import {
  Error as ErrorCtor,
  Map,
  Object,
  String,
  TypeError,
} from "ext:core/primordials";
import { promiseAll } from "ext:core/promises";
import {
  op_console_print,
  op_task_begin,
  op_task_digest,
  op_task_drop,
  op_task_finish,
  op_task_relevant,
  op_task_step,
} from "ext:core/ops";
import type {
  TaskActionJson,
  TaskGraphJson,
  TaskReadyJson,
  TaskReportJson,
} from "ext:core/ops";
import { spawn } from "ext:process/main.js";
import { watchFs } from "ext:file/main.js";
import type { AbortSignal } from "ext:web/events.js";
import { env } from "ext:base/env.js";
import { process, runtime } from "ext:base/host.js";
import { clearTimeout, setTimeout } from "ext:timers/timers.js";

/** The subset of `AbortSignal` that `avril:task` relies on; a real `AbortSignal` satisfies it. */
export interface AbortSignalLike {
  readonly aborted: boolean;
}

/** The context handed to a function task when it runs. */
export interface TaskContext {
  readonly name: string;
  /** The directory task paths are relative to. */
  readonly root: string;
  /** Extra arguments; non-empty only for the run's target. */
  readonly args: readonly string[];
  /** The task's effective environment: file defaults under the process environment. */
  readonly env: Record<string, string>;
  readonly signal?: AbortSignalLike;
}

export interface TaskDef {
  description?: string;
  /** A shell string (`sh -c` / `cmd /C`), or an argv array spawned without a shell. */
  command?: string | string[];
  /** An in-process action. Return a number to use it as the exit code. */
  run?: (ctx: TaskContext) => void | number | Promise<void | number>;
  dependencies?: string[];
  parallel?: boolean;
  envFile?: string;
  /** Declaring `files` opts the task into result caching. */
  files?: string | string[];
  output?: string | string[];
  env?: string | string[];
}

export interface FailedTaskInfo {
  name: string;
  code: number;
}

export interface TaskReport {
  readonly code: number;
  readonly ok: boolean;
  readonly completed: string[];
  readonly failed: FailedTaskInfo[];
  readonly cached: string[];
  /** Messages from function tasks that threw, by task name. */
  readonly errors: Record<string, string>;
  /** Throws a `TaskRunError` carrying this report when the run failed. */
  throwIfFailed(): void;
}

/** The error thrown by `TaskReport.throwIfFailed()`. */
export interface TaskRunError extends Error {
  readonly name: "TaskRunError";
  readonly report: TaskReport;
}

export type TaskEvent =
  | { type: "started"; name: string }
  | { type: "cached"; name: string }
  | { type: "finished"; name: string; code: number }
  | { type: "error"; name: string; message: string };

export interface RunOptions {
  /** The task to run. Defaults to `"all"`. */
  target?: string;
  /** Directory task paths are relative to. Defaults to the working directory. */
  root?: string;
  /** Extra arguments forwarded to the target. */
  args?: string[];
  /** Run cacheable tasks even when their outputs are intact. */
  force?: boolean;
  /** Task cache directory. Defaults to avril's shared task cache. */
  cacheDir?: string;
  /** Rerun when task inputs change, re-evaluating the graph each time. */
  watch?: boolean;
  signal?: AbortSignalLike;
  onEvent?: (event: TaskEvent) => void;
}

export type GraphInput =
  | Record<string, TaskDef>
  | (() => Record<string, TaskDef> | Promise<Record<string, TaskDef>>);

type TaskFn = (ctx: TaskContext) => void | number | Promise<void | number>;

function fail(path: string, message: string): never {
  throw new TypeError(`avril:task: ${path}: ${message}`);
}

function list(value: string | string[] | undefined, path: string): string[] | undefined {
  if (value === undefined) return undefined;
  const items = typeof value === "string" ? [value] : value;
  if (!Array.isArray(items) || items.some((item) => typeof item !== "string" || item === "")) {
    fail(path, "expected a string or an array of non-empty strings");
  }
  return [...items];
}

interface Prepared {
  graph: TaskGraphJson;
  functions: Map<number, TaskFn>;
}

async function prepare(input: GraphInput): Promise<Prepared> {
  const definitions = typeof input === "function" ? await input() : input;
  if (typeof definitions !== "object" || definitions === null || Array.isArray(definitions)) {
    fail("graph", "expected an object mapping task names to tasks");
  }
  const functions = new Map<number, TaskFn>();
  const tasks: TaskGraphJson["tasks"] = {};
  let nextId = 0;
  for (const [name, definition] of Object.entries(definitions)) {
    const path = `tasks.${name}`;
    if (typeof definition !== "object" || definition === null) {
      fail(path, "expected a task object");
    }
    const hasCommand = definition.command !== undefined;
    const hasRun = definition.run !== undefined;
    if (hasCommand && hasRun) {
      fail(path, "use either command or run, not both");
    }
    let action: TaskActionJson;
    if (!hasCommand && !hasRun) {
      action = "None";
    } else if (hasRun) {
      if (typeof definition.run !== "function") fail(`${path}.run`, "expected a function");
      const id = nextId++;
      functions.set(id, definition.run);
      // The function source is its fingerprint identity: editing the body
      // invalidates the task; editing its imports invalidates only via `files`.
      action = { Callback: { id, key: String(definition.run) } };
    } else if (typeof definition.command === "string") {
      if (definition.command.trim() === "") fail(`${path}.command`, "command cannot be empty");
      action = { Shell: definition.command };
    } else {
      const argv = list(definition.command, `${path}.command`);
      if (!argv || argv.length === 0) fail(`${path}.command`, "command array cannot be empty");
      action = { Argv: argv };
    }
    tasks[name] = {
      description: definition.description ?? null,
      action,
      dependencies: list(definition.dependencies, `${path}.dependencies`) ?? [],
      parallel: definition.parallel ?? false,
      env_file: definition.envFile ?? null,
      files: list(definition.files, `${path}.files`) ?? null,
      output: list(definition.output, `${path}.output`) ?? [],
      env: list(definition.env, `${path}.env`) ?? [],
    };
  }
  return { graph: { tasks }, functions };
}

function shellQuote(arg: string): string {
  if (runtime.os === "windows") return `"${arg.replaceAll('"', '\\"')}"`;
  if (/^[A-Za-z0-9._\-/:@%+=,]+$/.test(arg)) return arg;
  return `'${arg.replaceAll("'", "'\\''")}'`;
}

function environmentFor(defaults: Record<string, string>): Record<string, string> {
  const result: Record<string, string> = {};
  for (const [key, value] of Object.entries(defaults)) {
    let existing: string | undefined;
    try {
      existing = env.get(key);
    } catch {
      existing = undefined;
    }
    if (existing === undefined) result[key] = value;
  }
  return result;
}

function cacheDir(root: string, explicit?: string): string {
  if (explicit) return explicit;
  const fromEnv = (name: string): string | undefined => {
    try {
      return env.get(name);
    } catch {
      return undefined;
    }
  };
  const avrilCache = fromEnv("AVRIL_CACHE_DIR");
  const base = avrilCache ??
    (fromEnv("XDG_CACHE_HOME") ? `${fromEnv("XDG_CACHE_HOME")}/avril` : undefined) ??
    (fromEnv("HOME") ? `${fromEnv("HOME")}/.cache/avril` : undefined) ??
    `${process.cwd()}/.avril-cache`;
  void root;
  return `${base}/task-cache`;
}

interface RunState {
  root: string;
  target: string;
  options: RunOptions;
  errors: Record<string, string>;
}

async function executeReady(ready: TaskReadyJson, prepared: Prepared, state: RunState): Promise<number> {
  const { root, options } = state;
  const action = ready.action;
  if (typeof action === "object" && "Callback" in action) {
    const fn = prepared.functions.get(action.Callback.id);
    if (!fn) return 1;
    let snapshot: Record<string, string> = {};
    try {
      snapshot = { ...env.toObject() };
    } catch {
      snapshot = {};
    }
    try {
      const result = await fn({
        name: ready.name,
        root,
        args: ready.args,
        env: { ...ready.env, ...snapshot },
        signal: options.signal,
      });
      return typeof result === "number" ? result : 0;
    } catch (error) {
      const message = error instanceof ErrorCtor ? error.message : String(error);
      state.errors[ready.name] = message;
      options.onEvent?.({ type: "error", name: ready.name, message });
      if (!options.onEvent) op_console_print([true, `Task ${ready.name}: ${message}\n`]);
      return 1;
    }
  }
  let program: string;
  let argv: string[];
  if (typeof action === "object" && "Shell" in action) {
    const full = ready.args.length > 0
      ? `${action.Shell} ${ready.args.map(shellQuote).join(" ")}`
      : action.Shell;
    if (runtime.os === "windows") {
      program = "cmd";
      argv = ["/C", full];
    } else {
      program = "sh";
      argv = ["-c", full];
    }
  } else if (typeof action === "object" && "Argv" in action) {
    program = action.Argv[0];
    argv = [...action.Argv.slice(1), ...ready.args];
  } else {
    return 0;
  }
  const child = spawn(program, argv, {
    cwd: root,
    env: environmentFor(ready.env),
    stdin: "inherit",
    stdout: "inherit",
    stderr: "inherit",
    signal: options.signal as AbortSignal | undefined,
  });
  const status = await child.status;
  return status.code ?? 1;
}

function toReport(json: TaskReportJson, errors: Record<string, string>): TaskReport {
  const report: TaskReport = {
    code: json.code,
    ok: json.code === 0,
    completed: json.completed,
    failed: json.failed,
    cached: json.cached,
    errors,
    throwIfFailed() {
      if (json.code !== 0) {
        const error = new ErrorCtor(
          `Task run failed: ${json.failed.map((f) => `${f.name} (${f.code})`).join(", ") || "cancelled"}`,
        ) as TaskRunError;
        Object.assign(error, { name: "TaskRunError", report });
        throw error;
      }
    },
  };
  return report;
}

async function runOnce(prepared: Prepared, state: RunState, force: boolean): Promise<TaskReport> {
  const { root, target, options } = state;
  const session = op_task_begin({
    graph: prepared.graph,
    root,
    target,
    args: options.args ?? [],
    force,
    cache_dir: cacheDir(root, options.cacheDir),
  });
  try {
    for (;;) {
      const step = op_task_step(session);
      if ("Done" in step) {
        for (const name of step.Done.cached) {
          options.onEvent?.({ type: "cached", name });
        }
        return toReport(step.Done, state.errors);
      }
      await promiseAll(step.Ready.map(async (ready) => {
        options.onEvent?.({ type: "started", name: ready.name });
        const code = await executeReady(ready, prepared, state);
        op_task_finish({ session, name: ready.name, code });
        options.onEvent?.({ type: "finished", name: ready.name, code });
      }));
    }
  } finally {
    op_task_drop(session);
  }
}

/**
 * Runs a task graph with avril's task semantics: dependencies first
 * (concurrently where a task sets `parallel`), each task at most once,
 * and result caching for tasks that declare `files`. Resolves with a
 * report even when tasks fail; graph errors throw.
 */
export async function runTasks(input: GraphInput, options: RunOptions = {}): Promise<TaskReport> {
  const root = options.root ?? process.cwd();
  const state: RunState = {
    root,
    target: options.target ?? "all",
    options,
    errors: {},
  };

  let prepared = await prepare(input);
  let digest = op_task_digest(prepared.graph);
  let report = await runOnce(prepared, state, options.force ?? false);
  if (!options.watch) return report;

  const cacheRoot = cacheDir(root, options.cacheDir);
  const watcher = watchFs(root, { recursive: true, signal: options.signal as AbortSignal | undefined });
  let pendingPaths: { path: string; structural: boolean }[] = [];
  let timer: ReturnType<typeof setTimeout> | undefined;
  let regenerating = false;
  let dirty = false;

  const regenerate = async (): Promise<void> => {
    if (regenerating) {
      dirty = true;
      return;
    }
    regenerating = true;
    try {
      const paths = pendingPaths;
      pendingPaths = [];
      let relevant = true;
      try {
        relevant = op_task_relevant({
          graph: prepared.graph,
          target: state.target,
          root,
          paths,
        });
      } catch {
        relevant = true;
      }
      if (relevant) {
        prepared = await prepare(input);
        const nextDigest = op_task_digest(prepared.graph);
        const force = nextDigest !== digest;
        digest = nextDigest;
        report = await runOnce(prepared, state, force);
      }
    } catch (error) {
      const message = error instanceof ErrorCtor ? error.message : String(error);
      options.onEvent?.({ type: "error", name: state.target, message });
      if (!options.onEvent) op_console_print([true, `avril:task: ${message}\n`]);
    } finally {
      regenerating = false;
      if (dirty) {
        dirty = false;
        void regenerate();
      }
    }
  };

  const events = watcher as unknown as AsyncIterable<{
    kind: string;
    paths: readonly string[];
  }>;
  try {
    for await (const event of events) {
      const structural = event.kind === "create" || event.kind === "remove" ||
        event.kind === "rename" || event.kind === "rescan";
      for (const path of event.paths) {
        const text = String(path);
        if (text === cacheRoot || text.startsWith(`${cacheRoot}/`)) continue;
        pendingPaths.push({ path: text, structural });
      }
      if (timer !== undefined) clearTimeout(timer);
      timer = setTimeout(() => {
        timer = undefined;
        void regenerate();
      }, 50);
    }
  } finally {
    if (timer !== undefined) clearTimeout(timer);
    try {
      watcher.close();
    } catch {
      // Already closed by the abort signal.
    }
  }
  return report;
}