package engine

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/spf13/viper"
	"go.yaml.in/yaml/v3"
)

type Config struct {
	DefaultFilter  string `mapstructure:"default_filter" yaml:"default_filter"`
	DefaultSort    string `mapstructure:"default_sort" yaml:"default_sort"`
	DefaultReport  string `mapstructure:"default_report" yaml:"default_report"`
	ColorOutput    bool   `mapstructure:"color_output" yaml:"color_output"`
	WeekStartDay   string `mapstructure:"week_start_day" yaml:"week_start_day"`
	DefaultDueTime string `mapstructure:"default_due_time" yaml:"default_due_time"`

	// Urgency coefficients
	UrgencyDue         float64 `mapstructure:"urgency_due_coefficient" yaml:"urgency_due_coefficient"`
	UrgencyPriorityH   float64 `mapstructure:"urgency_priority_h_coefficient" yaml:"urgency_priority_h_coefficient"`
	UrgencyPriorityM   float64 `mapstructure:"urgency_priority_m_coefficient" yaml:"urgency_priority_m_coefficient"`
	UrgencyPriorityD   float64 `mapstructure:"urgency_priority_d_coefficient" yaml:"urgency_priority_d_coefficient"`
	UrgencyPriorityL   float64 `mapstructure:"urgency_priority_l_coefficient" yaml:"urgency_priority_l_coefficient"`
	UrgencyActive      float64 `mapstructure:"urgency_active_coefficient" yaml:"urgency_active_coefficient"`
	UrgencyAge         float64 `mapstructure:"urgency_age_coefficient" yaml:"urgency_age_coefficient"`
	UrgencyAgeMax      int     `mapstructure:"urgency_age_max" yaml:"urgency_age_max"`
	UrgencyTags        float64 `mapstructure:"urgency_tags_coefficient" yaml:"urgency_tags_coefficient"`
	UrgencyProject     float64 `mapstructure:"urgency_project_coefficient" yaml:"urgency_project_coefficient"`
	UrgencyWaiting     float64 `mapstructure:"urgency_waiting_coefficient" yaml:"urgency_waiting_coefficient"`
	UrgencyUrgentTag   string  `mapstructure:"urgency_urgent_tag" yaml:"urgency_urgent_tag"`
	UrgencyUrgentCoeff float64 `mapstructure:"urgency_urgent_coefficient" yaml:"urgency_urgent_coefficient"`
	NextLimit          int     `mapstructure:"next_limit" yaml:"next_limit"`

	// Sync settings
	SyncEnabled      bool   `mapstructure:"sync_enabled" yaml:"sync_enabled"`
	SyncURL          string `mapstructure:"sync_url" yaml:"sync_url"`
	SyncAPIKey       string `mapstructure:"sync_api_key" yaml:"sync_api_key"`
	SyncClientID     string `mapstructure:"sync_client_id" yaml:"sync_client_id"`
	SyncStrategy     string `mapstructure:"sync_strategy" yaml:"sync_strategy"`
	SyncQueueOffline bool   `mapstructure:"sync_queue_offline" yaml:"sync_queue_offline"`
}

var globalConfig *Config

// Global variables for flag/programmatic overrides
var (
	configDirOverride string
	dataDirOverride   string
)

// SetConfigDirOverride sets the config directory override (typically from --config-dir flag)
func SetConfigDirOverride(dir string) {
	configDirOverride = dir
}

// SetDataDirOverride sets the data directory override (typically from --data-dir flag)
func SetDataDirOverride(dir string) {
	dataDirOverride = dir
}

// GetConfigDir returns the configuration directory path
// Resolution priority:
// 1. Flag override (via SetConfigDirOverride)
// 2. OPAL_CONFIG_DIR environment variable
// 3. XDG_CONFIG_HOME/opal
// 4. /etc/opal (with fallback to ~/.config/opal if not writable)
func GetConfigDir() (string, error) {
	// Priority 1: Flag override
	if configDirOverride != "" {
		return configDirOverride, nil
	}

	// Priority 2: Environment variable
	if dir := os.Getenv("OPAL_CONFIG_DIR"); dir != "" {
		return dir, nil
	}

	// Priority 3: XDG_CONFIG_HOME
	if xdgConfig := os.Getenv("XDG_CONFIG_HOME"); xdgConfig != "" {
		return filepath.Join(xdgConfig, "opal"), nil
	}

	// Priority 4: Try /etc/opal, fallback to ~/.config/opal if not writable
	etcOpal := "/etc/opal"
	if isWritable(etcOpal) {
		return etcOpal, nil
	}

	// Fallback to user config directory
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("failed to get home directory: %w", err)
	}
	return filepath.Join(home, ".config", "opal"), nil
}

// GetDataDir returns the data directory path
// Resolution priority:
// 1. Flag override (via SetDataDirOverride)
// 2. OPAL_DATA_DIR environment variable
// 3. XDG_DATA_HOME/opal
// 4. /var/lib/opal (with fallback to ~/.local/share/opal if not writable)
func GetDataDir() (string, error) {
	// Priority 1: Flag override
	if dataDirOverride != "" {
		return dataDirOverride, nil
	}

	// Priority 2: Environment variable
	if dir := os.Getenv("OPAL_DATA_DIR"); dir != "" {
		return dir, nil
	}

	// Priority 3: XDG_DATA_HOME
	if xdgData := os.Getenv("XDG_DATA_HOME"); xdgData != "" {
		return filepath.Join(xdgData, "opal"), nil
	}

	// Priority 4: Try /var/lib/opal, fallback to ~/.local/share/opal if not writable
	varLibOpal := "/var/lib/opal"
	if isWritable(varLibOpal) {
		return varLibOpal, nil
	}

	// Fallback to user data directory
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("failed to get home directory: %w", err)
	}
	return filepath.Join(home, ".local", "share", "opal"), nil
}

// isWritable checks if a directory exists and is writable, or if parent exists and is writable
func isWritable(path string) bool {
	// Check if path exists
	info, err := os.Stat(path)
	if err == nil {
		// Path exists, check if it's a directory and writable
		if !info.IsDir() {
			return false
		}
		// Test write permission by trying to create a temp file
		testFile := filepath.Join(path, ".write-test")
		f, err := os.Create(testFile)
		if err != nil {
			return false
		}
		f.Close()
		os.Remove(testFile)
		return true
	}

	// Path doesn't exist, check if parent is writable
	parent := filepath.Dir(path)
	parentInfo, err := os.Stat(parent)
	if err != nil {
		return false
	}
	if !parentInfo.IsDir() {
		return false
	}

	// Test if we can create in parent
	testFile := filepath.Join(parent, ".write-test")
	f, err := os.Create(testFile)
	if err != nil {
		return false
	}
	f.Close()
	os.Remove(testFile)
	return true
}

// GetDBPath returns the path to the SQLite database
// Resolution priority:
// 1. OPAL_DB_PATH environment variable
// 2. {data-dir}/opal.db
func GetDBPath() (string, error) {
	// Priority 1: OPAL_DB_PATH override
	if dbPath := os.Getenv("OPAL_DB_PATH"); dbPath != "" {
		return dbPath, nil
	}

	// Priority 2: Data directory + opal.db
	dataDir, err := GetDataDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(dataDir, "opal.db"), nil
}

// GetConfigPath returns the path to the config file
func GetConfigPath() (string, error) {
	configDir, err := GetConfigDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(configDir, "opal.yml"), nil
}

// GetSyncQueuePath returns the path to the sync queue file
func GetSyncQueuePath() (string, error) {
	dataDir, err := GetDataDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(dataDir, "sync_queue.json"), nil
}

// GetSyncConflictLogPath returns the path to the sync conflict log
func GetSyncConflictLogPath() (string, error) {
	dataDir, err := GetDataDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(dataDir, "sync_conflicts.log"), nil
}

// ConfigExists checks if a configuration file exists
func ConfigExists() bool {
	configPath, err := GetConfigPath()
	if err != nil {
		return false
	}
	_, err = os.Stat(configPath)
	return err == nil
}

// IsFirstRun checks if this is the first time opal is being run
func IsFirstRun() bool {
	return !ConfigExists()
}

// DefaultConfig returns a Config populated with all default values.
// This is the single source of truth for defaults.
func DefaultConfig() *Config {
	return &Config{
		DefaultFilter:      "status:pending",
		DefaultSort:        "due,priority",
		DefaultReport:      "list",
		ColorOutput:        true,
		WeekStartDay:       "monday",
		DefaultDueTime:     "",
		UrgencyDue:         12.0,
		UrgencyPriorityH:   6.0,
		UrgencyPriorityM:   3.9,
		UrgencyPriorityD:   1.8,
		UrgencyPriorityL:   0.0,
		UrgencyActive:      4.0,
		UrgencyAge:         2.0,
		UrgencyAgeMax:      365,
		UrgencyTags:        1.0,
		UrgencyProject:     1.0,
		UrgencyWaiting:     -3.0,
		UrgencyUrgentTag:   "next",
		UrgencyUrgentCoeff: 15.0,
		NextLimit:          5,
		SyncEnabled:        false,
		SyncURL:            "",
		SyncAPIKey:         "",
		SyncClientID:       "",
		SyncStrategy:       "last-write-wins",
		SyncQueueOffline:   true,
	}
}

// setViperDefaults registers all default values with a Viper instance.
func setViperDefaults(v *viper.Viper) {
	d := DefaultConfig()
	v.SetDefault("default_filter", d.DefaultFilter)
	v.SetDefault("default_sort", d.DefaultSort)
	v.SetDefault("default_report", d.DefaultReport)
	v.SetDefault("color_output", d.ColorOutput)
	v.SetDefault("week_start_day", d.WeekStartDay)
	v.SetDefault("default_due_time", d.DefaultDueTime)
	v.SetDefault("urgency_due_coefficient", d.UrgencyDue)
	v.SetDefault("urgency_priority_h_coefficient", d.UrgencyPriorityH)
	v.SetDefault("urgency_priority_m_coefficient", d.UrgencyPriorityM)
	v.SetDefault("urgency_priority_d_coefficient", d.UrgencyPriorityD)
	v.SetDefault("urgency_priority_l_coefficient", d.UrgencyPriorityL)
	v.SetDefault("urgency_active_coefficient", d.UrgencyActive)
	v.SetDefault("urgency_age_coefficient", d.UrgencyAge)
	v.SetDefault("urgency_age_max", d.UrgencyAgeMax)
	v.SetDefault("urgency_tags_coefficient", d.UrgencyTags)
	v.SetDefault("urgency_project_coefficient", d.UrgencyProject)
	v.SetDefault("urgency_waiting_coefficient", d.UrgencyWaiting)
	v.SetDefault("urgency_urgent_tag", d.UrgencyUrgentTag)
	v.SetDefault("urgency_urgent_coefficient", d.UrgencyUrgentCoeff)
	v.SetDefault("next_limit", d.NextLimit)
	v.SetDefault("sync_enabled", d.SyncEnabled)
	v.SetDefault("sync_url", d.SyncURL)
	v.SetDefault("sync_api_key", d.SyncAPIKey)
	v.SetDefault("sync_client_id", d.SyncClientID)
	v.SetDefault("sync_strategy", d.SyncStrategy)
	v.SetDefault("sync_queue_offline", d.SyncQueueOffline)
}

// LoadConfig loads configuration using layered sources:
//  1. Hardcoded defaults (always present)
//  2. YAML config file (optional, read-only — never created as a side effect)
//  3. Environment variables with OPAL_ prefix (override everything)
//
// Returns a valid *Config even if no config file exists. Never returns nil.
// Returns an error only if the config file exists but is malformed.
func LoadConfig() (*Config, error) {
	if globalConfig != nil {
		return globalConfig, nil
	}

	v := viper.New()
	v.SetConfigType("yaml")

	// Layer 1: Hardcoded defaults
	setViperDefaults(v)

	// Layer 2: YAML config file (optional, read-only)
	if configPath, err := GetConfigPath(); err == nil {
		v.SetConfigFile(configPath)
		if err := v.ReadInConfig(); err != nil {
			// Distinguish "file doesn't exist" from "file is malformed"
			if _, statErr := os.Stat(configPath); statErr == nil {
				// File exists but couldn't be parsed
				return nil, fmt.Errorf("config file %s is invalid: %w", configPath, err)
			}
			// File doesn't exist — that's fine, defaults apply
		}
	}

	// Layer 3: Environment variable overrides (OPAL_DEFAULT_FILTER, etc.)
	v.SetEnvPrefix("OPAL")
	v.AutomaticEnv()

	cfg := &Config{}
	if err := v.Unmarshal(cfg); err != nil {
		return nil, fmt.Errorf("failed to unmarshal config: %w", err)
	}

	globalConfig = cfg
	return cfg, nil
}

// InitConfig creates the config directory and writes a default opal.yml.
// This should be called explicitly during CLI first-run or setup, never as a
// side effect of loading config.
func InitConfig() error {
	configDir, err := GetConfigDir()
	if err != nil {
		return err
	}
	if err := os.MkdirAll(configDir, 0755); err != nil {
		return fmt.Errorf("failed to create config directory: %w", err)
	}
	return SaveConfig(DefaultConfig())
}

// SaveConfig writes the configuration to the opal.yml file.
func SaveConfig(cfg *Config) error {
	configPath, err := GetConfigPath()
	if err != nil {
		return err
	}

	data, err := yaml.Marshal(cfg)
	if err != nil {
		return fmt.Errorf("failed to marshal config: %w", err)
	}
	if err := os.WriteFile(configPath, data, 0644); err != nil {
		return fmt.Errorf("failed to write config file: %w", err)
	}

	// Update the cached singleton
	globalConfig = cfg
	return nil
}

// GetConfig returns the loaded config or loads it if not already loaded.
// Never returns nil — falls back to defaults if no config file exists.
func GetConfig() (*Config, error) {
	if globalConfig != nil {
		return globalConfig, nil
	}
	return LoadConfig()
}

// GetWeekStart returns the configured week start day
func (c *Config) GetWeekStart() time.Weekday {
	if strings.ToLower(c.WeekStartDay) == "sunday" {
		return time.Sunday
	}
	return time.Monday // default
}

// GetDefaultDueTime returns the configured default due time (HH:MM format or empty)
func (c *Config) GetDefaultDueTime() string {
	return c.DefaultDueTime
}