package task

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"io/ioutil"
	"os"
	"runtime"
	"strings"
	"text/template"

	"github.com/go-task/task/execext"

	"github.com/BurntSushi/toml"
	"gopkg.in/yaml.v2"
)

var (
	// TaskvarsFilePath file containing additional variables
	TaskvarsFilePath = "Taskvars"
	// ErrMultilineResultCmd is returned when a command returns multiline result
	ErrMultilineResultCmd = errors.New("Got multiline result from command")
)

var varCmds = make(map[string]string)

func handleDynamicVariableContent(value string) (string, error) {
	if value == "" || value[0] != '$' {
		return value, nil
	}
	if result, ok := varCmds[value]; ok {
		return result, nil
	}
	cmd := execext.NewCommand(context.Background(), value[1:])
	cmd.Stdin = os.Stdin
	cmd.Stderr = os.Stderr
	b, err := cmd.Output()
	if err != nil {
		return "", err
	}
	if b[len(b)-1] == '\n' {
		b = b[:len(b)-1]
	}
	if bytes.ContainsRune(b, '\n') {
		return "", ErrMultilineResultCmd
	}
	result := strings.TrimSpace(string(b))
	varCmds[value] = result
	return result, nil
}

func (t *Task) handleVariables() (map[string]string, error) {
	localVariables := make(map[string]string)
	for key, value := range t.Vars {
		val, err := handleDynamicVariableContent(value)
		if err != nil {
			return nil, err
		}
		localVariables[key] = val
	}
	if fileVariables, err := readTaskvarsFile(); err == nil {
		for key, value := range fileVariables {
			val, err := handleDynamicVariableContent(value)
			if err != nil {
				return nil, err
			}
			localVariables[key] = val
		}
	} else {
		return nil, err
	}
	for key, value := range getEnvironmentVariables() {
		localVariables[key] = value
	}
	return localVariables, nil
}

var templateFuncs = template.FuncMap{
	"OS":   func() string { return runtime.GOOS },
	"ARCH": func() string { return runtime.GOARCH },
	"IsSH": func() bool { return execext.ShExists },
}

// ReplaceVariables writes vars into initial string
func ReplaceVariables(initial string, vars map[string]string) (string, error) {
	t, err := template.New("").Funcs(templateFuncs).Parse(initial)
	if err != nil {
		return "", err
	}
	b := bytes.NewBuffer(nil)
	if err = t.Execute(b, vars); err != nil {
		return "", err
	}
	return b.String(), nil
}

// GetEnvironmentVariables returns environment variables as map
func getEnvironmentVariables() map[string]string {
	var (
		env = os.Environ()
		m   = make(map[string]string, len(env))
	)

	for _, e := range env {
		keyVal := strings.SplitN(e, "=", 2)
		key, val := keyVal[0], keyVal[1]
		m[key] = val
	}
	return m
}

func readTaskvarsFile() (map[string]string, error) {
	var variables map[string]string
	if b, err := ioutil.ReadFile(TaskvarsFilePath + ".yml"); err == nil {
		if err := yaml.Unmarshal(b, &variables); err != nil {
			return nil, err
		}
		return variables, nil
	}
	if b, err := ioutil.ReadFile(TaskvarsFilePath + ".json"); err == nil {
		if err := json.Unmarshal(b, &variables); err != nil {
			return nil, err
		}
		return variables, nil
	}
	if b, err := ioutil.ReadFile(TaskvarsFilePath + ".toml"); err == nil {
		if err := toml.Unmarshal(b, &variables); err != nil {
			return nil, err
		}
		return variables, nil
	}
	return variables, nil
}