import type { z } from "zod";
import {
  AnalysisInputError,
  type AnalysisInputIssue,
} from "./analysisErrorCore.js";

/** Build the standard application input error while retaining schema causes and extra semantic issues. */
export const analysisInputErrorFromIssues = (
  operation: string,
  issues: readonly z.core.$ZodIssue[],
  input: unknown,
  options: {
    readonly cause?: unknown;
    readonly userMessage?: string;
    readonly additionalIssues?: readonly AnalysisInputIssue[];
  } = {},
): AnalysisInputError =>
  new AnalysisInputError(
    operation,
    {
      ...(options.cause === undefined ? {} : { cause: options.cause }),
      ...(options.userMessage === undefined
        ? {}
        : { userMessage: options.userMessage }),
    },
    [...projectInputIssues(issues, input), ...(options.additionalIssues ?? [])],
  );

/** Remove only the internal operation/input envelope from caller correction paths. */
export const analysisOperationInputErrorFromIssues = (
  operation: string,
  issues: readonly z.core.$ZodIssue[],
  input: unknown,
  cause: unknown,
): AnalysisInputError =>
  new AnalysisInputError(
    operation,
    { cause },
    projectInputIssues(issues, { operation, input }).map((issue) =>
      issue.path[0] === "input"
        ? { ...issue, path: issue.path.slice(1) }
        : issue,
    ),
  );

/** Project Zod failures to secret-safe caller correction metadata. */
export const projectInputIssues = (
  issues: readonly z.core.$ZodIssue[],
  input: unknown,
): readonly AnalysisInputIssue[] =>
  issues.flatMap((issue) => projectIssue(issue, input));

const projectionBudgetExceeded = Symbol(
  "input issue projection budget exceeded",
);

/** Bound representation expansion before constructing projected diagnostics. */
export const projectInputIssuesWithinBudget = (
  issues: readonly z.core.$ZodIssue[],
  input: unknown,
  budgetBytes: number,
): readonly AnalysisInputIssue[] | undefined => {
  return projectInputIssueGroupsWithinBudget(
    issues,
    input,
    budgetBytes,
  )?.flat();
};

/** Field diagnostics that fit a byte allowance, plus what was dropped. */
export interface BoundedInputIssues {
  readonly issues: readonly AnalysisInputIssue[];
  /** Validator issues whose field diagnostics did not fit the allowance. */
  readonly omittedIssueCount: number;
}

/**
 * Project as many validator issues as fit, in one forward pass, and count the
 * rest. A single pass keeps the returned group maximal: it stops exactly at the
 * allowance instead of at a coarse fraction of the list, and a compound issue
 * such as `unrecognized_keys` still charges every field diagnostic it expands
 * into because the recursion goes through `projectIssue` per nested issue.
 */
export const projectInputIssuesBounded = (
  issues: readonly z.core.$ZodIssue[],
  input: unknown,
  budgetBytes: number,
): BoundedInputIssues => {
  const budget = { remaining: budgetBytes };
  const output: AnalysisInputIssue[] = [];
  let index = 0;
  try {
    for (; index < issues.length; index += 1) {
      const issue = issues[index];
      if (issue === undefined) continue;
      output.push(...projectIssue(issue, input, budget));
    }
  } catch (error) {
    if (error !== projectionBudgetExceeded) throw error;
    // The issue that crossed the allowance and every later one contribute at
    // least one omitted field diagnostic each.
    const omittedIssueCount = issues.length - index;
    if (output.length > 0) return { issues: output, omittedIssueCount };
    // One compound issue, such as `unrecognized_keys` naming hundreds of keys,
    // can exceed the allowance on its own. Retain a diagnostic at its path so the
    // caller keeps the location instead of only an omission notice.
    const first = issues[0];
    if (first === undefined) return { issues: output, omittedIssueCount };
    const path = first.path.flatMap((part) =>
      typeof part === "string" || typeof part === "number" ? [part] : [],
    );
    return {
      issues: [
        {
          path,
          reason: "invalid_value",
          message: `${String(omittedIssueCount)} field diagnostics at this location were omitted because they do not fit the response budget.`,
        },
      ],
      omittedIssueCount,
    };
  }
  return { issues: output, omittedIssueCount: 0 };
};

/** Retain each projected issue's source through bounded SDK normalization. */
export const projectInputIssueGroupsWithinBudget = (
  issues: readonly z.core.$ZodIssue[],
  input: unknown,
  budgetBytes: number,
): readonly (readonly AnalysisInputIssue[])[] | undefined => {
  const budget = { remaining: budgetBytes };
  try {
    const groups: (readonly AnalysisInputIssue[])[] = [];
    for (const issue of issues) groups.push(projectIssue(issue, input, budget));
    return groups;
  } catch (error) {
    if (error === projectionBudgetExceeded) return undefined;
    throw error;
  }
};

const chargeProjection = (
  issue: z.core.$ZodIssue,
  budget: { remaining: number },
): void => {
  // Six bytes per UTF-16 code unit covers JSON escaping. The fixed allowance
  // covers the projected object, property names, scalar values and delimiters.
  const charge = (amount: number) => {
    budget.remaining -= amount;
    if (budget.remaining < 0) throw projectionBudgetExceeded;
  };
  charge(256);
  let pathCost = 0;
  for (const part of issue.path) {
    const cost = typeof part === "string" ? 6 * part.length + 16 : 32;
    pathCost += cost;
    charge(cost);
  }
  charge(6 * issue.message.length);
  if (issue.code === "invalid_union") {
    for (const branch of issue.errors) charge(32 + 32 * branch.length);
    if ("options" in issue && Array.isArray(issue.options))
      for (const value of issue.options)
        charge(typeof value === "string" ? 6 * value.length + 32 : 32);
  }
  if (issue.code === "invalid_key") charge(32 * issue.issues.length);
  if (issue.code === "unrecognized_keys")
    for (const key of issue.keys) charge(256 + pathCost + 6 * key.length);
  if (issue.code === "invalid_value")
    for (const value of issue.values)
      charge(typeof value === "string" ? 6 * value.length + 32 : 32);
};

const nestedIssue = (
  parent: z.core.$ZodIssue,
  child: z.core.$ZodIssue,
  budget: { remaining: number } | undefined,
): z.core.$ZodIssue => {
  if (budget !== undefined) {
    // The combined path is allocated before the child is projected. Charge
    // its references first so a long nested path cannot bypass the allowance.
    budget.remaining -= 32 + 8 * (parent.path.length + child.path.length);
    if (budget.remaining < 0) throw projectionBudgetExceeded;
  }
  return { ...child, path: [...parent.path, ...child.path] };
};

const projectIssue = (
  issue: z.core.$ZodIssue,
  input: unknown,
  budget?: { remaining: number },
): readonly AnalysisInputIssue[] => {
  if (budget !== undefined) chargeProjection(issue, budget);
  const path = issue.path.flatMap((part) =>
    typeof part === "string" || typeof part === "number" ? [part] : [],
  );
  // Branch issue paths are relative to the union; branches often agree.
  if (issue.code === "invalid_union") {
    // Unmatched discriminators and ambiguous unions have no branch issues.
    // Keep their outer failure instead of flattening it into an empty list.
    if (issue.errors.length === 0) {
      const expected =
        "options" in issue ? issue.options?.filter(isSafeExpected) : undefined;
      return [
        {
          path,
          reason:
            valueAtPath(input, path) === undefined
              ? "missing_argument"
              : "invalid_value",
          ...(expected === undefined ? {} : { expected }),
        },
      ];
    }
    return uniqueIssues(
      issue.errors.flatMap((branch) =>
        branch.flatMap((branchIssue) =>
          projectIssue(nestedIssue(issue, branchIssue, budget), input, budget),
        ),
      ),
    );
  }
  if (issue.code === "invalid_key")
    return issue.issues.flatMap((keyIssue) =>
      projectIssue(nestedIssue(issue, keyIssue, budget), input, budget),
    );
  if (issue.code === "unrecognized_keys")
    return issue.keys.map((key) => ({
      path: [...path, key],
      reason: "unknown_argument" as const,
    }));
  if (issue.code === "invalid_type")
    return [
      {
        path,
        reason:
          valueAtPath(input, path) === undefined
            ? "missing_argument"
            : "invalid_type",
        expected: safeExpected(issue.expected),
      },
    ];
  if (issue.code === "too_small")
    return [boundedIssue(path, "minimum", numericBound(issue.minimum))];
  if (issue.code === "too_big")
    return [boundedIssue(path, "maximum", numericBound(issue.maximum))];
  if (issue.code === "invalid_format")
    return [
      {
        path,
        reason: "invalid_format",
        expected: issue.format,
        ...(issue.format === "regex" && issue.message.length > 0
          ? { message: issue.message }
          : {}),
      },
    ];
  if (issue.code === "invalid_value")
    return [
      {
        path,
        reason: "invalid_value",
        expected: issue.values.filter(isSafeExpected),
      },
    ];
  return [
    {
      path,
      reason: "invalid_value",
      ...(issue.message.length > 0 ? { message: issue.message } : {}),
    },
  ];
};

const uniqueIssues = (
  issues: readonly AnalysisInputIssue[],
): AnalysisInputIssue[] => [
  ...new Map(issues.map((issue) => [JSON.stringify(issue), issue])).values(),
];

const valueAtPath = (
  input: unknown,
  path: readonly (string | number)[],
): unknown => {
  let current = input;
  for (const part of path) {
    if (typeof current !== "object" || current === null) return undefined;
    const next: unknown = Reflect.get(current, part);
    current = next;
  }
  return current;
};

const numericBound = (value: number | bigint): number | undefined =>
  typeof value === "number" && Number.isFinite(value) ? value : undefined;

const isSafeExpected = (
  value: unknown,
): value is string | number | boolean | null =>
  value === null || ["string", "number", "boolean"].includes(typeof value);

const safeExpected = (value: unknown) =>
  isSafeExpected(value) ? value : "schema-defined value";

const boundedIssue = (
  path: readonly (string | number)[],
  key: "minimum" | "maximum",
  value: number | undefined,
): AnalysisInputIssue => ({
  path,
  reason: "out_of_range",
  ...(value === undefined ? {} : { [key]: value }),
});