// Package backend defines the abstraction layer for window-manager-specific
// monitor management. Each supported compositor (Hyprland, Sway, etc.)
// implements the Backend interface, encapsulating how monitors are detected,
// configured, and how hotplug events are received.
//
// This is the only WM-dependent code in the project. To add support for a
// new window manager, implement this interface and register the backend in
// cmd/monitor-lets-go/main.go.
package backend

import (
	"context"
	"fmt"
	"log/slog"
	"math"
	"strconv"
	"strings"
)

// MonitorInfo represents a physical display as reported by the compositor.
// Fields use JSON tags matching hyprctl -j output; other compositors
// populate equivalent fields.
type MonitorInfo struct {
	Name        string  `json:"name"`
	Description string  `json:"description"`
	Make        string  `json:"make"`
	Model       string  `json:"model"`
	Serial      string  `json:"serial"`
	Width       int     `json:"width"`
	Height      int     `json:"height"`
	RefreshRate float64 `json:"refreshRate"`
	X           int     `json:"x"`
	Y           int     `json:"y"`
	Scale       float64 `json:"scale"`
	Enabled     bool    `json:"enabled"`
}

// MonitorConfig describes the desired state of a single monitor.
// Used in configuration and passed to ApplyLayout.
type MonitorConfig struct {
	Name     string  `yaml:"name"`
	Enabled  bool    `yaml:"enabled"`
	Mode     string  `yaml:"mode"`     // "1920x1080@144", "preferred", or empty
	Position string  `yaml:"position"` // "0x0", "auto", or empty
	Scale    float64 `yaml:"scale"`    // 1.0, 1.5, etc.
}

// State represents the current operational mode of the daemon.
type State int

const (
	StateUnknown  State = iota
	StatePortable       // built-in display only
	StateDocked         // external monitors connected
)

// String returns a human-readable state name used for config keys and logging.
func (s State) String() string {
	switch s {
	case StatePortable:
		return "portable"
	case StateDocked:
		return "docked"
	default:
		return "unknown"
	}
}

// EventType identifies the kind of monitor hotplug event.
type EventType int

const (
	EventMonitorAdded   EventType = iota
	EventMonitorRemoved
)

// Event carries a single monitor hotplug notification from the compositor.
type Event struct {
	Type        EventType
	MonitorName string
}

// Backend is the abstraction over a window manager's monitor management.
// Each implementation handles compositor-specific APIs for querying monitors,
// applying layouts, and subscribing to hotplug events.
type Backend interface {
	// Name returns a human-readable backend identifier (e.g. "hyprland").
	Name() string

	// GetMonitors returns all monitors known to the compositor,
	// both active and inactive (physically connected but disabled).
	GetMonitors(ctx context.Context) ([]MonitorInfo, error)

	// ApplyLayout applies a list of monitor configurations atomically.
	// The backend must ensure no intermediate state where zero monitors
	// are enabled is ever visible.
	ApplyLayout(ctx context.Context, monitors []MonitorConfig) error

	// Events returns a channel of hotplug events and a channel of errors.
	// The caller must read from both channels. When ctx is cancelled,
	// the backend closes both channels and stops listening.
	Events(ctx context.Context) (<-chan Event, <-chan error)

	// Close releases any resources held by the backend.
	Close() error
}

// resolveMonitorNames converts desc: or size: prefixed monitor config names
// to the actual connector names by matching against the current set of
// connected monitors.
//
// Matching logic:
//   - "desc:text" — substring match against description or serial
//   - "size:WxH" — match by exact pixel dimensions (e.g. "size:2560x1440")
//   - "size:WxH@R" — match by dimensions + refresh rate (e.g. "size:2560x1440@165")
//   - plain names are returned as-is
func resolveMonitorNames(ctx context.Context, monitors []MonitorConfig, getMonitors func(context.Context) ([]MonitorInfo, error), logger *slog.Logger) ([]MonitorConfig, error) {
	var needsResolution bool
	for _, m := range monitors {
		if strings.HasPrefix(m.Name, "desc:") || strings.HasPrefix(m.Name, "size:") {
			needsResolution = true
			break
		}
	}
	if !needsResolution {
		return monitors, nil
	}

	current, err := getMonitors(ctx)
	if err != nil {
		return nil, fmt.Errorf("get current monitors: %w", err)
	}

	resolved := make([]MonitorConfig, len(monitors))
	for i, m := range monitors {
		switch {
		case strings.HasPrefix(m.Name, "desc:"):
			resolved[i] = resolveDesc(m, current, logger)
		case strings.HasPrefix(m.Name, "size:"):
			resolved[i] = resolveSize(m, current, logger)
		default:
			resolved[i] = m
		}
		if resolved[i].Name == "" {
			return nil, fmt.Errorf("cannot resolve monitor name %q", m.Name)
		}
	}

	return resolved, nil
}

// resolveDesc resolves a desc: prefixed name to a connector name.
func resolveDesc(m MonitorConfig, current []MonitorInfo, logger *slog.Logger) MonitorConfig {
	needle := strings.TrimPrefix(m.Name, "desc:")
	var matches []MonitorInfo
	for _, mi := range current {
		if strings.Contains(mi.Description, needle) || strings.Contains(mi.Serial, needle) {
			matches = append(matches, mi)
		}
	}

	switch len(matches) {
	case 0:
		// Return as-is so the caller sees the empty name.
		m.Name = ""
		return m
	case 1:
		logger.Debug("resolved desc to connector",
			"desc", needle, "connector", matches[0].Name)
		m.Name = matches[0].Name
		return m
	default:
		var names []string
		for _, mat := range matches {
			names = append(names, mat.Name)
		}
		logger.Warn("desc:%q matches multiple monitors: %s — use a more specific identifier",
			needle, strings.Join(names, ", "))
		m.Name = ""
		return m
	}
}

// resolveSize resolves a size: prefixed name to a connector name.
// Format: "size:WxH" or "size:WxH@R" where W and H are pixel dimensions
// and R is the refresh rate in Hz.
func resolveSize(m MonitorConfig, current []MonitorInfo, logger *slog.Logger) MonitorConfig {
	spec := strings.TrimPrefix(m.Name, "size:")

	parts := strings.Split(spec, "@")
	dimParts := strings.Split(parts[0], "x")
	if len(dimParts) != 2 {
		logger.Warn("invalid size spec", "spec", spec)
		m.Name = ""
		return m
	}

	targetW, errW := strconv.Atoi(strings.TrimSpace(dimParts[0]))
	targetH, errH := strconv.Atoi(strings.TrimSpace(dimParts[1]))
	if errW != nil || errH != nil {
		logger.Warn("invalid size dimensions", "spec", spec)
		m.Name = ""
		return m
	}

	var targetR float64
	hasRefresh := len(parts) == 2
	if hasRefresh {
		var err error
		targetR, err = strconv.ParseFloat(strings.TrimSpace(parts[1]), 64)
		if err != nil {
			logger.Warn("invalid refresh rate in size spec", "spec", spec)
			m.Name = ""
			return m
		}
	}

	var matches []MonitorInfo
	for _, mi := range current {
		if mi.Width != targetW || mi.Height != targetH {
			continue
		}
		if hasRefresh {
			if math.Abs(mi.RefreshRate-targetR) > 1.0 {
				continue
			}
		}
		matches = append(matches, mi)
	}

	switch len(matches) {
	case 0:
		m.Name = ""
		return m
	case 1:
		logger.Debug("resolved size to connector",
			"size", spec, "connector", matches[0].Name)
		m.Name = matches[0].Name
		return m
	default:
		var names []string
		for _, mat := range matches {
			names = append(names, mat.Name)
		}
		if hasRefresh {
			logger.Warn("size:%q matches multiple monitors: %s — add @R to disambiguate",
				spec, strings.Join(names, ", "))
		} else {
			logger.Warn("size:%q matches multiple monitors: %s — use size:WxH@R for disambiguation",
				spec, strings.Join(names, ", "))
		}
		m.Name = ""
		return m
	}
}