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() {
            "rust" => Some((&["rust-analyzer"], "rs")),
            "python" => Some((&["pylsp"], "py")),
            "ruby" => 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"
            ) {
                return Err(format!(
                    "LSP language {language_id:?} has unknown option {key:?}"
                ));
            }
        }
        let command = match options.remove("command") {
            Some(value) => command(value, &language_id)?,
            None => match preset {
                Some((command, _)) => command.iter().map(|argument| (*argument).into()).collect(),
                None => {
                    return Err(format!(
                        "LSP language {language_id:?} requires command argv"
                    ));
                }
            },
        };
        let 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 initialization_options = object(
            options.remove("initialization_options"),
            &language_id,
            "initialization_options",
        )?;
        let settings = object(options.remove("settings"), &language_id, "settings")?;
        servers.push(ServerConfig {
            language_id,
            command,
            extensions,
            initialization_options,
            settings,
        });
        if servers.len() > 16 {
            return Err("LSP configuration supports at most 16 enabled languages".into());
        }
    }
    Ok(servers)
}

fn command(value: Value, language: &str) -> Result<Vec<String>, String> {
    let error = || {
        format!(
            "LSP language {language:?} 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>, language: &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!(
            "LSP language {language:?} {option} must be a JSON object"
        )),
    }
}