//go:build linux || freebsd
// +build linux freebsd

package compression

import (
	"io"
	"strings"
	"sync"
)

// Decompressor defines the interface for decompression
type Decompressor interface {
	Name() string
	CanHandle(contentEncoding string) bool
	CanHandleFile(filename string) bool
	// Reader returns an io.ReadCloser (not just an io.Reader) so
	// callers can release the decompressor's internal state — decoder
	// tables, dictionaries, etc. — when finished. Forgetting to call
	// Close on a long-lived mirror scan would let decoder state
	// accumulate without bound.
	Reader(r io.Reader) (io.ReadCloser, error)
}

// Compressor defines the interface for compression
type Compressor interface {
	Name() string
	Writer(w io.Writer) (io.WriteCloser, error)
}

// BaseDecompressor is the base implementation
type BaseDecompressor struct {
	name             string
	contentEncodings []string
	fileExtensions   []string
}

func NewBaseDecompressor(name string, contentEncodings, fileExtensions []string) *BaseDecompressor {
	return &BaseDecompressor{
		name:             name,
		contentEncodings: contentEncodings,
		fileExtensions:   fileExtensions,
	}
}

func (bd *BaseDecompressor) Name() string         { return bd.name }
func (bd *BaseDecompressor) Extensions() []string { return bd.fileExtensions }
func (bd *BaseDecompressor) CanHandle(contentEncoding string) bool {
	for _, e := range bd.contentEncodings {
		if strings.EqualFold(e, contentEncoding) {
			return true
		}
	}
	return false
}
func (bd *BaseDecompressor) CanHandleFile(filename string) bool {
	filename = strings.ToLower(filename)
	for _, e := range bd.fileExtensions {
		if strings.HasSuffix(filename, e) {
			return true
		}
	}
	return false
}

// Registry for decompressors
type registry struct {
	mu    sync.RWMutex
	items map[string]Decompressor
}

var globalRegistry = &registry{items: make(map[string]Decompressor)}

func Register(d Decompressor) {
	globalRegistry.mu.Lock()
	defer globalRegistry.mu.Unlock()
	globalRegistry.items[strings.ToLower(d.Name())] = d
}

func Get(name string) (Decompressor, bool) {
	globalRegistry.mu.RLock()
	defer globalRegistry.mu.RUnlock()
	d, ok := globalRegistry.items[strings.ToLower(name)]
	return d, ok
}

func GetByFilename(filename string) (Decompressor, bool) {
	format := DetectCompressionByFilename(filename)
	if format == "" || format == "identity" {
		return nil, false
	}
	return Get(format)
}

// GetCompressionFromHeader detects compression from the Content-Encoding header
func GetCompressionFromHeader(contentEncoding string) string {
	if contentEncoding == "" {
		return "identity"
	}
	encodings := ParseContentEncoding(contentEncoding)
	return GetEffectiveEncoding(encodings)
}

func ParseContentEncoding(header string) []string {
	if header == "" {
		return []string{"identity"}
	}
	parts := strings.Split(header, ",")
	result := make([]string, 0, len(parts))
	for _, p := range parts {
		p = strings.TrimSpace(p)
		if p != "" {
			result = append(result, strings.ToLower(p))
		}
	}
	if len(result) == 0 {
		return []string{"identity"}
	}
	return result
}

func GetEffectiveEncoding(encodings []string) string {
	for _, e := range encodings {
		if e != "identity" {
			return e
		}
	}
	return "identity"
}

func DetectCompressionByFilename(filename string) string {
	filename = strings.ToLower(filename)
	switch {
	case strings.HasSuffix(filename, ".gz"):
		return "gzip"
	case strings.HasSuffix(filename, ".zlib"), strings.HasSuffix(filename, ".zz"):
		return "zlib"
	case strings.HasSuffix(filename, ".deflate"), strings.HasSuffix(filename, ".fl"):
		return "flate"
	case strings.HasSuffix(filename, ".bz2"), strings.HasSuffix(filename, ".tbz"), strings.HasSuffix(filename, ".tbz2"):
		return "bzip2"
	case strings.HasSuffix(filename, ".z"), strings.HasSuffix(filename, ".lzw"):
		return "lzw"
	}
	return "identity"
}

func IsCompressedFile(filename string) bool {
	return DetectCompressionByFilename(filename) != "identity"
}