package main

import (
    "fmt"
    "log"
    "os"
    "os/exec"

    "github.com/jezek/xgb"
    "github.com/jezek/xgb/xinerama"
    "github.com/jezek/xgb/xproto"
)

// TODO: Make a separate keysym file and fully populate it.
const (
    XK_q      = 0x0071
    XK_Return = 0xff0d
)

// TODO: These module-level global variables have arisen while establishing
// basic functionality. Before proceeding much further, figure out what to do
// with them.
var xc *xgb.Conn
var attachedScreens []xinerama.ScreenInfo
var xroot xproto.ScreenInfo
var keymap [256][]xproto.Keysym

func main() {

    // Build a connection to the X server --------------------------------------

    xConn, err := xgb.NewConn()
    if err != nil {
        log.Fatal(err)
    }
    xc = xConn
    defer xc.Close()

    // Determine what sort of screen(s) will display output --------------------

    setup := xproto.Setup(xc)
    if setup == nil || len(setup.Roots) < 1 {
        log.Fatal("ILLI: Unable to parse received SetupInfo from X11 server.")
    }

    if err := xinerama.Init(xc); err != nil {
        log.Fatal(err)
    }

    if r, err := xinerama.QueryScreens(xc).Reply(); err != nil {
        log.Fatal(err)
    } else {
        if len(r.ScreenInfo) == 0 {
            attachedScreens = []xinerama.ScreenInfo{
                xinerama.ScreenInfo{
                    Width:  setup.Roots[0].WidthInPixels,
                    Height: setup.Roots[0].HeightInPixels,
                },
            }
        } else {
            attachedScreens = r.ScreenInfo
        }
    }

    // Establish a root for the tree -------------------------------------------

    connInfo := xproto.Setup(xc)
    if connInfo == nil {
        log.Fatal("ILLI: Unable to parse X connection information")
    }
    if len(connInfo.Roots) != 1 {
        log.Fatal("ILLI: Inappropriate number of roots. Did xinerama initialize correctly?")
    }
    xroot = connInfo.Roots[0]

    // Register with the X server as the new window manager --------------------

    if err := TakeWMOwnership(); err != nil {
        if _, ok := err.(xproto.AccessError); ok {
            log.Fatal("ILLI: Unable to register as window manager with X server. Perhaps another WM is already running?")
        }
        log.Fatal(err)
    }

    fmt.Println("ILLI: Successfully registered as WM with X server.")

    // Setup keysym mappings and register for WM-relevant key events -----------

    const (
        loKey = 8
        hiKey = 255
    )

    m := xproto.GetKeyboardMapping(xc, loKey, hiKey-loKey+1)
    reply, err := m.Reply()
    if err != nil {
        log.Fatal(err)
    }
    if reply == nil {
        log.Fatal("Could not load keyboard map")
    }

    for i := 0; i < hiKey-loKey+1; i++ {
        keymap[loKey+i] = reply.Keysyms[i*int(reply.KeysymsPerKeycode) : (i+1)*int(reply.KeysymsPerKeycode)]
    }
    grabs := []struct {
        sym       xproto.Keysym
        modifiers uint16
        codes     []xproto.Keycode
    }{
        {
            sym:       XK_q,
            modifiers: xproto.ModMask1 | xproto.ModMaskShift,
        },
        {
            sym:       XK_Return,
            modifiers: xproto.ModMask1 | xproto.ModMaskShift,
        },
    }

    for i, syms := range keymap {
        for _, sym := range syms {
            for c := range grabs {
                if grabs[c].sym == sym {
                    grabs[c].codes = append(grabs[c].codes, xproto.Keycode(i))
                }
            }
        }
    }
    for _, grabbed := range grabs {
        for _, code := range grabbed.codes {
            if err := xproto.GrabKeyChecked(
                xc,
                false,
                xroot.Root,
                grabbed.modifiers,
                code,
                xproto.GrabModeAsync,
                xproto.GrabModeAsync,
            ).Check(); err != nil {
                log.Print(err)
            }

        }
    }

    // Build a list of windows needing management ------------------------------

    tree, err := xproto.QueryTree(xc, xroot.Root).Reply()
    if err != nil {
        log.Fatal(err)
    }
    if tree != nil {
        //workspaces = make(map[string]*Workspace)
        //defaultw := &Workspace{mu: &sync.Mutex{}}
        for _, c := range tree.Children {
            if isMappedWindow(c) {
//                err := defaultw.Add(c)
//                if err != nil {
//                    log.Println(err)
//                }
                fmt.Println("ILLI: Found a client.")
            }

        }

//        if len(attachedScreens) > 0 {
//            defaultw.Screen = &attachedScreens[0]
//        }
//
//        workspaces["default"] = defaultw
//
//        if err := defaultw.TileWindows(); err != nil {
//            log.Println(err)
//        }

    }

    // Main program loop reacts to X events ------------------------------------

eventloop:
    for {
        xevent, err := xc.WaitForEvent()
        if err != nil {
            log.Println(err)
            continue
        }
        switch e := xevent.(type) {
            case xproto.KeyPressEvent:
                if err := handleKeyPressEvent(e); err != nil {
                    break eventloop
                }
            default:
                log.Println(xevent)
        }
    }
}

// In addition to the basic key/button press/release events, by registering for
// events like SubstructureRedirect, we are declaring our intent to act as
// window manager for this X server. Only one WM is allowed per X server, a
// policy enforced on the X server's side by refusing the registration request
// for events like SubstructureRedirect if an existing process already receives
// those events (i.e. is already the window manager).
func TakeWMOwnership() error {
    return xproto.ChangeWindowAttributesChecked(
        xc,
        xroot.Root,
        xproto.CwEventMask,
        []uint32{
            xproto.EventMaskKeyPress |
                xproto.EventMaskKeyRelease |
                xproto.EventMaskButtonPress |
                xproto.EventMaskButtonRelease |
                xproto.EventMaskStructureNotify |
                xproto.EventMaskSubstructureRedirect,
                // TODO: Should we also register for EventMaskSubstructureNotify ?
                //       Where is the authoritative list of events located?
        }).Check()
}

// The client list appears to have some entries for windows that shouldn't
// actually be viewable. For now, it appears that only windows with a
// `MapState` value of 2 should be viewable. TODO: Verify this.
//   - https://github.com/BurntSushi/xgb/blob/master/xproto/xproto.go#L3772
//   - https://github.com/BurntSushi/xgb/blob/master/xproto/xproto.go#L10287
func isMappedWindow(windowID xproto.Window) bool {
    reply, err := xproto.GetWindowAttributes(xc, windowID).Reply()
    if err != nil {
        log.Fatal(err)
    }
    if reply != nil && reply.MapState == 2 {
        return true
    }
    return false
}

// TODO: Determine how I want to split the main event loop from the various
// event handlers (like this keypress handler). It shouldn't grow too
// fragmented, nor should it grow into a monolithic beast, but the balance
// needs to be selected after the handlers are built out more completely.
func handleKeyPressEvent(key xproto.KeyPressEvent) error {
    switch keymap[key.Detail][0] {
        case XK_q:
            switch key.State {
                case xproto.ModMask1 | xproto.ModMaskShift:
                    // TODO: Where and how do I want to handle exit/restart?
                    // -------------------------
                    // We must manually close the X connection since we used
                    // `defer` when setting it up and os.Exit() short-circuits
                    // that deferral.
                    xc.Close()
                    os.Exit(0)
            }
        case XK_Return:
            switch key.State {
                case xproto.ModMask1 | xproto.ModMaskShift:
                    cmd := exec.Command("xterm")
                    err := cmd.Start()
                    if err != nil {
                        log.Fatal(err)
                    }
            }
        default:
            return nil
    }
    return nil // TODO: What do I actually want to return here?
}