// Package xgbkb provides keyboard input utilities to be used alongside xgb and
// xgbutil.
package xgbkb

import "unicode"
import "github.com/jezek/xgbutil"
import "github.com/jezek/xgb/xproto"
import "github.com/jezek/xgbutil/keybind"

// TODO: support dead keys/compose key

// when making changes to this file, look at keysymdef.h and
// https://tronche.com/gui/x/xlib/input/keyboard-encoding.html

var x *xgbutil.XUtil

var modifierMasks struct {
	capsLock   uint16
	shiftLock  uint16
	numLock    uint16
	modeSwitch uint16

	alt   uint16
	meta  uint16
	super uint16
	hyper uint16
}

// IsOnNumpad returns whether the given keysym resides on the numpad.
func IsOnNumpad (symbol xproto.Keysym) bool {
	return symbol >= 0xFF80 && symbol <= 0xFFB9
}

// Initialize grabs keyboard mapping information from the X server. This
// function must be called before calling any other functions in this package.
// keybind.Initialize must also be called before this function is called.
func Initialize (connection *xgbutil.XUtil) {
	x = connection

	modifierMasks.capsLock   = KeysymToMask(0xFFE5)
	modifierMasks.shiftLock  = KeysymToMask(0xFFE6)
	modifierMasks.numLock    = KeysymToMask(0xFF7F)
	modifierMasks.modeSwitch = KeysymToMask(0xFF7E)
	
	modifierMasks.hyper = KeysymToMask(0xffed)
	modifierMasks.super = KeysymToMask(0xffeb)
	modifierMasks.meta  = KeysymToMask(0xffe7)
	modifierMasks.alt   = KeysymToMask(0xffe9)
}

// Modifiers lists which modifier keys are toggled on or being pressed.
type Modifiers struct {
	CapsLock   bool
	ShiftLock  bool
	NumLock    bool
	ModeSwitch bool
	
	Alt   bool
	Meta  bool
	Super bool
	Hyper bool
}

// String returns a human-readable comma-separated list of all active modifiers.
func (modifiers Modifiers) String () (out string) {
	add := func (name string) {
		if out != "" {
			out += ", "
		}
		out += name
	}
	if modifiers.Hyper      { add("Hyper")      }
	if modifiers.Super      { add("Super")      }
	if modifiers.Meta       { add("Meta")       }
	if modifiers.Alt        { add("Alt")        }
	if modifiers.ModeSwitch { add("ModeSwitch") }
	if modifiers.NumLock    { add("NumLock")    }
	if modifiers.ShiftLock  { add("ShiftLock")  }
	if modifiers.CapsLock   { add("CapsLock")   }
	return
}

// StateToModifiers converts a modifier state given by a keyboard or mouse event
// to a Modifiers struct.
func StateToModifiers (state uint16) Modifiers {
	return Modifiers {
		CapsLock:   0 < state & modifierMasks.capsLock,
		ShiftLock:  0 < state & modifierMasks.shiftLock,
		NumLock:    0 < state & modifierMasks.numLock,
		ModeSwitch: 0 < state & modifierMasks.modeSwitch,
		Alt:        0 < state & modifierMasks.alt,
		Meta:       0 < state & modifierMasks.meta,
		Super:      0 < state & modifierMasks.super,
		Hyper:      0 < state & modifierMasks.hyper,
	}
}

// KeysymToKeycode converts an X keysym to an X keycode, instead of the other
// way around.
func KeysymToKeycode (
	symbol xproto.Keysym,
) (
	code xproto.Keycode,
) {
	mapping := keybind.KeyMapGet(x)
	
	for index, testSymbol := range mapping.Keysyms {
		if testSymbol == symbol {
			code = xproto.Keycode (
				index /
				int(mapping.KeysymsPerKeycode) +
				int(x.Setup().MinKeycode))
			break
		}
	}
	
	return
}

// KeysymToMask returns the X modmask for a given modifier key.
func KeysymToMask (symbol xproto.Keysym) uint16 {
	return keybind.ModGet(x, KeysymToKeycode(symbol))
}

// KeycodeToButton converts an X keycode to a tomo keycode. It implements a more
// fleshed out version of some of the logic found in xgbutil/keybind/encoding.go
// to get a full keycode to keysym conversion. To avoid redundant work, this
// function will also return the rune corresponding to the keycode.
func KeycodeToKeysym (keycode xproto.Keycode, state uint16) (xproto.Keysym, rune) {
	// PARAGRAPH 3
	//
	// A list of KeySyms is associated with each KeyCode. The list is
	// intended to convey the set of symbols on the corresponding key. If
	// the list (ignoring trailing NoSymbol entries) is a single KeySym
	// ``K'', then the list is treated as if it were the list ``K NoSymbol
	// K NoSymbol''. If the list (ignoring trailing NoSymbol entries) is a
	// pair of KeySyms ``K1 K2'', then the list is treated as if it were the
	// list ``K1 K2 K1 K2''. If the list (ignoring trailing NoSymbol
	// entries) is a triple of KeySyms ``K1 K2 K3'', then the list is
	// treated as if it were the list ``K1 K2 K3 NoSymbol''. When an
	// explicit ``void'' element is desired in the list, the value
	// VoidSymbol can be used.
	symbol1 := keybind.KeysymGet(x, keycode, 0)
	symbol2 := keybind.KeysymGet(x, keycode, 1)
	symbol3 := keybind.KeysymGet(x, keycode, 2)
	symbol4 := keybind.KeysymGet(x, keycode, 3)
	switch {
	case symbol2 == 0 && symbol3 == 0 && symbol4 == 0:
		symbol3 = symbol1
	case symbol3 == 0 && symbol4 == 0:
		symbol3 = symbol1
		symbol4 = symbol2
	case symbol4 == 0:
		symbol4 = 0
	}
	symbol1Rune := KeysymToRune(symbol1)
	symbol2Rune := KeysymToRune(symbol2)
	symbol3Rune := KeysymToRune(symbol3)
	symbol4Rune := KeysymToRune(symbol4)

	// PARAGRAPH 4
	//
	// The first four elements of the list are split into two groups of
	// KeySyms. Group 1 contains the first and second KeySyms; Group 2
	// contains the third and fourth KeySyms. Within each group, if the
	// second element of the group is NoSymbol , then the group should be
	// treated as if the second element were the same as the first element,
	// except when the first element is an alphabetic KeySym ``K'' for which
	// both lowercase and uppercase forms are defined. In that case, the
	// group should be treated as if the first element were the lowercase
	// form of ``K'' and the second element were the uppercase form of
	// ``K.''
	cased := false
	if symbol2 == 0 {
		upper := unicode.IsUpper(symbol1Rune)
		lower := unicode.IsLower(symbol1Rune)
		if upper || lower {
			symbol1Rune = unicode.ToLower(symbol1Rune)
			symbol2Rune = unicode.ToUpper(symbol1Rune)
			cased = true
		} else {
			symbol2     = symbol1
			symbol2Rune = symbol1Rune
		}
	}
	if symbol4 == 0 {
		upper := unicode.IsUpper(symbol3Rune)
		lower := unicode.IsLower(symbol3Rune)
		if upper || lower {
			symbol3Rune = unicode.ToLower(symbol3Rune)
			symbol4Rune = unicode.ToUpper(symbol3Rune)
			cased = true
		} else {
			symbol4     = symbol3
			symbol4Rune = symbol3Rune
		}
	}

	// PARAGRAPH 5
	//
	// The standard rules for obtaining a KeySym from a KeyPress event make
	// use of only the Group 1 and Group 2 KeySyms; no interpretation of/
	// other KeySyms in the list is given. Which group to use is determined
	// by the modifier state. Switching between groups is controlled by the
	// KeySym named MODE SWITCH, by attaching that KeySym to some KeyCode
	// and attaching that KeyCode to any one of the modifiers Mod1 through
	// Mod5. This modifier is called the group modifier. For any KeyCode,
	// Group 1 is used when the group modifier is off, and Group 2 is used
	// when the group modifier is on.
	modeSwitch := state & modifierMasks.modeSwitch > 0
	if modeSwitch {
		symbol1     = symbol3
		symbol1Rune = symbol3Rune
		symbol2     = symbol4
		symbol2Rune = symbol4Rune
		
	}
	
	// PARAGRAPH 6
	// 
	// The Lock modifier is interpreted as CapsLock when the KeySym named
	// XK_Caps_Lock is attached to some KeyCode and that KeyCode is attached
	// to the Lock modifier. The Lock modifier is interpreted as ShiftLock
	// when the KeySym named XK_Shift_Lock is attached to some KeyCode and
	// that KeyCode is attached to the Lock modifier. If the Lock modifier
	// could be interpreted as both CapsLock and ShiftLock, the CapsLock
	// interpretation is used.
	shift :=
		state & xproto.ModMaskShift                > 0 ||
		state & modifierMasks.shiftLock    > 0
	capsLock := state & modifierMasks.capsLock > 0

	// PARAGRAPH 7
	//
	// The operation of keypad keys is controlled by the KeySym named
	// XK_Num_Lock, by attaching that KeySym to some KeyCode and attaching
	// that KeyCode to any one of the modifiers Mod1 through Mod5 . This
	// modifier is called the numlock modifier. The standard KeySyms with
	// the prefix ``XK_KP_'' in their name are called keypad KeySyms; these
	// are KeySyms with numeric value in the hexadecimal range 0xFF80 to
	// 0xFFBD inclusive. In addition, vendor-specific KeySyms in the
	// hexadecimal range 0x11000000 to 0x1100FFFF are also keypad KeySyms.
	numLock := state & modifierMasks.numLock  > 0
	
	// PARAGRAPH 8
	//
	// Within a group, the choice of KeySym is determined by applying the
	// first rule that is satisfied from the following list:
	var selectedKeysym xproto.Keysym
	var selectedRune   rune
	symbol2IsNumPad := IsOnNumpad(symbol2)
	switch {
	case numLock && symbol2IsNumPad:
		// The numlock modifier is on and the second KeySym is a keypad
		// KeySym. In this case, if the Shift modifier is on, or if the
		// Lock modifier is on and is interpreted as ShiftLock, then the
		// first KeySym is used, otherwise the second KeySym is used.
		if shift {
			selectedKeysym = symbol1
			selectedRune   = symbol1Rune
		} else {
			selectedKeysym = symbol2
			selectedRune   = symbol2Rune
		}

	case !shift && !capsLock:
		// The Shift and Lock modifiers are both off. In this case, the
		// first KeySym is used.
		selectedKeysym = symbol1
		selectedRune   = symbol1Rune

	case !shift && capsLock:
		// The Shift modifier is off, and the Lock modifier is on and is
		// interpreted as CapsLock. In this case, the first KeySym is
		// used, but if that KeySym is lowercase alphabetic, then the
		// corresponding uppercase KeySym is used instead.
		if cased && unicode.IsLower(symbol1Rune) {
			selectedRune = symbol2Rune
		} else {
			selectedKeysym = symbol1
			selectedRune   = symbol1Rune
		}

	case shift && capsLock:
		// The Shift modifier is on, and the Lock modifier is on and is
		// interpreted as CapsLock. In this case, the second KeySym is
		// used, but if that KeySym is lowercase alphabetic, then the
		// corresponding uppercase KeySym is used instead.
		if cased && unicode.IsLower(symbol2Rune) {
			selectedRune = unicode.ToUpper(symbol2Rune)
		} else {
			selectedKeysym = symbol2
			selectedRune   = symbol2Rune
		}

	case shift:
		// The Shift modifier is on, or the Lock modifier is on and is
		// interpreted as ShiftLock, or both. In this case, the second
		// KeySym is used.
		selectedKeysym = symbol2
		selectedRune   = symbol2Rune
	}
	
	return selectedKeysym, selectedRune
}

// runeExceptions contains runes that violate the heuristics in KeysymToRune.
var runeExceptions = map[xproto.Keysym] rune {
	// TODO: flesh out this list

	// number pad
	0xFF9F: '\x7F', // delete
	0xFF80: ' ',
	0xFF89: '\t',
	0xFF8D: '\r', // enter
	0xFFBD: '=',
	0xFFAA: '*',
	0xFFAB: '+',
	0xFFAC: ',', // FIXME: not always comma, could be dot
	0xFFAD: '-',
	0xFFAE: '.', // FIXME: not always dot, could be comma
	0xFFAF: '/',

	// misc. control
	0xFFFF: '\x7F', // delete
	0xFF09: '\t',
	0xFE20: '\t',
	0xFE34: '\r', // enter
}

// KeysymToRune takes in an X keysym and outputs a utf32 code point. If a
// corresponding code point was not found, zero will be returned.
func KeysymToRune (keysym xproto.Keysym) rune {
	// there are a few keysyms that can be shoehorned into runes that don't
	// fit the below rules or warrant their own
	if char, ok := runeExceptions[keysym]; ok {
		return char
	}

	// TTY function keys
	if keysym >= 0xFF08 && keysym <= 0xFF1B {
		return rune(keysym & 0xF)
	}

	// number pad numbers
	if keysym >= 0xFFB0 && keysym <= 0xFFB9 {
		return '0' + rune(keysym & 0xF)
	}

	// X keysyms like 0xFF.. or 0xFE.. are non-character keys. these cannot
	// be converted so we return a zero.
	if (keysym >> 8) == 0xFF || (keysym >> 8) == 0xFE {
		return 0
	}
	
	// some X keysyms have a single bit set to 1 here. i believe this is to
	// prevent conflicts with existing codes. if we mask it off we will get
	// a correct utf-32 code point.
	if keysym & 0xF000000 == 0x1000000 {
		return rune(keysym & 0x0111111)
	}

	// if none of these things happened, we can safely (i think) assume that
	// the keysym is an exact utf-32 code point.
	return rune(keysym)
}