import { readdirSync } from "node:fs";
import { spawnSync } from "node:child_process";
import { basename, dirname, isAbsolute, join, resolve } from "node:path";
import type { AutocompleteItem, AutocompleteProvider, AutocompleteSuggestions } from "@earendil-works/pi-tui";
import { matchHistoryEntries, readGlobalShellHistory, readProjectHistory } from "./history.ts";
import type { ExtendedCompletionItem, GhostSuggestion } from "./types.ts";

interface TokenContext {
  line: string;
  cursorCol: number;
  beforeCursor: string;
  afterCursor: string;
  token: string;
  tokenStart: number;
  tokenEnd: number;
  tokenIndex: number;
  previousTokens: string[];
}

export interface OneOffBashCommandContext {
  prefix: string;
  command: string;
  offset: number;
}

const GIT_SUBCOMMANDS = [
  "add", "bisect", "branch", "checkout", "cherry-pick", "clean", "clone", "commit", "diff", "fetch",
  "grep", "init", "log", "merge", "mv", "pull", "push", "rebase", "reset", "restore", "revert", "rm",
  "show", "stash", "status", "switch", "tag", "worktree",
];

function tokenizeBeforeCursor(text: string): string[] {
  const tokens: string[] = [];
  let current = "";
  let quote: "'" | '"' | null = null;
  let escaped = false;

  for (const char of text) {
    if (escaped) {
      current += char;
      escaped = false;
      continue;
    }

    if (char === "\\") {
      escaped = true;
      current += char;
      continue;
    }

    if (quote) {
      current += char;
      if (char === quote) quote = null;
      continue;
    }

    if (char === "'" || char === '"') {
      quote = char;
      current += char;
      continue;
    }

    if (/\s/.test(char)) {
      if (current) {
        tokens.push(current);
        current = "";
      }
      continue;
    }

    current += char;
  }

  if (current) tokens.push(current);
  return tokens;
}

function getTokenContext(line: string, cursorCol: number): TokenContext {
  const beforeCursor = line.slice(0, cursorCol);
  const afterCursor = line.slice(cursorCol);
  const tokens = tokenizeBeforeCursor(beforeCursor);

  let tokenStart = 0;
  for (let i = beforeCursor.length - 1; i >= 0; i -= 1) {
    const char = beforeCursor[i];
    if (char && /\s/.test(char)) {
      tokenStart = i + 1;
      break;
    }
  }

  let tokenEnd = cursorCol;
  for (let i = cursorCol; i < line.length; i += 1) {
    const char = line[i];
    if (char && /\s/.test(char)) break;
    tokenEnd = i + 1;
  }

  return {
    line,
    cursorCol,
    beforeCursor,
    afterCursor,
    token: line.slice(tokenStart, tokenEnd),
    tokenStart,
    tokenEnd,
    tokenIndex: Math.max(0, tokens.length - 1),
    previousTokens: tokens,
  };
}

export function getOneOffBashCommandContext(line: string): OneOffBashCommandContext | null {
  if (line.startsWith("!!")) {
    return {
      prefix: "!!",
      command: line.slice(2),
      offset: 2,
    };
  }

  if (line.startsWith("!")) {
    return {
      prefix: "!",
      command: line.slice(1),
      offset: 1,
    };
  }

  return null;
}

export function supportsShouldTriggerFileCompletion(
  provider: AutocompleteProvider,
): provider is AutocompleteProvider & {
  shouldTriggerFileCompletion(lines: string[], cursorLine: number, cursorCol: number): boolean;
} {
  return "shouldTriggerFileCompletion" in provider && typeof provider.shouldTriggerFileCompletion === "function";
}

export function isExtendedCompletionItem(item: AutocompleteItem): item is ExtendedCompletionItem {
  return "replacement" in item
    && typeof item.replacement === "string"
    && "startCol" in item
    && typeof item.startCol === "number"
    && "endCol" in item
    && typeof item.endCol === "number";
}

function uniqueByReplacement(items: ExtendedCompletionItem[]): ExtendedCompletionItem[] {
  const best = new Map<string, ExtendedCompletionItem>();
  for (const item of items) {
    const key = `${item.startCol}:${item.endCol}:${item.replacement}`;
    const existing = best.get(key);
    if (!existing || item.score > existing.score) {
      best.set(key, item);
    }
  }
  return [...best.values()].sort((a, b) => b.score - a.score || a.label.localeCompare(b.label));
}

function pathBase(token: string, cwd: string): { dir: string; prefix: string; displayPrefix: string } {
  const expanded = token.startsWith("~/")
    ? join(process.env.HOME || "", token.slice(2))
    : token;

  const hasSlash = expanded.includes("/");
  if (!hasSlash) {
    return { dir: cwd, prefix: expanded, displayPrefix: "" };
  }

  const baseDir = expanded.endsWith("/") ? expanded.slice(0, -1) : dirname(expanded);
  const resolvedDir = isAbsolute(baseDir) ? baseDir : resolve(cwd, baseDir);
  const prefix = expanded.endsWith("/") ? "" : basename(expanded);
  const displayPrefix = token.endsWith("/") ? token : token.slice(0, Math.max(0, token.length - prefix.length));
  return { dir: resolvedDir, prefix, displayPrefix };
}

function escapeShellPath(value: string): string {
  return value.replace(/([\\\s"'`$&|;<>()[\]{}?!*])/g, "\\$1");
}

function getPathSuggestions(
  ctx: TokenContext,
  cwd: string,
): ExtendedCompletionItem[] {
  const token = ctx.token;
  if (!token) return [];
  const tokenStart = ctx.tokenStart;
  const tokenEnd = ctx.tokenEnd;

  // `~`, `.`, and `..` are directory shorthand, not filenames to match.
  if (token === "~" || token === "." || token === "..") {
    return [
      {
        value: `${token}/`,
        label: `${token}/`,
        replacement: `${token}/`,
        startCol: tokenStart,
        endCol: tokenEnd,
        source: "path",
        score: 50,
      } satisfies ExtendedCompletionItem,
    ];
  }

  const { dir, prefix, displayPrefix } = pathBase(token, cwd);

  try {
    const entries = readdirSync(dir, { withFileTypes: true })
      .filter((entry) => prefix.length === 0 || entry.name.startsWith(prefix))
      .slice(0, 100);

    // Complete only the basename part of the token and skip re-emitting the
    // directory prefix the user already typed. For a fully-typed dir (trailing
    // "/") replace the whole token so the new entry is appended correctly.
    const isFullDir = token.endsWith("/");
    const startCol = isFullDir
      ? tokenStart
      : displayPrefix.length === 0
        ? tokenStart
        : tokenStart + displayPrefix.length;

    return entries.map((entry) => {
      const suffix = entry.isDirectory() ? "/" : "";
      const label = `${displayPrefix}${entry.name}${suffix}`;
      const replacement = `${isFullDir ? displayPrefix : ""}${escapeShellPath(entry.name)}${suffix}`;
      return {
        value: replacement,
        label,
        replacement,
        startCol,
        endCol: tokenEnd,
        source: "path",
        score: 40 + (entry.isDirectory() ? 4 : 0),
      } satisfies ExtendedCompletionItem;
    });
  } catch {
    // Missing or unreadable directories should only remove this completion source.
    return [];
  }
}

function runGit(args: string[], cwd: string): string[] {
  try {
    const result = spawnSync("git", args, {
      cwd,
      encoding: "utf8",
      stdio: ["ignore", "pipe", "ignore"],
    });
    if (result.status !== 0 || !result.stdout) return [];
    return result.stdout.split("\n").map((line) => line.trim()).filter(Boolean);
  } catch {
    // Git-aware completions are optional and should not break the main completion flow.
    return [];
  }
}

function getGitSuggestions(ctx: TokenContext, cwd: string): ExtendedCompletionItem[] {
  const tokens = ctx.previousTokens;
  if (tokens[0] !== "git") return [];

  if (ctx.tokenIndex <= 1) {
    return GIT_SUBCOMMANDS
      .filter((command) => command.startsWith(ctx.token))
      .map((command) => ({
        value: command,
        label: command,
        replacement: command,
        startCol: 0,
        endCol: 0,
        source: "git",
        // Exact subcommand matches outrank mere prefixes (e.g. `git sta` → status).
        score: command === ctx.token ? 62 : 52,
      }));
  }

  const subcommand = tokens[1] ?? "";
  if (!["checkout", "switch", "merge", "rebase", "branch", "show", "diff"].includes(subcommand)) {
    return [];
  }

  const refs = [
    ...runGit(["branch", "--format=%(refname:short)"], cwd),
    ...runGit(["tag", "--list"], cwd),
  ];

  return [...new Set(refs)]
    .filter((ref) => ref.startsWith(ctx.token))
    .slice(0, 100)
    .map((ref) => ({
      value: ref,
      label: ref,
      replacement: ref,
      startCol: 0,
      endCol: 0,
      source: "git",
      score: 50,
    }));
}

function canUseHistorySuggestion(ctx: TokenContext): boolean {
  return ctx.cursorCol === ctx.line.length && ctx.line.trim().length > 0;
}

function withRange(items: ExtendedCompletionItem[], startCol: number, endCol: number): ExtendedCompletionItem[] {
  return items.map((item) => ({ ...item, startCol, endCol }));
}

function applyCompletionToLine(line: string, item: ExtendedCompletionItem): string {
  return line.slice(0, item.startCol) + item.replacement + line.slice(item.endCol);
}

function commandHead(value: string): string {
  return tokenizeBeforeCursor(value.trim())[0] ?? "";
}

function findNewestHistoryMatchForHead(entries: string[], prefix: string, head: string): string | null {
  for (const rawEntry of entries) {
    const entry = rawEntry.trim();
    if (!entry || !entry.startsWith(prefix)) continue;
    if (commandHead(entry) !== head) continue;
    return entry;
  }
  return null;
}

function getCuratedCommandFallback(prefix: string): GhostSuggestion | null {
  const trimmed = prefix.trim();
  if (!trimmed) return null;

  if ("cd".startsWith(trimmed)) {
    return { value: "cd ..", source: "path" };
  }

  if ("git".startsWith(trimmed)) {
    return { value: "git status", source: "git" };
  }

  return null;
}

function isLikelyGitCommandHead(prefix: string): boolean {
  const trimmed = prefix.trim();
  return trimmed.length >= 2 && "git".startsWith(trimmed);
}

function boostValidatedItemsFromGlobalHistory(
  line: string,
  items: ExtendedCompletionItem[],
  globalHistoryMatches: string[],
): ExtendedCompletionItem[] {
  if (items.length === 0 || globalHistoryMatches.length === 0) {
    return items;
  }

  const boosts = new Map<string, number>();
  for (const [index, value] of globalHistoryMatches.entries()) {
    boosts.set(value, Math.max(1, 4 - index));
  }

  return items.map((item) => {
    const boost = boosts.get(applyCompletionToLine(line, item));
    return boost ? { ...item, score: item.score + boost } : item;
  });
}

export class BashCompletionEngine {
  async getGhostSuggestion(line: string, cwd: string, shellPath: string, signal: AbortSignal): Promise<GhostSuggestion | null> {
    const projectHistoryEntries = readProjectHistory(cwd);

    if (line.trim().length === 0) {
      const prefix = line;
      const projectHistory = matchHistoryEntries(
        projectHistoryEntries.map((entry) => entry.command),
        line,
        1,
      );
      if (projectHistory.length > 0) {
        return { value: `${prefix}${projectHistory[0]!}`, source: "project-history" };
      }

      return null;
    }

    const ctx = getTokenContext(line, line.length);
    if (!canUseHistorySuggestion(ctx)) return null;

    const projectHistory = matchHistoryEntries(
      projectHistoryEntries.map((entry) => entry.command),
      line,
      10,
    );
    if (projectHistory.length > 0) {
      return { value: projectHistory[0]!, source: "project-history" };
    }

    if (ctx.tokenIndex === 0) {
      return this.getCommandPositionGhostSuggestion(line, readGlobalShellHistory(shellPath));
    }

    const deterministic = this.getDeterministicInlineSuggestions(ctx, cwd);
    const globalHistory = matchHistoryEntries(readGlobalShellHistory(shellPath), line, 5);
    const ranked = boostValidatedItemsFromGlobalHistory(
      line,
      uniqueByReplacement(deterministic),
      globalHistory,
    );

    for (const item of ranked) {
      const value = this.buildInlineSuggestionValue(line, item);
      if (value) {
        return { value, source: item.source };
      }
    }

    return null;
  }

  private getCommandPositionGhostSuggestion(
    line: string,
    globalHistoryEntries: string[],
  ): GhostSuggestion | null {
    if (isLikelyGitCommandHead(line)) {
      const globalMatch = findNewestHistoryMatchForHead(globalHistoryEntries, line, "git");
      if (globalMatch) {
        return { value: globalMatch, source: "global-history" };
      }
    }

    return getCuratedCommandFallback(line);
  }

  private getDeterministicInlineSuggestions(ctx: TokenContext, cwd: string): ExtendedCompletionItem[] {
    const items: ExtendedCompletionItem[] = [];
    items.push(...withRange(getGitSuggestions(ctx, cwd), ctx.tokenStart, ctx.tokenEnd));
    items.push(...getPathSuggestions(ctx, cwd));

    return uniqueByReplacement(items);
  }

  private buildInlineSuggestionValue(line: string, item: ExtendedCompletionItem): string | null {
    const value = applyCompletionToLine(line, item);
    if (!value.startsWith(line) || value === line) {
      return null;
    }
    return value;
  }

}