use crate::lsp::ServerConfig;
use serde_json::Value;

pub fn resolve(value: Value) -> Result<Vec<ServerConfig>, String> {
    let Value::Object(languages) = value else {
        return Err("LSP configuration must be a language-keyed object".into());
    };
    let mut servers = Vec::new();
    for (language_id, value) in languages {
        if language_id.is_empty() || language_id.chars().any(char::is_control) {
            return Err("LSP language keys must not be empty or contain control characters".into());
        }
        let preset: Option<(&[&[&str]], &str)> = match language_id.as_str() {
            crate::syntax::RUST_ID => Some((&[&["rust-analyzer"]], "rs")),
            crate::syntax::PYTHON_ID => Some((&[&["ty", "server"], &["ruff", "server"]], "py")),
            crate::syntax::RUBY_ID => Some((&[&["solargraph", "stdio"]], "rb")),
            _ => None,
        };
        let mut options = match value {
            Value::Bool(false) => continue,
            Value::Bool(true) => {
                if preset.is_none() {
                    return Err(format!(
                        "LSP language {language_id:?} has no built-in preset; provide command and extensions"
                    ));
                }
                serde_json::Map::new()
            }
            Value::Object(options) => options,
            _ => {
                return Err(format!(
                    "LSP language {language_id:?} must be true, false, or a configuration object"
                ));
            }
        };
        for key in options.keys() {
            if !matches!(
                key.as_str(),
                "command" | "extensions" | "initialization_options" | "settings" | "servers"
            ) {
                return Err(format!(
                    "LSP language {language_id:?} has unknown option {key:?}"
                ));
            }
        }
        let mut extensions = match options.remove("extensions") {
            Some(value) => extensions(value, &language_id)?,
            None => match preset {
                Some((_, extension)) => vec![extension.into()],
                None => return Err(format!("LSP language {language_id:?} requires extensions")),
            },
        };
        let explicit_servers = options.contains_key("servers");
        let configurations = match options.remove("servers") {
            Some(value) => {
                if ["command", "initialization_options", "settings"]
                    .iter()
                    .any(|key| options.contains_key(*key))
                {
                    return Err(format!(
                        "LSP language {language_id:?} servers cannot be combined with command, initialization_options, or settings"
                    ));
                }
                let Value::Array(configurations) = value else {
                    return Err(format!(
                        "LSP language {language_id:?} servers must be a nonempty array of configuration objects"
                    ));
                };
                if configurations.is_empty() {
                    return Err(format!(
                        "LSP language {language_id:?} servers must be a nonempty array of configuration objects"
                    ));
                }
                configurations
            }
            None if options.contains_key("command") => vec![Value::Object(options)],
            None => {
                let Some((commands, _)) = preset else {
                    return Err(format!(
                        "LSP language {language_id:?} requires command argv or servers"
                    ));
                };
                let mut configurations = Vec::with_capacity(commands.len());
                for (index, command) in commands.iter().enumerate() {
                    let mut configuration = if index + 1 == commands.len() {
                        std::mem::take(&mut options)
                    } else {
                        options.clone()
                    };
                    configuration.insert(
                        "command".into(),
                        Value::Array(
                            command
                                .iter()
                                .map(|argument| Value::from(*argument))
                                .collect(),
                        ),
                    );
                    if language_id == "python" && index == 0 {
                        configuration
                            .entry("initialization_options")
                            .or_insert_with(
                                || serde_json::json!({"experimental": {"useUv": "off"}}),
                            );
                    }
                    configurations.push(Value::Object(configuration));
                }
                configurations
            }
        };
        if servers.len() + configurations.len() > 16 {
            return Err("LSP configuration supports at most 16 configured servers".into());
        }
        let configuration_count = configurations.len();
        let mut language_id = language_id;
        for (index, configuration) in configurations.into_iter().enumerate() {
            let context = if explicit_servers {
                format!("LSP language {language_id:?} servers[{index}]")
            } else {
                format!("LSP language {language_id:?}")
            };
            let Value::Object(mut configuration) = configuration else {
                return Err(format!("{context} must be a configuration object"));
            };
            for key in configuration.keys() {
                if !matches!(
                    key.as_str(),
                    "command" | "initialization_options" | "settings"
                ) {
                    return Err(format!("{context} has unknown option {key:?}"));
                }
            }
            let command = match configuration.remove("command") {
                Some(value) => command(value, &context)?,
                None => return Err(format!("{context} requires command argv")),
            };
            let initialization_options = object(
                configuration.remove("initialization_options"),
                &context,
                "initialization_options",
            )?;
            let settings = object(configuration.remove("settings"), &context, "settings")?;
            servers.push(ServerConfig {
                language_id: if index + 1 == configuration_count {
                    std::mem::take(&mut language_id)
                } else {
                    language_id.clone()
                },
                command,
                extensions: if index + 1 == configuration_count {
                    std::mem::take(&mut extensions)
                } else {
                    extensions.clone()
                },
                initialization_options,
                settings,
            });
        }
    }
    Ok(servers)
}

fn command(value: Value, context: &str) -> Result<Vec<String>, String> {
    let error = || {
        format!(
            "{context} command must be nonempty argv with a nonempty executable and no NUL bytes"
        )
    };
    let Value::Array(values) = value else {
        return Err(error());
    };
    if values.is_empty() {
        return Err(error());
    }
    let mut command = Vec::with_capacity(values.len());
    for value in values {
        let Value::String(argument) = value else {
            return Err(error());
        };
        if argument.contains('\0') || (command.is_empty() && argument.is_empty()) {
            return Err(error());
        }
        command.push(argument);
    }
    Ok(command)
}

fn extensions(value: Value, language: &str) -> Result<Vec<String>, String> {
    let error = || {
        format!(
            "LSP language {language:?} extensions must be a nonempty array of suffixes without dots, separators, whitespace, or control characters"
        )
    };
    let Value::Array(values) = value else {
        return Err(error());
    };
    if values.is_empty() {
        return Err(error());
    }
    let mut extensions = Vec::with_capacity(values.len());
    for value in values {
        let Value::String(extension) = value else {
            return Err(error());
        };
        if extension.is_empty()
            || extension.chars().any(|character| {
                matches!(character, '.' | '/' | '\\')
                    || character.is_whitespace()
                    || character.is_control()
            })
        {
            return Err(error());
        }
        extensions.push(extension);
    }
    Ok(extensions)
}

fn object(value: Option<Value>, context: &str, option: &str) -> Result<Value, String> {
    match value {
        None => Ok(Value::Object(serde_json::Map::new())),
        Some(value) if value.is_object() => Ok(value),
        Some(_) => Err(format!("{context} {option} must be a JSON object")),
    }
}