Add support for signatures

Add config values to `composing` config section to enable signatures:

   signature_file Path                   (optional) Plain text file with signature that will pre-populate an email draft.  Signatures must be explicitly enabled to be used, otherwise this setting will be ignored.  (None)

   use_signature bool                    Pre-populate email drafts with signature, if any.  meli will lookup the signature value in this order:
                                         1.   The signature_file setting.
                                         2.   ${XDG_CONFIG_DIR}/meli/<account>/signature
                                         3.   ${XDG_CONFIG_DIR}/meli/signature
                                         4.   ${XDG_CONFIG_DIR}/signature
                                         5.   ${HOME}/.signature
                                         6.   No signature otherwise.
                                         (false)

   signature_delimiter String            (optional) Signature delimiter, that is, text that will be prefixed to your signature to separate it from the email body.  (‘\n\n-- \n’)

Closes #498

Resolves: https://git.meli-email.org/meli/meli/issues/498
Signed-off-by: Manos Pitsidianakis <manos@pitsidianak.is>

meli/docs/meli.conf.5

@@ -1030,6 +1030,36 @@ or draft body mention attachments but they are missing.
 .Ic empty-draft-warn
 — Warn if draft has no subject and no body.
 .El
+.It Ic signature_file Ar Path
+.Pq Em optional
+Plain text file with signature that will pre-populate an email draft.
+Signatures must be explicitly enabled to be used, otherwise this setting will be ignored.
+.Pq Em None \" default value
+.It Ic use_signature Ar bool
+Pre-populate email drafts with signature, if any.
+.Sy meli
+will lookup the signature value in this order:
+.Bl -enum -compact
+.It
+The
+.Ic signature_file
+setting.
+.It
+.Pa ${XDG_CONFIG_DIR}/meli/<account>/signature
+.It
+.Pa ${XDG_CONFIG_DIR}/meli/signature
+.It
+.Pa ${XDG_CONFIG_DIR}/signature
+.It
+.Pa ${HOME}/.signature
+.It
+No signature otherwise.
+.El
+.Pq Em false \" default value
+.It Ic signature_delimiter Ar String
+.Pq Em optional
+Signature delimiter, that is, text that will be prefixed to your signature to separate it from the email body.
+.Pq Ql \en\en\-\- \en
 .El
 .\"
 .\"

meli/src/accounts.rs

@@ -29,6 +29,7 @@ use std::{
     io,
     ops::{Index, IndexMut},
     os::unix::fs::PermissionsExt,
+    path::{Path, PathBuf},
     pin::Pin,
     result,
     sync::{Arc, RwLock},
@@ -42,7 +43,7 @@ use melib::{
     error::{Error, ErrorKind, NetworkErrorKind, Result},
     log,
     thread::Threads,
-    utils::{fnmatch::Fnmatch, futures::sleep, random},
+    utils::{fnmatch::Fnmatch, futures::sleep, random, shellexpand::ShellExpandTrait},
     Contacts, SortField, SortOrder,
 };
 use smallvec::SmallVec;
@@ -1800,6 +1801,33 @@ impl Account {
             IsAsync::Blocking
         }
     }
+
+    pub fn signature_file(&self) -> Option<PathBuf> {
+        xdg::BaseDirectories::with_profile("meli", &self.name)
+            .ok()
+            .and_then(|d| {
+                d.place_config_file("signature")
+                    .ok()
+                    .filter(|p| p.is_file())
+            })
+            .or_else(|| {
+                xdg::BaseDirectories::with_prefix("meli")
+                    .ok()
+                    .and_then(|d| {
+                        d.place_config_file("signature")
+                            .ok()
+                            .filter(|p| p.is_file())
+                    })
+            })
+            .or_else(|| {
+                xdg::BaseDirectories::new().ok().and_then(|d| {
+                    d.place_config_file("signature")
+                        .ok()
+                        .filter(|p| p.is_file())
+                })
+            })
+            .or_else(|| Some(Path::new("~/.signature").expand()).filter(|p| p.is_file()))
+    }
 }
 
 impl Index<&MailboxHash> for Account {

meli/src/conf/composing.rs

@@ -21,6 +21,8 @@
 
 //! Configuration for composing email.
 
+use std::path::PathBuf;
+
 use indexmap::IndexMap;
 use melib::{conf::ActionFlag, email::HeaderName};
 use serde::{de, Deserialize, Deserializer};
@@ -110,6 +112,34 @@ pub struct ComposingSettings {
     /// Disabled `compose-hooks`.
     #[serde(default, alias = "disabled-compose-hooks")]
     pub disabled_compose_hooks: Vec<String>,
+    /// Plain text file with signature that will pre-populate an email draft.
+    ///
+    /// Signatures must be explicitly enabled to be used, otherwise this setting
+    /// will be ignored.
+    ///
+    /// Default: `None`
+    #[serde(default, alias = "signature-file")]
+    pub signature_file: Option<PathBuf>,
+    /// Pre-populate email drafts with signature, if any.
+    ///
+    /// `meli` will lookup the signature value in this order:
+    ///
+    /// 1. The `signature_file` setting.
+    /// 2. `${XDG_CONFIG_DIR}/meli/<account>/signature`
+    /// 3. `${XDG_CONFIG_DIR}/meli/signature`
+    /// 4. `${XDG_CONFIG_DIR}/signature`
+    /// 5. `${HOME}/.signature`
+    /// 6. No signature otherwise.
+    ///
+    /// Default: `false`
+    #[serde(default = "false_val", alias = "use-signature")]
+    pub use_signature: bool,
+    /// Signature delimiter, that is, text that will be prefixed to your
+    /// signature to separate it from the email body.
+    ///
+    /// Default: `"\n\n-- \n"`
+    #[serde(default, alias = "signature-delimiter")]
+    pub signature_delimiter: Option<String>,
 }
 
 impl Default for ComposingSettings {
@@ -129,6 +159,9 @@ impl Default for ComposingSettings {
             reply_prefix: res(),
             custom_compose_hooks: vec![],
             disabled_compose_hooks: vec![],
+            signature_file: None,
+            use_signature: false,
+            signature_delimiter: None,
         }
     }
 }

meli/src/mail/compose.rs

@@ -20,7 +20,9 @@
  */
 
 use std::{
+    borrow::Cow,
     convert::TryInto,
+    fmt::Write as _,
     future::Future,
     io::Write,
     pin::Pin,
@@ -241,7 +243,41 @@ impl Composer {
                 format!("meli {}", option_env!("CARGO_PKG_VERSION").unwrap_or("0.0")),
             );
         }
-        if *account_settings!(context[account_hash].composing.format_flowed) {
+        let format_flowed = *account_settings!(context[account_hash].composing.format_flowed);
+        if *account_settings!(context[account_hash].composing.use_signature) {
+            let override_value = account_settings!(context[account_hash].composing.signature_file)
+                .as_deref()
+                .map(Cow::Borrowed)
+                .filter(|p| p.as_ref().is_file());
+            let account_value = || {
+                context.accounts[&account_hash]
+                    .signature_file()
+                    .map(Cow::Owned)
+            };
+            if let Some(path) = override_value.or_else(account_value) {
+                match std::fs::read_to_string(path.as_ref()).chain_err_related_path(path.as_ref()) {
+                    Ok(sig) => {
+                        let mut delimiter =
+                            account_settings!(context[account_hash].composing.signature_delimiter)
+                                .as_deref()
+                                .map(Cow::Borrowed)
+                                .unwrap_or_else(|| Cow::Borrowed("\n\n-- \n"));
+                        if format_flowed {
+                            delimiter = Cow::Owned(delimiter.replace(" \n", " \n\n"));
+                        }
+                        _ = write!(&mut ret.draft.body, "{}{}", delimiter.as_ref(), sig);
+                    }
+                    Err(err) => {
+                        log::error!(
+                            "Could not open signature file for account `{}`: {}.",
+                            context.accounts[&account_hash].name(),
+                            err
+                        );
+                    }
+                }
+            }
+        }
+        if format_flowed {
             ret.pager.set_reflow(melib::text::Reflow::FormatFlowed);
         }
         ret
@@ -420,7 +456,7 @@ impl Composer {
                 .set_header(HeaderName::TO, envelope.field_from_to_string());
         }
         ret.draft.body = {
-            let mut ret = attribution_string(
+            let mut quoted = attribution_string(
                 account_settings!(
                     context[ret.account_hash]
                         .composing
@@ -437,11 +473,12 @@ impl Composer {
                 ),
             );
             for l in reply_body.lines() {
-                ret.push('>');
-                ret.push_str(l);
-                ret.push('\n');
+                quoted.push('>');
+                quoted.push_str(l);
+                quoted.push('\n');
             }
-            ret
+            _ = write!(&mut quoted, "{}", ret.draft.body);
+            quoted
         };
 
         ret.account_hash = coordinates.0;