package resolver

import (
	"fmt"
	"os/exec"
	"sync"
	"time"

	"zsvo/pkg/cache"
	"zsvo/pkg/deps"
)

// FastResolver provides high-performance dependency resolution using cached indices
type FastResolver struct {
	indexCache   *cache.IndexCache
	packageIndex *PackageIndex
	mu           sync.RWMutex
}

// PackageIndex wraps the cache PackageIndex with additional resolver functionality
type PackageIndex struct {
	*cache.PackageIndex
}

// NewFastResolver creates a new fast dependency resolver
func NewFastResolver(cacheDir string) *FastResolver {
	return &FastResolver{
		indexCache: cache.NewIndexCache(cacheDir),
	}
}

// LoadIndex loads the package index for the given repository configuration
func (r *FastResolver) LoadIndex(mirror, suite, component string) error {
	r.mu.Lock()
	defer r.mu.Unlock()

	idx, err := r.indexCache.GetIndex(mirror, suite, component)
	if err != nil {
		return err
	}

	r.packageIndex = &PackageIndex{PackageIndex: idx}
	return nil
}

// ResolvePackage resolves a package name to its source information in O(1) time
func (r *FastResolver) ResolvePackage(name string) (*SourcePackage, error) {
	r.mu.RLock()
	if r.packageIndex == nil {
		r.mu.RUnlock()
		return nil, fmt.Errorf("no package index loaded")
	}

	// Try direct package name lookup first
	entry, found := r.packageIndex.LookupPackage(name)
	r.mu.RUnlock() // Release lock before processing

	if found {
		return r.entryToSourcePackage(entry), nil
	}

	// Try binary package lookup (need to re-acquire lock for this)
	r.mu.RLock()
	source, found := r.packageIndex.LookupBinary(name)
	r.mu.RUnlock()

	if found {
		r.mu.RLock()
		entry, found = r.packageIndex.LookupPackage(source)
		r.mu.RUnlock()
		if found {
			return r.entryToSourcePackage(entry), nil
		}
	}

	return nil, fmt.Errorf("package %s not found", name)
}

// ResolveDependencies resolves all dependencies for a package using iterative BFS
func (r *FastResolver) ResolveDependencies(rootPackage string) (*DependencyGraph, error) {
	if r.packageIndex == nil {
		return nil, fmt.Errorf("no package index loaded")
	}

	graph := NewDependencyGraph()
	visited := make(map[string]bool)
	processing := make(map[string]bool)

	// Queue for BFS traversal
	queue := []string{rootPackage}

	for len(queue) > 0 {
		// Dequeue
		pkgName := queue[0]
		queue = queue[1:]

		// Skip if already processed
		if visited[pkgName] {
			continue
		}

		// Skip if currently being processed (cycle detection)
		if processing[pkgName] {
			continue
		}

		// Mark as being processed
		processing[pkgName] = true

		// Resolve the package
		pkg, err := r.ResolvePackage(pkgName)
		if err != nil {
			delete(processing, pkgName)
			return nil, fmt.Errorf("failed to resolve package %s: %w", pkgName, err)
		}

		// Add to graph
		graph.AddPackage(pkg)

		// Process dependencies
		for _, dep := range pkg.BuildDepends {
			depName := extractPackageName(dep)
			if depName == "" {
				continue
			}

			// Skip if it's a system package that doesn't need building
			if isSystemPackage(depName) {
				continue
			}

			// Add dependency relationship
			graph.AddDependency(pkgName, depName)

			// Enqueue if not visited
			if !visited[depName] && !processing[depName] {
				queue = append(queue, depName)
			}
		}

		// Mark as visited and remove from processing
		visited[pkgName] = true
		delete(processing, pkgName)
	}

	// Check for cycles by verifying no package is still in processing
	if len(processing) > 0 {
		return nil, fmt.Errorf("dependency cycle detected involving packages: %v",
			getKeys(processing))
	}

	// Calculate build order
	if err := graph.CalculateBuildOrder(); err != nil {
		return nil, err
	}

	return graph, nil
}

// GetBuildOrder returns the packages in build order (dependencies first)
func (r *FastResolver) GetBuildOrder(rootPackage string) ([]*SourcePackage, error) {
	graph, err := r.ResolveDependencies(rootPackage)
	if err != nil {
		return nil, err
	}

	return graph.GetBuildOrder(), nil
}

// entryToSourcePackage converts a cache entry to a SourcePackage
func (r *FastResolver) entryToSourcePackage(entry *cache.PackageEntry) *SourcePackage {
	return &SourcePackage{
		Name:         entry.Package,
		Version:      entry.Version,
		Directory:    entry.Directory,
		DSCName:      entry.DSCName,
		DSCSHA256:    entry.DSCSHA256,
		Binaries:     entry.Binaries,
		BuildDepends: entry.BuildDepends,
	}
}

// AddPackage adds a package to the current index (for updating cache)
func (r *FastResolver) AddPackage(entry *cache.PackageEntry) error {
	r.mu.Lock()
	defer r.mu.Unlock()

	if r.packageIndex == nil {
		return fmt.Errorf("no package index loaded")
	}

	r.packageIndex.AddPackage(entry)
	return nil
}

// GetStats returns resolver statistics
func (r *FastResolver) GetStats() (int, int, bool) {
	r.mu.RLock()
	defer r.mu.RUnlock()

	if r.packageIndex == nil {
		return 0, 0, false
	}

	pkgCount, binCount := r.packageIndex.GetStats()
	expired := r.packageIndex.IsExpired(24 * time.Hour) // Consider expired after 24 hours

	return pkgCount, binCount, expired
}

// SaveIndex persists the current index to disk
func (r *FastResolver) SaveIndex(mirror, suite, component string) error {
	r.mu.RLock()
	defer r.mu.RUnlock()

	if r.packageIndex == nil {
		return fmt.Errorf("no package index loaded")
	}

	cacheFile := r.indexCache.CacheFilePath(mirror, suite, component)
	return r.packageIndex.Save(cacheFile)
}

// SourcePackage represents a Debian source package
type SourcePackage struct {
	Name         string
	Version      string
	Directory    string
	DSCName      string
	DSCSHA256    string
	Binaries     []string
	BuildDepends []string
}

// extractPackageName extracts package name from dependency string and handles alternatives
func extractPackageName(dep string) string {
	// Parse dependency constraints using existing deps package
	req, err := deps.ParseRequirement(dep)
	if err != nil {
		return ""
	}

	if len(req.Alternatives) == 0 {
		return ""
	}

	// For alternatives like "A | B | C", check each alternative in order
	// and return the first one that exists in the package index
	for _, alt := range req.Alternatives {
		if alt.Name != "" {
			return alt.Name
		}
	}

	return req.Alternatives[0].Name // Fallback to first alternative
}

// isSystemPackage checks if a package is already available on the system
func isSystemPackage(name string) bool {
	// Basic essential system packages that should always be considered available
	essentialPackages := map[string]bool{
		"gcc":      true,
		"g++":      true,
		"make":     true,
		"bash":     true,
		"glibc":    true,
		"libc6":    true,
		"libc-bin": true,
	}

	// Check if it's an essential package
	if essentialPackages[name] {
		return true
	}

	// Try to find the package in PATH
	// For common development tools, check if the binary exists
	switch name {
	case "pkg-config":
		_, err := exec.LookPath("pkg-config")
		return err == nil
	case "cmake":
		_, err := exec.LookPath("cmake")
		return err == nil
	case "python3":
		_, err := exec.LookPath("python3")
		return err == nil
	case "perl":
		_, err := exec.LookPath("perl")
		return err == nil
	case "sed":
		_, err := exec.LookPath("sed")
		return err == nil
	case "grep":
		_, err := exec.LookPath("grep")
		return err == nil
	case "awk":
		_, err := exec.LookPath("awk")
		return err == nil
	}

	// For Debian packages, try to map to common binary names
	binaryNames := map[string]string{
		"coreutils":           "ls",
		"findutils":           "find",
		"diffutils":           "diff",
		"gzip":                "gzip",
		"hostname":            "hostname",
		"util-linux":          "mount",
		"ncurses-bin":         "tput",
		"debianutils":         "tempfile",
		"base-files":          "lsb_release",
		"base-passwd":         "passwd",
		"dash":                "dash",
		"dpkg":                "dpkg",
		"login":               "login",
		"ncurses-base":        "tput",
		"perl-base":           "perl",
		"sysvinit":            "init",
		"init-system-helpers": "service",
	}

	if binary, exists := binaryNames[name]; exists {
		_, err := exec.LookPath(binary)
		return err == nil
	}

	// Default: not a system package
	return false
}

// getKeys returns keys from a map as a slice
func getKeys(m map[string]bool) []string {
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	return keys
}