package core

import (
	"bufio"
	"container/list"
	"context"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

// read and parse pdf form field keys
func readFormFields(filePath string) (map[string]struct{}, error) {
	file, err := os.Open(filePath)
	if err != nil {
		return nil, fmt.Errorf("fail to open file:%v", err)
	}
	defer file.Close()

	reader := bufio.NewReader(file)

	l := list.New()
	var line string
	for {
		line, err = reader.ReadString('\n')
		if err != nil {
			break
		}

		if strings.Contains(line, "[")  {
			l.PushBack("[")
		}
		if strings.Contains(line, "]")  {
			l.PushBack("]")
		}

		if strings.HasPrefix(line, "/T")  {
			l.PushBack(strings.TrimSuffix(strings.TrimPrefix(line, "/T ("), ")\n"))
		}
	}
	if err != io.EOF {
		return nil, fmt.Errorf("fail to read file:%v", err)
	}

	if l.Len() < 2 {
		return nil, nil
	}

	//trim first "["
	l.Remove(l.Front())
	//trim last "]"
	l.Remove(l.Back())

	keys := make(map[string]struct{})
	prefixes := make([]string, 0, 1)
	for l.Len() > 0 {
		str := l.Back().Value.(string)
		if str != "]" && str != "[" {

			//prev value
			prev := l.Back().Prev()
			if prev == nil {
				keys[str] = struct{}{}
				break
			}

			//last prefix
			prefix := ""
			if len(prefixes) > 0 {
				prefix = prefixes[len(prefixes)-1]
			}

			prevStr:= prev.Value.(string)
			if prevStr == "]" {
				//just prefix, don't need to add to keys
				if len(prefix) > 0 {
					prefix = fmt.Sprintf("%s.%s", prefix, str)
				}else {
					prefix = str
				}
				prefixes = append(prefixes, prefix)
			}else {

				// add to keys
				k := ""
				if len(prefix) > 0 {
					k = fmt.Sprintf("%s.%s", prefix, str)
				}else {
					k = str
				}
				keys[k] = struct{}{}

				// [[[a]b]c]
				if prevStr == "[" {
					for prevStr == "[" {
						prefixes = prefixes[0:len(prefixes)-1]
						prev = prev.Prev()
						if prev != nil {
							prevStr = prev.Value.(string)
						}else {
							prevStr = ""
						}
					}
				}
			}
		}
		l.Remove(l.Back())
	}

	return keys, nil
}