import {
  DIFFICULTY_LEVELS,
  NOUN_GENDERS,
  type DifficultyLevel,
  type NounGender,
  type SupportedLanguageCode,
  type SupportedPos,
} from "@lila/shared";

export type GeminiTranslation = {
  target_language: SupportedLanguageCode;
  word: string;
  gender: NounGender | null;
  difficulty: DifficultyLevel;
};

export type GeminiSense = {
  sense_index: number;
  difficulty: DifficultyLevel;
  definitions: string[];
  examples: string[];
  translations: GeminiTranslation[];
};

export type GeminiWordEntry = {
  headword: string;
  language: SupportedLanguageCode;
  pos: SupportedPos;
  senses: GeminiSense[];
};

export type ValidationContext = {
  sourceLanguage: SupportedLanguageCode;
  pos: SupportedPos;
  targetLanguages: readonly SupportedLanguageCode[];
  inputWords: ReadonlySet<string>;
};

/**
 * "empty" is the contract's way of saying "not a valid word of this POS"
 * (senses: []) — the word is skipped, not rejected.
 *
 * A "valid" result carries the *normalized* entry, which may differ from the
 * input — see `applySenseDifficultyFloor`. `normalizations` is a human-readable
 * record of any repair applied, so the pipeline can report how often the model
 * needed correcting instead of silently papering over it.
 */
export type ValidationResult =
  | { status: "valid"; entry: GeminiWordEntry; normalizations: string[] }
  | { status: "empty"; headword: string }
  | { status: "invalid"; errors: string[] };

const isRecord = (value: unknown): value is Record<string, unknown> =>
  typeof value === "object" && value !== null && !Array.isArray(value);

const isNonEmptyString = (value: unknown): value is string =>
  typeof value === "string" && value.trim() !== "";

const isDifficulty = (value: unknown): value is DifficultyLevel =>
  (DIFFICULTY_LEVELS as readonly unknown[]).includes(value);

const difficultyRank = (level: DifficultyLevel): number =>
  DIFFICULTY_LEVELS.indexOf(level);

const validGendersFor = (
  target: SupportedLanguageCode,
): readonly (NounGender | null)[] => {
  if (target === "en") return [null];
  if (target === "de") return NOUN_GENDERS;
  return ["masculine", "feminine"];
};

const checkStringArray = (
  value: unknown,
  label: string,
  errors: string[],
): void => {
  if (!Array.isArray(value) || value.length === 0) {
    errors.push(`${label} must be a non-empty array`);
    return;
  }
  if (!value.every(isNonEmptyString)) {
    errors.push(`${label} must contain only non-empty strings`);
  }
};

const checkTranslation = (
  raw: unknown,
  label: string,
  ctx: ValidationContext,
  errors: string[],
): void => {
  if (!isRecord(raw)) {
    errors.push(`${label} must be an object`);
    return;
  }
  const target = raw["target_language"];
  if (!(ctx.targetLanguages as readonly unknown[]).includes(target)) {
    errors.push(
      `${label}: target_language must be one of ${ctx.targetLanguages.join(", ")}`,
    );
  }
  if (!isNonEmptyString(raw["word"])) {
    errors.push(`${label}: word must be a non-empty string`);
  }
  // A translation ranked below its sense is not an error — the sense is the
  // derived value and gets floored to match. See applySenseDifficultyFloor.
  if (!isDifficulty(raw["difficulty"])) {
    errors.push(
      `${label}: difficulty must be one of ${DIFFICULTY_LEVELS.join(", ")}`,
    );
  }
  if (
    typeof target === "string" &&
    (ctx.targetLanguages as readonly string[]).includes(target)
  ) {
    const gender = raw["gender"];
    const allowed = validGendersFor(target as SupportedLanguageCode);
    if (!(allowed as readonly unknown[]).includes(gender)) {
      errors.push(
        `${label}: gender must be ${allowed.map((g) => g ?? "null").join(" or ")} for target "${target}"`,
      );
    }
  }
};

const checkSense = (
  raw: unknown,
  index: number,
  ctx: ValidationContext,
  errors: string[],
): void => {
  const label = `senses[${index}]`;
  if (!isRecord(raw)) {
    errors.push(`${label} must be an object`);
    return;
  }
  if (raw["sense_index"] !== index) {
    errors.push(`${label}: sense_index must be ${index} (sequential from 0)`);
  }
  const senseDifficulty = isDifficulty(raw["difficulty"])
    ? raw["difficulty"]
    : null;
  if (senseDifficulty === null) {
    errors.push(
      `${label}: difficulty must be one of ${DIFFICULTY_LEVELS.join(", ")}`,
    );
  }
  checkStringArray(raw["definitions"], `${label}.definitions`, errors);
  checkStringArray(raw["examples"], `${label}.examples`, errors);

  const translations = raw["translations"];
  if (!Array.isArray(translations) || translations.length === 0) {
    errors.push(`${label}.translations must be a non-empty array`);
    return;
  }
  translations.forEach((translation, i) => {
    checkTranslation(translation, `${label}.translations[${i}]`, ctx, errors);
  });

  const wordsPerTarget = new Map<string, string[]>();
  for (const translation of translations) {
    if (!isRecord(translation)) continue;
    const target = translation["target_language"];
    const word = translation["word"];
    if (typeof target !== "string" || typeof word !== "string") continue;
    const words = wordsPerTarget.get(target) ?? [];
    words.push(word);
    wordsPerTarget.set(target, words);
  }
  for (const target of ctx.targetLanguages) {
    const words = wordsPerTarget.get(target) ?? [];
    if (words.length === 0) {
      errors.push(
        `${label}: missing translation for target language "${target}"`,
      );
    }
    if (words.length > 2) {
      errors.push(
        `${label}: more than 2 translations for target language "${target}"`,
      );
    }
    if (new Set(words).size !== words.length) {
      errors.push(
        `${label}: duplicate translation word for target language "${target}"`,
      );
    }
  }
};

/**
 * Lowers a sense's difficulty to that of its easiest translation when the model
 * tagged the sense higher.
 *
 * Why this is a repair and not a rejection: design-doc §5.1 filters sense
 * difficulty as a *ceiling* and translation difficulty as an *exact* target, so
 * a translation ranked below its own sense can never be served — the sense is
 * gated out at exactly the level where that translation would be the answer.
 * The row is dead data. The prompt already defines sense difficulty as the
 * easiest translation difficulty in the sense, which makes it a derived value
 * rather than an independent judgement, so it is recomputed here instead of
 * discarding an otherwise-good entry.
 *
 * The floor only ever lowers. Raising a sense to match its translations would
 * gate a concept out of levels it belongs in, and would collapse the
 * concept-vs-word distinction that the two difficulty columns exist to express
 * (design-doc §4).
 */
const applySenseDifficultyFloor = (
  entry: GeminiWordEntry,
  normalizations: string[],
): GeminiWordEntry => ({
  ...entry,
  senses: entry.senses.map((sense) => {
    const easiest = sense.translations.reduce<DifficultyLevel>(
      (lowest, translation) =>
        difficultyRank(translation.difficulty) < difficultyRank(lowest)
          ? translation.difficulty
          : lowest,
      sense.difficulty,
    );
    if (easiest === sense.difficulty) return sense;
    normalizations.push(
      `senses[${sense.sense_index}]: difficulty "${sense.difficulty}" → "${easiest}" (floored to easiest translation)`,
    );
    return { ...sense, difficulty: easiest };
  }),
});

export const validateEntry = (
  raw: unknown,
  ctx: ValidationContext,
): ValidationResult => {
  const errors: string[] = [];
  if (!isRecord(raw)) {
    return { status: "invalid", errors: ["entry must be an object"] };
  }

  const headword = raw["headword"];
  if (!isNonEmptyString(headword)) {
    errors.push("headword must be a non-empty string");
  } else if (!ctx.inputWords.has(headword)) {
    errors.push(`headword "${headword}" is not in the input batch`);
  }
  if (raw["language"] !== ctx.sourceLanguage) {
    errors.push(`language must be "${ctx.sourceLanguage}"`);
  }
  if (raw["pos"] !== ctx.pos) {
    errors.push(`pos must be "${ctx.pos}"`);
  }

  const senses = raw["senses"];
  if (!Array.isArray(senses)) {
    errors.push("senses must be an array");
  } else if (senses.length === 0) {
    if (errors.length === 0 && isNonEmptyString(headword)) {
      return { status: "empty", headword };
    }
  } else {
    if (senses.length > 3) {
      errors.push("senses must contain at most 3 entries");
    }
    senses.forEach((sense, i) => checkSense(sense, i, ctx, errors));
  }

  if (errors.length > 0) {
    return { status: "invalid", errors };
  }
  const normalizations: string[] = [];
  return {
    status: "valid",
    entry: applySenseDifficultyFloor(raw as GeminiWordEntry, normalizations),
    normalizations,
  };
};