package main

import (
    "errors"
    "fmt"
    "net/http"
    "strconv"
    "strings"      // New import
    "unicode/utf8" // New import

    "snippetbox.alexedwards.net/internal/models"
)

...

func (app *application) snippetCreatePost(w http.ResponseWriter, r *http.Request) {
    err := r.ParseForm()
    if err != nil {
        app.clientError(w, http.StatusBadRequest)
        return
    }

    title := r.PostForm.Get("title")
    content := r.PostForm.Get("content")

    expires, err := strconv.Atoi(r.PostForm.Get("expires"))
    if err != nil {
        app.clientError(w, http.StatusBadRequest)
        return
    }

    // Initialize a map to hold any validation errors for the form fields.
    fieldErrors := make(map[string]string)

    // Check that the title value is not blank and is not more than 100
    // characters long. If it fails either of those checks, add a message to the
    // errors map using the field name as the key.
    if strings.TrimSpace(title) == "" {
        fieldErrors["title"] = "This field cannot be blank"
    } else if utf8.RuneCountInString(title) > 100 {
        fieldErrors["title"] = "This field cannot be more than 100 characters long"
    }

    // Check that the Content value isn't blank.
    if strings.TrimSpace(content) == "" {
        fieldErrors["content"] = "This field cannot be blank"
    }

    // Check the expires value matches one of the permitted values (1, 7 or
    // 365).
    if expires != 1 && expires != 7 && expires != 365 {
        fieldErrors["expires"] = "This field must equal 1, 7 or 365"
    }

    // If there are any errors, dump them in a plain text HTTP response and
    // return from the handler.
    if len(fieldErrors) > 0 {
        fmt.Fprint(w, fieldErrors)
        return
    }

    id, err := app.snippets.Insert(title, content, expires)
    if err != nil {
        app.serverError(w, r, err)
        return
    }

    http.Redirect(w, r, fmt.Sprintf("/snippet/view/%d", id), http.StatusSeeOther)
}