correspondents

backend/migrations/202503200001_add_correspondents/down.sql

@@ -0,0 +1,5 @@
+DROP INDEX IF EXISTS idx_document_correspondents_role;
+DROP INDEX IF EXISTS idx_document_correspondents_correspondent;
+DROP INDEX IF EXISTS idx_document_correspondents_document;
+DROP TABLE IF EXISTS document_correspondents;
+DROP TABLE IF EXISTS correspondents;

backend/migrations/202503200001_add_correspondents/up.sql

@@ -0,0 +1,27 @@
+CREATE TABLE correspondents (
+    id UUID PRIMARY KEY,
+    name VARCHAR(255) NOT NULL,
+    metadata JSONB NOT NULL DEFAULT '{}'::jsonb,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    CONSTRAINT correspondents_name_unique UNIQUE (name)
+);
+
+CREATE TABLE document_correspondents (
+    document_id UUID NOT NULL REFERENCES documents(id) ON DELETE CASCADE,
+    correspondent_id UUID NOT NULL REFERENCES correspondents(id) ON DELETE CASCADE,
+    role VARCHAR(32) NOT NULL,
+    assigned_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    assigned_by UUID REFERENCES users(id),
+    PRIMARY KEY (document_id, correspondent_id, role),
+    CONSTRAINT document_correspondents_role_check CHECK (role IN ('sender', 'receiver', 'other'))
+);
+
+CREATE INDEX idx_document_correspondents_document
+    ON document_correspondents(document_id);
+
+CREATE INDEX idx_document_correspondents_correspondent
+    ON document_correspondents(correspondent_id);
+
+CREATE INDEX idx_document_correspondents_role
+    ON document_correspondents(role);

backend/src/models.rs

@@ -188,6 +188,46 @@ pub struct NewDocumentTag {
     pub assigned_by: Option<Uuid>,
 }
 
+#[derive(Debug, Clone, Queryable, Identifiable)]
+#[diesel(table_name = correspondents)]
+pub struct Correspondent {
+    pub id: Uuid,
+    pub name: String,
+    pub metadata: serde_json::Value,
+    pub created_at: NaiveDateTime,
+    pub updated_at: NaiveDateTime,
+}
+
+#[derive(Debug, Insertable)]
+#[diesel(table_name = correspondents)]
+pub struct NewCorrespondent {
+    pub id: Uuid,
+    pub name: String,
+    pub metadata: serde_json::Value,
+}
+
+#[derive(Debug, Clone, Queryable, Associations)]
+#[diesel(table_name = document_correspondents)]
+#[diesel(belongs_to(Document))]
+#[diesel(belongs_to(Correspondent))]
+#[diesel(primary_key(document_id, correspondent_id, role))]
+pub struct DocumentCorrespondent {
+    pub document_id: Uuid,
+    pub correspondent_id: Uuid,
+    pub role: String,
+    pub assigned_at: NaiveDateTime,
+    pub assigned_by: Option<Uuid>,
+}
+
+#[derive(Debug, Insertable)]
+#[diesel(table_name = document_correspondents)]
+pub struct NewDocumentCorrespondent {
+    pub document_id: Uuid,
+    pub correspondent_id: Uuid,
+    pub role: String,
+    pub assigned_by: Option<Uuid>,
+}
+
 #[derive(Debug, Clone, Queryable, Identifiable, Associations)]
 #[diesel(table_name = refresh_tokens)]
 #[diesel(belongs_to(User))]

backend/src/routes/correspondents.rs

@@ -0,0 +1,258 @@
+use std::collections::{BTreeMap, HashMap};
+
+use axum::{
+    extract::{Path, State},
+    http::StatusCode,
+    response::IntoResponse,
+    Json,
+};
+use chrono::Utc;
+use diesel::{dsl::count_star, prelude::*, result::DatabaseErrorKind, PgConnection};
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+use uuid::Uuid;
+
+use crate::{
+    error::{AppError, AppResult},
+    models::{Correspondent, NewCorrespondent},
+    schema::{correspondents, document_correspondents},
+    state::AppState,
+};
+
+use super::documents::to_iso;
+
+#[derive(Serialize)]
+pub struct CorrespondentUsage {
+    pub total: i64,
+    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
+    pub by_role: BTreeMap<String, i64>,
+}
+
+#[derive(Serialize)]
+pub struct CorrespondentSummary {
+    pub id: Uuid,
+    pub name: String,
+    pub metadata: Value,
+    pub created_at: String,
+    pub updated_at: String,
+    pub usage: CorrespondentUsage,
+}
+
+#[derive(Deserialize)]
+pub struct CreateCorrespondentRequest {
+    pub name: String,
+    #[serde(default)]
+    pub metadata: Option<Value>,
+}
+
+#[derive(Deserialize)]
+pub struct UpdateCorrespondentRequest {
+    pub name: Option<String>,
+    pub metadata: Option<Value>,
+}
+
+#[derive(AsChangeset, Default)]
+#[diesel(table_name = correspondents)]
+struct CorrespondentChangeset<'a> {
+    name: Option<&'a str>,
+    metadata: Option<&'a Value>,
+}
+
+pub async fn list_correspondents(
+    State(state): State<AppState>,
+) -> AppResult<Json<Vec<CorrespondentSummary>>> {
+    let mut conn = state.db()?;
+
+    let correspondents_list: Vec<Correspondent> = correspondents::table
+        .order(correspondents::name.asc())
+        .load(&mut conn)?;
+
+    let usage_rows: Vec<(Uuid, String, i64)> = document_correspondents::table
+        .group_by((
+            document_correspondents::correspondent_id,
+            document_correspondents::role,
+        ))
+        .select((
+            document_correspondents::correspondent_id,
+            document_correspondents::role,
+            count_star(),
+        ))
+        .load(&mut conn)?;
+
+    let mut usage_map: HashMap<Uuid, BTreeMap<String, i64>> = HashMap::new();
+    for (correspondent_id, role, count) in usage_rows {
+        usage_map
+            .entry(correspondent_id)
+            .or_default()
+            .insert(role, count);
+    }
+
+    let mut response = Vec::with_capacity(correspondents_list.len());
+    for correspondent in correspondents_list {
+        let role_counts = usage_map.remove(&correspondent.id).unwrap_or_default();
+        response.push(build_summary(correspondent, role_counts));
+    }
+
+    Ok(Json(response))
+}
+
+pub async fn create_correspondent(
+    State(state): State<AppState>,
+    Json(payload): Json<CreateCorrespondentRequest>,
+) -> AppResult<Json<CorrespondentSummary>> {
+    let name = payload.name.trim();
+    if name.is_empty() {
+        return Err(AppError::bad_request("name must not be empty"));
+    }
+
+    let metadata_value = normalize_metadata(payload.metadata);
+    let new_id = Uuid::new_v4();
+    let new_correspondent = NewCorrespondent {
+        id: new_id,
+        name: name.to_string(),
+        metadata: metadata_value,
+    };
+
+    let mut conn = state.db()?;
+    match diesel::insert_into(correspondents::table)
+        .values(&new_correspondent)
+        .execute(&mut conn)
+    {
+        Ok(_) => {}
+        Err(diesel::result::Error::DatabaseError(DatabaseErrorKind::UniqueViolation, _)) => {
+            return Err(AppError::bad_request("correspondent name already exists"));
+        }
+        Err(err) => return Err(AppError::from(err)),
+    }
+
+    let correspondent: Correspondent = correspondents::table.find(new_id).first(&mut conn)?;
+    Ok(Json(build_summary(correspondent, BTreeMap::new())))
+}
+
+pub async fn update_correspondent(
+    State(state): State<AppState>,
+    Path(correspondent_id): Path<Uuid>,
+    Json(payload): Json<UpdateCorrespondentRequest>,
+) -> AppResult<Json<CorrespondentSummary>> {
+    let mut conn = state.db()?;
+    let existing: Correspondent = correspondents::table
+        .find(correspondent_id)
+        .first(&mut conn)?;
+
+    let mut new_name: Option<String> = None;
+    if let Some(ref candidate) = payload.name {
+        let trimmed = candidate.trim();
+        if trimmed.is_empty() {
+            return Err(AppError::bad_request("name must not be empty"));
+        }
+        if trimmed != existing.name {
+            let duplicate = correspondents::table
+                .filter(correspondents::name.eq(trimmed))
+                .filter(correspondents::id.ne(correspondent_id))
+                .first::<Correspondent>(&mut conn)
+                .optional()?;
+            if duplicate.is_some() {
+                return Err(AppError::bad_request("correspondent name already exists"));
+            }
+            new_name = Some(trimmed.to_string());
+        }
+    }
+
+    let mut new_metadata: Option<Value> = None;
+    if let Some(metadata) = payload.metadata.clone() {
+        let candidate = normalize_metadata(Some(metadata));
+        if candidate != existing.metadata {
+            new_metadata = Some(candidate);
+        }
+    }
+
+    if new_name.is_none() && new_metadata.is_none() {
+        return Err(AppError::bad_request("no changes supplied"));
+    }
+
+    let mut changeset = CorrespondentChangeset::default();
+    if let Some(ref name) = new_name {
+        changeset.name = Some(name.as_str());
+    }
+    if let Some(ref metadata) = new_metadata {
+        changeset.metadata = Some(metadata);
+    }
+
+    let now = Utc::now().naive_utc();
+    diesel::update(correspondents::table.find(correspondent_id))
+        .set((&changeset, correspondents::updated_at.eq(now)))
+        .execute(&mut conn)?;
+
+    let updated: Correspondent = correspondents::table
+        .find(correspondent_id)
+        .first(&mut conn)?;
+    let usage = load_usage_for_correspondent(&mut conn, correspondent_id)?;
+    Ok(Json(build_summary(updated, usage)))
+}
+
+pub async fn delete_correspondent(
+    State(state): State<AppState>,
+    Path(correspondent_id): Path<Uuid>,
+) -> AppResult<impl IntoResponse> {
+    let mut conn = state.db()?;
+
+    let usage: i64 = document_correspondents::table
+        .filter(document_correspondents::correspondent_id.eq(correspondent_id))
+        .select(count_star())
+        .first(&mut conn)?;
+
+    if usage > 0 {
+        return Err(AppError::bad_request(
+            "cannot delete correspondent that is still assigned to documents",
+        ));
+    }
+
+    let deleted =
+        diesel::delete(correspondents::table.find(correspondent_id)).execute(&mut conn)?;
+    if deleted == 0 {
+        return Err(AppError::not_found());
+    }
+    Ok(StatusCode::NO_CONTENT)
+}
+
+fn build_summary(
+    correspondent: Correspondent,
+    role_counts: BTreeMap<String, i64>,
+) -> CorrespondentSummary {
+    let total = role_counts.values().copied().sum();
+    CorrespondentSummary {
+        id: correspondent.id,
+        name: correspondent.name,
+        metadata: correspondent.metadata,
+        created_at: to_iso(correspondent.created_at),
+        updated_at: to_iso(correspondent.updated_at),
+        usage: CorrespondentUsage {
+            total,
+            by_role: role_counts,
+        },
+    }
+}
+
+fn normalize_metadata(input: Option<Value>) -> Value {
+    match input {
+        None | Some(Value::Null) => Value::Object(Default::default()),
+        Some(value) => value,
+    }
+}
+
+fn load_usage_for_correspondent(
+    conn: &mut PgConnection,
+    correspondent_id: Uuid,
+) -> AppResult<BTreeMap<String, i64>> {
+    let rows: Vec<(String, i64)> = document_correspondents::table
+        .filter(document_correspondents::correspondent_id.eq(correspondent_id))
+        .group_by(document_correspondents::role)
+        .select((document_correspondents::role, count_star()))
+        .load(conn)?;
+
+    let mut map = BTreeMap::new();
+    for (role, count) in rows {
+        map.insert(role, count);
+    }
+    Ok(map)
+}

backend/src/routes/documents.rs

@@ -1,4 +1,8 @@
-use std::{collections::HashMap, path::Path as FsPath, time::Duration};
+use std::{
+    collections::{HashMap, HashSet},
+    path::Path as FsPath,
+    time::Duration,
+};
 
 use axum::extract::{Json, Multipart, Path, Query, State};
 use axum::http::StatusCode;
@@ -16,15 +20,25 @@ use crate::auth::AuthenticatedUser;
 use crate::error::{AppError, AppResult};
 use crate::jobs::{enqueue_job, JOB_ANALYZE_DOCUMENT};
 use crate::models::{
-    Document, DocumentAsset, DocumentVersion, NewDocument, NewDocumentTag, NewDocumentVersion, Tag,
+    Correspondent, Document, DocumentAsset, DocumentCorrespondent, DocumentVersion, NewDocument,
+    NewDocumentCorrespondent, NewDocumentTag, NewDocumentVersion, Tag,
 };
 use crate::schema::{
-    document_assets, document_tags, document_versions, documents, folders,
+    correspondents, document_assets, document_correspondents, document_tags, document_versions,
-    refresh_tokens::dsl as refresh_dsl, tags,
+    documents, folders, refresh_tokens::dsl as refresh_dsl, tags,
 };
 use crate::state::AppState;
 
 const PRESIGNED_URL_EXPIRY_SECONDS: u64 = 300;
+pub const CORRESPONDENT_ROLES: &[&str] = &["sender", "receiver", "other"];
+
+fn normalize_role(value: &str) -> String {
+    value.trim().to_lowercase()
+}
+
+fn is_valid_correspondent_role(role: &str) -> bool {
+    CORRESPONDENT_ROLES.iter().any(|allowed| *allowed == role)
+}
 
 fn inline_content_disposition(filename: &str) -> Option<String> {
     if filename.is_empty() {
@@ -108,6 +122,15 @@ pub struct DocumentCurrentVersionResponse {
     pub download_path: String,
 }
 
+#[derive(Serialize, Clone)]
+pub struct DocumentCorrespondentResponse {
+    pub id: Uuid,
+    pub name: String,
+    pub role: String,
+    pub metadata: Value,
+    pub assigned_at: String,
+}
+
 #[derive(Serialize)]
 pub struct DocumentResponse {
     pub id: Uuid,
@@ -122,6 +145,8 @@ pub struct DocumentResponse {
     pub issued_at: Option<String>,
     pub metadata: Value,
     pub tags: Vec<TagResponse>,
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub correspondents: Vec<DocumentCorrespondentResponse>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub current_version: Option<DocumentCurrentVersionResponse>,
 }
@@ -180,6 +205,24 @@ pub struct BulkTagResponse {
     pub removed: usize,
 }
 
+#[derive(Deserialize)]
+pub struct CorrespondentAssignmentInput {
+    pub correspondent_id: Uuid,
+    pub role: String,
+}
+
+#[derive(Deserialize)]
+pub struct AssignCorrespondentsRequest {
+    pub assignments: Vec<CorrespondentAssignmentInput>,
+    #[serde(default)]
+    pub replace: bool,
+}
+
+#[derive(Deserialize)]
+pub struct CorrespondentRoleQuery {
+    pub role: String,
+}
+
 #[derive(Deserialize)]
 pub struct BulkReanalyzeSelectionRequest {
     pub document_ids: Vec<Uuid>,
@@ -242,6 +285,7 @@ pub async fn list_documents(
 
     let doc_ids: Vec<Uuid> = docs.iter().map(|doc| doc.id).collect();
     let tags_map = load_tags_for_documents(&mut conn, &doc_ids)?;
+    let mut correspondents_map = load_correspondents_for_documents(&mut conn, &doc_ids)?;
     drop(conn);
 
     let primary_versions = load_primary_assets(&state, &docs).await?;
@@ -249,12 +293,14 @@ pub async fn list_documents(
     let mut response = Vec::with_capacity(doc_ids.len());
     for doc in docs {
         let tags = tags_map.get(&doc.id).cloned();
+        let correspondents = correspondents_map.remove(&doc.id).unwrap_or_default();
         let current_version = primary_versions.get(&doc.id).cloned();
         response.push(to_document_response(
             &state,
             user.user_id,
             doc,
             tags,
+            correspondents,
             current_version,
         )?);
     }
@@ -279,6 +325,7 @@ pub async fn get_document(
         .first(&mut conn)?;
 
     let tags_map = load_tags_for_documents(&mut conn, &[document_id])?;
+    let mut correspondents_map = load_correspondents_for_documents(&mut conn, &[document_id])?;
     let version_id = current_version.id;
     drop(conn);
 
@@ -291,6 +338,7 @@ pub async fn get_document(
             user.user_id,
             doc,
             tags_map.get(&document_id).cloned(),
+            correspondents_map.remove(&document_id).unwrap_or_default(),
             Some((version_response, assets)),
         )?,
     }))
@@ -689,6 +737,7 @@ pub async fn update_document(
         .first(&mut conn)?;
 
     let tags_map = load_tags_for_documents(&mut conn, &[document_id])?;
+    let mut correspondents_map = load_correspondents_for_documents(&mut conn, &[document_id])?;
     let version_id = current_version.id;
     drop(conn);
 
@@ -701,6 +750,7 @@ pub async fn update_document(
             user.user_id,
             document,
             tags_map.get(&document_id).cloned(),
+            correspondents_map.remove(&document_id).unwrap_or_default(),
             Some((version_response, assets)),
         )?,
     }))
@@ -775,6 +825,157 @@ pub async fn bulk_move_documents(
     Ok((StatusCode::OK, Json(BulkMoveResponse { updated })))
 }
 
+pub async fn assign_correspondents(
+    State(state): State<AppState>,
+    Path(document_id): Path<Uuid>,
+    user: AuthenticatedUser,
+    Json(payload): Json<AssignCorrespondentsRequest>,
+) -> AppResult<impl IntoResponse> {
+    if payload.assignments.is_empty() {
+        return Err(AppError::bad_request("assignments must not be empty"));
+    }
+
+    let mut unique_pairs: HashSet<(Uuid, String)> = HashSet::new();
+    let mut normalized_pairs: Vec<(Uuid, String)> = Vec::new();
+    let mut role_set: HashSet<String> = HashSet::new();
+    let mut correspondent_ids: HashSet<Uuid> = HashSet::new();
+
+    for assignment in &payload.assignments {
+        let role = normalize_role(&assignment.role);
+        if role.is_empty() {
+            return Err(AppError::bad_request("role must not be empty"));
+        }
+        if !is_valid_correspondent_role(&role) {
+            return Err(AppError::bad_request(format!(
+                "invalid correspondent role '{role}'. Allowed roles: {}",
+                CORRESPONDENT_ROLES.join(", ")
+            )));
+        }
+
+        if !unique_pairs.insert((assignment.correspondent_id, role.clone())) {
+            continue;
+        }
+
+        normalized_pairs.push((assignment.correspondent_id, role.clone()));
+        role_set.insert(role);
+        correspondent_ids.insert(assignment.correspondent_id);
+    }
+
+    if normalized_pairs.is_empty() {
+        return Err(AppError::bad_request(
+            "assignments must contain at least one unique correspondent/role pair",
+        ));
+    }
+
+    let correspondents_vec: Vec<Uuid> = correspondent_ids.into_iter().collect();
+    let roles_vec: Vec<String> = role_set.into_iter().collect();
+    let replace = payload.replace;
+    let user_id = user.user_id;
+
+    let mut conn = state.db()?;
+    conn.transaction::<(), AppError, _>(|conn| {
+        let document: Document = documents::table.find(document_id).first(conn)?;
+        if document.deleted_at.is_some() {
+            return Err(AppError::not_found());
+        }
+
+        if !correspondents_vec.is_empty() {
+            let existing: Vec<Correspondent> = correspondents::table
+                .filter(correspondents::id.eq_any(&correspondents_vec))
+                .load(conn)?;
+            if existing.len() != correspondents_vec.len() {
+                return Err(AppError::bad_request(
+                    "one or more correspondents do not exist",
+                ));
+            }
+        }
+
+        let mut changed = false;
+        if replace {
+            let deleted = diesel::delete(
+                document_correspondents::table
+                    .filter(document_correspondents::document_id.eq(document_id))
+                    .filter(document_correspondents::role.eq_any(&roles_vec)),
+            )
+            .execute(conn)?;
+            if deleted > 0 {
+                changed = true;
+            }
+        }
+
+        let new_rows: Vec<NewDocumentCorrespondent> = normalized_pairs
+            .iter()
+            .map(|(correspondent_id, role)| NewDocumentCorrespondent {
+                document_id,
+                correspondent_id: *correspondent_id,
+                role: role.clone(),
+                assigned_by: Some(user_id),
+            })
+            .collect();
+
+        if !new_rows.is_empty() {
+            let inserted = diesel::insert_into(document_correspondents::table)
+                .values(&new_rows)
+                .on_conflict_do_nothing()
+                .execute(conn)?;
+            if inserted > 0 {
+                changed = true;
+            }
+        }
+
+        if changed {
+            diesel::update(documents::table.find(document_id))
+                .set(documents::updated_at.eq(Utc::now().naive_utc()))
+                .execute(conn)?;
+        }
+
+        Ok(())
+    })?;
+
+    Ok(StatusCode::NO_CONTENT)
+}
+
+pub async fn remove_correspondent(
+    State(state): State<AppState>,
+    Path((document_id, correspondent_id)): Path<(Uuid, Uuid)>,
+    Query(query): Query<CorrespondentRoleQuery>,
+) -> AppResult<impl IntoResponse> {
+    let role = normalize_role(&query.role);
+    if role.is_empty() {
+        return Err(AppError::bad_request("role must not be empty"));
+    }
+    if !is_valid_correspondent_role(&role) {
+        return Err(AppError::bad_request(format!(
+            "invalid correspondent role '{role}'. Allowed roles: {}",
+            CORRESPONDENT_ROLES.join(", ")
+        )));
+    }
+
+    let mut conn = state.db()?;
+    let document: Document = documents::table.find(document_id).first(&mut conn)?;
+    if document.deleted_at.is_some() {
+        return Err(AppError::not_found());
+    }
+
+    let deleted = diesel::delete(
+        document_correspondents::table
+            .filter(document_correspondents::document_id.eq(document_id))
+            .filter(document_correspondents::correspondent_id.eq(correspondent_id))
+            .filter(document_correspondents::role.eq(&role)),
+    )
+    .execute(&mut conn)?;
+
+    if deleted == 0 {
+        return Err(AppError::not_found());
+    }
+
+    diesel::update(documents::table.find(document_id))
+        .set(documents::updated_at.eq(Utc::now().naive_utc()))
+        .execute(&mut conn)?;
+
+    Ok(StatusCode::NO_CONTENT)
+}
+
 pub async fn assign_tags(
     State(state): State<AppState>,
     Path(document_id): Path<Uuid>,
@@ -975,7 +1176,10 @@ async fn process_upload(
             }
 
             let tags_map = load_tags_for_documents(&mut conn, &[document.id])?;
+            let mut correspondents_map =
+                load_correspondents_for_documents(&mut conn, &[document.id])?;
             let tags = tags_map.get(&document.id).cloned();
+            let correspondents = correspondents_map.remove(&document.id).unwrap_or_default();
             drop(conn);
             let assets = load_asset_responses(state, version.id).await?;
             let version_response = to_version_response(version.clone());
@@ -993,6 +1197,7 @@ async fn process_upload(
                         user_id,
                         document,
                         tags,
+                        correspondents,
                         Some((version_response, assets)),
                     )?,
                 },
@@ -1068,6 +1273,7 @@ async fn process_upload(
             user_id,
             document,
             None,
+            Vec::new(),
             Some((to_version_response(version.clone()), Vec::new())),
         )?,
     };
@@ -1126,6 +1332,40 @@ pub(crate) fn load_tags_for_documents(
     Ok(map)
 }
 
+pub(crate) fn load_correspondents_for_documents(
+    conn: &mut PgConnection,
+    document_ids: &[Uuid],
+) -> AppResult<HashMap<Uuid, Vec<DocumentCorrespondentResponse>>> {
+    if document_ids.is_empty() {
+        return Ok(HashMap::new());
+    }
+
+    let rows: Vec<(DocumentCorrespondent, Correspondent)> = document_correspondents::table
+        .inner_join(correspondents::table)
+        .filter(document_correspondents::document_id.eq_any(document_ids))
+        .order((
+            document_correspondents::document_id.asc(),
+            document_correspondents::role.asc(),
+            document_correspondents::assigned_at.asc(),
+        ))
+        .load(conn)?;
+
+    let mut map: HashMap<Uuid, Vec<DocumentCorrespondentResponse>> = HashMap::new();
+    for (assignment, correspondent) in rows {
+        map.entry(assignment.document_id)
+            .or_default()
+            .push(DocumentCorrespondentResponse {
+                id: correspondent.id,
+                name: correspondent.name,
+                role: assignment.role,
+                metadata: correspondent.metadata,
+                assigned_at: to_iso(assignment.assigned_at),
+            });
+    }
+
+    Ok(map)
+}
+
 pub(crate) async fn load_primary_assets(
     state: &AppState,
     documents: &[Document],
@@ -1191,6 +1431,7 @@ pub(crate) fn to_document_response(
     user_id: Uuid,
     doc: Document,
     tags: Option<Vec<Tag>>,
+    correspondents: Vec<DocumentCorrespondentResponse>,
     current_version: Option<(DocumentVersionResponse, Vec<DocumentAssetResponse>)>,
 ) -> AppResult<DocumentResponse> {
     let current_version = if let Some((version, assets)) = current_version {
@@ -1221,6 +1462,7 @@ pub(crate) fn to_document_response(
             .into_iter()
             .map(TagResponse::from)
             .collect(),
+        correspondents,
         current_version,
     })
 }

backend/src/routes/folders.rs

@@ -19,7 +19,8 @@ use crate::{
 };
 
 use super::documents::{
-    load_primary_assets, load_tags_for_documents, to_document_response, to_iso, DocumentResponse,
+    load_correspondents_for_documents, load_primary_assets, load_tags_for_documents,
+    to_document_response, to_iso, DocumentResponse,
 };
 
 const QUICKWIT_MAX_HITS: usize = 200;
@@ -213,6 +214,7 @@ pub async fn list_folder_contents(
 
     let doc_ids: Vec<Uuid> = docs.iter().map(|doc| doc.id).collect();
     let tags_map = load_tags_for_documents(&mut conn, &doc_ids)?;
+    let mut correspondents_map = load_correspondents_for_documents(&mut conn, &doc_ids)?;
     drop(conn);
 
     let primary_versions = load_primary_assets(&state, &docs).await?;
@@ -220,12 +222,14 @@ pub async fn list_folder_contents(
     let mut documents = Vec::with_capacity(doc_ids.len());
     for doc in docs {
         let tags = tags_map.get(&doc.id).cloned();
+        let correspondents = correspondents_map.remove(&doc.id).unwrap_or_default();
         let current_version = primary_versions.get(&doc.id).cloned();
         documents.push(to_document_response(
             &state,
             user.user_id,
             doc,
             tags,
+            correspondents,
             current_version,
         )?);
     }
@@ -397,18 +401,21 @@ pub async fn search_documents(
 
     let doc_ids: Vec<Uuid> = docs.iter().map(|doc| doc.id).collect();
     let tags_map = load_tags_for_documents(&mut conn, &doc_ids)?;
+    let mut correspondents_map = load_correspondents_for_documents(&mut conn, &doc_ids)?;
     drop(conn);
 
     let primary_versions = load_primary_assets(&state, &docs).await?;
     let mut response = Vec::with_capacity(doc_ids.len());
     for doc in docs {
         let tags = tags_map.get(&doc.id).cloned();
+        let correspondents = correspondents_map.remove(&doc.id).unwrap_or_default();
         let current_version = primary_versions.get(&doc.id).cloned();
         response.push(to_document_response(
             &state,
             user.user_id,
             doc,
             tags,
+            correspondents,
             current_version,
         )?);
     }

backend/src/routes/mod.rs

@@ -10,6 +10,7 @@ use tower_http::cors::{AllowOrigin, CorsLayer};
 use crate::{auth::AuthenticatedUser, state::AppState};
 
 pub mod auth;
+pub mod correspondents;
 pub mod documents;
 pub mod folders;
 pub mod health;
@@ -76,7 +77,15 @@ pub fn create_router(state: AppState) -> Router<()> {
         )
         .route("/:id/folder", patch(documents::move_document))
         .route("/:id/tags", post(documents::assign_tags))
-        .route("/:id/tags/:tag_id", delete(documents::remove_tag));
+        .route("/:id/tags/:tag_id", delete(documents::remove_tag))
+        .route(
+            "/:id/correspondents",
+            post(documents::assign_correspondents),
+        )
+        .route(
+            "/:id/correspondents/:correspondent_id",
+            delete(documents::remove_correspondent),
+        );
 
     let download_routes =
         Router::new().route("/download/:token", get(documents::download_with_token));
@@ -93,19 +102,31 @@ pub fn create_router(state: AppState) -> Router<()> {
 
     let tags_routes = Router::new()
         .route("/", get(tags::list_tags).post(tags::create_tag))
-        .route("/:id", patch(tags::update_tag));
+        .route("/:id", patch(tags::update_tag).delete(tags::delete_tag));
+
+    let correspondents_routes = Router::new()
+        .route(
+            "/",
+            get(correspondents::list_correspondents).post(correspondents::create_correspondent),
+        )
+        .route(
+            "/:id",
+            patch(correspondents::update_correspondent)
+                .delete(correspondents::delete_correspondent),
+        );
 
     let protected_state = state.clone();
     let protected_routes = Router::new()
         .nest("/api/documents", documents_routes)
         .nest("/api/folders", folders_routes)
         .nest("/api/tags", tags_routes)
-        .route("/api/health", get(health::health_check))
+        .nest("/api/correspondents", correspondents_routes)
         .layer(middleware::from_extractor_with_state::<AuthenticatedUser, _>(protected_state));
 
     Router::new()
         .merge(download_routes)
         .nest("/api/auth", auth_routes)
+        .route("/api/health", get(health::health_check))
         .merge(protected_routes)
         .with_state(state)
         .layer(cors)

backend/src/routes/tags.rs

@@ -1,6 +1,7 @@
 use crate::utils::json::{classify_nullable, NullableValue};
 use axum::{
     extract::{Path, State},
+    http::StatusCode,
     Json,
 };
 use diesel::{dsl::count_star, prelude::*};
@@ -189,3 +190,28 @@ pub async fn update_tag(
         usage_count,
     }))
 }
+
+pub async fn delete_tag(
+    State(state): State<AppState>,
+    Path(tag_id): Path<Uuid>,
+) -> AppResult<impl axum::response::IntoResponse> {
+    let mut conn = state.db()?;
+
+    let usage: i64 = document_tags::table
+        .filter(document_tags::tag_id.eq(tag_id))
+        .select(count_star())
+        .first(&mut conn)?;
+
+    if usage > 0 {
+        return Err(AppError::bad_request(
+            "cannot delete tag that is still assigned to documents",
+        ));
+    }
+
+    let deleted = diesel::delete(tags::table.find(tag_id)).execute(&mut conn)?;
+    if deleted == 0 {
+        return Err(AppError::not_found());
+    }
+
+    Ok(StatusCode::NO_CONTENT)
+}

backend/src/schema.rs

@@ -1,5 +1,16 @@
 // @generated automatically by Diesel CLI.
 
+diesel::table! {
+    correspondents (id) {
+        id -> Uuid,
+        #[max_length = 255]
+        name -> Varchar,
+        metadata -> Jsonb,
+        created_at -> Timestamptz,
+        updated_at -> Timestamptz,
+    }
+}
+
 diesel::table! {
     document_assets (id) {
         id -> Uuid,
@@ -12,6 +23,17 @@ diesel::table! {
     }
 }
 
+diesel::table! {
+    document_correspondents (document_id, correspondent_id, role) {
+        document_id -> Uuid,
+        correspondent_id -> Uuid,
+        #[max_length = 32]
+        role -> Varchar,
+        assigned_at -> Timestamptz,
+        assigned_by -> Nullable<Uuid>,
+    }
+}
+
 diesel::table! {
     document_tags (document_id, tag_id) {
         document_id -> Uuid,
@@ -123,6 +145,9 @@ diesel::table! {
 }
 
 diesel::joinable!(document_assets -> document_versions (document_version_id));
+diesel::joinable!(document_correspondents -> correspondents (correspondent_id));
+diesel::joinable!(document_correspondents -> documents (document_id));
+diesel::joinable!(document_correspondents -> users (assigned_by));
 diesel::joinable!(document_tags -> documents (document_id));
 diesel::joinable!(document_tags -> tags (tag_id));
 diesel::joinable!(document_tags -> users (assigned_by));
@@ -130,7 +155,9 @@ diesel::joinable!(documents -> folders (folder_id));
 diesel::joinable!(refresh_tokens -> users (user_id));
 
 diesel::allow_tables_to_appear_in_same_query!(
+    correspondents,
     document_assets,
+    document_correspondents,
     document_tags,
     document_versions,
     documents,

docs/api.txt

@@ -0,0 +1,66 @@
+Papercrate REST API
+===================
+
+Unless noted otherwise, endpoints below require a valid `Authorization: Bearer <token>` header.
+
+Authentication
+--------------
+- POST /api/auth/login - Exchange username/password for an access token and refresh cookie (public).
+- POST /api/auth/refresh - Rotate the refresh cookie and return a new access token (public, requires refresh cookie).
+- POST /api/auth/logout - Revoke the caller's refresh tokens and clear the cookie.
+- GET  /api/auth/me - Return the authenticated principal payload.
+
+Health
+------
+- GET  /api/health - Lightweight liveness probe (no authentication required).
+
+Documents
+---------
+- GET  /api/documents - List documents, optionally filtered by `folder_id` and `include_deleted`; each entry includes tags, correspondent assignments, and current version info.
+- POST /api/documents - Upload a document via multipart form-data (`file`, optional metadata/folder fields).
+- POST /api/documents/reanalyze - Queue re-analysis for every non-deleted document.
+- POST /api/documents/bulk/move - Move multiple documents to a target folder.
+- POST /api/documents/bulk/tags - Add or remove tags across multiple documents.
+- POST /api/documents/bulk/reanalyze - Queue re-analysis jobs for selected documents.
+- GET  /api/documents/:id - Retrieve metadata and current version details for a document.
+- PATCH /api/documents/:id - Update document metadata (currently title).
+- DELETE /api/documents/:id - Soft-delete a document.
+- GET  /api/documents/:id/download - Create a pre-signed download URL for the current version.
+- PATCH /api/documents/:id/folder - Move a document to another folder.
+- POST /api/documents/:id/tags - Assign one or more tags to a document.
+- DELETE /api/documents/:id/tags/:tag_id - Remove a single tag from a document.
+- POST /api/documents/:id/correspondents - Assign correspondents to roles (`assignments[]` with `correspondent_id` and `role`; optional `replace=true` overwrites existing assignments for those roles). Valid roles: `sender`, `receiver`, `other`.
+- DELETE /api/documents/:id/correspondents/:correspondent_id - Remove a correspondent assignment (requires `role` query string).
+
+Document Assets
+---------------
+- GET  /api/documents/:id/assets - List generated assets for the current version.
+- POST /api/documents/:id/assets - Request (re)generation of document assets; accepts optional `force` query flag.
+- GET  /api/documents/:id/assets/:asset_id - Fetch metadata and a pre-signed URL for a specific asset.
+
+Downloads
+---------
+- GET  /download/:token - Follow a one-time download token; redirects to a pre-signed URL (public token required).
+
+Folders
+-------
+- POST /api/folders - Create a folder (optionally under a parent).
+- POST /api/folders/path - Ensure a nested folder path exists, creating missing segments.
+- GET  /api/folders/:id/contents - List subfolders and documents inside a folder; use `root` for the workspace root.
+- GET  /api/folders/:id/documents - Search within a folder tree with optional `query` and `tags` filters.
+- DELETE /api/folders/:id - Soft-delete a folder.
+- PATCH /api/folders/:id - Change a folder's parent.
+
+Tags
+----
+- GET  /api/tags - List all tags with usage counts.
+- POST /api/tags - Create a new tag.
+- PATCH /api/tags/:id - Update a tag's label or color.
+- DELETE /api/tags/:id - Remove a tag; fails with 400 if still assigned to any document.
+
+Correspondents
+--------------
+- GET  /api/correspondents - List correspondents with usage totals and per-role counts (roles: `sender`, `receiver`, `other`).
+- POST /api/correspondents - Create a correspondent (name + optional metadata JSON).
+- PATCH /api/correspondents/:id - Update name and/or metadata.
+- DELETE /api/correspondents/:id - Remove a correspondent; fails with 400 if referenced by any document.

frontend/src/documents/DocumentsTable.jsx

@@ -275,7 +275,13 @@ const DocumentsTable = ({
                           focusedRowKey === `folder:${folder.id}` ? ' focused' : ''
                         }`}
                         id={`folder-row-${folder.id}`}
-                        onClick={() => onFolderSelect(folder.id)}
+                        onClick={() => {
+                          onFolderSelect(folder.id);
+                          if (scrollRef.current) {
+                            scrollRef.current.focus({ preventScroll: true });
+                          }
+                          onFocusedRowChange?.(`folder:${folder.id}`);
+                        }}
                         onDragOver={(event) => onFolderDragOver(event, folder.id)}
                         onDragLeave={onFolderDragLeave}
                         onDrop={(event) => onFolderDrop(event, folder.id)}

frontend/src/sidebar/Sidebar.jsx

@@ -1,6 +1,12 @@
 import React, { useCallback } from 'react';
 import { useMatch } from 'react-router-dom';
-import { ChevronIcon, FolderIcon, TagIcon, TrashIcon } from '../ui/icons';
+import {
+  ChevronIcon,
+  FolderIcon,
+  TagIcon,
+  TrashIcon,
+  CorrespondentIcon,
+} from '../ui/icons';
 
 const FolderNode = ({
   node,
@@ -56,12 +62,14 @@ const FolderNode = ({
           }
         }}
       >
-        <span
+        {!isRoot && (
-          className={`toggle${showChevron ? '' : ' invisible'}${isExpanded ? ' expanded' : ''}`}
+          <span
-          onClick={handleToggleClick}
+            className={`toggle${showChevron ? '' : ' invisible'}${isExpanded ? ' expanded' : ''}`}
-        >
+            onClick={handleToggleClick}
-          {icon}
+          >
-        </span>
+            {icon}
+          </span>
+        )}
         <span className="name">
           <FolderIcon className="folder-icon" />
           {node.name}
@@ -104,10 +112,15 @@ const Sidebar = ({
   draggedFolderId,
   onShowTags,
   tags = [],
+  onShowCorrespondents,
+  correspondents = [],
 }) => {
   const handleShowTags = onShowTags || (() => {});
   const tagsRouteMatch = useMatch('/tags');
   const isTagsRoute = Boolean(tagsRouteMatch);
+  const handleShowCorrespondents = onShowCorrespondents || (() => {});
+  const correspondentsRouteMatch = useMatch('/correspondents');
+  const isCorrespondentsRoute = Boolean(correspondentsRouteMatch);
 
   const renderNodes = useCallback(
     (ids, depth) =>
@@ -181,6 +194,27 @@ const Sidebar = ({
           <span>All tags</span>
         </span>
       </div>
+      <div className="sidebar-section">
+        <div className="sidebar-section__header">
+          <h3>Correspondents</h3>
+          <span className="meta">{correspondents.length}</span>
+        </div>
+        <span
+          role="button"
+          tabIndex={0}
+          className={`sidebar-item${isCorrespondentsRoute ? ' active' : ''}`}
+          onClick={handleShowCorrespondents}
+          onKeyDown={(event) => {
+            if (event.key === 'Enter' || event.key === ' ') {
+              event.preventDefault();
+              handleShowCorrespondents();
+            }
+          }}
+        >
+          <CorrespondentIcon className="sidebar-item__icon" />
+          <span>All correspondents</span>
+        </span>
+      </div>
     </aside>
   );
 };

frontend/src/skeuomorphic_ws.jsx

@@ -7,6 +7,7 @@ import React, {
   useState,
 } from 'react';
 import { resolveDocumentAssetUrl } from './asset_manager';
+import { generateRandomTagColor, getReadableTextColor } from './utils/colors';
 import './skeuomorphic_ws.css';
 
 const ITEM_WIDTH = 220;
@@ -299,15 +300,7 @@ const normalizeColor = (input) => {
   return null;
 };
 
-const getContrastingTextColor = (hex) => {
+const getContrastingTextColor = (hex) => getReadableTextColor(hex, { light: '#1f2125' });
-  if (!hex) return '#1b1f24';
-  const value = parseInt(hex.slice(1), 16);
-  const r = (value >> 16) & 0xff;
-  const g = (value >> 8) & 0xff;
-  const b = value & 0xff;
-  const luminance = (0.299 * r + 0.587 * g + 0.114 * b) / 255;
-  return luminance > 0.6 ? '#1b1f24' : '#ffffff';
-};
 
 const SkeuomorphicWorkspace = ({
   documents = [],
@@ -1555,11 +1548,8 @@ const SkeuomorphicWorkspace = ({
                   if (!label) {
                     return;
                   }
-                  const randomColor = `#${Math.floor(Math.random() * 0xffffff)
-                    .toString(16)
-                    .padStart(6, '0')}`;
                   try {
-                    await onCreateTag({ label, color: randomColor });
+                    await onCreateTag({ label, color: generateRandomTagColor() });
                     setActiveShelfTagId(null);
                   } catch (error) {
                     console.error('Failed to create tag', error);

frontend/src/styles.css

@@ -13,6 +13,8 @@
   --overlay-backdrop: rgba(30, 33, 39, 0.45);
   --overlay-shadow: rgba(30, 33, 39, 0.18);
 
+  --app-bar-background: var(--surface-subtle);
+
   /* Accent (primary action, selection, focus) */
   --accent: #3f6ad8;
   --accent-hover: #365cb9;
@@ -209,7 +211,7 @@ button.icon-button.ghost:hover:not([disabled]) {
   flex-direction: column;
   gap: 0.4rem;
   padding: 0.6rem 1.5rem 0.4rem;
-  background: var(--surface);
+  background: var(--app-bar-background);
   border-bottom: 1px solid var(--border);
   position: sticky;
   top: 0;
@@ -422,6 +424,80 @@ button.icon-button.ghost:hover:not([disabled]) {
   gap: 0.4rem;
 }
 
+.tags-table__row-actions {
+  display: flex;
+  justify-content: flex-end;
+  gap: 0.4rem;
+}
+
+.correspondents-panel .header-actions {
+  gap: 0.5rem;
+}
+
+.correspondents-actions__form {
+  display: flex;
+  gap: 0.4rem;
+}
+
+.correspondents-actions__form input {
+  min-width: 14rem;
+}
+
+.correspondent-list {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.4rem;
+  margin-bottom: 0.5rem;
+}
+
+.correspondent-pill {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.35rem;
+  background: var(--surface-subtle);
+  border: 1px solid var(--border-subtle);
+  border-radius: 999px;
+  padding: 0.15rem 0.5rem;
+  font-size: 0.9rem;
+}
+
+.correspondent-pill__label {
+  display: flex;
+  flex-direction: column;
+  line-height: 1.2;
+}
+
+.correspondent-pill__label strong {
+  font-size: 0.8rem;
+  text-transform: capitalize;
+  color: var(--muted);
+}
+
+.correspondent-pill__remove {
+  border: none;
+  background: none;
+  cursor: pointer;
+  font-size: 1rem;
+  line-height: 1;
+  color: var(--muted);
+  padding: 0;
+}
+
+.correspondent-pill__remove:hover {
+  color: var(--danger);
+}
+
+.correspondent-form {
+  display: flex;
+  gap: 0.4rem;
+  align-items: center;
+}
+
+.correspondent-form input,
+.correspondent-form select {
+  min-height: 32px;
+}
+
 .preview-workspace__message {
   color: var(--muted);
   font-size: 0.95rem;

frontend/src/ui/icons.js

@@ -4,6 +4,7 @@ import {
   IconFolderFilled,
   IconPencil,
   IconTagFilled,
+  IconUserFilled,
   IconTrash,
 } from '@tabler/icons-react';
 
@@ -54,6 +55,15 @@ export const TagIcon = ({ className, size = '1em', stroke = 0, ...rest }) => (
   />
 );
 
+export const CorrespondentIcon = ({ className, size = '1em', stroke = 0, ...rest }) => (
+  <IconUserFilled
+    className={composeClassName('icon icon--fill', className)}
+    size={size}
+    stroke={stroke}
+    {...rest}
+  />
+);
+
 export const DownloadIcon = ({ className, size = '1em', stroke = 1.6, ...rest }) => (
   <TablerDownload
     className={composeClassName('icon', className)}
@@ -69,5 +79,6 @@ export default {
   EditIcon,
   FolderIcon,
   TagIcon,
+  CorrespondentIcon,
   DownloadIcon,
 };

frontend/src/utils/colors.js

@@ -1,5 +1,38 @@
 const HEX_COLOR_PATTERN = /^#?([0-9a-fA-F]{6})$/;
 
+const clamp01 = (value) => Math.min(1, Math.max(0, value));
+
+const gammaEncode = (channel) =>
+  channel <= 0.0031308 ? 12.92 * channel : 1.055 * Math.pow(channel, 1 / 2.4) - 0.055;
+
+const oklchToHex = (l, c, h) => {
+  const hr = (h * Math.PI) / 180;
+  const a = Math.cos(hr) * c;
+  const b = Math.sin(hr) * c;
+
+  const l1 = l + 0.3963377774 * a + 0.2158037573 * b;
+  const m1 = l - 0.1055613458 * a - 0.0638541728 * b;
+  const s1 = l - 0.0894841775 * a - 1.291485548 * b;
+
+  const l3 = l1 ** 3;
+  const m3 = m1 ** 3;
+  const s3 = s1 ** 3;
+
+  const r = 4.0767416621 * l3 - 3.3077115913 * m3 + 0.2309699292 * s3;
+  const g = -1.2684380046 * l3 + 2.6097574011 * m3 - 0.3413193965 * s3;
+  const bLin = -0.0041960863 * l3 - 0.7034186147 * m3 + 1.707614701 * s3;
+
+  if ([r, g, bLin].some((channel) => channel < 0 || channel > 1)) {
+    return null;
+  }
+
+  const sr = Math.round(clamp01(gammaEncode(r)) * 255);
+  const sg = Math.round(clamp01(gammaEncode(g)) * 255);
+  const sb = Math.round(clamp01(gammaEncode(bLin)) * 255);
+
+  return `#${((sr << 16) | (sg << 8) | sb).toString(16).padStart(6, '0')}`;
+};
+
 export const hexToRgb = (input) => {
   if (!input) return null;
   const match = HEX_COLOR_PATTERN.exec(input.trim());
@@ -13,28 +46,49 @@ export const hexToRgb = (input) => {
   };
 };
 
-const relativeLuminance = ({ r, g, b }) => {
+export const relativeLuminance = ({ r, g, b }) => {
-  const transform = (channel) => {
+  const toLinear = (channel) => {
     const normalized = channel / 255;
     return normalized <= 0.03928
       ? normalized / 12.92
       : ((normalized + 0.055) / 1.055) ** 2.4;
   };
 
-  const [red, green, blue] = [transform(r), transform(g), transform(b)];
+  const [red, green, blue] = [toLinear(r), toLinear(g), toLinear(b)];
   return 0.2126 * red + 0.7152 * green + 0.0722 * blue;
 };
 
+export const getReadableTextColor = (hex, { light = '#1f1f1f', dark = '#ffffff' } = {}) => {
+  const rgb = hexToRgb(hex);
+  if (!rgb) return dark;
+  const luminance = relativeLuminance(rgb);
+  return luminance > 0.6 ? light : dark;
+};
+
 export const getTagColorStyle = (hex) => {
   const rgb = hexToRgb(hex);
   if (!rgb) return null;
-  const luminance = relativeLuminance(rgb);
-  const textColor = luminance > 0.6 ? '#1f1f1f' : '#ffffff';
   return {
     backgroundColor: rgb.hex,
     borderColor: rgb.hex,
-    color: textColor,
+    color: getReadableTextColor(rgb.hex),
   };
 };
 
+export const generateRandomTagColor = () => {
+  const lightness = 0.72 + (Math.random() - 0.5) * 0.08;
+  let chroma = 0.8;
+  const hue = Math.random() * 360;
+
+  for (let attempt = 0; attempt < 5; attempt += 1) {
+    const hex = oklchToHex(lightness, chroma, hue);
+    if (hex) {
+      return hex;
+    }
+    chroma *= 0.82;
+  }
+
+  return '#8c8982';
+};
+
 export { HEX_COLOR_PATTERN };

frontend/src/utils/format.js

@@ -0,0 +1,18 @@
+export const formatFileSize = (value) => {
+  const bytes = Number(value);
+  if (!Number.isFinite(bytes) || bytes <= 0) {
+    return '0 B';
+  }
+
+  const units = ['B', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB'];
+  let index = 0;
+  let amount = bytes;
+
+  while (amount >= 1024 && index < units.length - 1) {
+    amount /= 1024;
+    index += 1;
+  }
+
+  return `${amount.toFixed(2)} ${units[index]}`;
+};
+