/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
/*
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
*/
// beam-playground:
//   name: TextIO
//   description: TextIO example.
//   multifile: false
//   context_line: 46
//   categories:
//     - Quickstart
//   complexity: BASIC
//   tags:
//     - hellobeam

package main

import (
    "context"
    "fmt"
    "github.com/apache/beam/sdks/v2/go/pkg/beam"
    "github.com/apache/beam/sdks/v2/go/pkg/beam/io/textio"
    "github.com/apache/beam/sdks/v2/go/pkg/beam/log"
    "github.com/apache/beam/sdks/v2/go/pkg/beam/transforms/filter"
    "github.com/apache/beam/sdks/v2/go/pkg/beam/x/beamx"
    "regexp"
    "github.com/apache/beam/sdks/v2/go/pkg/beam/transforms/top"
)

var (
    wordRE = regexp.MustCompile(`[a-zA-Z]+('[a-z])?`)
)

func less(a, b string) bool{
    return len(a)>len(b)
}

func main() {
    p, s := beam.NewPipelineWithRoot()

    file := Read(s, "gs://apache-beam-samples/shakespeare/kinglear.txt")

    lines := getLines(s, file)
    fixedSizeLines := top.Largest(s,lines,10,less)
    output(s, "Lines: ", fixedSizeLines)

    words := getWords(s,lines)
    fixedSizeWords := top.Largest(s,words,10,less)
    output(s, "Words: ", fixedSizeWords)

    err := beamx.Run(context.Background(), p)
    if err != nil {
        log.Exitf(context.Background(), "Failed to execute job: %v", err)
    }
}

// Read reads from fiename(s) specified by a glob string and a returns a PCollection<string>.
func Read(s beam.Scope, glob string) beam.PCollection {
    return textio.Read(s, glob)
}

// Read text file content line by line. resulting PCollection contains elements, where each element contains a single line of text from the input file.
func getLines(s beam.Scope, input beam.PCollection) beam.PCollection {
    return filter.Include(s, input, func(element string) bool {
        return element != ""
    })
}

// getWords read text lines and split into PCollection of words.
func getWords(s beam.Scope, input beam.PCollection) beam.PCollection {
    return beam.ParDo(s, func(line string, emit func(string)) {
        for _, word := range wordRE.FindAllString(line, -1) {
            emit(word)
        }
    }, input)
}

func output(s beam.Scope, prefix string, input beam.PCollection) {
    beam.ParDo0(s, func(elements []string) {
        for _, element := range elements {
        fmt.Println(prefix,element)
        }
    }, input)
}
