/**
 * File reference parsing and building for handoff sessions.
 *
 * Handles extraction of @file references from handoff prompts and
 * building synthetic text parts that match OpenCode's Read tool output format.
 */

import * as path from "node:path"
import * as fs from "node:fs/promises"
import type { TextPartInput } from "@opencode-ai/sdk"
import { isBinaryFile, formatFileContent } from "./vendor"

/**
 * File reference regex matching OpenCode's internal pattern.
 * Matches @file references like @src/plugin.ts
 */
export const FILE_REGEX = /(?<![\w`])@(\.?[^\s`,.]*(?:\.[^\s`,.]+)*)/g

/**
 * Parse @file references from text.
 *
 * @param text - Text to search for @file references
 * @returns Set of file paths referenced in the text
 */
export function parseFileReferences(text: string): Set<string> {
  const fileRefs = new Set<string>()

  for (const match of text.matchAll(FILE_REGEX)) {
    if (match[1]) {
      fileRefs.add(match[1])
    }
  }

  return fileRefs
}

/**
 * Build synthetic text parts matching OpenCode's Read tool output.
 *
 * Creates two synthetic text parts for each file:
 * 1. Header describing the Read tool call
 * 2. Formatted file content with line numbers
 *
 * @param directory - Project directory to resolve relative paths against
 * @param refs - Set of file path references to check
 * @returns Array of synthetic text parts (non-existent and binary files are skipped)
 */
export async function buildSyntheticFileParts(
  directory: string,
  refs: Set<string>
): Promise<TextPartInput[]> {
  const parts: TextPartInput[] = []

  for (const ref of refs) {
    const filepath = path.resolve(directory, ref)

    try {
      // Check if file exists
      const stats = await fs.stat(filepath)
      if (!stats.isFile()) continue

      // Skip binary files
      if (await isBinaryFile(filepath)) continue

      // Read file content
      const content = await fs.readFile(filepath, "utf-8")

      // Create header part (matching OpenCode's prompt.ts:820 format)
      parts.push({
        type: "text",
        synthetic: true,
        text: `Called the Read tool with the following input: ${JSON.stringify({ filePath: filepath })}`
      })

      // Create content part (matching OpenCode's ReadTool format)
      parts.push({
        type: "text",
        synthetic: true,
        text: formatFileContent(filepath, content)
      })
    } catch {
      // Skip silently if file can't be read
    }
  }

  return parts
}