package mailparser

import (
	"bufio"
	"bytes"
	"strings"
)

// SplitMbox splits a raw mbox file into individual RFC 2822 message bytes.
// Each message starts with a "From " separator line which is skipped.
func SplitMbox(data []byte) [][]byte {
	var messages [][]byte
	var current bytes.Buffer

	scanner := bufio.NewScanner(bytes.NewReader(data))
	scanner.Buffer(make([]byte, 1024*1024), 10*1024*1024)

	inMessage := false
	for scanner.Scan() {
		line := scanner.Text()
		// mbox separator: line starts with "From " but not "From:" header
		if strings.HasPrefix(line, "From ") && !strings.HasPrefix(line, "From: ") {
			if inMessage && current.Len() > 0 {
				messages = append(messages, bytes.TrimSpace(current.Bytes()))
				current.Reset()
			}
			inMessage = true
			continue
		}
		if inMessage {
			// unescape ">From " lines (mbox quoting)
			if strings.HasPrefix(line, ">From ") {
				line = line[1:]
			}
			current.WriteString(line)
			current.WriteByte('\n')
		}
	}
	if inMessage && current.Len() > 0 {
		messages = append(messages, bytes.TrimSpace(current.Bytes()))
	}
	return messages
}