// Dynamic scenario generation — the two LLM steps (v0.31, #52).
//
// This is the additive "Create scenario" path. Two plain `chat()` calls (no
// tools, no separate advisor endpoint — the advisor is embodied in step 1's
// checkpoint list):
//
//   1. `generateDraft` — from an era template + a free-text description + a
//      year, the model designs a draft {@link WorldDraft} (nations with ISO_A3
//      territory, stats, relations, optional backstory) AND an opening
//      checkpoint list (the advisor's briefing of the world's live tensions).
//
//   2. `finalizeWorld` — on commit, the model is re-asked to produce the
//      final world, constrained to the player's APPROVED checkpoints (and,
//      when the client re-sends the step-1 draft, based on it so the player's
//      chosen nation survives). The result is converted to a playable
//      {@link GameState} (region-key territory via the injected `expand`
//      resolver, per-region stats seeded) and returned for the caller to
//      persist — a normal game at `#/game/<id>`.
//
// Both steps are defensive like the rest of the engine: raw model output is
// fence-stripped, the first balanced object is extracted, JSON.parsed, and
// validated via the pure `validateWorldDraft` (which never throws and returns
// `null` for unusable input). A transport-level failure (the model being down)
// throws and is mapped to an HTTP 502 by the route; a bad *answer* degrades to
// a null world, never a crash. The `LlmClient` is injected so unit tests and
// the deterministic scenario stub (server/stubScenario.ts) can replace the
// network call exactly like the turn path does.
import type { LlmClient } from './llm';
import { DEFAULT_MAX_TOKENS } from './llm';
import type { EraTemplate, WorldDraft } from '../shared/scenario';
import { validateWorldDraft } from '../shared/scenario';
import type { GameState } from '../shared/types';
import { worldDraftToGameState } from '../shared/scenario';

// --- Defensive parsing (shared with the engine's approach) --------------------

/** The system-prompt markers the deterministic scenario stub keys off. */
export const SCENARIO_GENERATE_MARKER = '<<SCENARIO_GENERATE>>';
export const SCENARIO_REGENERATE_MARKER = '<<SCENARIO_REGENERATE>>';

/** Strip a leading/trailing ``` code fence (mirrors engine.stripFence). */
function stripFence(text: string): string {
  let t = text.trim();
  const lead = t.match(/^```[a-zA-Z]*\s*\n?/);
  if (lead) t = t.slice(lead[0].length);
  const tail = t.match(/\n?\s*```\s*$/);
  if (tail) t = t.slice(0, t.length - tail[0].length);
  return t.trim();
}

/** Extract the first balanced `{ ... }` substring (string-aware). */
function extractBalancedObject(text: string): string | null {
  const start = text.indexOf('{');
  if (start === -1) return null;
  let depth = 0;
  let inStr = false;
  let esc = false;
  for (let i = start; i < text.length; i++) {
    const c = text[i];
    if (inStr) {
      if (esc) esc = false;
      else if (c === '\\') esc = true;
      else if (c === '"') inStr = false;
      continue;
    }
    if (c === '"') inStr = true;
    else if (c === '{') depth++;
    else if (c === '}' && --depth === 0) return text.slice(start, i + 1);
  }
  return null;
}

/** Parse a raw top-level JSON object, or `null` when none is recoverable. */
function parseObject(raw: string): Record<string, unknown> | null {
  const jsonText = extractBalancedObject(stripFence(raw));
  if (!jsonText) return null;
  try {
    const obj: unknown = JSON.parse(jsonText);
    return obj && typeof obj === 'object' && !Array.isArray(obj)
      ? (obj as Record<string, unknown>)
      : null;
  } catch {
    return null;
  }
}

// --- Prompt building ------------------------------------------------------------

/**
 * The shared nation JSON contract text, embedded in both system prompts so the
 * model sees the exact shape it must emit. Mirrors the engine's strict "ONLY a
 * valid JSON object" style.
 */
const WORLD_SHAPE = [
  '{',
  '  "world": {',
  '    "nations": [',
  '      {',
  '        "id": "short-stable-id",',
  '        "name": "Human readable name",',
  '        "type": "major|minor|power|alliance|faction",',
  '        "stats": {"military":0-100,"economy":0-100,"stability":0-100,"population":0-100},',
  '        "territory": ["ISO_A3","ISO_A3"],',
  '        "relations": {"<other nation id or name>": -100..100}',
  '      }',
  '    ],',
  '    "events": [',
  '      {"nation":"<id or name>","type":"<military|diplomatic|economic|political|social|disaster|scientific|cultural>","title":"short headline","text":"1-3 sentences","outcome":"<success|failure|partial|neutral>"}',
  '    ]',
  '  },',
  '  "checkpoints": ["short advisor checkpoint", "..."]',
  '}',
].join('\n');

/**
 * The system prompt for step 1 (generate). Tells the model to design a fresh
 * world for the era AND to emit an opening advisor checkpoint list.
 */
export function buildGeneratePrompt(
  template: EraTemplate,
  description: string,
  year: number,
  validCountryCodes: ReadonlySet<string> | undefined,
): { system: string; user: string } {
  const codes = validCountryCodes ? [...validCountryCodes].sort() : null;
  const system = [
    `${SCENARIO_GENERATE_MARKER} You are a world-builder for an alternate-history strategy game.`,
    'Given an era, a starting year, and the designer\'s description, create a plausible, self-consistent world of 3 to 8 nations for that moment in (or diverged from) history.',
    'Respond with ONLY a valid JSON object of exactly this shape. No prose, no commentary, no markdown fences, no trailing commas:',
    WORLD_SHAPE,
    '',
    'RULES',
    '- "nations": 3 to 8 nations, each with a short stable id, a human name, a type, and four 0-100 stats (military, economy, stability, population).',
    codes
      ? '- Each nation\'s "territory" MUST use ONLY ISO 3166-1 alpha-3 country codes from this list: ' +
        codes.join(', ') +
        '. A nation may control several codes; together the nations should cover a plausible portion of the world.'
      : '- Each nation\'s "territory" uses standard ISO 3166-1 alpha-3 country codes (e.g. FRA, RUS, USA).',
    '- "relations": a nation\'s sentiment toward each other nation, an integer from -100 (warring) to +100 (allied). Omit or set 0 for neutrality.',
    '- "events" (optional): 1 to 4 short backstory events that already happened and set up the current tensions; each names one of the nations above.',
    '- "checkpoints": 3 to 6 short strings — the advisor\'s opening briefing of the world\'s live strategic questions (the pressures, rivalries, and opportunities the player should know before leading a nation). Keep each under 20 words.',
    '- Keep every stat value between 0 and 100. Do not invent nations outside the "nations" array.',
  ].join('\n');
  const user = JSON.stringify(
    {
      era: {
        id: template.id,
        name: template.name,
        year,
        description: template.eraDescription,
      },
      suggestedPowers: template.suggestedPowers,
      tensions: template.tensions,
      description,
      year,
      ...(codes ? { validCountryCodes: codes } : {}),
    },
    null,
    2,
  );
  return { system, user };
}

/**
 * The system prompt for step 2 (regenerate/finalize). Same world contract, but
 * the model must now respect the player's APPROVED checkpoints (and, when a
 * draft is supplied, stay close to it so the player's chosen nation survives).
 */
export function buildRegeneratePrompt(
  template: EraTemplate,
  description: string,
  year: number,
  approvedCheckpoints: string[],
  validCountryCodes: ReadonlySet<string> | undefined,
  draft?: WorldDraft,
): { system: string; user: string } {
  const codes = validCountryCodes ? [...validCountryCodes].sort() : null;
  const system = [
    `${SCENARIO_REGENERATE_MARKER} You are finalizing a world for an alternate-history strategy game.`,
    'A draft world was generated and the player has APPROVED a set of checkpoints that the final world MUST respect. Produce the final, playable world.',
    'Respond with ONLY a valid JSON object of exactly this shape (same as the draft, but the "checkpoints" field is NOT repeated — omit it). No prose, no commentary, no markdown fences, no trailing commas:',
    [
      '{',
      '  "world": {',
      '    "nations": [',
      '      {',
      '        "id": "short-stable-id",',
      '        "name": "Human readable name",',
      '        "type": "major|minor|power|alliance|faction",',
      '        "stats": {"military":0-100,"economy":0-100,"stability":0-100,"population":0-100},',
      '        "territory": ["ISO_A3","ISO_A3"],',
      '        "relations": {"<other nation id or name>": -100..100}',
      '      }',
      '    ],',
      '    "events": [',
      '      {"nation":"<id or name>","type":"<military|diplomatic|economic|political|social|disaster|scientific|cultural>","title":"short headline","text":"1-3 sentences","outcome":"<success|failure|partial|neutral>"}',
      '    ]',
      '  }',
      '}',
    ].join('\n'),
    '',
    'RULES',
    '- Base the final world on the provided draft (the "draft" field of the user message) and keep the same nations — do not rename, drop, or invent nations beyond what the draft established, UNLESS an approved checkpoint demands it.',
    '- You MUST respect EVERY approved checkpoint (the "approvedCheckpoints" field of the user message): reflect each one in the nations\' stats, borders, relations, or backstory events.',
    codes
      ? '- Each nation\'s "territory" MUST use ONLY ISO 3166-1 alpha-3 country codes from this list: ' +
        codes.join(', ') +
        '.'
      : '- Each nation\'s "territory" uses standard ISO 3166-1 alpha-3 country codes (e.g. FRA, RUS, USA).',
    '- Keep every stat value between 0 and 100.',
  ].join('\n');
  const user = JSON.stringify(
    {
      era: {
        id: template.id,
        name: template.name,
        year,
        description: template.eraDescription,
      },
      description,
      year,
      approvedCheckpoints,
      ...(draft ? { draft } : {}),
      ...(codes ? { validCountryCodes: codes } : {}),
    },
    null,
    2,
  );
  return { system, user };
}

// --- Parsing the model's answers ----------------------------------------------

/** Parse the step-1 (generate) answer into a validated world + checkpoint list. */
export function parseGenerate(
  raw: string,
  validCountryCodes?: ReadonlySet<string>,
): { world: WorldDraft | null; checkpoints: string[] } {
  const obj = parseObject(raw);
  if (!obj) return { world: null, checkpoints: [] };
  const world = validateWorldDraft(obj.world, { validCountryCodes });
  const checkpoints: string[] = [];
  if (Array.isArray(obj.checkpoints)) {
    const seen = new Set<string>();
    for (const c of obj.checkpoints) {
      if (typeof c !== 'string') continue;
      const t = c.trim();
      if (t.length > 2 && !seen.has(t)) {
        seen.add(t);
        checkpoints.push(t);
      }
    }
  }
  return { world, checkpoints: checkpoints.slice(0, 12) };
}

/** Parse the step-2 (finalize) answer into a validated world (or null). */
export function parseRegenerate(
  raw: string,
  validCountryCodes?: ReadonlySet<string>,
): WorldDraft | null {
  const obj = parseObject(raw);
  if (!obj) return null;
  return validateWorldDraft(obj.world, { validCountryCodes });
}

// --- Orchestration -------------------------------------------------------------

export interface GenerateDraftOptions {
  llm: LlmClient;
  template: EraTemplate;
  description: string;
  year: number;
  /** ISO_A3 codes to accept (undefined = no filtering). */
  validCountryCodes?: ReadonlySet<string>;
}

/**
 * Step 1: ask the model to design a draft world + an advisor checkpoint list.
 * Throws only on a transport-level failure (the model is down) — a bad answer
 * yields `{ world: null, checkpoints: [] }` and is the caller's to surface as
 * an error, never a crash.
 */
export async function generateDraft(
  opts: GenerateDraftOptions,
): Promise<{ world: WorldDraft | null; checkpoints: string[] }> {
  const { llm, template, description, year, validCountryCodes } = opts;
  const { system, user } = buildGeneratePrompt(template, description, year, validCountryCodes);
  const nudge =
    'Your previous output was invalid. Respond with ONLY the JSON object described above — no prose, no fences.';
  const out = await llm.chat(
    [{ role: 'system', content: system }, { role: 'user', content: user }],
    { temperature: 0.7, maxTokens: DEFAULT_MAX_TOKENS },
  );
  const parsed = parseGenerate(out, validCountryCodes);
  if (parsed.world) return parsed;
  // One nudge re-send with a fresh history, mirroring the engine's retry.
  const retry = await llm.chat(
    [
      { role: 'system', content: system },
      { role: 'user', content: user },
      { role: 'assistant', content: '' },
      { role: 'user', content: nudge },
    ],
    { temperature: 0.7, maxTokens: DEFAULT_MAX_TOKENS },
  );
  return parseGenerate(retry, validCountryCodes);
}

export interface FinalizeWorldOptions {
  llm: LlmClient;
  template: EraTemplate;
  description: string;
  year: number;
  approvedCheckpoints: string[];
  /** The step-1 draft (re-sent by the client) — the base the final world refines. */
  draft?: WorldDraft;
  /** The nation id the player will lead (kept in the final world when present). */
  playerNationId: string;
  /** ISO_A3 codes to accept (undefined = no filtering). */
  validCountryCodes?: ReadonlySet<string>;
  /** Expand ISO_A3 territory to sub-region keys (injected from server/regions). */
  expand: (countries: string[]) => string[];
  /** The new game's id (the route sets randomUUID()). */
  id?: string;
  /** The scenario title (becomes presetTitle; default 'Custom World'). */
  title?: string;
  /** The game's start date (YYYY-MM-DD, from the chosen year). */
  startDate?: string;
}

/**
 * Step 2: ask the model to produce the final world constrained to the approved
 * checkpoints, convert it to a playable {@link GameState}, and return it for the
 * caller to persist. Throws only on a transport-level failure; a bad answer
 * that still yields a usable world is committed, and if the final world drops
 * the player's chosen nation the conversion falls back to the first nation so
 * the game is always playable.
 */
export async function finalizeWorld(opts: FinalizeWorldOptions): Promise<GameState> {
  const {
    llm,
    template,
    description,
    year,
    approvedCheckpoints,
    draft,
    playerNationId,
    validCountryCodes,
    expand,
    id,
    title,
    startDate,
  } = opts;
  const { system, user } = buildRegeneratePrompt(
    template,
    description,
    year,
    approvedCheckpoints,
    validCountryCodes,
    draft,
  );
  const nudge =
    'Your previous output was invalid. Respond with ONLY the JSON object described above — no prose, no fences.';
  const out = await llm.chat(
    [{ role: 'system', content: system }, { role: 'user', content: user }],
    { temperature: 0.4, maxTokens: DEFAULT_MAX_TOKENS },
  );
  let world = parseRegenerate(out, validCountryCodes);
  if (!world) {
    const retry = await llm.chat(
      [
        { role: 'system', content: system },
        { role: 'user', content: user },
        { role: 'assistant', content: '' },
        { role: 'user', content: nudge },
      ],
      { temperature: 0.4, maxTokens: DEFAULT_MAX_TOKENS },
    );
    world = parseRegenerate(retry, validCountryCodes);
  }
  if (!world) {
    // The model could not produce a usable final world. Rather than fail the
    // whole commit, fall back to the draft the player already approved (if any)
    // so the commit still yields a playable game.
    if (draft) world = draft;
    else throw new Error('finalize: the model returned no usable world');
  }
  return worldDraftToGameState(world, expand, playerNationId, { id, title, startDate });
}