package sources

import (
	"context"
	"os"

	"golang.org/x/exp/mmap"

	"github.com/salvacybersec/keyhunter/pkg/types"
)

const defaultChunkSize = 4096
const chunkOverlap = 256 // overlap between chunks to avoid splitting keys at boundaries

// FileSource reads a single file and emits overlapping chunks.
// For files >= MmapThreshold it uses golang.org/x/exp/mmap for zero-copy reads.
type FileSource struct {
	Path      string
	ChunkSize int
}

// NewFileSource creates a FileSource for the given path with the default chunk size.
func NewFileSource(path string) *FileSource {
	return &FileSource{Path: path, ChunkSize: defaultChunkSize}
}

// Chunks reads the file in overlapping segments and sends each chunk to out.
// Uses mmap for files >= MmapThreshold (10MB) and os.ReadFile for smaller files.
// Binary files (NUL byte in the first 512 bytes) are skipped.
func (f *FileSource) Chunks(ctx context.Context, out chan<- types.Chunk) error {
	fi, err := os.Stat(f.Path)
	if err != nil {
		return err
	}
	size := fi.Size()
	if size == 0 {
		return nil
	}
	var data []byte
	if size >= MmapThreshold {
		ra, err := mmap.Open(f.Path)
		if err != nil {
			return err
		}
		defer ra.Close()
		data = make([]byte, ra.Len())
		if _, err := ra.ReadAt(data, 0); err != nil {
			return err
		}
	} else {
		data, err = os.ReadFile(f.Path)
		if err != nil {
			return err
		}
	}
	if isBinary(data) {
		return nil
	}
	return emitChunks(ctx, data, f.Path, f.ChunkSize, out)
}