//! Codegen configuration — deserialized from `mizan.toml` at the consumer
//! project root.
//!
//! Example:
//!
//! ```toml
//! project_id = "blazr-studio"
//! output = "src/api"
//! targets = ["react"]
//!
//! [source.fastapi]
//! module = "blazr_session.handlers"
//! cwd = "../.."
//! command = ["uv", "run", "python"]
//!
//! [rust_kernel]
//! path = "../../mizan/frontends/mizan-rust"
//! ```

use std::collections::BTreeMap;
use std::path::PathBuf;

use serde::{Deserialize, Deserializer};


/// Every field carries a value once deserialization returns — a key absent
/// from the TOML takes the corresponding field of `Config::default()`.
#[derive(Debug, Deserialize)]
#[serde(default)]
pub struct Config {
    pub project_id: Option<String>,

    pub output: PathBuf,

    pub targets: Vec<String>,

    pub source: SourceConfig,

    pub rust_kernel: Option<RustKernelSpec>,

    pub rust_crate_name: String,
}


impl Default for Config {
    fn default() -> Self {
        Self {
            project_id: None,
            output: PathBuf::from("src/api"),
            targets: vec!["react".to_string()],
            source: SourceConfig::default(),
            rust_kernel: None,
            rust_crate_name: "mizan_client".to_string(),
        }
    }
}


fn default_python() -> String {
    "python".to_string()
}


/// A subprocess invocation split into the program and its argv. The
/// deserializer rejects an empty array, so every `CommandLine` in hand names
/// a program.
#[derive(Debug, Clone)]
pub struct CommandLine {
    program: String,
    args: Vec<String>,
}


impl CommandLine {
    pub fn program_only(program: &str) -> Self {
        Self { program: program.to_string(), args: Vec::new() }
    }

    pub fn program(&self) -> &str {
        &self.program
    }

    pub fn args(&self) -> &[String] {
        &self.args
    }
}


impl<'de> Deserialize<'de> for CommandLine {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        let mut parts = Vec::<String>::deserialize(deserializer)?.into_iter();
        match parts.next() {
            Some(program) => Ok(CommandLine { program, args: parts.collect() }),
            None => Err(serde::de::Error::custom(
                "command must be a non-empty array naming the program first",
            )),
        }
    }
}


#[derive(Debug, Deserialize, Default)]
pub struct SourceConfig {
    #[serde(default)]
    pub fastapi: Option<FastapiSource>,

    #[serde(default)]
    pub django: Option<DjangoSource>,

    #[serde(default)]
    pub rust: Option<RustSource>,

    /// `[source.script]` — spawn an arbitrary command and read its stdout
    /// as KDL IR.
    #[serde(default)]
    pub script: Option<ScriptSource>,
}


#[derive(Debug, Deserialize)]
pub struct FastapiSource {
    pub module: String,

    #[serde(default)]
    pub cwd: Option<PathBuf>,

    #[serde(default = "default_python")]
    pub python: String,

    #[serde(default)]
    pub command: Option<CommandLine>,

    #[serde(default)]
    pub env: BTreeMap<String, String>,
}


#[derive(Debug, Deserialize)]
pub struct DjangoSource {
    pub manage_path: PathBuf,

    #[serde(default = "default_python")]
    pub python: String,

    #[serde(default)]
    pub command: Option<CommandLine>,

    #[serde(default)]
    pub env: BTreeMap<String, String>,
}


/// `[source.rust]` — spawn a Cargo binary that emits the Mizan IR (KDL)
/// to stdout. The binary uses `mizan_core::build_ir()` after force-linking
/// the consumer crate's `#[derive(Mizan)]` types and `#[mizan::client]`
/// functions.
#[derive(Debug, Deserialize)]
pub struct RustSource {
    /// Path to the consumer's Cargo.toml, relative to the codegen config
    /// directory.
    #[serde(default = "default_manifest_path")]
    pub manifest_path: PathBuf,

    /// Name of the binary under `[[bin]]` that exports the IR.
    #[serde(default = "default_rust_bin")]
    pub bin: String,

    /// Cargo features to enable when building the bin.
    #[serde(default)]
    pub features: Vec<String>,

    /// Build in release mode.
    #[serde(default)]
    pub release: bool,

    /// Environment overrides for the cargo subprocess.
    #[serde(default)]
    pub env: BTreeMap<String, String>,

    /// Pre-step run before the Cargo bin: decoru writes Rust types from a
    /// Pydantic source module to `pydantic.output`.
    #[serde(default)]
    pub pydantic: Option<PydanticPreStep>,
}


fn default_manifest_path() -> PathBuf {
    PathBuf::from("Cargo.toml")
}


fn default_rust_bin() -> String {
    "emit-mizan-ir".to_string()
}


/// Pydantic → Rust pre-step. Runs an embedded Python helper that reports
/// the module's `BaseModel` and `Enum` declarations, then writes the Rust
/// file those shapes render to.
#[derive(Debug, Deserialize)]
pub struct PydanticPreStep {
    /// Python module name to import (e.g. `claude_manage.schema`).
    pub module: String,

    /// Path to write the generated Rust file, relative to the codegen
    /// config directory.
    pub output: PathBuf,

    /// Working directory for the python subprocess, relative to the
    /// codegen config directory. Defaults to the config directory itself.
    /// The script prepends this to `sys.path` so the module imports.
    #[serde(default)]
    pub cwd: Option<PathBuf>,

    /// Python executable.
    #[serde(default = "default_python")]
    pub python: String,

    /// Full command override (e.g. `["uv", "run", "python"]`). Wins over
    /// `python` when present.
    #[serde(default)]
    pub command: Option<CommandLine>,

    /// Derive macros applied to every generated struct.
    #[serde(default = "default_pydantic_derives")]
    pub derives: Vec<String>,

    /// Prelude inserted at the top of the generated file — the leading
    /// comment plus `use` statements for referenced types decoru does not
    /// itself produce.
    #[serde(default)]
    pub header: String,

    /// Environment overrides for the python subprocess.
    #[serde(default)]
    pub env: BTreeMap<String, String>,
}


fn default_pydantic_derives() -> Vec<String> {
    vec![
        "Debug".to_string(),
        "Clone".to_string(),
        "::serde::Serialize".to_string(),
        "::serde::Deserialize".to_string(),
        "::mizan_core::Mizan".to_string(),
    ]
}


/// `[source.script]` — spawns `command`, reads its stdout, and parses it as
/// KDL Mizan IR.
///
/// Example:
///
/// ```toml
/// [source.script]
/// command = ["uv", "run", "python", "-m", "holomorphic.emit_ir"]
/// ```
#[derive(Debug, Deserialize)]
pub struct ScriptSource {
    /// Program plus argv.
    pub command: CommandLine,

    /// Working directory for the subprocess, relative to the codegen
    /// config directory. Defaults to the config directory itself.
    #[serde(default)]
    pub cwd: Option<PathBuf>,

    /// Environment overrides.
    #[serde(default)]
    pub env: BTreeMap<String, String>,
}


#[derive(Debug, Deserialize, Clone)]
#[serde(untagged)]
pub enum RustKernelSpec {
    Path {
        path: String,
    },
    Git {
        git: String,
        #[serde(default)]
        tag: Option<String>,
        #[serde(default)]
        rev: Option<String>,
        #[serde(default)]
        branch: Option<String>,
    },
    Version {
        version: String,
    },
}