#!/usr/bin/env bash
# Configuration drift detection - compare actual system state to dotfiles
# Follows the μέτρον principle: measure what is, against what should be

set -euo pipefail

DOTFILES_DIR="$HOME/dotfiles"
DRIFT_REPORT_DIR="$HOME/.drift-reports"
TIMESTAMP=$(date +%Y%m%d_%H%M%S)
REPORT_FILE="$DRIFT_REPORT_DIR/drift-$TIMESTAMP.txt"

# Colors
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
RED='\033[0;31m'
BLUE='\033[0;34m'
NC='\033[0m'

echo -e "${BLUE}Configuration Drift Detection${NC}"
echo "===================================="

# Create report directory
mkdir -p "$DRIFT_REPORT_DIR"

# Initialize report
cat > "$REPORT_FILE" << EOF
Configuration Drift Report
Generated: $(date)
System: $(sw_vers -productVersion)

EOF

# Function to detect package drift
detect_package_drift() {
    echo -e "${YELLOW}🔍 Analyzing package drift...${NC}"
    
    local brewfile="$DOTFILES_DIR/Brewfile"
    local lockfile="$DOTFILES_DIR/Brewfile.lock"
    local drift_found=false
    
    echo "=== PACKAGE DRIFT ANALYSIS ===" >> "$REPORT_FILE"
    
    if [[ ! -f "$brewfile" ]]; then
        echo "❌ Brewfile not found at $brewfile" | tee -a "$REPORT_FILE"
        return 1
    fi
    
    # Check for packages in Brewfile but not installed
    echo "Packages defined but not installed:" >> "$REPORT_FILE"
    while IFS= read -r line; do
        if [[ "$line" =~ ^brew\ \"([^\"]+)\" ]]; then
            package="${BASH_REMATCH[1]}"
            if ! brew list --formula | grep -q "^$package$"; then
                echo "  - $package (formula)" | tee -a "$REPORT_FILE"
                drift_found=true
            fi
        elif [[ "$line" =~ ^cask\ \"([^\"]+)\" ]]; then
            package="${BASH_REMATCH[1]}"
            if ! brew list --cask | grep -q "^$package$"; then
                echo "  - $package (cask)" | tee -a "$REPORT_FILE"
                drift_found=true
            fi
        fi
    done < "$brewfile"
    
    # Check for installed packages not in Brewfile
    echo "" >> "$REPORT_FILE"
    echo "Packages installed but not in Brewfile:" >> "$REPORT_FILE"
    
    # Check formulae
    while IFS= read -r package; do
        if ! grep -q "brew \"$package\"" "$brewfile" 2>/dev/null; then
            echo "  - $package (formula)" | tee -a "$REPORT_FILE"
            drift_found=true
        fi
    done < <(brew list --formula)
    
    # Check casks
    while IFS= read -r package; do
        if ! grep -q "cask \"$package\"" "$brewfile" 2>/dev/null; then
            echo "  - $package (cask)" | tee -a "$REPORT_FILE"
            drift_found=true
        fi
    done < <(brew list --cask)
    
    # Version drift (if lockfile exists)
    if [[ -f "$lockfile" ]]; then
        echo "" >> "$REPORT_FILE"
        echo "Version drift from lockfile:" >> "$REPORT_FILE"
        
        # Compare current versions to locked versions
        while IFS= read -r line; do
            if [[ "$line" =~ ^([^[:space:]]+)[[:space:]]+(.+)$ ]]; then
                package="${BASH_REMATCH[1]}"
                locked_version="${BASH_REMATCH[2]}"
                
                # Get current version
                current_version=$(brew list --versions "$package" 2>/dev/null | head -1 | cut -d' ' -f2- || echo "not installed")
                
                if [[ "$current_version" != "$locked_version" && "$current_version" != "not installed" ]]; then
                    echo "  - $package: locked($locked_version) vs current($current_version)" | tee -a "$REPORT_FILE"
                    drift_found=true
                fi
            fi
        done < <(grep -v '^#' "$lockfile" 2>/dev/null || true)
    fi
    
    if [[ "$drift_found" == "false" ]]; then
        echo -e "${GREEN}✅ No package drift detected${NC}"
        echo "No package drift detected" >> "$REPORT_FILE"
    else
        echo -e "${YELLOW}⚠️  Package drift detected - see report${NC}"
    fi
    
    echo "" >> "$REPORT_FILE"
}

# Function to detect configuration file drift
detect_config_drift() {
    echo -e "${YELLOW}🔍 Analyzing configuration drift...${NC}"
    
    echo "=== CONFIGURATION FILE DRIFT ===" >> "$REPORT_FILE"
    
    local config_files=(
        ".zshrc:$HOME/.zshrc:$DOTFILES_DIR/shell/.zshrc"
        ".gitconfig:$HOME/.gitconfig:$DOTFILES_DIR/.gitconfig"
        ".vimrc:$HOME/.vimrc:$DOTFILES_DIR/.vimrc"
    )
    
    local drift_found=false
    
    for config_spec in "${config_files[@]}"; do
        IFS=':' read -r name home_path dotfiles_path <<< "$config_spec"
        
        if [[ -f "$home_path" && -f "$dotfiles_path" ]]; then
            if ! diff -q "$home_path" "$dotfiles_path" >/dev/null 2>&1; then
                echo "Configuration drift detected: $name" | tee -a "$REPORT_FILE"
                echo "  Home: $home_path" >> "$REPORT_FILE"
                echo "  Dotfiles: $dotfiles_path" >> "$REPORT_FILE"
                echo "  Run: diff \"$home_path\" \"$dotfiles_path\"" >> "$REPORT_FILE"
                echo "" >> "$REPORT_FILE"
                drift_found=true
            fi
        elif [[ -f "$home_path" && ! -f "$dotfiles_path" ]]; then
            echo "File exists in home but not in dotfiles: $name" | tee -a "$REPORT_FILE"
            drift_found=true
        elif [[ ! -f "$home_path" && -f "$dotfiles_path" ]]; then
            echo "File exists in dotfiles but not deployed: $name" | tee -a "$REPORT_FILE"
            drift_found=true
        fi
    done
    
    if [[ "$drift_found" == "false" ]]; then
        echo -e "${GREEN}✅ No configuration drift detected${NC}"
        echo "No configuration drift detected" >> "$REPORT_FILE"
    else
        echo -e "${YELLOW}⚠️  Configuration drift detected - see report${NC}"
    fi
    
    echo "" >> "$REPORT_FILE"
}

# Function to detect system settings drift
detect_system_drift() {
    echo -e "${YELLOW}🔍 Analyzing system settings drift...${NC}"
    
    echo "=== SYSTEM SETTINGS DRIFT ===" >> "$REPORT_FILE"
    
    local defaults_script="$DOTFILES_DIR/scripts/set-macos-defaults.sh"
    
    if [[ ! -f "$defaults_script" ]]; then
        echo "No macOS defaults script found" >> "$REPORT_FILE"
        return 0
    fi
    
    # Extract settings from defaults script and check current values
    local drift_found=false
    
    # Look for defaults write commands and check current values
    while IFS= read -r line; do
        if [[ "$line" =~ defaults\ write\ ([^[:space:]]+)\ ([^[:space:]]+)\ (.+) ]]; then
            domain="${BASH_REMATCH[1]}"
            key="${BASH_REMATCH[2]}"
            expected_value="${BASH_REMATCH[3]}"
            
            # Get current value
            current_value=$(defaults read "$domain" "$key" 2>/dev/null || echo "not set")
            
            # Simple comparison (could be enhanced for complex types)
            if [[ "$current_value" != "$expected_value" ]]; then
                echo "Setting drift: $domain $key" >> "$REPORT_FILE"
                echo "  Expected: $expected_value" >> "$REPORT_FILE"
                echo "  Current: $current_value" >> "$REPORT_FILE"
                echo "" >> "$REPORT_FILE"
                drift_found=true
            fi
        fi
    done < <(grep "defaults write" "$defaults_script" 2>/dev/null || true)
    
    if [[ "$drift_found" == "false" ]]; then
        echo -e "${GREEN}✅ No system settings drift detected${NC}"
        echo "No system settings drift detected" >> "$REPORT_FILE"
    else
        echo -e "${YELLOW}⚠️  System settings drift detected - see report${NC}"
    fi
    
    echo "" >> "$REPORT_FILE"
}

# Function to generate drift summary
generate_summary() {
    echo -e "${BLUE}📊 Generating drift summary...${NC}"
    
    echo "=== DRIFT SUMMARY ===" >> "$REPORT_FILE"
    echo "Report generated: $(date)" >> "$REPORT_FILE"
    echo "Next recommended actions:" >> "$REPORT_FILE"
    
    if grep -q "drift detected" "$REPORT_FILE"; then
        echo "1. Review specific drift items above" >> "$REPORT_FILE"
        echo "2. Update dotfiles or system as appropriate" >> "$REPORT_FILE"
        echo "3. Run: ~/dotfiles/scripts/generate-lockfile.sh (for package versions)" >> "$REPORT_FILE"
        echo "4. Consider running: ~/dotfiles/engage (to re-sync configurations)" >> "$REPORT_FILE"
    else
        echo "✅ System is in sync with dotfiles configuration" >> "$REPORT_FILE"
    fi
    
    echo "" >> "$REPORT_FILE"
    echo "To fix drift automatically, consider:" >> "$REPORT_FILE"
    echo "- Package drift: brew bundle --file=$DOTFILES_DIR/Brewfile" >> "$REPORT_FILE"
    echo "- Config drift: re-run relevant sections of ~/dotfiles/engage" >> "$REPORT_FILE"
    echo "- System drift: ~/dotfiles/scripts/set-macos-defaults.sh" >> "$REPORT_FILE"
}

# Main execution
main() {
    detect_package_drift
    detect_config_drift
    detect_system_drift
    generate_summary
    
    echo -e "${BLUE}📋 Full report saved to: $REPORT_FILE${NC}"
    
    # Show summary
    if grep -q "drift detected" "$REPORT_FILE"; then
        echo -e "${YELLOW}⚠️  Configuration drift detected${NC}"
        echo "Run: cat $REPORT_FILE | less"
        echo "Or: ~/dotfiles/scripts/detect-drift.sh --fix (future feature)"
        
        # Clean old reports (keep last 10)
        find "$DRIFT_REPORT_DIR" -name "drift-*.txt" | sort -r | tail -n +11 | xargs rm -f 2>/dev/null || true
        
        return 1
    else
        echo -e "${GREEN}✅ System configuration is consistent with dotfiles${NC}"
        return 0
    fi
}

# Command line options
case "${1:-}" in
    --quiet|-q)
        main >/dev/null
        ;;
    --report|-r)
        if [[ -f "$REPORT_FILE" ]]; then
            cat "$REPORT_FILE"
        else
            main
            cat "$REPORT_FILE"
        fi
        ;;
    *)
        main
        ;;
esac