window.fairchild_bios1 = { size: 0x400, byte1: 0x70 };
window.fairchild_bios2 = { size: 0x400, byte1: 0x04 };
window.fairchild_cart = { byte1: 0x55 };
window.fairchild_transfer_active = false;
// Load one rom from file to javascript
window.fairchild_load_rom = function(input) {
    var target = window[input.id];

    var reader = new FileReader();
    reader.addEventListener("loadend", function() {
        var data = new Uint8Array(reader.result);
        if ((target.size && data.length != target.size) ||
            (target.byte1 && data[0] != target.byte1)) {
            if (!confirm("This file doesn't look right, use it anyway?")) {
                input.value = ''; // resets files
                return;
            }
        }

        target.data = data;
        window.fairchild_update(target);
    });
    reader.readAsArrayBuffer(input.files[0]);
}
// Enable/disable UI & send to pico8 based on state
window.fairchild_update = function(lastUpdated) {
    var cartElem = document.getElementById('fairchild_cart');
    var noCartElem = document.getElementById('fairchild_nocart');
    var hasBios = window.fairchild_bios1.data && window.fairchild_bios2.data;
    var hasCart = hasBios && window.fairchild_cart.data
    cartElem.disabled = !hasBios;
    noCartElem.disabled = !hasBios;
    if (hasCart && lastUpdated == window.fairchild_cart) {
        window.fairchild_send_to_pico8(true);
    }
}
// Send the roms from javascript to pico8 cart
window.fairchild_send_to_pico8 = function(withCart) {
    var elem = document.getElementById(withCart ? 'fairchild_cart' : 'fairchild_nocart');
    elem.insertAdjacentHTML('afterend', "<b id='fairchild_loading'>Loading... (Make sure pico8 is running!)</b>");

    var endLoading = function() {
        var loadingELem = document.getElementById('fairchild_loading');
        loadingELem.parentNode.removeChild(loadingELem);
    };

    if (window.fairchild_transfer_active) {
        alert("Error - Transfer already active!");
        return;
    }

    window.fairchild_send_rom_to_pico8(window.fairchild_bios1.data, 0x0, function () {
        window.fairchild_send_rom_to_pico8(window.fairchild_bios2.data, 0x400, function () {
            if (withCart) {
                window.fairchild_send_rom_to_pico8(window.fairchild_cart.data, 0x800, endLoading, true);
            } else {
                window.fairchild_send_rom_to_pico8([0, 0], 0x800, endLoading, true); // empty cart header
            }
        });
    });
}
// Send one rom from javascript to pico8 cart
window.fairchild_send_rom_to_pico8 = function(data, targetAddr, nextCallback, endTransfer) {
    if (!window.fairchild_transfer_active) {
        window.fairchild_transfer_active = true;
        // Init gpio array, for transfering data to pico8
        window.pico8_gpio = Array(128);
        window.pico8_gpio[0] = 0xca; // request transfer
    }

    var gpio = window.pico8_gpio;
    var index = 0;
    var interval;
    interval = setInterval(function () {
        if (gpio[0] >= 0xc0) { // 0xca/0xcb
            return; // pico8 cart didn't process the last block (or request) yet, wait for next interval
        }

        if (index < data.length) { // more data to transfer
            gpio[1] = Math.min(data.length - index, 0x7c); // block size
            gpio[2] = (targetAddr + index) & 0xff; // target addr (low)
            gpio[3] = ((targetAddr + index) >> 8) & 0xff; // target addr (high)
            for (var i = 0; i < gpio[1]; i++) {
                gpio[4 + i] = data[index++]; // block data
            }
            gpio[0] = 0xcb; // block is now valid
        } else if (endTransfer && gpio[0] != 1) { // end of transfer
            gpio[1] = 0; // end of transfer
            gpio[0] = 0xcb; // end-of-transfer block is now valid
            // this will be acknoledged by pico8 with gpio[0] == 1, so we won't re-enter this case again
        } else {
            clearInterval(interval)
            if (endTransfer) { window.fairchild_transfer_active = false; }
            if (nextCallback) { nextCallback(); }
        }
    }, 1);
}
document.body.insertAdjacentHTML('beforeend',
    "<div style='position:fixed;left:0;bottom:0'>" +
    "Step 1: Load Bios #1 (SL31253 or SL90025):<br> <input id='fairchild_bios1' type='file' onchange='fairchild_load_rom(this)'> <br>" +
    "Step 2: Load Bios #2 (SL31254):<br> <input id='fairchild_bios2' type='file' onchange='fairchild_load_rom(this)'> <br>" +
    "Step 3: Load Cart:<br> <input id='fairchild_cart' type='file' onchange='fairchild_load_rom(this)' disabled> <br>" +
    "Or just <button id='fairchild_nocart' onclick='fairchild_send_to_pico8(false)' disabled>Run Bios</button>" +
    "</div>"
);