sources.go

package conf

import (
	"errors"
	"fmt"
	"os"
	"strings"
)

var (
	// ErrHelpWanted provides an indication help was requested.
	ErrHelpWanted = errors.New("help wanted")

	// errVersionWanted provides an indication version was requested.
	errVersionWanted = errors.New("version wanted")
)

// sourcer provides the ability to source data from a configuration source.
// Consider the use of lazy-loading for sourcing large datasets or systems.
type sourcer interface {

	// Source takes the field key and attempts to locate that key in its
	// configuration data. Returns true if found with the value.
	Source(fld Field) (string, bool)
}

// =============================================================================
// Environment Variable Sourcer

// env is a source for environmental variables.
type env struct {
	m map[string]string
}

// newSourceEnv accepts a namespace and parses the environment into a Env for
// use by the configuration package.
func newSourceEnv(namespace string) *env {
	m := make(map[string]string)

	// Create the uppercase version to meet the standard {NAMESPACE_} format.
	// If the namespace is empty, remove the _ from the beginning of the string.
	uspace := fmt.Sprintf("%s_", strings.ToUpper(namespace))
	if namespace == "" {
		uspace = uspace[1:]
	}

	// Loop and match each variable using the uppercase namespace.
	for _, val := range os.Environ() {
		if !strings.HasPrefix(val, uspace) {
			continue
		}

		idx := strings.Index(val, "=")
		m[strings.ToUpper(strings.TrimPrefix(val[0:idx], uspace))] = val[idx+1:]
	}

	return &env{m: m}
}

// Source implements the conf.sourcer interface. It returns the stringfied value
// stored at the specified key from the environment.
func (e *env) Source(fld Field) (string, bool) {
	k := strings.ToUpper(strings.Join(fld.EnvKey, `_`))
	v, ok := e.m[k]
	return v, ok
}

// envUsage constructs a usage string for the environment variable.
func envUsage(namespace string, fld Field) string {
	uspace := strings.ToUpper(namespace) + "_" + strings.ToUpper(strings.Join(fld.EnvKey, `_`))
	if namespace == "" {
		uspace = uspace[1:]
	}
	return "$" + uspace
}

// =============================================================================
// Command Line Flag Sourcer

type flagValue struct {
	HasValue bool
	Value    string
}

// flag is a source for command line arguments.
type flag struct {
	m    map[string]flagValue
	args []string
}

// newSourceFlag parsing a string of command line arguments. NewFlag will return
// errHelpWanted, if the help flag is identified. This code is adapted
// from the Go standard library flag package.
func newSourceFlag(args []string) (*flag, error) {
	m := make(map[string]flagValue)

	if len(args) != 0 {
		for {
			if len(args) == 0 {
				break
			}

			// Look at the next arg.
			s := args[0]

			// If it's too short or doesn't begin with a `-`, assume we're at
			// the end of the flags.
			if len(s) < 2 || s[0] != '-' {
				break
			}

			numMinuses := 1
			if s[1] == '-' {
				numMinuses++
				if len(s) == 2 { // "--" terminates the flags
					args = args[1:]
					break
				}
			}

			name := s[numMinuses:]
			if len(name) == 0 || name[0] == '-' || name[0] == '=' {
				return nil, fmt.Errorf("bad flag syntax: %s", s)
			}

			// It's a flag. Does it have an argument?
			args = args[1:]
			hasValue := false
			value := ""
			for i := 1; i < len(name); i++ { // equals cannot be first
				if name[i] == '=' {
					value = name[i+1:]
					hasValue = true
					name = name[0:i]
					break
				}
			}

			if name == "help" || name == "h" || name == "?" {
				return nil, ErrHelpWanted
			}

			if name == "version" || name == "v" {
				return nil, errVersionWanted
			}

			// If we don't have a value yet, it's possible the flag was not in the
			// -flag=value format which means it might still have a value which would be
			// the next argument, provided the next argument isn't a flag.
			if !hasValue {
				if len(args) > 0 && len(args[0]) > 0 && args[0][0] != '-' {
					// Doesn't look like a flag. Must be a value.
					value, args = args[0], args[1:]
				}
			}

			// Store the flag/value pair.
			m[name] = flagValue{
				HasValue: hasValue,
				Value:    value,
			}
		}
	}

	return &flag{m: m, args: args}, nil
}

// source returns the stringfied value stored at the specified key with special handling for bool flags.
func (f *flag) source(key string, isBool bool) (string, bool) {
	k := strings.ToLower(key)

	val, found := f.m[k]
	if !found || !isBool {
		return val.Value, found
	}

	if val.HasValue {
		return val.Value, found
	}

	// bools are defaulted to true if the flag was present.
	if val.Value != "" {
		f.args = append([]string{val.Value}, f.args...)
	}

	return "true", found
}

// Source implements the conf.sourcer interface. Returns the stringfied value
// stored at the specified key from the flag source.
func (f *flag) Source(fld Field) (string, bool) {
	if fld.Options.ShortFlagChar != 0 {
		if val, found := f.source(string(fld.Options.ShortFlagChar), fld.BoolField); found {
			return val, found
		}
	}

	return f.source(strings.Join(fld.FlagKey, `-`), fld.BoolField)
}

// flagUsage constructs a usage string for the flag argument.
func flagUsage(fld Field) string {
	usage := "--" + strings.ToLower(strings.Join(fld.FlagKey, `-`))
	if fld.Options.ShortFlagChar != 0 {
		flagKey := []string{string(fld.Options.ShortFlagChar)}
		usage += "/-" + strings.ToLower(strings.Join(flagKey, `-`))
	}

	return usage
}

/*
Portions Copyright (c) 2009 The Go Authors. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

   * Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
   * Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following disclaimer
in the documentation and/or other materials provided with the
distribution.
   * Neither the name of Google Inc. nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/