#![allow(missing_docs)]

use std::fmt;
use elements::{BlockType, External, GlobalEntry, GlobalType, Internal, MemoryType,
               Module, Opcode, ResizableLimits, TableType, ValueType, InitExpr};
use common::stack;
use self::context::ModuleContext;
use self::func::Validator;

pub use self::module::ValidatedModule;

mod context;
mod module;
mod func;

#[cfg(test)]
mod tests;

#[derive(Debug)]
pub struct Error(String);

impl fmt::Display for Error {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		write!(f, "{}", self.0)
	}
}

impl From<stack::Error> for Error {
	fn from(e: stack::Error) -> Error {
		Error(format!("Stack: {}", e))
	}
}

pub fn validate_module(module: &Module) -> Result<ValidatedModule, Error> {
	let context = prepare_context(module)?;

	let function_section_len = module
		.function_section()
		.map(|s| s.entries().len())
		.unwrap_or(0);
	let code_section_len = module.code_section().map(|s| s.bodies().len()).unwrap_or(0);
	if function_section_len != code_section_len {
		return Err(Error(format!(
			"length of function section is {}, while len of code section is {}",
			function_section_len,
			code_section_len
		)));
	}

	// validate every function body in user modules
	if function_section_len != 0 {
		// tests use invalid code
		let function_section = module
			.function_section()
			.expect("function_section_len != 0; qed");
		let code_section = module
			.code_section()
			.expect("function_section_len != 0; function_section_len == code_section_len; qed");
		// check every function body
		for (index, function) in function_section.entries().iter().enumerate() {
			let function_body = code_section
				.bodies()
				.get(index as usize)
				.ok_or(Error(format!("Missing body for function {}", index)))?;
			Validator::validate_function(&context, function, function_body).map_err(|e| {
				let Error(ref msg) = e;
				Error(format!("Function #{} validation error: {}", index, msg))
			})?;
		}
	}

	// validate start section
	if let Some(start_function) = module.start_section() {
		let (params, return_ty) = context.require_function(start_function)?;
		if return_ty != BlockType::NoResult || params.len() != 0 {
			return Err(Error(
				"start function expected to have type [] -> []".into(),
			));
		}
	}

	// validate export section
	if let Some(export_section) = module.export_section() {
		for export in export_section.entries() {
			match *export.internal() {
				Internal::Function(function_index) => {
					context.require_function(function_index)?;
				}
				Internal::Global(global_index) => {
					context.require_global(global_index, Some(false))?;
				}
				Internal::Memory(memory_index) => {
					context.require_memory(memory_index)?;
				}
				Internal::Table(table_index) => {
					context.require_table(table_index)?;
				}
			}
		}
	}

	// validate import section
	if let Some(import_section) = module.import_section() {
		for import in import_section.entries() {
			match *import.external() {
				External::Function(function_type_index) => {
					context.require_function(function_type_index)?;
				},
				External::Global(ref global_type) => {
					if global_type.is_mutable() {
						return Err(Error(format!("trying to import mutable global {}", import.field())));
					}
				},
				External::Memory(ref memory_type) => {
					memory_type.validate()?;
				},
				External::Table(ref table_type) => {
					table_type.validate()?;
				},
			}
		}
	}

	// there must be no greater than 1 table in tables index space
	if context.tables().len() > 1 {
		return Err(Error(format!("too many tables in index space: {}", context.tables().len())));
	}

	// there must be no greater than 1 linear memory in memory index space
	if context.memories().len() > 1 {
		return Err(Error(format!("too many memory regions in index space: {}", context.memories().len())));
	}

	// use data section to initialize linear memory regions
	if let Some(data_section) = module.data_section() {
		for data_segment in data_section.entries() {
			context.require_memory(data_segment.index())?;
			let init_ty = data_segment.offset().expr_const_type(context.globals())?;
			if init_ty != ValueType::I32 {
				return Err(Error("segment offset should return I32".into()));
			}
		}
	}

	// use element section to fill tables
	if let Some(element_section) = module.elements_section() {
		for element_segment in element_section.entries() {
			context.require_table(element_segment.index())?;

			let init_ty = element_segment.offset().expr_const_type(context.globals())?;
			if init_ty != ValueType::I32 {
				return Err(Error("segment offset should return I32".into()));
			}

			for function_index in element_segment.members() {
				context.require_function(*function_index)?;
			}
		}
	}

	let ModuleContext {
		types,
		tables,
		memories,
		globals,
		func_type_indexes,
	} = context;

	Ok(ValidatedModule {
		types,
		tables,
		memories,
		globals,
		func_type_indexes,
	})
}

fn prepare_context(module: &Module) -> Result<ModuleContext, Error> {
	// Copy types from module as is.
	let types = module
		.type_section()
		.map(|ts| ts.types().into_iter().cloned().collect())
		.unwrap_or_default();

	// Fill elements with imported values.
	let mut func_type_indexes = Vec::new();
	let mut tables = Vec::new();
	let mut memories = Vec::new();
	let mut globals = Vec::new();

	for import_entry in module
		.import_section()
		.map(|i| i.entries())
		.unwrap_or_default()
	{
		match *import_entry.external() {
			External::Function(idx) => func_type_indexes.push(idx),
			External::Table(ref table) => tables.push(table.clone()),
			External::Memory(ref memory) => memories.push(memory.clone()),
			External::Global(ref global) => globals.push(global.clone()),
		}
	}

	// Concatenate elements with defined in the module.
	if let Some(function_section) = module.function_section() {
		for func_entry in function_section.entries() {
			func_type_indexes.push(func_entry.type_ref());
		}
	}
	if let Some(table_section) = module.table_section() {
		for table_entry in table_section.entries() {
			table_entry.validate()?;
			tables.push(table_entry.clone());
		}
	}
	if let Some(mem_section) = module.memory_section() {
		for mem_entry in mem_section.entries() {
			mem_entry.validate()?;
			memories.push(mem_entry.clone());
		}
	}
	if let Some(global_section) = module.global_section() {
		// Validation of globals is defined over modified context C', which
		// contains only imported globals. So we do globals validation
		// in two passes, in first we validate globals and after all globals are validated
		// add them in globals list.
		for global_entry in global_section.entries() {
			global_entry.validate(&globals)?;
		}

		for global_entry in global_section.entries() {
			globals.push(global_entry.global_type().clone());
		}
	}

	Ok(ModuleContext {
		types,
		tables,
		memories,
		globals,
		func_type_indexes,
	})
}

impl ResizableLimits {
	fn validate(&self) -> Result<(), Error> {
		if let Some(maximum) = self.maximum() {
			if self.initial() > maximum {
				return Err(Error(format!(
					"maximum limit {} is lesser than minimum {}",
					maximum,
					self.initial()
				)));
			}
		}
		Ok(())
	}
}

impl MemoryType {
	fn validate(&self) -> Result<(), Error> {
		self.limits().validate()
	}
}

impl TableType {
	fn validate(&self) -> Result<(), Error> {
		self.limits().validate()
	}
}

impl GlobalEntry {
	fn validate(&self, globals: &[GlobalType]) -> Result<(), Error> {
		let init = self.init_expr();
		let init_expr_ty = init.expr_const_type(globals)?;
		if init_expr_ty != self.global_type().content_type() {
			return Err(Error(format!(
				"Trying to initialize variable of type {:?} with value of type {:?}",
				self.global_type().content_type(),
				init_expr_ty
			)));
		}
		Ok(())
	}
}

impl InitExpr {
	/// Returns type of this constant expression.
	fn expr_const_type(&self, globals: &[GlobalType]) -> Result<ValueType, Error> {
		let code = self.code();
		if code.len() != 2 {
			return Err(Error("Init expression should always be with length 2".into()));
		}
		let expr_ty: ValueType = match code[0] {
			Opcode::I32Const(_) => ValueType::I32,
			Opcode::I64Const(_) => ValueType::I64,
			Opcode::F32Const(_) => ValueType::F32,
			Opcode::F64Const(_) => ValueType::F64,
			Opcode::GetGlobal(idx) => match globals.get(idx as usize) {
				Some(target_global) => {
					if target_global.is_mutable() {
						return Err(Error(format!("Global {} is mutable", idx)));
					}
					target_global.content_type()
				}
				None => {
					return Err(Error(
						format!("Global {} doesn't exists or not yet defined", idx),
					))
				}
			},
			_ => return Err(Error("Non constant opcode in init expr".into())),
		};
		if code[1] != Opcode::End {
			return Err(Error("Expression doesn't ends with `end` opcode".into()));
		}
		Ok(expr_ty)
	}
}