/**
 * Shell completion script generation.
 *
 * Loads shell-native template files and replaces placeholders with
 * dynamic values. This approach keeps the shell scripts readable
 * and auditable in their native format.
 *
 * The generated scripts use the `xo-complete` helper binary for dynamic
 * completions (invitation IDs, template names, resources, etc.).
 *
 * Usage:
 *   eval "$(xo-cli completions bash)"
 *   eval "$(xo-cli completions zsh)"
 *   xo-cli completions fish | source
 *
 * Install to shell config:
 *   xo-cli completions bash --install
 *   xo-cli completions zsh --install
 *   xo-cli completions fish --install
 */

import {
  existsSync,
  readFileSync,
  appendFileSync,
  writeFileSync,
} from "node:fs";
import { dirname, join } from "node:path";
import { fileURLToPath } from "node:url";
import { homedir } from "node:os";

/**
 * Single source of truth for the CLI command tree.
 * Each top-level key is a command, and its value is an array of sub-commands.
 *
 * IMPORTANT: Keep this in sync with actual switch statements in command handlers:
 * - mnemonic.ts: create, import, list, expose
 * - template.ts: import, list, inspect, set-default
 * - invitation.ts: create, append, sign, broadcast, requirements, import, inspect, list
 * - resource.ts: list, unreserve, unreserve-all
 */

/** Subcommands for the mnemonic command */
const MNEMONIC_SUBS = ["create", "import", "list", "expose"];
/** Subcommands for the template command */
const TEMPLATE_SUBS = ["import", "list", "inspect", "set-default"];
/** Subcommands for the invitation command */
const INVITATION_SUBS = [
  "create",
  "append",
  "sign",
  "broadcast",
  "requirements",
  "import",
  "inspect",
  "list",
];
/** Subcommands for the resource command */
const RESOURCE_SUBS = ["list", "unreserve", "unreserve-all"];
/** Subcommands for the completions command */
const COMPLETIONS_SUBS = ["bash", "zsh", "fish"];

export const COMMAND_TREE = {
  mnemonic: MNEMONIC_SUBS,
  template: TEMPLATE_SUBS,
  invitation: INVITATION_SUBS,
  receive: [],
  resource: RESOURCE_SUBS,
  help: [],
  completions: COMPLETIONS_SUBS,
} as const;

/** Global option flags available on every command. */
const GLOBAL_OPTIONS = [
  "-h",
  "--help",
  "-v",
  "--verbose",
  "-m",
  "--mnemonic-file",
  "-o",
  "--output",
];

/**
 * Gets the path to the scripts directory containing shell templates.
 */
function getScriptsDir(): string {
  const currentFile = fileURLToPath(import.meta.url);
  return join(dirname(currentFile), "scripts");
}

/**
 * Loads a shell template file and replaces placeholders.
 * @param templateName - The template file name (e.g., "bash.sh")
 * @param binName - The CLI binary name
 */
function loadAndProcessTemplate(templateName: string, binName: string): string {
  const scriptsDir = getScriptsDir();
  const templatePath = join(scriptsDir, templateName);

  if (!existsSync(templatePath)) {
    throw new Error(`Template file not found: ${templatePath}`);
  }

  let content = readFileSync(templatePath, "utf8");
  const funcName = binName.replace(/-/g, "_");
  const commands = Object.keys(COMMAND_TREE).join(" ");
  const options = GLOBAL_OPTIONS.join(" ");

  // Replace all placeholders
  content = content.replace(/\{\{BIN_NAME\}\}/g, binName);
  content = content.replace(/\{\{FUNC_NAME\}\}/g, funcName);
  content = content.replace(/\{\{COMMANDS\}\}/g, commands);
  content = content.replace(/\{\{OPTIONS\}\}/g, options);
  content = content.replace(/\{\{MNEMONIC_SUBS\}\}/g, MNEMONIC_SUBS.join(" "));
  content = content.replace(/\{\{TEMPLATE_SUBS\}\}/g, TEMPLATE_SUBS.join(" "));
  content = content.replace(
    /\{\{INVITATION_SUBS\}\}/g,
    INVITATION_SUBS.join(" "),
  );
  content = content.replace(/\{\{RESOURCE_SUBS\}\}/g, RESOURCE_SUBS.join(" "));

  // Fish-specific placeholders
  if (templateName.endsWith(".fish")) {
    content = content.replace(
      /\{\{TOP_LEVEL_COMMANDS\}\}/g,
      generateFishTopLevelCommands(binName),
    );
    content = content.replace(
      /\{\{STATIC_SUBCOMMANDS\}\}/g,
      generateFishStaticSubcommands(binName),
    );
  }

  return content;
}

/**
 * Generates fish top-level command completions.
 */
function generateFishTopLevelCommands(binName: string): string {
  const lines: string[] = [];
  for (const cmd of Object.keys(COMMAND_TREE)) {
    lines.push(
      `complete -c ${binName} -n "__fish_use_subcommand" -a "${cmd}" -d "${cmd} command"`,
    );
  }
  return lines.join("\n");
}

/**
 * Generates fish static subcommand completions.
 */
function generateFishStaticSubcommands(binName: string): string {
  const lines: string[] = [];
  for (const [cmd, subs] of Object.entries(COMMAND_TREE)) {
    for (const sub of subs) {
      lines.push(
        `complete -c ${binName} -n "__fish_seen_subcommand_from ${cmd}; and not __fish_seen_subcommand_from ${subs.join(" ")}" -a "${sub}" -d "${cmd} ${sub}"`,
      );
    }
  }
  return lines.join("\n");
}

/**
 * Generates a bash completion script.
 * @param binName - The name of the CLI binary.
 */
export function generateBashCompletions(binName: string): string {
  return loadAndProcessTemplate("bash.sh", binName);
}

/**
 * Generates a zsh completion script.
 * @param binName - The name of the CLI binary.
 */
export function generateZshCompletions(binName: string): string {
  return loadAndProcessTemplate("zsh.zsh", binName);
}

/**
 * Generates a fish completion script.
 * @param binName - The name of the CLI binary.
 */
export function generateFishCompletions(binName: string): string {
  return loadAndProcessTemplate("fish.fish", binName);
}

type ShellType = "bash" | "zsh" | "fish";

const generators: Record<ShellType, (binName: string) => string> = {
  bash: generateBashCompletions,
  zsh: generateZshCompletions,
  fish: generateFishCompletions,
};

/**
 * Shell config file paths and eval commands for each shell type.
 */
const shellConfigs: Record<
  ShellType,
  { configFile: string; evalCommand: (binName: string) => string }
> = {
  bash: {
    configFile: join(homedir(), ".bashrc"),
    evalCommand: (binName) => `eval "$(${binName} completions bash)"`,
  },
  zsh: {
    configFile: join(homedir(), ".zshrc"),
    evalCommand: (binName) => `eval "$(${binName} completions zsh)"`,
  },
  fish: {
    configFile: join(homedir(), ".config", "fish", "config.fish"),
    evalCommand: (binName) => `${binName} completions fish | source`,
  },
};

/**
 * Installs completions to the user's shell config file.
 * Adds the eval command if not already present.
 * @param shell - The shell type
 * @param binName - The CLI binary name
 * @returns true if installed, false if already present
 */
function installCompletions(shell: ShellType, binName: string): boolean {
  const config = shellConfigs[shell];
  const evalCommand = config.evalCommand(binName);

  // Check if config file exists and already has the completion line
  let existingContent = "";
  if (existsSync(config.configFile)) {
    existingContent = readFileSync(config.configFile, "utf8");
    if (existingContent.includes(evalCommand)) {
      return false; // Already installed
    }
  }

  // Append the completion line
  const newLine =
    existingContent.endsWith("\n") || existingContent === "" ? "" : "\n";
  const completionBlock = `${newLine}\n# ${binName} shell completions\n${evalCommand}\n`;

  appendFileSync(config.configFile, completionBlock);
  return true;
}

/**
 * Handles the `completions` command.
 * Prints the generated completion script for the given shell to stdout,
 * or installs it to the shell config file with --install.
 * @param args - Positional args after "completions", e.g. ["bash"].
 * @param options - Parsed command options (may include "install").
 * @param binName - The CLI binary name to use in the completion script.
 */
export function handleCompletionsCommand(
  args: string[],
  options: Record<string, string> = {},
  binName: string = "xo-cli",
): void {
  const shell = args[0] as ShellType | undefined;
  const installFlag = options["install"] === "true";

  if (!shell || !generators[shell]) {
    const supported = Object.keys(generators).join(", ");
    console.error(`Usage: ${binName} completions <${supported}> [--install]`);
    console.error("");
    console.error("Examples:");
    console.error(
      `  eval "$(${binName} completions bash)"   # Output to stdout (add to ~/.bashrc)`,
    );
    console.error(
      `  eval "$(${binName} completions zsh)"    # Output to stdout (add to ~/.zshrc)`,
    );
    console.error(
      `  ${binName} completions fish | source    # Output to stdout (add to fish config)`,
    );
    console.error("");
    console.error("Install directly to shell config:");
    console.error(
      `  ${binName} completions bash --install   # Appends to ~/.bashrc`,
    );
    console.error(
      `  ${binName} completions zsh --install    # Appends to ~/.zshrc`,
    );
    console.error(
      `  ${binName} completions fish --install   # Appends to ~/.config/fish/config.fish`,
    );
    process.exit(1);
  }

  if (installFlag) {
    const config = shellConfigs[shell];
    const installed = installCompletions(shell, binName);

    if (installed) {
      console.log(`Completions installed to ${config.configFile}`);
      console.log(`Restart your shell or run: source ${config.configFile}`);
    } else {
      console.log(`Completions already installed in ${config.configFile}`);
    }
    return;
  }

  process.stdout.write(generators[shell](binName));
}