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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/

// This file is just a place to put example code from the book.
// It does not actually run any code in gopl.io/ch8/thumbnail.

package thumbnail_test

import (
    "log"
    "os"
    "sync"

    "gopl.io/ch8/thumbnail"
)

//!+1
// makeThumbnails makes thumbnails of the specified files.
func makeThumbnails(filenames []string) {
    for _, f := range filenames {
        if _, err := thumbnail.ImageFile(f); err != nil {
            log.Println(err)
        }
    }
}

//!-1

//!+2
// NOTE: incorrect!
func makeThumbnails2(filenames []string) {
    for _, f := range filenames {
        go thumbnail.ImageFile(f) // NOTE: ignoring errors
    }
}

//!-2

//!+3
// makeThumbnails3 makes thumbnails of the specified files in parallel.
func makeThumbnails3(filenames []string) {
    ch := make(chan struct{})
    for _, f := range filenames {
        go func(f string) {
            thumbnail.ImageFile(f) // NOTE: ignoring errors
            ch <- struct{}{}
        }(f)
    }

    // Wait for goroutines to complete.
    for range filenames {
        <-ch
    }
}

//!-3

//!+4
// makeThumbnails4 makes thumbnails for the specified files in parallel.
// It returns an error if any step failed.
func makeThumbnails4(filenames []string) error {
    errors := make(chan error)

    for _, f := range filenames {
        go func(f string) {
            _, err := thumbnail.ImageFile(f)
            errors <- err
        }(f)
    }

    for range filenames {
        if err := <-errors; err != nil {
            return err // NOTE: incorrect: goroutine leak!
        }
    }

    return nil
}

//!-4

//!+5
// makeThumbnails5 makes thumbnails for the specified files in parallel.
// It returns the generated file names in an arbitrary order,
// or an error if any step failed.
func makeThumbnails5(filenames []string) (thumbfiles []string, err error) {
    type item struct {
        thumbfile string
        err       error
    }

    ch := make(chan item, len(filenames))
    for _, f := range filenames {
        go func(f string) {
            var it item
            it.thumbfile, it.err = thumbnail.ImageFile(f)
            ch <- it
        }(f)
    }

    for range filenames {
        it := <-ch
        if it.err != nil {
            return nil, it.err
        }
        thumbfiles = append(thumbfiles, it.thumbfile)
    }

    return thumbfiles, nil
}

//!-5

//!+6
// makeThumbnails6 makes thumbnails for each file received from the channel.
// It returns the number of bytes occupied by the files it creates.
func makeThumbnails6(filenames <-chan string) int64 {
    sizes := make(chan int64)
    var wg sync.WaitGroup // number of working goroutines
    for f := range filenames {
        wg.Add(1)
        // worker
        go func(f string) {
            defer wg.Done()
            thumb, err := thumbnail.ImageFile(f)
            if err != nil {
                log.Println(err)
                return
            }
            info, _ := os.Stat(thumb) // OK to ignore error
            sizes <- info.Size()
        }(f)
    }

    // closer
    go func() {
        wg.Wait()
        close(sizes)
    }()

    var total int64
    for size := range sizes {
        total += size
    }
    return total
}

//!-6