/**
 * @file LaneConflictView.tsx
 * @description The Changes panel's view of ONE conflicted file during a merge
 * (issue #45): the file with each conflict block drawn as its two sides —
 * "mine" and "theirs", labelled from git's own markers and tinted apart — and
 * a Keep mine / Take theirs / Keep both choice per block, undoable. Save and
 * mark resolved writes the chosen text over exactly the version it opened
 * (`gitSaveFile` with its `sha`, 409 ESTALE otherwise) and then runs
 * `resolve done`, which re-checks that no marker is left. Take all mine /
 * theirs is `resolve ours|theirs` for the whole file; Edit by hand hands the
 * file to the panel's plain editor.
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */

import { useEffect, useRef, useState } from "react";
import { useTranslation } from "react-i18next";
import { ChevronDown, ChevronUp } from "lucide-react";
import { api, gitTarget } from "../../lib/api";
import {
  applyChoices,
  parseConflicts,
  type ConflictChoice,
  type ConflictPart,
} from "../../lib/conflicts";

const BASE =
  "rounded border px-1.5 py-0.5 text-[11px] hover:bg-surface-2 disabled:cursor-not-allowed disabled:opacity-40";
const BTN = `${BASE} border-border-light text-fg-secondary hover:text-fg-primary`;

function Lines({ lines, className = "" }: { lines: string[]; className?: string }) {
  return (
    <pre className={`whitespace-pre px-2 font-mono text-[11px] leading-5 ${className}`}>
      {lines.length ? lines.join("\n") : " "}
    </pre>
  );
}

export function LaneConflictView({
  laneId,
  session,
  source,
  path,
  onResolved,
  onEdit,
}: {
  laneId: number;
  /** Work in that session's own worktree (see `gitTarget`). */
  session?: string;
  /** Work in that extra folder's repo instead (`lane_sources` id, see `gitTarget`). */
  source?: number;
  path: string;
  /** The file left the conflict (resolved, or a whole side taken). */
  onResolved: () => void;
  /** Open the file in the panel's plain editor instead. */
  onEdit: () => void;
}) {
  const { t } = useTranslation(["lanes"]);
  const [file, setFile] = useState<{ lines: string[]; sha?: string; usable: boolean } | null>(null);
  const [choices, setChoices] = useState<(ConflictChoice | undefined)[]>([]);
  const [busy, setBusy] = useState(false);
  const [error, setError] = useState<string | null>(null);
  const blockRefs = useRef<(HTMLDivElement | null)[]>([]);
  const [at, setAt] = useState(0);

  useEffect(() => {
    let live = true;
    setFile(null);
    setChoices([]);
    setError(null);
    api.lanes
      .gitFile(gitTarget(laneId, session, source), path, "work")
      .then((r) => {
        if (!live) return;
        setFile(
          r.available
            ? { lines: r.lines, sha: r.sha, usable: !r.binary && !r.truncated && !!r.sha }
            : { lines: [], usable: false }
        );
      })
      .catch((e) => live && setError(e instanceof Error ? e.message : String(e)));
    return () => {
      live = false;
    };
  }, [laneId, session, source, path]);

  const parts: ConflictPart[] | null = file?.usable ? parseConflicts(file.lines) : null;
  const total = parts ? parts.filter((p) => p.kind === "conflict").length : 0;
  const chosen = choices.filter(Boolean).length;
  const done = total > 0 && chosen === total;

  const run = async (fn: () => Promise<unknown>) => {
    setBusy(true);
    setError(null);
    try {
      await fn();
      onResolved();
    } catch (e) {
      setError(e instanceof Error ? e.message : String(e));
    } finally {
      setBusy(false);
    }
  };

  const save = () =>
    run(async () => {
      if (!parts || !file?.sha) return;
      await api.lanes.gitSaveFile(
        gitTarget(laneId, session, source),
        path,
        applyChoices(parts, choices).join("\n"),
        file.sha
      );
      await api.lanes.gitAction(gitTarget(laneId, session, source), "resolve", {
        path,
        side: "done",
      });
    });
  const takeAll = (side: "ours" | "theirs") =>
    run(() => api.lanes.gitAction(gitTarget(laneId, session, source), "resolve", { path, side }));

  const choose = (i: number, c: ConflictChoice | undefined) =>
    setChoices((prev) => {
      const next = [...prev];
      next[i] = c;
      return next;
    });

  const jump = (step: number) => {
    if (!total) return;
    const i = (at + step + total) % total;
    setAt(i);
    blockRefs.current[i]?.scrollIntoView({ block: "center" });
  };

  let blockIndex = -1;
  return (
    <div data-testid="lane-conflict-view" className="flex min-h-0 flex-1 flex-col gap-1.5">
      <div className="flex flex-wrap items-center gap-1.5">
        <span className="min-w-0 flex-1 truncate font-mono text-[11px] text-fg-primary">
          {path}
        </span>
        {total > 0 && (
          <span className="text-[11px] text-status-warning">
            {t("conflict.left", { left: total - chosen, total })}
          </span>
        )}
        <button
          type="button"
          className={BTN}
          aria-label={t("conflict.prev")}
          disabled={!total}
          onClick={() => jump(-1)}
        >
          <ChevronUp className="h-3 w-3" />
        </button>
        <button
          type="button"
          className={BTN}
          aria-label={t("conflict.next")}
          disabled={!total}
          onClick={() => jump(1)}
        >
          <ChevronDown className="h-3 w-3" />
        </button>
        <button type="button" className={BTN} disabled={busy} onClick={() => void takeAll("ours")}>
          {t("conflict.allOurs")}
        </button>
        <button
          type="button"
          className={BTN}
          disabled={busy}
          onClick={() => void takeAll("theirs")}
        >
          {t("conflict.allTheirs")}
        </button>
        <button type="button" className={BTN} disabled={busy} onClick={onEdit}>
          {t("conflict.editByHand")}
        </button>
      </div>

      {error && (
        <p role="alert" className="whitespace-pre-wrap text-[11px] text-status-danger">
          {error}
        </p>
      )}

      {!file ? (
        <p className="text-[11px] text-fg-muted">{t("changes.loading")}</p>
      ) : !parts ? (
        <p className="text-[11px] text-status-warning">
          {file.usable ? t("conflict.unbalanced") : t("conflict.unusable")}
        </p>
      ) : (
        <div className="min-h-0 flex-1 overflow-auto rounded border border-border-light bg-surface-0">
          {parts.map((p, n) => {
            if (p.kind === "text")
              return <Lines key={n} lines={p.lines} className="text-fg-primary" />;
            const i = ++blockIndex;
            const c = choices[i];
            return (
              <div
                key={n}
                ref={(el) => {
                  blockRefs.current[i] = el;
                }}
                data-testid="conflict-block"
                className="my-1 border-y-2 border-status-warning/70"
              >
                <div className="flex flex-wrap items-center gap-1 bg-surface-2 px-2 py-0.5 text-[11px]">
                  {c ? (
                    <>
                      <span className="text-fg-muted">{t(`conflict.chose.${c}`)}</span>
                      <button type="button" className={BTN} onClick={() => choose(i, undefined)}>
                        {t("conflict.undo")}
                      </button>
                    </>
                  ) : (
                    <>
                      <button
                        type="button"
                        className={`${BASE} border-status-success/70 font-medium text-status-success`}
                        onClick={() => choose(i, "ours")}
                      >
                        {t("conflict.keepOurs")}
                      </button>
                      <button
                        type="button"
                        className={`${BASE} border-accent/70 font-medium text-accent`}
                        onClick={() => choose(i, "theirs")}
                      >
                        {t("conflict.takeTheirs")}
                      </button>
                      <button type="button" className={BTN} onClick={() => choose(i, "both")}>
                        {t("conflict.keepBoth")}
                      </button>
                    </>
                  )}
                  <span className="ml-auto text-fg-muted">
                    {i + 1}/{total}
                  </span>
                </div>
                {c ? (
                  <Lines
                    lines={
                      c === "ours" ? p.ours : c === "theirs" ? p.theirs : [...p.ours, ...p.theirs]
                    }
                    className="bg-surface-2 text-fg-primary"
                  />
                ) : (
                  <>
                    <div className="border-l-4 border-status-success bg-status-success/20">
                      <div className="bg-status-success/30 px-2 py-0.5 text-[11px] font-semibold text-status-success">
                        {t("conflict.ours", { label: p.oursLabel || "HEAD" })}
                      </div>
                      <Lines lines={p.ours} className="text-fg-primary" />
                    </div>
                    <div className="border-l-4 border-accent bg-accent/20">
                      <div className="bg-accent/30 px-2 py-0.5 text-[11px] font-semibold text-accent">
                        {t("conflict.theirs", { label: p.theirsLabel || "?" })}
                      </div>
                      <Lines lines={p.theirs} className="text-fg-primary" />
                    </div>
                  </>
                )}
              </div>
            );
          })}
        </div>
      )}

      {parts && total > 0 && (
        <div className="flex items-center justify-end gap-1.5">
          <button
            type="button"
            className={BTN}
            disabled={busy || !chosen}
            onClick={() => setChoices([])}
          >
            {t("conflict.reset")}
          </button>
          <button
            type="button"
            disabled={busy || !done}
            onClick={() => void save()}
            className="rounded border border-accent/40 bg-accent/15 px-2 py-0.5 text-[11px] text-accent hover:bg-accent/25 disabled:cursor-not-allowed disabled:opacity-40"
          >
            {t("conflict.save")}
          </button>
        </div>
      )}
    </div>
  );
}