter(|license| !unavoidable.contains(license))
                .collect()
        }
        _ => {
            let already = old.mandatory_copyleft();
            if new.satisfiable(|r| !is_copyleft_license(&r.license) || already.contains(&r.license))
            {
                return BTreeSet::new();
            }
            new.requirements()
                .into_iter()
                .filter(|r| is_copyleft_license(&r.license) && !already.contains(&r.license))
                .map(|r| r.license)
                .collect()
        }
    }
}

/// reports whether two SPDX license expressions impose the same obligations.
///
/// spelling that does not change which licenses satisfy the expression —
/// redundant parentheses, whitespace, operand order — is not a difference;
/// `AND` against `OR`, `WITH` exceptions and `+` are. an expression too wide to
/// expand compares by parse tree, and one that fails to parse as a plain string.
///
/// # Example
///
/// ```
/// use sbom_model::license_expressions_equivalent;
///
/// assert!(license_expressions_equivalent("MIT OR Apache-2.0", "(Apache-2.0 OR MIT)"));
/// assert!(!license_expressions_equivalent("MIT OR Apache-2.0", "MIT AND Apache-2.0"));
/// assert!(!license_expressions_equivalent(
///     "GPL-2.0-only",
///     "GPL-2.0-only WITH Classpath-exception-2.0",
/// ));
/// ```
pub fn license_expressions_equivalent(a: &str, b: &str) -> bool {
    match (spdx::Expression::parse(a), spdx::Expression::parse(b)) {
        (Ok(x), Ok(y)) => match (expression_choices(&x), expression_choices(&y)) {
            (Some(cx), Some(cy)) => cx == cy,
            _ => x == y,
        },
        _ => a == b,
    }
}

/// normalizes a hash algorithm name to its canonical form.
///
/// handles variations in casing and hyphenation so that algorithm names
/// from different SBOM formats (SPDX, CycloneDX) compare equal.
///
/// # Example
///
/// ```
/// use sbom_model::canonical_algorithm_name;
///
/// assert_eq!(canonical_algorithm_name("SHA256"), "SHA-256");
/// assert_eq!(canonical_algorithm_name("SHA-256"), "SHA-256");
/// assert_eq!(canonical_algorithm_name("sha256"), "SHA-256");
/// ```
pub fn canonical_algorithm_name(name: &str) -> String {
    match name.replace('-', "").to_uppercase().as_str() {
        "MD2" => "MD2",
        "MD4" => "MD4",
        "MD5" => "MD5",
        "MD6" => "MD6",
        "SHA1" => "SHA-1",
        "SHA224" => "SHA-224",
        "SHA256" => "SHA-256",
        "SHA384" => "SHA-384",
        "SHA512" => "SHA-512",
        "SHA3256" => "SHA3-256",
        "SHA3384" => "SHA3-384",
        "SHA3512" => "SHA3-512",
        "BLAKE2B256" => "BLAKE2b-256",
        "BLAKE2B384" => "BLAKE2b-384",
        "BLAKE2B512" => "BLAKE2b-512",
        "BLAKE3" => "BLAKE3",
        "ADLER32" => "ADLER-32",
        _ => return name.to_string(),
    }
    .to_string()
}

/// returns the strength tier of a hash algorithm, where higher values
/// indicate stronger algorithms.
///
/// returns `None` for unrecognized algorithms. The tiers are:
/// - 0: Non-cryptographic checksums (ADLER-32)
/// - 1: Broken cryptographic hashes (MD2, MD4, MD5)
/// - 2: Weak cryptographic hashes (SHA-1)
/// - 3: 112-bit security (SHA-224)
/// - 4: 128-bit security (SHA-256, SHA3-256, BLAKE2b-256, BLAKE3, MD6)
/// - 5: 192-bit security (SHA-384, SHA3-384, BLAKE2b-384)
/// - 6: 256-bit security (SHA-512, SHA3-512, BLAKE2b-512)
///
/// # Example
///
/// ```
/// use sbom_model::hash_algorithm_strength;
///
/// assert!(hash_algorithm_strength("SHA-256").unwrap() > hash_algorithm_strength("MD5").unwrap());
/// assert!(hash_algorithm_strength("SHA-512").unwrap() > hash_algorithm_strength("SHA-256").unwrap());
/// assert_eq!(hash_algorithm_strength("UNKNOWN"), None);
/// ```
pub fn hash_algorithm_strength(name: &str) -> Option<u8> {
    let canonical = canonical_algorithm_name(name);
    match canonical.as_str() {
        "ADLER-32" => Some(0),
        "MD2" | "MD4" | "MD5" => Some(1),
        "SHA-1" => Some(2),
        "SHA-224" => Some(3),
        "SHA-256" | "SHA3-256" | "BLAKE2b-256" | "BLAKE3" | "MD6" => Some(4),
        "SHA-384" | "SHA3-384" | "BLAKE2b-384" => Some(5),
        "SHA-512" | "SHA3-512" | "BLAKE2b-512" => Some(6),
        _ => None,
    }
}

/// detects whether the hash algorithms in a component were downgraded.
///
/// compares the strongest known algorithm in `old_hashes` against the
/// strongest known algorithm in `new_hashes`. Returns `true` if the new
/// set's strongest algorithm is weaker than the old set's strongest.
///
/// returns `false` when:
/// - either hash set is empty (use `missing-hashes` for that)
/// - neither set contains a recognized algorithm
/// - the new set is at least as strong as the old set
///
/// # Example
///
/// ```
/// use sbom_model::is_hash_algorithm_downgrade;
/// use std::collections::BTreeMap;
///
/// let old: BTreeMap<String, String> = [("sha-256".into(), "abc".into())].into();
/// let new: BTreeMap<String, String> = [("md5".into(), "def".into())].into();
/// assert!(is_hash_algorithm_downgrade(&old, &new));
///
/// let new_strong: BTreeMap<String, String> = [("sha-512".into(), "ghi".into())].into();
/// assert!(!is_hash_algorithm_downgrade(&old, &new_strong));
/// ```
pub fn is_hash_algorithm_downgrade(
    old_hashes: &BTreeMap<String, String>,
    new_hashes: &BTreeMap<String, String>,
) -> bool {
    if old_hashes.is_empty() || new_hashes.is_empty() {
        return false;
    }

    let old_max = old_hashes
        .keys()
        .filter_map(|k| hash_algorithm_strength(k))
        .max();
    let new_max = new_hashes
        .keys()
        .filter_map(|k| hash_algorithm_strength(k))
        .max();

    match (old_max, new_max) {
        (Some(old_strength), Some(new_strength)) => new_strength < old_strength,
        _ => false,
    }
}

/// classifies an SPDX license identifier as copyleft.
///
/// looks the ID up in the compile-time SPDX license list and returns whether
/// it carries the copyleft flag (the GPL/AGPL/LGPL family, MPL, etc.).
///
/// returns `false` for anything SPDX doesn't recognize — `LicenseRef-`
/// identifiers, full license expressions, and free-text names — a conservative
/// default so unknown terms never trip a copyleft gate.
///
/// # Example
///
/// ```
/// use sbom_model::is_copyleft_license;
///
/// assert!(is_copyleft_license("GPL-3.0-only"));
/// assert!(is_copyleft_license("AGPL-3.0-only"));
/// assert!(!is_copyleft_license("MIT"));
/// assert!(!is_copyleft_license("LicenseRef-proprietary"));
/// ```
pub fn is_copyleft_license(id: &str) -> bool {
    spdx::license_id(id)
        .map(|l| l.is_copyleft())
        .unwrap_or(false)
}

/// detects whether a copyleft license was newly introduced between two license sets.
///
/// returns `true` iff `new` contains a copyleft license (per
/// [`is_copyleft_license`]) that is not present in `old`. A copyleft license
/// carried over from `old` is not an introduction, and permissive-only changes
/// never fire.
///
/// # Example
///
/// ```
/// use sbom_model::copyleft_introduced;
/// use std::collections::BTreeSet;
///
/// let old: BTreeSet<String> = ["MIT".into()].into();
/// let new: BTreeSet<String> = ["GPL-3.0-only".into()].into();
/// assert!(copyleft_introduced(&old, &new));
///
/// let permissive: BTreeSet<String> = ["Apache-2.0".into()].into();
/// assert!(!copyleft_introduced(&old, &permissive));
/// ```
pub fn copyleft_introduced(old: &BTreeSet<String>, new: &BTreeSet<String>) -> bool {
    new.iter()
        .any(|id| is_copyleft_license(id) && !old.contains(id))
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_component_id_purl() {
        let purl = "pkg:npm/left-pad@1.3.0";
        let id = ComponentId::new(Some(purl), &[]);
        assert_eq!(id.as_str(), purl);
    }

    #[test]
    fn test_component_id_hash_stability() {
        let props = [("name", "foo"), ("version", "1.0")];
        let id1 = ComponentId::new(None, &props);
        let id2 = ComponentId::new(None, &props);
        assert_eq!(id1, id2);
        assert!(id1.as_str().starts_with("h:"));
    }

    #[test]
    fn test_normalization() {
        let mut comp = Component::new("test".to_string(), Some("1.0".to_string()));
        comp.licenses.insert("MIT".to_string());
        comp.licenses.insert("Apache-2.0".to_string());
        comp.hashes.insert("SHA-256".to_string(), "ABC".to_string());

        comp.normalize();

        assert_eq!(
            comp.licenses,
            BTreeSet::from(["Apache-2.0".to_string(), "MIT".to_string()])
        );
        assert_eq!(comp.hashes.get("sha-256").unwrap(), "abc");
    }

    fn licensing<'a>(expression: &'a str, ids: &'a BTreeSet<String>) -> Licensing<'a> {
        Licensing {
            expression: Some(expression),
            ids,
        }
    }

    #[test]
    fn test_licensing_satisfiable_operators() {
        let ids: BTreeSet<String> = ["Apache-2.0".into(), "MIT".into()].into();
        let only_mit = |r: &LicenseRequirement| r.license == "MIT";

        assert!(licensing("MIT OR Apache-2.0", &ids).satisfiable(only_mit));
        assert!(!licensing("MIT AND Apache-2.0", &ids).satisfiable(only_mit));

        let nested: BTreeSet<String> =
            ["Apache-2.0".into(), "BSD-3-Clause".into(), "MIT".into()].into();
        let allowed: BTreeSet<String> = ["BSD-3-Clause".into(), "MIT".into()].into();
        assert!(licensing("(MIT OR Apache-2.0) AND BSD-3-Clause", &nested)
            .satisfiable(|r| allowed.contains(&r.license)));
        assert!(!licensing("(MIT AND Apache-2.0) AND BSD-3-Clause", &nested)
            .satisfiable(|r| allowed.contains(&r.license)));
    }

    #[test]
    fn test_licensing_without_expression_is_a_conjunction() {
        let ids: BTreeSet<String> = ["Apache-2.0".into(), "MIT".into()].into();
        assert!(!Licensing::from_ids(&ids).satisfiable(|r| r.license == "MIT"));
        assert!(Licensing::from_ids(&ids).satisfiable(|_| true));
    }

    #[test]
    fn test_licensing_falls_back_on_free_text() {
        let ids: BTreeSet<String> = ["Custom License".into()].into();
        let free_text = licensing("Custom License", &ids);
        assert!(free_text.satisfiable(|r| r.license == "Custom License"));
        assert!(!free_text.satisfiable(|_| false));
    }

    #[test]
    fn test_licensing_requirements_keep_exceptions() {
        let ids: BTreeSet<String> = ["GPL-2.0-only".into()].into();
        let reqs = licensing("GPL-2.0-only WITH Classpath-exception-2.0", &ids).requirements();

        assert_eq!(reqs.len(), 1);
        let req = reqs.iter().next().unwrap();
        assert_eq!(req.license, "GPL-2.0-only");
        assert_eq!(req.exception.as_deref(), Some("Classpath-exception-2.0"));
        assert_eq!(req.to_string(), "GPL-2.0-only WITH Classpath-exception-2.0");
    }

    #[test]
    fn test_licensing_requirements_keep_or_later() {
        let ids: BTreeSet<String> = ["Apache-2.0".into()].into();
        let req = licensing("Apache-2.0+", &ids)
            .requirements()
            .into_iter()
            .next()
            .unwrap();

        assert_eq!(req.license, "Apache-2.0");
        assert!(req.or_later);
        assert_eq!(req.to_string(), "Apache-2.0+");
    }

    #[test]
    fn test_copyleft_obligations_added_respects_choice() {
        let mit: BTreeSet<String> = ["MIT".into()].into();
        let both: BTreeSet<String> = ["GPL-3.0-only".into(), "MIT".into()].into();
        let old = licensing("MIT", &mit);

        assert!(
            copyleft_obligations_added(old, licensing("MIT OR GPL-3.0-only", &both)).is_empty()
        );
        assert_eq!(
            copyleft_obligations_added(old, licensing("MIT AND GPL-3.0-only", &both)),
            BTreeSet::from(["GPL-3.0-only".to_string()])
        );
    }

    #[test]
    fn test_copyleft_obligations_added_carried_over() {
        let gpl: BTreeSet<String> = ["GPL-3.0-only".into()].into();
        let both: BTreeSet<String> = ["GPL-3.0-only".into(), "MIT".into()].into();

        assert!(copyleft_obligations_added(
            licensing("GPL-3.0-only", &gpl),
            licensing("GPL-3.0-only AND MIT", &both)
        )
        .is_empty());

        // a different copyleft license is still a new obligation
        let agpl: BTreeSet<String> = ["AGPL-3.0-only".into()].into();
        assert_eq!(
            copyleft_obligations_added(
                licensing("GPL-3.0-only", &gpl),
                licensing("AGPL-3.0-only", &agpl)
            ),
            BTreeSet::from(["AGPL-3.0-only".to_string()])
        );
    }

    #[test]
    fn test_copyleft_obligations_added_losing_the_permissive_choice() {
        let both: BTreeSet<String> = ["GPL-3.0-only".into(), "MIT".into()].into();
        let gpl: BTreeSet<String> = ["GPL-3.0-only".into()].into();

        assert_eq!(
            copyleft_obligations_added(
                licensing("MIT OR GPL-3.0-only", &both),
                licensing("GPL-3.0-only", &gpl)
            ),
            BTreeSet::from(["GPL-3.0-only".to_string()])
        );
    }

    fn copyleft_added(old: &str, new: &str) -> BTreeSet<String> {
        let old_ids = parse_license_expression(old);
        let new_ids = parse_license_expression(new);
        copyleft_obligations_added(licensing(old, &old_ids), licensing(new, &new_ids))
    }

    fn licenses(names: &[&str]) -> BTreeSet<String> {
        names.iter().map(|n| n.to_string()).collect()
    }

    #[test]
    fn test_copyleft_obligations_added_ignores_a_choice_between_copyleft_licenses() {
        for (old, new) in [
            (
                "GPL-2.0-only OR GPL-3.0-only",
                "GPL-2.0-only OR GPL-3.0-only OR LGPL-3.0-only",
            ),
            (
                "MIT AND (GPL-2.0-only OR GPL-3.0-only)",
                "Apache-2.0 AND (GPL-2.0-only OR GPL-3.0-only)",
            ),
            (
                "MPL-2.0 OR GPL-2.0-only OR LGPL-2.1-only",
                "MPL-2.0 OR GPL-2.0-only OR LGPL-2.1-only",
            ),
        ] {
            assert!(
                copyleft_added(old, new).is_empty(),
                "{old} -> {new} forces no copyleft the consumer could not already have taken"
            );
        }
    }

    #[test]
    fn test_copyleft_obligations_added_fires_on_every_tightening() {
        for (old, new, introduced) in [
            (
                "GPL-2.0-only OR GPL-3.0-only",
                "GPL-2.0-only AND GPL-3.0-only",
                &["GPL-2.0-only", "GPL-3.0-only"][..],
            ),
            ("MIT OR GPL-3.0-only", "GPL-3.0-only", &["GPL-3.0-only"]),
            ("GPL-3.0-only", "AGPL-3.0-only", &["AGPL-3.0-only"]),
            ("MIT", "MIT AND GPL-3.0-only", &["GPL-3.0-only"]),
            (
                "GPL-2.0-only OR GPL-3.0-only",
                "AGPL-3.0-only",
                &["AGPL-3.0-only"],
            ),
        ] {
            assert_eq!(
                copyleft_added(old, new),
                licenses(introduced),
                "{old} -> {new}"
            );
        }
    }

    #[test]
    fn test_copyleft_obligations_added_spans_the_minimal_choices_less_what_old_forced() {
        for (old, new, introduced) in [
            (
                "MIT",
                "GPL-3.0-only AND (MPL-2.0 OR ISC)",
                &["GPL-3.0-only"][..],
            ),
            (
                "GPL-2.0-only",
                "GPL-2.0-only AND GPL-3.0-only",
                &["GPL-3.0-only"],
            ),
            (
                "MIT",
                "GPL-2.0-only OR AGPL-3.0-only",
                &["AGPL-3.0-only", "GPL-2.0-only"],
            ),
            (
                "MIT",
                "(GPL-3.0-only AND MPL-2.0) OR (AGPL-3.0-only AND EPL-2.0)",
                &["AGPL-3.0-only", "GPL-3.0-only", "MPL-2.0"],
            ),
        ] {
            assert_eq!(
                copyleft_added(old, new),
                licenses(introduced),
                "{old} -> {new}"
            );
        }
    }

    #[test]
    fn test_copyleft_obligations_added_falls_back_past_max_choices() {
        let wide = "(MIT OR Apache-2.0) AND (BSD-2-Clause OR BSD-3-Clause) \
                    AND (ISC OR Zlib) AND (MPL-2.0 OR EPL-2.0) \
                    AND (GPL-2.0-only OR GPL-3.0-only) AND (LGPL-2.1-only OR LGPL-3.0-only) \
                    AND (CC0-1.0 OR Unlicense)";

        assert_eq!(
            copyleft_added("MIT", wide),
            licenses(&[
                "GPL-2.0-only",
                "GPL-3.0-only",
                "LGPL-2.1-only",
                "LGPL-3.0-only",
                "MPL-2.0",
            ])
        );
    }

    #[test]
    fn test_copyleft_obligations_added_matches_flat_sets() {
        let old: BTreeSet<String> = ["MIT".into()].into();
        let new: BTreeSet<String> = ["GPL-3.0-only".into(), "MIT".into()].into();

        assert_eq!(
            copyleft_obligations_added(Licensing::from_ids(&old), Licensing::from_ids(&new)),
            BTreeSet::from(["GPL-3.0-only".to_string()])
        );
        assert!(copyleft_introduced(&old, &new));

        assert!(
            copyleft_obligations_added(Licensing::from_ids(&new), Licensing::from_ids(&new))
                .is_empty()
        );
        assert!(!copyleft_introduced(&new, &new));
    }

    #[test]
    fn test_license_expressions_equivalent() {
        assert!(license_expressions_equivalent(
            "MIT OR Apache-2.0",
            "( MIT OR (Apache-2.0) )"
        ));
        assert!(!license_expressions_equivalent(
            "MIT OR Apache-2.0",
            "MIT AND Apache-2.0"
        ));
        assert!(!license_expressions_equivalent(
            "GPL-2.0-only",
            "GPL-2.0-only WITH Classpath-exception-2.0"
        ));
        assert!(license_expressions_equivalent("Custom Text", "Custom Text"));
        assert!(!license_expressions_equivalent("Custom Text", "Other Text"));
    }

    #[test]
    fn test_license_expressions_equivalent_falls_back_past_max_choices() {
        let wide = "(MIT OR Apache-2.0) AND (BSD-2-Clause OR BSD-3-Clause) \
                    AND (ISC OR Zlib) AND (MPL-2.0 OR EPL-2.0) \
                    AND (GPL-2.0-only OR GPL-3.0-only) AND (LGPL-2.1-only OR LGPL-3.0-only) \
                    AND (CC0-1.0 OR Unlicense)";

        assert!(license_expressions_equivalent(wide, wide));
        assert!(license_expressions_equivalent(
            wide,
            &wide.replace("(MIT OR Apache-2.0)", "((MIT OR Apache-2.0))")
        ));
        assert!(!license_expressions_equivalent(
            wide,
            &wide.replace("MIT OR Apache-2.0", "Apache-2.0 OR MIT")
        ));

        let ids: BTreeSet<String> = wide
            .split_whitespace()
            .map(|word| word.trim_matches(['(', ')']).to_string())
            .filter(|word| word != "AND" && word != "OR")
            .collect();
        assert!(!licensings_equivalent(
            Licensing {
                expression: Some(wide),
                ids: &ids,
            },
            Licensing::from_ids(&ids)
        ));
    }

    #[test]
    fn test_license_expressions_equivalent_ignores_operand_order() {
        assert!(license_expressions_equivalent(
            "MIT OR Apache-2.0",
            "Apache-2.0 OR MIT"
        ));
        assert!(license_expressions_equivalent(
            "(MIT OR Apache-2.0) AND BSD-3-Clause",
            "(BSD-3-Clause AND Apache-2.0) OR (BSD-3-Clause AND MIT)"
        ));
        assert!(license_expressions_equivalent(
            "MIT",
            "MIT OR (MIT AND Apache-2.0)"
        ));
        assert!(!license_expressions_equivalent(
            "MIT OR Apache-2.0",
            "MIT OR BSD-3-Clause"
        ));
    }

    #[test]
    fn test_licensings_equivalent_reads_a_bare_set_as_a_conjunction() {
        let ids: BTreeSet<String> = ["GPL-3.0-only".to_string(), "MIT".to_string()].into();
        let flat = Licensing::from_ids(&ids);

        assert!(licensings_equivalent(
            Licensing {
                expression: Some("MIT AND GPL-3.0-only"),
                ids: &ids,
            },
            flat
        ));
        assert!(!licensings_equivalent(
            Licensing {
                expression: Some("MIT OR GPL-3.0-only"),
                ids: &ids,
            },
            flat
        ));
        assert!(licensings_equivalent(flat, flat));
    }

    #[test]
    fn test_licensings_equivalent_keeps_decorated_requirements() {
        let gpl: BTreeSet<String> = ["GPL-2.0-only".to_string()].into();
        assert!(!licensings_equivalent(
            Licensing {
                expression: Some("GPL-2.0-only WITH Classpath-exception-2.0"),
                ids: &gpl,
            },
            Licensing::from_ids(&gpl)
        ));
        let apache: BTreeSet<String> = ["Apache-2.0".to_string()].into();
        assert!(!licensings_equivalent(
            Licensing {
                expression: Some("Apache-2.0+"),
                ids: &apache,
            },
            Licensing::from_ids(&apache)
        ));
    }

    #[test]
    fn test_licensings_equivalent_falls_back_to_the_identifier_set() {
        let ids: BTreeSet<String> = ["Custom Text".to_string()].into();
        assert!(licensings_equivalent(
            Licensing {
                expression: Some("Custom Text"),
                ids: &ids,
            },
            Licensing::from_ids(&ids)
        ));
    }

    #[test]
    fn test_component_licensing_defaults_to_ids() {
        let mut comp = Component::new("demo".into(), None);
        comp.licenses.insert("MIT".into());

        assert_eq!(comp.licensing().expression, None);
        assert_eq!(
            comp.licensing().requirements(),
            BTreeSet::from([LicenseRequirement::new("MIT")])
        );
    }

    #[test]
    fn test_parse_license_expression() {
        // OR expression extracts both IDs
        let ids = parse_license_expression("MIT OR Apache-2.0");
        assert!(ids.contains("MIT"));
        assert!(ids.contains("Apache-2.0"));
        assert_eq!(ids.len(), 2);

        // single license
        let ids = parse_license_expression("MIT");
        assert_eq!(ids, BTreeSet::from(["MIT".to_string()]));

        // AND expression extracts both IDs
        let ids = parse_license_expression("MIT AND Apache-2.0");
        assert!(ids.contains("MIT"));
        assert!(ids.contains("Apache-2.0"));

        // invalid expression kept as-is
        let ids = parse_license_expression("Custom License");
        assert_eq!(ids, BTreeSet::from(["Custom License".to_string()]));

        // pure LicenseRef
        let ids = parse_license_expression("LicenseRef-proprietary");
        assert_eq!(ids, BTreeSet::from(["LicenseRef-proprietary".to_string()]));
    }

    #[test]
    fn test_parse_license_expression_licenseref_and_spdx() {
        // mixed LicenseRef + SPDX-ID with AND: both must be extracted
        let ids = parse_license_expression("LicenseRef-proprietary AND Apache-2.0");
        assert!(ids.contains("LicenseRef-proprietary"));
        assert!(ids.contains("Apache-2.0"));
        assert_eq!(ids.len(), 2);
    }

    #[test]
    fn test_parse_license_expression_licenseref_or_spdx() {
        // mixed LicenseRef + SPDX-ID with OR
        let ids = parse_license_expression("LicenseRef-custom OR MIT");
        assert!(ids.contains("LicenseRef-custom"));
        assert!(ids.contains("MIT"));
        assert_eq!(ids.len(), 2);
    }

    #[test]
    fn test_parse_license_expression_multiple_licenserefs() {
        // multiple LicenseRef terms
        let ids = parse_license_expression("LicenseRef-a AND LicenseRef-b");
        assert!(ids.contains("LicenseRef-a"));
        assert!(ids.contains("LicenseRef-b"));
        assert_eq!(ids.len(), 2);
    }

    #[test]
    fn test_parse_license_expression_complex_mixed() {
        // complex expression mixing LicenseRef and standard IDs
        let ids = parse_license_expression("(MIT OR LicenseRef-custom) AND Apache-2.0");
        assert!(ids.contains("MIT"));
        assert!(ids.contains("LicenseRef-custom"));
        assert!(ids.contains("Apache-2.0"));
        assert_eq!(ids.len(), 3);
    }

    #[test]
    fn test_parse_license_expression_documentref() {
        // DocumentRef-prefixed LicenseRef
        let ids = parse_license_expression("DocumentRef-ext:LicenseRef-custom");
        assert_eq!(
            ids,
            BTreeSet::from(["DocumentRef-ext:LicenseRef-custom".to_string()])
        );
    }

    #[test]
    fn test_license_set_equality() {
        // two components with same licenses in different order are equal
        let mut c1 = Component::new("test".into(), None);
        c1.licenses.insert("MIT".into());
        c1.licenses.insert("Apache-2.0".into());

        let mut c2 = Component::new("test".into(), None);
        c2.licenses.insert("Apache-2.0".into());
        c2.licenses.insert("MIT".into());

        assert_eq!(c1.licenses, c2.licenses);
    }

    #[test]
    fn test_query_api() {
        let mut sbom = Sbom::default();
        let c1 = Component::new("a".into(), Some("1".into()));
        let c2 = Component::new("b".into(), Some("1".into()));
        let c3 = Component::new("c".into(), Some("1".into()));

        let id1 = c1.id.clone();
        let id2 = c2.id.clone();
        let id3 = c3.id.clone();

        sbom.components.insert(id1.clone(), c1);
        sbom.components.insert(id2.clone(), c2);
        sbom.components.insert(id3.clone(), c3);

        // id1 -> id2 -> id3
        sbom.dependencies
            .entry(id1.clone())
            .or_default()
            .insert(id2.clone(), DependencyKind::Runtime);
        sbom.dependencies
            .entry(id2.clone())
            .or_default()
            .insert(id3.clone(), DependencyKind::Runtime);
        sbom.rebuild_reverse_deps();

        assert_eq!(sbom.roots(), vec![id1.clone()]);
        assert_eq!(sbom.deps(&id1), vec![id2.clone()]);
        assert_eq!(sbom.rdeps(&id2), vec![id1.clone()]);

        let transitive = sbom.transitive_deps(&id1);
        assert!(transitive.contains(&id2));
        assert!(transitive.contains(&id3));
        assert_eq!(transitive.len(), 2);

        assert_eq!(sbom.missing_hashes().len(), 3);
    }

    #[test]
    fn test_ecosystems_query() {
        let mut sbom = Sbom::default();

        let mut c1 = Component::new("lodash".into(), Some("1.0".into()));
        c1.ecosystem = Some("npm".into());
        let mut c2 = Component::new("serde".into(), Some("1.0".into()));
        c2.ecosystem = Some("cargo".into());
        let mut c3 = Component::new("other-npm".into(), Some("1.0".into()));
        c3.ecosystem = Some("npm".into());
        let c4 = Component::new("no-ecosystem".into(), Some("1.0".into()));

        sbom.components.insert(c1.id.clone(), c1);
        sbom.components.insert(c2.id.clone(), c2);
        sbom.components.insert(c3.id.clone(), c3);
        sbom.components.insert(c4.id.clone(), c4);

        let ecosystems = sbom.ecosystems();
        assert_eq!(ecosystems.len(), 2);
        assert!(ecosystems.contains("npm"));
        assert!(ecosystems.contains("cargo"));
    }

    #[test]
    fn test_licenses_query() {
        let mut sbom = Sbom::default();

        let mut c1 = Component::new("a".into(), Some("1.0".into()));
        c1.licenses.insert("MIT".into());
        c1.licenses.insert("Apache-2.0".into());
        let mut c2 = Component::new("b".into(), Some("1.0".into()));
        c2.licenses.insert("MIT".into());
        c2.licenses.insert("GPL-3.0-only".into());
        let c3 = Component::new("c".into(), Some("1.0".into()));

        sbom.components.insert(c1.id.clone(), c1);
        sbom.components.insert(c2.id.clone(), c2);
        sbom.components.insert(c3.id.clone(), c3);

        let licenses = sbom.licenses();
        assert_eq!(licenses.len(), 3);
        assert!(licenses.contains("MIT"));
        assert!(licenses.contains("Apache-2.0"));
        assert!(licenses.contains("GPL-3.0-only"));
    }

    #[test]
    fn test_by_purl() {
        let mut sbom = Sbom::default();

        let mut c1 = Component::new("lodash".into(), Some("4.17.21".into()));
        c1.purl = Some("pkg:npm/lodash@4.17.21".into());
        c1.id = ComponentId::new(c1.purl.as_deref(), &[]);
        let c2 = Component::new("no-purl".into(), Some("1.0".into()));

        sbom.components.insert(c1.id.clone(), c1);
        sbom.components.insert(c2.id.clone(), c2);

        let found = sbom.by_purl("pkg:npm/lodash@4.17.21");
        assert!(found.is_some());
        assert_eq!(found.unwrap().name, "lodash");

        assert!(sbom.by_purl("pkg:npm/nonexistent@1.0").is_none());
    }

    #[test]
    fn test_component_id_unparseable_purl() {
        // a purl string that can't be parsed should still be used as-is
        let id = ComponentId::new(Some("not-a-valid-purl-but-still-a-string"), &[]);
        assert_eq!(id.as_str(), "not-a-valid-purl-but-still-a-string");
    }

    #[test]
    fn test_component_id_display() {
        let id = ComponentId::new(Some("pkg:npm/foo@1.0"), &[]);
        assert_eq!(format!("{}", id), "pkg:npm/foo@1.0");
    }

    #[test]
    fn test_sbom_normalize_clears_metadata() {
        let mut sbom = Sbom::default();
        sbom.metadata.timestamp = Some("2024-01-01T00:00:00Z".into());
        sbom.metadata.tools.push("syft".into());
        sbom.metadata.authors.push("alice".into());

        let c = Component::new("a".into(), Some("1".into()));
        sbom.components.insert(c.id.clone(), c);

        sbom.normalize();

        assert!(sbom.metadata.timestamp.is_none());
        assert!(sbom.metadata.tools.is_empty());
        assert!(sbom.metadata.authors.is_empty());
    }

    #[test]
    fn test_missing_hashes_mixed() {
        let mut sbom = Sbom::default();

        let c1 = Component::new("no-hash".into(), Some("1.0".into()));
        let mut c2 = Component::new("has-hash".into(), Some("1.0".into()));
        c2.hashes.insert("sha256".into(), "abc".into());

        sbom.components.insert(c1.id.clone(), c1);
        sbom.components.insert(c2.id.clone(), c2);

        let missing = sbom.missing_hashes();
        assert_eq!(missing.len(), 1);
    }

    #[test]
    fn test_ecosystem_from_purl() {
        use super::ecosystem_from_purl;

        assert_eq!(
            ecosystem_from_purl("pkg:npm/lodash@4.17.21"),
            Some("npm".to_string())
        );
        assert_eq!(
            ecosystem_from_purl("pkg:cargo/serde@1.0.0"),
            Some("cargo".to_string())
        );
        assert_eq!(
            ecosystem_from_purl("pkg:pypi/requests@2.28.0"),
            Some("pypi".to_string())
        );
        assert_eq!(
            ecosystem_from_purl("pkg:maven/org.apache/commons@1.0"),
            Some("maven".to_string())
        );
        assert_eq!(ecosystem_from_purl("invalid-purl"), None);
        assert_eq!(ecosystem_from_purl(""), None);
    }

    #[test]
    fn test_canonical_algorithm_name() {
        // SHA family without hyphens (SPDX style)
        assert_eq!(canonical_algorithm_name("SHA256"), "SHA-256");
        assert_eq!(canonical_algorithm_name("SHA1"), "SHA-1");
        assert_eq!(canonical_algorithm_name("SHA384"), "SHA-384");
        assert_eq!(canonical_algorithm_name("SHA512"), "SHA-512");
        assert_eq!(canonical_algorithm_name("SHA224"), "SHA-224");

        // SHA family with hyphens (CycloneDX style)
        assert_eq!(canonical_algorithm_name("SHA-256"), "SHA-256");
        assert_eq!(canonical_algorithm_name("SHA-1"), "SHA-1");
        assert_eq!(canonical_algorithm_name("SHA-384"), "SHA-384");

        // case-insensitive
        assert_eq!(canonical_algorithm_name("sha256"), "SHA-256");
        assert_eq!(canonical_algorithm_name("sha-256"), "SHA-256");

        // SHA-3
        assert_eq!(canonical_algorithm_name("SHA3-256"), "SHA3-256");
        assert_eq!(canonical_algorithm_name("SHA3256"), "SHA3-256");

        // MD family
        assert_eq!(canonical_algorithm_name("MD5"), "MD5");
        assert_eq!(canonical_algorithm_name("md5"), "MD5");

        // BLAKE
        assert_eq!(canonical_algorithm_name("BLAKE2b-256"), "BLAKE2b-256");
        assert_eq!(canonical_algorithm_name("BLAKE2B256"), "BLAKE2b-256");
        assert_eq!(canonical_algorithm_name("BLAKE3"), "BLAKE3");

        // ADLER
        assert_eq!(canonical_algorithm_name("ADLER32"), "ADLER-32");
        assert_eq!(canonical_algorithm_name("ADLER-32"), "ADLER-32");

        // unknown algorithm passes through
        assert_eq!(canonical_algorithm_name("TIGER"), "TIGER");
    }

    #[test]
    fn test_hash_algorithm_strength_ordering() {
        // ordering: MD5 < SHA-1 < SHA-224 < SHA-256 < SHA-384 < SHA-512
        let md5 = hash_algorithm_strength("MD5").unwrap();
        let sha1 = hash_algorithm_strength("SHA-1").unwrap();
        let sha224 = hash_algorithm_strength("SHA-224").unwrap();
        let sha256 = hash_algorithm_strength("SHA-256").unwrap();
        let sha384 = hash_algorithm_strength("SHA-384").unwrap();
        let sha512 = hash_algorithm_strength("SHA-512").unwrap();

        assert!(md5 < sha1);
        assert!(sha1 < sha224);
        assert!(sha224 < sha256);
        assert!(sha256 < sha384);
        assert!(sha384 < sha512);
    }

    #[test]
    fn test_hash_algorithm_strength_variants() {
        // case and hyphenation variants resolve to same strength
        assert_eq!(
            hash_algorithm_strength("sha256"),
            hash_algorithm_strength("SHA-256")
        );
        assert_eq!(
            hash_algorithm_strength("sha-1"),
            hash_algorithm_strength("SHA1")
        );

        // SHA-3 at same tier as SHA-2 equivalent
        assert_eq!(
            hash_algorithm_strength("SHA3-256"),
            hash_algorithm_strength("SHA-256")
        );
        assert_eq!(
            hash_algorithm_strength("SHA3-512"),
            hash_algorithm_strength("SHA-512")
        );

        // BLAKE at same tier as SHA-2 equivalent
        assert_eq!(
            hash_algorithm_strength("BLAKE2b-256"),
            hash_algorithm_strength("SHA-256")
        );
        assert_eq!(
            hash_algorithm_strength("BLAKE3"),
            hash_algorithm_strength("SHA-256")
        );

        // unknown returns None
        assert_eq!(hash_algorithm_strength("TIGER"), None);
        assert_eq!(hash_algorithm_strength("UNKNOWN"), None);
    }

    #[test]
    fn test_hash_algorithm_strength_adler() {
        let adler = hash_algorithm_strength("ADLER-32").unwrap();
        let md5 = hash_algorithm_strength("MD5").unwrap();
        assert!(adler < md5);
    }

    #[test]
    fn test_is_hash_algorithm_downgrade_sha256_to_md5() {
        let old: BTreeMap<String, String> = [("sha-256".into(), "abc".into())].into();
        let new: BTreeMap<String, String> = [("md5".into(), "def".into())].into();
        assert!(is_hash_algorithm_downgrade(&old, &new));
    }

    #[test]
    fn test_is_hash_algorithm_downgrade_upgrade_not_flagged() {
        let old: BTreeMap<String, String> = [("sha-1".into(), "abc".into())].into();
        let new: BTreeMap<String, String> = [("sha-256".into(), "def".into())].into();
        assert!(!is_hash_algorithm_downgrade(&old, &new));
    }

    #[test]
    fn test_is_hash_algorithm_downgrade_same_algorithm() {
        let old: BTreeMap<String, String> = [("sha-256".into(), "abc".into())].into();
        let new: BTreeMap<String, String> = [("sha-256".into(), "def".into())].into();
        assert!(!is_hash_algorithm_downgrade(&old, &new));
    }

    #[test]
    fn test_is_hash_algorithm_downgrade_empty_old() {
        let old: BTreeMap<String, String> = BTreeMap::new();
        let new: BTreeMap<String, String> = [("md5".into(), "def".into())].into();
        assert!(!is_hash_algorithm_downgrade(&old, &new));
    }

    #[test]
    fn test_is_hash_algorithm_downgrade_empty_new() {
        let old: BTreeMap<String, String> = [("sha-256".into(), "abc".into())].into();
        let new: BTreeMap<String, String> = BTreeMap::new();
        assert!(!is_hash_algorithm_downgrade(&old, &new));
    }

    #[test]
    fn test_is_hash_algorithm_downgrade_multi_algorithm() {
        // old has SHA-256 + MD5, new has only MD5 → downgrade (strongest dropped)
        let old: BTreeMap<String, String> = [
            ("sha-256".into(), "abc".into()),
            ("md5".into(), "xyz".into()),
        ]
        .into();
        let new: BTreeMap<String, String> = [("md5".into(), "def".into())].into();
        assert!(is_hash_algorithm_downgrade(&old, &new));
    }

    #[test]
    fn test_is_hash_algorithm_downgrade_multi_algorithm_kept() {
        // old has SHA-256 + MD5, new has SHA-256 + SHA-1 → not a downgrade
        let old: BTreeMap<String, String> = [
            ("sha-256".into(), "abc".into()),
            ("md5".into(), "xyz".into()),
        ]
        .into();
        let new: BTreeMap<String, String> = [
            ("sha-256".into(), "def".into()),
            ("sha-1".into(), "ghi".into()),
        ]
        .into();
        assert!(!is_hash_algorithm_downgrade(&old, &new));
    }

    #[test]
    fn test_detect_cycles_none() {
        let mut sbom = Sbom::default();
        let c1 = Component::new("a".into(), Some("1".into()));
        let c2 = Component::new("b".into(), Some("1".into()));
        let c3 = Component::new("c".into(), Some("1".into()));

        let id1 = c1.id.clone();
        let id2 = c2.id.clone();
        let id3 = c3.id.clone();

        sbom.components.insert(id1.clone(), c1);
        sbom.components.insert(id2.clone(), c2);
        sbom.components.insert(id3.clone(), c3);

        // a -> b -> c (no cycle)
        sbom.dependencies
            .entry(id1.clone())
            .or_default()
            .insert(id2.clone(), DependencyKind::Runtime);
        sbom.dependencies
            .entry(id2.clone())
            .or_default()
            .insert(id3.clone(), DependencyKind::Runtime);

        assert!(sbom.detect_cycles().is_empty());
    }

    #[test]
    fn test_detect_cycles_simple() {
        let mut sbom = Sbom::default();
        let c1 = Component::new("a".into(), Some("1".into()));
        let c2 = Component::new("b".into(), Some("1".into()));

        let id1 = c1.id.clone();
        let id2 = c2.id.clone();

        sbom.components.insert(id1.clone(), c1);
        sbom.components.insert(id2.clone(), c2);

        // a -> b -> a (cycle)
        sbom.dependencies
            .entry(id1.clone())
            .or_default()
            .insert(id2.clone(), DependencyKind::Runtime);
        sbom.dependencies
            .entry(id2.clone())
            .or_default()
            .insert(id1.clone(), DependencyKind::Runtime);

        let cycles = sbom.detect_cycles();
        assert_eq!(cycles.len(), 1);
        // cycle should start and end with the same node
        assert_eq!(cycles[0].first(), cycles[0].last());
    }

    #[test]
    fn test_detect_cycles_self_loop() {
        let mut sbom = Sbom::default();
        let c1 = Component::new("a".into(), Some("1".into()));
        let id1 = c1.id.clone();
        sbom.components.insert(id1.clone(), c1);

        // a -> a (self-loop)
        sbom.dependencies
            .entry(id1.clone())
            .or_default()
            .insert(id1.clone(), DependencyKind::Runtime);

        let cycles = sbom.detect_cycles();
        assert_eq!(cycles.len(), 1);
        assert_eq!(cycles[0].len(), 2); // [a, a]
    }

    #[test]
    fn test_detect_cycles_empty_graph() {
        let sbom = Sbom::default();
        assert!(sbom.detect_cycles().is_empty());
    }

    #[test]
    fn test_detect_cycles_three_node() {
        let mut sbom = Sbom::default();
        let c1 = Component::new("a".into(), Some("1".into()));
        let c2 = Component::new("b".into(), Some("1".into()));
        let c3 = Component::new("c".into(), Some("1".into()));

        let id1 = c1.id.clone();
        let id2 = c2.id.clone();
        let id3 = c3.id.clone();

        sbom.components.insert(id1.clone(), c1);
        sbom.components.insert(id2.clone(), c2);
        sbom.components.insert(id3.clone(), c3);

        // a -> b -> c -> a (three-node cycle)
        sbom.dependencies
            .entry(id1.clone())
            .or_default()
            .insert(id2.clone(), DependencyKind::Runtime);
        sbom.dependencies
            .entry(id2.clone())
            .or_default()
            .insert(id3.clone(), DependencyKind::Runtime);
        sbom.dependencies
            .entry(id3.clone())
            .or_default()
            .insert(id1.clone(), DependencyKind::Runtime);

        let cycles = sbom.detect_cycles();
        assert_eq!(cycles.len(), 1);
        assert_eq!(cycles[0].first(), cycles[0].last());
        assert_eq!(cycles[0].len(), 4); // [a, b, c, a]
    }

    #[test]
    fn test_is_hash_algorithm_downgrade_unknown_algorithms() {
        // both have only unknown algorithms → false (can't determine ordering)
        let old: BTreeMap<String, String> = [("TIGER".into(), "abc".into())].into();
        let new: BTreeMap<String, String> = [("WHIRLPOOL".into(), "def".into())].into();
        assert!(!is_hash_algorithm_downgrade(&old, &new));
    }

    #[test]
    fn test_is_copyleft_license() {
        // GPL family and its relatives are copyleft
        assert!(is_copyleft_license("GPL-3.0-only"));
        assert!(is_copyleft_license("AGPL-3.0-only"));
        assert!(is_copyleft_license("LGPL-3.0-only"));
        // permissive licenses are not
        assert!(!is_copyleft_license("MIT"));
        assert!(!is_copyleft_license("Apache-2.0"));
        assert!(!is_copyleft_license("BSD-3-Clause"));
        // LicenseRef and unrecognized ids are conservatively not copyleft
        assert!(!is_copyleft_license("LicenseRef-proprietary"));
        assert!(!is_copyleft_license("NOT-A-LICENSE"));
    }

    #[test]
    fn test_copyleft_introduced_permissive_to_copyleft() {
        let old: BTreeSet<String> = ["MIT".into()].into();
        let new: BTreeSet<String> = ["GPL-3.0-only".into()].into();
        assert!(copyleft_introduced(&old, &new));
    }

    #[test]
    fn test_copyleft_introduced_permissive_to_permissive() {
        let old: BTreeSet<String> = ["MIT".into()].into();
        let new: BTreeSet<String> = ["Apache-2.0".into()].into();
        assert!(!copyleft_introduced(&old, &new));
    }

    #[test]
    fn test_copyleft_introduced_carried_over_not_flagged() {
        // a copyleft license already present in old is not a new introduction
        let old: BTreeSet<String> = ["GPL-3.0-only".into()].into();
        let new: BTreeSet<String> = ["GPL-3.0-only".into()].into();
        assert!(!copyleft_introduced(&old, &new));
    }

    #[test]
    fn test_copyleft_introduced_added_alongside_existing() {
        // a second, newly added copyleft id fires even when old already had one
        let old: BTreeSet<String> = ["GPL-3.0-only".into()].into();
        let new: BTreeSet<String> = ["GPL-3.0-only".into(), "AGPL-3.0-only".into()].into();
        assert!(copyleft_introduced(&old, &new));
    }
}