/**
 * Snippet library state (docs/architecture/01).
 *
 * Holds the durable domain state for the library: the snippets, which one is
 * active, and the live editor buffer (`draftText`). Actions are the single place
 * snippet state mutates, so they are unit-testable without a DOM or IndexedDB.
 *
 * Persistence is NOT done here — a startup subscriber (orchestration/persistence)
 * observes this store and writes through to the IndexedDB adapter. That keeps the
 * store pure and free of browser APIs.
 *
 * Draft/published model (spec §03D): every snippet carries a published `spec`
 * and a working `draftSpec`. Ordinary editing — keystrokes, auto-save — touches
 * the **draft** only; `publish` promotes the draft to published, `revert`
 * discards it back to published. `editorView` selects which version the editor
 * shows (and therefore which the preview renders); the live editable buffer
 * `draftText` always mirrors the draft, regardless of view.
 */

import { create } from 'zustand';
import { createSnippet, type CreateSnippetOptions, type Snippet } from '@core/snippet';

/** Which version of the active snippet the editor is showing (spec §03D). */
export type EditorView = 'draft' | 'published';

export interface SnippetState {
  snippets: Snippet[];
  activeSnippetId: string | null;
  /** The live Monaco buffer for the active snippet's draft (may be mid-edit/invalid). */
  draftText: string;
  /** Which version the editor shows; `'published'` is read-only (spec §03D). */
  editorView: EditorView;
  /**
   * Bumped whenever the buffer is loaded *programmatically* (hydrate, select,
   * create, delete-fallback, revert) — never on keystrokes. The editor reloads
   * its content when this changes, so an external buffer load (e.g. revert)
   * refreshes the editor without setValue fighting the cursor mid-typing.
   */
  bufferEpoch: number;

  /** Replace the library from storage and choose an active snippet. */
  hydrate: (snippets: Snippet[], activeId?: string | null) => void;
  /** Create a new snippet (sample template by default), prepend, and select it. */
  createSnippet: (options?: CreateSnippetOptions) => string;
  /** Make a snippet active and load its draft into the editor buffer. */
  selectSnippet: (id: string) => void;
  /** Remove a snippet; if it was active, fall back to the newest remaining one. */
  removeSnippet: (id: string) => void;
  /** Update the draft buffer only (no persistence; debounced commit follows). */
  updateDraft: (text: string) => void;
  /**
   * Persist the editor buffer into the active snippet's **draft**, if it parses
   * as JSON. Returns whether it committed (a half-typed, unparseable buffer is
   * skipped, per spec §03B). Never touches the published `spec`. `now` is
   * injectable for deterministic tests.
   */
  commitDraft: (now?: Date) => boolean;
  /** Switch the editor between the draft and published views (spec §03D). */
  setEditorView: (view: EditorView) => void;
  /**
   * Promote the active snippet's current draft to its published version (spec
   * §03D → Publish). Flushes the live buffer first, then makes `spec` identical
   * to `draftSpec`. Returns whether a snippet was active. `now` injectable.
   */
  publish: (now?: Date) => boolean;
  /**
   * Discard the active snippet's draft, restoring it to the published version
   * (spec §03D → Revert), and reload the editor on the draft view. Returns
   * whether a snippet was active. `now` injectable.
   */
  revert: (now?: Date) => boolean;
  /** Reset to initial state (tests, future "new workspace"). */
  reset: () => void;
}

/** Newest-modified first — the library's default ordering (spec §02 → Sort). */
function byModifiedDesc(a: Snippet, b: Snippet): number {
  return b.modified.localeCompare(a.modified);
}

/** The id of the most-recently-modified snippet, or null if there are none. */
function newestId(snippets: Snippet[]): string | null {
  if (snippets.length === 0) return null;
  return [...snippets].sort(byModifiedDesc)[0].id;
}

function draftFor(snippets: Snippet[], id: string | null): string {
  return snippets.find((s) => s.id === id)?.draftSpec ?? '';
}

export const useSnippetStore = create<SnippetState>((set, get) => ({
  snippets: [],
  activeSnippetId: null,
  draftText: '',
  editorView: 'draft',
  bufferEpoch: 0,

  hydrate: (snippets, activeId) => {
    const id = activeId !== undefined ? activeId : newestId(snippets);
    set((s) => ({
      snippets,
      activeSnippetId: id,
      draftText: draftFor(snippets, id),
      editorView: 'draft',
      bufferEpoch: s.bufferEpoch + 1,
    }));
  },

  createSnippet: (options) => {
    get().commitDraft(); // flush the outgoing snippet's valid edits before switching away
    const snippet = createSnippet(options);
    set((s) => ({
      snippets: [snippet, ...s.snippets],
      activeSnippetId: snippet.id,
      draftText: snippet.draftSpec,
      editorView: 'draft', // a fresh snippet always opens on its editable draft
      bufferEpoch: s.bufferEpoch + 1,
    }));
    return snippet.id;
  },

  selectSnippet: (id) => {
    if (id === get().activeSnippetId) return;
    // Flush the outgoing snippet's valid in-progress edits before switching, so
    // navigating away within the auto-save debounce window doesn't drop them
    // (spec §03B — auto-save preserves in-progress work). An unparseable buffer
    // is left uncommitted, exactly as the debounced auto-save would.
    get().commitDraft();
    set((s) => ({
      activeSnippetId: id,
      draftText: draftFor(s.snippets, id),
      editorView: 'draft',
      bufferEpoch: s.bufferEpoch + 1,
    }));
  },

  removeSnippet: (id) => {
    set((s) => {
      const snippets = s.snippets.filter((x) => x.id !== id);
      if (s.activeSnippetId !== id) return { snippets };
      const activeSnippetId = newestId(snippets);
      return {
        snippets,
        activeSnippetId,
        draftText: draftFor(snippets, activeSnippetId),
        editorView: 'draft',
        bufferEpoch: s.bufferEpoch + 1, // the buffer was reloaded for the new active snippet
      };
    });
  },

  updateDraft: (draftText) => set({ draftText }),

  commitDraft: (now) => {
    const { activeSnippetId, draftText, snippets } = get();
    if (!activeSnippetId) return false;

    try {
      JSON.parse(draftText);
    } catch {
      return false; // half-typed spec — skip, retry after the next pause
    }

    const active = snippets.find((s) => s.id === activeSnippetId);
    // Auto-save writes the DRAFT only — never the published spec (spec §03B/§03D).
    if (!active || active.draftSpec === draftText) {
      return false; // nothing changed in the draft
    }

    const modified = (now ?? new Date()).toISOString();
    set({
      snippets: snippets.map((s) =>
        s.id === activeSnippetId ? { ...s, draftSpec: draftText, modified } : s,
      ),
    });
    return true;
  },

  setEditorView: (editorView) => set({ editorView }),

  publish: (now) => {
    // Flush the live buffer into the draft first, so Publish promotes exactly
    // what the user sees (an invalid buffer leaves the last valid draft in place).
    get().commitDraft(now);
    const { activeSnippetId, snippets } = get();
    if (!activeSnippetId) return false;

    const modified = (now ?? new Date()).toISOString();
    set({
      snippets: snippets.map((s) =>
        s.id === activeSnippetId
          ? // M3: recompute datasetRefs from the now-published spec (spec §03D).
            { ...s, spec: s.draftSpec, modified }
          : s,
      ),
    });
    return true;
  },

  revert: (now) => {
    const { activeSnippetId, snippets } = get();
    if (!activeSnippetId) return false;

    const active = snippets.find((s) => s.id === activeSnippetId);
    if (!active) return false;

    const modified = (now ?? new Date()).toISOString();
    set((s) => ({
      snippets: s.snippets.map((x) =>
        x.id === activeSnippetId ? { ...x, draftSpec: x.spec, modified } : x,
      ),
      // Reload the editor with the restored draft, on the editable view (spec §03D).
      draftText: active.spec,
      editorView: 'draft',
      bufferEpoch: s.bufferEpoch + 1,
    }));
    return true;
  },

  reset: () =>
    set({
      snippets: [],
      activeSnippetId: null,
      draftText: '',
      editorView: 'draft',
      bufferEpoch: 0,
    }),
}));

/** Selector: the active snippet record, or null. Derive — never store. */
export const selectActiveSnippet = (s: SnippetState): Snippet | null =>
  s.snippets.find((x) => x.id === s.activeSnippetId) ?? null;

/**
 * Selector: the text the editor shows and the preview renders. The draft view
 * shows the live editable buffer; the published view shows the stored published
 * spec (spec §03D — "the preview always reflects the version in the editor").
 */
export const selectShownText = (s: SnippetState): string => {
  if (s.editorView === 'published') {
    return selectActiveSnippet(s)?.spec ?? '';
  }
  return s.draftText;
};