debtmap 0.16.4

//! Exponential scaling and risk-based boosting for technical debt scores.
//!
//! This module implements score amplification through:
//! 1. Exponential scaling based on debt type (architectural issues get stronger boost)
//! 2. Risk-based discrete boosts for high dependencies, entry points, etc.
//!
//! The approach replaces tier-based ranking with transparent score amplification,
//! ensuring higher scores always rank higher while naturally surfacing critical issues.

use crate::priority::semantic_classifier::FunctionRole;
use crate::priority::{DebtType, UnifiedDebtItem};
use serde::{Deserialize, Serialize};

/// Calculate debt-type-specific severity multiplier.
///
/// This differentiates scores for different debt types at the same location.
/// Applied AFTER the cached unified score computation to preserve caching
/// while providing meaningful score differentiation.
///
/// # Rationale
///
/// | Debt Type | Multiplier | Rationale |
/// |-----------|------------|-----------|
/// | GodObject | 1.4 | Architectural debt, hardest to fix |
/// | ComplexityHotspot | 1.2 | Direct code quality issue |
/// | MixedConcerns | 1.15 | Moderate architectural issue |
/// | DependencyCluster | 1.1 | Coupling concern |
/// | LegacyPattern | 1.05 | Technical debt, often tolerable |
/// | TestingGap | 1.0 | Important but secondary to complexity |
///
/// # Examples
///
/// ```ignore
/// use crate::priority::DebtType;
/// let mult = calculate_debt_type_severity_multiplier(&DebtType::GodObject { ... });
/// assert_eq!(mult, 1.4);
/// ```
pub fn calculate_debt_type_severity_multiplier(debt_type: &DebtType) -> f64 {
    match debt_type {
        // Architectural debt - hardest to fix, highest multiplier
        DebtType::GodObject { .. } => 1.4,

        // Direct code quality issues
        DebtType::ComplexityHotspot { .. } | DebtType::Complexity { .. } => 1.2,
        DebtType::TestComplexityHotspot { .. } | DebtType::TestComplexity { .. } => 1.2,

        // Moderate architectural issues
        DebtType::FeatureEnvy { .. }
        | DebtType::ScatteredType { .. }
        | DebtType::CodeOrganization { .. } => 1.15,

        // Coupling and dependency concerns
        DebtType::Dependency { .. }
        | DebtType::OrphanedFunctions { .. }
        | DebtType::UtilitiesSprawl { .. } => 1.1,

        // Resource and error handling issues
        DebtType::ResourceLeak { .. }
        | DebtType::ErrorSwallowing { .. }
        | DebtType::AsyncMisuse { .. }
        | DebtType::BlockingIO { .. } => 1.1,

        // Legacy patterns and minor issues
        DebtType::PrimitiveObsession { .. }
        | DebtType::MagicValues { .. }
        | DebtType::SuboptimalDataStructure { .. }
        | DebtType::CollectionInefficiency { .. }
        | DebtType::AllocationInefficiency { .. }
        | DebtType::StringConcatenation { .. }
        | DebtType::NestedLoops { .. } => 1.05,

        // Testing gaps - important but secondary to complexity
        DebtType::TestingGap { .. } => 1.0,

        // Dead code - typically low priority
        DebtType::DeadCode { .. } => 0.9,

        // All other types (TODOs, FIXMEs, etc.) - neutral
        DebtType::Todo { .. }
        | DebtType::Fixme { .. }
        | DebtType::CodeSmell { .. }
        | DebtType::ResourceManagement { .. }
        | DebtType::TestQuality { .. }
        | DebtType::Duplication { .. }
        | DebtType::TestDuplication { .. }
        | DebtType::Risk { .. }
        | DebtType::TestTodo { .. }
        | DebtType::AssertionComplexity { .. }
        | DebtType::FlakyTestPattern { .. } => 1.0,
    }
}

/// Configuration for exponential scaling and risk boosting
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ScalingConfig {
    // Exponential scaling exponents (>1.0 = amplification, 1.0 = linear)
    pub god_object_exponent: f64,
    pub god_module_exponent: f64,
    pub high_complexity_exponent: f64,     // cyclomatic > 30
    pub moderate_complexity_exponent: f64, // cyclomatic > 15

    // Risk boost multipliers (>1.0 = boost, 1.0 = no change)
    pub high_dependency_boost: f64,  // total deps > 15
    pub entry_point_boost: f64,      // entry points
    pub complex_untested_boost: f64, // complexity > 20 + untested
    pub error_swallowing_boost: f64, // functions with error swallowing patterns
}

impl Default for ScalingConfig {
    fn default() -> Self {
        Self {
            god_object_exponent: 1.4,
            god_module_exponent: 1.4,
            high_complexity_exponent: 1.2,
            moderate_complexity_exponent: 1.1,
            high_dependency_boost: 1.2,
            entry_point_boost: 1.15,
            complex_untested_boost: 1.25,
            error_swallowing_boost: 1.15, // 15% boost for error swallowing patterns
        }
    }
}

/// Apply exponential scaling based on debt type.
///
/// Returns the scaled score using debt-type-specific exponents.
/// Higher exponents create more separation at higher base scores.
fn apply_exponential_scaling(base_score: f64, debt_type: &DebtType, config: &ScalingConfig) -> f64 {
    // Ensure minimum base score to avoid zero^exponent = 0
    let safe_base = base_score.max(1.0);

    let exponent = match debt_type {
        // Architectural issues get strong exponential scaling
        DebtType::GodObject { .. } => config.god_object_exponent,

        // High complexity gets moderate exponential scaling
        DebtType::ComplexityHotspot { cyclomatic, .. } => {
            if *cyclomatic > 30 {
                config.high_complexity_exponent
            } else if *cyclomatic > 15 {
                config.moderate_complexity_exponent
            } else {
                1.0
            }
        }

        // Complex untested code gets slight exponential boost
        DebtType::TestingGap { cyclomatic, .. } if *cyclomatic > 20 => {
            config.moderate_complexity_exponent
        }

        // Everything else stays linear (exponent = 1.0)
        _ => 1.0,
    };

    safe_base.powf(exponent)
}

/// Check if item is untested (coverage < 10%).
fn is_untested(item: &UnifiedDebtItem) -> bool {
    matches!(
        item.debt_type,
        DebtType::TestingGap { coverage, .. } if coverage < 0.1
    )
}

/// Calculate final score with exponential scaling, risk boosting, and debt type multiplier.
///
/// Pipeline:
/// 1. Apply exponential scaling based on debt type complexity
/// 2. Apply debt-type-specific severity multiplier (differentiates scores at same location)
/// 3. Apply discrete risk boosts based on dependencies, entry points, etc.
///
/// Returns tuple of (final_score, exponent_used, boost_applied, debt_type_multiplier).
pub fn calculate_final_score(
    base_score: f64,
    debt_type: &DebtType,
    item: &UnifiedDebtItem,
    config: &ScalingConfig,
) -> (f64, f64, f64, f64) {
    // Determine exponent (for transparency)
    let exponent = match debt_type {
        DebtType::GodObject { .. } => config.god_object_exponent,
        DebtType::ComplexityHotspot { cyclomatic, .. } => {
            if *cyclomatic > 30 {
                config.high_complexity_exponent
            } else if *cyclomatic > 15 {
                config.moderate_complexity_exponent
            } else {
                1.0
            }
        }
        DebtType::TestingGap { cyclomatic, .. } if *cyclomatic > 20 => {
            config.moderate_complexity_exponent
        }
        _ => 1.0,
    };

    // Step 1: Apply exponential scaling
    let scaled = apply_exponential_scaling(base_score, debt_type, config);

    // Step 2: Calculate debt type severity multiplier
    let debt_multiplier = calculate_debt_type_severity_multiplier(debt_type);
    let after_debt_multiplier = scaled * debt_multiplier;

    // Step 3: Calculate risk boost factor
    let mut boost = 1.0;
    let total_deps = item.upstream_dependencies + item.downstream_dependencies;
    if total_deps > 15 {
        boost *= config.high_dependency_boost;
    }
    if matches!(item.function_role, FunctionRole::EntryPoint) {
        boost *= config.entry_point_boost;
    }
    if is_untested(item) && item.cyclomatic_complexity > 20 {
        boost *= config.complex_untested_boost;
    }
    if item.error_swallowing_count.unwrap_or(0) > 0 {
        boost *= config.error_swallowing_boost;
    }

    // Step 4: Apply risk boosts (to the debt-multiplied score)
    let final_score = after_debt_multiplier * boost;

    (final_score, exponent, boost, debt_multiplier)
}

#[cfg(test)]
mod tests {
    use super::*;
    use proptest::prelude::*;
    use std::path::PathBuf;

    fn create_test_item(
        base_score: f64,
        debt_type: DebtType,
        upstream_deps: usize,
        downstream_deps: usize,
        role: FunctionRole,
        cyclomatic: u32,
    ) -> UnifiedDebtItem {
        use crate::priority::unified_scorer::{Location, UnifiedScore};
        use crate::priority::ActionableRecommendation;
        use crate::priority::ImpactMetrics;

        UnifiedDebtItem {
            location: Location {
                file: PathBuf::from("test.rs"),
                function: "test_func".to_string(),
                line: 1,
            },
            debt_type,
            unified_score: UnifiedScore {
                complexity_factor: 5.0,
                coverage_factor: 5.0,
                dependency_factor: 5.0,
                role_multiplier: 1.0,
                final_score: base_score.max(0.0),
                base_score: Some(base_score),
                exponential_factor: Some(1.0),
                risk_boost: Some(1.0),
                pre_adjustment_score: None,
                adjustment_applied: None,
                purity_factor: None,
                refactorability_factor: None,
                pattern_factor: None,
                // Spec 260: Score transparency fields
                debt_adjustment: None,
                pre_normalization_score: None,
                structural_multiplier: Some(1.0),
                has_coverage_data: false,
                contextual_risk_multiplier: None,
                pre_contextual_score: None,
                debt_type_multiplier: None,
            },
            function_role: role,
            recommendation: ActionableRecommendation {
                primary_action: "Test".to_string(),
                rationale: "Test".to_string(),
                implementation_steps: vec![],
                related_items: vec![],
                steps: None,
                estimated_effort_hours: None,
            },
            expected_impact: ImpactMetrics {
                coverage_improvement: 0.0,
                lines_reduction: 0,
                complexity_reduction: 0.0,
                risk_reduction: 0.0,
            },
            transitive_coverage: None,
            upstream_dependencies: upstream_deps,
            downstream_dependencies: downstream_deps,
            upstream_callers: vec![],
            downstream_callees: vec![],
            upstream_production_callers: vec![],
            upstream_test_callers: vec![],
            production_blast_radius: 0,
            nesting_depth: 1,
            function_length: 10,
            cyclomatic_complexity: cyclomatic,
            cognitive_complexity: cyclomatic,
            is_pure: None,
            purity_confidence: None,
            purity_level: None,
            god_object_indicators: None,
            tier: None,
            function_context: None,
            context_confidence: None,
            contextual_recommendation: None,
            pattern_analysis: None,
            file_context: None,
            context_multiplier: None,
            context_type: None,
            language_specific: None, // spec 190
            detected_pattern: None,
            contextual_risk: None, // spec 203
            file_line_count: None,
            responsibility_category: None,
            error_swallowing_count: None,
            error_swallowing_patterns: None,
            entropy_analysis: None,
            context_suggestion: None,
        }
    }

    /// Test helper: Apply discrete risk-based boosts.
    /// This function was moved from production code to test-only code since
    /// the logic is now inlined in calculate_final_score.
    fn apply_risk_boosts(score: f64, item: &UnifiedDebtItem, config: &ScalingConfig) -> f64 {
        let mut boost = 1.0;

        // High dependency count indicates central, critical code
        let total_deps = item.upstream_dependencies + item.downstream_dependencies;
        if total_deps > 15 {
            boost *= config.high_dependency_boost;
        }

        // Entry points are critical paths
        if matches!(item.function_role, FunctionRole::EntryPoint) {
            boost *= config.entry_point_boost;
        }

        // Complex + untested is particularly risky
        if is_untested(item) && item.cyclomatic_complexity > 20 {
            boost *= config.complex_untested_boost;
        }

        // Error swallowing indicates poor error handling practices
        if item.error_swallowing_count.unwrap_or(0) > 0 {
            boost *= config.error_swallowing_boost;
        }

        score * boost
    }

    #[test]
    fn test_exponential_scaling_god_object() {
        let config = ScalingConfig::default();
        let base = 10.0;

        let scaled = apply_exponential_scaling(
            base,
            &DebtType::GodObject {
                methods: 50,
                fields: Some(20),
                responsibilities: 10,
                god_object_score: 85.0,
                lines: 400,
            },
            &config,
        );

        // 10^1.4 ≈ 25.1
        assert!(
            (scaled - 25.1).abs() < 0.5,
            "Expected ~25.1, got {}",
            scaled
        );
    }

    #[test]
    fn test_exponential_scaling_creates_separation() {
        let config = ScalingConfig::default();
        let base = 20.0;

        let god_object_scaled = apply_exponential_scaling(
            base,
            &DebtType::GodObject {
                methods: 50,
                fields: Some(20),
                responsibilities: 10,
                god_object_score: 85.0,
                lines: 400,
            },
            &config,
        );

        let testing_gap_scaled = apply_exponential_scaling(
            base,
            &DebtType::TestingGap {
                coverage: 0.0,
                cyclomatic: 10,
                cognitive: 10,
            },
            &config,
        );

        // God object should score significantly higher
        // 20^1.4 ≈ 66 vs 20^1.0 = 20
        assert!(god_object_scaled > testing_gap_scaled * 2.0);
    }

    #[test]
    fn test_risk_boosts_multiply() {
        let config = ScalingConfig::default();
        let item = create_test_item(
            10.0,
            DebtType::TestingGap {
                coverage: 0.0,
                cyclomatic: 25,
                cognitive: 30,
            },
            10, // High upstream deps
            10, // High downstream deps
            FunctionRole::EntryPoint,
            25,
        );

        let boosted = apply_risk_boosts(10.0, &item, &config);

        // Should apply: high_deps (1.2) * entry_point (1.15) * complex_untested (1.25)
        // 10.0 * 1.2 * 1.15 * 1.25 = 17.25
        assert!(
            (boosted - 17.25).abs() < 0.1,
            "Expected ~17.25, got {}",
            boosted
        );
    }

    #[test]
    fn test_calculate_final_score_integration() {
        let config = ScalingConfig::default();
        let item = create_test_item(
            30.0,
            DebtType::GodObject {
                methods: 50,
                fields: Some(1000),
                responsibilities: 10,
                god_object_score: 85.0,
                lines: 600,
            },
            20, // High deps
            10,
            FunctionRole::EntryPoint,
            35,
        );

        let (final_score, exponent, boost, debt_multiplier) =
            calculate_final_score(30.0, &item.debt_type, &item, &config);

        // 30^1.4 ≈ 108, then * 1.4 (debt_mult) * 1.2 (high_deps) * 1.15 (entry_point) ≈ 209
        assert!(exponent == 1.4, "Expected exponent 1.4, got {}", exponent);
        assert!(boost > 1.3, "Expected boost > 1.3, got {}", boost);
        assert!(
            debt_multiplier == 1.4,
            "Expected debt_multiplier 1.4 for GodObject, got {}",
            debt_multiplier
        );
        assert!(
            final_score > 190.0,
            "Expected score > 190, got {}",
            final_score
        );
    }

    #[test]
    fn test_architectural_issues_naturally_surface() {
        let config = ScalingConfig::default();

        let god_object_item = create_test_item(
            30.0,
            DebtType::GodObject {
                methods: 50,
                fields: Some(1000),
                responsibilities: 10,
                god_object_score: 85.0,
                lines: 600,
            },
            5,
            5,
            FunctionRole::PureLogic,
            30,
        );

        let simple_gap_item = create_test_item(
            50.0,
            DebtType::TestingGap {
                coverage: 0.0,
                cyclomatic: 10,
                cognitive: 10,
            },
            5,
            5,
            FunctionRole::PureLogic,
            10,
        );

        let (god_score, _, _, god_debt_mult) =
            calculate_final_score(30.0, &god_object_item.debt_type, &god_object_item, &config);

        let (gap_score, _, _, gap_debt_mult) =
            calculate_final_score(50.0, &simple_gap_item.debt_type, &simple_gap_item, &config);

        // God object gets 1.4x debt multiplier, testing gap gets 1.0x
        assert!(
            god_debt_mult == 1.4,
            "Expected GodObject debt_multiplier 1.4, got {}",
            god_debt_mult
        );
        assert!(
            gap_debt_mult == 1.0,
            "Expected TestingGap debt_multiplier 1.0, got {}",
            gap_debt_mult
        );

        // 30^1.4 ≈ 108, * 1.4 (debt mult) ≈ 151 should beat 50^1.0 * 1.0 = 50
        assert!(
            god_score > gap_score,
            "God object (score {}) should rank higher than simple testing gap (score {})",
            god_score,
            gap_score
        );
    }

    #[test]
    fn test_minimum_base_score_prevents_zero() {
        let config = ScalingConfig::default();

        let scaled = apply_exponential_scaling(
            0.0,
            &DebtType::GodObject {
                methods: 50,
                fields: Some(1000),
                responsibilities: 10,
                god_object_score: 85.0,
                lines: 600,
            },
            &config,
        );

        // Should use minimum of 1.0, so 1.0^1.4 = 1.0
        assert!(
            scaled >= 1.0,
            "Scaled score should be at least 1.0, got {}",
            scaled
        );
    }

    #[test]
    fn test_error_swallowing_boost() {
        let config = ScalingConfig::default();

        // Create item without error swallowing
        let item_no_swallowing = create_test_item(
            10.0,
            DebtType::TestingGap {
                coverage: 0.5,
                cyclomatic: 10,
                cognitive: 12,
            },
            5,
            5,
            FunctionRole::PureLogic,
            10,
        );

        // Create item with error swallowing
        let mut item_with_swallowing = create_test_item(
            10.0,
            DebtType::TestingGap {
                coverage: 0.5,
                cyclomatic: 10,
                cognitive: 12,
            },
            5,
            5,
            FunctionRole::PureLogic,
            10,
        );
        item_with_swallowing.error_swallowing_count = Some(3);
        item_with_swallowing.error_swallowing_patterns =
            Some(vec!["if_let_ok_without_else".to_string()]);

        let boosted_no_swallowing = apply_risk_boosts(10.0, &item_no_swallowing, &config);
        let boosted_with_swallowing = apply_risk_boosts(10.0, &item_with_swallowing, &config);

        // Item with error swallowing should have higher score
        assert!(
            boosted_with_swallowing > boosted_no_swallowing,
            "Error swallowing should boost score. Without: {}, With: {}",
            boosted_no_swallowing,
            boosted_with_swallowing
        );

        // Should apply 1.15 boost
        let expected_boost = 10.0 * config.error_swallowing_boost;
        assert!(
            (boosted_with_swallowing - expected_boost).abs() < 0.1,
            "Expected ~{}, got {}",
            expected_boost,
            boosted_with_swallowing
        );
    }

    // Property test: score ordering should be strict and monotonic
    proptest! {
        #[test]
        fn prop_score_ordering_is_strict(
            base_scores in prop::collection::vec(0.0f64..100.0f64, 2..50)
        ) {
            let config = ScalingConfig::default();

            // Create items with random base scores
            let items: Vec<_> = base_scores.iter().enumerate().map(|(i, &score)| {
                let debt_type = if i % 3 == 0 {
                    DebtType::GodObject {
                        methods: 50,
                        fields: Some(20),
                        responsibilities: 10,
                        god_object_score: 85.0,
                        lines: 400,
                    }
                } else if i % 3 == 1 {
                    DebtType::ComplexityHotspot {
                        cyclomatic: 35,
                        cognitive: 40,
                    }
                } else {
                    DebtType::TestingGap {
                        coverage: 0.0,
                        cyclomatic: 15,
                        cognitive: 20,
                    }
                };

                create_test_item(
                    score,
                    debt_type,
                    5,
                    5,
                    FunctionRole::PureLogic,
                    20,
                )
            }).collect();

            // Calculate final scores
            let mut scored_items: Vec<_> = items.iter().enumerate().map(|(idx, item)| {
                let (final_score, _, _, _) = calculate_final_score(
                    base_scores[idx],
                    &item.debt_type,
                    item,
                    &config
                );
                (final_score, idx)
            }).collect();

            // Sort by score descending (as in get_top_mixed_priorities)
            scored_items.sort_by(|a, b| {
                b.0.partial_cmp(&a.0).unwrap_or(std::cmp::Ordering::Equal)
            });

            // Verify no score inversions: score[i] >= score[i+1]
            for i in 0..scored_items.len().saturating_sub(1) {
                let score_i = scored_items[i].0;
                let score_next = scored_items[i + 1].0;
                prop_assert!(
                    score_i >= score_next,
                    "Score inversion at index {}: {} < {} (items {} and {})",
                    i,
                    score_i,
                    score_next,
                    scored_items[i].1,
                    scored_items[i + 1].1
                );
            }
        }

        #[test]
        fn prop_exponential_scaling_monotonic(
            base_score in 1.0f64..100.0f64,
            higher_score in 1.0f64..100.0f64,
        ) {
            // Ensure higher_score > base_score
            let (lower, higher) = if base_score < higher_score {
                (base_score, higher_score)
            } else {
                (higher_score, base_score)
            };

            if (higher - lower).abs() < 0.01 {
                return Ok(());
            }

            let config = ScalingConfig::default();
            let debt_type = DebtType::GodObject {
                methods: 50,
                fields: Some(20),
                responsibilities: 10,
                god_object_score: 85.0,
                lines: 400,
            };

            let scaled_lower = apply_exponential_scaling(lower, &debt_type, &config);
            let scaled_higher = apply_exponential_scaling(higher, &debt_type, &config);

            // Exponential scaling must preserve ordering
            prop_assert!(
                scaled_higher >= scaled_lower,
                "Exponential scaling violated monotonicity: {}^1.4={} should be >= {}^1.4={}",
                higher, scaled_higher, lower, scaled_lower
            );
        }

        #[test]
        fn prop_risk_boosts_non_negative(
            base_score in 1.0f64..100.0f64,
            upstream_deps in 0usize..30,
            downstream_deps in 0usize..30,
        ) {
            let config = ScalingConfig::default();
            let role = if upstream_deps > 20 {
                FunctionRole::EntryPoint
            } else {
                FunctionRole::PureLogic
            };

            let item = create_test_item(
                base_score,
                DebtType::TestingGap {
                    coverage: 0.0,
                    cyclomatic: 25,
                    cognitive: 30,
                },
                upstream_deps,
                downstream_deps,
                role,
                25,
            );

            let boosted = apply_risk_boosts(base_score, &item, &config);

            // Risk boosts should never decrease score
            prop_assert!(
                boosted >= base_score,
                "Risk boost decreased score: {} -> {}",
                base_score,
                boosted
            );
        }

        #[test]
        fn prop_final_score_never_decreases_from_base(
            base_score in 1.0f64..100.0f64,
        ) {
            let config = ScalingConfig::default();
            let item = create_test_item(
                base_score,
                DebtType::GodObject {
                    methods: 50,
                    fields: Some(20),
                    responsibilities: 10,
                    god_object_score: 85.0,
                    lines: 400,
                },
                10,
                10,
                FunctionRole::EntryPoint,
                30,
            );

            let (final_score, _, _, _) = calculate_final_score(
                base_score,
                &item.debt_type,
                &item,
                &config,
            );

            // With exponent >= 1.0, debt_mult >= 1.0, and boost >= 1.0, final score should never be less than base
            // (for base_score >= 1.0)
            prop_assert!(
                final_score >= base_score * 0.99, // Allow tiny floating point errors
                "Final score {} is less than base score {}",
                final_score,
                base_score
            );
        }
    }

    // Unit tests for debt type severity multiplier
    #[test]
    fn test_debt_type_severity_multiplier_god_object() {
        let debt_type = DebtType::GodObject {
            methods: 50,
            fields: Some(20),
            responsibilities: 10,
            god_object_score: 85.0,
            lines: 400,
        };
        assert_eq!(calculate_debt_type_severity_multiplier(&debt_type), 1.4);
    }

    #[test]
    fn test_debt_type_severity_multiplier_complexity_hotspot() {
        let debt_type = DebtType::ComplexityHotspot {
            cyclomatic: 25,
            cognitive: 30,
        };
        assert_eq!(calculate_debt_type_severity_multiplier(&debt_type), 1.2);
    }

    #[test]
    fn test_debt_type_severity_multiplier_testing_gap() {
        let debt_type = DebtType::TestingGap {
            coverage: 0.0,
            cyclomatic: 15,
            cognitive: 20,
        };
        assert_eq!(calculate_debt_type_severity_multiplier(&debt_type), 1.0);
    }

    #[test]
    fn test_debt_type_severity_multiplier_dead_code() {
        let debt_type = DebtType::DeadCode {
            visibility: crate::priority::FunctionVisibility::Private,
            cyclomatic: 5,
            cognitive: 3,
            usage_hints: vec![],
        };
        // Dead code gets reduced priority (0.9x)
        assert_eq!(calculate_debt_type_severity_multiplier(&debt_type), 0.9);
    }

    #[test]
    fn test_debt_type_severity_multiplier_differentiation() {
        // Same base score, different debt types should produce different final scores
        let config = ScalingConfig::default();
        let base_score = 20.0;

        // Create items with different debt types but same base metrics
        let god_object = create_test_item(
            base_score,
            DebtType::GodObject {
                methods: 50,
                fields: Some(20),
                responsibilities: 10,
                god_object_score: 85.0,
                lines: 400,
            },
            5,
            5,
            FunctionRole::PureLogic,
            20,
        );

        let complexity = create_test_item(
            base_score,
            DebtType::ComplexityHotspot {
                cyclomatic: 15,
                cognitive: 20,
            },
            5,
            5,
            FunctionRole::PureLogic,
            20,
        );

        let testing_gap = create_test_item(
            base_score,
            DebtType::TestingGap {
                coverage: 0.0,
                cyclomatic: 15,
                cognitive: 20,
            },
            5,
            5,
            FunctionRole::PureLogic,
            20,
        );

        let (god_score, _, _, god_mult) =
            calculate_final_score(base_score, &god_object.debt_type, &god_object, &config);
        let (complexity_score, _, _, complexity_mult) =
            calculate_final_score(base_score, &complexity.debt_type, &complexity, &config);
        let (gap_score, _, _, gap_mult) =
            calculate_final_score(base_score, &testing_gap.debt_type, &testing_gap, &config);

        // Verify multipliers are different
        assert!(
            god_mult > complexity_mult,
            "GodObject should have higher multiplier than ComplexityHotspot"
        );
        assert!(
            complexity_mult > gap_mult,
            "ComplexityHotspot should have higher multiplier than TestingGap"
        );

        // Verify resulting scores reflect the differentiation
        // Note: god_object also gets exponential scaling (1.4 exponent), so its final score is significantly higher
        assert!(
            god_score > complexity_score,
            "GodObject score {} should be > ComplexityHotspot score {}",
            god_score,
            complexity_score
        );
        assert!(
            complexity_score > gap_score,
            "ComplexityHotspot score {} should be > TestingGap score {}",
            complexity_score,
            gap_score
        );
    }
}