class CommandBar extends HTMLElement {
    static observedAttributes = [
        "presented"
    ];

    #shadowRoot;
    rootElement;
    inputElement;
    rulerElement;
    scrollPositionElement;

    #leader = ":";

    #commandExecutor = new CommandExecutor();
    #indexOfLastShownCommandFromHistory = null;
    #shouldPresentAfterConnection = false;

    constructor() {
        super();
        this.#shadowRoot = this.attachShadow({ mode: "closed" });
    }

    get #elementHasPresentedAttribute() {
        return this.rootElement.hasAttribute("presented");
    }

    // MARK: Presentation

    show(options) {
        if (options === undefined || options === null) {
            options = {
                leader: null,
            };
        }

        const inputElement = this.inputElement;
        if (inputElement) {
            inputElement.value = options.leader ? options.leader.toString() : "";
            inputElement.focus();
        }

        this.rootElement?.setAttribute("presented", "");
    }

    hide() {
        if (!this.#elementHasPresentedAttribute) {
            return;
        }

        const inputElement = this.inputElement;
        if (inputElement) {
            inputElement.value = "";
            inputElement.blur();
        }

        this.rootElement?.removeAttribute("presented");
    }

    // MARK: Command Handling

    executeCommand(commandString) {
        this.#indexOfLastShownCommandFromHistory = null;

        try {
            const command = Command.parse(commandString);
            this.#commandExecutor.executeCommand(command);
        } catch (e) {
            console.error("Error executing command:", e);
        }
    }

    addCommandHandler(name, handler) {
        this.#commandExecutor.addHandler(name, handler);
    }

    updateRuler(x, y) {
        this.rulerElement.innerText = `${x || 0},${y || 0}`;
    }

    /**
     * Compute the percentage that the document is scrolled relative to the full length
     * of the document. This algorithm is largely cribbed from neovim's sources.
     *
     * @param scrollingElement  The element on which to track scrolling
     */
    updateScrollPosition(scrollingElement) {
        if (!this.scrollPositionElement) {
            return;
        }

        const scrollY = scrollingElement.scrollTop;
        const scrollHeight = scrollingElement.clientHeight;
        const totalHeight = scrollingElement.scrollHeight;
        const bottomY = scrollY + scrollHeight;

        const pixelLinesBelow = totalHeight - bottomY;

        const scrollPercentage = Math.round(scrollY * 100 / (scrollY + pixelLinesBelow));

        let newScrollPositionText;
        if (pixelLinesBelow <= 0) {
            newScrollPositionText = "Bot";
        } else if (scrollY <= 0) {
            newScrollPositionText = "Top";
        } else {
            newScrollPositionText = `${scrollPercentage}%`;
        }

        const currentScrollPositionText = this.scrollPositionElement.innerText;
        const scrollPositionIsEmpty = !currentScrollPositionText || currentScrollPositionText.length === 0;

        if (scrollPositionIsEmpty || newScrollPositionText != currentScrollPositionText) {
            this.scrollPositionElement.innerText = newScrollPositionText;
        }
    }

    // MARK: Custom Element

    connectedCallback() {
        let template = document.getElementById("command-bar-template");
        console.assert(template, "Couldn't find CommandBar component template in the document");

        const shadowRoot = this.#shadowRoot;
        shadowRoot.appendChild(template.content.cloneNode(true));

        this.rootElement = shadowRoot.querySelector(".command-bar");
        this.rulerElement = shadowRoot.querySelector(".command-bar__ruler");
        this.scrollPositionElement = shadowRoot.querySelector(".command-bar__scrollposition");

        const inputElement = shadowRoot.querySelector(".command-bar__input");
        this.inputElement = inputElement;

        this.updateRuler();
        this.updateScrollPosition(document.scrollingElement);

        inputElement.addEventListener("input", this.handleInputEvent.bind(this));
        inputElement.addEventListener("keydown", this.handleInputKeydownEvent.bind(this));

        document.addEventListener("keypress", event => this.handleDocumentKeypressEvent(event));
        document.addEventListener("mousemove", event => this.updateRuler(event.x, event.y));
        document.addEventListener("scroll", () => this.updateScrollPosition(document.scrollingElement));

        if (this.#shouldPresentAfterConnection) {
            this.show({ leader: this.#leader });
            this.#shouldPresentAfterConnection = false;
        }
    }

    attributeChangedCallback(name, _oldValue, newValue) {
        if (name === "presented") {
            const rootElement = this.rootElement;
            if (rootElement) {
                rootElement.setAttribute("presented", newValue !== undefined && newValue !== null);
            } else {
                // The CommandBar custom element hasn't been connected to a document yet.
                this.#shouldPresentAfterConnection = true;
            }
        }
    }

    // MARK: Event Listeners

    handleInputEvent(event) {
        const target = event.target;
        if (!target.value.length) {
            this.hide();
        }
    }

    handleInputKeydownEvent(event) {
        const target = event.target;

        switch (event.key) {
            case "Escape": {
                event.preventDefault();
                target.value = "";
                this.hide();
                break;
            }
            case "Enter": {
                event.preventDefault();

                // Trim the leader
                let command = target.value.substring(1);
                if (command.length) {
                    this.executeCommand(command);
                }

                target.value = this.#leader;
                break;
            }
            case "ArrowUp": {
                event.preventDefault();

                let historyIndex = this.#indexOfLastShownCommandFromHistory;
                if (historyIndex === null) {
                    historyIndex = this.#commandExecutor.historyLength - 1;
                } else {
                    historyIndex--;
                }

                if (historyIndex >= 0) {
                    const commandFromHistory = this.#commandExecutor.commandAtHistoryIndex(historyIndex);
                    target.value = this.#leader + commandFromHistory.originalString;
                    this.#indexOfLastShownCommandFromHistory = historyIndex;
                }

                break;
            }
            case "ArrowDown": {
                event.preventDefault();

                const historyLength = this.#commandExecutor.historyLength;

                let historyIndex = this.#indexOfLastShownCommandFromHistory;
                if (historyIndex === null) {
                    historyIndex = historyLength - 1;
                }
                historyIndex++;

                if (historyIndex < historyLength) {
                    const commandFromHistory = this.#commandExecutor.commandAtHistoryIndex(historyIndex);
                    target.value = this.#leader + commandFromHistory.originalString;
                    this.#indexOfLastShownCommandFromHistory = historyIndex;
                } else {
                    target.value = this.#leader;
                    this.#indexOfLastShownCommandFromHistory = null;
                }

                break;
            }
        }
    }

    handleDocumentKeypressEvent(event) {
        if (event.repeat) {
            return;
        }

        if (event.key == "Escape") {
            this.hide();
        }

        const currentTarget = event.currentTarget;
        if (currentTarget === this.inputElement) {

            return;
        }

        switch (event.key) {
            case this.#leader:
                this.show();
                break;
            case "Escape":
                this.hide();
                break;
            default:
                break;
        }
    }
}

class CommandExecutor {
    #history = [];
    handlers = new Map();

    addHandler(handler) {
        this.handlers.set(handler.name, handler);
    }

    executeCommand(command) {
        this.appendCommandToHistory(command);

        const handler = this.#handlerForCommand(command);
        if (!handler) {
            throw new Error(`No handler for '${command.verb.valueOf()}' command`);
        }

        let result;
        try {
            result = handler.handler(command);
        } catch (e) {
            result = null;
        }

        if (result !== undefined && !result) {
            console.error(`Command failed: ${command}`);
        }
    }

    #handlerForCommand(command) {
        const verb = command.verb.valueOf();
        return this.handlers.get(verb);
    }

    // MARK: History

    get historyLength() {
        return this.#history.length;
    }

    appendCommandToHistory(command) {
        this.#history.push(command);
    }

    commandAtHistoryIndex(index) {
        return this.#history[index];
    }
}

class ParseCommandError extends SyntaxError { }

class Parameter {
    name;
    value;

    constructor(name, value) {
        if (!name instanceof NameTerm) {
            throw new TypeError("Parameter name must be a NameTerm");
        }

        this.name = name;
        this.value = value;
    }

    toString() {
        return this.value ? `${this.name}=${this.value}` : `${this.name}`;
    }

    valueOf() {
        if (this.value !== undefined) {
            return this.value.valueOf();
        } else {
            return this.name;
        }
    }
}

class Term {
    stringValue;

    constructor(stringValue) {
        this.stringValue = stringValue;
    }

    toString() {
        return `Term[${stringValue}]`;
    }

    valueOf() {
        return this.stringValue;
    }
}

class NumberTerm extends Term {
    value;

    constructor(stringValue) {
        super(stringValue);

        const parsedValue = parseInt(stringValue);
        if (isNaN(parsedValue)) {
            throw new TypeError("Number value is not a valid number");
        }

        this.value = parsedValue;
    }

    valueOf() {
        return this.value;
    }

    toString() {
        return `Number[${this.value}]`;
    }
}

class NameTerm extends Term {
    static regex = /[-\w]+/;

    constructor(stringValue) {
        if (!NameTerm.regex.test(stringValue)) {
            throw new TypeError("Name must be string with non-zero length");
        }

        super(stringValue);
    }

    toString() {
        return `Name[${this.stringValue}]`;
    }
}

class Command {
    static stringRegex = /'[^'"]*'|"[^'"]*"/;
    static whitespaceRegex = /\s+/;

    static parse(commandString) {
        const terms = commandString.split(Command.whitespaceRegex).filter(s => !!s);

        if (terms.length < 1) {
            return null;
        }

        let verb;
        try {
            verb = new NameTerm(terms[0]);
        } catch {
            throw new ParseCommandError(`Invalid verb: ${verb}`);
        }

        const parameters = terms.slice(1).map(t => {
            const [nameString, valueString, ...rest] = t.split("=");

            if (rest.length > 0) {
                throw new ParseCommandError(`Invalid parameter: ${t}`);
            }

            let name;
            try {
                name = new NameTerm(nameString);
            } catch {
                throw new ParseCommandError(`Invalid parameter name: ${t}`);
            }

            let value;
            if (valueString) {
                for (const termClass of [NameTerm, NumberTerm]) {
                    try {
                        value = new termClass(valueString);
                        break;
                    } catch {
                        continue;
                    }
                }

                if (!value) {
                    throw new ParseCommandError(`Invalid parameter value: ${t}`);
                }
            }

            return new Parameter(name, value);
        });

        return new Command(commandString, verb, parameters);
    }

    originalString;
    verb;
    parameters = []

    constructor(originalString, verb, parameters) {
        if (!verb instanceof String) {
            throw new TypeError("Command verb must be a string");
        }

        this.originalString = originalString;
        this.verb = verb;
        this.parameters = parameters;
    }

    parameter(nameOrIndex) {
        if (typeof nameOrIndex === "string" || nameOrIndex instanceof String) {
            return this.parameters.find(p => p.name == nameOrIndex);
        } else if (nameOrIndex instanceof Number) {
            return this.parameters[nameOrIndex].valueOf();
        }

        return null;
    }

    toString() {
        return `Command: {verb: "${this.verb.toString()}", parameters: [${this.parameters.join(", ")}] }`;
    }
}

window.customElements.define("command-bar", CommandBar);