// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

import { Dispatcher } from "agent-dispatcher";
import { CompletionDirection } from "@typeagent/agent-sdk";
import { SearchMenu } from "./search";
import { SearchMenuItem } from "./searchMenuUI/searchMenuUI";
import {
    ICompletionDispatcher,
    ISearchMenu,
    PartialCompletionSession,
} from "./partialCompletionSession";

import registerDebug from "debug";
import { ExpandableTextArea } from "./chat/expandableTextArea";

const debug = registerDebug("typeagent:shell:partial");
const debugError = registerDebug("typeagent:shell:partial:error");

function getLeafNode(node: Node, offset: number) {
    let curr = 0;
    let currNode: Node | undefined = node;
    while (currNode !== undefined) {
        const childNodes = currNode.childNodes;
        if (childNodes.length === 0) {
            if (
                currNode.textContent === null ||
                currNode.textContent.length < offset - curr
            ) {
                return undefined;
            }

            return { node: currNode, offset: offset - curr };
        }

        currNode = undefined;
        for (const child of childNodes) {
            if (child.textContent === null) {
                continue;
            }
            const len = child.textContent.length;
            if (curr + len >= offset) {
                currNode = child;
                break;
            }
            curr += len;
        }
    }
    return undefined;
}

// Architecture: docs/architecture/completion.md — §6 Shell — DOM Adapter
export class PartialCompletion {
    private readonly searchMenu: SearchMenu;
    private readonly session: PartialCompletionSession;
    public closed: boolean = false;
    // Track previous input to determine direction: shorter = backspace
    // ("backward"), longer/same = forward action.
    private previousInput: string = "";

    private readonly cleanupEventListeners: () => void;
    constructor(
        private readonly container: HTMLDivElement,
        private readonly input: ExpandableTextArea,
        dispatcher: Dispatcher,
        private readonly inline: boolean = true,
    ) {
        this.searchMenu = new SearchMenu(
            (item) => {
                this.handleSelect(item);
            },
            this.inline,
            this.input.getTextEntry(),
        );

        // Wrap SearchMenu to implement ISearchMenu (same shape, just typed).
        const menuAdapter: ISearchMenu = this.searchMenu;
        // Wrap Dispatcher to implement ICompletionDispatcher.
        const dispatcherAdapter: ICompletionDispatcher = dispatcher;

        this.session = new PartialCompletionSession(
            menuAdapter,
            dispatcherAdapter,
        );

        const selectionChangeHandler = () => {
            debug("Partial completion update on selection changed");
            this.update(false);
        };
        document.addEventListener("selectionchange", selectionChangeHandler);
        this.cleanupEventListeners = () => {
            document.removeEventListener(
                "selectionchange",
                selectionChangeHandler,
            );
        };

        if (document.activeElement === this.input.getTextEntry()) {
            // If the input is already focused, we need to update immediately.
            this.update(false);
        }
    }

    public update(contentChanged: boolean) {
        if (this.closed) {
            throw new Error("Using a closed PartialCompletion");
        }
        if (contentChanged) {
            // Normalize the input text to ensure selection at end is correct.
            this.input.getTextEntry().normalize();
        }
        if (!this.isSelectionAtEnd(contentChanged)) {
            this.session.hide();
            return;
        }
        const input = this.getCurrentInputForCompletion();
        debug(`Partial completion input: '${input}'`);

        // Only use "backward" when the user is genuinely backspacing:
        // the new input must be a strict prefix of the previous input.
        const direction: CompletionDirection =
            input.length < this.previousInput.length &&
            this.previousInput.startsWith(input)
                ? "backward"
                : "forward";
        this.previousInput = input;

        this.session.update(
            input,
            (prefix) => this.getSearchMenuPosition(prefix),
            direction,
        );
    }

    public hide() {
        this.session.hide();
    }

    public close() {
        this.closed = true;
        this.session.hide();
        this.cleanupEventListeners();
    }

    private getCurrentInput() {
        // Strip inline ghost text if present
        const textEntry = this.input.getTextEntry();
        const ghost = textEntry.querySelector(".inline-ghost");
        if (ghost) {
            const ghostText = ghost.textContent ?? "";
            const raw = textEntry.textContent ?? "";
            return raw.slice(0, raw.length - ghostText.length);
        }
        return textEntry.textContent ?? "";
    }

    private getCurrentInputForCompletion() {
        // Normalize non-breaking spaces (U+00A0) that contenteditable
        // inserts for trailing whitespace.  When the user types a
        // character after a trailing \u00A0, Chromium may convert it
        // back to a regular space — breaking the session's startsWith
        // anchor check and causing unnecessary re-fetches.
        return this.getCurrentInput()
            .trimStart()
            .replace(/\u00a0/g, " ");
    }

    private isSelectionAtEnd(trace: boolean = false) {
        const s = document.getSelection();
        if (!s || s.rangeCount !== 1) {
            if (trace) {
                debug(
                    `Partial completion skipped: invalid selection count ${s?.rangeCount}`,
                );
            }
            return false;
        }
        const r = s.getRangeAt(0);
        if (!r.collapsed) {
            if (trace) {
                debug(`Partial completion skipped: non-collapsed range`);
            }
            return false;
        }

        const textEntry = this.input.getTextEntry();
        const ghost = textEntry.querySelector(".inline-ghost");

        if (ghost) {
            // With inline ghost text, "at end" means the cursor is right
            // before the ghost span. setCursorBeforeGhost places the cursor
            // using setStartBefore(ghost), so endContainer=textEntry and
            // endOffset=ghost's child index.
            if (r.endContainer === textEntry) {
                const ghostIndex = Array.from(textEntry.childNodes).indexOf(
                    ghost as ChildNode,
                );
                if (r.endOffset === ghostIndex) {
                    return true;
                }
            }
            // Also handle: cursor at the end of a text node that is the
            // immediate previous sibling of the ghost span.
            if (r.endContainer.nodeType === Node.TEXT_NODE) {
                if (
                    r.endContainer.nextSibling === ghost &&
                    r.endOffset === (r.endContainer.textContent?.length ?? 0)
                ) {
                    return true;
                }
            }
            if (trace) {
                debug(
                    `Partial completion skipped: selection not at end (ghost present)`,
                );
            }
            return false;
        }

        const endNode = this.input.getSelectionEndNode();
        if (r.endContainer !== endNode) {
            if (trace) {
                debug(`Partial completion skipped: selection not in text area`);
            }
            return false;
        }
        if (r.endOffset !== endNode.textContent?.length) {
            if (trace) {
                debug(`Partial completion skipped: selection not at end`);
            }
            return false;
        }
        return true;
    }

    private getSearchMenuPosition(prefix: string) {
        const textEntry = this.input.getTextEntry();
        let x: number;
        if (textEntry.childNodes.length === 0) {
            x = textEntry.getBoundingClientRect().left;
        } else {
            const offset = this.getCurrentInput().length - prefix.length;
            const leaf = getLeafNode(textEntry, offset);
            if (leaf === undefined) {
                debugError(
                    "Partial completion skipped: unable to determine leaf node",
                );
                return;
            }
            const r = document.createRange();
            r.setStart(leaf.node, leaf.offset);
            r.collapse(true);
            const rects = r.getClientRects();
            if (rects.length !== 1) {
                debugError("Partial completion skipped: invalid rects");
                return;
            }
            x = rects[0].left;
        }

        const { top } = this.container.getBoundingClientRect();
        return { left: x, bottom: window.innerHeight - top };
    }

    private handleSelect(item: SearchMenuItem) {
        debug(`Partial completion selected: ${item.selectedText}`);
        this.searchMenu.hide();

        // Compute the filter prefix relative to the current anchor.
        // Must be read before resetToIdle() clears the session's anchor.
        const currentInput = this.getCurrentInputForCompletion();
        const completionPrefix = this.session.getCompletionPrefix(currentInput);
        if (completionPrefix === undefined) {
            debugError(`Partial completion abort select: prefix not found`);
            return;
        }

        const replaceText =
            item.needQuotes !== false && /\s/.test(item.selectedText)
                ? `"${item.selectedText.replaceAll('"', '\\"')}"`
                : item.selectedText;

        const offset = this.getCurrentInput().length - completionPrefix.length;
        const leafNode = getLeafNode(this.input.getTextEntry(), offset);
        if (leafNode === undefined) {
            debugError(
                "Partial completion abort select: unable to determine leaf node",
            );
            return;
        }
        const endLeafNode = getLeafNode(
            this.input.getTextEntry(),
            offset + completionPrefix.length,
        );
        if (endLeafNode === undefined) {
            debugError(
                "Partial completion abort select: unable to determine end leaf node",
            );
            return;
        }

        const newNode = document.createTextNode(replaceText);
        const r = document.createRange();
        r.setStart(leafNode.node, leafNode.offset);
        r.setEnd(endLeafNode.node, endLeafNode.offset);
        r.deleteContents();
        r.insertNode(newNode);

        // Normalize merges adjacent text nodes so getSelectionEndNode()
        // returns a single text node.  Then place the cursor at its end
        // so isSelectionAtEnd() passes.  Without this, r.collapse(false)
        // leaves endContainer pointing at the parent element, which does
        // not match the deepest-last-child that isSelectionAtEnd() expects.
        const textEntry = this.input.getTextEntry();
        textEntry.normalize();
        const endNode = this.input.getSelectionEndNode();
        const cursorRange = document.createRange();
        cursorRange.setStart(endNode, endNode.textContent?.length ?? 0);
        cursorRange.collapse(true);
        const s = document.getSelection();
        if (s) {
            s.removeAllRanges();
            s.addRange(cursorRange);
        }

        // Make sure the text entry remains focused after replacement.
        textEntry.focus();

        // Reset completion state so the next update requests fresh completions.
        this.session.resetToIdle();

        debug(`Partial completion replaced: ${replaceText}`);

        // Clear previousInput so auto-detection picks "forward" for the
        // post-selection update (the new input won't be a prefix of "").
        this.previousInput = "";
        this.update(false);
    }

    public handleSpecialKeys(event: KeyboardEvent) {
        if (!this.searchMenu.isActive()) {
            return false;
        }
        if (event.key === "Escape") {
            this.searchMenu.hide();
            event.preventDefault();
            return true;
        }
        return this.searchMenu.handleSpecialKeys(event);
    }

    public handleMouseWheel(event: WheelEvent) {
        this.searchMenu.handleMouseWheel(event.deltaY);
    }
}
