const VK_PATTERN = (new TextEncoder()).encode("vkDestroyInstance");
const YUZU_PATTERN = (new TextEncoder()).encode("yuzu Emulator");

addEventListener("load", () => {
    const input = document.getElementById("input");
    const button = document.getElementById("upload");

    input.addEventListener("change", (e) => {
        if (e.target.files.length) {
            handleFile(e.target.files[0]);
        }
    });

    button.addEventListener("click", () => input.click());
    button.addEventListener("drop", (e) => {
        e.preventDefault();
        button.classList.remove("dragover");
        if (e.dataTransfer.files.length) {
            handleFile(e.dataTransfer.files[0]);
        }
    });
    button.addEventListener("dragover", (e) => {
        e.preventDefault();
        button.classList.add("dragover");
    });
    button.addEventListener("dragleave", (e) => {
        button.classList.remove("dragover");
    });
});

/**
 * @param {File} file 
 */
function handleFile(file) {
    const filename = file.name ?? "yuzu.exe";
    const reader = new FileReader();
    reader.onload = (e) => {
        const buff = e.target.result;
        const view = new DataView(buff);

        const patternLen = VK_PATTERN.byteLength;
        const buffLen = buff.byteLength;

        // Find the pattern
        let foundIndex = -1;
        for (let i = 0; i <= buffLen - patternLen; i++) {
            let found = true;
            for (let j = 0; j < patternLen; j++) {
                if (view.getUint8(i + j) !== VK_PATTERN[j]) {
                    found = false;
                    break;
                }
            }

            if (found) {
                foundIndex = i;
                break;
            }
        }

        if (foundIndex == -1) {
            console.error("Could not find pattern in file");
            alert("Could not find pattern in file");
            return;
        }

        // Walk backwards until we hit the start of the Emulator string
        let startIndex = -1;
        let emuLen = 0;
        for (let i = foundIndex - 2;; i--) { // skip over first 0 byte right before current index
            if (view.getUint8(i) == 0) {
                startIndex = i + 1;
                break;
            }
            emuLen++;
        }

        const yuzuLen = YUZU_PATTERN.byteLength;
        if (emuLen < yuzuLen) {
            console.error("Cannot patch emulator with smaller default name then yuzu");
            alert("Cannot patch emulator with smaller default name then yuzu");
            return;
        }

        if (emuLen == yuzuLen) {
            let isYuzu = true;
            for (let i = 0; i < emuLen; i++) {
                if (view.getUint8(startIndex + i) != YUZU_PATTERN[i]) {
                    isYuzu = false;
                    break;
                }
            }

            if (isYuzu) {
                console.error("Either this is an already patched fork or its real yuzu");
                alert("Either this is an already patched fork or its real yuzu");
                return;
            }
        }

        for (let i = 0; i < emuLen; i++) {
            view.setUint8(startIndex + i, YUZU_PATTERN[i] || 0);
        }

        const blobPatched = new Blob([buff]);
        saveAs(blobPatched, filename.replace(".exe", "_patched.exe"));
    }
    reader.readAsArrayBuffer(file);
}