package storage

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"time"
)

// JSONLWriter writes records as line-delimited JSON and rotates files by size.
type JSONLWriter struct {
	keyword  string
	outDir   string
	file     *os.File
	writer   *bufio.Writer
	maxBytes int64
	written  int64
	part     int
}

// NewJSONLWriter creates a writer for a keyword in outDir. maxBytes triggers rotation.
func NewJSONLWriter(keyword, outDir string, maxBytes int64) (*JSONLWriter, error) {
	w := &JSONLWriter{keyword: keyword, outDir: outDir, maxBytes: maxBytes}
	if err := w.rotate(); err != nil {
		return nil, err
	}
	return w, nil
}

func (w *JSONLWriter) rotate() error {
	if w.writer != nil {
		w.writer.Flush()
	}
	if w.file != nil {
		w.file.Close()
	}
	w.part++
	ts := time.Now().UTC().Format("20060102T150405Z")
	name := fmt.Sprintf("%s_%s_part%d.jsonl", w.keyword, ts, w.part)
	path := filepath.Join(w.outDir, name)
	f, err := os.Create(path)
	if err != nil {
		return err
	}
	w.file = f
	w.writer = bufio.NewWriterSize(f, 16*1024)
	w.written = 0
	return nil
}

// Write marshals v to JSON and writes it as a newline-delimited record.
func (w *JSONLWriter) Write(v interface{}) error {
	b, err := json.Marshal(v)
	if err != nil {
		return err
	}
	n, err := w.writer.Write(append(b, '\n'))
	if err != nil {
		return err
	}
	w.written += int64(n)
	if w.maxBytes > 0 && w.written >= w.maxBytes {
		return w.rotate()
	}
	return nil
}

// Close flushes and closes the underlying file.
func (w *JSONLWriter) Close() error {
	if w.writer != nil {
		if err := w.writer.Flush(); err != nil {
			return err
		}
	}
	if w.file != nil {
		return w.file.Close()
	}
	return nil
}