import type { CodePointSpan } from 'source-region';
import type { ParseError } from './parse_errors';

export type ConcreteInfo = { span: CodePointSpan };

export type ConcreteError = ConcreteErrorNode[] // Convention: can't be empty.
export type ConcreteErrorNode = {
  span: CodePointSpan,
  error: ParseError,
  panickedOver?: CodePointSpan,
}

export namespace ConcreteError {
  export function single(node: ConcreteErrorNode): ConcreteError {
    return [node];
  }
}

export type DelimiterToken =
  | { tag: "open-paren", span: CodePointSpan }
  | { tag: "close-paren", span: CodePointSpan }
  | { tag: "open-bracket", span: CodePointSpan }
  | { tag: "close-bracket", span: CodePointSpan }

export namespace DelimiterToken {
  export function openParen(span: CodePointSpan): DelimiterToken {
    return { tag: "open-paren", span };
  }

  export function closeParen(span: CodePointSpan): DelimiterToken {
    return { tag: "close-paren", span };
  }

  export function openBracket(span: CodePointSpan): DelimiterToken {
    return { tag: "open-bracket", span };
  }

  export function closeBracket(span: CodePointSpan): DelimiterToken {
    return { tag: "close-bracket", span };
  }
}

export type Program<Info, Error> = {
  tag: "program",
  expressions: Expr<Info, Error>[],
  error?: Error,
} & Info

export type Expr<Info, Error> =
| Literal<Info, Error>
| List<Info, Error>
| { tag: "error-expression", error: Error } & Info // This is for errors that don't really correspond to any sort of node. Unknown errors.

export type List<Info, Error> =
  { tag: "list", open: DelimiterToken, items: ListItem<Info, Error>[], close?: DelimiterToken, error?: Error } & Info

export type ListItem<Info, Error> =
| Expr<Info, Error>
| { tag: "error-list-separator", error: Error } & Info

export type Literal<Info, Error> =
// === number ===
| { tag: "number", value: number } & Info
| { tag: "error-number", error: Error } & Info
// === identifier ===
| { tag: "identifier", value: Identifier } & Info
| { tag: "error-identifier", error: Error } & Info

export type Identifier = string

export namespace Program {
  export function make<Info, Error>(
    expressions: Expr<Info, Error>[],
    info: Info,
    error?: Error,
  ): Program<Info, Error> {
    return error === undefined
      ? { tag: "program", expressions, ...info }
      : { tag: "program", expressions, error, ...info };
  }

  export function show<Info, Error>(program: Program<Info, Error>): string {
    return program.expressions.map(Expr.show).join(" ");
  }
}

export namespace Expr {
  export function number(value: number, span: CodePointSpan): Expr<ConcreteInfo, ConcreteError> {
    return { tag: "number", value, span };
  }

  export function errorNumber(error: ConcreteError, span: CodePointSpan): Expr<ConcreteInfo, ConcreteError> {
    return { tag: "error-number", error, span };
  }

  export function identifier(value: Identifier, span: CodePointSpan): Expr<ConcreteInfo, ConcreteError> {
    return { tag: "identifier", value, span };
  }

  export function errorIdentifier(error: ConcreteError, span: CodePointSpan): Expr<ConcreteInfo, ConcreteError> {
    return { tag: "error-identifier", error, span };
  }

  export function list(
    open: DelimiterToken,
    items: ListItem<ConcreteInfo, ConcreteError>[],
    span: CodePointSpan,
    close?: DelimiterToken,
    error?: ConcreteError,
  ): Expr<ConcreteInfo, ConcreteError> {
    return { tag: "list", open, items, close, error, span };
  }

  export function errorExpression(error: ConcreteError, span: CodePointSpan): Expr<ConcreteInfo, ConcreteError> {
    return { tag: "error-expression", error, span };
  }

  export function show<Info, Error>(expr: Expr<Info, Error>): string {
    switch (expr.tag) {
      case "number":
        return `${expr.value}`;
      case "identifier":
        return expr.value;
      case "error-number":
        return "<error-number>";
      case "error-identifier":
        return "<error-identifier>";
      case "error-expression":
        return "<error-expression>";
      case "list":
        return showList(expr);
    }
  }

  function showList<Info, Error>(list: List<Info, Error>): string {
    const open = list.open.tag === "open-bracket" ? "[" : "(";
    const close = list.open.tag === "open-bracket" ? "]" : ")";
    const sep = list.open.tag === "open-bracket" ? ", " : " ";
    return `${open}${list.items.map(ListItem.show).join(sep)}${close}`;
  }
}

export namespace ListItem {
  export function errorSeparator(error: ConcreteError, span: CodePointSpan): ListItem<ConcreteInfo, ConcreteError> {
    return { tag: "error-list-separator", error, span };
  }

  export function show<Info, Error>(item: ListItem<Info, Error>): string {
    if (item.tag === "error-list-separator") return "<error-separator>";
    return Expr.show(item);
  }
}