/**
 * Memory layers, v0 (#27). Reginald's context is tiered so the model always sees
 * what matters without ever copying ticket data into the prompt:
 *
 * - HOT (this module) — charter + active directives + the focus snapshot, packed
 *   under a hard token budget. Assembled fresh each turn; it's the system-prompt seed.
 * - WARM — the append-only directive/event ledger + periodic digest, in pm-state.
 *   Not inlined; summarized on demand.
 * - COLD — gitea + the sidecar, reached through `query_project` tools. Ticket bodies,
 *   comments, and per-issue detail live here and are NEVER copied into memory —
 *   the model fetches them by number when it needs them.
 *
 * The invariant: HOT stays under budget, and nothing ticket-shaped is inlined.
 */

import type { DirectiveEntry } from '../directives/record-directive-v0.js'
import type { Focus } from '../scheduler/scheduler-v0.js'

/** The hot layer's hard ceiling (#27: hot context assembles under 2k tokens). */
export const HOT_CONTEXT_BUDGET_TOKENS = 2000

/**
 * Tokenizer-free estimate (~4 chars/token). Deliberately a slight over-estimate so
 * a real tokenizer never exceeds what this predicts — the budget stays safe.
 */
export function estimateTokens(text: string): number {
  return Math.ceil(text.length / 4)
}

/** Directives that still bind: accepted or amended, most-recent-first. */
export function activeDirectives(all: DirectiveEntry[]): DirectiveEntry[] {
  return all
    .filter((d) => d.status === 'accepted' || d.status === 'amended')
    .slice()
    .sort((a, b) => (a.ts < b.ts ? 1 : a.ts > b.ts ? -1 : 0))
}

export interface HotContextInputs {
  /** The project charter markdown (hot-memory seed). */
  charter: string
  /** The directive ledger (any status — filtered to active here). */
  directives: DirectiveEntry[]
  /** The current Now/Next/Later focus, or null when nothing is scheduled. */
  focus: Focus | null
}

function focusBlock(focus: Focus | null): string {
  if (!focus) return ''
  const slot = (label: string, item: Focus['now']) => (item ? `${label}: #${item.number} ${item.title}` : `${label}: ·`)
  return ['## Focus', slot('Now', focus.now), slot('Next', focus.next), slot('Later', focus.later)].join('\n')
}

function directivesBlock(directives: DirectiveEntry[]): string[] {
  // one compact line each; the verbatim quote is the payload, kind is the tag
  return directives.map((d) => `- [${d.kind}] ${d.quote}`)
}

/** Truncate to a token budget on a whitespace boundary, with an ellipsis marker. */
function clampToTokens(text: string, budgetTokens: number): string {
  if (estimateTokens(text) <= budgetTokens) return text
  const maxChars = Math.max(0, budgetTokens * 4 - 1)
  const cut = text.slice(0, maxChars)
  const lastBreak = cut.lastIndexOf('\n')
  return `${(lastBreak > maxChars * 0.6 ? cut.slice(0, lastBreak) : cut).trimEnd()}\n…`
}

/**
 * Assemble the HOT context under `budget` tokens. Priority when space is tight:
 * the focus snapshot (tiny, always kept) → the most recent active directives
 * (each while they fit) → the charter fills whatever budget remains (truncated).
 * Never inlines ticket bodies — only charter text, directive quotes, and focus
 * titles, all authored/short. Returns a single prompt-ready block.
 */
export function assembleHotContext(inputs: HotContextInputs, budget = HOT_CONTEXT_BUDGET_TOKENS): string {
  const focus = focusBlock(inputs.focus)
  const focusTokens = focus ? estimateTokens(focus) : 0

  // fit the most recent active directives into ~⅔ of what's left after focus
  const active = activeDirectives(inputs.directives)
  const directiveCap = Math.max(0, Math.floor((budget - focusTokens) * (2 / 3)))
  const keptDirectives: string[] = []
  let directiveTokens = 0
  for (const line of directivesBlock(active)) {
    const t = estimateTokens(line) + 1
    if (directiveTokens + t > directiveCap) break
    keptDirectives.push(line)
    directiveTokens += t
  }
  const directives = keptDirectives.length ? ['## Active directives', ...keptDirectives].join('\n') : ''

  // Measure the fixed tail (directives + focus, with their joiner) exactly, then
  // give the charter the true remainder — reserving for the "## Charter" header,
  // the block joiner, and the truncation ellipsis so the total never exceeds budget.
  const tail = [directives, focus].filter(Boolean).join('\n\n')
  const tailTokens = tail ? estimateTokens(tail) : 0
  const reserve = estimateTokens(`## Charter\n${tail ? '\n\n' : ''}\n…`)
  const charterBudget = Math.max(0, budget - tailTokens - reserve)
  const charterBody = inputs.charter.trim() ? clampToTokens(inputs.charter.trim(), charterBudget) : ''
  const charter = charterBody ? `## Charter\n${charterBody}` : ''

  return [charter, tail].filter(Boolean).join('\n\n')
}