//============
//  CONTROLS
//============

MOVE_NEXT = "ArrowRight"
MOVE_BACK = "ArrowLeft"
TOGGLE_FULLSCREEN = "F"


//========================
//  NAVIGATION CONSTANTS
//========================

PAGE_TRANSITION_SPEED = "1.5s"
MOUSEWHELL_MIN_DELAY = 50
DELAY_BEFORE_HIDDING_CONTROLS = 4000;

//====================
//  STATES CONSTANTS
//====================

READER_FRAME = document.getElementById("reader-frame")
READER_PAGES = document.getElementById("reader-pages")
FOCUS_OVERLAY = document.getElementById("focus-overlay")
HELP_CONTROLS = document.getElementById("help-controls")

CURRENT_ZOOM = 0
CURRENT_PAGE = 1
CURRENT_WIDTH = 0
CURRENT_HEIGHT = 0
CURRENT_X = 0
CURRENT_Y = 0

IS_PAGE_MODE = false
MOUSEWHELL_WAIT = false


// =============
//   UTILITIES
// =============

// Zooms utilites
// --------------

function getFirstZoomOfPage(pageNumber){
   
    for (var zoom_idx = 0; zoom_idx < zooms.length; zoom_idx++){
        if (zooms[zoom_idx][0] == pageNumber) {
            return zoom_idx
        }
    }
}

function getLastZoomOfPage(pageNumber){
    let res = null
    
    for (var zoom_idx = 0; zoom_idx < zooms.length; zoom_idx++){
        if (zooms[zoom_idx][0] == pageNumber) {
            res = zoom_idx
        }
        
        if (res != null && zooms[zoom_idx][0] != pageNumber) {
            break
        }
    }
    
    return res
}

// Dimensions utilites
// -------------------

function getPagesCount() {
    return READER_PAGES.childElementCount
}

function pageOriginalHeight() {
    return parseInt(READER_PAGES.dataset.pagesHeight)
}

function pageOriginalWidth() {
    return parseInt(READER_PAGES.dataset.pagesWidth)
}

function readerFrameRatio() {
    return READER_FRAME.clientWidth / READER_FRAME.clientHeight
}

function pageRatio() {
    return READER_PAGES.dataset.pagesWidth / READER_PAGES.dataset.pagesHeight
}

function isFrameRatioWiderThanPage(){
    return readerFrameRatio() > pageRatio()
}

function pageToFrameScaleFactor(useHeight){
    // The scale factor to apply to a page so it exactly fit in the reader frame
    if (useHeight) {
        return READER_FRAME.clientHeight / pageOriginalHeight()
    }
    return READER_FRAME.clientWidth / pageOriginalWidth()
}

function totalPagesWidth() {
    // The width of all cumuled pages with scale factor applied
    return pageOriginalWidth() * getPagesCount()
}

// =========
//  ACTIONS
// =========

function initReader(){
    moveReaderDisplayToZoom(0)
    
    // Smoothly show pictures when they intersect with the viewport
    let visibilityObserver = new IntersectionObserver((entries, observer) => {
        entries.forEach((entry) => {
            if (entry.isIntersecting) {
                entry.target.style.opacity = 1
                entry.target.style.visibility = "visible"
            } else {
                entry.target.style.opacity = 0
                entry.target.style.visibility = "hidden"
            }
        });
    }, { root: READER_FRAME, rootMargin: "-10px" });
    
    for (var i = 0; i < READER_PAGES.children.length; i++) {
        let img = READER_PAGES.children[i];
        img.style.width = 100 / getPagesCount() + "%"
        visibilityObserver.observe(img)
    }
    
    READER_PAGES.style.display = "flex"
    
    setTimeout(() => {
        READER_PAGES.hidden = false
    }, "300")
    
    setTimeout(() => {
        HELP_CONTROLS.style.opacity = null;
    }, DELAY_BEFORE_HIDDING_CONTROLS)
}


function moveReaderDisplayToArea(pageNumber, width, height, posx, posy){
    
    if (width == 0){
        width = pageOriginalWidth()
    }
    
    if (height == 0){
        height = pageOriginalHeight()
    }
    
    zoomRatio = width / height
    
    if (readerFrameRatio() > zoomRatio) {
        // Frame wider than zoom
        var zoomToFrameScaleFactor = pageToFrameScaleFactor(true) * pageOriginalHeight() / height
        var zoomToFrameCenteringOffset = [(READER_FRAME.clientWidth - width * zoomToFrameScaleFactor) / 2, 0]
        updateFocusByWidth(width * zoomToFrameScaleFactor)
    } else {
        var zoomToFrameScaleFactor = pageToFrameScaleFactor(false) * pageOriginalWidth() / width
        var zoomToFrameCenteringOffset = [0, (READER_FRAME.clientHeight - height * zoomToFrameScaleFactor) / 2]
        updateFocusByHeight(height * zoomToFrameScaleFactor)
    }
    
    previousPagesOffset = pageOriginalWidth() * (pageNumber - 1) * zoomToFrameScaleFactor
    
    READER_PAGES.style.width = totalPagesWidth() * zoomToFrameScaleFactor + "px"
    READER_PAGES.style.height = pageOriginalHeight() * zoomToFrameScaleFactor + "px"
    
    READER_PAGES.style.left = (- posx * zoomToFrameScaleFactor + zoomToFrameCenteringOffset[0] - previousPagesOffset) + "px"
    READER_PAGES.style.top = (- posy * zoomToFrameScaleFactor + zoomToFrameCenteringOffset[1]) + "px"
    
    CURRENT_PAGE = pageNumber
    CURRENT_WIDTH = width
    CURRENT_HEIGHT = height
    CURRENT_X = posx
    CURRENT_Y = posy
}


function moveReaderDisplayToPage(pageNumber) {
    moveReaderDisplayToArea(pageNumber, 0, 0, 0, 0)
}

function moveReaderDisplayToZoom(index) {
    
    moveReaderDisplayToArea(zooms[index][0], zooms[index][1], zooms[index][2], zooms[index][3], zooms[index][4])
    
    CURRENT_ZOOM = index
}

function updateFocusByWidth(width){
    
    side_width = (READER_FRAME.clientWidth - width) / 2
    
    FOCUS_OVERLAY.style.gridTemplateColumns = side_width +"px auto " + side_width + "px"
    FOCUS_OVERLAY.style.gridTemplateRows = "0px auto 0px";
}

function updateFocusByHeight(height){
    
    side_width = (READER_FRAME.clientHeight - height) / 2
    
    FOCUS_OVERLAY.style.gridTemplateRows = side_width +"px auto " + side_width + "px"
    FOCUS_OVERLAY.style.gridTemplateColumns = "0px auto 0px";
}

function moveReader(to_next, move_page) {
    
    if (move_page){
        
        if (IS_PAGE_MODE){
            if (to_next && CURRENT_PAGE < getPagesCount()) {
                moveReaderDisplayToPage(CURRENT_PAGE + 1)
                IS_PAGE_MODE = true
            }
            
            else if (!to_next && CURRENT_PAGE > 1) {
                moveReaderDisplayToPage(CURRENT_PAGE - 1)
                IS_PAGE_MODE = true
            }
        }
        
        else {
            
            if (to_next && CURRENT_PAGE < getPagesCount()) {
                moveReaderDisplayToPage(CURRENT_PAGE + 1)
                IS_PAGE_MODE = true
            }
                
            else {
                moveReaderDisplayToPage(CURRENT_PAGE)
                IS_PAGE_MODE = true
            }
            
        }
    
    } else {
        
        if (IS_PAGE_MODE){
            
            if (to_next) {
                moveReaderDisplayToZoom(getFirstZoomOfPage(CURRENT_PAGE))
                IS_PAGE_MODE = false
            }
            else {
                if (CURRENT_PAGE == 1) {
                    moveReaderDisplayToZoom(0)
                    IS_PAGE_MODE = false
                } else {
                    moveReaderDisplayToZoom(getLastZoomOfPage(CURRENT_PAGE - 1))
                    IS_PAGE_MODE = false
                }
            }
            
        } else {
            
            if (to_next && CURRENT_ZOOM < zooms.length - 1) {
                moveReaderDisplayToZoom(CURRENT_ZOOM + 1)
                IS_PAGE_MODE = false
            }
            
            else if (!to_next && CURRENT_ZOOM > 0) {
                moveReaderDisplayToZoom(CURRENT_ZOOM - 1)
                IS_PAGE_MODE = false
            }
            
        }
    }
    
}


// =============
//   CALLBACKS
// =============

function handleKeyPress(key, has_shift){
    
    if (key == MOVE_NEXT) {
        moveReader(true, has_shift)
    }
    
    else if (key == MOVE_BACK) {
        moveReader(false, has_shift)
    }
    
    else if (key.toUpperCase() == TOGGLE_FULLSCREEN){
        if (document.fullscreenElement == null){
            READER_FRAME.requestFullscreen();
        } else {
            document.exitFullscreen();
        }
        
    }

}

function handleMouseWhell(deltaY){
    
    if (MOUSEWHELL_WAIT){
        return
    } else {
        MOUSEWHELL_WAIT = true
        setTimeout(() => {
            MOUSEWHELL_WAIT = false
        }, MOUSEWHELL_MIN_DELAY)
    }
    
    if (deltaY > 0) {
        moveReader(true, false)
    }
    
    else {
        moveReader(false, false)
    }
}

// ======
//  INIT
// ======

window.addEventListener("load", (event) => {
  initReader()
});

addEventListener("resize", (event) => {
    moveReaderDisplayToArea(CURRENT_PAGE, CURRENT_WIDTH, CURRENT_HEIGHT, CURRENT_X, CURRENT_Y)
});

addEventListener("keydown", (event) => {
    handleKeyPress(event.key, event.shiftKey)
});

addEventListener("wheel", (event) => {
    handleMouseWhell(event.deltaY)
});