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Filename : visit.js
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'use strict';

var identity = require('./nodes/identity.js');

const BREAK = Symbol('break visit');
const SKIP = Symbol('skip children');
const REMOVE = Symbol('remove node');
/**
 * Apply a visitor to an AST node or document.
 *
 * Walks through the tree (depth-first) starting from `node`, calling a
 * `visitor` function with three arguments:
 *   - `key`: For sequence values and map `Pair`, the node's index in the
 *     collection. Within a `Pair`, `'key'` or `'value'`, correspondingly.
 *     `null` for the root node.
 *   - `node`: The current node.
 *   - `path`: The ancestry of the current node.
 *
 * The return value of the visitor may be used to control the traversal:
 *   - `undefined` (default): Do nothing and continue
 *   - `visit.SKIP`: Do not visit the children of this node, continue with next
 *     sibling
 *   - `visit.BREAK`: Terminate traversal completely
 *   - `visit.REMOVE`: Remove the current node, then continue with the next one
 *   - `Node`: Replace the current node, then continue by visiting it
 *   - `number`: While iterating the items of a sequence or map, set the index
 *     of the next step. This is useful especially if the index of the current
 *     node has changed.
 *
 * If `visitor` is a single function, it will be called with all values
 * encountered in the tree, including e.g. `null` values. Alternatively,
 * separate visitor functions may be defined for each `Map`, `Pair`, `Seq`,
 * `Alias` and `Scalar` node. To define the same visitor function for more than
 * one node type, use the `Collection` (map and seq), `Value` (map, seq & scalar)
 * and `Node` (alias, map, seq & scalar) targets. Of all these, only the most
 * specific defined one will be used for each node.
 */
function visit(node, visitor) {
    const visitor_ = initVisitor(visitor);
    if (identity.isDocument(node)) {
        const cd = visit_(null, node.contents, visitor_, Object.freeze([node]));
        if (cd === REMOVE)
            node.contents = null;
    }
    else
        visit_(null, node, visitor_, Object.freeze([]));
}
// Without the `as symbol` casts, TS declares these in the `visit`
// namespace using `var`, but then complains about that because
// `unique symbol` must be `const`.
/** Terminate visit traversal completely */
visit.BREAK = BREAK;
/** Do not visit the children of the current node */
visit.SKIP = SKIP;
/** Remove the current node */
visit.REMOVE = REMOVE;
function visit_(key, node, visitor, path) {
    const ctrl = callVisitor(key, node, visitor, path);
    if (identity.isNode(ctrl) || identity.isPair(ctrl)) {
        replaceNode(key, path, ctrl);
        return visit_(key, ctrl, visitor, path);
    }
    if (typeof ctrl !== 'symbol') {
        if (identity.isCollection(node)) {
            path = Object.freeze(path.concat(node));
            for (let i = 0; i < node.items.length; ++i) {
                const ci = visit_(i, node.items[i], visitor, path);
                if (typeof ci === 'number')
                    i = ci - 1;
                else if (ci === BREAK)
                    return BREAK;
                else if (ci === REMOVE) {
                    node.items.splice(i, 1);
                    i -= 1;
                }
            }
        }
        else if (identity.isPair(node)) {
            path = Object.freeze(path.concat(node));
            const ck = visit_('key', node.key, visitor, path);
            if (ck === BREAK)
                return BREAK;
            else if (ck === REMOVE)
                node.key = null;
            const cv = visit_('value', node.value, visitor, path);
            if (cv === BREAK)
                return BREAK;
            else if (cv === REMOVE)
                node.value = null;
        }
    }
    return ctrl;
}
/**
 * Apply an async visitor to an AST node or document.
 *
 * Walks through the tree (depth-first) starting from `node`, calling a
 * `visitor` function with three arguments:
 *   - `key`: For sequence values and map `Pair`, the node's index in the
 *     collection. Within a `Pair`, `'key'` or `'value'`, correspondingly.
 *     `null` for the root node.
 *   - `node`: The current node.
 *   - `path`: The ancestry of the current node.
 *
 * The return value of the visitor may be used to control the traversal:
 *   - `Promise`: Must resolve to one of the following values
 *   - `undefined` (default): Do nothing and continue
 *   - `visit.SKIP`: Do not visit the children of this node, continue with next
 *     sibling
 *   - `visit.BREAK`: Terminate traversal completely
 *   - `visit.REMOVE`: Remove the current node, then continue with the next one
 *   - `Node`: Replace the current node, then continue by visiting it
 *   - `number`: While iterating the items of a sequence or map, set the index
 *     of the next step. This is useful especially if the index of the current
 *     node has changed.
 *
 * If `visitor` is a single function, it will be called with all values
 * encountered in the tree, including e.g. `null` values. Alternatively,
 * separate visitor functions may be defined for each `Map`, `Pair`, `Seq`,
 * `Alias` and `Scalar` node. To define the same visitor function for more than
 * one node type, use the `Collection` (map and seq), `Value` (map, seq & scalar)
 * and `Node` (alias, map, seq & scalar) targets. Of all these, only the most
 * specific defined one will be used for each node.
 */
async function visitAsync(node, visitor) {
    const visitor_ = initVisitor(visitor);
    if (identity.isDocument(node)) {
        const cd = await visitAsync_(null, node.contents, visitor_, Object.freeze([node]));
        if (cd === REMOVE)
            node.contents = null;
    }
    else
        await visitAsync_(null, node, visitor_, Object.freeze([]));
}
// Without the `as symbol` casts, TS declares these in the `visit`
// namespace using `var`, but then complains about that because
// `unique symbol` must be `const`.
/** Terminate visit traversal completely */
visitAsync.BREAK = BREAK;
/** Do not visit the children of the current node */
visitAsync.SKIP = SKIP;
/** Remove the current node */
visitAsync.REMOVE = REMOVE;
async function visitAsync_(key, node, visitor, path) {
    const ctrl = await callVisitor(key, node, visitor, path);
    if (identity.isNode(ctrl) || identity.isPair(ctrl)) {
        replaceNode(key, path, ctrl);
        return visitAsync_(key, ctrl, visitor, path);
    }
    if (typeof ctrl !== 'symbol') {
        if (identity.isCollection(node)) {
            path = Object.freeze(path.concat(node));
            for (let i = 0; i < node.items.length; ++i) {
                const ci = await visitAsync_(i, node.items[i], visitor, path);
                if (typeof ci === 'number')
                    i = ci - 1;
                else if (ci === BREAK)
                    return BREAK;
                else if (ci === REMOVE) {
                    node.items.splice(i, 1);
                    i -= 1;
                }
            }
        }
        else if (identity.isPair(node)) {
            path = Object.freeze(path.concat(node));
            const ck = await visitAsync_('key', node.key, visitor, path);
            if (ck === BREAK)
                return BREAK;
            else if (ck === REMOVE)
                node.key = null;
            const cv = await visitAsync_('value', node.value, visitor, path);
            if (cv === BREAK)
                return BREAK;
            else if (cv === REMOVE)
                node.value = null;
        }
    }
    return ctrl;
}
function initVisitor(visitor) {
    if (typeof visitor === 'object' &&
        (visitor.Collection || visitor.Node || visitor.Value)) {
        return Object.assign({
            Alias: visitor.Node,
            Map: visitor.Node,
            Scalar: visitor.Node,
            Seq: visitor.Node
        }, visitor.Value && {
            Map: visitor.Value,
            Scalar: visitor.Value,
            Seq: visitor.Value
        }, visitor.Collection && {
            Map: visitor.Collection,
            Seq: visitor.Collection
        }, visitor);
    }
    return visitor;
}
function callVisitor(key, node, visitor, path) {
    if (typeof visitor === 'function')
        return visitor(key, node, path);
    if (identity.isMap(node))
        return visitor.Map?.(key, node, path);
    if (identity.isSeq(node))
        return visitor.Seq?.(key, node, path);
    if (identity.isPair(node))
        return visitor.Pair?.(key, node, path);
    if (identity.isScalar(node))
        return visitor.Scalar?.(key, node, path);
    if (identity.isAlias(node))
        return visitor.Alias?.(key, node, path);
    return undefined;
}
function replaceNode(key, path, node) {
    const parent = path[path.length - 1];
    if (identity.isCollection(parent)) {
        parent.items[key] = node;
    }
    else if (identity.isPair(parent)) {
        if (key === 'key')
            parent.key = node;
        else
            parent.value = node;
    }
    else if (identity.isDocument(parent)) {
        parent.contents = node;
    }
    else {
        const pt = identity.isAlias(parent) ? 'alias' : 'scalar';
        throw new Error(`Cannot replace node with ${pt} parent`);
    }
}

exports.visit = visit;
exports.visitAsync = visitAsync;