// Package config handles parsing, validation, and defaults for the
// monitor-lets-go YAML configuration file.
package config

import (
	"errors"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
	"time"

	"gopkg.in/yaml.v3"
)

// Duration is a time.Duration that supports YAML string unmarshaling.
type Duration time.Duration

// UnmarshalYAML parses a duration string like "1200ms", "5s", "2m".
func (d *Duration) UnmarshalYAML(value *yaml.Node) error {
	var s string
	if err := value.Decode(&s); err != nil {
		return err
	}
	dur, err := time.ParseDuration(s)
	if err != nil {
		return fmt.Errorf("invalid duration %q: %w", s, err)
	}
	*d = Duration(dur)
	return nil
}

func (d Duration) String() string { return time.Duration(d).String() }

// Config holds the complete monitor-lets-go configuration.
type Config struct {
	// Backend selects the window manager backend.
	// "auto" (default) probes for an available backend.
	Backend string `yaml:"backend"`

	// Debounce is the quiet period after the last hotplug event before
	// querying and applying a new layout. Defaults to 1200ms.
	Debounce Duration `yaml:"debounce"`

	// PollInterval is the fallback polling period when socket events
	// are unavailable. Set to 0 to disable. Defaults to 5s.
	PollInterval Duration `yaml:"poll_interval"`

	// RestoreOnExit, if true, applies the portable layout before the
	// daemon shuts down (on SIGTERM). Defaults to true.
	// Uses *bool so we can distinguish "not set" from explicit false.
	RestoreOnExit *bool `yaml:"restore_on_exit"`

	// OutputPath overrides the generated monitor config file path.
	// Supports ~ for home directory expansion.
	// Deprecated: use backend_config.output_path instead.
	// Empty means the default: ~/.config/hypr/monitors.lua.
	OutputPath string `yaml:"output_path"`

	// BackendConfig holds backend-specific configuration options.
	// Keys and values vary by the selected backend.
	// Hyprland supports:
	//   output_path — path to the generated monitor config file
	BackendConfig map[string]any `yaml:"backend_config"`

	// External lists monitor identifiers that trigger docked mode.
	// Each entry is a name (DP-1) or a desc: prefix (desc:Dell U2723QE).
	External []string `yaml:"external"`

	// Modes maps mode names to monitor layouts.
	// Required keys: "portable" and "docked".
	Modes map[string]Mode `yaml:"modes"`

	// Hooks maps event names to shell commands executed after a layout change.
	// Supported keys: "on_dock", "on_undock".
	Hooks map[string][]string `yaml:"hooks"`
}

// Mode describes a single monitor layout.
type Mode struct {
	Monitors []MonitorEntry `yaml:"monitors"`
}

// MonitorEntry defines the desired state of one monitor in a mode.
type MonitorEntry struct {
	Name     string  `yaml:"name"`
	Enabled  bool    `yaml:"enabled"`
	Mode     string  `yaml:"mode"`
	Position string  `yaml:"position"`
	Scale    float64 `yaml:"scale"`
}

// Load reads and validates a configuration file.
func Load(path string) (*Config, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read config: %w", err)
	}

	cfg := &Config{}
	if err := yaml.Unmarshal(data, cfg); err != nil {
		return nil, fmt.Errorf("parse config: %w", err)
	}

	if err := cfg.applyDefaults(); err != nil {
		return nil, err
	}
	if err := cfg.validate(); err != nil {
		return nil, err
	}
	return cfg, nil
}

// applyDefaults fills in default values for unset fields.
func (c *Config) applyDefaults() error {
	if c.Backend == "" {
		c.Backend = "auto"
	}
	if c.Debounce == 0 {
		c.Debounce = Duration(1200 * time.Millisecond)
	}
	if c.PollInterval == 0 {
		c.PollInterval = Duration(5 * time.Second)
	}
	if c.RestoreOnExit == nil {
		t := true
		c.RestoreOnExit = &t
	}
	if c.Modes == nil {
		c.Modes = make(map[string]Mode)
	}
	if c.Hooks == nil {
		c.Hooks = make(map[string][]string)
	}
	return nil
}

// validate checks that the configuration is usable.
func (c *Config) validate() error {
	if c.Backend != "auto" && c.Backend != "hyprland" && c.Backend != "sway" {
		return fmt.Errorf("unknown backend %q", c.Backend)
	}

	portable, ok := c.Modes["portable"]
	if !ok {
		return errors.New("missing required mode 'portable'")
	}
	docked, ok := c.Modes["docked"]
	if !ok {
		return errors.New("missing required mode 'docked'")
	}

	// Portable mode must have at least one enabled monitor.
	if countEnabled(portable.Monitors) == 0 {
		return errors.New("portable mode must have at least one enabled monitor")
	}
	// Docked mode must have at least one enabled monitor.
	if countEnabled(docked.Monitors) == 0 {
		return errors.New("docked mode must have at least one enabled monitor")
	}
	// External list is optional. When empty, the daemon auto-detects
	// external monitors (any non-internal display with non-zero dimensions).

	return nil
}

// EffectiveBackendConfig merges top-level deprecated backend keys
// (OutputPath) into the BackendConfig map. backend_config values
// take priority over deprecated top-level keys.
//
// The caller receives a non-nil map even when no backend_config is
// set and no deprecated keys are present.
func (c *Config) EffectiveBackendConfig() map[string]any {
	bc := c.BackendConfig
	if bc == nil {
		bc = make(map[string]any)
	}
	if c.OutputPath != "" {
		if _, exists := bc["output_path"]; !exists {
			bc["output_path"] = c.OutputPath
		}
	}
	return bc
}

// countEnabled returns how many MonitorEntries are enabled.
func countEnabled(entries []MonitorEntry) int {
	n := 0
	for _, e := range entries {
		if e.Enabled {
			n++
		}
	}
	return n
}

// isInternalConnector returns true if the connector name matches a known
// internal display pattern (eDP, LVDS, DSI) or Hyprland's synthetic
// "FALLBACK" output. Internal and synthetic displays are always part of the
// laptop/tablet (or a no-display fallback) and should never trigger docked
// mode.
func isInternalConnector(name string) bool {
	if strings.EqualFold(name, "fallback") {
		return true
	}
	prefixes := []string{"eDP-", "LVDS-", "DSI-", "EDP-"}
	for _, p := range prefixes {
		if strings.HasPrefix(name, p) {
			return true
		}
	}
	return false
}

// ExternalMonitor carries the identity of a detected monitor so the
// external list can match by name, description, serial, or resolution.
type ExternalMonitor struct {
	Name        string
	Description string
	Serial      string
	Width       int
	Height      int
	RefreshRate float64
}

// MatchesExternal checks whether a monitor matches the External list.
// Supports match modes:
//
//   - Plain name: exact match against the connector name
//   - desc: prefix: substring match against description or serial
//   - serial: prefix: substring match against serial
//   - size:WxH / size:WxH@R: exact pixel dimensions, optionally plus
//     refresh rate (within ±1 Hz)
//
// When the External list is empty, any monitor that is not an internal
// display connector (eDP-, LVDS-, DSI-) or synthetic output (FALLBACK)
// is automatically external.
func (c *Config) MatchesExternal(m ExternalMonitor) bool {
	if len(c.External) == 0 {
		return !isInternalConnector(m.Name)
	}

	for _, ext := range c.External {
		switch {
		case strings.HasPrefix(ext, "desc:"):
			needle := strings.TrimPrefix(ext, "desc:")
			if strings.Contains(m.Description, needle) || strings.Contains(m.Serial, needle) {
				return true
			}
		case strings.HasPrefix(ext, "serial:"):
			needle := strings.TrimPrefix(ext, "serial:")
			if strings.Contains(m.Serial, needle) {
				return true
			}
		case strings.HasPrefix(ext, "size:"):
			if matchSize(ext, m.Width, m.Height, m.RefreshRate) {
				return true
			}
		default:
			if m.Name == ext {
				return true
			}
		}
	}
	return false
}

// matchSize reports whether a monitor matches a "size:WxH" or "size:WxH@R"
// spec by exact pixel dimensions and, when a refresh rate is given, by
// refresh rate within ±1 Hz.
func matchSize(spec string, width, height int, refresh float64) bool {
	spec = strings.TrimPrefix(spec, "size:")

	parts := strings.Split(spec, "@")
	dimParts := strings.Split(parts[0], "x")
	if len(dimParts) != 2 {
		return false
	}

	w, errW := strconv.Atoi(strings.TrimSpace(dimParts[0]))
	h, errH := strconv.Atoi(strings.TrimSpace(dimParts[1]))
	if errW != nil || errH != nil {
		return false
	}
	if w != width || h != height {
		return false
	}

	if len(parts) == 2 {
		r, err := strconv.ParseFloat(strings.TrimSpace(parts[1]), 64)
		if err != nil || math.Abs(r-refresh) > 1.0 {
			return false
		}
	}
	return true
}