import {
  type ModuleDatabaseField,
  ModuleDatabaseError,
  type ModuleDatabaseValue,
} from "@ekklesia/contracts";

/**
 * The value contract of Module Database ABI v1 (ADR 0050): how parameters are encoded before they
 * reach PostgreSQL, and how result text is decoded after. Both are Core's, and neither consults
 * `pg`'s process-global type registry or any ORM, which module code could change or differ from.
 *
 * Every value travels in PostgreSQL's text format. The session settings the decoding depends on
 * (`DateStyle`, `IntervalStyle`, `TimeZone`, `bytea_output`, `extra_float_digits`) are pinned by the
 * executor for every ABI operation (`./database-abi.ts`).
 */

/** PostgreSQL's limit on bound parameters in one statement (the protocol's 16-bit count). */
export const MODULE_DATABASE_MAX_PARAMETERS = 65_535;
/** PostgreSQL's limit on array dimensions (`MAXDIM`). */
const maximumArrayDimensions = 6;

function parameterInvalid(): ModuleDatabaseError {
  return new ModuleDatabaseError("MODULE_DATABASE_PARAMETER_INVALID");
}

function isScalar(value: unknown): boolean {
  return (
    value === null ||
    typeof value === "boolean" ||
    typeof value === "number" ||
    typeof value === "bigint" ||
    typeof value === "string" ||
    value instanceof Uint8Array
  );
}

function scalarText(value: boolean | number | bigint | string): string {
  // `String` spells NaN, Infinity, and -Infinity exactly as PostgreSQL's float and numeric input
  // accepts them.
  return typeof value === "string" ? value : String(value);
}

function byteaText(value: Uint8Array): string {
  return `\\x${Buffer.from(value.buffer, value.byteOffset, value.byteLength).toString("hex")}`;
}

function quoteArrayElement(text: string): string {
  return `"${text.replaceAll("\\", "\\\\").replaceAll('"', '\\"')}"`;
}

/**
 * Validates one array level and returns its PostgreSQL array literal. Every element of a level is
 * either a sub-array or a scalar, and sibling sub-arrays have equal lengths, because PostgreSQL
 * arrays are rectangular. Every non-null element is quoted, which PostgreSQL accepts for any element
 * type.
 */
function arrayLiteral(values: readonly unknown[], depth: number): string {
  if (depth > maximumArrayDimensions) {
    throw parameterInvalid();
  }
  const elements: string[] = [];
  let nestedLength: number | undefined;
  let nested: boolean | undefined;
  for (let index = 0; index < values.length; index += 1) {
    if (!Object.hasOwn(values, index)) {
      throw parameterInvalid();
    }
    const element = values[index];
    const isNested = Array.isArray(element);
    if (nested === undefined) {
      nested = isNested;
    } else if (nested !== isNested) {
      throw parameterInvalid();
    }
    if (isNested) {
      if (nestedLength === undefined) {
        nestedLength = element.length;
      } else if (nestedLength !== element.length) {
        throw parameterInvalid();
      }
      elements.push(arrayLiteral(element, depth + 1));
    } else if (element === null) {
      elements.push("NULL");
    } else if (element instanceof Uint8Array) {
      elements.push(quoteArrayElement(byteaText(element)));
    } else if (isScalar(element)) {
      elements.push(quoteArrayElement(scalarText(element as boolean | number | bigint | string)));
    } else {
      throw parameterInvalid();
    }
  }
  return `{${elements.join(",")}}`;
}

/**
 * Validates `values` against the ABI's parameter set and encodes each one into the only forms the
 * driver then passes through unchanged: `null`, a string, or a `Buffer` copy of a `Uint8Array`.
 * Anything else, including `undefined`, `Date`, plain objects, other class instances, functions,
 * symbols, sparse or ragged arrays, and arrays deeper than PostgreSQL allows, is refused before
 * anything reaches PostgreSQL. The error never names the value.
 */
export function encodeModuleDatabaseParameters(values: unknown): (string | Buffer | null)[] {
  if (values === undefined) {
    return [];
  }
  if (!Array.isArray(values) || values.length > MODULE_DATABASE_MAX_PARAMETERS) {
    throw parameterInvalid();
  }
  const encoded: (string | Buffer | null)[] = [];
  for (let index = 0; index < values.length; index += 1) {
    if (!Object.hasOwn(values, index)) {
      throw parameterInvalid();
    }
    const value: unknown = values[index];
    if (value === null) {
      encoded.push(null);
    } else if (value instanceof Uint8Array) {
      // A copy: the driver serializes when the statement is sent, which may be after the caller
      // has changed its own bytes.
      encoded.push(Buffer.from(value));
    } else if (Array.isArray(value)) {
      encoded.push(arrayLiteral(value, 1));
    } else if (isScalar(value)) {
      encoded.push(scalarText(value as boolean | number | bigint | string));
    } else {
      throw parameterInvalid();
    }
  }
  return encoded;
}

// --- Results -----------------------------------------------------------------------------------

type ScalarDecoder = (text: string) => ModuleDatabaseValue;

const asText: ScalarDecoder = (text) => text;
const asBoolean: ScalarDecoder = (text) => text === "t";
const asInteger: ScalarDecoder = (text) => Number.parseInt(text, 10);
// `Number` reads PostgreSQL's NaN, Infinity, -Infinity, and exponent forms. With
// `extra_float_digits` pinned to 1 the text is the shortest form that round-trips exactly.
const asFloat: ScalarDecoder = (text) => Number(text);

function hexDigit(code: number): number {
  if (code >= 48 && code <= 57) {
    return code - 48;
  }
  if (code >= 97 && code <= 102) {
    return code - 87;
  }
  if (code >= 65 && code <= 70) {
    return code - 55;
  }
  return -1;
}

/**
 * `bytea` text to bytes. The executor pins `bytea_output` to `hex`; the older `escape` form is read
 * too, so a transaction that changed the setting still decodes faithfully rather than failing.
 * Always a plain `Uint8Array`, never a `Buffer`.
 */
const asBytes: ScalarDecoder = (text) => {
  if (text.startsWith("\\x")) {
    const length = (text.length - 2) / 2;
    const bytes = new Uint8Array(length);
    for (let index = 0; index < length; index += 1) {
      const high = hexDigit(text.charCodeAt(2 + index * 2));
      const low = hexDigit(text.charCodeAt(3 + index * 2));
      bytes[index] = high * 16 + low;
    }
    return bytes;
  }
  const bytes: number[] = [];
  for (let index = 0; index < text.length; index += 1) {
    const code = text.charCodeAt(index);
    if (code === 92 && text.charCodeAt(index + 1) === 92) {
      bytes.push(92);
      index += 1;
    } else if (code === 92) {
      bytes.push(Number.parseInt(text.slice(index + 1, index + 4), 8));
      index += 3;
    } else {
      bytes.push(code);
    }
  }
  return Uint8Array.from(bytes);
};

/** Built-in scalar type OIDs with a decoding other than "PostgreSQL's text output, unchanged". Every
 * type not listed here, `int8`, `numeric`, date and time types, `json`, and `jsonb` included,
 * arrives as its exact text. */
const scalarDecoders: ReadonlyMap<number, ScalarDecoder> = new Map([
  [16, asBoolean], // bool
  [17, asBytes], // bytea
  [21, asInteger], // int2
  [23, asInteger], // int4
  [26, asInteger], // oid
  [700, asFloat], // float4
  [701, asFloat], // float8
]);

/** Built-in array type OIDs, each with its element type OID. An array of a type not listed here
 * (an enum, a domain, an extension type) arrives as its text, like any other type. */
const arrayElementTypes: ReadonlyMap<number, number> = new Map([
  [1000, 16], // bool[]
  [1001, 17], // bytea[]
  [1002, 18], // "char"[]
  [1003, 19], // name[]
  [1005, 21], // int2[]
  [1007, 23], // int4[]
  [1009, 25], // text[]
  [1014, 1042], // bpchar[]
  [1015, 1043], // varchar[]
  [1016, 20], // int8[]
  [1021, 700], // float4[]
  [1022, 701], // float8[]
  [1028, 26], // oid[]
  [1115, 1114], // timestamp[]
  [1182, 1082], // date[]
  [1183, 1083], // time[]
  [1185, 1184], // timestamptz[]
  [1187, 1186], // interval[]
  [1231, 1700], // numeric[]
  [1270, 1266], // timetz[]
  [2951, 2950], // uuid[]
  [199, 114], // json[]
  [3807, 3802], // jsonb[]
]);

class ArrayTextError extends Error {}

/**
 * Parses PostgreSQL's array text output into nested arrays, each element decoded by `decode`.
 * Unquoted `NULL` is null; a quoted `"NULL"` is the string. A non-default lower bound
 * (`[0:1]={…}`) is not represented: a JavaScript array is a zero-based list. Every element type this
 * decodes uses `,` as its delimiter.
 */
export function parsePostgresArrayText(text: string, decode: ScalarDecoder): ModuleDatabaseValue[] {
  let position = 0;
  if (text.startsWith("[")) {
    const equals = text.indexOf("=");
    if (equals === -1) {
      throw new ArrayTextError();
    }
    position = equals + 1;
  }

  function parseArray(): ModuleDatabaseValue[] {
    if (text[position] !== "{") {
      throw new ArrayTextError();
    }
    position += 1;
    const items: ModuleDatabaseValue[] = [];
    if (text[position] === "}") {
      position += 1;
      return items;
    }
    for (;;) {
      const character = text[position];
      if (character === "{") {
        items.push(parseArray());
      } else if (character === '"') {
        position += 1;
        let element = "";
        for (;;) {
          const next = text[position];
          if (next === undefined) {
            throw new ArrayTextError();
          }
          if (next === "\\") {
            element += text[position + 1] ?? "";
            position += 2;
          } else if (next === '"') {
            position += 1;
            break;
          } else {
            element += next;
            position += 1;
          }
        }
        items.push(decode(element));
      } else {
        const start = position;
        while (position < text.length && text[position] !== "," && text[position] !== "}") {
          position += 1;
        }
        const element = text.slice(start, position);
        items.push(element.toUpperCase() === "NULL" ? null : decode(element));
      }
      if (text[position] === ",") {
        position += 1;
      } else if (text[position] === "}") {
        position += 1;
        return items;
      } else {
        throw new ArrayTextError();
      }
    }
  }

  const parsed = parseArray();
  if (position !== text.length) {
    throw new ArrayTextError();
  }
  return parsed;
}

function scalarDecoder(typeOid: number): ScalarDecoder {
  return scalarDecoders.get(typeOid) ?? asText;
}

/** Decodes one non-null column value from its PostgreSQL text by the column's type OID. */
export function decodeModuleDatabaseValue(typeOid: number, text: string): ModuleDatabaseValue {
  const elementType = arrayElementTypes.get(typeOid);
  if (elementType === undefined) {
    return scalarDecoder(typeOid)(text);
  }
  try {
    return parsePostgresArrayText(text, scalarDecoder(elementType));
  } catch {
    // PostgreSQL produced this text, so it cannot be malformed; should it ever be, the column still
    // arrives faithfully, as text, rather than as a guess.
    return text;
  }
}

/**
 * The `types` object handed to `pg` for every ABI statement. Its parser returns the raw text for
 * every type, so the driver's global registry, which module code could change, is never consulted
 * and the ABI decodes from text itself. It is an empty array as well because the driver also reads
 * the same option as the Parse message's parameter-type list: empty, so PostgreSQL infers every
 * parameter type from the statement.
 */
export const rawTextTypes: { getTypeParser: () => (text: string) => string } & never[] =
  Object.freeze(
    Object.assign([] as never[], {
      getTypeParser: () => (text: string) => text,
    }),
  );

/** Decodes one positional row of raw driver text. */
export function decodeModuleDatabaseRow(
  fields: readonly ModuleDatabaseField[],
  raw: readonly unknown[],
): ModuleDatabaseValue[] {
  return fields.map((field, index) => {
    const value = raw[index];
    return typeof value === "string" ? decodeModuleDatabaseValue(field.typeOid, value) : null;
  });
}