// Minimal LSP client over stdio (JSON-RPC 2.0 with Content-Length framing).
import { spawn } from 'node:child_process'
import { EventEmitter } from 'node:events'
import fs from 'node:fs'
import path from 'node:path'
import { pathToFileURL, fileURLToPath } from 'node:url'

export const toUri = (p) => pathToFileURL(p).href
export const fromUri = (u) => { try { return fileURLToPath(u) } catch { return u } }

export class LspClient extends EventEmitter {
  constructor({ id, command, args = [], root, env, initializationOptions, settings, languageIdFor }) {
    super()
    this.id = id
    this.command = command
    this.args = args
    this.root = root
    this.env = env
    this.initializationOptions = initializationOptions
    this.settings = settings
    this.languageIdFor = languageIdFor
    this.seq = 0
    this.pending = new Map()
    this.buffer = Buffer.alloc(0)
    this.docs = new Map() // uri -> { version, text }
    this.diagnostics = new Map() // uri -> { version, items, at }
    this.capabilities = null
    this.state = 'new'
    this.stderr = ''
    this.lastUsed = Date.now()
  }

  async start(timeoutMs = 30000) {
    if (this.state !== 'new') return this.ready
    this.state = 'starting'
    this.ready = (async () => {
      this.proc = spawn(this.command, this.args, { cwd: this.root, env: { ...process.env, ...this.env }, stdio: ['pipe', 'pipe', 'pipe'] })
      this.proc.on('error', (e) => this.fail(e))
      this.proc.on('exit', (code, sig) => this.fail(new Error(`${this.id} exited (${sig ?? code})${this.stderr ? `: ${this.stderr.slice(-400)}` : ''}`)))
      this.proc.stdout.on('data', (d) => this.onData(d))
      this.proc.stderr.on('data', (d) => { this.stderr = (this.stderr + d).slice(-4000) })
      this.proc.stdin.on('error', () => {})
      const res = await this.request('initialize', {
        processId: process.pid,
        rootUri: toUri(this.root),
        rootPath: this.root,
        workspaceFolders: [{ uri: toUri(this.root), name: path.basename(this.root) }],
        initializationOptions: this.initializationOptions,
        capabilities: {
          general: { positionEncodings: ['utf-16'] },
          workspace: { workspaceFolders: true, configuration: true, applyEdit: true, workspaceEdit: { documentChanges: true }, symbol: {}, didChangeWatchedFiles: { dynamicRegistration: false } },
          textDocument: {
            synchronization: { didSave: true, dynamicRegistration: false },
            publishDiagnostics: { relatedInformation: true, versionSupport: true, codeDescriptionSupport: true },
            diagnostic: { dynamicRegistration: false, relatedDocumentSupport: false },
            hover: { contentFormat: ['markdown', 'plaintext'] },
            definition: { linkSupport: true }, typeDefinition: { linkSupport: true }, implementation: { linkSupport: true },
            references: {}, documentSymbol: { hierarchicalDocumentSymbolSupport: true },
            rename: { prepareSupport: true },
            codeAction: { codeActionLiteralSupport: { codeActionKind: { valueSet: ['', 'quickfix', 'refactor', 'refactor.extract', 'refactor.inline', 'refactor.rewrite', 'source', 'source.organizeImports', 'source.fixAll'] } }, resolveSupport: { properties: ['edit'] } },
          },
        },
      }, timeoutMs)
      this.capabilities = res?.capabilities ?? {}
      this.notify('initialized', {})
      if (this.settings) this.notify('workspace/didChangeConfiguration', { settings: this.settings })
      this.state = 'ready'
      return this
    })()
    try { return await this.ready } catch (e) { this.fail(e); throw e }
  }

  fail(err) {
    if (this.state === 'dead') return
    this.state = 'dead'
    this.error = err
    for (const { reject, timer } of this.pending.values()) { clearTimeout(timer); reject(err) }
    this.pending.clear()
    try { this.proc?.kill() } catch {}
    this.emit('dead', err)
  }

  onData(chunk) {
    this.buffer = Buffer.concat([this.buffer, chunk])
    for (;;) {
      const sep = this.buffer.indexOf('\r\n\r\n')
      if (sep < 0) return
      const header = this.buffer.slice(0, sep).toString('ascii')
      const m = /Content-Length:\s*(\d+)/i.exec(header)
      if (!m) { this.buffer = this.buffer.slice(sep + 4); continue }
      const len = Number(m[1])
      if (this.buffer.length < sep + 4 + len) return
      const body = this.buffer.slice(sep + 4, sep + 4 + len).toString('utf8')
      this.buffer = this.buffer.slice(sep + 4 + len)
      let msg
      try { msg = JSON.parse(body) } catch { continue }
      this.onMessage(msg)
    }
  }

  onMessage(msg) {
    if (msg.id !== undefined && (msg.result !== undefined || msg.error !== undefined) && !msg.method) {
      const p = this.pending.get(msg.id)
      if (!p) return
      this.pending.delete(msg.id)
      clearTimeout(p.timer)
      if (msg.error) p.reject(Object.assign(new Error(msg.error.message || 'LSP error'), { code: msg.error.code }))
      else p.resolve(msg.result)
      return
    }
    if (msg.method && msg.id !== undefined) return this.onServerRequest(msg)
    if (msg.method === 'textDocument/publishDiagnostics') {
      const { uri, diagnostics = [], version } = msg.params || {}
      this.diagnostics.set(uri, { version, items: diagnostics, at: Date.now() })
      this.emit('diagnostics', uri)
    }
  }

  onServerRequest(msg) {
    const reply = (result) => this.send({ jsonrpc: '2.0', id: msg.id, result })
    switch (msg.method) {
      case 'workspace/configuration':
        return reply((msg.params?.items || []).map((it) => pick(this.settings, it.section)))
      case 'workspace/workspaceFolders':
        return reply([{ uri: toUri(this.root), name: path.basename(this.root) }])
      case 'client/registerCapability': case 'client/unregisterCapability': case 'window/workDoneProgress/create':
        return reply(null)
      case 'workspace/applyEdit':
        // Edits the server asks for are applied by the tool layer, which owns fs policy.
        this.emit('applyEdit', msg.params)
        return reply({ applied: false, failureReason: 'apply edits through the lsp tool' })
      default:
        return reply(null)
    }
  }

  send(obj) {
    if (!this.proc?.stdin?.writable) return
    const s = JSON.stringify(obj)
    this.proc.stdin.write(`Content-Length: ${Buffer.byteLength(s, 'utf8')}\r\n\r\n${s}`)
  }

  request(method, params, timeoutMs = 20000) {
    if (this.state === 'dead') return Promise.reject(this.error || new Error(`${this.id} is not running`))
    this.lastUsed = Date.now()
    const id = ++this.seq
    return new Promise((resolve, reject) => {
      const timer = setTimeout(() => {
        this.pending.delete(id)
        this.send({ jsonrpc: '2.0', method: '$/cancelRequest', params: { id } })
        reject(new Error(`${this.id}: ${method} timed out after ${timeoutMs}ms`))
      }, timeoutMs)
      this.pending.set(id, { resolve, reject, timer })
      this.send({ jsonrpc: '2.0', id, method, params })
    })
  }

  notify(method, params) {
    this.lastUsed = Date.now()
    this.send({ jsonrpc: '2.0', method, params })
  }

  /** Open or update a document from disk (full sync). Returns the uri and version. */
  sync(file) {
    const uri = toUri(file)
    let text
    try { text = fs.readFileSync(file, 'utf8') } catch { text = null }
    const doc = this.docs.get(uri)
    if (text === null) {
      if (doc) { this.notify('textDocument/didClose', { textDocument: { uri } }); this.docs.delete(uri) }
      return { uri, version: null, missing: true }
    }
    if (!doc) {
      const d = { version: 1, text }
      this.docs.set(uri, d)
      this.notify('textDocument/didOpen', { textDocument: { uri, languageId: this.languageIdFor(file), version: 1, text } })
      return { uri, version: 1, changed: true }
    }
    if (doc.text === text) return { uri, version: doc.version, changed: false }
    doc.version++
    doc.text = text
    this.notify('textDocument/didChange', { textDocument: { uri, version: doc.version }, contentChanges: [{ text }] })
    this.notify('textDocument/didSave', { textDocument: { uri }, text })
    return { uri, version: doc.version, changed: true }
  }

  /**
   * Fresh diagnostics for a synced document: pull when supported, otherwise wait for a
   * publish newer than the sync (matching version when the server reports one), then let
   * it settle briefly because many servers publish twice (syntax, then semantic).
   */
  async diagnosticsFor(file, { budgetMs = 4000, settleMs = 350 } = {}) {
    const startedAt = Date.now()
    const { uri, version, missing } = this.sync(file)
    if (missing) return { uri, items: [], fresh: true }
    if (this.capabilities?.diagnosticProvider) {
      try {
        const r = await this.request('textDocument/diagnostic', { textDocument: { uri } }, budgetMs)
        if (r?.kind === 'full') return { uri, items: r.items || [], fresh: true }
        if (r?.kind === 'unchanged') return { uri, items: this.diagnostics.get(uri)?.items ?? [], fresh: true }
      } catch { /* fall back to push */ }
    }
    const deadline = startedAt + budgetMs
    const isFresh = () => {
      const d = this.diagnostics.get(uri)
      if (!d) return false
      if (d.version != null && version != null) return d.version >= version
      return d.at >= startedAt
    }
    await new Promise((resolve) => {
      let settle = null
      const done = () => { clearTimeout(timer); clearTimeout(settle); this.off('diagnostics', on); resolve() }
      const on = (u) => {
        if (u !== uri || !isFresh()) return
        clearTimeout(settle)
        settle = setTimeout(done, settleMs)
      }
      const timer = setTimeout(done, Math.max(0, deadline - Date.now()))
      this.on('diagnostics', on)
      if (isFresh()) on(uri)
    })
    return { uri, items: this.diagnostics.get(uri)?.items ?? [], fresh: isFresh() }
  }

  async stop() {
    if (this.state === 'dead') return
    try { await this.request('shutdown', null, 3000) } catch {}
    this.notify('exit', null)
    setTimeout(() => { try { this.proc?.kill() } catch {} }, 500)
    this.state = 'dead'
  }
}

function pick(obj, section) {
  if (!section || !obj) return obj ?? null
  let cur = obj
  for (const k of String(section).split('.')) { if (cur == null) return null; cur = cur[k] }
  return cur ?? null
}