//! Configuration: built-in defaults, then configuration files (`--config`, in order),
//! then command-line arguments. Every option can be set in each.
//!
//! An argument that replaces a value from a file is logged (info), as is a file that
//! replaces one from another file (debug; warning between two includes of one file).
//! Values can be imported instead of written out (`import`): imported values are never
//! logged, only where they come from.
//!
//! All options are described once, in [`OPTIONS`]: the command line, the file keys and
//! the conversion of text values all derive from it. The merged values are then read
//! into [`Settings`] and checked.

mod file;
mod import;

use std::collections::BTreeMap;
use std::net::SocketAddr;
use std::path::{Path, PathBuf};

use anyhow::{Context, Result, anyhow, bail};
use clap::parser::ValueSource;
use clap::{Arg, ArgAction, ArgMatches, Command};
use serde::{Deserialize, Serialize};
use serde_json::Value as JsonValue;
use tracing::{debug, info, warn};

use import::{Imported, Raw};

/// How an option's value is written as text (command line, text imports).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum Kind {
    /// `true`/`false`; on the command line, present or not.
    Flag,
    Text,
    Integer,
    /// Comma- or line-separated; repeatable on the command line.
    List,
}

#[derive(Debug)]
pub(crate) struct OptionSpec {
    pub(crate) name: &'static str,
    pub(crate) kind: Kind,
    pub(crate) value_name: &'static str,
    /// For `--help` only; the effective defaults are in [`Settings`].
    pub(crate) default: Option<&'static str>,
    pub(crate) help: &'static str,
    pub(crate) hidden: bool,
}

const fn option(
    name: &'static str,
    kind: Kind,
    value_name: &'static str,
    default: Option<&'static str>,
    help: &'static str,
) -> OptionSpec {
    OptionSpec {
        name,
        kind,
        value_name,
        default,
        help,
        hidden: false,
    }
}

/// Every option. Names are the long option names and the configuration file keys.
pub(crate) const OPTIONS: &[OptionSpec] = &[
    option(
        "bind-addr",
        Kind::Text,
        "HOSTNAME:PORT",
        Some("127.0.0.1:3000"),
        "Address of the HTTP API.",
    ),
    option(
        "htpasswd",
        Kind::Text,
        "PATH",
        None,
        "Users of the HTTP API (htpasswd file with Argon2 hashes). Required.",
    ),
    option(
        "protocol-writers",
        Kind::List,
        "USER,[USER...]",
        None,
        "HTTP API users (from htpasswd) who may write protocol data under /store/_continuum (remake records, members, forget records), e.g. to repair a stuck remake. Such writes act on the whole swarm and are logged. Epoch metadata is never writable.",
    ),
    option(
        "debug-api",
        Kind::Flag,
        "BOOL",
        Some("false"),
        "Enable the /debug endpoints (tests only).",
    ),
    option(
        "seeds",
        Kind::List,
        "STRING,[STRING...]",
        None,
        "How to reach a node of the swarm to join: a Mycelium public key, a Mycelium IPv6 address, or a host name with an AAAA record for one. Without seeds, the node starts a new swarm (genesis).",
    ),
    option(
        "swarm-key-file",
        Kind::Text,
        "PATH",
        None,
        "Pre-shared swarm key: only nodes that know it may join (raw bytes, at least 16; e.g. `head -c 32 /dev/urandom`). Without it, any node that can reach a member may join.",
    ),
    option(
        "alias",
        Kind::Text,
        "NAME",
        None,
        "A name for this node, shown next to its public key (/peers, metrics). Published in the swarm's member list; not unique, never an identity.",
    ),
    option(
        "keepalive-secs",
        Kind::Integer,
        "SECONDS",
        Some("60"),
        "Keepalive interval; dormancy, resync and probe timings derive from it.",
    ),
    option(
        "neighbours",
        Kind::Integer,
        "COUNT",
        Some("12"),
        "Neighbours each node keeps (at least 2). Swarms of up to this many + 1 nodes are a full mesh; larger ones sync over several hops.",
    ),
    option(
        "electorate-window-days",
        Kind::Integer,
        "DAYS",
        Some("7"),
        "Members that renewed their alive stamp within this many days vote on remakes (a majority of them must agree). Matters on the node that coordinates a remake.",
    ),
    option(
        "blob-chunk-kib",
        Kind::Integer,
        "KIB",
        Some("64"),
        "Chunk size when serving large transfers to other nodes (e.g. an epoch's snapshot to a rejoining node), in KiB (1 to 4096).",
    ),
    option(
        "mycelium-rest-url",
        Kind::Text,
        "SCHEME://HOSTNAME:PORT",
        None,
        "Use a Mycelium daemon running elsewhere (its REST API) instead of supervising one. Excludes the other mycelium options except mycelium-peers.",
    ),
    option(
        "mycelium-key-file",
        Kind::Text,
        "PATH",
        None,
        "Private key of the supervised Mycelium daemon (its identity); a new one each start if absent.",
    ),
    option(
        "mycelium-network-key-file",
        Kind::Text,
        "PATH",
        None,
        "Key of a private Mycelium network for the supervised daemon.",
    ),
    option(
        "mycelium-network-name",
        Kind::Text,
        "NAME",
        None,
        "Name of that private Mycelium network.",
    ),
    option(
        "mycelium-tcp-listen-port",
        Kind::Integer,
        "PORT",
        None,
        "TCP port the supervised Mycelium daemon listens on for overlay peers; a free port if absent.",
    ),
    option(
        "mycelium-peers",
        Kind::List,
        "URL,[URL...]",
        Some("tls://127.0.0.1:9651"),
        "Peers of the supervised Mycelium daemon (overlay links such as `tls://host:9651`), not continuum peers.",
    ),
    OptionSpec {
        name: "debug-epoch",
        kind: Kind::Integer,
        value_name: "GENERATION",
        default: None,
        help: "Test hook: start on a non-genesis epoch of this generation (with a fixed dummy id). Needs debug-api.",
        hidden: true,
    },
];

pub(crate) fn spec(name: &str) -> Option<&'static OptionSpec> {
    OPTIONS.iter().find(|spec| spec.name == name)
}

/// The effective configuration.
#[derive(Debug, Clone, Deserialize, Serialize)]
#[serde(rename_all = "kebab-case", deny_unknown_fields)]
pub(crate) struct Settings {
    #[serde(default = "default_bind_addr")]
    pub(crate) bind_addr: SocketAddr,
    pub(crate) htpasswd: String,
    #[serde(default)]
    pub(crate) protocol_writers: Vec<String>,
    #[serde(default)]
    pub(crate) debug_api: bool,
    #[serde(default)]
    pub(crate) seeds: Vec<String>,
    pub(crate) swarm_key_file: Option<PathBuf>,
    pub(crate) alias: Option<String>,
    #[serde(default = "default_keepalive_secs")]
    pub(crate) keepalive_secs: u64,
    #[serde(default = "default_neighbours")]
    pub(crate) neighbours: usize,
    #[serde(default = "default_electorate_window_days")]
    pub(crate) electorate_window_days: u64,
    #[serde(default = "default_blob_chunk_kib")]
    pub(crate) blob_chunk_kib: u32,
    pub(crate) mycelium_rest_url: Option<String>,
    pub(crate) mycelium_key_file: Option<PathBuf>,
    pub(crate) mycelium_network_key_file: Option<PathBuf>,
    pub(crate) mycelium_network_name: Option<String>,
    pub(crate) mycelium_tcp_listen_port: Option<u16>,
    #[serde(default = "default_mycelium_peers")]
    pub(crate) mycelium_peers: Vec<String>,
    pub(crate) debug_epoch: Option<u64>,
}

fn default_bind_addr() -> SocketAddr {
    SocketAddr::from(([127, 0, 0, 1], 3000))
}
fn default_keepalive_secs() -> u64 {
    60
}
fn default_neighbours() -> usize {
    12
}
fn default_electorate_window_days() -> u64 {
    7
}
fn default_blob_chunk_kib() -> u32 {
    64
}
fn default_mycelium_peers() -> Vec<String> {
    vec!["tls://127.0.0.1:9651".to_owned()]
}

impl Settings {
    /// `mycelium-rest-url`, parsed (checked when loading).
    pub(crate) fn mycelium_rest_url(&self) -> Option<url::Url> {
        self.mycelium_rest_url
            .as_deref()
            .and_then(|url| url::Url::parse(url).ok())
    }

    fn check(&self) -> Result<()> {
        if let Some(url) = &self.mycelium_rest_url {
            url::Url::parse(url).with_context(|| format!("mycelium-rest-url {url:?}"))?;
        }
        if self.mycelium_rest_url.is_some() {
            let supervised_only = [
                ("mycelium-key-file", self.mycelium_key_file.is_some()),
                (
                    "mycelium-network-key-file",
                    self.mycelium_network_key_file.is_some(),
                ),
                (
                    "mycelium-network-name",
                    self.mycelium_network_name.is_some(),
                ),
                (
                    "mycelium-tcp-listen-port",
                    self.mycelium_tcp_listen_port.is_some(),
                ),
            ];
            if let Some((name, _)) = supervised_only.iter().find(|(_, set)| *set) {
                bail!(
                    "{name} is for a supervised Mycelium daemon and can't be combined with mycelium-rest-url"
                );
            }
        }
        if self.debug_epoch.is_some() && !self.debug_api {
            bail!("debug-epoch needs debug-api");
        }
        if self.neighbours < 2 {
            bail!("neighbours must be at least 2");
        }
        if self.keepalive_secs == 0 {
            bail!("keepalive-secs must be at least 1");
        }
        if !(1..=4096).contains(&self.blob_chunk_kib) {
            bail!("blob-chunk-kib must be between 1 and 4096");
        }
        if self.electorate_window_days == 0 {
            bail!("electorate-window-days must be at least 1");
        }
        if let Some(alias) = &self.alias {
            check_alias(alias)?;
        }
        Ok(())
    }
}

/// Up to 64 characters, no control characters, not blank.
fn check_alias(alias: &str) -> Result<()> {
    if alias.trim().is_empty() {
        bail!("alias must not be blank");
    }
    if alias.chars().count() > 64 {
        bail!("alias must be at most 64 characters");
    }
    if alias.chars().any(char::is_control) {
        bail!("alias must not contain control characters");
    }
    Ok(())
}

// --- values and where they came from -------------------------------------------

#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) enum Provenance {
    File(PathBuf),
    Argument,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) struct Origin {
    pub(crate) provenance: Provenance,
    /// The option was unset here (back to its default): `--unset`, `unset = [...]` in a
    /// file, or `null` in a JSON file.
    pub(crate) unset: bool,
    /// Importers the value (or some list elements) came from, e.g. `env:HOSTNAME`.
    pub(crate) imports: Vec<String>,
}

impl Origin {
    pub(crate) fn is_imported(&self) -> bool {
        !self.imports.is_empty()
    }
}

impl std::fmt::Display for Origin {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match &self.provenance {
            Provenance::File(path) => write!(f, "{}", path.display())?,
            Provenance::Argument => write!(f, "the command line")?,
        }
        if self.unset {
            write!(f, " (unset)")?;
        }
        if self.is_imported() {
            write!(f, " ({})", self.imports.join(", "))?;
        }
        Ok(())
    }
}

#[derive(Debug, Clone)]
pub(crate) struct Entry {
    pub(crate) value: JsonValue,
    pub(crate) origin: Origin,
}

impl Entry {
    /// The value for logs: imported values are never shown.
    pub(crate) fn shown(&self) -> String {
        if self.origin.unset {
            "<default>".to_owned()
        } else if self.origin.is_imported() {
            "<imported>".to_owned()
        } else {
            self.value.to_string()
        }
    }
}

/// Option name to value. A `null` value unsets the option (back to its default).
pub(crate) type Layer = BTreeMap<String, Entry>;

/// An unset of `name` from `provenance`.
fn unset_entry(provenance: Provenance) -> Entry {
    Entry {
        value: JsonValue::Null,
        origin: Origin {
            provenance,
            unset: true,
            imports: Vec::new(),
        },
    }
}

/// Options that can't be combined. A source that sets one side drops the other side's
/// values from earlier sources (lower precedence), so e.g. `--mycelium-rest-url` on the
/// command line overrides `mycelium-key-file` from a file. Both set in one source is an
/// error (`Settings::check`).
const CONFLICTS: &[(&[&str], &[&str])] = &[(
    &["mycelium-rest-url"],
    &[
        "mycelium-key-file",
        "mycelium-network-key-file",
        "mycelium-network-name",
        "mycelium-tcp-listen-port",
    ],
)];

/// The options `name` can't be combined with.
fn conflicting(name: &str) -> impl Iterator<Item = &'static str> + '_ {
    CONFLICTS.iter().flat_map(move |(a, b)| {
        let other: &'static [&'static str] = if a.contains(&name) {
            b
        } else if b.contains(&name) {
            a
        } else {
            &[]
        };
        other.iter().copied()
    })
}

/// How a later source relates to the earlier ones it overrides (for logging).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum Overlay {
    /// A later include over an earlier include of the same file: usually a mistake.
    IncludeOverInclude,
    /// A file's own values over its includes, or a later `--config` over an earlier.
    FileOverFile,
    /// The command line over files.
    ArgumentOverFile,
}

/// Puts `entry` for `name` into `layer`, which holds earlier sources, logging what it
/// replaces and dropping earlier values it can't be combined with.
pub(crate) fn overlay(layer: &mut Layer, name: String, entry: Entry, how: Overlay) {
    let log = |message: &str, option: &str, previous: &Entry| match how {
        Overlay::IncludeOverInclude => warn!(
            option,
            value = %entry.shown(),
            from = %entry.origin,
            overrides = %previous.shown(),
            overridden_from = %previous.origin,
            "{message}"
        ),
        Overlay::FileOverFile => debug!(
            option,
            from = %entry.origin,
            overrides = %previous.origin,
            "{message}"
        ),
        Overlay::ArgumentOverFile => info!(
            option,
            value = %entry.shown(),
            overrides = %previous.shown(),
            from = %previous.origin,
            "{message}"
        ),
    };

    if !entry.value.is_null() {
        for other in conflicting(&name) {
            let earlier = layer
                .get(other)
                .is_some_and(|previous| previous.origin.provenance != entry.origin.provenance);
            if earlier {
                if let Some(previous) = layer.remove(other) {
                    log(
                        &format!(
                            "{name} can't be combined with {other}; dropped the earlier value"
                        ),
                        other,
                        &previous,
                    );
                }
            }
        }
    }
    if let Some(previous) = layer.get(&name) {
        let message = match how {
            Overlay::IncludeOverInclude => {
                "Two included configuration files set the same option; the later one wins"
            }
            Overlay::FileOverFile => "Configuration file overrides an earlier one",
            Overlay::ArgumentOverFile => "Command-line argument overrides the configuration file",
        };
        log(message, &name, previous);
    }
    layer.insert(name, entry);
}

/// The value of a text, by the option's kind.
fn from_text(kind: Kind, text: &str) -> Result<JsonValue> {
    Ok(match kind {
        Kind::Text => JsonValue::String(text.to_owned()),
        Kind::Integer => {
            let number: u64 = text
                .trim()
                .parse()
                .map_err(|_| anyhow!("{text:?} is not a non-negative integer"))?;
            JsonValue::from(number)
        }
        Kind::Flag => match text.trim() {
            "true" | "yes" | "1" => JsonValue::Bool(true),
            "false" | "no" | "0" => JsonValue::Bool(false),
            _ => bail!("{text:?} is not true or false"),
        },
        Kind::List => JsonValue::Array(
            text.split([',', '\n'])
                .map(str::trim)
                .filter(|item| !item.is_empty())
                .map(|item| JsonValue::String(item.to_owned()))
                .collect(),
        ),
    })
}

fn from_import(kind: Kind, importer: &import::Importer) -> Result<JsonValue> {
    match importer.fetch()? {
        Imported::Text(text) => from_text(kind, &text),
        Imported::Json(value) => Ok(value),
    }
}

/// A value from a file in `dir`: importer tables are resolved, also as list elements.
fn resolve_file_value(
    spec: &OptionSpec,
    value: JsonValue,
    dir: &Path,
) -> Result<(JsonValue, Vec<String>)> {
    match value {
        JsonValue::Object(table) => match import::parse_table(&table, dir)? {
            Some(importer) => Ok((
                from_import(spec.kind, &importer)?,
                vec![importer.describe()],
            )),
            None => bail!("a table here must be an importer (env, file or command)"),
        },
        JsonValue::Array(items) if spec.kind == Kind::List => {
            let mut imports = Vec::new();
            let mut values = Vec::new();
            for item in items {
                match item {
                    JsonValue::Object(table) => {
                        let importer = import::parse_table(&table, dir)?.ok_or_else(|| {
                            anyhow!("a table here must be an importer (env, file or command)")
                        })?;
                        match from_import(Kind::List, &importer)? {
                            JsonValue::Array(more) => values.extend(more),
                            other => values.push(other),
                        }
                        imports.push(importer.describe());
                    }
                    other => values.push(other),
                }
            }
            Ok((JsonValue::Array(values), imports))
        }
        other => Ok((other, Vec::new())),
    }
}

/// The first option whose value alone doesn't fit (serde doesn't name it).
fn culprit(merged: &Layer) -> Option<(&String, &Entry)> {
    merged.iter().find(|(name, entry)| {
        if entry.value.is_null() {
            return false;
        }
        let mut alone = serde_json::Map::new();
        alone.insert("htpasswd".to_owned(), JsonValue::String(String::new()));
        alone.insert((*name).clone(), entry.value.clone());
        serde_json::from_value::<Settings>(JsonValue::Object(alone)).is_err()
    })
}

// --- command line --------------------------------------------------------------

const CONFIG: &str = "config";
const PRINT_CONFIG: &str = "print-config";
const UNSET: &str = "unset";

fn command() -> Command {
    let mut command = Command::new("continuum")
        .version(env!("CARGO_PKG_VERSION"))
        .about("continuum: a replicated key-value store over Mycelium")
        .after_help(
            "Every option can also be set in a configuration file (--config); arguments win.\n\
             A value can be imported instead of written out: env:NAME, file:PATH or cmd:COMMAND \
             (as text), or env+json:, file+json:, cmd+json: (parsed as JSON). \
             literal:VALUE passes a value that starts with one of these prefixes.",
        )
        .arg(
            Arg::new(CONFIG)
                .long(CONFIG)
                .value_name("PATH")
                .action(ArgAction::Append)
                .help("Configuration file (.toml or .json); repeatable, later files win."),
        )
        .arg(
            Arg::new(UNSET)
                .long(UNSET)
                .value_name("OPTION")
                .action(ArgAction::Append)
                .help("Unset an option set by a configuration file (back to its default); repeatable."),
        )
        .arg(
            Arg::new(PRINT_CONFIG)
                .long(PRINT_CONFIG)
                .action(ArgAction::SetTrue)
                .help("Print the effective configuration as JSON (with each value's source) and exit."),
        );
    for spec in OPTIONS {
        let help = match spec.default {
            Some(default) => format!("{} [default: {default}]", spec.help),
            None => spec.help.to_owned(),
        };
        let arg = Arg::new(spec.name)
            .long(spec.name)
            .help(help)
            .hide(spec.hidden);
        command = command.arg(match spec.kind {
            Kind::Flag => arg.action(ArgAction::SetTrue),
            Kind::List => arg.value_name(spec.value_name).action(ArgAction::Append),
            Kind::Text | Kind::Integer => arg.value_name(spec.value_name).action(ArgAction::Set),
        });
    }
    command
}

/// The values given as arguments (unsets first, so a value given too wins).
fn arguments(matches: &ArgMatches) -> Result<Layer> {
    let mut layer = Layer::new();
    for name in matches.get_many::<String>(UNSET).into_iter().flatten() {
        if spec(name).is_none() {
            bail!("--unset {name}: no such option");
        }
        layer.insert(name.clone(), unset_entry(Provenance::Argument));
    }
    for spec in OPTIONS {
        if matches.value_source(spec.name) != Some(ValueSource::CommandLine) {
            continue;
        }
        let mut imports = Vec::new();
        let value = if spec.kind == Kind::Flag {
            JsonValue::Bool(true)
        } else {
            let mut values = Vec::new();
            for raw in matches.get_many::<String>(spec.name).into_iter().flatten() {
                let value = match import::parse_argument(raw) {
                    Raw::Literal(text) => from_text(spec.kind, text),
                    Raw::Import(importer) => {
                        imports.push(importer.describe());
                        from_import(spec.kind, &importer)
                    }
                }
                .with_context(|| format!("--{}", spec.name))?;
                values.push(value);
            }
            if spec.kind == Kind::List {
                JsonValue::Array(
                    values
                        .into_iter()
                        .flat_map(|value| match value {
                            JsonValue::Array(items) => items,
                            other => vec![other],
                        })
                        .collect(),
                )
            } else {
                values.pop().unwrap_or(JsonValue::Null)
            }
        };
        layer.insert(
            spec.name.to_owned(),
            Entry {
                value,
                origin: Origin {
                    provenance: Provenance::Argument,
                    unset: false,
                    imports,
                },
            },
        );
    }
    Ok(layer)
}

/// The configuration, and where each value set came from (absent: default).
#[derive(Debug, Clone)]
pub(crate) struct Loaded {
    pub(crate) settings: Settings,
    pub(crate) origins: BTreeMap<String, Origin>,
    pub(crate) files: Vec<PathBuf>,
    /// `--print-config`: print [`Loaded::report`] and exit.
    pub(crate) print_only: bool,
}

impl Loaded {
    /// The effective configuration with each value's source, for `--print-config` and
    /// `GET /admin/config`. Imported values are left out (they may be secret); their
    /// importers are listed instead.
    pub(crate) fn report(&self) -> JsonValue {
        let values = match serde_json::to_value(&self.settings) {
            Ok(JsonValue::Object(values)) => values,
            _ => serde_json::Map::new(),
        };
        let options: serde_json::Map<String, JsonValue> = OPTIONS
            .iter()
            .filter(|spec| !spec.hidden || self.origins.contains_key(spec.name))
            .map(|spec| {
                let mut entry = serde_json::Map::new();
                match self.origins.get(spec.name) {
                    None => {
                        entry.insert("source".into(), "default".into());
                    }
                    Some(origin) => {
                        match &origin.provenance {
                            Provenance::File(path) => {
                                entry.insert("source".into(), "file".into());
                                entry.insert("file".into(), path.display().to_string().into());
                            }
                            Provenance::Argument => {
                                entry.insert("source".into(), "argument".into());
                            }
                        }
                        if origin.is_imported() {
                            entry.insert("imported".into(), origin.imports.clone().into());
                        }
                        if origin.unset {
                            entry.insert("unset".into(), true.into());
                        }
                    }
                }
                let imported = self.origins.get(spec.name).is_some_and(Origin::is_imported);
                if !imported {
                    entry.insert(
                        "value".into(),
                        values.get(spec.name).cloned().unwrap_or(JsonValue::Null),
                    );
                }
                (spec.name.to_owned(), JsonValue::Object(entry))
            })
            .collect();
        serde_json::json!({
            "files": self.files.iter().map(|path| path.display().to_string()).collect::<Vec<_>>(),
            "options": options,
        })
    }
}

/// Reads the command line and the configuration files it names. Exits on `--help`,
/// `--version` and command-line syntax errors, like any command.
pub(crate) fn load() -> Result<Loaded> {
    let matches = command().get_matches();
    let print_only = matches.get_flag(PRINT_CONFIG);
    if print_only {
        // Logs go to stdout too; the report says where each value came from anyway.
        let _ = crate::logging::set_filter("off");
    }
    let files: Vec<PathBuf> = matches
        .get_many::<String>(CONFIG)
        .into_iter()
        .flatten()
        .map(PathBuf::from)
        .collect();

    let mut merged = Layer::new();
    for path in &files {
        for (name, entry) in file::load(path)? {
            overlay(&mut merged, name, entry, Overlay::FileOverFile);
        }
    }
    for (name, entry) in arguments(&matches)? {
        overlay(&mut merged, name, entry, Overlay::ArgumentOverFile);
    }
    let mut loaded = resolve(merged, files)?;
    loaded.print_only = print_only;
    Ok(loaded)
}

fn resolve(merged: Layer, files: Vec<PathBuf>) -> Result<Loaded> {
    // Unset options take their defaults.
    let object: serde_json::Map<String, JsonValue> = merged
        .iter()
        .filter(|(_, entry)| !entry.value.is_null())
        .map(|(name, entry)| (name.clone(), entry.value.clone()))
        .collect();
    let mut settings: Settings =
        serde_json::from_value(JsonValue::Object(object)).map_err(|error| {
            match culprit(&merged) {
                Some((name, entry)) => anyhow!(
                    "invalid configuration: option {name} (set in {}): {error}",
                    entry.origin
                ),
                None => anyhow!("invalid configuration: {error}"),
            }
        })?;
    settings.alias = settings.alias.map(|alias| alias.trim().to_owned());
    settings.check().context("invalid configuration")?;
    Ok(Loaded {
        settings,
        origins: merged
            .into_iter()
            .map(|(name, entry)| (name, entry.origin))
            .collect(),
        files,
        print_only: false,
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    fn layer(values: JsonValue) -> Layer {
        values
            .as_object()
            .unwrap()
            .iter()
            .map(|(name, value)| {
                (
                    name.clone(),
                    Entry {
                        value: value.clone(),
                        origin: Origin {
                            provenance: Provenance::Argument,
                            unset: false,
                            imports: Vec::new(),
                        },
                    },
                )
            })
            .collect()
    }

    #[test]
    fn options_and_settings_agree() {
        // Every option is a Settings field, and every field an option.
        let loaded = resolve(layer(json!({ "htpasswd": "users" })), Vec::new()).unwrap();
        let JsonValue::Object(fields) = serde_json::to_value(&loaded.settings).unwrap() else {
            panic!()
        };
        let mut names: Vec<&str> = fields.keys().map(String::as_str).collect();
        let mut options: Vec<&str> = OPTIONS.iter().map(|spec| spec.name).collect();
        names.sort_unstable();
        options.sort_unstable();
        assert_eq!(names, options);

        // Help defaults match the real ones.
        for spec in OPTIONS {
            if let Some(default) = spec.default {
                assert_eq!(
                    from_text(spec.kind, default).unwrap(),
                    fields[spec.name],
                    "default of {}",
                    spec.name
                );
            }
        }
        command().debug_assert();
    }

    #[test]
    fn later_sources_override_conflicts_and_unset() {
        let from = |provenance: Provenance, value: JsonValue| Entry {
            value,
            origin: Origin {
                provenance,
                unset: false,
                imports: Vec::new(),
            },
        };
        let file = |value| from(Provenance::File("/etc/continuum.toml".into()), value);
        let argument = |value| from(Provenance::Argument, value);
        let url = json!("http://[::1]:8989");

        let mut merged = Layer::new();
        overlay(
            &mut merged,
            "htpasswd".into(),
            file(json!("u")),
            Overlay::FileOverFile,
        );
        overlay(
            &mut merged,
            "mycelium-key-file".into(),
            file(json!("k")),
            Overlay::FileOverFile,
        );
        overlay(
            &mut merged,
            "alias".into(),
            file(json!("a")),
            Overlay::FileOverFile,
        );

        // Both in one source: an error.
        let mut same = merged.clone();
        overlay(
            &mut same,
            "mycelium-rest-url".into(),
            file(url.clone()),
            Overlay::FileOverFile,
        );
        assert!(resolve(same, Vec::new()).is_err());

        // The command line wins over the conflicting file value, and unsets.
        overlay(
            &mut merged,
            "mycelium-rest-url".into(),
            argument(url),
            Overlay::ArgumentOverFile,
        );
        overlay(
            &mut merged,
            "alias".into(),
            unset_entry(Provenance::Argument),
            Overlay::ArgumentOverFile,
        );
        let loaded = resolve(merged, Vec::new()).unwrap();
        assert!(loaded.settings.mycelium_key_file.is_none());
        assert!(loaded.settings.mycelium_rest_url.is_some());
        assert!(loaded.settings.alias.is_none());
        assert_eq!(
            loaded.report()["options"]["alias"],
            json!({ "source": "argument", "unset": true, "value": null })
        );
    }

    #[test]
    fn report_hides_imported_values() {
        let mut values = layer(json!({ "htpasswd": "users", "alias": "secret-ish" }));
        values.get_mut("alias").unwrap().origin.imports = vec!["env:HOSTNAME".into()];
        let report = resolve(values, Vec::new()).unwrap().report();
        let options = &report["options"];
        assert_eq!(
            options["htpasswd"],
            json!({ "source": "argument", "value": "users" })
        );
        assert_eq!(
            options["alias"],
            json!({ "source": "argument", "imported": ["env:HOSTNAME"] })
        );
        assert_eq!(
            options["neighbours"],
            json!({ "source": "default", "value": 12 })
        );
        assert!(options.get("debug-epoch").is_none());
    }

    #[test]
    fn text_values() {
        assert_eq!(from_text(Kind::Integer, " 30 ").unwrap(), json!(30));
        assert!(from_text(Kind::Integer, "-1").is_err());
        assert_eq!(
            from_text(Kind::List, "a, b\nc,").unwrap(),
            json!(["a", "b", "c"])
        );
        assert_eq!(from_text(Kind::Flag, "yes").unwrap(), json!(true));
    }

    #[test]
    fn checks() {
        assert!(resolve(layer(json!({})), Vec::new()).is_err()); // htpasswd is required
        assert!(
            resolve(
                layer(json!({ "htpasswd": "u", "neighbours": 1 })),
                Vec::new()
            )
            .is_err()
        );
        assert!(
            resolve(
                layer(json!({ "htpasswd": "u", "debug-epoch": 3 })),
                Vec::new()
            )
            .is_err()
        );
        assert!(
            resolve(
                layer(json!({
                    "htpasswd": "u",
                    "mycelium-rest-url": "http://[::1]:8989",
                    "mycelium-key-file": "k",
                })),
                Vec::new()
            )
            .is_err()
        );
        assert!(resolve(layer(json!({ "htpasswd": "u", "alias": " " })), Vec::new()).is_err());
        assert!(
            resolve(
                layer(json!({ "htpasswd": "u", "keepalive-secs": "x" })),
                Vec::new()
            )
            .is_err()
        );
    }

    #[test]
    fn arguments_with_importers() {
        // SAFETY: tests in this module don't read this variable concurrently.
        unsafe { std::env::set_var("CONTINUUM_TEST_SEEDS", "[\"a\", \"b\"]") };
        let matches = command()
            .try_get_matches_from([
                "continuum",
                "--seeds",
                "env+json:CONTINUUM_TEST_SEEDS",
                "--seeds",
                "c,d",
                "--alias",
                "literal:env:x",
                "--debug-api",
            ])
            .unwrap();
        let layer = arguments(&matches).unwrap();
        assert_eq!(layer["seeds"].value, json!(["a", "b", "c", "d"]));
        assert_eq!(
            layer["seeds"].origin.imports,
            ["env+json:CONTINUUM_TEST_SEEDS"]
        );
        assert_eq!(layer["alias"].value, json!("env:x"));
        assert_eq!(layer["debug-api"].value, json!(true));
        assert!(!layer.contains_key("neighbours"));
    }
}