const Math = require('./bnmath');

const EMPTY = Symbol('empty');

class Glib {
  // NB: this assumes all inputs are iterable
  static concat(...args) {
    return Glib.fromIterable(args).flatMap((i) => {
      return i;
    });
  }
  static infiniteFromIterable(iterable) {
    const cache = Array.from(iterable);
    return new Glib(
      (function*() {
        while (true) {
          yield* cache;
        }
      })(),
    );
  }
  static fromSplit(string, separator = '\n') {
    return new Glib(
      (function*() {
        let partial = '';
        for (const char of string) {
          partial += char;
          if (!partial.endsWith(separator)) {
            continue;
          }
          yield partial.slice(0, -separator.length);
          partial = '';
        }
        yield partial;
      })(),
    );
  }
  static fromParsedString(string, separator, parse) {
    return new Glib(
      (function*() {
        let partial = '';
        for (const char of string) {
          partial += char;
          if (!partial.endsWith(separator)) {
            continue;
          }
          yield parse(partial.slice(0, -separator.length));
          partial = '';
        }
        yield parse(partial);
      })(),
    );
  }
  static fromLines(lines) {
    const g = Glib.fromIterable(lines.split('\n'));
    return g.map((line) => {
      // console.log(line);
      return line.trim();
    });
  }
  static fromSequence(start = 1n, end = Infinity, step = 1n) {
    if (typeof start === 'number') {
      start = BigInt(start);
    }
    if (typeof end === 'number' && (end !== Infinity && end !== -Infinity)) {
      end = BigInt(end);
    }
    if (typeof step === 'number') {
      step = BigInt(step);
    }
    return new Glib(
      (function*() {
        for (let i = start; i <= end; i += step) {
          yield i;
        }
      })(),
    );
  }
  static fromIterable(iterable) {
    return new Glib(
      (function*() {
        yield* iterable;
      })(),
    );
  }
  constructor(iterator) {
    this._ = iterator;
  }
  flatMap(mapFn) {
    return new Glib(
      (function*(iterable) {
        let index = 0;
        for (const entry of iterable) {
          yield* mapFn(entry, index++);
        }
      })(this),
    );
  }
  map(mapFn) {
    return this.flatMap((...args) => {
      return [mapFn(...args)];
    });
  }
  filter(filterFn) {
    return this.flatMap((entry, ...args) =>
      filterFn(entry, ...args) ? [entry] : [],
    );
  }
  reduce(reduceFn, accumulator = EMPTY) {
    return this.partialReduce(reduceFn, () => true, accumulator);
  }
  join(sep = ',') {
    return this.reduce((acc, e, i) => acc + (i === 0 ? e : sep + e), '');
  }
  partialReduce(reduceFn, continueFn, accumulator = EMPTY) {
    let index = 0;
    for (const entry of this) {
      // console.log(accumulator);
      if (index === 0 && accumulator === EMPTY) {
        accumulator = entry;
      } else {
        // console.log(`${accumulator} ${JSON.stringify(entry)}`);
        accumulator = reduceFn(accumulator, entry, index++);
        if (!continueFn(accumulator, entry, index - 1)) {
          break;
        }
      }
    }
    // console.log(accumulator);
    if (index === 0 && accumulator === EMPTY) {
      throw new Error(
        'reduce of empty Glib with no starting value for accumulator',
      );
    }
    return accumulator;
  }
  take(count = 1) {
    return new Glib(
      (function*(iterable) {
        let taken = 0;
        if (taken >= count) {
          return;
        }
        for (const entry of iterable) {
          yield entry;
          if (++taken >= count) {
            return;
          }
        }
      })(this),
    );
  }
  first() {
    for (const entry of this) {
      return entry;
    }
  }
  toInts(base = 10) {
    switch (base) {
      case 10:
        return this.map((i) => BigInt(i));
      default:
        throw new Error('unimplemented base');
    }
  }
  sum() {
    return this.reduce((a, b) => {
      return a + b;
    }, 0n);
  }
  product() {
    return this.partialReduce(
      (a, b) => {
        return a * b;
      },
      (p) => p !== 0n,
    );
  }
  min() {
    return this.reduce((a, b) => (a < b ? a : b));
  }
  max() {
    return this.reduce((a, b) => (a > b ? a : b));
  }
  minMax() {
    return this.reduce(
      ([min, max], current) => {
        return [Math.min(min, current), Math.max(max, current)];
      },
      [Infinity, -Infinity],
    );
  }
  then(fn) {
    return fn(this);
  }
  infinite() {
    return Glib.infiniteFromIterable(this);
  }
  forEach(eachFn) {
    let i = BigInt(0);
    for (let entry of this) {
      eachFn(entry, i);
      i++;
    }
  }
  chunk(chunkLength = EMPTY, leftoversOk = false) {
    if (chunkLength === EMPTY) {
      throw new Error('must provide chunk length');
    }
    return new Glib(
      (function*(iterable) {
        let chunk = [];
        for (const entry of iterable) {
          chunk.push(entry);
          if (chunk.length === chunkLength) {
            yield chunk;
            chunk = [];
          }
        }
        if (chunk.length !== 0) {
          if (leftoversOk) {
            yield chunk;
          } else {
            throw new Error('chunk operation had leftovers');
          }
        }
      })(this),
    );
  }
  frequency() {
    return this.reduce((counts, k) => {
      counts.set(k, (counts.get(k) || 0n) + 1n);
      return counts;
    }, new Map());
  }
  every(everyFn) {
    return this.map(everyFn)
      .filter((i) => i === false)
      .isEmpty();
  }
  lookupInMap(map, allowMissing = false) {
    if (!allowMissing) {
      throw new Error('todo');
    }
    return this.flatMap((k) => {
      // console.log(k);
      return map.has(k) ? [map.get(k)] : [];
    });
  }
  filterBySet(set, invert) {
    if (invert) {
      return this.filter((k) => !set.has(k));
    }
    return this.filter((k) => set.has(k));
  }
  unique() {
    const seen = new Set();
    // better than converting whole iterable to set
    // allows for iterative/partial compoutation
    // normal set creation from iterable is eager
    return this.filter((e) => {
      if (seen.has(e)) {
        return false;
      }
      seen.add(e);
      return true;
    });
  }
  skip(n = 1n) {
    return this.filter((_, i) => i >= n);
  }
  drop(n = 1n) {
    return this.filter((_, i) => i >= n);
  }
  // NB: this assumes all inputs are iterable
  concat(...iterables) {
    return Glib.concat(this, ...iterables);
  }
  [Symbol.iterator]() {
    return this._;
  }
  get array() {
    return Array.from(this);
  }
  get string() {
    return this.join('');
  }
  get set() {
    return new Set(this);
  }
  get length() {
    let i = 0n;
    for (const _ of this) {
      i++;
    }
    return i;
  }
  isEmpty() {
    for (const entry of this) {
      return false;
    }
    return true;
  }
  toMap() {
    return new Map(this);
  }
  // need dvFn to not resuse sets, arrays, etc
  toMapReduce(reduceFn, dvFn) {
    const output = new Map();
    for (const [k, v] of this) {
      output.set(k, reduceFn(output.has(k) ? output.get(k) : dvFn(), v));
    }
    return output;
  }
  toMapArray() {
    return this.toMapReduce(
      (acc, a) => {
        return [...acc, a];
      },
      () => [],
    );
  }
  toMapSet() {
    return this.toMapReduce(
      (acc, a) => {
        acc.add(a);
        return acc;
      },
      () => new Set(),
    );
  }
  reduceScoreK(chooseFn) {
    return this.reduce((a, b) => (chooseFn(a[1] > b[1]) ? a : b))[0];
  }
  minScoreK() {
    return this.reduceScoreK((a, b) => a < b);
  }
  maxScoreK() {
    return this.reduceScoreK((a, b) => a > b);
  }
}

module.exports = Glib;