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// Perform a depth-first walk of a tree, ONLY doing the descent (visit)
//
// This uses a stack rather than recursion, so that it can handle deeply
// nested trees without call stack overflows. (My kingdom for proper TCO!)
//
// This is only used for cases where leave() is not specified.
//
// a
// +-- b
// | +-- 1
// | +-- 2
// +-- c
// +-- 3
// +-- 4
//
// Expect:
// visit a
// visit b
// visit 1
// visit 2
// visit c
// visit 3
// visit 4
//
// stack.push(tree)
// while stack not empty
// pop T from stack
// VISIT(T)
// get children C of T
// push each C onto stack
const depth = ({
visit,
filter,
getChildren,
tree,
}) => {
const stack = []
const seen = new Map()
const next = () => {
while (stack.length) {
const node = stack.pop()
const res = visitNode(node)
if (isPromise(res)) {
return res.then(() => next())
}
}
return seen.get(tree)
}
const visitNode = (visitTree) => {
if (seen.has(visitTree)) {
return seen.get(visitTree)
}
seen.set(visitTree, null)
const res = visit ? visit(visitTree) : visitTree
if (isPromise(res)) {
const fullResult = res.then(resThen => {
seen.set(visitTree, resThen)
return kidNodes(visitTree)
})
seen.set(visitTree, fullResult)
return fullResult
} else {
seen.set(visitTree, res)
return kidNodes(visitTree)
}
}
const kidNodes = (kidTree) => {
const kids = getChildren(kidTree, seen.get(kidTree))
return isPromise(kids) ? kids.then(processKids) : processKids(kids)
}
const processKids = (kids) => {
kids = (kids || []).filter(filter)
stack.push(...kids)
}
stack.push(tree)
return next()
}
const isPromise = p => p && typeof p.then === 'function'
module.exports = depth