// Copyright (c) 2026 Storm Dragon
// Authors: Storm Dragon, Angus Kola
// SPDX-License-Identifier: GPL-3.0-or-later

package i3ipc

import (
	"encoding/json"
	"errors"
	"slices"
	"strings"
)

type Kind uint8

const (
	Mode Kind = iota
	Workspace
	Fullscreen
	Floating
	Urgent
	MarkAdded
	MarkRemoved
	WorkspaceMove
)

// Event carries confirmed state, leaving wording and preferences to the app.
type Event struct {
	Kind                     Kind
	Name, Window, Workspace  string
	Focused, Enabled, Markup bool
	FullscreenMode           int
}

type node struct {
	ID         uint64   `json:"id"`
	Name       string   `json:"name"`
	Type       string   `json:"type"`
	Window     uint64   `json:"window"`
	Focused    bool     `json:"focused"`
	Urgent     *bool    `json:"urgent"`
	Fullscreen *int     `json:"fullscreen_mode"`
	Scratchpad string   `json:"scratchpad_state"`
	Floating   string   `json:"floating"`
	Marks      []string `json:"marks"`
	Properties struct {
		Class string `json:"class"`
	} `json:"window_properties"`
	Nodes         []node `json:"nodes"`
	FloatingNodes []node `json:"floating_nodes"`
}

type workspace struct {
	ID      uint64 `json:"id"`
	Name    string `json:"name"`
	Focused bool   `json:"focused"`
}

type location struct {
	id   uint64
	name string
}
type nodeState struct {
	Marks  []string
	Urgent *bool
}

type state struct {
	nodes            map[uint64]nodeState
	locations        map[uint64]location
	focusedWorkspace uint64
}

func (s *state) baseline(root node, spaces []workspace) {
	s.nodes = make(map[uint64]nodeState)
	s.locations = make(map[uint64]location)
	s.walk(root, location{}, true)
	for _, ws := range spaces {
		if ws.Focused {
			s.focusedWorkspace = ws.ID
		}
	}
}

func (s *state) walk(n node, ws location, baseline bool) {
	if n.Type == "workspace" {
		ws = location{n.ID, n.Name}
	}
	if n.ID != 0 {
		if baseline {
			s.nodes[n.ID] = nodeState{Marks: n.Marks, Urgent: n.Urgent}
		}
		// i3's private scratch workspace is deliberately outside this feature.
		if ws.id != 0 && ws.name != "__i3_scratch" {
			s.locations[n.ID] = ws
		}
	}
	for _, children := range [][]node{n.Nodes, n.FloatingNodes} {
		for _, child := range children {
			s.walk(child, ws, baseline)
		}
	}
}

func (s *state) refreshLocations(root node) {
	s.locations = make(map[uint64]location)
	s.walk(root, location{}, false)
}

func windowName(n node) string {
	if n.Name != "" {
		return n.Name
	}
	return n.Properties.Class
}

func (s *state) apply(m message, queryTree func() (node, error)) ([]Event, error) {
	var payload struct {
		Change    string `json:"change"`
		Markup    bool   `json:"pango_markup"`
		Current   *node  `json:"current"`
		Container *node  `json:"container"`
	}
	if err := json.Unmarshal(m.body, &payload); err != nil {
		return nil, err
	}
	if m.kind == modeEvent {
		if payload.Change == "" {
			return nil, nil
		}
		return []Event{{Kind: Mode, Name: payload.Change, Markup: payload.Markup}}, nil
	}
	if m.kind == workspaceEvent {
		n := payload.Current
		if n == nil || n.ID == 0 {
			return nil, nil
		}
		switch payload.Change {
		case "focus":
			s.focusedWorkspace = n.ID
			return []Event{{Kind: Workspace, Name: n.Name}}, nil
		case "rename":
			for id, ws := range s.locations {
				if ws.id == n.ID {
					ws.name = n.Name
					s.locations[id] = ws
				}
			}
			if n.ID == s.focusedWorkspace {
				return []Event{{Kind: Workspace, Name: n.Name}}, nil
			}
		}
		// Workspace urgency is aggregate state, already handled at the window.
		return nil, nil
	}
	if m.kind != windowEvent || payload.Container == nil || payload.Container.ID == 0 {
		return nil, nil
	}
	n := *payload.Container
	old, known := s.nodes[n.ID]
	previous := s.locations[n.ID]
	if payload.Change == "close" {
		delete(s.nodes, n.ID)
		delete(s.locations, n.ID)
		return nil, nil
	}
	s.nodes[n.ID] = nodeState{Marks: n.Marks, Urgent: n.Urgent}
	if len(s.nodes) > 65536 {
		return nil, errors.New("i3 comparison cache exceeded")
	}
	if payload.Change == "new" || payload.Change == "move" || payload.Change == "urgent" || payload.Change == "floating" {
		root, err := queryTree()
		if err != nil {
			return nil, err
		}
		s.refreshLocations(root)

	}
	base := Event{Window: windowName(n), Focused: n.Focused, Workspace: s.locations[n.ID].name}
	switch payload.Change {
	case "fullscreen_mode":
		if n.Fullscreen != nil && *n.Fullscreen >= 0 && *n.Fullscreen <= 2 {
			base.Kind, base.Enabled, base.FullscreenMode = Fullscreen, *n.Fullscreen != 0, *n.Fullscreen
			return []Event{base}, nil
		}
	case "floating":
		// Sending a tiled window to the scratchpad also enables floating.
		// That implicit transition belongs to the excluded scratchpad feature.
		// Its event can precede assignment, so require a confirmed public
		// workspace in the resulting tree as well as the reported state.
		if s.locations[n.ID].id == 0 || n.Scratchpad != "" && n.Scratchpad != "none" {
			return nil, nil
		}
		switch n.Floating {
		case "auto_on", "user_on", "auto_off", "user_off":
			base.Kind, base.Enabled = Floating, strings.HasSuffix(n.Floating, "_on")
			return []Event{base}, nil
		}
	case "urgent":
		if n.Urgent != nil && *n.Urgent && (!known || old.Urgent == nil || !*old.Urgent) {
			base.Kind = Urgent
			return []Event{base}, nil
		}
	case "mark":
		if !known || old.Marks == nil || n.Marks == nil {
			return nil, nil
		}
		var events []Event
		// Stable order even if i3 reorders an unchanged set.
		for _, diff := range []struct {
			before, after []string
			kind          Kind
		}{{n.Marks, old.Marks, MarkRemoved}, {old.Marks, n.Marks, MarkAdded}} {
			before := make(map[string]struct{}, len(diff.before))
			for _, name := range diff.before {
				before[name] = struct{}{}
			}
			names := slices.Clone(diff.after)
			slices.Sort(names)
			names = slices.Compact(names)
			for _, name := range names {
				if _, exists := before[name]; !exists {
					e := base
					e.Kind, e.Name = diff.kind, name
					if len(events) >= maxPending {
						return nil, errors.New("i3 mark changes exceeded")
					}
					events = append(events, e)
				}
			}
		}
		return events, nil
	case "move":
		current := s.locations[n.ID]
		if n.Window != 0 && previous.id != 0 && current.id != 0 && previous.id != current.id {
			base.Kind = WorkspaceMove
			return []Event{base}, nil
		}
	}
	return nil, nil
}