import gleam/dict
import gleam/list
import gleam/option.{None, Some}
import gleam/string
import oaspec/internal/codegen/context.{type Context}
import oaspec/internal/openapi/spec.{
  type HttpMethod, type Operation, type Resolved,
}

/// Collect all operations from the spec with their IDs, paths, and methods.
/// Handles path-level parameter inheritance, security inheritance, and
/// operationId generation from method + path when not specified.
pub fn collect_operations(
  ctx: Context,
) -> List(#(String, Operation(Resolved), String, HttpMethod)) {
  let paths =
    list.sort(dict.to_list(context.spec(ctx).paths), fn(a, b) {
      string.compare(a.0, b.0)
    })
  list.flat_map(paths, fn(entry) {
    let #(path, ref_or) = entry
    // All path-level refs are resolved by this point
    let path_item = spec.unwrap_ref(ref_or)
    {
      let ops = [
        #(path_item.get, spec.Get),
        #(path_item.post, spec.Post),
        #(path_item.put, spec.Put),
        #(path_item.delete, spec.Delete),
        #(path_item.patch, spec.Patch),
        #(path_item.head, spec.Head),
        #(path_item.options, spec.Options),
        #(path_item.trace, spec.Trace),
      ]
      list.filter_map(ops, fn(op_entry) {
        let #(maybe_op, method) = op_entry
        case maybe_op {
          Some(operation) -> {
            // Merge path-level parameters with operation parameters.
            // Operation params take precedence by (name, in) key per OpenAPI spec.
            let op_param_keys =
              list.map(operation.parameters, fn(ref_p) {
                let parameter = spec.unwrap_ref(ref_p)
                #(parameter.name, parameter.in_)
              })
            let inherited_params =
              list.filter(path_item.parameters, fn(ref_p) {
                let parameter = spec.unwrap_ref(ref_p)
                !list.contains(op_param_keys, #(parameter.name, parameter.in_))
              })
            let merged_params =
              list.append(inherited_params, operation.parameters)
            // Inherit top-level security if operation doesn't define its own.
            // operation.security = None → inherit, Some([]) → no security,
            // Some([...]) → use operation-level.
            let effective_security = case operation.security {
              Some(sec) -> sec
              None -> context.spec(ctx).security
            }
            // Inherit path-level servers when operation doesn't define its own.
            // OpenAPI precedence: operation.servers > path_item.servers > spec.servers
            let effective_servers = case operation.servers {
              [_, ..] -> operation.servers
              [] -> path_item.servers
            }
            let operation =
              spec.Operation(
                ..operation,
                parameters: merged_params,
                security: Some(effective_security),
                servers: effective_servers,
              )

            let op_id = case operation.operation_id {
              Some(id) -> id
              None ->
                spec.method_to_lower(method)
                <> "_"
                <> string.replace(path, "/", "_")
                |> string.replace("{", "")
                |> string.replace("}", "")
            }
            Ok(#(op_id, operation, path, method))
          }
          None -> Error(Nil)
        }
      })
    }
  })
}