//
// Generic TreeDataProvider over the node model. Subclasses only implement
// roots(); everything else — lazy children, TreeItem mapping — happens here.
//

const log = require("../util/log.js");
const { message } = require("./nodes.js");

// The parts of a node that end up on screen; a change to any of them means the
// row has to be redrawn.
const RENDERED_FIELDS = [
    "name",
    "descriptiveText",
    "tooltip",
    "image",
    "path",
    "command",
    "contextValue",
];

/** Drops nodes that are already covered by an ancestor in the same list. */
function topmost(nodes) {
    const unique = [...new Set(nodes)];
    return unique.filter((node) => {
        for (let parent = node.parent; parent; parent = parent.parent) {
            if (unique.includes(parent)) return false;
        }
        return true;
    });
}

class NodeProvider {
    constructor(store) {
        this.store = store;
        this._roots = null;

        // Expansion has to be tracked here. A reload rebuilds every node, and
        // the collapsible state we hand back is what Nova applies, so without
        // this every refresh would close whatever the user had opened.
        this._expanded = new Set();
        this._known = new Set();
    }

    /** Records what the user opened or closed, keyed by node identifier. */
    setExpanded(element, expanded) {
        if (!element || !element.identifier) return;
        if (expanded) this._expanded.add(element.identifier);
        else this._expanded.delete(element.identifier);
    }

    /**
     * Whether a row should render open. A node marked `expanded` seeds the set
     * the first time it is seen, so a default-open section can still be closed
     * by hand and stay closed.
     */
    isExpanded(element) {
        const id = element.identifier;
        if (!id) return element.expanded === true;

        if (!this._known.has(id)) {
            this._known.add(id);
            if (element.expanded) this._expanded.add(id);
        }
        return this._expanded.has(id);
    }

    /** Subclasses return an array of nodes (or a Promise of one). */
    roots() {
        return [];
    }

    /** Drops memoised roots so the next getChildren rebuilds from the store. */
    invalidate() {
        this._roots = null;
    }

    /**
     * Rebuilds from the store and merges the result into the node objects Nova
     * is already holding, rather than replacing them.
     *
     * This is what lets the tree update as often as it likes without the view
     * jumping: a full `TreeView.reload()` rebuilds every row and drops the
     * scroll position, so instead this reports the smallest set of rows that
     * actually changed and only those get reloaded.
     *
     * Returns `{ full: true }` when the shape changed too much to patch,
     * `{ full: false, nodes }` for a targeted reload, or null when nothing
     * changed at all.
     */
    async update() {
        const built = await this.roots();
        for (const root of built) root.parent = null;

        if (!this._roots) {
            this._roots = built;
            return { full: true };
        }

        const changed = [];
        this._roots = this._merge(this._roots, built, changed, null);

        if (changed.includes(null)) return { full: true };
        if (!changed.length) return null;

        return { full: false, nodes: topmost(changed) };
    }

    /**
     * Reconciles one level. Rows are matched by identifier and updated in
     * place; if the row set itself moved, the owner is rebuilt instead.
     */
    _merge(previous, next, changed, owner) {
        const sameRows =
            previous.length === next.length &&
            previous.every((node, index) => node.identifier === next[index].identifier);

        if (!sameRows) {
            for (const node of next) node.parent = owner;
            changed.push(owner);
            return next;
        }

        return previous.map((node, index) => {
            const fresh = next[index];
            if (this._apply(node, fresh)) changed.push(node);

            if (node.children && fresh.children) {
                node.children = this._merge(node.children, fresh.children, changed, node);
            } else if (node.children && fresh.load) {
                // An open row that fetches its own children: drop the cache so
                // the reload refetches, which is the running-job case.
                node.children = null;
                changed.push(node);
            }

            return node;
        });
    }

    /** Copies the fresh row's content onto the live node; true if visibly different. */
    _apply(node, fresh) {
        let dirty = false;
        for (const field of RENDERED_FIELDS) {
            if (node[field] !== fresh[field]) {
                node[field] = fresh[field];
                dirty = true;
            }
        }

        // Carried across whether or not they are drawn: commands read them.
        node.data = fresh.data;
        node.repo = fresh.repo;
        node.load = fresh.load;
        node.expanded = fresh.expanded;

        return dirty;
    }

    async getChildren(element) {
        try {
            if (!element) {
                if (!this._roots) {
                    this._roots = await this.roots();
                    // A section may hoist a repository's children to the top
                    // level; those nodes must not keep a parent Nova cannot see.
                    for (const root of this._roots) root.parent = null;
                }
                return this._roots;
            }

            if (element.children) return element.children;

            if (element.load) {
                const children = await element.load();
                element.children = children || [];
                for (const child of element.children) child.parent = element;
                return element.children;
            }

            return [];
        } catch (error) {
            log.error("tree build failed", String(error && error.stack ? error.stack : error));
            return [message(`⚠ ${error.message || error}`)];
        }
    }

    /**
     * Finds a rebuilt node by identifier, walking only branches the user has
     * open. That is enough to locate anything currently on screen, and it
     * avoids triggering a fetch for collapsed rows.
     */
    async findByIdentifier(identifier) {
        if (!identifier) return null;

        const walk = async (candidates) => {
            for (const candidate of candidates) {
                if (candidate.identifier === identifier) return candidate;
                if (!this._expanded.has(candidate.identifier)) continue;

                const found = await walk(await this.getChildren(candidate));
                if (found) return found;
            }
            return null;
        };

        return await walk(await this.getChildren(null));
    }

    /** Overridden per section: what this section draws, as a comparable string. */
    signature() {
        return null;
    }

    getParent(element) {
        return element ? element.parent : null;
    }

    getTreeItem(element) {
        const expandable = Boolean(element.children || element.load);
        const collapsible = !expandable
            ? TreeItemCollapsibleState.None
            : this.isExpanded(element)
              ? TreeItemCollapsibleState.Expanded
              : TreeItemCollapsibleState.Collapsed;

        const item = new TreeItem(element.name, collapsible);
        item.identifier = element.identifier;
        item.contextValue = element.contextValue;

        if (element.descriptiveText) item.descriptiveText = element.descriptiveText;
        if (element.tooltip) item.tooltip = element.tooltip;
        if (element.image) item.image = element.image;
        if (element.path) item.path = element.path;
        if (element.command) item.command = element.command;

        return item;
    }
}

exports.NodeProvider = NodeProvider;