oaspec

import gleam/dict
import gleam/float
import gleam/int
import gleam/list
import gleam/option.{type Option, None, Some}
import gleam/string
import oaspec/codegen/context.{type Context, type GeneratedFile, GeneratedFile}
import oaspec/codegen/types as type_gen
import oaspec/openapi/resolver
import oaspec/openapi/schema.{
  type SchemaObject, type SchemaRef, AllOfSchema, ArraySchema, Inline,
  IntegerSchema, NumberSchema, ObjectSchema, Reference, StringSchema,
}
import oaspec/util/naming
import oaspec/util/string_extra as se

/// Generate guard/validation functions from OpenAPI schemas that have constraints.
pub fn generate(ctx: Context) -> List(GeneratedFile) {
  let content = generate_guards(ctx)
  case string.contains(content, "pub fn validate_") {
    True -> [
      GeneratedFile(
        path: "guards.gleam",
        content: content,
        target: context.SharedTarget,
      ),
    ]
    False -> []
  }
}

/// Generate validation guard functions for schemas with constraints.
fn generate_guards(ctx: Context) -> String {
  let schemas = case ctx.spec.components {
    Some(components) ->
      list.sort(dict.to_list(components.schemas), fn(a, b) {
        string.compare(a.0, b.0)
      })
    None -> []
  }

  // Determine which imports are needed based on constraint types present.
  // Generated guard functions use string/list.length for validation;
  // constraint values (min/max) are baked as literals at generation time,
  // so gleam/int and gleam/float are NOT needed in the generated output.
  let constraint_types = collect_constraint_types(schemas, ctx)
  let imports = []
  let imports = case constraint_types.has_string {
    True -> ["gleam/string", ..imports]
    False -> imports
  }
  let imports = case constraint_types.has_list {
    True -> ["gleam/list", ..imports]
    False -> imports
  }
  let imports = case constraint_types.has_dict {
    True -> ["gleam/dict.{type Dict}", ..imports]
    False -> imports
  }
  let imports = case constraint_types.has_float_multiple_of {
    True -> ["gleam/int", "gleam/float", ..imports]
    False -> imports
  }
  // Import types module when composite validators reference named types
  let needs_types =
    list.any(schemas, fn(entry) {
      let #(name, schema_ref) = entry
      let guard_calls = collect_guard_calls(name, schema_ref, ctx)
      case list.is_empty(guard_calls) {
        True -> False
        False -> {
          let resolved = case schema_ref {
            Inline(s) -> Ok(s)
            Reference(..) -> resolver.resolve_schema_ref(schema_ref, ctx.spec)
          }
          case resolved {
            Ok(ObjectSchema(..)) | Ok(AllOfSchema(..)) -> True
            _ -> False
          }
        }
      }
    })
  let imports = case needs_types {
    True -> [ctx.config.package <> "/types", ..imports]
    False -> imports
  }
  // Import option module when composite validators handle optional fields
  let needs_option =
    list.any(schemas, fn(entry) {
      let #(name, schema_ref) = entry
      let guard_calls = collect_guard_calls(name, schema_ref, ctx)
      list.any(guard_calls, fn(call) {
        let #(_, _, is_required) = call
        !is_required
      })
    })
  let imports = case needs_option {
    True -> ["gleam/option", ..imports]
    False -> imports
  }

  let sb =
    se.file_header(context.version)
    |> se.imports(imports)

  let sb =
    list.fold(schemas, sb, fn(sb, entry) {
      let #(name, schema_ref) = entry
      generate_guards_for_schema(sb, name, schema_ref, ctx)
    })

  // Generate composite validate_<type> functions that call all field validators
  let sb =
    list.fold(schemas, sb, fn(sb, entry) {
      let #(name, schema_ref) = entry
      generate_composite_validator(sb, name, schema_ref, ctx)
    })

  se.to_string(sb)
}

/// Track which constraint types exist in the schema set.
type ConstraintTypes {
  ConstraintTypes(
    has_string: Bool,
    has_integer: Bool,
    has_float: Bool,
    has_list: Bool,
    has_float_multiple_of: Bool,
    has_dict: Bool,
  )
}

/// Scan all schemas to find which constraint types are present.
fn collect_constraint_types(
  schemas: List(#(String, SchemaRef)),
  ctx: Context,
) -> ConstraintTypes {
  list.fold(
    schemas,
    ConstraintTypes(False, False, False, False, False, False),
    fn(acc, entry) {
      let #(_name, schema_ref) = entry
      collect_schema_constraint_types(acc, schema_ref, ctx)
    },
  )
}

/// Collect constraint types from a single schema ref.
fn collect_schema_constraint_types(
  acc: ConstraintTypes,
  schema_ref: SchemaRef,
  ctx: Context,
) -> ConstraintTypes {
  let schema = case schema_ref {
    Inline(s) -> Ok(s)
    Reference(..) -> resolver.resolve_schema_ref(schema_ref, ctx.spec)
  }
  case schema {
    Ok(StringSchema(min_length: Some(_), ..))
    | Ok(StringSchema(max_length: Some(_), ..)) ->
      ConstraintTypes(..acc, has_string: True)
    Ok(IntegerSchema(minimum: Some(_), ..))
    | Ok(IntegerSchema(maximum: Some(_), ..))
    | Ok(IntegerSchema(exclusive_minimum: Some(_), ..))
    | Ok(IntegerSchema(exclusive_maximum: Some(_), ..))
    | Ok(IntegerSchema(multiple_of: Some(_), ..)) ->
      ConstraintTypes(..acc, has_integer: True)
    Ok(NumberSchema(minimum: Some(_), ..))
    | Ok(NumberSchema(maximum: Some(_), ..))
    | Ok(NumberSchema(exclusive_minimum: Some(_), ..))
    | Ok(NumberSchema(exclusive_maximum: Some(_), ..)) ->
      ConstraintTypes(..acc, has_float: True)
    Ok(NumberSchema(multiple_of: Some(_), ..)) ->
      ConstraintTypes(..acc, has_float: True, has_float_multiple_of: True)
    Ok(ArraySchema(min_items: Some(_), ..))
    | Ok(ArraySchema(max_items: Some(_), ..))
    | Ok(ArraySchema(unique_items: True, ..)) ->
      ConstraintTypes(..acc, has_list: True)
    Ok(ObjectSchema(min_properties: Some(_), ..))
    | Ok(ObjectSchema(max_properties: Some(_), ..)) ->
      ConstraintTypes(..acc, has_dict: True)
    Ok(ObjectSchema(properties:, ..)) ->
      dict.to_list(properties)
      |> list.fold(acc, fn(a, prop) {
        let #(_, prop_ref) = prop
        collect_schema_constraint_types(a, prop_ref, ctx)
      })
    Ok(AllOfSchema(schemas:, ..)) ->
      list.fold(schemas, acc, fn(a, s) {
        collect_schema_constraint_types(a, s, ctx)
      })
    _ -> acc
  }
}

/// Generate guard functions for a single schema's constrained fields.
fn generate_guards_for_schema(
  sb: se.StringBuilder,
  name: String,
  schema_ref: SchemaRef,
  ctx: Context,
) -> se.StringBuilder {
  case schema_ref {
    Inline(schema) -> generate_guards_for_schema_object(sb, name, schema, ctx)
    Reference(name:, ..) -> {
      let resolved_name = name
      case resolver.resolve_schema_ref(schema_ref, ctx.spec) {
        Ok(schema) ->
          generate_guards_for_schema_object(sb, resolved_name, schema, ctx)
        _ -> sb
      }
    }
  }
}

/// Generate guard functions for fields within a schema object.
fn generate_guards_for_schema_object(
  sb: se.StringBuilder,
  name: String,
  schema: SchemaObject,
  ctx: Context,
) -> se.StringBuilder {
  case schema {
    ObjectSchema(properties:, min_properties:, max_properties:, ..) -> {
      let sb =
        generate_properties_count_guard(
          sb,
          name,
          "",
          min_properties,
          max_properties,
        )
      let props = dict.to_list(properties)
      list.fold(props, sb, fn(sb, entry) {
        let #(prop_name, prop_ref) = entry
        generate_field_guard(sb, name, prop_name, prop_ref, ctx)
      })
    }
    AllOfSchema(schemas:, ..) -> {
      let merged_props =
        list.fold(schemas, dict.new(), fn(acc, s_ref) {
          case s_ref {
            Inline(ObjectSchema(properties:, ..)) -> dict.merge(acc, properties)
            Reference(..) ->
              case resolver.resolve_schema_ref(s_ref, ctx.spec) {
                Ok(ObjectSchema(properties:, ..)) -> dict.merge(acc, properties)
                _ -> acc
              }
            _ -> acc
          }
        })
      let props = dict.to_list(merged_props)
      list.fold(props, sb, fn(sb, entry) {
        let #(prop_name, prop_ref) = entry
        generate_field_guard(sb, name, prop_name, prop_ref, ctx)
      })
    }
    // Top-level string/integer constraints (type aliases with constraints)
    StringSchema(min_length:, max_length:, ..) ->
      generate_string_guard(sb, name, "", min_length, max_length)
    IntegerSchema(
      minimum:,
      maximum:,
      exclusive_minimum:,
      exclusive_maximum:,
      multiple_of:,
      ..,
    ) -> {
      let sb = generate_integer_guard(sb, name, "", minimum, maximum)
      let sb =
        generate_integer_exclusive_guard(
          sb,
          name,
          "",
          exclusive_minimum,
          exclusive_maximum,
        )
      generate_integer_multiple_of_guard(sb, name, "", multiple_of)
    }
    NumberSchema(
      minimum:,
      maximum:,
      exclusive_minimum:,
      exclusive_maximum:,
      multiple_of:,
      ..,
    ) -> {
      let sb = generate_float_guard(sb, name, "", minimum, maximum)
      let sb =
        generate_float_exclusive_guard(
          sb,
          name,
          "",
          exclusive_minimum,
          exclusive_maximum,
        )
      generate_float_multiple_of_guard(sb, name, "", multiple_of)
    }
    ArraySchema(min_items:, max_items:, unique_items:, ..) -> {
      let sb = generate_list_guard(sb, name, "", min_items, max_items)
      generate_unique_items_guard(sb, name, "", unique_items)
    }
    _ -> sb
  }
}

/// Generate a guard for a specific field based on its schema type and constraints.
fn generate_field_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  prop_ref: SchemaRef,
  ctx: Context,
) -> se.StringBuilder {
  let resolved = case prop_ref {
    Inline(schema) -> Ok(schema)
    Reference(..) -> resolver.resolve_schema_ref(prop_ref, ctx.spec)
  }
  case resolved {
    Ok(StringSchema(min_length:, max_length:, ..)) ->
      generate_string_guard(sb, schema_name, prop_name, min_length, max_length)
    Ok(IntegerSchema(
      minimum:,
      maximum:,
      exclusive_minimum:,
      exclusive_maximum:,
      multiple_of:,
      ..,
    )) -> {
      let sb =
        generate_integer_guard(sb, schema_name, prop_name, minimum, maximum)
      let sb =
        generate_integer_exclusive_guard(
          sb,
          schema_name,
          prop_name,
          exclusive_minimum,
          exclusive_maximum,
        )
      generate_integer_multiple_of_guard(
        sb,
        schema_name,
        prop_name,
        multiple_of,
      )
    }
    Ok(NumberSchema(
      minimum:,
      maximum:,
      exclusive_minimum:,
      exclusive_maximum:,
      multiple_of:,
      ..,
    )) -> {
      let sb =
        generate_float_guard(sb, schema_name, prop_name, minimum, maximum)
      let sb =
        generate_float_exclusive_guard(
          sb,
          schema_name,
          prop_name,
          exclusive_minimum,
          exclusive_maximum,
        )
      generate_float_multiple_of_guard(sb, schema_name, prop_name, multiple_of)
    }
    Ok(ArraySchema(min_items:, max_items:, unique_items:, ..)) -> {
      let sb =
        generate_list_guard(sb, schema_name, prop_name, min_items, max_items)
      generate_unique_items_guard(sb, schema_name, prop_name, unique_items)
    }
    _ -> sb
  }
}

/// Generate a string length validation guard.
fn generate_string_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  min_length: Option(Int),
  max_length: Option(Int),
) -> se.StringBuilder {
  case min_length, max_length {
    None, None -> sb
    _, _ -> {
      let fn_name = guard_function_name(schema_name, prop_name, "length")
      let sb =
        sb
        |> se.line(
          "/// Validate string length for "
          <> schema_name
          <> field_label(prop_name)
          <> ".",
        )
      let sb =
        sb
        |> se.line(
          "pub fn " <> fn_name <> "(value: String) -> Result(String, String) {",
        )
      let sb = sb |> se.indent(1, "let len = string.length(value)")
      let sb = case min_length, max_length {
        Some(min), Some(max) ->
          sb
          |> se.indent(1, "case len < " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at least "
              <> int.to_string(min)
              <> " characters\")",
          )
          |> se.indent(2, "False ->")
          |> se.indent(3, "case len > " <> int.to_string(max) <> " {")
          |> se.indent(
            4,
            "True -> Error(\"must be at most "
              <> int.to_string(max)
              <> " characters\")",
          )
          |> se.indent(4, "False -> Ok(value)")
          |> se.indent(3, "}")
          |> se.indent(1, "}")
        Some(min), None ->
          sb
          |> se.indent(1, "case len < " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at least "
              <> int.to_string(min)
              <> " characters\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, Some(max) ->
          sb
          |> se.indent(1, "case len > " <> int.to_string(max) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at most "
              <> int.to_string(max)
              <> " characters\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, None -> sb
      }
      sb
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate an integer range validation guard.
fn generate_integer_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  minimum: Option(Int),
  maximum: Option(Int),
) -> se.StringBuilder {
  case minimum, maximum {
    None, None -> sb
    _, _ -> {
      let fn_name = guard_function_name(schema_name, prop_name, "range")
      let sb =
        sb
        |> se.line(
          "/// Validate integer range for "
          <> schema_name
          <> field_label(prop_name)
          <> ".",
        )
      let sb =
        sb
        |> se.line(
          "pub fn " <> fn_name <> "(value: Int) -> Result(Int, String) {",
        )
      let sb = case minimum, maximum {
        Some(min), Some(max) ->
          sb
          |> se.indent(1, "case value < " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at least " <> int.to_string(min) <> "\")",
          )
          |> se.indent(2, "False ->")
          |> se.indent(3, "case value > " <> int.to_string(max) <> " {")
          |> se.indent(
            4,
            "True -> Error(\"must be at most " <> int.to_string(max) <> "\")",
          )
          |> se.indent(4, "False -> Ok(value)")
          |> se.indent(3, "}")
          |> se.indent(1, "}")
        Some(min), None ->
          sb
          |> se.indent(1, "case value < " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at least " <> int.to_string(min) <> "\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, Some(max) ->
          sb
          |> se.indent(1, "case value > " <> int.to_string(max) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at most " <> int.to_string(max) <> "\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, None -> sb
      }
      sb
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate a float range validation guard.
fn generate_float_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  minimum: Option(Float),
  maximum: Option(Float),
) -> se.StringBuilder {
  case minimum, maximum {
    None, None -> sb
    _, _ -> {
      let fn_name = guard_function_name(schema_name, prop_name, "range")
      let sb =
        sb
        |> se.line(
          "/// Validate float range for "
          <> schema_name
          <> field_label(prop_name)
          <> ".",
        )
      let sb =
        sb
        |> se.line(
          "pub fn " <> fn_name <> "(value: Float) -> Result(Float, String) {",
        )
      let sb = case minimum, maximum {
        Some(min), Some(max) ->
          sb
          |> se.indent(1, "case value <. " <> float.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at least " <> float.to_string(min) <> "\")",
          )
          |> se.indent(2, "False ->")
          |> se.indent(3, "case value >. " <> float.to_string(max) <> " {")
          |> se.indent(
            4,
            "True -> Error(\"must be at most " <> float.to_string(max) <> "\")",
          )
          |> se.indent(4, "False -> Ok(value)")
          |> se.indent(3, "}")
          |> se.indent(1, "}")
        Some(min), None ->
          sb
          |> se.indent(1, "case value <. " <> float.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at least " <> float.to_string(min) <> "\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, Some(max) ->
          sb
          |> se.indent(1, "case value >. " <> float.to_string(max) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must be at most " <> float.to_string(max) <> "\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, None -> sb
      }
      sb
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate an integer exclusive range validation guard.
fn generate_integer_exclusive_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  exclusive_minimum: Option(Int),
  exclusive_maximum: Option(Int),
) -> se.StringBuilder {
  case exclusive_minimum, exclusive_maximum {
    None, None -> sb
    _, _ -> {
      let fn_name =
        guard_function_name(schema_name, prop_name, "exclusive_range")
      let sb =
        sb
        |> se.line(
          "/// Validate integer exclusive range for "
          <> schema_name
          <> field_label(prop_name)
          <> ".",
        )
      let sb =
        sb
        |> se.line(
          "pub fn " <> fn_name <> "(value: Int) -> Result(Int, String) {",
        )
      let sb = case exclusive_minimum, exclusive_maximum {
        Some(min), Some(max) ->
          sb
          |> se.indent(1, "case value > " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "False -> Error(\"must be greater than "
              <> int.to_string(min)
              <> "\")",
          )
          |> se.indent(2, "True ->")
          |> se.indent(3, "case value < " <> int.to_string(max) <> " {")
          |> se.indent(
            4,
            "False -> Error(\"must be less than " <> int.to_string(max) <> "\")",
          )
          |> se.indent(4, "True -> Ok(value)")
          |> se.indent(3, "}")
          |> se.indent(1, "}")
        Some(min), None ->
          sb
          |> se.indent(1, "case value > " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "False -> Error(\"must be greater than "
              <> int.to_string(min)
              <> "\")",
          )
          |> se.indent(2, "True -> Ok(value)")
          |> se.indent(1, "}")
        None, Some(max) ->
          sb
          |> se.indent(1, "case value < " <> int.to_string(max) <> " {")
          |> se.indent(
            2,
            "False -> Error(\"must be less than " <> int.to_string(max) <> "\")",
          )
          |> se.indent(2, "True -> Ok(value)")
          |> se.indent(1, "}")
        None, None -> sb
      }
      sb
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate an integer multipleOf validation guard.
fn generate_integer_multiple_of_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  multiple_of: Option(Int),
) -> se.StringBuilder {
  case multiple_of {
    None -> sb
    Some(m) -> {
      let fn_name = guard_function_name(schema_name, prop_name, "multiple_of")
      sb
      |> se.line(
        "/// Validate integer multipleOf for "
        <> schema_name
        <> field_label(prop_name)
        <> ".",
      )
      |> se.line(
        "pub fn " <> fn_name <> "(value: Int) -> Result(Int, String) {",
      )
      |> se.indent(1, "case value % " <> int.to_string(m) <> " == 0 {")
      |> se.indent(
        2,
        "False -> Error(\"must be a multiple of " <> int.to_string(m) <> "\")",
      )
      |> se.indent(2, "True -> Ok(value)")
      |> se.indent(1, "}")
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate a float exclusive range validation guard.
fn generate_float_exclusive_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  exclusive_minimum: Option(Float),
  exclusive_maximum: Option(Float),
) -> se.StringBuilder {
  case exclusive_minimum, exclusive_maximum {
    None, None -> sb
    _, _ -> {
      let fn_name =
        guard_function_name(schema_name, prop_name, "exclusive_range")
      let sb =
        sb
        |> se.line(
          "/// Validate float exclusive range for "
          <> schema_name
          <> field_label(prop_name)
          <> ".",
        )
      let sb =
        sb
        |> se.line(
          "pub fn " <> fn_name <> "(value: Float) -> Result(Float, String) {",
        )
      let sb = case exclusive_minimum, exclusive_maximum {
        Some(min), Some(max) ->
          sb
          |> se.indent(1, "case value >. " <> float.to_string(min) <> " {")
          |> se.indent(
            2,
            "False -> Error(\"must be greater than "
              <> float.to_string(min)
              <> "\")",
          )
          |> se.indent(2, "True ->")
          |> se.indent(3, "case value <. " <> float.to_string(max) <> " {")
          |> se.indent(
            4,
            "False -> Error(\"must be less than "
              <> float.to_string(max)
              <> "\")",
          )
          |> se.indent(4, "True -> Ok(value)")
          |> se.indent(3, "}")
          |> se.indent(1, "}")
        Some(min), None ->
          sb
          |> se.indent(1, "case value >. " <> float.to_string(min) <> " {")
          |> se.indent(
            2,
            "False -> Error(\"must be greater than "
              <> float.to_string(min)
              <> "\")",
          )
          |> se.indent(2, "True -> Ok(value)")
          |> se.indent(1, "}")
        None, Some(max) ->
          sb
          |> se.indent(1, "case value <. " <> float.to_string(max) <> " {")
          |> se.indent(
            2,
            "False -> Error(\"must be less than "
              <> float.to_string(max)
              <> "\")",
          )
          |> se.indent(2, "True -> Ok(value)")
          |> se.indent(1, "}")
        None, None -> sb
      }
      sb
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate a float multipleOf validation guard.
fn generate_float_multiple_of_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  multiple_of: Option(Float),
) -> se.StringBuilder {
  case multiple_of {
    None -> sb
    Some(m) -> {
      let fn_name = guard_function_name(schema_name, prop_name, "multiple_of")
      sb
      |> se.line(
        "/// Validate float multipleOf for "
        <> schema_name
        <> field_label(prop_name)
        <> ".",
      )
      |> se.line(
        "pub fn " <> fn_name <> "(value: Float) -> Result(Float, String) {",
      )
      |> se.indent(
        1,
        "let remainder = value -. float.truncate(value /. "
          <> float.to_string(m)
          <> " |> int.to_float) *. "
          <> float.to_string(m),
      )
      |> se.indent(1, "case remainder == 0.0 || remainder == -0.0 {")
      |> se.indent(
        2,
        "False -> Error(\"must be a multiple of " <> float.to_string(m) <> "\")",
      )
      |> se.indent(2, "True -> Ok(value)")
      |> se.indent(1, "}")
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate a list length validation guard.
fn generate_list_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  min_items: Option(Int),
  max_items: Option(Int),
) -> se.StringBuilder {
  case min_items, max_items {
    None, None -> sb
    _, _ -> {
      let fn_name = guard_function_name(schema_name, prop_name, "length")
      let sb =
        sb
        |> se.line(
          "/// Validate list length for "
          <> schema_name
          <> field_label(prop_name)
          <> ".",
        )
      let sb =
        sb
        |> se.line(
          "pub fn "
          <> fn_name
          <> "(value: List(a)) -> Result(List(a), String) {",
        )
      let sb =
        sb
        |> se.indent(1, "let len = list.length(value)")
      let sb = case min_items, max_items {
        Some(min), Some(max) ->
          sb
          |> se.indent(1, "case len < " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must have at least "
              <> int.to_string(min)
              <> " items\")",
          )
          |> se.indent(2, "False ->")
          |> se.indent(3, "case len > " <> int.to_string(max) <> " {")
          |> se.indent(
            4,
            "True -> Error(\"must have at most "
              <> int.to_string(max)
              <> " items\")",
          )
          |> se.indent(4, "False -> Ok(value)")
          |> se.indent(3, "}")
          |> se.indent(1, "}")
        Some(min), None ->
          sb
          |> se.indent(1, "case len < " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must have at least "
              <> int.to_string(min)
              <> " items\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, Some(max) ->
          sb
          |> se.indent(1, "case len > " <> int.to_string(max) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must have at most "
              <> int.to_string(max)
              <> " items\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, None -> sb
      }
      sb
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate a uniqueItems validation guard.
fn generate_unique_items_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  unique_items: Bool,
) -> se.StringBuilder {
  case unique_items {
    False -> sb
    True -> {
      let fn_name = guard_function_name(schema_name, prop_name, "unique")
      sb
      |> se.line(
        "/// Validate unique items for "
        <> schema_name
        <> field_label(prop_name)
        <> ".",
      )
      |> se.line(
        "pub fn " <> fn_name <> "(value: List(a)) -> Result(List(a), String) {",
      )
      |> se.indent(
        1,
        "case list.length(value) == list.length(list.unique(value)) {",
      )
      |> se.indent(2, "True -> Ok(value)")
      |> se.indent(2, "False -> Error(\"items must be unique\")")
      |> se.indent(1, "}")
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Generate a minProperties/maxProperties validation guard for objects.
fn generate_properties_count_guard(
  sb: se.StringBuilder,
  schema_name: String,
  prop_name: String,
  min_properties: Option(Int),
  max_properties: Option(Int),
) -> se.StringBuilder {
  case min_properties, max_properties {
    None, None -> sb
    _, _ -> {
      let fn_name = guard_function_name(schema_name, prop_name, "properties")
      let sb =
        sb
        |> se.line(
          "/// Validate property count for "
          <> schema_name
          <> field_label(prop_name)
          <> ".",
        )
        |> se.line(
          "pub fn "
          <> fn_name
          <> "(value: Dict(k, v)) -> Result(Dict(k, v), String) {",
        )
        |> se.indent(1, "let count = dict.size(value)")
      let sb = case min_properties, max_properties {
        Some(min), Some(max) ->
          sb
          |> se.indent(1, "case count < " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must have at least "
              <> int.to_string(min)
              <> " properties\")",
          )
          |> se.indent(2, "False ->")
          |> se.indent(3, "case count > " <> int.to_string(max) <> " {")
          |> se.indent(
            4,
            "True -> Error(\"must have at most "
              <> int.to_string(max)
              <> " properties\")",
          )
          |> se.indent(4, "False -> Ok(value)")
          |> se.indent(3, "}")
          |> se.indent(1, "}")
        Some(min), None ->
          sb
          |> se.indent(1, "case count < " <> int.to_string(min) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must have at least "
              <> int.to_string(min)
              <> " properties\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, Some(max) ->
          sb
          |> se.indent(1, "case count > " <> int.to_string(max) <> " {")
          |> se.indent(
            2,
            "True -> Error(\"must have at most "
              <> int.to_string(max)
              <> " properties\")",
          )
          |> se.indent(2, "False -> Ok(value)")
          |> se.indent(1, "}")
        None, None -> sb
      }
      sb
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Build the guard function name from schema name, property name, and constraint type.
fn guard_function_name(
  schema_name: String,
  prop_name: String,
  constraint: String,
) -> String {
  let base = naming.to_snake_case(schema_name)
  case prop_name {
    "" -> "validate_" <> base <> "_" <> constraint
    _ ->
      "validate_"
      <> base
      <> "_"
      <> naming.to_snake_case(prop_name)
      <> "_"
      <> constraint
  }
}

/// Format a field label for documentation.
fn field_label(prop_name: String) -> String {
  case prop_name {
    "" -> ""
    _ -> "." <> prop_name
  }
}

/// Generate a composite validate function for a schema that calls all
/// individual field validators. This enables auto-validation by calling
/// a single function rather than individual field guards.
fn generate_composite_validator(
  sb: se.StringBuilder,
  name: String,
  schema_ref: SchemaRef,
  ctx: Context,
) -> se.StringBuilder {
  let guard_calls = collect_guard_calls(name, schema_ref, ctx)
  case list.is_empty(guard_calls) {
    True -> sb
    False -> {
      let fn_name = "validate_" <> naming.to_snake_case(name)
      let type_name = naming.schema_to_type_name(name)
      let gleam_type = composite_validator_type(name, schema_ref, ctx)
      let sb =
        sb
        |> se.doc_comment("Validate all constraints for " <> type_name <> ".")
        |> se.doc_comment(
          "Auto-calls all field validators and collects errors.",
        )
        |> se.line(
          "pub fn "
          <> fn_name
          <> "(value: "
          <> gleam_type
          <> ") -> Result("
          <> gleam_type
          <> ", List(String)) {",
        )
        |> se.indent(1, "let errors = []")
      let sb =
        list.fold(guard_calls, sb, fn(sb, call) {
          let #(guard_fn, accessor, is_required) = call
          case is_required {
            True ->
              sb
              |> se.indent(
                1,
                "let errors = case " <> guard_fn <> "(" <> accessor <> ") {",
              )
              |> se.indent(2, "Ok(_) -> errors")
              |> se.indent(2, "Error(msg) -> [msg, ..errors]")
              |> se.indent(1, "}")
            False ->
              sb
              |> se.indent(1, "let errors = case " <> accessor <> " {")
              |> se.indent(2, "option.Some(v) -> case " <> guard_fn <> "(v) {")
              |> se.indent(3, "Ok(_) -> errors")
              |> se.indent(3, "Error(msg) -> [msg, ..errors]")
              |> se.indent(2, "}")
              |> se.indent(2, "option.None -> errors")
              |> se.indent(1, "}")
          }
        })
      sb
      |> se.indent(1, "case errors {")
      |> se.indent(2, "[] -> Ok(value)")
      |> se.indent(2, "_ -> Error(errors)")
      |> se.indent(1, "}")
      |> se.line("}")
      |> se.blank_line()
    }
  }
}

/// Determine the Gleam type for the composite validator parameter.
fn composite_validator_type(
  name: String,
  schema_ref: SchemaRef,
  ctx: Context,
) -> String {
  let schema = case schema_ref {
    Inline(s) -> Ok(s)
    Reference(..) -> resolver.resolve_schema_ref(schema_ref, ctx.spec)
  }
  case schema {
    Ok(ObjectSchema(..)) | Ok(AllOfSchema(..)) ->
      "types." <> naming.schema_to_type_name(name)
    Ok(s) -> {
      type_gen.schema_to_gleam_type(s, ctx)
    }
    _ -> "types." <> naming.schema_to_type_name(name)
  }
}

/// A guard call with metadata about whether the field is optional.
/// #(guard_fn_name, accessor_expr, is_optional)
type GuardCall =
  #(String, String, Bool)

/// Collect all guard function calls for a schema's constrained fields.
fn collect_guard_calls(
  name: String,
  schema_ref: SchemaRef,
  ctx: Context,
) -> List(GuardCall) {
  let schema = case schema_ref {
    Inline(s) -> Ok(s)
    Reference(..) -> resolver.resolve_schema_ref(schema_ref, ctx.spec)
  }
  case schema {
    Ok(ObjectSchema(
      properties:,
      required:,
      min_properties:,
      max_properties:,
      ..,
    )) -> {
      let prop_calls =
        dict.to_list(properties)
        |> list.flat_map(fn(entry) {
          let #(prop_name, prop_ref) = entry
          let is_required = list.contains(required, prop_name)
          collect_field_guard_calls(name, prop_name, prop_ref, is_required, ctx)
        })
      let size_calls = case min_properties, max_properties {
        None, None -> []
        _, _ -> [
          #(guard_function_name(name, "", "properties"), "value", True),
        ]
      }
      list.append(prop_calls, size_calls)
    }
    Ok(AllOfSchema(schemas:, ..)) -> {
      let merged = merge_allof_props_and_required(schemas, ctx)
      dict.to_list(merged.properties)
      |> list.flat_map(fn(entry) {
        let #(prop_name, prop_ref) = entry
        let is_required = list.contains(merged.required, prop_name)
        collect_field_guard_calls(name, prop_name, prop_ref, is_required, ctx)
      })
    }
    Ok(StringSchema(min_length:, max_length:, ..)) ->
      case min_length, max_length {
        None, None -> []
        _, _ -> [
          #(guard_function_name(name, "", "length"), "value", True),
        ]
      }
    Ok(IntegerSchema(
      minimum:,
      maximum:,
      exclusive_minimum:,
      exclusive_maximum:,
      multiple_of:,
      ..,
    )) -> {
      let calls = case minimum, maximum {
        None, None -> []
        _, _ -> [
          #(guard_function_name(name, "", "range"), "value", True),
        ]
      }
      let calls = case exclusive_minimum, exclusive_maximum {
        None, None -> calls
        _, _ ->
          list.append(calls, [
            #(guard_function_name(name, "", "exclusive_range"), "value", True),
          ])
      }
      case multiple_of {
        None -> calls
        Some(_) ->
          list.append(calls, [
            #(guard_function_name(name, "", "multiple_of"), "value", True),
          ])
      }
    }
    Ok(NumberSchema(
      minimum:,
      maximum:,
      exclusive_minimum:,
      exclusive_maximum:,
      multiple_of:,
      ..,
    )) -> {
      let calls = case minimum, maximum {
        None, None -> []
        _, _ -> [
          #(guard_function_name(name, "", "range"), "value", True),
        ]
      }
      let calls = case exclusive_minimum, exclusive_maximum {
        None, None -> calls
        _, _ ->
          list.append(calls, [
            #(guard_function_name(name, "", "exclusive_range"), "value", True),
          ])
      }
      case multiple_of {
        None -> calls
        Some(_) ->
          list.append(calls, [
            #(guard_function_name(name, "", "multiple_of"), "value", True),
          ])
      }
    }
    Ok(ArraySchema(min_items:, max_items:, unique_items:, ..)) -> {
      let length_calls = case min_items, max_items {
        None, None -> []
        _, _ -> [
          #(guard_function_name(name, "", "length"), "value", True),
        ]
      }
      let unique_calls = case unique_items {
        True -> [
          #(guard_function_name(name, "", "unique"), "value", True),
        ]
        False -> []
      }
      list.append(length_calls, unique_calls)
    }
    _ -> []
  }
}

/// Collect guard calls for a single field.
fn collect_field_guard_calls(
  schema_name: String,
  prop_name: String,
  prop_ref: SchemaRef,
  is_required: Bool,
  ctx: Context,
) -> List(GuardCall) {
  let resolved = case prop_ref {
    Inline(schema) -> Ok(schema)
    Reference(..) -> resolver.resolve_schema_ref(prop_ref, ctx.spec)
  }
  let accessor = "value." <> naming.to_snake_case(prop_name)
  case resolved {
    Ok(StringSchema(min_length:, max_length:, ..)) ->
      case min_length, max_length {
        None, None -> []
        _, _ -> [
          #(
            guard_function_name(schema_name, prop_name, "length"),
            accessor,
            is_required,
          ),
        ]
      }
    Ok(IntegerSchema(
      minimum:,
      maximum:,
      exclusive_minimum:,
      exclusive_maximum:,
      multiple_of:,
      ..,
    )) -> {
      let calls = case minimum, maximum {
        None, None -> []
        _, _ -> [
          #(
            guard_function_name(schema_name, prop_name, "range"),
            accessor,
            is_required,
          ),
        ]
      }
      let calls = case exclusive_minimum, exclusive_maximum {
        None, None -> calls
        _, _ ->
          list.append(calls, [
            #(
              guard_function_name(schema_name, prop_name, "exclusive_range"),
              accessor,
              is_required,
            ),
          ])
      }
      case multiple_of {
        None -> calls
        Some(_) ->
          list.append(calls, [
            #(
              guard_function_name(schema_name, prop_name, "multiple_of"),
              accessor,
              is_required,
            ),
          ])
      }
    }
    Ok(NumberSchema(
      minimum:,
      maximum:,
      exclusive_minimum:,
      exclusive_maximum:,
      multiple_of:,
      ..,
    )) -> {
      let calls = case minimum, maximum {
        None, None -> []
        _, _ -> [
          #(
            guard_function_name(schema_name, prop_name, "range"),
            accessor,
            is_required,
          ),
        ]
      }
      let calls = case exclusive_minimum, exclusive_maximum {
        None, None -> calls
        _, _ ->
          list.append(calls, [
            #(
              guard_function_name(schema_name, prop_name, "exclusive_range"),
              accessor,
              is_required,
            ),
          ])
      }
      case multiple_of {
        None -> calls
        Some(_) ->
          list.append(calls, [
            #(
              guard_function_name(schema_name, prop_name, "multiple_of"),
              accessor,
              is_required,
            ),
          ])
      }
    }
    Ok(ArraySchema(min_items:, max_items:, unique_items:, ..)) -> {
      let length_calls = case min_items, max_items {
        None, None -> []
        _, _ -> [
          #(
            guard_function_name(schema_name, prop_name, "length"),
            accessor,
            is_required,
          ),
        ]
      }
      let unique_calls = case unique_items {
        True -> [
          #(
            guard_function_name(schema_name, prop_name, "unique"),
            accessor,
            is_required,
          ),
        ]
        False -> []
      }
      list.append(length_calls, unique_calls)
    }
    _ -> []
  }
}

/// Merge properties and required lists from allOf sub-schemas.
type MergedProps {
  MergedProps(properties: dict.Dict(String, SchemaRef), required: List(String))
}

fn merge_allof_props_and_required(
  schemas: List(SchemaRef),
  ctx: Context,
) -> MergedProps {
  list.fold(
    schemas,
    MergedProps(properties: dict.new(), required: []),
    fn(acc, s_ref) {
      case s_ref {
        Inline(ObjectSchema(properties:, required:, ..)) ->
          MergedProps(
            properties: dict.merge(acc.properties, properties),
            required: list.append(acc.required, required),
          )
        Reference(..) ->
          case resolver.resolve_schema_ref(s_ref, ctx.spec) {
            Ok(ObjectSchema(properties:, required:, ..)) ->
              MergedProps(
                properties: dict.merge(acc.properties, properties),
                required: list.append(acc.required, required),
              )
            _ -> acc
          }
        _ -> acc
      }
    },
  )
}