import type { FileHandle } from "node:fs/promises";
import type { Readable } from "node:stream";
import type { Charset } from "./charset/charset.ts";
import { utf8 } from "./charset/utf8.ts";
import { escapeRegExp } from "./util/escapeRegExp.ts";

export class CsvReader {
  private reader: Promise<ReadableStreamDefaultReader<string>>;
  private fieldSeparator: string;
  private skipEmptyLine: boolean;
  private reSeparator: RegExp;

  private endsWithCR = false;
  private buf = "";
  private index = 0;

  constructor(
    src:
      | string
      | Uint8Array
      | Blob
      | ReadableStream<Uint8Array>
      | FileHandle
      | Readable,
    options?: {
      charset?: Charset;
      bom?: boolean;
      fieldSeparator?: string;
      skipEmptyLine?: boolean;
      fatal?: boolean;
    },
  ) {
    const charset = options?.charset ?? utf8;
    this.fieldSeparator = options?.fieldSeparator ?? ",";
    this.skipEmptyLine = options?.skipEmptyLine ?? false;
    this.reSeparator = new RegExp(
      `\n|\r\n?|${escapeRegExp(this.fieldSeparator)}`,
      "g",
    );

    if (typeof src === "string") {
      this.reader = Promise.resolve(
        new ReadableStream<string>({
          start(controller) {
            controller.enqueue(src);
            controller.close();
          },
        }).getReader(),
      );
    } else {
      let stream: Promise<ReadableStream<Uint8Array>>;
      if (src instanceof Uint8Array) {
        stream = Promise.resolve(
          new ReadableStream<Uint8Array>({
            start(controller) {
              controller.enqueue(src);
              controller.close();
            },
          }),
        );
      } else if (src instanceof Blob) {
        stream = Promise.resolve(src.stream());
      } else if (src instanceof ReadableStream) {
        stream = Promise.resolve(src);
      } else {
        const readable =
          "createReadStream" in src ? src.createReadStream() : src;
        if (
          "constructor" in readable &&
          "toWeb" in readable.constructor &&
          typeof readable.constructor.toWeb === "function"
        ) {
          stream = Promise.resolve(readable.constructor.toWeb(readable));
        } else {
          throw new TypeError(`Unsuppoted source: ${src}`);
        }
      }

      const decoder = charset.createDecoder({
        fatal: options?.fatal ?? true,
        ignoreBOM: options?.bom != null ? !options.bom : false,
      });

      this.reader = stream.then((value) =>
        value
          .pipeThrough(
            new TransformStream({
              transform(chunk, controller) {
                controller.enqueue(decoder.decode(chunk, { stream: true }));
              },
              flush() {
                decoder.decode(new Uint8Array());
              },
            }),
          )
          .getReader(),
      );
    }
  }

  async read(): Promise<string[] | undefined> {
    const items = new Array<string>();

    let buf = this.buf;
    let pos = 0;
    let quoted = false;
    let done = false;

    const reader = await this.reader;
    loop: do {
      const readed = await reader.read();
      done = readed.done;

      if (readed.value) {
        let value = readed.value;
        if (this.endsWithCR && value.startsWith("\n")) {
          value = value.substring(1);
          this.endsWithCR = false;
        }
        if (value.endsWith("\r")) {
          this.endsWithCR = true;
        }
        buf = buf ? buf + value : value;
      }

      while (pos < buf.length) {
        if (!quoted && buf.startsWith('"')) {
          if (pos === 0) {
            pos = 1;
          }
          const lpos = buf.indexOf('"', pos);
          if (lpos === -1) {
            pos = buf.length;
            continue loop;
          } else if (buf.startsWith('"', lpos + 1)) {
            pos = lpos + 2;
            continue;
          } else {
            const unquoted = buf.substring(1, lpos).replaceAll('""', '"');
            buf = unquoted + buf.substring(lpos + 1);
            pos = unquoted.length;
            quoted = true;
            continue;
          }
        }

        this.reSeparator.lastIndex = pos;
        if (!this.reSeparator.test(buf)) {
          pos = buf.length;
          continue loop;
        }

        const item = buf.substring(
          0,
          this.reSeparator.lastIndex -
            (buf.endsWith("\r\n", this.reSeparator.lastIndex) ? 2 : 1),
        );
        if (!buf.endsWith(this.fieldSeparator, this.reSeparator.lastIndex)) {
          if (item || items.length > 0 || quoted) {
            items.push(item);
          }
          if (items.length > 0 || !this.skipEmptyLine) {
            this.buf = buf.substring(this.reSeparator.lastIndex);
            this.index++;
            return items;
          }
        } else {
          items.push(item);
        }
        buf = buf.substring(this.reSeparator.lastIndex);
        pos = 0;
        quoted = false;
      }

      if (done) {
        if (buf || items.length > 0 || quoted) {
          items.push(buf);
        }
        if (items.length > 0) {
          this.buf = "";
          this.index++;
          return items;
        }
      }
    } while (buf || !done);
  }

  async *[Symbol.asyncIterator](): AsyncGenerator<string[]> {
    let record: string[] | undefined;
    while ((record = await this.read()) != null) {
      yield record;
    }
  }

  get count() {
    return this.index;
  }

  async close() {
    const reader = await this.reader;
    await reader.cancel();
  }
}