import type { IncomingMessage } from "node:http";
import type { Etag } from "./etag";

type EtagMatchType =
  | {
      type: "match";
      value: Etag[];
    }
  | {
      type: "wildcard";
    };

class EtagMatch {
  private constructor(private readonly etagMatch: EtagMatchType) {}

  static parse(etagMatch: string | undefined): EtagMatch | null {
    if (etagMatch === undefined) return null;
    if (etagMatch === "*") {
      return new EtagMatch({ type: "wildcard" });
    } else {
      return new EtagMatch({
        type: "match",
        value: etagMatch.split(",").map((etag) => etag.trim() as Etag),
      });
    }
  }

  matches(etag: Etag): boolean {
    switch (this.etagMatch.type) {
      case "match":
        return this.etagMatch.value.includes(etag);
      case "wildcard":
        return true;
    }
  }
}

class DateMatch {
  private constructor(private readonly mtime: Date) {}

  static parse(dateMatch: string | undefined): DateMatch | null {
    if (dateMatch === undefined) return null;
    const time = Date.parse(dateMatch);
    if (isNaN(time)) return null;
    return new DateMatch(new Date(time));
  }

  matches(mtime: Date): boolean {
    return this.mtime.getTime() / 1_000 === mtime.getTime() / 1_000;
  }
}

export class Options {
  /**
   * See <https://datatracker.ietf.org/doc/html/rfc9110#name-if-match>
   *
   * Examples:
   *
   * ```text
   * If-Match: "xyzzy"
   * If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
   * If-Match: *
   * ```
   */
  private ifMatch: EtagMatch | null;

  /**
   * See <https://datatracker.ietf.org/doc/html/rfc9110#section-13.1.2>
   *
   * Examples:
   *
   * ```text
   * If-None-Match: "xyzzy"
   * If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
   * If-None-Match: *
   * ```
   */
  private ifNoneMatch: EtagMatch | null;

  /**
   * See <https://datatracker.ietf.org/doc/html/rfc9110#section-13.1.3>
   *
   * Examples:
   *
   * ```text
   * If-Modified-Since: Mon, 07 Jan 2002 19:43:36 GMT
   * ```
   */
  private ifModifiedSince: DateMatch | null;

  /**
   * See <https://datatracker.ietf.org/doc/html/rfc9110#section-13.1.4>
   *
   * Examples:
   *
   * ```text
   * If-Unmodified-Since: Mon, 07 Jan 2002 19:43:36 GMT
   * ```
   */
  private ifUnmodifiedSince: DateMatch | null;

  constructor(request: IncomingMessage) {
    this.ifMatch = EtagMatch.parse(request.headers["if-match"]);
    this.ifNoneMatch = EtagMatch.parse(request.headers["if-none-match"]);
    this.ifModifiedSince = DateMatch.parse(request.headers["if-modified-since"]);
    this.ifUnmodifiedSince = DateMatch.parse(request.headers["if-unmodified-since"]);
  }

  /**
   * RFC 9110 section 13.1.1: If-Match precondition evaluation
   * RFC 9110 section 13.1.4: If-Unmodified-Since precondition evaluation
   * See <https://datatracker.ietf.org/doc/html/rfc9110#section-13.1.1>
   * See <https://datatracker.ietf.org/doc/html/rfc9110#section-13.1.4>
   */
  preconditionFailed(etag: Etag, mtime: Date): boolean {
    // If-Match precondition takes precedence
    if (this.ifMatch !== null && !this.ifMatch.matches(etag)) {
      return true;
    }

    // If-Unmodified-Since precondition (only if no If-Match header)
    if (this.ifMatch === null && this.ifUnmodifiedSince !== null) {
      return !this.ifUnmodifiedSince.matches(mtime);
    }

    return false;
  }

  /**
   * RFC 9110 section 13.1.2: If-None-Match precondition evaluation
   * RFC 9110 section 13.1.3: If-Modified-Since precondition evaluation
   * See <https://datatracker.ietf.org/doc/html/rfc9110#section-13.1.2>
   * See <https://datatracker.ietf.org/doc/html/rfc9110#section-13.1.3>
   */
  notModified(etag: Etag, mtime: Date): boolean {
    // If-None-Match takes precedence over If-Modified-Since
    if (this.ifNoneMatch !== null) {
      return this.ifNoneMatch.matches(etag);
    }

    // If-Modified-Since (only if no If-None-Match header)
    if (this.ifModifiedSince !== null) {
      return this.ifModifiedSince.matches(mtime);
    }

    return false;
  }
}