package device

import (
	"fmt"
	"sort"

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

// Device is a connected QMK Raw HID keyboard.
// Index is 1-based and is what --device accepts.
type Device struct {
	Index     int    `json:"index"`
	Path      string `json:"path"`
	VendorID  uint16 `json:"vendorId"`
	ProductID uint16 `json:"productId"`
	Name      string `json:"name,omitempty"`
}

// DiscoverAll returns every connected QMK Raw HID keyboard, ordered
// deterministically and numbered from 1. A keyboard that does not report a USB
// product string comes back with no Name; that costs the name and nothing else.
func DiscoverAll() ([]Device, error) {
	infos, err := hid.DiscoverAll()
	if err != nil {
		return nil, fmt.Errorf("discover qmk devices: %w", err)
	}

	devices := make([]Device, 0, len(infos))
	for _, info := range infos {
		devices = append(devices, Device{
			Path:      info.Path,
			VendorID:  info.VendorID,
			ProductID: info.ProductID,
			Name:      info.ProductString,
		})
	}

	return indexDevices(devices), nil
}

// UsagePair is one HID collection of a device: its usage page and its usage.
// Both are needed to describe a collection, because a keyboard reports several
// on one device and the page alone does not tell them apart.
type UsagePair struct {
	UsagePage uint16 `json:"usagePage"`
	Usage     uint16 `json:"usage"`
}

// HIDDevice is a connected device whose HID collections are not the QMK Raw HID
// one, which is what a discovery failure has to name: a board that is connected
// but not reachable is a different fact from a board that is not connected, and
// the usage pages are the only thing that tells the two apart.
//
// It is per device rather than per collection, because a device that is not
// reachable usually has several collections and one line per collection buries
// the one line that says something. A keyboard over USB typically has five: a
// keyboard page, two consumer-control pages, mouse and a vendor page. What is
// missing is the vendor page at 0xFF60.
//
// There is deliberately no Index and no Path. A number would look like something
// --device accepts, and nothing accepts these.
type HIDDevice struct {
	VendorID   uint16      `json:"vendorId"`
	ProductID  uint16      `json:"productId"`
	Name       string      `json:"name,omitempty"`
	UsagePairs []UsagePair `json:"usagePages"`
}

// DiscoverOther returns every connected HID device that is not a QMK Raw HID
// keyboard, each with the usage pages it does expose. Devices this tool drives
// are left out: they are what DiscoverAll numbers, and a list repeating them
// would suggest a second way to select a keyboard.
//
// Order is the order the HID layer reported the devices in, and the pairs within
// a device are in the order they were reported. Neither is sorted, because
// neither carries a number a user could act on and a keyboard's collections mean
// nothing in an order.
func DiscoverOther() ([]HIDDevice, error) {
	infos, err := hid.DiscoverEvery()
	if err != nil {
		return nil, fmt.Errorf("discover hid collections: %w", err)
	}
	return groupOther(infos), nil
}

// groupOther turns HID collections into the per-device list the commands report.
// It is separate from DiscoverOther because the grouping is the whole of the
// decision and nothing about it needs a keyboard plugged in to be checked.
func groupOther(infos []hid.DeviceInfo) []HIDDevice {
	var devices []HIDDevice
	index := make(map[string]int)
	for _, info := range infos {
		if info.RawHID {
			continue
		}
		key := fmt.Sprintf("%04X/%04X/%s", info.VendorID, info.ProductID, info.ProductString)
		at, seen := index[key]
		if !seen {
			devices = append(devices, HIDDevice{
				VendorID:  info.VendorID,
				ProductID: info.ProductID,
				Name:      info.ProductString,
			})
			at = len(devices) - 1
			index[key] = at
		}
		pair := UsagePair{UsagePage: info.UsagePage, Usage: info.Usage}
		if !containsUsagePair(devices[at].UsagePairs, pair) {
			devices[at].UsagePairs = append(devices[at].UsagePairs, pair)
		}
	}

	return devices
}

// containsUsagePair reports whether a device already lists a collection. The HID
// layer reports some devices once per interface, so the same pair arrives twice
// for one device and a line that says it twice is a line about nothing.
func containsUsagePair(pairs []UsagePair, want UsagePair) bool {
	for _, p := range pairs {
		if p == want {
			return true
		}
	}
	return false
}

// indexDevices sorts devices deterministically and assigns 1-based indexes.
// The input slice is left untouched.
func indexDevices(devices []Device) []Device {
	sorted := make([]Device, len(devices))
	copy(sorted, devices)

	sort.SliceStable(sorted, func(i, j int) bool {
		a, b := sorted[i], sorted[j]
		switch {
		case a.VendorID != b.VendorID:
			return a.VendorID < b.VendorID
		case a.ProductID != b.ProductID:
			return a.ProductID < b.ProductID
		default:
			return a.Path < b.Path
		}
	})

	for i := range sorted {
		sorted[i].Index = i + 1
	}

	return sorted
}