package sources

import (
	"context"
	"os"

	"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.
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 os.ReadFile for simplicity in Phase 1. mmap for files > 10MB is implemented
// in Phase 4 (Input Sources) alongside all other source adapter enhancements.
func (f *FileSource) Chunks(ctx context.Context, out chan<- types.Chunk) error {
	data, err := os.ReadFile(f.Path)
	if err != nil {
		return err
	}
	size := f.ChunkSize
	if size <= 0 {
		size = defaultChunkSize
	}
	if len(data) <= size {
		// File fits in one chunk
		select {
		case <-ctx.Done():
			return ctx.Err()
		case out <- types.Chunk{Data: data, Source: f.Path, Offset: 0}:
		}
		return nil
	}
	// Emit overlapping chunks
	var offset int64
	for start := 0; start < len(data); start += size - chunkOverlap {
		end := start + size
		if end > len(data) {
			end = len(data)
		}
		chunk := types.Chunk{
			Data:   data[start:end],
			Source: f.Path,
			Offset: offset,
		}
		select {
		case <-ctx.Done():
			return ctx.Err()
		case out <- chunk:
		}
		offset += int64(end - start)
		if end == len(data) {
			break
		}
	}
	return nil
}