package mail

import (
	"bufio"
	"encoding/json"
	"errors"
	"os"
	"path/filepath"
	"sort"
)

// Common errors
var (
	ErrMessageNotFound = errors.New("message not found")
	ErrEmptyInbox      = errors.New("inbox is empty")
)

// Mailbox manages a JSONL-based inbox.
type Mailbox struct {
	path string
}

// NewMailbox creates a mailbox at the given path.
func NewMailbox(path string) *Mailbox {
	return &Mailbox{path: path}
}

// Path returns the mailbox file path.
func (m *Mailbox) Path() string {
	return m.path
}

// List returns all messages in the mailbox.
func (m *Mailbox) List() ([]*Message, error) {
	file, err := os.Open(m.path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}
	defer file.Close()

	var messages []*Message
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			continue
		}

		var msg Message
		if err := json.Unmarshal([]byte(line), &msg); err != nil {
			continue // Skip malformed lines
		}
		messages = append(messages, &msg)
	}

	if err := scanner.Err(); err != nil {
		return nil, err
	}

	// Sort by timestamp (newest first)
	sort.Slice(messages, func(i, j int) bool {
		return messages[i].Timestamp.After(messages[j].Timestamp)
	})

	return messages, nil
}

// ListUnread returns unread messages.
func (m *Mailbox) ListUnread() ([]*Message, error) {
	all, err := m.List()
	if err != nil {
		return nil, err
	}

	var unread []*Message
	for _, msg := range all {
		if !msg.Read {
			unread = append(unread, msg)
		}
	}

	return unread, nil
}

// Get returns a message by ID.
func (m *Mailbox) Get(id string) (*Message, error) {
	messages, err := m.List()
	if err != nil {
		return nil, err
	}

	for _, msg := range messages {
		if msg.ID == id {
			return msg, nil
		}
	}

	return nil, ErrMessageNotFound
}

// Append adds a message to the mailbox.
func (m *Mailbox) Append(msg *Message) error {
	// Ensure directory exists
	dir := filepath.Dir(m.path)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return err
	}

	// Open for append
	file, err := os.OpenFile(m.path, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		return err
	}
	defer file.Close()

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

	_, err = file.WriteString(string(data) + "\n")
	return err
}

// MarkRead marks a message as read.
func (m *Mailbox) MarkRead(id string) error {
	messages, err := m.List()
	if err != nil {
		return err
	}

	found := false
	for _, msg := range messages {
		if msg.ID == id {
			msg.Read = true
			found = true
		}
	}

	if !found {
		return ErrMessageNotFound
	}

	return m.rewrite(messages)
}

// Delete removes a message from the mailbox.
func (m *Mailbox) Delete(id string) error {
	messages, err := m.List()
	if err != nil {
		return err
	}

	var filtered []*Message
	found := false
	for _, msg := range messages {
		if msg.ID == id {
			found = true
		} else {
			filtered = append(filtered, msg)
		}
	}

	if !found {
		return ErrMessageNotFound
	}

	return m.rewrite(filtered)
}

// Count returns the total and unread message counts.
func (m *Mailbox) Count() (total, unread int, err error) {
	messages, err := m.List()
	if err != nil {
		return 0, 0, err
	}

	total = len(messages)
	for _, msg := range messages {
		if !msg.Read {
			unread++
		}
	}

	return total, unread, nil
}

// rewrite rewrites the mailbox with the given messages.
func (m *Mailbox) rewrite(messages []*Message) error {
	// Sort by timestamp (oldest first for JSONL)
	sort.Slice(messages, func(i, j int) bool {
		return messages[i].Timestamp.Before(messages[j].Timestamp)
	})

	// Write to temp file
	tmpPath := m.path + ".tmp"
	file, err := os.Create(tmpPath)
	if err != nil {
		return err
	}

	for _, msg := range messages {
		data, err := json.Marshal(msg)
		if err != nil {
			file.Close()
			os.Remove(tmpPath)
			return err
		}
		file.WriteString(string(data) + "\n")
	}

	if err := file.Close(); err != nil {
		os.Remove(tmpPath)
		return err
	}

	// Atomic rename
	return os.Rename(tmpPath, m.path)
}