rewrite checkpoint

vendor/github.com/AlecAivazis/survey/survey.go

@@ -0,0 +1,180 @@
+package survey
+
+import (
+	"errors"
+
+	"github.com/AlecAivazis/survey/core"
+)
+
+// PageSize is the default maximum number of items to show in select/multiselect prompts
+var PageSize = 7
+
+// Validator is a function passed to a Question after a user has provided a response.
+// If the function returns an error, then the user will be prompted again for another
+// response.
+type Validator func(interface{}) error
+
+// Question is the core data structure for a survey questionnaire.
+type Question struct {
+	Name     string
+	Prompt   Prompt
+	Validate Validator
+}
+
+// Prompt is the primary interface for the objects that can take user input
+// and return a response.
+type Prompt interface {
+	Prompt() (interface{}, error)
+	Cleanup(interface{}) error
+	Error(error) error
+}
+
+/*
+AskOne performs the prompt for a single prompt and asks for validation if required.
+Response types should be something that can be casted from the response type designated
+in the documentation. For example:
+
+	name := ""
+	prompt := &survey.Input{
+		Message: "name",
+	}
+
+	survey.AskOne(prompt, &name, nil)
+
+*/
+func AskOne(p Prompt, response interface{}, v Validator) error {
+	err := Ask([]*Question{{Prompt: p, Validate: v}}, response)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+/*
+Ask performs the prompt loop, asking for validation when appropriate. The response
+type can be one of two options. If a struct is passed, the answer will be written to
+the field whose name matches the Name field on the corresponding question. Field types
+should be something that can be casted from the response type designated in the
+documentation. Note, a survey tag can also be used to identify a Otherwise, a
+map[string]interface{} can be passed, responses will be written to the key with the
+matching name. For example:
+
+	qs := []*survey.Question{
+		{
+			Name:     "name",
+			Prompt:   &survey.Input{Message: "What is your name?"},
+			Validate: survey.Required,
+		},
+	}
+
+	answers := struct{ Name string }{}
+
+
+	err := survey.Ask(qs, &answers)
+*/
+func Ask(qs []*Question, response interface{}) error {
+
+	// if we weren't passed a place to record the answers
+	if response == nil {
+		// we can't go any further
+		return errors.New("cannot call Ask() with a nil reference to record the answers")
+	}
+
+	// go over every question
+	for _, q := range qs {
+		// grab the user input and save it
+		ans, err := q.Prompt.Prompt()
+		// if there was a problem
+		if err != nil {
+			return err
+		}
+
+		// if there is a validate handler for this question
+		if q.Validate != nil {
+			// wait for a valid response
+			for invalid := q.Validate(ans); invalid != nil; invalid = q.Validate(ans) {
+				err := q.Prompt.Error(invalid)
+				// if there was a problem
+				if err != nil {
+					return err
+				}
+
+				// ask for more input
+				ans, err = q.Prompt.Prompt()
+				// if there was a problem
+				if err != nil {
+					return err
+				}
+			}
+		}
+
+		// tell the prompt to cleanup with the validated value
+		q.Prompt.Cleanup(ans)
+
+		// if something went wrong
+		if err != nil {
+			// stop listening
+			return err
+		}
+
+		// add it to the map
+		err = core.WriteAnswer(response, q.Name, ans)
+		// if something went wrong
+		if err != nil {
+			return err
+		}
+
+	}
+	// return the response
+	return nil
+}
+
+// paginate returns a single page of choices given the page size, the total list of
+// possible choices, and the current selected index in the total list.
+func paginate(page int, choices []string, sel int) ([]string, int) {
+	// the number of elements to show in a single page
+	var pageSize int
+	// if the select has a specific page size
+	if page != 0 {
+		// use the specified one
+		pageSize = page
+		// otherwise the select does not have a page size
+	} else {
+		// use the package default
+		pageSize = PageSize
+	}
+
+	var start, end, cursor int
+
+	if len(choices) < pageSize {
+		// if we dont have enough options to fill a page
+		start = 0
+		end = len(choices)
+		cursor = sel
+
+	} else if sel < pageSize/2 {
+		// if we are in the first half page
+		start = 0
+		end = pageSize
+		cursor = sel
+
+	} else if len(choices)-sel-1 < pageSize/2 {
+		// if we are in the last half page
+		start = len(choices) - pageSize
+		end = len(choices)
+		cursor = sel - start
+
+	} else {
+		// somewhere in the middle
+		above := pageSize / 2
+		below := pageSize - above
+
+		cursor = pageSize / 2
+		start = sel - above
+		end = sel + below
+	}
+
+	// return the subset we care about and the index
+	return choices[start:end], cursor
+}