// A conversation's repository through its environment: jj's when there is one, else git's.

import type { Context } from "@earendil-works/chord";
import { getOrThrow } from "@earendil-works/pi-durable/env";
import type { Environment } from "@berry/api";
import { type FileDiff, narrow, parsePatch } from "./patch.ts";
import type { Id, Revision, Shown } from "./types.ts";

/** Enough context that each file's one hunk is the whole file, so the view can highlight and unfold all of it. */
const WHOLE = 1_000_000;
/** Files longer than this keep only some context around their changes. */
const LONG = 20_000;
const CONTEXT = 5;
/** How many untracked files git's working tree shows in full. */
const UNTRACKED = 100;

type Repository = { vcs: "jj" | "git"; root: string };

async function run(
  env: Environment,
  argv: string[],
  context: Context,
  { ok = [0], cwd = env.cwd }: { ok?: number[]; cwd?: string } = {},
) {
  const streams = { stdout: "", stderr: "" };
  const result = getOrThrow(
    await env.exec(argv, {
      cwd,
      onOutput: (text, _, { stream }) => void (streams[stream] += text),
    }, context),
  );
  if (!ok.includes(result.exitCode ?? -1)) {
    throw new Error(streams.stderr.trim() || `${argv[0]} exited with ${result.exitCode}`);
  }
  return streams.stdout;
}

const jj = (env: Environment, repo: Repository, args: string[], context: Context) =>
  run(env, ["jj", "--no-pager", "--color=never", ...args], context, { cwd: repo.root });

const git = (
  env: Environment,
  repo: Repository,
  args: string[],
  context: Context,
  ok?: number[],
) =>
  run(
    env,
    ["git", "--no-pager", "-c", "core.quotePath=false", "-c", "color.ui=false", ...args],
    context,
    { cwd: repo.root, ok },
  );

/** The repository around the environment's working directory: jj's first, so a colocated one reads as jj. */
async function repository(env: Environment, context: Context): Promise<Repository> {
  const attempt = async (vcs: Repository["vcs"], argv: string[]) => {
    try {
      return { vcs, root: (await run(env, argv, context)).trim() };
    } catch {
      return null;
    }
  };
  const found = await attempt("jj", ["jj", "--ignore-working-copy", "root"]) ??
    await attempt("git", ["git", "rev-parse", "--show-toplevel"]);
  if (found === null) throw new Error(`${env.cwd} is in neither a jj nor a git repository`);
  return found;
}

const id = (full: string, prefix: string, rest: string): Id => ({ full, prefix, rest });

const JJ_REVISION = [
  "json(self)",
  "change_id.shortest(8).prefix()",
  "change_id.shortest(8).rest()",
  "commit_id.shortest(8).prefix()",
  "commit_id.shortest(8).rest()",
  'if(current_working_copy, "@") ++ if(empty, "e") ++ if(immutable, "i") ++ if(conflict, "c")',
  'separate(" ", bookmarks, tags)',
].join(' ++ "\\x1f" ++ ') + ' ++ "\\n"';

async function jjRevisions(
  env: Environment,
  repo: Repository,
  revset: string,
  limit: number,
  context: Context,
  snapshot: boolean,
): Promise<Revision[]> {
  const out = await jj(env, repo, [
    "log",
    ...(snapshot ? [] : ["--ignore-working-copy"]),
    "--no-graph",
    `--revisions=${revset}`,
    `--limit=${limit}`,
    `--template=${JJ_REVISION}`,
  ], context);
  return out.split("\n").filter(Boolean).map((line) => {
    const [json, changePrefix, changeRest, commitPrefix, commitRest, flags, refs] = line.split(
      "\x1f",
    );
    const commit = JSON.parse(json) as {
      change_id: string;
      commit_id: string;
      description: string;
      author: { name: string; email: string; timestamp: string };
    };
    return {
      route: flags.includes("@") ? "" : commit.change_id,
      change: id(commit.change_id, changePrefix, changeRest),
      commit: id(commit.commit_id, commitPrefix, commitRest),
      description: commit.description,
      author: commit.author,
      refs: refs ? refs.split(" ") : [],
      workingCopy: flags.includes("@"),
      empty: flags.includes("e"),
      immutable: flags.includes("i"),
      conflict: flags.includes("c"),
    };
  });
}

const GIT_REVISION = "%H%x1f%h%x1f%an%x1f%ae%x1f%aI%x1f%D%x1f%B%x1e";

async function gitRevisions(
  env: Environment,
  repo: Repository,
  args: string[],
  context: Context,
): Promise<Revision[]> {
  const out = await git(env, repo, ["log", `--format=${GIT_REVISION}`, ...args, "--"], context);
  return out.split("\x1e").map((record) => record.replace(/^\n/, "")).filter(Boolean).map(
    (record) => {
      const [hash, short, name, email, timestamp, refs, description] = record.split("\x1f");
      return {
        route: hash,
        change: null,
        commit: id(hash, "", short),
        description,
        author: { name, email, timestamp },
        refs: refs ? refs.split(", ") : [],
        workingCopy: false,
        empty: false,
        immutable: false,
        conflict: false,
      };
    },
  );
}

const WORKING_TREE: Revision = {
  route: "",
  change: null,
  commit: null,
  description: "",
  author: null,
  refs: [],
  workingCopy: true,
  empty: false,
  immutable: false,
  conflict: false,
};

/** jj in the repository at `root`, for edits to its history. */
export const jjAt = (env: Environment, root: string, args: string[], context: Context) =>
  jj(env, { vcs: "jj", root }, args, context);

/** A jj change as it is now; `snapshot` takes in the working copy's edits first. */
export async function jjRevision(
  env: Environment,
  root: string,
  change: string,
  context: Context,
  snapshot: boolean,
): Promise<Revision | undefined> {
  return (await jjRevisions(env, { vcs: "jj", root }, checked(change, "jj"), 1, context, snapshot))[
    0
  ];
}

/** Routes name a jj change or a commit by its id, never by a revset or an option. */
function checked(route: string, vcs: Repository["vcs"]) {
  const valid = vcs === "jj" ? /^(?:[k-z]{1,64}|[0-9a-f]{4,64})$/ : /^[0-9a-f]{4,64}$/;
  if (!valid.test(route)) {
    throw new Error(`Not a ${vcs === "jj" ? "change or commit" : "commit"} id: ${route}`);
  }
  return route;
}

export const bounded = (files: FileDiff[]) =>
  files.map((file) =>
    file.hunks.reduce((sum, hunk) => sum + hunk.lines.length, 0) > LONG
      ? narrow(file, CONTEXT)
      : file
  );

/**
 * The repository's recent history and one revision's changes: `route` names it, or the working copy when empty. jj
 * snapshots the working copy once, first, so that the log and the changes agree.
 */
export async function show(
  env: Environment,
  route: string,
  limit: number,
  context: Context,
  whole = false,
): Promise<Shown> {
  const repo = await repository(env, context);
  if (repo.vcs === "jj") {
    const log = await jjRevisions(env, repo, "ancestors(@) ~ root()", limit, context, true);
    const revset = route === "" ? "@" : checked(route, "jj");
    const revision = log.find((revision) => revision.route === route) ??
      (await jjRevisions(env, repo, revset, 1, context, false))[0];
    if (revision === undefined) throw new Error(`No revision ${route}`);
    const patch = await jj(env, repo, [
      "diff",
      "--ignore-working-copy",
      "--git",
      `--context=${WHOLE}`,
      `--revisions=${revset}`,
    ], context);
    const files = parsePatch(patch);
    return { ...repo, log, revision, files: whole ? files : bounded(files), omitted: 0 };
  }

  const head = await git(env, repo, ["rev-parse", "--verify", "--quiet", "HEAD"], context, [0, 1]);
  const log = [
    {
      ...WORKING_TREE,
      conflict: !!(await git(env, repo, ["ls-files", "--unmerged", "-z"], context)),
    },
    ...(head.trim()
      ? await gitRevisions(env, repo, [`--max-count=${limit - 1}`, "HEAD"], context)
      : []),
  ];
  const options = [
    "-M",
    "--no-ext-diff",
    "--no-relative",
    "--src-prefix=a/",
    "--dst-prefix=b/",
    `--unified=${WHOLE}`,
  ];
  if (route !== "") {
    const hash = checked(route, "git");
    const revision = log.find((revision) => revision.route === hash) ??
      (await gitRevisions(env, repo, ["--max-count=1", hash], context))[0];
    const patch = await git(env, repo, [
      "show",
      "--format=",
      "--diff-merges=first-parent",
      ...options,
      revision.route,
      "--",
    ], context);
    const files = parsePatch(patch);
    return { ...repo, log, revision, files: whole ? files : bounded(files), omitted: 0 };
  }

  // the working tree against HEAD, or against nothing before the first commit
  const base = head.trim() || "4b825dc642cb6eb9a060e54bf8d69288fbee4904";
  const tracked = parsePatch(await git(env, repo, ["diff", ...options, base, "--"], context));
  const untracked =
    (await git(env, repo, ["ls-files", "--others", "--exclude-standard", "-z"], context))
      .split("\0").filter(Boolean);
  const added = await Promise.all(
    untracked.slice(0, UNTRACKED).map(async (path) =>
      parsePatch(
        await git(env, repo, ["diff", "--no-index", ...options, "--", "/dev/null", path], context, [
          0,
          1,
        ]),
      )
    ),
  );
  const files = [...tracked, ...added.flat()].sort((a, b) =>
    a.path < b.path ? -1 : a.path > b.path ? 1 : 0
  );
  return {
    ...repo,
    log,
    revision: log[0],
    files: whole ? files : bounded(files),
    omitted: Math.max(0, untracked.length - UNTRACKED),
  };
}