import { splitPromptIntoComposerSegments } from "./composer-editor-mentions";

export type ComposerTriggerKind = "path" | "slash-command" | "slash-model";
export type ComposerSlashCommand = "model" | "plan" | "default";

export interface ComposerTrigger {
  kind: ComposerTriggerKind;
  query: string;
  rangeStart: number;
  rangeEnd: number;
}

const SLASH_COMMANDS: readonly ComposerSlashCommand[] = ["model", "plan", "default"];

function clampCursor(text: string, cursor: number): number {
  if (!Number.isFinite(cursor)) return text.length;
  return Math.max(0, Math.min(text.length, Math.floor(cursor)));
}

function isWhitespace(char: string): boolean {
  return char === " " || char === "\n" || char === "\t" || char === "\r";
}

function tokenStartForCursor(text: string, cursor: number): number {
  let index = cursor - 1;
  while (index >= 0 && !isWhitespace(text[index] ?? "")) {
    index -= 1;
  }
  return index + 1;
}

export function expandCollapsedComposerCursor(text: string, cursorInput: number): number {
  const collapsedCursor = clampCursor(text, cursorInput);
  const segments = splitPromptIntoComposerSegments(text);
  if (segments.length === 0) {
    return collapsedCursor;
  }

  let remaining = collapsedCursor;
  let expandedCursor = 0;

  for (const segment of segments) {
    if (segment.type === "mention") {
      const expandedLength = segment.path.length + 1;
      if (remaining <= 1) {
        return expandedCursor + (remaining === 0 ? 0 : expandedLength);
      }
      remaining -= 1;
      expandedCursor += expandedLength;
      continue;
    }

    const segmentLength = segment.text.length;
    if (remaining <= segmentLength) {
      return expandedCursor + remaining;
    }
    remaining -= segmentLength;
    expandedCursor += segmentLength;
  }

  return expandedCursor;
}

function collapsedSegmentLength(segment: { type: "text"; text: string } | { type: "mention" }): number {
  return segment.type === "mention" ? 1 : segment.text.length;
}

function clampCollapsedComposerCursor(
  segments: ReadonlyArray<{ type: "text"; text: string } | { type: "mention" }>,
  cursorInput: number,
): number {
  const collapsedLength = segments.reduce(
    (total, segment) => total + collapsedSegmentLength(segment),
    0,
  );
  if (!Number.isFinite(cursorInput)) {
    return collapsedLength;
  }
  return Math.max(0, Math.min(collapsedLength, Math.floor(cursorInput)));
}

export function isCollapsedCursorAdjacentToMention(
  text: string,
  cursorInput: number,
  direction: "left" | "right",
): boolean {
  const segments = splitPromptIntoComposerSegments(text);
  if (!segments.some((segment) => segment.type === "mention")) {
    return false;
  }

  const cursor = clampCollapsedComposerCursor(segments, cursorInput);
  let collapsedOffset = 0;

  for (const segment of segments) {
    if (segment.type === "mention") {
      if (direction === "left" && cursor === collapsedOffset + 1) {
        return true;
      }
      if (direction === "right" && cursor === collapsedOffset) {
        return true;
      }
    }
    collapsedOffset += collapsedSegmentLength(segment);
  }

  return false;
}

export function detectComposerTrigger(text: string, cursorInput: number): ComposerTrigger | null {
  const cursor = clampCursor(text, cursorInput);
  const lineStart = text.lastIndexOf("\n", Math.max(0, cursor - 1)) + 1;
  const linePrefix = text.slice(lineStart, cursor);

  if (linePrefix.startsWith("/")) {
    const commandMatch = /^\/(\S*)$/.exec(linePrefix);
    if (commandMatch) {
      const commandQuery = commandMatch[1] ?? "";
      if (commandQuery.toLowerCase() === "model") {
        return {
          kind: "slash-model",
          query: "",
          rangeStart: lineStart,
          rangeEnd: cursor,
        };
      }
      if (SLASH_COMMANDS.some((command) => command.startsWith(commandQuery.toLowerCase()))) {
        return {
          kind: "slash-command",
          query: commandQuery,
          rangeStart: lineStart,
          rangeEnd: cursor,
        };
      }
      return null;
    }

    const modelMatch = /^\/model(?:\s+(.*))?$/.exec(linePrefix);
    if (modelMatch) {
      return {
        kind: "slash-model",
        query: (modelMatch[1] ?? "").trim(),
        rangeStart: lineStart,
        rangeEnd: cursor,
      };
    }
  }

  const tokenStart = tokenStartForCursor(text, cursor);
  const token = text.slice(tokenStart, cursor);
  if (!token.startsWith("@")) {
    return null;
  }

  return {
    kind: "path",
    query: token.slice(1),
    rangeStart: tokenStart,
    rangeEnd: cursor,
  };
}

export function parseStandaloneComposerSlashCommand(text: string): Exclude<
  ComposerSlashCommand,
  "model"
> | null {
  const match = /^\/(plan|default)\s*$/i.exec(text.trim());
  if (!match) {
    return null;
  }
  return match[1]?.toLowerCase() === "plan" ? "plan" : "default";
}

export function replaceTextRange(
  text: string,
  rangeStart: number,
  rangeEnd: number,
  replacement: string,
): { text: string; cursor: number } {
  const safeStart = Math.max(0, Math.min(text.length, rangeStart));
  const safeEnd = Math.max(safeStart, Math.min(text.length, rangeEnd));
  const nextText = `${text.slice(0, safeStart)}${replacement}${text.slice(safeEnd)}`;
  return { text: nextText, cursor: safeStart + replacement.length };
}