//// Lexicon -> Gleam codegen. Reads `<lexicons_dir>/**/*.json` and writes
//// typed modules into `<out_dir>`, importable as `<out_module>/...`.
////
//// Pipeline: read lexicon files, decode via `atproto_lexicon/decoding` into
//// `ast.LexiconDoc`, `codegen/lower` flattens those into the view plugins
//// consume, `codegen/plugin` runs the registered plugins and assembles
//// their per-module sections, `codegen/module_header` computes each
//// module's import header, then this module writes the files.

import argv
import atproto_codegen/config.{type Config, Config}
import atproto_codegen/lower.{type FlatLexicon}
import atproto_codegen/module_header
import atproto_codegen/naming
import atproto_codegen/plugin
import atproto_codegen/plugins/decode_json
import atproto_codegen/plugins/types
import atproto_codegen/plugins/xrpc_client
import atproto_lexicon/ast.{type LexiconDoc}
import atproto_lexicon/decoding
import gleam/dict
import gleam/erlang/application
import gleam/io
import gleam/list
import gleam/option.{None, Some}
import gleam/result
import gleam/string
import simplifile

const generated_banner = "//// Generated by codegen from priv/internal.gleam. Do not edit by hand.\n\n"

const module_banner = "//// Generated by codegen from lexicons/. Do not edit by hand.\n\n"

const usage = "usage: gleam run -- <lexicons_dir> <out_dir> <out_module> <nsid_prefix>[,<nsid_prefix>...] [<client_module_subpath>]"

pub fn main() -> Nil {
  case argv.load().arguments {
    [lexicons_dir, out_dir, out_module, prefixes] ->
      run(Config(
        lexicons_dir:,
        out_dir:,
        out_module:,
        nsid_prefixes: string.split(prefixes, ","),
        client: None,
      ))
    [lexicons_dir, out_dir, out_module, prefixes, client] ->
      run(Config(
        lexicons_dir:,
        out_dir:,
        out_module:,
        nsid_prefixes: string.split(prefixes, ","),
        client: Some(client),
      ))
    _ -> io.println(usage)
  }
}

/// `types` then `decode-json` interleave per section; the opt-in `xrpc-client` runs last and owns its own whole file, so it never interleaves.
fn plugin_order(config: Config) -> List(String) {
  case config.client {
    Some(_) -> ["types", "decode-json", "xrpc-client"]
    None -> ["types", "decode-json"]
  }
}

fn plugins(config: Config) -> List(plugin.Plugin) {
  case config.client {
    Some(_) -> [types.plugin(), decode_json.plugin(), xrpc_client.plugin()]
    None -> [types.plugin(), decode_json.plugin()]
  }
}

fn run(config: Config) -> Nil {
  let assert Ok(files) = simplifile.get_files(config.lexicons_dir)
  let docs =
    files
    |> list.filter(string.ends_with(_, ".json"))
    |> list.filter_map(fn(path) {
      case load_doc(path) {
        Ok(doc) -> Ok(doc)
        Error(reason) -> {
          io.println("  WARN  skipping " <> path <> ": " <> reason)
          Error(Nil)
        }
      }
    })

  let lexicons = lower.lower(docs)
  report_unsupported(lexicons)
  report_unresolved_refs(lexicons)

  let assert Ok(_) = simplifile.create_directory_all(config.out_dir)
  let assert Ok(internal) = simplifile.read(internal_template())
  let assert Ok(_) =
    simplifile.write(
      to: config.out_dir <> "/internal.gleam",
      contents: generated_banner <> internal,
    )

  let assert Ok(outputs) = plugin.run(plugins(config), config, docs, lexicons)
  let assert Ok(assembled) = plugin.assemble(outputs, plugin_order(config))
  let bodies = dict.from_list(assembled)

  list.each(lexicons, fn(lex) {
    case list.filter(lex.defs, lower.is_emittable) {
      [] -> Nil
      defs -> {
        let subpath = naming.module_subpath(config.nsid_prefixes, lex.nsid)
        let path = subpath <> ".gleam"
        let assert Ok(body) = dict.get(bodies, path)
        let header = module_header.header(config, lex.nsid, defs)
        let source = module_banner <> header <> "\n" <> body <> "\n"
        let full_path = config.out_dir <> "/" <> path
        let assert Ok(_) =
          simplifile.create_directory_all(parent_dir(full_path))
        let assert Ok(_) = simplifile.write(to: full_path, contents: source)
        io.println("  gen  " <> full_path)
      }
    }
  })

  write_client(config, bodies)
  io.println("codegen: done")
}

/// The xrpc-client plugin owns a whole file, so this writes its `WholeFile` content verbatim instead of the per-lexicon banner/header wrapping above.
fn write_client(config: Config, bodies: dict.Dict(String, String)) -> Nil {
  case config.client {
    None -> Nil
    Some(path) -> {
      let full_path = config.out_dir <> "/" <> path <> ".gleam"
      let assert Ok(content) = dict.get(bodies, path <> ".gleam")
      let assert Ok(_) = simplifile.create_directory_all(parent_dir(full_path))
      let assert Ok(_) = simplifile.write(to: full_path, contents: content)
      io.println("  gen  " <> full_path)
    }
  }
}

// Resolved via the app priv dir so the tool also works installed as a dep.
fn internal_template() -> String {
  let priv =
    application.priv_directory("atproto_codegen")
    |> result.unwrap("priv")
  priv <> "/internal.gleam"
}

fn load_doc(path: String) -> Result(LexiconDoc, String) {
  use contents <- result.try(
    simplifile.read(path)
    |> result.map_error(fn(e) { "read failed: " <> string.inspect(e) }),
  )
  decoding.decode_json(contents)
  |> result.map_error(fn(e) { "parse failed: " <> string.inspect(e) })
}

/// Loud on purpose: a dropped def must never be silent. Exhaustive over
/// `FlatDef` so a future variant forces a decision here instead of falling
/// through a wildcard.
fn report_unsupported(lexicons: List(FlatLexicon)) -> Nil {
  list.each(lexicons, fn(lex) {
    list.each(lex.defs, fn(d) {
      case d {
        lower.FlatUnsupported(nsid, name, reason) ->
          io.println(
            "  WARN  skipping " <> nsid <> "#" <> name <> ": " <> reason,
          )
        lower.FlatRecord(..) -> Nil
        lower.FlatObject(..) -> Nil
        lower.FlatMethod(_) -> Nil
        lower.FlatIgnored -> Nil
      }
    })
  })
}

/// Warn about any `ref` pointing at a def we never generate, which would otherwise emit Gleam that doesn't compile with no signal from codegen.
fn report_unresolved_refs(lexicons: List(FlatLexicon)) -> Nil {
  let known =
    list.flat_map(lexicons, fn(lex) {
      list.filter_map(lex.defs, fn(d) {
        case d {
          lower.FlatRecord(nsid, _) -> Ok(nsid <> "#main")
          lower.FlatObject(nsid, name, _) -> Ok(nsid <> "#" <> name)
          _ -> Error(Nil)
        }
      })
    })
  let refs =
    list.flat_map(lexicons, fn(lex) {
      list.flat_map(lex.defs, fn(d) {
        list.flat_map(lower.properties_of(d), fn(p) {
          field_ref_keys(lex.nsid, p.field_type)
        })
      })
    })
  refs
  |> list.unique
  |> list.filter(fn(key) { !list.contains(known, key) })
  |> list.each(fn(key) {
    io.println(
      "  WARN  unresolved ref " <> key <> " (referencing def won't compile)",
    )
  })
}

fn field_ref_keys(current: String, ft: lower.FlatType) -> List(String) {
  case ft {
    lower.TRef(ref) -> ref_key(current, ref)
    lower.TUnion(refs, _) -> list.flat_map(refs, ref_key(current, _))
    lower.TArray(inner) -> field_ref_keys(current, inner)
    _ -> []
  }
}

fn ref_key(current: String, ref: String) -> List(String) {
  let r = naming.parse_ref(current, ref)
  [r.nsid <> "#" <> r.def_name]
}

fn parent_dir(path: String) -> String {
  case string.split(path, "/") |> list.reverse {
    [_, ..rest] -> rest |> list.reverse |> string.join("/")
    [] -> "."
  }
}