package history

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"strings"
	"time"
)

var (
	errOpenHistoryFile = errors.New("failed to open history file")
	errNegativeIndex   = errors.New("cannot use a negative index when requesting historic commands")
	errOutOfRangeIndex = errors.New("index requested greater than number of items in history")
)

// fileHistory provides a history source based on a file.
type fileHistory struct {
	file  string
	lines []Item
}

// Item is the structure of an individual item in the History.list slice.
type Item struct {
	Index    int
	DateTime time.Time
	Block    string
}

// NewSourceFromFile returns a new history source writing to and reading from a file.
//
//nolint:ireturn // Returns the Source interface by design: the concrete type is unexported.
func NewSourceFromFile(file string) (Source, error) {
	var err error

	hist := new(fileHistory)
	hist.file = file
	hist.lines, err = openHist(file)

	return hist, err
}

func openHist(filename string) (list []Item, err error) {
	file, err := os.Open(filename)
	if err != nil {
		return list, fmt.Errorf("%w: %s", errOpenHistoryFile, err.Error())
	}

	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		var item Item

		err := json.Unmarshal(scanner.Bytes(), &item)
		if err != nil || len(item.Block) == 0 {
			continue
		}

		item.Index = len(list)
		list = append(list, item)
	}

	file.Close()

	return list, nil
}

// Write item to history file.
func (h *fileHistory) Write(s string) (int, error) {
	block := strings.TrimSpace(s)
	if block == "" {
		return 0, nil
	}

	item := Item{
		DateTime: time.Now(),
		Block:    block,
		Index:    len(h.lines),
	}

	if len(h.lines) == 0 || h.lines[len(h.lines)-1].Block != block {
		h.lines = append(h.lines, item)
	}

	line := struct {
		DateTime time.Time `json:"datetime"`
		Block    string    `json:"block"`
	}{
		Block:    block,
		DateTime: item.DateTime,
	}

	data, err := json.Marshal(line)
	if err != nil {
		return h.Len(), err
	}

	f, err := os.OpenFile(h.file, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o600)
	if err != nil {
		return 0, fmt.Errorf("%w: %s", errOpenHistoryFile, err.Error())
	}

	_, err = f.Write(append(data, '\n'))
	f.Close()

	return h.Len(), err
}

// GetLine returns a specific line from the history file.
func (h *fileHistory) GetLine(pos int) (string, error) {
	if pos < 0 {
		return "", errNegativeIndex
	}

	if pos < len(h.lines) {
		return h.lines[pos].Block, nil
	}

	return "", errOutOfRangeIndex
}

// Len returns the number of items in the history file.
func (h *fileHistory) Len() int {
	return len(h.lines)
}

// Dump returns the entire history file.
func (h *fileHistory) Dump() interface{} {
	return h.lines
}