/*
The MIT License (MIT)

Copyright © 2020-2025 pacman64

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the “Software”), to deal
in the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
of the Software, and to permit persons to whom the Software is furnished to do
so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

/*
Single-file source-code for get.

To compile a smaller-sized command-line app, you can use the `go` command as
follows:

go build -ldflags "-s -w" -trimpath get.go
*/

package main

import (
	"bufio"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
)

const info = `
get [files/URIs...]

Load all files and/or web-resources given.
`

// errNoMoreOutput is a dummy error whose message is ignored, and which
// causes the app to quit immediately and successfully
var errNoMoreOutput = errors.New(`no more output`)

func main() {
	if len(os.Args) > 1 {
		switch os.Args[1] {
		case `-h`, `--h`, `-help`, `--help`:
			os.Stderr.WriteString(info[1:])
			return
		}
	}

	if err := run(os.Args[1:]); err != nil && err != errNoMoreOutput {
		fmt.Fprintf(os.Stderr, "\x1b[31m%s\x1b[0m\n", err.Error())
		os.Exit(1)
	}
}

func run(names []string) error {
	w := bufio.NewWriter(os.Stdout)
	defer w.Flush()

	dashes := 0
	for _, s := range names {
		if s == `-` {
			dashes++
		}
	}

	var stdin []byte
	gotStdin := false

	for _, name := range names {
		w.Flush()

		// handle reading from stdin, keeping its data for reuse if needed
		if name == `-` {
			if dashes > 1 {
				if !gotStdin {
					stdin, _ = io.ReadAll(os.Stdin)
					gotStdin = true
				}

				n, err := w.Write(stdin)
				if n < len(stdin) || err != nil {
					return nil
				}
				continue
			}

			_, err := io.Copy(os.Stdout, os.Stdin)
			if err != nil {
				return nil
			}
			continue
		}

		// handle data-URIs
		if seemsDataURI(name) {
			if err := handleDataURI(w, name); err != nil {
				return err
			}
			continue
		}

		// handle web-requests and actual files
		handle := handleFile
		if seemsURI(name) {
			handle = handleURI
		}
		if err := handle(w, name); err != nil {
			return err
		}
	}

	// use stdin when no filenames were given
	if len(names) == 0 {
		io.Copy(os.Stdout, os.Stdin)
	}
	return nil
}

// handleDataURI decodes base64 explicitly, so decoding errors can be told
// apart from output-writing ones
func handleDataURI(w *bufio.Writer, data string) error {
	i := strings.Index(data, `;base64,`)
	if i < 0 {
		return errors.New(`invalid data URI`)
	}
	r := strings.NewReader(data[i+len(`;base64,`):])
	dec := base64.NewDecoder(base64.StdEncoding, r)

	var buf [16 * 1024]byte

	for {
		n, err := dec.Read(buf[:])
		if n < 1 && err == io.EOF {
			return nil
		}
		if err != nil {
			return err
		}

		_, err = w.Write(buf[:n])
		if err != nil {
			return errNoMoreOutput
		}
	}
}

func handleFile(w *bufio.Writer, path string) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()

	_, err = io.Copy(w, f)
	if err != nil {
		return errNoMoreOutput
	}
	return nil
}

func handleURI(w *bufio.Writer, uri string) error {
	r, err := http.Get(uri)
	if err != nil {
		return err
	}
	defer r.Body.Close()

	_, err = io.Copy(w, r.Body)
	if err != nil {
		return errNoMoreOutput
	}
	return nil
}

func seemsDataURI(s string) bool {
	start := s
	if len(s) > 64 {
		start = s[:64]
	}
	return strings.HasPrefix(s, `data:`) && strings.Contains(start, `;base64,`)
}

func seemsURI(s string) bool {
	return false ||
		strings.HasPrefix(s, `https://`) ||
		strings.HasPrefix(s, `http://`)
}