import type { Point, Range, Tree } from '@vscode/tree-sitter-wasm'
import type { LanguageAdapter, SourceRange } from './contract'
import * as path from 'node:path'
import { Language, Parser } from '@vscode/tree-sitter-wasm'

/** 打进扩展包里的 wasm 目录：dist/index.cjs 旁边的 dist/tree-sitter（esbuild 构建时复制）。只在打包产物里成立。 */
export function bundledWasmDir(): string {
  return path.join(__dirname, 'tree-sitter')
}

/** 没有语言插件、只给工作区索引解析的语言（接口契约 openapi.json）：languageId → 语法包的文件名。 */
const INDEX_GRAMMARS: Record<string, string> = { json: 'tree-sitter-json.wasm' }

/**
 * 工作区索引按 languageId 解析时，没有语言插件的语言用哪个语法包；不是这几种语言时没有。
 * @param wasmDir 放语法包的目录
 */
export function indexGrammar(wasmDir: string, languageId: string): Pick<LanguageAdapter, 'grammarPath'> | undefined {
  const file = INDEX_GRAMMARS[languageId]
  return file === undefined ? undefined : { grammarPath: () => path.join(wasmDir, file) }
}

/** 源码下标的行列（行从 0 起，列按 UTF-16，同 web-tree-sitter 解析 JS 字符串时的算法）。 */
function pointAt(source: string, index: number): Point {
  const lineStart = source.lastIndexOf('\n', index - 1) + 1
  let row = 0
  for (let at = source.indexOf('\n'); at !== -1 && at < index; at = source.indexOf('\n', at + 1))
    row++
  return { row, column: index - lineStart }
}

function includedRange(source: string, { startIndex, endIndex }: SourceRange): Range {
  return { startIndex, endIndex, startPosition: pointAt(source, startIndex), endPosition: pointAt(source, endIndex) }
}

// web-tree-sitter 的运行时是进程级单例：Parser.init 只能有效调用一次，后来的 wasm 目录不再生效
let runtimeReady: Promise<void> | undefined

function initRuntime(wasmDir: string): Promise<void> {
  runtimeReady ??= Parser.init({ locateFile: (file: string) => path.join(wasmDir, file) })
    .catch((err: unknown) => {
      runtimeReady = undefined
      throw err
    })
  return runtimeReady
}

/** 解析运行时：初始化一次 web-tree-sitter，语法包按 wasm 路径懒加载并缓存。 */
export class TreeSitterRuntime {
  private readonly parsers = new Map<string, Promise<Parser>>()

  /** @param wasmDir 放 tree-sitter.wasm 的目录 */
  constructor(private readonly wasmDir: string) {}

  /**
   * 返回的语法树占着 wasm 内存，用完必须 `tree.delete()`。给了 ranges 就只解析源码里的这几段（嵌着的代码，见 EmbeddedCode），
   * 节点的下标、行列照旧是整份源码的。
   */
  async parse(adapter: Pick<LanguageAdapter, 'grammarPath'>, languageId: string, source: string, ranges?: readonly SourceRange[]): Promise<Tree> {
    const parser = await this.parserFor(adapter.grammarPath(languageId))
    const tree = parser.parse(source, null, ranges ? { includedRanges: ranges.map(range => includedRange(source, range)) } : undefined)
    if (!tree)
      throw new Error(`tree-sitter 没能解析 ${languageId} 源码`)
    return tree
  }

  private parserFor(grammarPath: string): Promise<Parser> {
    let parser = this.parsers.get(grammarPath)
    if (!parser) {
      parser = initRuntime(this.wasmDir)
        .then(() => Language.load(grammarPath))
        .then(language => new Parser().setLanguage(language))
      parser.catch(() => this.parsers.delete(grammarPath))
      this.parsers.set(grammarPath, parser)
    }
    return parser
  }
}