/**
 * Pure side-conversation ("Side Chat") logic shared by the host routes and
 * the client tab. Framework-free (no React, no Node) so both halves and the
 * node test environment can import it.
 *
 * A side thread is a child session the plugin creates ITSELF with a custom
 * seed — the parent session's FULL event log up to the click moment
 * (completed turns, the unanswered user message, and — when the parent is
 * mid-turn — the in-progress assistant output and tool activity). The log
 * model forbids open-turn seeds, so an in-flight parent turn is copied
 * verbatim and CLOSED with synthetic `step/end` + `turn/end{reason:
 * 'interrupted'}` events: the child sees the partial turn as honestly
 * frozen ("cut off"), never as a completed answer. The one case that cannot
 * be closed honestly — a tool call still executing (no `tool/result` yet;
 * providers reject dangling assistant calls) — falls back to cutting before
 * the open turn and carrying the partial content as a structured text
 * snapshot inside the boundary prompt.
 */
import type { SidebarHistoryEntry, SidebarSessionSummary } from './context-types.ts'
import type { AssistantLiveChunk } from './assistant-live.ts'

/** The durable thread-label prefix (also the row filter in the client list). */
export const SIDE_LABEL_PREFIX = 'Side: '

/** The pinned label of a freshly created thread that no prompt has reached
 *  yet (Codex-style immediate create: the tab opens an EMPTY thread, the
 *  first composer message carries the boundary and earns the real label).
 *  The client renders it localized; the prefix keeps the row filter honest. */
export const SIDE_NEW_THREAD_TITLE = 'Side: New thread'

/** Maximum code points kept in a durable thread label (matches subagent labels). */
export const LABEL_MAX_CHARS = 48

/** The boundary message's opening line — the transcript mapping drops user
 *  rows starting with it (same first line as dsh-sidechain's boundary, so
 *  the two plugins' threads render consistently in either UI). */
export const SIDE_BOUNDARY_PREFIX = 'Side conversation boundary'

/** The plugin identity stamped on the source of context-injection messages
 *  (boundary prompt + parked snapshot), so the transcript recognizes them
 *  structurally — not by text prefix. */
export const SIDE_INJECTION_PLUGIN = 'dsh-better-sidebar'

/**
 * The boundary prompt delivered as the thread's first user message: the
 * inherited seed is reference context only, never active instruction.
 * Model-facing contract — change only with intent, tests pin the sentences.
 */
export const SIDE_BOUNDARY_PROMPT = `Side conversation boundary.

Everything before this boundary is inherited history from the parent session: its completed turns, its pending question, and — if the parent was mid-turn — its in-progress output frozen at the moment this side conversation started. It is reference context only. It is not your current task.

Do not continue, execute, or complete any instructions, plans, tool calls, approvals, edits, or requests from before this boundary. Only messages submitted after this boundary are active user instructions for this side conversation.

Mode: this is a continuable side conversation. Your answers stay in this side thread and are viewed in the side panel; they are never delivered into the parent session.`

/** One seed event (structural mirror of the durable SessionEvent). The
 *  envelope fields are preserved verbatim: surface-eligible events
 *  (user/message, assistant/message, tool/result) REQUIRE the `surfaceOp`
 *  marker (and may carry `sourceEventSeqs`) — the seed validator rejects
 *  them without it. */
export interface SeedEvent {
  type: string
  seq: number
  time: number
  data: Record<string, unknown>
  /** Surface marker of message-producing events ('append' | replace op). */
  surfaceOp?: unknown
  /** Seq numbers of earlier events this event cites as sources. */
  sourceEventSeqs?: unknown
  /** Reader-skip marker of purely informational events. */
  ignorable?: true
}

/** The minimal structural face of a session-log event this module reads
 *  (loose enough to accept both the host's real SessionEvent and the
 *  client's SidebarSessionEvent mirror). */
export interface SidechatLogEvent {
  type: string
  seq: number
  time: number
  data: unknown
}

/**
 * One live assistant delta on the plugin's wire, mirroring DSH 0.1.5's
 * client-only `assistant/live-chunk` presentation row.
 *
 * DSH 0.1.5 no longer logs `assistant/chunk`: an in-flight attempt's deltas
 * are process-local frames (`agent/assistant-stream`, folded by
 * {@link ./assistant-live.ts}) and reach the transcript through the plugin's
 * own `sidechat.events` route as these rows. They are NOT durable — the
 * route returns the current attempt's rows on every poll and the client
 * replaces its live set each time; the durable `assistant/message` settles
 * them by `turn:step`.
 */
export interface SidechatLiveEvent {
  type: 'assistant/live-chunk'
  /** Ordering key among live rows only; durable seqs stay authoritative. */
  seq: number
  time: number
  data: {
    attemptId: string
    turn: number
    step: number
    /** Dense zero-based position within the attempt. */
    index: number
    /** The raw model stream chunk. */
    chunk: Record<string, unknown>
  }
}

/**
 * Project buffered live chunks into wire rows.
 * @param chunks - the session's active-attempt chunks, in index order.
 * @param tailSeq - the session's last durable seq (live rows order after it).
 * @returns the rows to append to the transcript feed.
 */
export function liveEventsOf(chunks: readonly AssistantLiveChunk[], tailSeq: number): SidechatLiveEvent[] {
  return chunks.map((delta, position) => ({
    type: 'assistant/live-chunk',
    seq: tailSeq + 1 + position,
    time: delta.time,
    data: {
      attemptId: delta.attemptId,
      turn: delta.turn,
      step: delta.step,
      index: delta.index,
      chunk: delta.chunk,
    },
  }))
}

/** The result of cutting a parent log into a side-thread inheritance. */
export interface SidechatInheritance {
  /** The child seed: contiguous from seq 0, ends outside any open turn. */
  seed: SeedEvent[]
  /**
   * Structured snapshot of the parent's in-progress turn when it could NOT
   * be included as events (a tool call was still executing); null when the
   * seed already carries the whole picture.
   */
  snapshot: string | null
}

/** The data record of one event (narrowed from the loose face). */
function dataOf(event: SidechatLogEvent): Record<string, unknown> {
  return event.data as Record<string, unknown>
}

/** Copy parent events verbatim (their live seq === array index contract).
 *  The FULL envelope is preserved — stripping `surfaceOp` would make the
 *  seed validator reject every surface-eligible message event. */
function copyEvents(events: readonly SidechatLogEvent[]): SeedEvent[] {
  return events.map(event => {
    const source = event as SidechatLogEvent & {
      surfaceOp?: unknown
      sourceEventSeqs?: unknown
      ignorable?: true
    }
    return {
      type: source.type,
      seq: source.seq,
      time: source.time,
      data: dataOf(source),
      ...(source.surfaceOp === undefined ? {} : { surfaceOp: source.surfaceOp }),
      ...(source.sourceEventSeqs === undefined ? {} : { sourceEventSeqs: source.sourceEventSeqs }),
      ...(source.ignorable === undefined ? {} : { ignorable: source.ignorable }),
    }
  })
}

/** Index of the last `turn/start` or `turn/end`, or -1. */
function lastTurnBoundary(events: readonly SidechatLogEvent[]): number {
  for (let index = events.length - 1; index >= 0; index--) {
    const type = events[index]?.type
    if (type === 'turn/start' || type === 'turn/end') return index
  }
  return -1
}

/** Numeric field of an event's data (turn / step numbers). */
function numberAt(data: Record<string, unknown>, key: string): number {
  const value = data[key]
  return typeof value === 'number' && Number.isSafeInteger(value) ? value : 0
}

/** The step number still open at the log tail inside the turn starting at
 *  `turnStart` (undefined when no step is open). */
function openStepInTurn(events: readonly SidechatLogEvent[], turnStart: number): number | undefined {
  let open: number | undefined
  for (let index = turnStart + 1; index < events.length; index++) {
    const event = events[index]
    if (event === undefined) continue
    if (event.type === 'step/start') open = numberAt(dataOf(event), 'step')
    else if (event.type === 'step/end') open = undefined
  }
  return open
}

/**
 * Whether the open turn ending the log has a `tool/call` without its paired
 * `tool/result` in the CURRENT open step. Providers reject dangling
 * assistant calls, so such a turn cannot be honestly closed and the
 * inheritance must fall back to the snapshot.
 */
export function hasDanglingToolCall(events: readonly SidechatLogEvent[], turnStart: number): boolean {
  const pending = new Set<string>()
  for (let index = turnStart + 1; index < events.length; index++) {
    const event = events[index]
    if (event === undefined) continue
    const data = dataOf(event)
    if (event.type === 'step/end') {
      pending.clear()
      continue
    }
    if (event.type === 'tool/call') {
      const callId = data.callId
      if (typeof callId === 'string') pending.add(callId)
      continue
    }
    if (event.type === 'tool/result') {
      const source = data.message as { source?: { callId?: unknown } } | undefined
      const callId = source?.source?.callId
      if (typeof callId === 'string') pending.delete(callId)
    }
  }
  return pending.size > 0
}

/** The plain text of one tool/result message (text blocks inside its
 *  `tool-result` content block). */
function toolResultText(data: Record<string, unknown>): string {
  const message = data.message as { content?: unknown } | undefined
  const content = message?.content
  if (!Array.isArray(content)) return ''
  const parts: string[] = []
  for (const block of content) {
    if (block === null || typeof block !== 'object') continue
    const candidate = block as { type?: unknown; content?: unknown }
    if (candidate.type !== 'tool-result') continue
    const inner = candidate.content
    if (!Array.isArray(inner)) continue
    for (const item of inner) {
      if (item === null || typeof item !== 'object') continue
      const textItem = item as { type?: unknown; text?: unknown }
      if (textItem.type === 'text' && typeof textItem.text === 'string') {
        parts.push(textItem.text)
      }
    }
  }
  return parts.join('\n')
}

/** Cap applied to one tool-result's text inside a snapshot (prompt budget). */
const SNAPSHOT_RESULT_CAP = 2000
/** Cap applied to the whole snapshot (prompt budget). */
const SNAPSHOT_TOTAL_CAP = 8000

/**
 * Build the side-thread inheritance for one parent log: the full event log
 * up to the click moment, honestly closed when it ends inside an open turn.
 * @param events - the parent's log (live or persisted).
 * @param live - the parent's in-flight stream chunks (DSH 0.1.5+ publishes
 *   them outside the log); used only by the snapshot fallback.
 */
export function buildSidechatInheritance(
  events: readonly SidechatLogEvent[],
  live: readonly AssistantLiveChunk[] = [],
): SidechatInheritance {
  if (events.length === 0) return { seed: [], snapshot: null }
  const boundary = lastTurnBoundary(events)
  if (boundary < 0 || events[boundary]?.type === 'turn/end') {
    // Ends outside any turn (or has no turns at all): the whole log is a
    // valid, balanced seed — possibly ending with a pending user message.
    return { seed: copyEvents(events), snapshot: null }
  }
  // Ends inside the open turn starting at `boundary`.
  if (hasDanglingToolCall(events, boundary)) {
    // Cannot close honestly: cut before the open turn; the caller attaches
    // the structured snapshot to the boundary prompt instead.
    return {
      seed: copyEvents(events.slice(0, boundary)),
      snapshot: buildOpenTurnSnapshot(events, live),
    }
  }
  const seed = copyEvents(events)
  const last = events[events.length - 1]
  const turn = numberAt(dataOf(events[boundary]!), 'turn')
  const now = last?.time ?? 0
  const openStep = openStepInTurn(events, boundary)
  if (openStep !== undefined) {
    seed.push({ type: 'step/end', seq: seed.length, time: now, data: { turn, step: openStep } })
  }
  seed.push({
    type: 'turn/end',
    seq: seed.length,
    time: now,
    data: { turn, reason: { kind: 'interrupted' } },
  })
  return { seed, snapshot: null }
}

/** One assistant content block reduced to the text the snapshot shows. */
function messageTexts(message: unknown): { text: string; reasoning: string } {
  const content = (message as { content?: unknown } | undefined)?.content
  let text = ''
  let reasoning = ''
  if (!Array.isArray(content)) return { text, reasoning }
  for (const block of content) {
    if (block === null || typeof block !== 'object') continue
    const candidate = block as { type?: unknown; text?: unknown }
    if (typeof candidate.text !== 'string' || candidate.text === '') continue
    if (candidate.type === 'text') text += candidate.text
    else if (candidate.type === 'reasoning') reasoning += candidate.text
  }
  return { text, reasoning }
}

/**
 * Expand one attempt's compact `AssistantStreamRecord[]` (the durable stream
 * DSH 0.1.5 embeds in `assistant/message.stream` and `assistant/attempt.stream`)
 * into the text/reasoning it carried. Tool-call records contribute no text.
 */
function streamTexts(stream: unknown): { text: string; reasoning: string } {
  let text = ''
  let reasoning = ''
  if (!Array.isArray(stream)) return { text, reasoning }
  for (const record of stream) {
    if (record === null || typeof record !== 'object') continue
    const entry = record as { type?: unknown; texts?: unknown; chunk?: unknown }
    if (entry.type === 'text-chunks' || entry.type === 'reasoning-chunks') {
      if (!Array.isArray(entry.texts)) continue
      const joined = entry.texts.filter((part): part is string => typeof part === 'string').join('')
      if (entry.type === 'text-chunks') text += joined
      else reasoning += joined
      continue
    }
    if (entry.type === 'chunk') {
      const chunk = entry.chunk as { type?: unknown; text?: unknown } | undefined
      if (chunk === null || typeof chunk !== 'object' || typeof chunk.text !== 'string') continue
      if (chunk.type === 'text-delta') text += chunk.text
      else if (chunk.type === 'reasoning-delta') reasoning += chunk.text
    }
  }
  return { text, reasoning }
}

/** One live delta's contribution to the snapshot. */
function liveTexts(chunk: Record<string, unknown>): { text: string; reasoning: string } {
  if (typeof chunk.text !== 'string' || chunk.text === '') return { text: '', reasoning: '' }
  if (chunk.type === 'text-delta') return { text: chunk.text, reasoning: '' }
  if (chunk.type === 'reasoning-delta') return { text: '', reasoning: chunk.text }
  return { text: '', reasoning: '' }
}

/**
 * Structured text snapshot of the parent's OPEN turn (from its `turn/start`
 * to the log tail): the assistant/reasoning output so far and the tool
 * activity — executed tools with their result text, the still-executing one
 * marked. Returns null when there is no open turn or nothing to show.
 *
 * The in-flight step's text is NOT in the log on DSH 0.1.5 (the model stream
 * is process-local until it settles), so it comes from `live`; settled steps
 * read their durable `assistant/message` content, and a failed attempt reads
 * its embedded `assistant/attempt.stream`.
 * @param events - the parent's log.
 * @param live - the parent's in-flight stream chunks, in index order.
 */
export function buildOpenTurnSnapshot(
  events: readonly SidechatLogEvent[],
  live: readonly AssistantLiveChunk[] = [],
): string | null {
  const boundary = lastTurnBoundary(events)
  if (boundary < 0 || events[boundary]?.type !== 'turn/start') return null
  const openTurn = numberAt(dataOf(events[boundary]!), 'turn')
  let text = ''
  let reasoning = ''
  const tools: string[] = []
  const pendingCalls = new Map<string, { name: string; args: string }>()
  for (let index = boundary + 1; index < events.length; index++) {
    const event = events[index]
    if (event === undefined) continue
    const data = dataOf(event)
    if (event.type === 'step/end') {
      pendingCalls.clear()
      continue
    }
    if (event.type === 'assistant/message') {
      const settled = messageTexts(data.message)
      text += settled.text
      reasoning += settled.reasoning
      continue
    }
    if (event.type === 'assistant/attempt') {
      const attempt = streamTexts(data.stream)
      text += attempt.text
      reasoning += attempt.reasoning
      continue
    }
    if (event.type === 'tool/call') {
      const callId = data.callId
      if (typeof callId === 'string') {
        pendingCalls.set(callId, {
          name: typeof data.name === 'string' ? data.name : 'tool',
          args: typeof data.arguments === 'string' ? data.arguments : '',
        })
      }
      continue
    }
    if (event.type === 'tool/result') {
      const source = data.message as { source?: { callId?: unknown } } | undefined
      const callId = typeof source?.source?.callId === 'string' ? source.source.callId : undefined
      const name = callId !== undefined ? pendingCalls.get(callId)?.name : undefined
      const args = callId !== undefined ? pendingCalls.get(callId)?.args : undefined
      if (callId !== undefined) pendingCalls.delete(callId)
      const result = toolResultText(data).slice(0, SNAPSHOT_RESULT_CAP)
      const failed = data.error !== undefined
      const line = [
        `- \`${name ?? 'tool'}\`${failed ? ' (failed)' : ''}`
          + (args !== undefined && args !== '' ? ` — arguments: \`${args}\`` : ''),
        ...(result === '' ? [] : [`  Result: ${result}`]),
      ].join('\n')
      tools.push(line)
    }
  }
  for (const [, call] of pendingCalls) {
    const line = `- \`${call.name}\` (executing) — arguments: \`${call.args}\``
    tools.push(line)
  }
  // The in-flight step: its deltas never reached the log.
  for (const delta of live) {
    if (delta.turn !== openTurn) continue
    const contribution = liveTexts(delta.chunk)
    text += contribution.text
    reasoning += contribution.reasoning
  }
  const sections: string[] = []
  if (text.trim() !== '') sections.push(`Assistant output so far:\n\n${text}`)
  if (reasoning.trim() !== '') sections.push(`Reasoning so far:\n\n${reasoning}`)
  if (tools.length > 0) sections.push(`Tool activity:\n${tools.join('\n')}`)
  if (sections.length === 0) return null
  const body = sections.join('\n\n')
  return body.length > SNAPSHOT_TOTAL_CAP
    ? `Parent session in-progress turn (reference only):\n\n${body.slice(0, SNAPSHOT_TOTAL_CAP)}…`
    : `Parent session in-progress turn (reference only):\n\n${body}`
}

/** One side-thread row in the client's thread list. */
export interface SideThreadRow {
  id: string
  /** The durable thread title ('Side: …'). */
  title: string
  /** Whether the thread's agent is currently running. */
  running: boolean
}

/**
 * Derive the side threads of one parent session from the client session list:
 * durable `origin: 'subagent'` children of the parent whose pinned title
 * carries the thread label prefix (our creation path pins it via
 * sessionTitle.rename; dsh-sidechain threads share the convention, so they
 * are visible here too).
 */
export function sideThreadRows(
  byId: Readonly<Record<string, SidebarSessionSummary>>,
  sessionId: string,
): SideThreadRow[] {
  const rows: SideThreadRow[] = []
  for (const summary of Object.values(byId)) {
    if (summary.origin !== 'subagent' || summary.parentId !== sessionId) continue
    if (!summary.displayTitle.startsWith(SIDE_LABEL_PREFIX)) continue
    rows.push({ id: summary.id, title: summary.displayTitle, running: summary.running === true })
  }
  return rows
}

/** Truncate + prefix a question into a durable thread label. */
export function sideLabel(question: string): string {
  const flat = question.replace(/\s+/g, ' ').trim()
  const max = Math.max(1, LABEL_MAX_CHARS - SIDE_LABEL_PREFIX.length)
  const body = flat.length > max ? `${flat.slice(0, max - 1)}…` : flat
  return `${SIDE_LABEL_PREFIX}${body}`
}

/**
 * Whether the thread log already carries the side boundary message — i.e.
 * the first prompt was delivered. Tolerant to the content shape (block
 * array or bare string) and to inherited seed messages (only an OWN
 * boundary message starts with the prefix; seed messages came from the
 * parent's log, which never contains one).
 */
export function boundaryDelivered(events: readonly SidechatLogEvent[]): boolean {
  for (const event of events) {
    if (event.type !== 'user/message') continue
    if (messageLeadText(dataOf(event)).startsWith(SIDE_BOUNDARY_PREFIX)) return true
  }
  return false
}

/** The leading text of a user/message's content (block array or bare string). */
function messageLeadText(data: Record<string, unknown>): string {
  const content = data.content
  const first = Array.isArray(content) ? content[0] : content
  return typeof first === 'string'
    ? first
    : (typeof first === 'object' && first !== null && 'text' in first
      ? String((first as { text: unknown }).text)
      : '')
}

/**
 * Whether a logged user/message is a CONTEXT INJECTION (the boundary prompt
 * plus the parked in-progress snapshot) rather than a real user message.
 * New threads deliver the injection via `agent.inject` stamped with a
 * non-'user' source kind; threads created before that split carry
 * boundary+question in ONE 'user' message, recognized by the boundary
 * prefix. Both render as one collapsible injection row — never as a user
 * bubble.
 */
export function isContextInjectionMessage(data: Record<string, unknown>): boolean {
  const source = data.source as { kind?: unknown } | null | undefined
  if (source?.kind !== undefined && source.kind !== 'user') return true
  return messageLeadText(data).startsWith(SIDE_BOUNDARY_PREFIX)
}

/** The info the thread header shows (live runtime state + agent identity). */
export interface SidechatThreadInfo {
  /** A live agent drives the thread right now (false = cold/persisted). */
  live: boolean
  /** Live lifecycle state; absent on cold threads. */
  status?: 'idle' | 'running'
  /** Provider route of the live agent. */
  provider?: string
  /** Model id of the live agent. */
  model?: string
  /** The recorded agent preset (live header, or persisted on cold reads). */
  preset?: string
}

/** The events a thread produced itself: everything after the LAST
 *  `session/end-seed` marker (the fork-seed boundary). A log with no marker
 *  (a thread created before seeding existed) is returned whole. */
export function threadOwnLogEvents(events: readonly SidechatLogEvent[]): SidechatLogEvent[] {
  for (let index = events.length - 1; index >= 0; index--) {
    if (events[index]?.type === 'session/end-seed') return events.slice(index + 1)
  }
  return [...events]
}

/** {@link threadOwnLogEvents} over history rows (the client cache shape). */
export function threadOwnEvents(entries: readonly SidebarHistoryEntry[]): SidechatLogEvent[] {
  return threadOwnLogEvents(entries.map(entry => entry.event))
}

/**
 * Whether the thread has at least one completed turn — the save-as-new-
 * session precondition (`session.fork` refuses to fork before the first
 * `turn/end`).
 */
export function threadHasCompletedTurn(entries: readonly SidebarHistoryEntry[]): boolean {
  return threadOwnEvents(entries).some(event => event.type === 'turn/end')
}

/** Whether the thread ends with a user message that no completed turn
 *  answered yet — such a pending follow-up is NOT carried into the saved
 *  session (the fork cut is the last `turn/end`). */
export function threadTrailingPending(entries: readonly SidebarHistoryEntry[]): boolean {
  const own = threadOwnEvents(entries)
  let lastUser = -1
  let lastTurnEnd = -1
  own.forEach((event, index) => {
    if (event.type === 'user/message') lastUser = index
    if (event.type === 'turn/end') lastTurnEnd = index
  })
  return lastUser > lastTurnEnd
}

/**
 * The agent preset a session actually runs: newest `agent-preset/selected`
 * event wins, else the creation header (mirror of the dsh-agent-presets
 * resolveSessionPreset helper — replicated here to avoid a host dependency
 * on that package).
 */
export function resolvePresetId(
  header: { agentPreset?: string },
  events: readonly SidechatLogEvent[],
): string | undefined {
  for (let index = events.length - 1; index >= 0; index--) {
    const event = events[index]
    if (event?.type !== 'agent-preset/selected') continue
    const preset = dataOf(event).agentPreset
    if (typeof preset === 'string') return preset
  }
  return header.agentPreset
}