// A study's true outline: main points, sub-points under them, and so on (I. / A. / 1. / a.). It is a tree
// of nodes { id, text, ref, chunkId, children } kept on the project as `project.outline`. Every function
// returns a new tree and leaves the one it was given alone.
import { formatChunkReference, makeId } from './bibleUtils.jsx';
import { labelFor, toRoman } from './outlineLabels.js';

export { labelFor, toRoman };

export const MAX_DEPTH = 5; // levels below the main points

export const newNode = (text = '', extra = {}) => ({ id: makeId(), text, ref: '', chunkId: null, children: [], ...extra });

// ---- finding ---------------------------------------------------------------

// Where a node sits: the list of indexes from the top, or null.
export function pathTo(tree, id, base = []) {
  for (let i = 0; i < tree.length; i += 1) {
    if (tree[i].id === id) return [...base, i];
    const deeper = pathTo(tree[i].children, id, [...base, i]);
    if (deeper) return deeper;
  }
  return null;
}

export const getNode = (tree, id) => {
  const path = pathTo(tree, id);
  if (!path) return null;
  return path.reduce((nodes, i, depth) => (depth === path.length - 1 ? nodes[i] : nodes[i].children), tree);
};

// The list of siblings a node is in (a new copy) and its index there, via a path.
function withSiblings(tree, path, change) {
  const [head, ...rest] = path;
  if (rest.length === 0) return change(tree, head);
  return tree.map((n, i) => (i === head ? { ...n, children: withSiblings(n.children, rest, change) } : n));
}

// Depth of the deepest node below `node` (0 when it has no children).
const heightBelow = (node) => (node.children.length === 0 ? 0 : 1 + Math.max(...node.children.map(heightBelow)));

// ---- editing ---------------------------------------------------------------

export const updateNode = (tree, id, patch) => tree.map((n) => (n.id === id ? { ...n, ...patch } : { ...n, children: updateNode(n.children, id, patch) }));

export function addRoot(tree, node) {
  return [...tree, node];
}

export function addAfter(tree, id, node) {
  const path = pathTo(tree, id);
  if (!path) return tree;
  return withSiblings(tree, path, (list, i) => [...list.slice(0, i + 1), node, ...list.slice(i + 1)]);
}

export function addChild(tree, id, node) {
  if (!getNode(tree, id)) return tree;
  return updateChildren(tree, id, (children) => [...children, node]);
}

function updateChildren(tree, id, fn) {
  return tree.map((n) => (n.id === id ? { ...n, children: fn(n.children) } : { ...n, children: updateChildren(n.children, id, fn) }));
}

export function removeNode(tree, id) {
  const path = pathTo(tree, id);
  if (!path) return tree;
  return withSiblings(tree, path, (list, i) => list.filter((_, j) => j !== i));
}

// Makes the node a sub-point of the one just above it (if there is one and there is room).
export function indent(tree, id) {
  const path = pathTo(tree, id);
  if (!path || path[path.length - 1] === 0) return tree;
  const node = getNode(tree, id);
  if (path.length + heightBelow(node) >= MAX_DEPTH) return tree;
  return withSiblings(tree, path, (list, i) => {
    const above = list[i - 1];
    return [...list.slice(0, i - 1), { ...above, children: [...above.children, node] }, ...list.slice(i + 1)];
  });
}

// Brings a sub-point up a level, to sit just after its parent. Its later siblings stay behind, under the parent.
export function outdent(tree, id) {
  const path = pathTo(tree, id);
  if (!path || path.length < 2) return tree;
  const node = getNode(tree, id);
  const without = removeNode(tree, id);
  return addAfter(without, getNode(tree, parentIdOf(tree, id)).id, node);
}

export function parentIdOf(tree, id, parent = null) {
  for (const n of tree) {
    if (n.id === id) return parent;
    const found = parentIdOf(n.children, id, n.id);
    if (found !== null) return found;
  }
  return null;
}

// Swaps a node with the sibling above (-1) or below (+1).
export function moveNode(tree, id, direction) {
  const path = pathTo(tree, id);
  if (!path) return tree;
  return withSiblings(tree, path, (list, i) => {
    const j = i + direction;
    if (j < 0 || j >= list.length) return list;
    const next = [...list];
    [next[i], next[j]] = [next[j], next[i]];
    return next;
  });
}

// Where a node is: its parent (null at the top) and its place among that parent's children. With
// insertAt this puts a deleted point back exactly where it was.
export function locate(tree, id) {
  const path = pathTo(tree, id);
  if (!path) return null;
  return { parentId: path.length > 1 ? parentIdOf(tree, id) : null, index: path[path.length - 1] };
}

export function insertAt(tree, parentId, index, node) {
  const put = (list) => [...list.slice(0, Math.min(index, list.length)), node, ...list.slice(Math.min(index, list.length))];
  if (parentId == null || !getNode(tree, parentId)) return put(tree);
  return updateChildren(tree, parentId, put);
}

// ---- reading it ------------------------------------------------------------

// Every node in reading order with its depth and label: [{ node, depth, label, parentId }]
export function flatten(tree, depth = 0, parentId = null) {
  return tree.flatMap((node, index) => [
    { node, depth, label: labelFor(depth, index), parentId },
    ...flatten(node.children, depth + 1, node.id),
  ]);
}

export const countNodes = (tree) => flatten(tree).length;

const pointText = (n) => `${n.text.trim() || '(untitled)'}${n.ref.trim() ? ` (${n.ref.trim()})` : ''}`;

export function outlineToText(tree) {
  return flatten(tree).map(({ node, depth, label }) => `${'    '.repeat(depth)}${label} ${pointText(node)}`).join('\n');
}

export function outlineToMarkdown(tree) {
  return flatten(tree).map(({ node, depth, label }) => `${'    '.repeat(depth)}- **${label}** ${pointText(node)}`).join('\n');
}

// ---- starting one ------------------------------------------------------------

// One main point per chunk that isn't already in the outline, named after the session title, or the
// first line of the observation, or the passage. Existing points are kept.
export function seedFromChunks(project, tree = []) {
  const linked = new Set(flatten(tree).map((f) => f.node.chunkId).filter(Boolean));
  const added = [];
  (project?.chapters ?? []).forEach((chapter, chapterIndex) => {
    for (const chunk of chapter.chunks ?? []) {
      if (linked.has(chunk.id)) continue;
      const firstLine = (chunk.observation ?? '').trim().split('\n')[0].slice(0, 90);
      added.push(newNode(chunk.episodeTitle?.trim() || firstLine || '', { ref: formatChunkReference(project, chapterIndex, chunk, '–'), chunkId: chunk.id }));
    }
  });
  return [...tree, ...added];
}