import type { JsonValue } from "@berry/api";
import type { ViewContext, ViewDestination } from "@berry/api/web.ts";
import type { DiffEditor, Layout } from "./editor.ts";
import {
  type Draft,
  draftKey,
  editId,
  loadDrafts,
  recover,
  type Stored,
  storeDrafts,
} from "./drafts.ts";
import type { OpenFile, Saved, WorkingCopy } from "./edit-types.ts";
import type { FileDiff } from "./types.ts";

type Loaded = {
  diffEditor: typeof import("./editor.ts").diffEditor;
  merge3: typeof import("./merge.ts").merge3;
};

let loaded: Loaded | null = null;
let loading: Promise<Loaded> | null = null;
/** CodeMirror and the merge are most of the bundle, and only editing needs them. */
function load(): Promise<Loaded> {
  loading ??= Promise.all([import("./editor.ts"), import("./merge.ts")]).then(
    ([editor, merge]) => loaded = { diffEditor: editor.diffEditor, merge3: merge.merge3 },
    (error) => {
      loading = null;
      throw new Error(
        `Could not load the editor; reload the page. (${
          error instanceof Error ? error.message : error
        })`,
      );
    },
  );
  return loading;
}

type Editing = {
  draft: Draft;
  element: HTMLElement;
  editor: DiffEditor;
  status: HTMLElement;
  save: HTMLButtonElement;
  cancel: HTMLButtonElement;
  force: HTMLButtonElement;
  saving: Promise<boolean> | null;
  syncing: Promise<void> | null;
  /** Whether the disk may have changed since the last look. */
  stale: boolean;
  /** The disk's version, while it conflicts with the draft. */
  conflict: OpenFile | null;
  resolve: HTMLElement;
};

/** How long typing goes before its draft is written down for recovery. */
const TYPED_MS = 250;

export function editing(
  redraw: (path: string) => void,
  refreshed: (path: string) => void,
  failure: (message: string) => void,
) {
  let context: ViewContext;
  let key: string;
  let stored: Stored;
  let ready: Promise<void> = Promise.resolve();
  let disposed = false;
  let leaving: Promise<boolean> | null = null;
  /** A report leaving kicked off without holding navigation open, which a flush still waits for. */
  let backgroundReport: Promise<void> | null = null;
  let destination: ViewDestination;
  let cancelChoice: (() => void) | null = null;
  const edits = new Map<string, Editing>();
  const opening = new Map<string, Promise<OpenFile>>();
  /** The view's route a draft belongs to: its jj change, or the working copy's empty one. */
  const routeOf = (draft: Draft) => draft.opened.working.change ?? "";
  const dirty = (draft: Draft) => draft.content !== draft.opened.content || !!draft.pending;
  const staying = () =>
    destination.tid === context.tid &&
    destination.extension === "diff" && destination.route === context.route;
  const exiting = () => destination.tid !== context.tid || destination.extension !== "diff";
  /** A keystroke's write, held back a moment: each writes every draft whole, which per key is too slow to type in. */
  let typed: ReturnType<typeof setTimeout> | undefined;
  const persist = () => {
    clearTimeout(typed);
    typed = undefined;
    try {
      storeDrafts(key, stored);
    } catch {
      failure("Draft recovery storage is full. Keep this tab open until your edits are saved.");
    }
  };

  function close(path: string) {
    edits.get(path)?.editor.destroy();
    edits.delete(path);
    delete stored.drafts[path];
    persist();
    refreshed(path);
  }

  async function save(edit: Editing): Promise<boolean> {
    if (edit.saving) return await edit.saving;
    if (!dirty(edit.draft)) {
      close(edit.draft.opened.file.path);
      return true;
    }
    const { draft } = edit;
    draft.pending ??= {
      session: stored.id,
      id: editId(),
      working: draft.opened.working,
      path: draft.opened.file.path,
      version: draft.opened.version,
      content: draft.content,
    };
    stored.saved = true;
    persist();
    edit.save.disabled = true;
    edit.cancel.disabled = true;
    edit.status.textContent = "saving…";
    edit.force.hidden = true;
    let changedOnDisk = false;
    const task = (async () => {
      try {
        const saved = await context.request(
          "save",
          draft.pending as unknown as JsonValue,
        ) as unknown as Saved;
        draft.opened.content = draft.pending!.content;
        draft.opened.version = saved.version;
        draft.opened.working = saved.working;
        delete draft.pending;
        if (!stored.saves.some((receipt) => receipt.id === saved.id)) stored.saves.push(saved);
        stored.saved = true;
        persist();
        if (dirty(draft)) {
          edit.status.textContent = "unsaved edits";
          refreshed(draft.opened.file.path);
        } else {
          close(draft.opened.file.path);
        }
        return true;
      } catch (error) {
        const message = error instanceof Error ? error.message : String(error);
        changedOnDisk = message.includes("since you opened it");
        edit.force.hidden = !message.includes("would cause conflicts");
        edit.status.textContent = edit.force.hidden
          ? message
          : `${message} Save anyway to keep them?`;
        return false;
      } finally {
        edit.save.disabled = false;
        edit.cancel.disabled = false;
        edit.saving = null;
      }
    })();
    edit.saving = task;
    const saved = await task;
    if (changedOnDisk) {
      await sync(edit);
      const current = edits.get(draft.opened.file.path);
      if (current && !current.conflict) {
        current.status.textContent =
          "since you opened this file, it changed. your edits have been merged.";
      }
    }
    return saved;
  }

  /** Bring changes made on disk since the draft's base into the editor, as a rebase would. */
  function sync(edit: Editing): Promise<void> {
    edit.stale = true;
    return edit.syncing ??= (async () => {
      try {
        while (edit.stale && !disposed && edits.get(edit.draft.opened.file.path) === edit) {
          await edit.saving;
          edit.stale = false;
          await pull(edit);
        }
      } finally {
        edit.syncing = null;
      }
    })();
  }

  async function pull(edit: Editing) {
    const { draft } = edit;
    const path = draft.opened.file.path;
    let latest: OpenFile;
    try {
      latest = await context.request("open", {
        root: draft.opened.working.root,
        path,
        route: routeOf(draft),
      }) as unknown as OpenFile;
    } catch (error) {
      edit.status.textContent = `Could not check the file on disk: ${
        error instanceof Error ? error.message : error
      }`;
      return;
    }
    if (disposed || edits.get(path) !== edit || edit.saving) return;
    if (latest.version === draft.opened.version) {
      // a commit rewritten around the file still moves the draft to the new commit
      draft.opened.working = latest.working;
      return persist();
    }
    // a save whose answer was lost may have landed, and is then the base
    const base = draft.pending?.content === latest.content ? latest.content : draft.opened.content;
    const merged = loaded!.merge3(base, draft.content, latest.content);
    if (merged === false) {
      edit.conflict = latest;
      edit.resolve.hidden = false;
      edit.status.textContent = "The file changed on disk where you edited it.";
      return;
    }
    adopt(
      edit,
      latest,
      merged,
      merged === latest.content ? "updated from disk" : "merged changes from disk",
      false,
    );
  }

  /** Take `latest` as the draft's base, with `content` as its text; a new original or working copy remounts it. */
  function adopt(
    edit: Editing,
    latest: OpenFile,
    content: string,
    message: string,
    undoable: boolean,
  ) {
    const { draft } = edit;
    const path = draft.opened.file.path;
    const moved = latest.original !== draft.opened.original ||
      (Object.keys(latest.working) as (keyof WorkingCopy)[]).some((key) =>
        latest.working[key] !== draft.opened.working[key]
      );
    edit.conflict = null;
    edit.resolve.hidden = true;
    delete draft.pending;
    draft.opened = latest;
    if (moved) {
      edit.editor.destroy();
      edits.delete(path);
      draft.content = content;
      persist();
      redraw(path);
    } else {
      edit.editor.replace(content, undoable);
      draft.content = content;
      persist();
    }
    const current = edits.get(path);
    if (current) current.status.textContent = message;
  }

  function mount(draft: Draft, layout: Layout): Editing {
    const status = <span role="status" /> as HTMLElement;
    let escaped = 0;
    const surface = <div class="diff-edit-surface" /> as HTMLElement;
    const saveButton = (
      <button
        type="button"
        class="primary diff-save"
        title="Ctrl+Enter"
        _onclick={() => void save(edit)}
      >
        save
      </button>
    ) as HTMLButtonElement;
    const force = (
      <button
        type="button"
        class="link diff-force"
        hidden
        _onclick={() => {
          if (draft.pending) draft.pending.force = true;
          persist();
          void save(edit);
        }}
      >
        save anyway
      </button>
    ) as HTMLButtonElement;
    const cancel = (
      <button
        type="button"
        class="link"
        title="Escape-Escape"
        _onclick={() => {
          if (
            !edit.saving && (!dirty(draft) || document.defaultView!.confirm("Discard this draft?"))
          ) {
            close(draft.opened.file.path);
          }
        }}
      >
        cancel
      </button>
    ) as HTMLButtonElement;
    const element = (
      <div class="diff-edit">
        <div class="diff-edit-tools">
          {status}
          <span class="diff-conflict" hidden>
            <button
              type="button"
              class="link"
              _onclick={() =>
                edit.conflict && adopt(
                  edit,
                  edit.conflict,
                  draft.content,
                  "keeping your changes (press save to replace!)",
                  false,
                )}
            >
              keep mine
            </button>
            <button
              type="button"
              class="link"
              _onclick={() =>
                edit.conflict && adopt(
                  edit,
                  edit.conflict,
                  edit.conflict.content,
                  "taking on-disk changes (press undo to restore!)",
                  true,
                )}
            >
              take disk's
            </button>
          </span>
          <button
            type="button"
            class="link"
            _onclick={() => {
              void navigator.clipboard.writeText(draft.content).catch(() => {
                status.textContent = "Could not copy; select and copy the draft in the editor.";
              });
            }}
          >
            copy draft
          </button>
          {force}
          {cancel}
          {saveButton}
        </div>
        {surface}
      </div>
    ) as HTMLElement;
    const editor = loaded!.diffEditor(
      surface,
      { ...draft.opened, content: draft.content },
      layout,
      {
        changed(content) {
          escaped = 0;
          draft.content = content;
          status.textContent = dirty(draft) ? "unsaved edits" : "saved";
          typed ??= setTimeout(persist, TYPED_MS);
        },
        save: () => void save(edit),
        // a second press soon after the first is the confirmation that cancel asks for
        escape() {
          if (edit.saving) return;
          if (Date.now() - escaped < 1500) return close(draft.opened.file.path);
          escaped = Date.now();
          status.textContent = dirty(draft)
            ? "press Escape again to discard your edits"
            : "press Escape again to exit edit mode";
        },
      },
    );
    const edit: Editing = {
      draft,
      element,
      editor,
      status,
      save: saveButton,
      cancel,
      force,
      saving: null,
      syncing: null,
      stale: false,
      conflict: null,
      resolve: element.querySelector(".diff-conflict") as HTMLElement,
    };
    status.textContent = dirty(draft) ? "recovered draft · unsaved edits" : "editing new side";
    edits.set(draft.opened.file.path, edit);
    return edit;
  }

  function choose(): Promise<"save" | "discard" | "stay"> {
    return new Promise((resolve) => {
      const dialog = (
        <dialog class="diff-leave">
          <p>You have unsaved diff edits.</p>
        </dialog>
      ) as HTMLDialogElement;
      const finish = (choice: "save" | "discard" | "stay") => {
        cancelChoice = null;
        dialog.close();
        dialog.remove();
        resolve(choice);
      };
      cancelChoice = () => finish("stay");
      for (
        const [label, choice] of [
          ["save and leave", "save"],
          ["discard and leave", "discard"],
          ["stay", "stay"],
        ] as const
      ) {
        dialog.append(
          <button
            type="button"
            class={choice === "save" ? "primary" : ""}
            _onclick={() => finish(choice)}
          >
            {label}
          </button>,
        );
      }
      dialog.addEventListener("cancel", (event) => {
        event.preventDefault();
        finish("stay");
      });
      document.body.append(dialog);
      dialog.showModal();
    });
  }

  async function leave(): Promise<boolean> {
    await ready;
    await Promise.all([...edits.values()].map((edit) => edit.saving));
    if (staying()) return true;
    if (Object.values(stored.drafts).some(dirty)) {
      const choice = await choose();
      if (choice === "stay") return false;
      if (choice === "save") {
        try {
          await load();
        } catch (error) {
          failure(error instanceof Error ? error.message : String(error));
          return false;
        }
        for (const draft of Object.values(stored.drafts)) {
          const edit = edits.get(draft.opened.file.path) ?? mount(draft, "unified");
          while (dirty(draft)) if (!await save(edit)) return false;
        }
      }
    }
    if (staying()) return true;
    if (exiting() && stored.saved) {
      // Reporting saved edits can wait for the agent's turn to end, which must not hold navigation open.
      const id = stored.id;
      const saves = stored.saves;
      stored.id = editId();
      stored.saved = false;
      stored.saves = [];
      persist();
      const task = report(id, saves);
      backgroundReport = task;
      void task.finally(() => {
        if (backgroundReport === task) backgroundReport = null;
      });
    }
    if (staying()) return true;
    for (const path of Object.keys(stored.drafts)) close(path);
    if (exiting()) localStorage.removeItem(key);
    return true;
  }

  /** Report saved edits without holding navigation open; a failure stays to retry on a later visit. */
  async function report(id: string, saves: Saved[], throwOnFailure = false) {
    try {
      await context.command("diff-finish", JSON.stringify({ session: id, saves }));
    } catch (error) {
      const message = `Could not report your saved edits: ${
        error instanceof Error ? error.message : error
      }`;
      const restore = () => {
        stored.id = id;
        stored.saved = true;
        stored.saves = [
          ...saves,
          ...stored.saves.filter((receipt) => !saves.some((save) => save.id === receipt.id)),
        ];
        persist();
      };
      if (disposed) {
        try {
          if (localStorage.getItem(key) === null) restore();
        } catch { /* keep the navigation the user already made */ }
        console.error(`[berry] ${message}`);
      } else {
        restore();
        failure(message);
      }
      if (throwOnFailure) throw error instanceof Error ? error : new Error(message);
    }
  }

  /**
   * Report saved edits while staying in the view, so an idle message sends after them. Dirty drafts stay
   * unsaved; a failure keeps the message in the composer by throwing.
   */
  async function flush(): Promise<void> {
    await ready;
    await Promise.all([...edits.values()].map((edit) => edit.saving));
    if (disposed) return;
    if (backgroundReport) await backgroundReport;
    if (disposed || !stored?.saved) return;
    const id = stored.id;
    const saves = stored.saves;
    stored.id = editId();
    stored.saved = false;
    stored.saves = [];
    persist();
    if (!saves.length) return;
    await report(id, saves, true);
  }

  const onUnload = (event: BeforeUnloadEvent) => {
    if (stored && Object.values(stored.drafts).some(dirty)) {
      event.preventDefault();
      event.returnValue = "";
    }
  };
  const onHide = () => {
    if (!stored) return;
    stored.closed = true;
    persist();
  };
  globalThis.addEventListener("beforeunload", onUnload);
  globalThis.addEventListener("pagehide", onHide);

  return {
    update(next: ViewContext) {
      context = next;
      if (!key) {
        key = draftKey(next.tid);
        ready = recover(key, next).catch((error) => failure(String(error))).then(() => {
          stored = loadDrafts(key);
          if (!disposed) { for (const path of Object.keys(stored.drafts)) redraw(path); }
        });
      }
    },
    async begin(file: FileDiff, root: string, line?: number) {
      await ready;
      const route = context.route;
      try {
        const editor = load();
        editor.catch(() => {});
        if (!stored.drafts[file.path]) {
          const request = opening.get(file.path) ??
            context.request("open", { root, path: file.path, route }) as Promise<OpenFile>;
          opening.set(file.path, request);
          const opened = await request.finally(() => opening.delete(file.path));
          if (disposed || context.route !== route) return;
          stored.drafts[file.path] ??= { opened, content: opened.content };
          persist();
        }
        await editor;
        if (disposed || context.route !== route) return;
        redraw(file.path);
        const view = edits.get(file.path)?.editor.view;
        if (view) {
          if (line) {
            view.dispatch({
              selection: {
                anchor: view.state.doc.line(Math.min(line, view.state.doc.lines)).from,
              },
            });
          }
          view.focus();
        }
      } catch (error) {
        failure(error instanceof Error ? error.message : String(error));
      }
    },
    /** Look at the file on disk again, as when its diff changes. */
    sync(path: string) {
      const edit = edits.get(path);
      if (edit) void sync(edit);
    },
    has(path: string, route?: string) {
      const draft = stored?.drafts[path];
      return !!draft && (route === undefined || routeOf(draft) === route);
    },
    files(root: string, route: string): FileDiff[] {
      return Object.values(stored?.drafts ?? {}).filter((draft) =>
        draft.opened.working.root === root && routeOf(draft) === route
      )
        .map((draft) => draft.opened.file);
    },
    attach(body: HTMLElement, file: FileDiff, layout: Layout, route: string) {
      const draft = stored?.drafts[file.path];
      if (!draft || routeOf(draft) !== route) return false;
      let edit = edits.get(file.path);
      if (!edit && !loaded) {
        body.replaceChildren(<p class="meta file-note">loading editor…</p>);
        load().then(
          () => redraw(file.path),
          (error) => failure(error instanceof Error ? error.message : String(error)),
        );
        return true;
      }
      if (!edit) {
        edit = mount(draft, layout);
        void sync(edit);
      }
      edit.editor.layout(layout);
      if (!body.contains(edit.element)) body.replaceChildren(edit.element);
      return true;
    },
    beforeLeave(next: ViewDestination) {
      destination = next;
      if (staying()) {
        cancelChoice?.();
        if (!leaving) return true;
      }
      leaving ??= leave().finally(() => {
        leaving = null;
      });
      return leaving;
    },
    flush,
    dispose() {
      if (typed !== undefined) persist();
      disposed = true;
      cancelChoice?.();
      for (const edit of edits.values()) edit.editor.destroy();
      edits.clear();
      globalThis.removeEventListener("beforeunload", onUnload);
      globalThis.removeEventListener("pagehide", onHide);
    },
  };
}