//go:build mage

package main

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/magefile/mage/mg"
	"github.com/magefile/mage/sh"
)

// BuildCache manages incremental build artifacts and dependency tracking
type BuildCache struct {
	cacheDir    string
	metadataDir string
}

// BuildMetadata tracks build dependencies and outputs
type BuildMetadata struct {
	Target       string            `json:"target"`
	Sources      []SourceFile      `json:"sources"`
	Dependencies []string          `json:"dependencies"`
	Outputs      []string          `json:"outputs"`
	Environment  map[string]string `json:"environment"`
	Timestamp    time.Time         `json:"timestamp"`
	Checksum     string            `json:"checksum"`
}

// SourceFile represents a source file with its modification time and hash
type SourceFile struct {
	Path     string    `json:"path"`
	ModTime  time.Time `json:"mod_time"`
	Size     int64     `json:"size"`
	Checksum string    `json:"checksum"`
}

const (
	buildCacheDir = ".build-cache"
	metadataExt   = ".meta.json"
)

// NewBuildCache creates a new build cache instance
func NewBuildCache() *BuildCache {
	cacheDir := filepath.Join(buildCacheDir, "artifacts")
	metadataDir := filepath.Join(buildCacheDir, "metadata")

	// Ensure cache directories exist
	os.MkdirAll(cacheDir, 0755)
	os.MkdirAll(metadataDir, 0755)

	return &BuildCache{
		cacheDir:    cacheDir,
		metadataDir: metadataDir,
	}
}

// NeedsBuild checks if a target needs to be rebuilt based on source changes
func (bc *BuildCache) NeedsBuild(target string, sources []string, dependencies []string, outputs []string) (bool, error) {
	if mg.Verbose() {
		fmt.Printf("Cache: Checking if %s needs build\n", target)
	}

	// Check if any output files are missing
	for _, output := range outputs {
		if _, err := os.Stat(output); os.IsNotExist(err) {
			if mg.Verbose() {
				fmt.Printf("Cache: Output %s missing, needs build\n", output)
			}
			return true, nil
		}
	}

	// Load existing metadata
	metadata, err := bc.loadMetadata(target)
	if err != nil {
		if mg.Verbose() {
			fmt.Printf("Cache: No metadata for %s, needs build\n", target)
		}
		return true, nil // No cached data, needs build
	}

	// Check if dependencies have changed
	if !stringSlicesEqual(metadata.Dependencies, dependencies) {
		if mg.Verbose() {
			fmt.Printf("Cache: Dependencies changed for %s, needs build\n", target)
		}
		return true, nil
	}

	// Check if any source files have changed
	currentSources, err := bc.analyzeSourceFiles(sources)
	if err != nil {
		return true, err
	}

	if bc.sourcesChanged(metadata.Sources, currentSources) {
		if mg.Verbose() {
			fmt.Printf("Cache: Sources changed for %s, needs build\n", target)
		}
		return true, nil
	}

	// Check if environment has changed for critical variables
	criticalEnvVars := []string{"CGO_ENABLED", "GOOS", "GOARCH", "LDFLAGS"}
	for _, envVar := range criticalEnvVars {
		currentValue := os.Getenv(envVar)
		cachedValue, exists := metadata.Environment[envVar]
		if !exists || cachedValue != currentValue {
			if mg.Verbose() {
				fmt.Printf("Cache: Environment variable %s changed for %s, needs build\n", envVar, target)
			}
			return true, nil
		}
	}

	if mg.Verbose() {
		fmt.Printf("Cache: %s is up to date\n", target)
	}
	return false, nil
}

// RecordBuild records successful build metadata
func (bc *BuildCache) RecordBuild(target string, sources []string, dependencies []string, outputs []string) error {
	if mg.Verbose() {
		fmt.Printf("Cache: Recording build metadata for %s\n", target)
	}

	currentSources, err := bc.analyzeSourceFiles(sources)
	if err != nil {
		return err
	}

	// Create environment snapshot
	environment := make(map[string]string)
	criticalEnvVars := []string{"CGO_ENABLED", "GOOS", "GOARCH", "LDFLAGS"}
	for _, envVar := range criticalEnvVars {
		environment[envVar] = os.Getenv(envVar)
	}

	// Calculate overall checksum
	checksum := bc.calculateBuildChecksum(currentSources, dependencies, environment)

	metadata := BuildMetadata{
		Target:       target,
		Sources:      currentSources,
		Dependencies: dependencies,
		Outputs:      outputs,
		Environment:  environment,
		Timestamp:    time.Now(),
		Checksum:     checksum,
	}

	return bc.saveMetadata(target, &metadata)
}

// CopyToCache copies build artifacts to cache
func (bc *BuildCache) CopyToCache(target string, files []string) error {
	if mg.Verbose() {
		fmt.Printf("Cache: Copying artifacts for %s to cache\n", target)
	}

	targetDir := filepath.Join(bc.cacheDir, target)
	if err := os.MkdirAll(targetDir, 0755); err != nil {
		return err
	}

	for _, file := range files {
		if _, err := os.Stat(file); os.IsNotExist(err) {
			continue // Skip missing files
		}

		dest := filepath.Join(targetDir, filepath.Base(file))
		if err := copyFile(file, dest); err != nil {
			return fmt.Errorf("failed to copy %s to cache: %w", file, err)
		}
	}

	return nil
}

// RestoreFromCache restores build artifacts from cache
func (bc *BuildCache) RestoreFromCache(target string, files []string) error {
	if mg.Verbose() {
		fmt.Printf("Cache: Restoring artifacts for %s from cache\n", target)
	}

	targetDir := filepath.Join(bc.cacheDir, target)
	
	for _, file := range files {
		source := filepath.Join(targetDir, filepath.Base(file))
		if _, err := os.Stat(source); os.IsNotExist(err) {
			continue // Skip missing cached files
		}

		if err := copyFile(source, file); err != nil {
			return fmt.Errorf("failed to restore %s from cache: %w", file, err)
		}
	}

	return nil
}

// CleanCache removes all cached artifacts and metadata
func (bc *BuildCache) CleanCache() error {
	fmt.Println("Cache: Cleaning build cache")
	return sh.Rm(buildCacheDir)
}

// CacheStats returns statistics about the build cache
func (bc *BuildCache) CacheStats() (map[string]interface{}, error) {
	stats := make(map[string]interface{})

	// Count cached targets
	metadataFiles, err := filepath.Glob(filepath.Join(bc.metadataDir, "*"+metadataExt))
	if err != nil {
		return nil, err
	}
	stats["targets_cached"] = len(metadataFiles)

	// Calculate cache size
	var totalSize int64
	err = filepath.Walk(buildCacheDir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if !info.IsDir() {
			totalSize += info.Size()
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	stats["cache_size_bytes"] = totalSize
	stats["cache_size_mb"] = totalSize / (1024 * 1024)

	return stats, nil
}

// analyzeSourceFiles calculates checksums and metadata for source files
func (bc *BuildCache) analyzeSourceFiles(sources []string) ([]SourceFile, error) {
	var result []SourceFile

	for _, source := range sources {
		// Handle glob patterns
		matches, err := filepath.Glob(source)
		if err != nil {
			return nil, err
		}

		if len(matches) == 0 {
			// Not a glob, treat as literal path
			matches = []string{source}
		}

		for _, match := range matches {
			info, err := os.Stat(match)
			if os.IsNotExist(err) {
				continue // Skip missing files
			} else if err != nil {
				return nil, err
			}

			if info.IsDir() {
				// For directories, walk and include all relevant files
				err = filepath.Walk(match, func(path string, info os.FileInfo, err error) error {
					if err != nil {
						return err
					}
					if info.IsDir() {
						return nil
					}
					// Only include source code files
					if bc.isSourceFile(path) {
						checksum, err := bc.calculateFileChecksum(path)
						if err != nil {
							return err
						}
						result = append(result, SourceFile{
							Path:     path,
							ModTime:  info.ModTime(),
							Size:     info.Size(),
							Checksum: checksum,
						})
					}
					return nil
				})
				if err != nil {
					return nil, err
				}
			} else {
				checksum, err := bc.calculateFileChecksum(match)
				if err != nil {
					return nil, err
				}
				result = append(result, SourceFile{
					Path:     match,
					ModTime:  info.ModTime(),
					Size:     info.Size(),
					Checksum: checksum,
				})
			}
		}
	}

	return result, nil
}

// isSourceFile determines if a file is a source code file we should track
func (bc *BuildCache) isSourceFile(path string) bool {
	ext := strings.ToLower(filepath.Ext(path))
	return ext == ".go" || ext == ".js" || ext == ".ts" || ext == ".vue" || 
		   ext == ".py" || ext == ".yaml" || ext == ".yml" ||
		   filepath.Base(path) == "go.mod" || filepath.Base(path) == "go.sum" ||
		   filepath.Base(path) == "package.json" || filepath.Base(path) == "yarn.lock"
}

// calculateFileChecksum calculates SHA256 checksum of a file
func (bc *BuildCache) calculateFileChecksum(path string) (string, error) {
	file, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer file.Close()

	hash := sha256.New()
	if _, err := io.Copy(hash, file); err != nil {
		return "", err
	}

	return hex.EncodeToString(hash.Sum(nil)), nil
}

// calculateBuildChecksum creates a composite checksum for the entire build
func (bc *BuildCache) calculateBuildChecksum(sources []SourceFile, dependencies []string, environment map[string]string) string {
	hash := sha256.New()
	
	// Add source file checksums
	for _, source := range sources {
		hash.Write([]byte(source.Path + source.Checksum))
	}
	
	// Add dependencies
	for _, dep := range dependencies {
		hash.Write([]byte(dep))
	}
	
	// Add environment variables
	for key, value := range environment {
		hash.Write([]byte(key + "=" + value))
	}

	return hex.EncodeToString(hash.Sum(nil))
}

// sourcesChanged checks if source files have changed compared to cached data
func (bc *BuildCache) sourcesChanged(cached []SourceFile, current []SourceFile) bool {
	if len(cached) != len(current) {
		return true
	}

	// Create lookup maps
	cachedMap := make(map[string]SourceFile)
	for _, file := range cached {
		cachedMap[file.Path] = file
	}

	for _, currentFile := range current {
		cachedFile, exists := cachedMap[currentFile.Path]
		if !exists {
			return true // New file
		}
		if cachedFile.Checksum != currentFile.Checksum {
			return true // File changed
		}
	}

	return false
}

// loadMetadata loads build metadata from disk
func (bc *BuildCache) loadMetadata(target string) (*BuildMetadata, error) {
	metaPath := filepath.Join(bc.metadataDir, target+metadataExt)
	data, err := os.ReadFile(metaPath)
	if err != nil {
		return nil, err
	}

	var metadata BuildMetadata
	if err := json.Unmarshal(data, &metadata); err != nil {
		return nil, err
	}

	return &metadata, nil
}

// saveMetadata saves build metadata to disk
func (bc *BuildCache) saveMetadata(target string, metadata *BuildMetadata) error {
	metaPath := filepath.Join(bc.metadataDir, target+metadataExt)
	data, err := json.MarshalIndent(metadata, "", "  ")
	if err != nil {
		return err
	}

	return os.WriteFile(metaPath, data, 0644)
}

// copyFile copies a file from src to dst
func copyFile(src, dst string) error {
	source, err := os.Open(src)
	if err != nil {
		return err
	}
	defer source.Close()

	// Ensure destination directory exists
	if err := os.MkdirAll(filepath.Dir(dst), 0755); err != nil {
		return err
	}

	destination, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer destination.Close()

	_, err = io.Copy(destination, source)
	return err
}

// stringSlicesEqual compares two string slices for equality
func stringSlicesEqual(a, b []string) bool {
	if len(a) != len(b) {
		return false
	}
	for i, v := range a {
		if v != b[i] {
			return false
		}
	}
	return true
}