import wasmInit, {
    CursorPosition as wasmCursorPosition,
    reconcile as wasmReconcile,
    TextWithCursors as wasmTextWithCursors,
    TextWithHistory as wasmTextWithHistory,
    BuiltinTokenizer,
    reconcileWithHistory as wasmReconcileWithHistory,
    History,
    InitInput,
} from "reconcile";

export interface TextWithCursors {
    /** The document's entire content */
    text: string;
    /** List of cursor positions, can be null or undefined if there are no cursors */
    cursors: null | undefined | CursorPosition[];
}

/**
 * Represents a cursor position with a unique identifier.
 */
export interface CursorPosition {
    /** Unique identifier for the cursor */
    id: number;
    /** Character position in the text, 0-based */
    position: number;
}

export interface TextWithCursorsAndHistory {
    /** The document's entire content */
    text: string;
    /** List of cursor positions, can be null or undefined if there are no cursors */
    cursors: null | undefined | CursorPosition[];
    /** List of operations leading to `text` from the 3 ancestors */
    history: TextWithHistory[];
}

export interface TextWithHistory {
    /** Span of text associated with the historical opearion */
    text: string;
    /** Origin of the `text` span */
    history: History;
}

/**
 * Supported tokenizer types for text processing.
 */
export type Tokenizer = "word" | "character";

let isInitialised = false;

const UNINITIALISED_MODULE_ERROR =
    "Reconcile module has not been initialized. Please call init() before using any other functions.";

/**
 * Initializes the WASM module for text reconciliation.
 * Must be called before using any other functions.
 *
 * The function is idempotent.
 *
 * @param content - Optional initialization input for the WASM module during testing.
 * @returns Promise that resolves when initialization is complete
 */
export async function init(content?: InitInput) {
    if (isInitialised) {
        return;
    }

    await wasmInit(content);

    isInitialised = true;
}

/**
 * Merges three versions of text (original, left, right) and cursor positions.
 *
 * @param original - The original/base version of the text
 * @param left - The left version of the text, either as string or TextWithCursors
 * @param right - The right version of the text, either as string or TextWithCursors
 * @param tokenizer - The tokenization strategy to use (default: "Word")
 * @returns The reconciled text with merged cursor positions
 */
export function reconcile(
    original: string,
    left: string | TextWithCursors,
    right: string | TextWithCursors,
    tokenizer: BuiltinTokenizer = "Word"
): TextWithCursors {
    if (!isInitialised) {
        throw new Error(UNINITIALISED_MODULE_ERROR);
    }

    const leftCursor = toWasmTextWithCursors(left);
    const rightCursor = toWasmTextWithCursors(right);

    const result = wasmReconcile(original, leftCursor, rightCursor, tokenizer);

    leftCursor.free();
    rightCursor.free();

    const jsResult = toTextWithCursors(result);
    result.free();

    return jsResult;
}

/**
 * Merges three versions of text and returns the result with historical information.
 *
 * Calculating the `history` is somewhat more expensive, otherwise this function behaves like `reconcile`.
 *
 * @param original - The original/base version of the text
 * @param left - The left version of the text, either as string or TextWithCursors
 * @param right - The right version of the text, either as string or TextWithCursors
 * @param tokenizer - The tokenization strategy to use (default: "Word")
 * @returns The reconciled text with cursor positions and history of changes
 */
export function reconcileWithHistory(
    original: string,
    left: string | TextWithCursors,
    right: string | TextWithCursors,
    tokenizer: BuiltinTokenizer = "Word"
): TextWithCursorsAndHistory {
    if (!isInitialised) {
        throw new Error(UNINITIALISED_MODULE_ERROR);
    }

    const leftCursor = toWasmTextWithCursors(left);
    const rightCursor = toWasmTextWithCursors(right);

    const result = wasmReconcileWithHistory(
        original,
        leftCursor,
        rightCursor,
        tokenizer
    );

    leftCursor.free();
    rightCursor.free();

    const jsResult = toTextWithCursors(result);
    const history = result.history().map(toTextWithHistory);
    result.free();

    return {
        ...jsResult,
        history,
    };
}

function toWasmTextWithCursors(
    text: string | TextWithCursors
): wasmTextWithCursors {
    const isInputString = typeof text == "string";
    const leftText = isInputString ? text : text.text;
    const leftCursors = isInputString ? [] : text.cursors ?? [];

    return new wasmTextWithCursors(
        leftText,
        leftCursors.map(toWasmCursorPosition)
    );
}

function toWasmCursorPosition({
    id,
    position,
}: CursorPosition): wasmCursorPosition {
    return new wasmCursorPosition(id, position);
}

function toTextWithCursors(
    textWithCursor: wasmTextWithCursors
): TextWithCursors {
    return {
        text: textWithCursor.text(),
        cursors: textWithCursor.cursors().map(toCursorPosition),
    };
}

function toCursorPosition(cursor: wasmCursorPosition): CursorPosition {
    return {
        id: cursor.id(),
        position: cursor.characterPosition(),
    };
}

function toTextWithHistory(
    textWithHistory: wasmTextWithHistory
): TextWithHistory {
    return {
        text: textWithHistory.text(),
        history: textWithHistory.history(),
    };
}