package config

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

const DefaultUserAgent = "pan.baidu.com"

type Config struct {
	ClientID     string    `json:"client_id"`
	ClientSecret string    `json:"client_secret"`
	RedirectURI  string    `json:"redirect_uri"`
	AccessToken  string    `json:"access_token,omitempty"`
	RefreshToken string    `json:"refresh_token,omitempty"`
	ExpiresAt    time.Time `json:"expires_at,omitempty"`
	Root         string    `json:"root"`
	UserAgent    string    `json:"user_agent"`
	UploadParts  int       `json:"upload_parts"`
	PartSize     int64     `json:"part_size,omitempty"`
}

func DefaultPath() (string, error) {
	dir, err := os.UserConfigDir()
	if err != nil {
		return "", fmt.Errorf("find config directory: %w", err)
	}
	return filepath.Join(dir, "bdrclone", "config.json"), nil
}

func Load(path string) (*Config, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil, fmt.Errorf("config %q does not exist; run `bdrclone config` first", path)
		}
		return nil, fmt.Errorf("read config: %w", err)
	}
	var cfg Config
	if err := json.Unmarshal(b, &cfg); err != nil {
		return nil, fmt.Errorf("parse config: %w", err)
	}
	cfg.applyDefaults()
	return &cfg, cfg.Validate(false)
}

func Save(path string, cfg *Config) error {
	cfg.applyDefaults()
	if err := cfg.Validate(false); err != nil {
		return err
	}
	b, err := json.MarshalIndent(cfg, "", "  ")
	if err != nil {
		return fmt.Errorf("encode config: %w", err)
	}
	b = append(b, '\n')
	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return fmt.Errorf("create config directory: %w", err)
	}
	tmp, err := os.CreateTemp(filepath.Dir(path), ".config-*")
	if err != nil {
		return fmt.Errorf("create temporary config: %w", err)
	}
	tmpName := tmp.Name()
	defer os.Remove(tmpName)
	if err := tmp.Chmod(0o600); err != nil {
		tmp.Close()
		return fmt.Errorf("secure config: %w", err)
	}
	if _, err := tmp.Write(b); err != nil {
		tmp.Close()
		return fmt.Errorf("write config: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("close config: %w", err)
	}
	if err := os.Rename(tmpName, path); err != nil {
		return fmt.Errorf("replace config: %w", err)
	}
	return nil
}

func (c *Config) Validate(requireToken bool) error {
	if strings.TrimSpace(c.ClientID) == "" || strings.TrimSpace(c.ClientSecret) == "" {
		return errors.New("client_id and client_secret are required")
	}
	if requireToken && c.RefreshToken == "" && c.AccessToken == "" {
		return errors.New("no OAuth token; run `bdrclone auth` first")
	}
	if c.UploadParts < 1 || c.UploadParts > 32 {
		return errors.New("upload_parts must be between 1 and 32")
	}
	if c.PartSize != 0 && c.PartSize < 4<<20 {
		return errors.New("part_size must be 0 or at least 4 MiB")
	}
	if c.PartSize > 32<<20 {
		return errors.New("part_size cannot exceed Baidu's 32 MiB maximum")
	}
	return nil
}

func (c *Config) applyDefaults() {
	if c.RedirectURI == "" {
		c.RedirectURI = "http://127.0.0.1:53682/callback"
	}
	if c.Root == "" {
		c.Root = "/"
	}
	if !strings.HasPrefix(c.Root, "/") {
		c.Root = "/" + c.Root
	}
	c.Root = strings.TrimSuffix(c.Root, "/")
	if c.Root == "" {
		c.Root = "/"
	}
	if c.UserAgent == "" {
		c.UserAgent = DefaultUserAgent
	}
	if c.UploadParts == 0 {
		c.UploadParts = 3
	}
}