package rgb

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"

	"netdome.biz/paul/qmk-rgb/internal/via"
)

// DefinitionsDir is the name of the directory definition files are kept in. It
// is a name and not a location: the tool resolves where that directory is, and
// where it is written to when created, in definitionsPath. The keyboard is
// identified first, so a file is only ever read for a board whose vendor and
// product ID match.
const DefinitionsDir = "definitions"

// VendorProductID is the key a definition is filed under, and the key the
// keyboard is looked up with: vendorID * 65536 + productID. The multiplication
// rather than a shift is what VIA uses, and the two must stay equal.
func VendorProductID(vendorID, productID uint16) int64 {
	return int64(vendorID)*65536 + int64(productID)
}

// effectValueKeys are the value keys whose control is a list of effects. A
// definition that invents its own key for effects does not name them, because
// nothing distinguishes such a control from any other dropdown.
var effectValueKeys = map[string]via.Channel{
	"id_qmk_backlight_effect":  via.ChannelBacklight,
	"id_qmk_rgblight_effect":   via.ChannelRgblight,
	"id_qmk_rgb_matrix_effect": via.ChannelRgbMatrix,
	"id_qmk_audio_effect":      via.ChannelAudio,
	"id_qmk_led_matrix_effect": via.ChannelLedMatrix,
}

// Definition is one keyboard definition file: the board it describes, and the
// effect names it holds per lighting channel.
type Definition struct {
	Path      string
	Name      string
	VendorID  uint16
	ProductID uint16
	Catalog   *Catalog
	// Labels is the name each lighting channel has in VIA's own interface, taken
	// from the sub-menu the definition puts it under. It is board data the file
	// already carries, and using it means the tool and VIA call the same channel
	// the same thing instead of the tool adding a third name of its own.
	Labels map[uint16]string
}

// ErrNotADefinition is returned for a file that is deliberately a different kind
// of document — a names file, which this tool also keeps as JSON. It is separate
// from a parse failure because the two call for opposite answers: a broken
// definition is a file the user has to fix, and a names file in the wrong
// directory is a file to skip or move.
var ErrNotADefinition = errors.New("not a VIA definition")

// NamesFileKind is the value the "kind" field of a names file carries. A file
// declaring it is not a definition, whatever its name and wherever it sits, which
// is the only reliable way to tell the two apart: a names file has the board's
// identifiers and no menus, so it parses as a definition and would otherwise take
// the board's place.
const NamesFileKind = "names"

// definitionFile is the part of a VIA definition this tool reads. VIA serves
// built definitions that carry vendorProductId as a number and no vendorId and
// productId pair, so both spellings are optional and at least one is required.
type definitionFile struct {
	Kind            string          `json:"kind"`
	Name            string          `json:"name"`
	VendorID        string          `json:"vendorId"`
	ProductID       string          `json:"productId"`
	VendorProductID int64           `json:"vendorProductId"`
	Menus           json.RawMessage `json:"menus"`
}

// Matches reports whether a definition is the one for a board. A definition
// for another board must not be used for this one, however it was found.
func (d *Definition) Matches(vendorID, productID uint16) bool {
	return d.VendorID == vendorID && d.ProductID == productID
}

// LoadDefinition reads one definition file.
func LoadDefinition(path string) (*Definition, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read %s: %w", path, err)
	}
	def, err := ParseDefinition(path, data)
	if err != nil {
		return nil, err
	}
	return def, nil
}

// ParseDefinition reads a definition from bytes, and is what LoadDefinition
// hands them to. A file fetched from a server is not a file on disk, and this
// is also the check that rejects a page which is not a definition: VIA answers
// an unknown board with its own web page and a success status, so a fetched
// document has to be parsed and matched before it is believed.
func ParseDefinition(source string, data []byte) (*Definition, error) {
	var file definitionFile
	if err := json.Unmarshal(data, &file); err != nil {
		return nil, fmt.Errorf("parse %s: not a keyboard definition: %w", source, err)
	}
	if file.Kind == NamesFileKind {
		return nil, fmt.Errorf("parse %s: %w, it is a names file (kind %q)", source, ErrNotADefinition, NamesFileKind)
	}

	vendorID, productID, err := file.identifiers()
	if err != nil {
		return nil, fmt.Errorf("%s: %w", source, err)
	}

	board := file.Name
	if board == "" {
		board = filepath.Base(source)
	}

	return &Definition{
		Path:      source,
		Name:      board,
		VendorID:  vendorID,
		ProductID: productID,
		Catalog:   NewCatalog(board, parseEffects(file.Menus)),
		Labels:    parseLabels(file.Menus),
	}, nil
}

// lightingValueKeys are the value keys a lighting channel binds. A control on one
// of them says which channel the sub-menu around it is about.
var lightingValueKeys = map[string]bool{
	"id_qmk_backlight_brightness":    true,
	"id_qmk_backlight_effect":        true,
	"id_qmk_rgblight_brightness":     true,
	"id_qmk_rgblight_effect":         true,
	"id_qmk_rgblight_effect_speed":   true,
	"id_qmk_rgblight_color":          true,
	"id_qmk_rgb_matrix_brightness":   true,
	"id_qmk_rgb_matrix_effect":       true,
	"id_qmk_rgb_matrix_effect_speed": true,
	"id_qmk_rgb_matrix_color":        true,
	"id_qmk_audio_brightness":        true,
	"id_qmk_audio_effect":            true,
	"id_qmk_audio_effect_speed":      true,
	"id_qmk_audio_color":             true,
	"id_qmk_led_matrix_brightness":   true,
	"id_qmk_led_matrix_effect":       true,
	"id_qmk_led_matrix_color":        true,
}

// parseLabels returns the sub-menu label per lighting channel: the name VIA
// shows for that channel. A definition that names no channel yields nothing, so
// the name a keyboard has elsewhere stays in charge.
func parseLabels(menus json.RawMessage) map[uint16]string {
	if len(menus) == 0 {
		return nil
	}
	var decoded any
	if err := json.Unmarshal(menus, &decoded); err != nil {
		return nil
	}

	labels := make(map[uint16]string)
	var walk func(node any, submenu string)
	walk = func(node any, submenu string) {
		switch v := node.(type) {
		case []any:
			for _, child := range v {
				walk(child, submenu)
			}
		case map[string]any:
			label, _ := v["label"].(string)
			// A sub-menu is an object holding controls; a control is an object
			// holding a value binding. Which one this is tells us whether the
			// label around a control is the channel's name.
			if controls, ok := v["content"].([]any); ok && len(controls) > 0 {
				if _, isControl := controls[0].(map[string]any); isControl && label != "" {
					submenu = label
				}
			}
			if c, ok := v["content"].([]any); ok && len(c) >= 2 {
				if key, isString := c[0].(string); isString && lightingValueKeys[key] {
					if number, isNumber := c[1].(float64); isNumber && submenu != "" {
						labels[uint16(number)] = submenu
					}
				}
			}
			for _, child := range v {
				walk(child, submenu)
			}
		}
	}
	walk(decoded, "")
	if len(labels) == 0 {
		return nil
	}
	return labels
}

// identifiers returns the board a definition is for, from whichever of the two
// spellings the file carries.
func (f definitionFile) identifiers() (uint16, uint16, error) {
	if f.VendorProductID != 0 {
		return uint16(f.VendorProductID / 65536), uint16(f.VendorProductID % 65536), nil
	}
	if f.VendorID == "" || f.ProductID == "" {
		return 0, 0, fmt.Errorf("neither vendorProductId nor vendorId/productId; not a keyboard definition")
	}
	vendorID, err := parseHexID(f.VendorID)
	if err != nil {
		return 0, 0, fmt.Errorf("vendorId %q: %w", f.VendorID, err)
	}
	productID, err := parseHexID(f.ProductID)
	if err != nil {
		return 0, 0, fmt.Errorf("productId %q: %w", f.ProductID, err)
	}
	return vendorID, productID, nil
}

func parseHexID(s string) (uint16, error) {
	v, err := strconv.ParseUint(strings.TrimPrefix(strings.TrimSpace(s), "0x"), 16, 16)
	if err != nil {
		return 0, fmt.Errorf("not a hexadecimal USB ID: %w", err)
	}
	return uint16(v), nil
}

// parseEffects walks the menus of a definition and returns the effect list of
// every lighting channel it names. The walk is generic because a definition
// nests its controls as it likes; what identifies an effect list is the value
// key and an options array beside it.
func parseEffects(menus json.RawMessage) map[via.Channel][]Effect {
	if len(menus) == 0 {
		return nil
	}
	var found map[via.Channel][]Effect
	var walk func(node any)
	walk = func(node any) {
		switch v := node.(type) {
		case map[string]any:
			if effects, ok := effectList(v); ok {
				if found == nil {
					found = make(map[via.Channel][]Effect)
				}
				found[effects.channel] = append(found[effects.channel], effects.list...)
			}
			for _, child := range v {
				walk(child)
			}
		case []any:
			for _, child := range v {
				walk(child)
			}
		}
	}

	var decoded any
	if err := json.Unmarshal(menus, &decoded); err != nil {
		return nil
	}
	walk(decoded)
	return found
}

type channelEffects struct {
	channel via.Channel
	list    []Effect
}

// effectList reads one UI control and reports the effects it offers, if it is an
// effect list at all.
func effectList(control map[string]any) (channelEffects, bool) {
	content, ok := control["content"].([]any)
	if !ok || len(content) < 2 {
		return channelEffects{}, false
	}
	valueKey, ok := content[0].(string)
	if !ok {
		return channelEffects{}, false
	}
	if _, known := effectValueKeys[valueKey]; !known {
		return channelEffects{}, false
	}
	channelNumber, ok := content[1].(float64)
	if !ok {
		return channelEffects{}, false
	}

	options, ok := control["options"].([]any)
	if !ok {
		return channelEffects{}, false
	}

	out := channelEffects{channel: via.Channel(int(channelNumber))}
	for position, option := range options {
		name, id, hasID, ok := optionName(option)
		if !ok {
			// An option that is neither a string nor a name/number pair has
			// no name to report; skipping it keeps the rest of the list.
			continue
		}
		if strings.TrimSpace(name) == "" {
			// An option with an empty name states a slot without naming it. That
			// is what a scaffold a user is meant to fill in looks like, and a
			// board that has one is not a board with an effect called "": the
			// slot is known and the name is not, so the channel reports no
			// effects until the name is there.
			continue
		}
		if !hasID {
			id = uint8(position)
		}
		out.list = append(out.list, Effect{ID: id, Name: name})
	}
	if len(out.list) == 0 {
		return channelEffects{}, false
	}
	sort.Slice(out.list, func(i, j int) bool { return out.list[i].ID < out.list[j].ID })
	return out, true
}

// optionName reads one dropdown option. VIA allows a bare string, which takes
// its number from the position, or a name and number pair, whose number is the
// value and need not be the position. The second is why an index into a name
// list is not an effect ID.
func optionName(option any) (name string, id uint8, hasID bool, ok bool) {
	switch v := option.(type) {
	case string:
		return v, 0, false, true
	case []any:
		if len(v) == 0 {
			return "", 0, false, false
		}
		label, isString := v[0].(string)
		if !isString {
			return "", 0, false, false
		}
		if len(v) < 2 {
			return label, 0, false, true
		}
		number, isNumber := v[1].(float64)
		if !isNumber {
			return label, 0, false, true
		}
		return label, uint8(number), true, true
	default:
		return "", 0, false, false
	}
}

// LoadDefinitionsDir reads every definition file in a directory. A file it
// cannot use is an error rather than a silent skip: a definition the user
// placed there and that does not work is worth saying out loud.
func LoadDefinitionsDir(dir string) ([]*Definition, error) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, fmt.Errorf("read %s: %w", dir, err)
	}

	var defs []*Definition
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".json") {
			continue
		}
		def, err := LoadDefinition(filepath.Join(dir, entry.Name()))
		if errors.Is(err, ErrNotADefinition) {
			// A names file in the definitions directory is not a definition that
			// failed to parse, it is a different kind of document, and it must not
			// be read as one. It carries vendorId and productId and no menus, so
			// without this it parses and shadows the board's real file.
			continue
		}
		if err != nil {
			return nil, err
		}
		defs = append(defs, def)
	}
	sort.Slice(defs, func(i, j int) bool { return defs[i].Path < defs[j].Path })
	return defs, nil
}

// LoadDefinitionsFS reads every definition file in a filesystem, which is what a
// directory read and the set built into the binary have in common. The path is
// only used to name the files in errors, so a caller that has an embed.FS can
// pass the directory it presents itself as.
//
// A file it cannot use is an error rather than a silent skip, for the same
// reason as in a directory: a definition that does not work is worth saying out
// loud. A vendored file that fails this is a build defect, not a user's file, so
// the caller decides what an error here means.
func LoadDefinitionsFS(fsys fs.FS, dir string) ([]*Definition, error) {
	entries, err := fs.ReadDir(fsys, ".")
	if err != nil {
		return nil, fmt.Errorf("read %s: %w", dir, err)
	}

	var defs []*Definition
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".json") {
			continue
		}
		data, err := fs.ReadFile(fsys, entry.Name())
		if err != nil {
			return nil, fmt.Errorf("read %s: %w", filepath.Join(dir, entry.Name()), err)
		}
		def, err := ParseDefinition(filepath.Join(dir, entry.Name()), data)
		if err != nil {
			return nil, err
		}
		defs = append(defs, def)
	}
	sort.Slice(defs, func(i, j int) bool { return defs[i].Path < defs[j].Path })
	return defs, nil
}

// FindDefinition returns the definition for a board, or nil when none of the
// definitions is for it. The first match wins, so the order the definitions are
// passed in is the order the tool trusts: a file in a directory a user controls
// before one built into the binary.
func FindDefinition(defs []*Definition, vendorID, productID uint16) *Definition {
	for _, def := range defs {
		if def.VendorID == vendorID && def.ProductID == productID {
			return def
		}
	}
	return nil
}

// EffectValueKey returns the VIA value key a channel's effect list is filed
// under, and whether one is registered for it. The lookup goes through
// effectValueKeys rather than a second table, because that map is where a value
// key is registered and a second one would fall behind it.
func EffectValueKey(ch via.Channel) (string, bool) {
	for key, channel := range effectValueKeys {
		if channel == ch {
			return key, true
		}
	}
	return "", false
}