cargo_coupling/

balance.rs

//! Balance score calculation and refactoring recommendations
//!
//! Implements the balance equation from "Balancing Coupling in Software Design":
//! BALANCE = (STRENGTH XOR DISTANCE) OR NOT VOLATILITY
//!
//! Key principle: The goal is NOT to eliminate coupling, but to balance it appropriately.
//! - Strong coupling + close distance = Good (cohesion)
//! - Weak coupling + far distance = Good (loose coupling)
//! - Strong coupling + far distance = Bad (global complexity)
//! - High volatility + strong coupling = Bad (cascading changes)

use std::collections::HashMap;

use crate::metrics::{CouplingMetrics, Distance, IntegrationStrength, ProjectMetrics, Volatility};

/// Issue severity levels
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum Severity {
    /// Minor issue, consider addressing
    Low,
    /// Should be addressed in regular maintenance
    Medium,
    /// Needs attention soon, potential source of bugs
    High,
    /// Must be fixed, actively causing problems
    Critical,
}

impl std::fmt::Display for Severity {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Severity::Low => write!(f, "Low"),
            Severity::Medium => write!(f, "Medium"),
            Severity::High => write!(f, "High"),
            Severity::Critical => write!(f, "Critical"),
        }
    }
}

/// Types of coupling problems
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum IssueType {
    /// Strong coupling spanning a long distance
    GlobalComplexity,
    /// Strong coupling to a frequently changing component
    CascadingChangeRisk,
    /// Intrusive coupling across boundaries (field/internals access)
    InappropriateIntimacy,
    /// A module with too many dependencies
    HighEfferentCoupling,
    /// A module that too many others depend on
    HighAfferentCoupling,
    /// Weak coupling where stronger might be appropriate
    UnnecessaryAbstraction,
    /// Circular dependency detected
    CircularDependency,

    // === APOSD-inspired issues (A Philosophy of Software Design) ===
    /// Module with interface complexity close to implementation complexity
    ShallowModule,
    /// Method that only delegates to another method without adding value
    PassThroughMethod,
    /// Module requiring too much knowledge to understand/modify
    HighCognitiveLoad,
}

impl std::fmt::Display for IssueType {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            IssueType::GlobalComplexity => write!(f, "Global Complexity"),
            IssueType::CascadingChangeRisk => write!(f, "Cascading Change Risk"),
            IssueType::InappropriateIntimacy => write!(f, "Inappropriate Intimacy"),
            IssueType::HighEfferentCoupling => write!(f, "High Efferent Coupling"),
            IssueType::HighAfferentCoupling => write!(f, "High Afferent Coupling"),
            IssueType::UnnecessaryAbstraction => write!(f, "Unnecessary Abstraction"),
            IssueType::CircularDependency => write!(f, "Circular Dependency"),
            // APOSD-inspired
            IssueType::ShallowModule => write!(f, "Shallow Module"),
            IssueType::PassThroughMethod => write!(f, "Pass-Through Method"),
            IssueType::HighCognitiveLoad => write!(f, "High Cognitive Load"),
        }
    }
}

impl IssueType {
    /// Get a detailed description of what this issue type means
    pub fn description(&self) -> &'static str {
        match self {
            IssueType::GlobalComplexity => {
                "Strong coupling to distant components increases cognitive load and makes the system harder to understand and modify."
            }
            IssueType::CascadingChangeRisk => {
                "Strongly coupling to volatile components means changes will cascade through the system, requiring updates in many places."
            }
            IssueType::InappropriateIntimacy => {
                "Direct access to internal details (fields, private methods) across module boundaries violates encapsulation."
            }
            IssueType::HighEfferentCoupling => {
                "A module depending on too many others is fragile and hard to test. Changes anywhere affect this module."
            }
            IssueType::HighAfferentCoupling => {
                "A module that many others depend on is hard to change. Any modification risks breaking dependents."
            }
            IssueType::UnnecessaryAbstraction => {
                "Using abstract interfaces for closely-related stable components may add complexity without benefit."
            }
            IssueType::CircularDependency => {
                "Circular dependencies make it impossible to understand, test, or modify components in isolation."
            }
            // APOSD-inspired descriptions
            IssueType::ShallowModule => {
                "Interface complexity is close to implementation complexity. The module doesn't hide enough complexity behind a simple interface. (APOSD: Deep vs Shallow Modules)"
            }
            IssueType::PassThroughMethod => {
                "Method only delegates to another method without adding significant functionality. Indicates unclear responsibility division. (APOSD: Pass-Through Methods)"
            }
            IssueType::HighCognitiveLoad => {
                "Module requires too much knowledge to understand and modify. Too many public APIs, dependencies, or complex type signatures. (APOSD: Cognitive Load)"
            }
        }
    }
}

/// A detected coupling issue with refactoring recommendation
#[derive(Debug, Clone)]
pub struct CouplingIssue {
    /// Type of issue
    pub issue_type: IssueType,
    /// Severity of the issue
    pub severity: Severity,
    /// Source component
    pub source: String,
    /// Target component
    pub target: String,
    /// Specific description of this instance
    pub description: String,
    /// Concrete refactoring action to take
    pub refactoring: RefactoringAction,
    /// Balance score that triggered this issue
    pub balance_score: f64,
}

/// Specific refactoring actions
#[derive(Debug, Clone)]
pub enum RefactoringAction {
    /// Introduce a trait to abstract the coupling
    IntroduceTrait {
        suggested_name: String,
        methods: Vec<String>,
    },
    /// Move the component closer (same module/crate)
    MoveCloser { target_location: String },
    /// Extract an interface/adapter
    ExtractAdapter {
        adapter_name: String,
        purpose: String,
    },
    /// Split a large module
    SplitModule { suggested_modules: Vec<String> },
    /// Remove unnecessary abstraction
    SimplifyAbstraction { direct_usage: String },
    /// Break circular dependency
    BreakCycle { suggested_direction: String },
    /// Add stable interface
    StabilizeInterface { interface_name: String },
    /// General refactoring suggestion
    General { action: String },
}

impl std::fmt::Display for RefactoringAction {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            RefactoringAction::IntroduceTrait {
                suggested_name,
                methods,
            } => {
                write!(
                    f,
                    "Introduce trait `{}` with methods: {}",
                    suggested_name,
                    methods.join(", ")
                )
            }
            RefactoringAction::MoveCloser { target_location } => {
                write!(f, "Move component to `{}`", target_location)
            }
            RefactoringAction::ExtractAdapter {
                adapter_name,
                purpose,
            } => {
                write!(f, "Extract adapter `{}` to {}", adapter_name, purpose)
            }
            RefactoringAction::SplitModule { suggested_modules } => {
                write!(f, "Split into modules: {}", suggested_modules.join(", "))
            }
            RefactoringAction::SimplifyAbstraction { direct_usage } => {
                write!(f, "Replace with direct usage: {}", direct_usage)
            }
            RefactoringAction::BreakCycle {
                suggested_direction,
            } => {
                write!(f, "Break cycle by {}", suggested_direction)
            }
            RefactoringAction::StabilizeInterface { interface_name } => {
                write!(f, "Add stable interface `{}`", interface_name)
            }
            RefactoringAction::General { action } => {
                write!(f, "{}", action)
            }
        }
    }
}

/// Balance score for a coupling relationship
#[derive(Debug, Clone)]
pub struct BalanceScore {
    /// The coupling being scored
    pub coupling: CouplingMetrics,
    /// Overall balance score (0.0 - 1.0, higher = better balanced)
    pub score: f64,
    /// Whether strength and distance are aligned
    pub alignment: f64,
    /// Impact of volatility
    pub volatility_impact: f64,
    /// Interpretation of the score
    pub interpretation: BalanceInterpretation,
}

/// How to interpret a balance score
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum BalanceInterpretation {
    /// Well-balanced, no action needed
    Balanced,
    /// Acceptable but could be improved
    Acceptable,
    /// Should be reviewed
    NeedsReview,
    /// Should be refactored
    NeedsRefactoring,
    /// Critical issue, must fix
    Critical,
}

impl std::fmt::Display for BalanceInterpretation {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            BalanceInterpretation::Balanced => write!(f, "Balanced"),
            BalanceInterpretation::Acceptable => write!(f, "Acceptable"),
            BalanceInterpretation::NeedsReview => write!(f, "Needs Review"),
            BalanceInterpretation::NeedsRefactoring => write!(f, "Needs Refactoring"),
            BalanceInterpretation::Critical => write!(f, "Critical"),
        }
    }
}

impl BalanceScore {
    /// Calculate balance score for a coupling
    ///
    /// The formula implements: BALANCE = (STRENGTH XOR DISTANCE) OR NOT VOLATILITY
    ///
    /// Ideal patterns:
    /// - Strong (1.0) + Close (0.0) → High alignment (cohesion)
    /// - Weak (0.0) + Far (1.0) → High alignment (loose coupling)
    ///
    /// Problematic patterns:
    /// - Strong (1.0) + Far (1.0) → Low alignment (global complexity)
    /// - Any + High volatility → Reduced by volatility impact
    pub fn calculate(coupling: &CouplingMetrics) -> Self {
        let strength = coupling.strength_value();
        let distance = coupling.distance_value();
        let volatility = coupling.volatility_value();

        // Alignment: how well strength and distance match the ideal patterns
        // Ideal: (strong + close) OR (weak + far)
        // XOR-like: difference between strength and distance
        // If both high or both low = misaligned, if opposite = aligned
        let alignment = 1.0 - (strength - (1.0 - distance)).abs();

        // Volatility impact: high volatility with strong coupling is bad
        // Only applies when there's actual coupling (strength > 0)
        let volatility_penalty = volatility * strength;
        let volatility_impact = 1.0 - volatility_penalty;

        // Combined score: both alignment AND stability matter
        // Using AND (multiplication) instead of OR (max) for stricter scoring
        let score = alignment * volatility_impact;

        // Determine interpretation based on score
        let interpretation = match score {
            s if s >= 0.8 => BalanceInterpretation::Balanced,
            s if s >= 0.6 => BalanceInterpretation::Acceptable,
            s if s >= 0.4 => BalanceInterpretation::NeedsReview,
            s if s >= 0.2 => BalanceInterpretation::NeedsRefactoring,
            _ => BalanceInterpretation::Critical,
        };

        Self {
            coupling: coupling.clone(),
            score,
            alignment,
            volatility_impact,
            interpretation,
        }
    }

    /// Check if this coupling is well-balanced (no action needed)
    pub fn is_balanced(&self) -> bool {
        matches!(
            self.interpretation,
            BalanceInterpretation::Balanced | BalanceInterpretation::Acceptable
        )
    }

    /// Check if this coupling needs refactoring
    pub fn needs_refactoring(&self) -> bool {
        matches!(
            self.interpretation,
            BalanceInterpretation::NeedsRefactoring | BalanceInterpretation::Critical
        )
    }
}

/// Thresholds for identifying issues
#[derive(Debug, Clone)]
pub struct IssueThresholds {
    /// Minimum strength value considered "strong"
    pub strong_coupling: f64,
    /// Minimum distance value considered "far"
    pub far_distance: f64,
    /// Minimum volatility value considered "high"
    pub high_volatility: f64,
    /// Number of dependencies to consider "high efferent coupling"
    pub max_dependencies: usize,
    /// Number of dependents to consider "high afferent coupling"
    pub max_dependents: usize,
}

impl Default for IssueThresholds {
    fn default() -> Self {
        Self {
            strong_coupling: 0.75, // Functional strength or higher (was 0.5)
            far_distance: 0.5,     // DifferentModule or higher
            high_volatility: 0.75, // High volatility only (was 0.5)
            max_dependencies: 20,  // More than 20 outgoing dependencies (was 15)
            max_dependents: 30,    // More than 30 incoming dependencies (was 20)
        }
    }
}

/// Crate stability classification
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CrateStability {
    /// Rust language fundamentals (std, core, alloc) - always ignore
    Fundamental,
    /// Highly stable, ubiquitous crates (serde, thiserror) - low concern
    Stable,
    /// Infrastructure crates (tokio, tracing) - medium concern
    Infrastructure,
    /// Regular external crate - normal analysis
    Normal,
}

/// Check the stability classification of a crate
pub fn classify_crate_stability(crate_name: &str) -> CrateStability {
    // Extract the base crate name (before ::)
    let base_name = crate_name.split("::").next().unwrap_or(crate_name).trim();

    match base_name {
        // Rust fundamentals - always safe to depend on
        "std" | "core" | "alloc" => CrateStability::Fundamental,

        // Highly stable, de-facto standard crates
        "serde" | "serde_json" | "serde_yaml" | "toml" |  // Serialization
        "thiserror" | "anyhow" |                           // Error handling
        "log" |                                            // Logging trait
        "chrono" | "time" |                                // Date/time
        "uuid" |                                           // UUIDs
        "regex" |                                          // Regex
        "lazy_static" | "once_cell" |                      // Statics
        "bytes" | "memchr" |                               // Byte utilities
        "itertools" |                                      // Iterator utilities
        "derive_more" | "strum"                            // Derive macros
        => CrateStability::Stable,

        // Infrastructure crates - stable but architectural decisions
        "tokio" | "async-std" | "smol" |                   // Async runtimes
        "async-trait" |                                    // Async traits
        "futures" | "futures-util" |                       // Futures
        "tracing" | "tracing-subscriber" |                 // Tracing
        "tracing-opentelemetry" | "opentelemetry" |        // Observability
        "opentelemetry-otlp" | "opentelemetry_sdk" |
        "hyper" | "reqwest" | "http" |                     // HTTP
        "tonic" | "prost" |                                // gRPC
        "sqlx" | "diesel" | "sea-orm" |                    // Database
        "clap" | "structopt"                               // CLI
        => CrateStability::Infrastructure,

        // Everything else
        _ => CrateStability::Normal,
    }
}

/// Check if a crate should be excluded from issue detection
pub fn should_skip_crate(crate_name: &str) -> bool {
    matches!(
        classify_crate_stability(crate_name),
        CrateStability::Fundamental
    )
}

/// Check if a crate should have reduced severity
pub fn should_reduce_severity(crate_name: &str) -> bool {
    matches!(
        classify_crate_stability(crate_name),
        CrateStability::Stable | CrateStability::Infrastructure
    )
}

/// Check if this is an external crate (not part of the workspace)
/// External crates are identified by not containing "::" or starting with known external patterns
pub fn is_external_crate(target: &str, source: &str) -> bool {
    // If target doesn't have ::, it might be external
    // But we need to check if it's the same workspace member

    // Extract the crate/module prefix
    let target_prefix = target.split("::").next().unwrap_or(target);
    let source_prefix = source.split("::").next().unwrap_or(source);

    // If they have the same prefix, it's internal
    if target_prefix == source_prefix {
        return false;
    }

    // If target looks like an external crate pattern (no workspace prefix match)
    // Check if it's a known stable/infrastructure crate
    let stability = classify_crate_stability(target);
    matches!(
        stability,
        CrateStability::Fundamental | CrateStability::Stable | CrateStability::Infrastructure
    )
}

/// Identify issues in a coupling relationship
pub fn identify_issues(coupling: &CouplingMetrics) -> Vec<CouplingIssue> {
    identify_issues_with_thresholds(coupling, &IssueThresholds::default())
}

/// Identify issues with custom thresholds
pub fn identify_issues_with_thresholds(
    coupling: &CouplingMetrics,
    _thresholds: &IssueThresholds,
) -> Vec<CouplingIssue> {
    let mut issues = Vec::new();

    // Skip ALL external crate dependencies - we can't control them
    // Focus only on internal workspace coupling issues
    if coupling.distance == Distance::DifferentCrate {
        return issues;
    }

    let balance = BalanceScore::calculate(coupling);

    // Pattern 1: Global Complexity (INTRUSIVE coupling + different module)
    // Only flag intrusive coupling across module boundaries - functional coupling is normal
    if coupling.strength == IntegrationStrength::Intrusive
        && coupling.distance == Distance::DifferentModule
    {
        issues.push(CouplingIssue {
            issue_type: IssueType::GlobalComplexity,
            severity: Severity::Medium, // Medium, not High - it's internal
            source: coupling.source.clone(),
            target: coupling.target.clone(),
            description: format!(
                "Intrusive coupling to {} across module boundary",
                coupling.target,
            ),
            refactoring: RefactoringAction::IntroduceTrait {
                suggested_name: format!("{}Trait", extract_type_name(&coupling.target)),
                methods: vec!["// Extract required methods".to_string()],
            },
            balance_score: balance.score,
        });
    }

    // Pattern 2: Cascading Change Risk (intrusive coupling + high volatility)
    // Only flag if volatility is actually high (from Git data)
    if coupling.strength == IntegrationStrength::Intrusive
        && coupling.volatility == Volatility::High
    {
        issues.push(CouplingIssue {
            issue_type: IssueType::CascadingChangeRisk,
            severity: Severity::High,
            source: coupling.source.clone(),
            target: coupling.target.clone(),
            description: format!(
                "Intrusive coupling to frequently-changed component {}",
                coupling.target,
            ),
            refactoring: RefactoringAction::StabilizeInterface {
                interface_name: format!("{}Interface", extract_type_name(&coupling.target)),
            },
            balance_score: balance.score,
        });
    }

    // Pattern 3: Inappropriate Intimacy (Intrusive coupling across DIFFERENT MODULE only)
    // Same module intrusive coupling is fine (it's cohesion)
    if coupling.strength == IntegrationStrength::Intrusive
        && coupling.distance == Distance::DifferentModule
        && balance.score < 0.5
    {
        // Only add if not already added as GlobalComplexity
        if !issues
            .iter()
            .any(|i| i.issue_type == IssueType::GlobalComplexity)
        {
            issues.push(CouplingIssue {
                issue_type: IssueType::InappropriateIntimacy,
                severity: Severity::Medium,
                source: coupling.source.clone(),
                target: coupling.target.clone(),
                description: format!(
                    "Direct internal access to {} across module boundary",
                    coupling.target,
                ),
                refactoring: RefactoringAction::IntroduceTrait {
                    suggested_name: format!("{}Api", extract_type_name(&coupling.target)),
                    methods: vec!["// Expose only necessary operations".to_string()],
                },
                balance_score: balance.score,
            });
        }
    }

    // Pattern 4: Unnecessary Abstraction - DISABLED
    // This pattern generates too much noise and is rarely actionable
    // Trait abstractions are generally good, even for nearby stable components

    issues
}

/// Analyze all couplings in a project and identify issues
pub fn analyze_project_balance(metrics: &ProjectMetrics) -> ProjectBalanceReport {
    analyze_project_balance_with_thresholds(metrics, &IssueThresholds::default())
}

/// Analyze all couplings with custom thresholds
pub fn analyze_project_balance_with_thresholds(
    metrics: &ProjectMetrics,
    thresholds: &IssueThresholds,
) -> ProjectBalanceReport {
    let thresholds = thresholds.clone();
    let mut all_issues = Vec::new();
    let mut internal_balance_scores: Vec<BalanceScore> = Vec::new();
    let mut all_balance_scores: Vec<BalanceScore> = Vec::new();

    // Analyze individual couplings
    // Only INTERNAL couplings affect the health score
    for coupling in &metrics.couplings {
        let score = BalanceScore::calculate(coupling);
        all_balance_scores.push(score.clone());

        // Only count internal couplings for scoring
        if coupling.distance != Distance::DifferentCrate {
            internal_balance_scores.push(score);
            let issues = identify_issues_with_thresholds(coupling, &thresholds);
            all_issues.extend(issues);
        }
    }

    // Analyze module-level coupling patterns (already filters external)
    let module_issues = analyze_module_coupling(metrics, &thresholds);
    all_issues.extend(module_issues);

    // Sort by severity (critical first), then by balance score (worst first)
    all_issues.sort_by(|a, b| {
        b.severity
            .cmp(&a.severity)
            .then_with(|| a.balance_score.partial_cmp(&b.balance_score).unwrap())
    });

    // Calculate summary statistics based on INTERNAL couplings only
    let total_couplings = metrics.couplings.len();
    let internal_couplings = internal_balance_scores.len();

    let balanced_count = internal_balance_scores
        .iter()
        .filter(|s| s.is_balanced())
        .count();
    let needs_review = internal_balance_scores
        .iter()
        .filter(|s| s.interpretation == BalanceInterpretation::NeedsReview)
        .count();
    let needs_refactoring = internal_balance_scores
        .iter()
        .filter(|s| s.needs_refactoring())
        .count();

    // Average score based on internal couplings only
    let average_score = if internal_balance_scores.is_empty() {
        1.0 // No internal couplings = perfect score
    } else {
        internal_balance_scores
            .iter()
            .map(|s| s.score)
            .sum::<f64>()
            / internal_balance_scores.len() as f64
    };

    // Count issues by severity
    let mut issues_by_severity: HashMap<Severity, usize> = HashMap::new();
    for issue in &all_issues {
        *issues_by_severity.entry(issue.severity).or_insert(0) += 1;
    }

    // Count issues by type
    let mut issues_by_type: HashMap<IssueType, usize> = HashMap::new();
    for issue in &all_issues {
        *issues_by_type.entry(issue.issue_type).or_insert(0) += 1;
    }

    // Determine overall health grade based on INTERNAL coupling issues
    let health_grade = calculate_health_grade(&issues_by_severity, internal_couplings);

    ProjectBalanceReport {
        total_couplings,
        balanced_count,
        needs_review,
        needs_refactoring,
        average_score,
        health_grade,
        issues_by_severity,
        issues_by_type,
        issues: all_issues,
        top_priorities: Vec::new(), // Will be filled below
    }
    .with_top_priorities(5) // Increased from 3 to 5 for better actionability
}

/// Analyze module-level coupling (hub detection)
fn analyze_module_coupling(
    metrics: &ProjectMetrics,
    thresholds: &IssueThresholds,
) -> Vec<CouplingIssue> {
    let mut issues = Vec::new();

    // Count outgoing (efferent) and incoming (afferent) couplings per module
    // Only count INTERNAL dependencies (within workspace), not external crates
    let mut efferent: HashMap<&str, usize> = HashMap::new();
    let mut afferent: HashMap<&str, usize> = HashMap::new();

    for coupling in &metrics.couplings {
        // Skip external crate dependencies entirely
        if coupling.distance == Distance::DifferentCrate {
            continue;
        }

        *efferent.entry(&coupling.source).or_insert(0) += 1;
        *afferent.entry(&coupling.target).or_insert(0) += 1;
    }

    // Check for high efferent coupling (depends on too many things)
    for (module, count) in &efferent {
        if *count > thresholds.max_dependencies {
            issues.push(CouplingIssue {
                issue_type: IssueType::HighEfferentCoupling,
                severity: if *count > thresholds.max_dependencies * 2 {
                    Severity::High
                } else {
                    Severity::Medium
                },
                source: module.to_string(),
                target: format!("{} dependencies", count),
                description: format!(
                    "Module {} depends on {} other components (threshold: {})",
                    module, count, thresholds.max_dependencies
                ),
                refactoring: RefactoringAction::SplitModule {
                    suggested_modules: vec![
                        format!("{}_core", module),
                        format!("{}_integration", module),
                    ],
                },
                balance_score: 1.0
                    - (*count as f64 / (thresholds.max_dependencies * 3) as f64).min(1.0),
            });
        }
    }

    // Check for high afferent coupling (too many things depend on this)
    // Only internal modules are counted (external crates already filtered above)
    for (module, count) in &afferent {
        if *count > thresholds.max_dependents {
            issues.push(CouplingIssue {
                issue_type: IssueType::HighAfferentCoupling,
                severity: if *count > thresholds.max_dependents * 2 {
                    Severity::High
                } else {
                    Severity::Medium
                },
                source: format!("{} dependents", count),
                target: module.to_string(),
                description: format!(
                    "Module {} is depended on by {} other components (threshold: {})",
                    module, count, thresholds.max_dependents
                ),
                refactoring: RefactoringAction::IntroduceTrait {
                    suggested_name: format!("{}Interface", extract_type_name(module)),
                    methods: vec!["// Define stable public API".to_string()],
                },
                balance_score: 1.0
                    - (*count as f64 / (thresholds.max_dependents * 3) as f64).min(1.0),
            });
        }
    }

    issues
}

/// Health grade for the overall project
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum HealthGrade {
    A, // Excellent
    B, // Good
    C, // Acceptable
    D, // Needs Improvement
    F, // Critical Issues
}

impl std::fmt::Display for HealthGrade {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            HealthGrade::A => write!(f, "A (Excellent)"),
            HealthGrade::B => write!(f, "B (Good)"),
            HealthGrade::C => write!(f, "C (Acceptable)"),
            HealthGrade::D => write!(f, "D (Needs Improvement)"),
            HealthGrade::F => write!(f, "F (Critical Issues)"),
        }
    }
}

/// Calculate health grade based on multiple quality factors
///
/// Unlike the previous version that only checked for issues,
/// this version also considers positive quality indicators:
/// - Contract coupling rate (trait usage)
/// - Balance score distribution
/// - Internal coupling complexity
fn calculate_health_grade(
    issues_by_severity: &HashMap<Severity, usize>,
    internal_couplings: usize,
) -> HealthGrade {
    let critical = *issues_by_severity.get(&Severity::Critical).unwrap_or(&0);
    let high = *issues_by_severity.get(&Severity::High).unwrap_or(&0);
    let medium = *issues_by_severity.get(&Severity::Medium).unwrap_or(&0);

    // No internal couplings = B (not A - we can't assess quality without data)
    if internal_couplings == 0 {
        return HealthGrade::B;
    }

    // F: Multiple critical issues
    if critical > 3 {
        return HealthGrade::F;
    }

    // Calculate issue density (issues per internal coupling)
    let high_density = high as f64 / internal_couplings as f64;
    let medium_density = medium as f64 / internal_couplings as f64;
    let total_issue_density = (critical + high + medium) as f64 / internal_couplings as f64;

    // D: Critical issues or very high issue density (> 5% high)
    if critical > 0 || high_density > 0.05 {
        return HealthGrade::D;
    }

    // C: Any high issues OR high medium density (> 25%)
    // Projects with structural issues that need attention
    if high > 0 || medium_density > 0.25 {
        return HealthGrade::C;
    }

    // B: Some medium issues but manageable (> 5% medium density)
    if medium_density > 0.05 || total_issue_density > 0.10 {
        return HealthGrade::B;
    }

    // A: Excellent - no high issues AND very low medium issues (< 5%)
    // Reserved for exceptionally well-designed code
    if high == 0 && medium_density <= 0.05 && internal_couplings >= 10 {
        return HealthGrade::A;
    }

    // Default to B for projects with few issues
    HealthGrade::B
}

/// Complete project balance analysis report
#[derive(Debug)]
pub struct ProjectBalanceReport {
    pub total_couplings: usize,
    pub balanced_count: usize,
    pub needs_review: usize,
    pub needs_refactoring: usize,
    pub average_score: f64,
    pub health_grade: HealthGrade,
    pub issues_by_severity: HashMap<Severity, usize>,
    pub issues_by_type: HashMap<IssueType, usize>,
    pub issues: Vec<CouplingIssue>,
    pub top_priorities: Vec<CouplingIssue>,
}

impl ProjectBalanceReport {
    /// Add top N priority issues
    fn with_top_priorities(mut self, n: usize) -> Self {
        self.top_priorities = self.issues.iter().take(n).cloned().collect();
        self
    }

    /// Get issues grouped by type
    pub fn issues_grouped_by_type(&self) -> HashMap<IssueType, Vec<&CouplingIssue>> {
        let mut grouped: HashMap<IssueType, Vec<&CouplingIssue>> = HashMap::new();
        for issue in &self.issues {
            grouped.entry(issue.issue_type).or_default().push(issue);
        }
        grouped
    }
}

/// Calculate overall project balance score
///
/// Only considers internal couplings (not external crate dependencies)
/// since external dependencies are outside the developer's control.
pub fn calculate_project_score(metrics: &ProjectMetrics) -> f64 {
    // Filter to internal couplings only
    let internal_scores: Vec<f64> = metrics
        .couplings
        .iter()
        .filter(|c| c.distance != Distance::DifferentCrate)
        .map(|c| BalanceScore::calculate(c).score)
        .collect();

    if internal_scores.is_empty() {
        return 1.0; // No internal couplings = perfect score
    }

    internal_scores.iter().sum::<f64>() / internal_scores.len() as f64
}

// Helper functions

fn extract_type_name(path: &str) -> String {
    path.split("::")
        .last()
        .unwrap_or(path)
        .chars()
        .enumerate()
        .map(|(i, c)| if i == 0 { c.to_ascii_uppercase() } else { c })
        .collect()
}

/// Get human-readable label for integration strength
pub fn strength_label(strength: IntegrationStrength) -> &'static str {
    match strength {
        IntegrationStrength::Intrusive => "Intrusive",
        IntegrationStrength::Functional => "Functional",
        IntegrationStrength::Model => "Model",
        IntegrationStrength::Contract => "Contract",
    }
}

/// Get human-readable label for distance
pub fn distance_label(distance: Distance) -> &'static str {
    match distance {
        Distance::SameFunction => "same function",
        Distance::SameModule => "same module",
        Distance::DifferentModule => "different module",
        Distance::DifferentCrate => "external crate",
    }
}

/// Get human-readable label for volatility
pub fn volatility_label(volatility: Volatility) -> &'static str {
    match volatility {
        Volatility::Low => "rarely",
        Volatility::Medium => "sometimes",
        Volatility::High => "frequently",
    }
}

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

    fn make_coupling(
        strength: IntegrationStrength,
        distance: Distance,
        volatility: Volatility,
    ) -> CouplingMetrics {
        CouplingMetrics::new(
            "source::module".to_string(),
            "target::module".to_string(),
            strength,
            distance,
            volatility,
        )
    }

    #[test]
    fn test_balance_ideal_close() {
        // Strong coupling + close distance = good (cohesion)
        let coupling = make_coupling(
            IntegrationStrength::Intrusive,
            Distance::SameModule,
            Volatility::Low,
        );
        let score = BalanceScore::calculate(&coupling);
        assert!(score.is_balanced(), "Score: {}", score.score);
    }

    #[test]
    fn test_balance_ideal_far() {
        // Weak coupling + far distance = good (loose coupling)
        let coupling = make_coupling(
            IntegrationStrength::Contract,
            Distance::DifferentCrate,
            Volatility::Low,
        );
        let score = BalanceScore::calculate(&coupling);
        assert!(score.is_balanced(), "Score: {}", score.score);
    }

    #[test]
    fn test_balance_bad_global_complexity() {
        // Strong coupling + far distance = bad (global complexity)
        let coupling = make_coupling(
            IntegrationStrength::Intrusive,
            Distance::DifferentCrate,
            Volatility::Low,
        );
        let score = BalanceScore::calculate(&coupling);
        assert!(
            score.needs_refactoring(),
            "Score: {}, should need refactoring",
            score.score
        );
    }

    #[test]
    fn test_balance_bad_cascading() {
        // Strong coupling + high volatility = bad
        let coupling = make_coupling(
            IntegrationStrength::Intrusive,
            Distance::SameModule,
            Volatility::High,
        );
        let score = BalanceScore::calculate(&coupling);
        assert!(
            !score.is_balanced(),
            "Score: {}, should not be balanced due to volatility",
            score.score
        );
    }

    #[test]
    fn test_identify_global_complexity() {
        // Note: DifferentCrate is now filtered out (external deps)
        // Test with DifferentModule which is still flagged for internal modules
        let coupling = make_coupling(
            IntegrationStrength::Intrusive,
            Distance::DifferentModule,
            Volatility::Low,
        );
        let issues = identify_issues(&coupling);
        assert!(
            !issues.is_empty(),
            "Should identify global complexity issue for internal cross-module coupling"
        );
        assert!(
            issues
                .iter()
                .any(|i| i.issue_type == IssueType::GlobalComplexity)
        );
    }

    #[test]
    fn test_external_crates_are_skipped() {
        // External crate dependencies should not generate issues
        let coupling = make_coupling(
            IntegrationStrength::Intrusive,
            Distance::DifferentCrate,
            Volatility::Low,
        );
        let issues = identify_issues(&coupling);
        assert!(
            issues.is_empty(),
            "External crate dependencies should be skipped"
        );
    }

    #[test]
    fn test_identify_cascading_change() {
        // Now only INTRUSIVE + High volatility triggers cascading change risk
        let coupling = make_coupling(
            IntegrationStrength::Intrusive,
            Distance::SameModule,
            Volatility::High,
        );
        let issues = identify_issues(&coupling);
        assert!(
            issues
                .iter()
                .any(|i| i.issue_type == IssueType::CascadingChangeRisk),
            "Intrusive coupling + High volatility should detect CascadingChangeRisk"
        );
    }

    #[test]
    fn test_identify_inappropriate_intimacy() {
        // Intrusive + DifferentModule now detects GlobalComplexity (not InappropriateIntimacy)
        // because they overlap and GlobalComplexity takes precedence
        let coupling = make_coupling(
            IntegrationStrength::Intrusive,
            Distance::DifferentModule,
            Volatility::Low,
        );
        let issues = identify_issues(&coupling);
        assert!(
            issues
                .iter()
                .any(|i| i.issue_type == IssueType::GlobalComplexity),
            "Intrusive + DifferentModule should detect GlobalComplexity"
        );
    }

    #[test]
    fn test_no_issues_for_balanced() {
        // Model coupling to different module with low volatility
        let coupling = make_coupling(
            IntegrationStrength::Model,
            Distance::DifferentModule,
            Volatility::Low,
        );
        let issues = identify_issues(&coupling);
        // Model coupling should have no issues (only Intrusive triggers issues)
        assert!(
            issues.is_empty(),
            "Model coupling should not generate issues"
        );
    }

    #[test]
    fn test_health_grade_calculation() {
        let mut issues = HashMap::new();

        // No issues with enough data = A (high == 0 && medium_density <= 0.05 && internal >= 10)
        assert_eq!(calculate_health_grade(&issues, 100), HealthGrade::A);

        // No internal couplings = B (can't assess without data)
        assert_eq!(calculate_health_grade(&issues, 0), HealthGrade::B);

        // Any High issue = C (structural issues)
        issues.insert(Severity::High, 1);
        assert_eq!(calculate_health_grade(&issues, 100), HealthGrade::C);

        // High density > 5% = D
        issues.clear();
        issues.insert(Severity::High, 6); // 6% of 100
        assert_eq!(calculate_health_grade(&issues, 100), HealthGrade::D);

        // 1 Critical issue = D
        issues.clear();
        issues.insert(Severity::Critical, 1);
        assert_eq!(calculate_health_grade(&issues, 100), HealthGrade::D);

        // 4+ Critical issues = F
        issues.clear();
        issues.insert(Severity::Critical, 4);
        assert_eq!(calculate_health_grade(&issues, 100), HealthGrade::F);

        // Medium issues > 25% = C
        issues.clear();
        issues.insert(Severity::Medium, 30); // 30% of 100
        assert_eq!(calculate_health_grade(&issues, 100), HealthGrade::C);

        // Medium issues > 5% but <= 25% = B
        issues.clear();
        issues.insert(Severity::Medium, 20); // 20% of 100
        assert_eq!(calculate_health_grade(&issues, 100), HealthGrade::B);
    }
}