package lower

import "../hir"
import "../ir"
import "../source"
import "../types"
import "core:fmt"
import "core:mem"

State :: struct {
	hir_module:   ^hir.Module,
	instructions: [dynamic]ir.Instruction,
	local_values: []ir.Instruction_Id,
	local_slots:  []ir.Instruction_Id,
	expr_stack:   [dynamic]Lower_Expr_Frame,
	allocator:    mem.Allocator,
}

append_instruction :: proc(state: ^State, instruction: ir.Instruction) -> ir.Instruction_Id {
	id := ir.instruction_id(len(state.instructions))
	append(&state.instructions, instruction)
	return id
}

clone_args :: proc(values: []ir.Instruction_Id, allocator: mem.Allocator) -> []ir.Instruction_Id {
	result := make([]ir.Instruction_Id, len(values), allocator)
	copy(result, values)
	return result
}

sentinel :: proc(value_type: types.Type) -> i64 {
	switch value_type.bits {
	case 8:  return -86
	case 16: return -21846
	case 32: return -1431655766
	case:    return -6148914691236517206
	}
}

append_recovery_value :: proc(
	state: ^State,
	span: source.Span,
	value_type: types.Type,
	diagnostic := source.INVALID_DIAGNOSTIC,
) -> ir.Instruction_Id {
	append_instruction(state, ir.Instruction{
		op=.Trap,
		span=span,
		type=types.VOID,
		target=ir.INVALID_REF,
		a=ir.INVALID_INSTRUCTION,
		b=ir.INVALID_INSTRUCTION,
		diagnostic=diagnostic,
	})
	fallback := value_type
	if !types.is_concrete_integer(fallback) {
		fallback = types.I64
	}
	return append_instruction(state, ir.Instruction{
		op=.Const,
		span=span,
		type=fallback,
		integer=sentinel(fallback),
		target=ir.INVALID_REF,
		a=ir.INVALID_INSTRUCTION,
		b=ir.INVALID_INSTRUCTION,
		diagnostic=source.INVALID_DIAGNOSTIC,
	})
}

Lower_Expr_Frame :: struct {
	expr:      hir.Expr_Id,
	stage:     u8,
	left:      ir.Instruction_Id,
	arg_index: int,
	args:      []ir.Instruction_Id,
}

lower_expr :: proc(state: ^State, expr_id: hir.Expr_Id) -> ir.Instruction_Id {
	stack := state.expr_stack
	clear_dynamic_array(&stack)
	defer {
		for frame in stack {
			delete(frame.args, state.allocator)
		}
		clear_dynamic_array(&stack)
		state.expr_stack = stack
	}
	append(&stack, Lower_Expr_Frame{expr=expr_id})
	last := ir.INVALID_INSTRUCTION
	for len(stack) > 0 {
		frame_index := len(stack)-1
		frame := stack[frame_index]
		if frame.expr == hir.INVALID_EXPR || int(frame.expr) >= len(state.hir_module.exprs) {
			last = append_recovery_value(state, source.Span{}, types.I64)
			_ = pop(&stack)
			continue
		}
		expr := state.hir_module.exprs[frame.expr]
		if frame.stage == 0 {
			switch expr.kind {
			case .Invalid:
				last = append_recovery_value(state, expr.span, expr.type, expr.diagnostic)
				_ = pop(&stack)
			case .Integer:
				last = append_instruction(state, ir.Instruction{
					op=.Const, span=expr.span, type=expr.type, integer=expr.integer,
					target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION, diagnostic=source.INVALID_DIAGNOSTIC,
				})
				_ = pop(&stack)
			case .Local:
				last = ir.INVALID_INSTRUCTION
				local := hir.as_local(expr.target)
				if local != hir.INVALID_LOCAL && int(local) < len(state.local_slots) && state.local_slots[local] != ir.INVALID_INSTRUCTION {
					last = append_instruction(state, ir.Instruction{
						op=.Load, span=expr.span, type=expr.type, target=ir.INVALID_REF,
						a=state.local_slots[local], b=ir.INVALID_INSTRUCTION, diagnostic=source.INVALID_DIAGNOSTIC,
					})
				} else if local != hir.INVALID_LOCAL && int(local) < len(state.local_values) &&
				          state.local_values[local] != ir.INVALID_INSTRUCTION {
					last = state.local_values[local]
				}
				if last == ir.INVALID_INSTRUCTION {
					last = append_recovery_value(state, expr.span, expr.type, expr.diagnostic)
				}
				_ = pop(&stack)
			case .Global:
				global := hir.as_global(expr.target)
				if global == hir.INVALID_GLOBAL || int(global) >= len(state.hir_module.globals) {
					last = append_recovery_value(state, expr.span, expr.type, expr.diagnostic)
				} else {
					last = append_instruction(state, ir.Instruction{
						op=.Load_Global, span=expr.span, type=expr.type, target=ir.global_ref(ir.Global_Id(global)),
						a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION, diagnostic=source.INVALID_DIAGNOSTIC,
					})
				}
				_ = pop(&stack)
			case .Widen:
				stack[frame_index].stage = 1
				append(&stack, Lower_Expr_Frame{expr=expr.left})
			case .Add:
				stack[frame_index].stage = 2
				append(&stack, Lower_Expr_Frame{expr=expr.left})
			case .Call:
				function := hir.as_function(expr.target)
				if function == hir.INVALID_FUNCTION || int(function) >= len(state.hir_module.functions) {
					last = append_recovery_value(state, expr.span, expr.type, expr.diagnostic)
					_ = pop(&stack)
					continue
				}
				stack[frame_index].args = make([]ir.Instruction_Id, len(expr.args), state.allocator)
				stack[frame_index].stage = 4
				if len(expr.args) > 0 {
					append(&stack, Lower_Expr_Frame{expr=expr.args[0]})
				}
			}
			continue
		}
		if frame.stage == 1 {
			last = append_instruction(state, ir.Instruction{
				op=.Widen, span=expr.span, type=expr.type, target=ir.INVALID_REF,
				a=last, b=ir.INVALID_INSTRUCTION, diagnostic=source.INVALID_DIAGNOSTIC,
			})
			_ = pop(&stack)
			continue
		}
		if frame.stage == 2 {
			stack[frame_index].left = last
			stack[frame_index].stage = 3
			append(&stack, Lower_Expr_Frame{expr=expr.right})
			continue
		}
		if frame.stage == 3 {
			last = append_instruction(state, ir.Instruction{
				op=.Add_Checked, span=expr.span, type=expr.type, target=ir.INVALID_REF,
				a=frame.left, b=last, diagnostic=source.INVALID_DIAGNOSTIC,
			})
			_ = pop(&stack)
			continue
		}
		if frame.stage == 4 {
			if frame.arg_index < len(expr.args) {
				stack[frame_index].args[frame.arg_index] = last
				stack[frame_index].arg_index += 1
				if frame.arg_index+1 < len(expr.args) {
					append(&stack, Lower_Expr_Frame{expr=expr.args[frame.arg_index+1]})
					continue
				}
			}
			last = append_instruction(state, ir.Instruction{
				op=.Call, span=expr.span, type=expr.type, target=ir.function_ref(ir.Function_Id(hir.as_function(expr.target))),
				a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION, args=stack[frame_index].args, diagnostic=source.INVALID_DIAGNOSTIC,
			})
			stack[frame_index].args = nil
			_ = pop(&stack)
		}
	}
	return last
}

lower_body :: proc(hir_module: ^hir.Module, function: hir.Function, allocator: mem.Allocator) -> []ir.Instruction {
	state := State{
		hir_module=hir_module,
		allocator=allocator,
		local_values=make([]ir.Instruction_Id, len(function.locals), allocator),
		local_slots=make([]ir.Instruction_Id, len(function.locals), allocator),
	}
	state.instructions.allocator = allocator
	state.expr_stack.allocator = allocator
	defer {
		delete(state.local_values, allocator)
		delete(state.local_slots, allocator)
		delete(state.expr_stack)
	}
	for _, index in state.local_values {
		state.local_values[index] = ir.INVALID_INSTRUCTION
		state.local_slots[index] = ir.INVALID_INSTRUCTION
	}
	for local_id in function.params {
		param := append_instruction(&state, ir.Instruction{
			op=.Param,
			type=function.locals[local_id].type,
			target=ir.local_ref(ir.Local_Id(local_id)),
			a=ir.INVALID_INSTRUCTION,
			b=ir.INVALID_INSTRUCTION,
			diagnostic=source.INVALID_DIAGNOSTIC,
		})
		state.local_values[local_id] = param
	}

	for statement_id in function.body {
		statement := hir_module.statements[statement_id]
		switch statement.kind {
		case .Declaration:
			value := lower_expr(&state, statement.expr)
			if statement.local == hir.INVALID_LOCAL || int(statement.local) >= len(function.locals) {
				append_instruction(&state, ir.Instruction{
					op=.Trap, span=statement.span, type=types.VOID,
					target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION, diagnostic=statement.diagnostic,
				})
				continue
			}
			local := function.locals[statement.local]
			if local.mutable {
				slot := append_instruction(&state, ir.Instruction{
					op=.Alloca,
					span=statement.span,
					type=local.type,
					target=ir.local_ref(ir.Local_Id(statement.local)),
					a=ir.INVALID_INSTRUCTION,
					b=ir.INVALID_INSTRUCTION,
					diagnostic=source.INVALID_DIAGNOSTIC,
				})
				state.local_slots[statement.local] = slot
				append_instruction(&state, ir.Instruction{
					op=.Store,
					span=statement.span,
					type=local.type,
					target=ir.INVALID_REF,
					a=slot,
					b=value,
					diagnostic=source.INVALID_DIAGNOSTIC,
				})
			} else {
				state.local_values[statement.local] = value
			}
		case .Assignment:
			value := lower_expr(&state, statement.expr)
			slot := ir.INVALID_INSTRUCTION
			if statement.local != hir.INVALID_LOCAL && int(statement.local) < len(state.local_slots) {
				slot = state.local_slots[statement.local]
			}
			if slot == ir.INVALID_INSTRUCTION || statement.local == hir.INVALID_LOCAL || int(statement.local) >= len(function.locals) {
				append_instruction(&state, ir.Instruction{
					op=.Trap, span=statement.span, type=types.VOID,
					target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION, diagnostic=statement.diagnostic,
				})
				continue
			}
			append_instruction(&state, ir.Instruction{
				op=.Store,
				span=statement.span,
				type=function.locals[statement.local].type,
				target=ir.INVALID_REF,
				a=slot,
				b=value,
				diagnostic=source.INVALID_DIAGNOSTIC,
			})
		case .Return:
			if statement.expr == hir.INVALID_EXPR {
				append_instruction(&state, ir.Instruction{
					op=.Return_Void,
					span=statement.span,
					type=types.VOID,
					target=ir.INVALID_REF,
					a=ir.INVALID_INSTRUCTION,
					b=ir.INVALID_INSTRUCTION,
					diagnostic=source.INVALID_DIAGNOSTIC,
				})
			} else {
				value := lower_expr(&state, statement.expr)
				append_instruction(&state, ir.Instruction{
					op=.Return,
					span=statement.span,
					type=function.result,
					target=ir.INVALID_REF,
					a=value,
					b=ir.INVALID_INSTRUCTION,
					diagnostic=source.INVALID_DIAGNOSTIC,
				})
			}
		case .Expression, .Sink:
			_ = lower_expr(&state, statement.expr)
		case .Trap:
			append_instruction(&state, ir.Instruction{
				op=.Trap,
				span=statement.span,
				type=types.VOID,
				target=ir.INVALID_REF,
				a=ir.INVALID_INSTRUCTION,
				b=ir.INVALID_INSTRUCTION,
				diagnostic=statement.diagnostic,
			})
		}
	}
	if len(state.instructions) == 0 ||
	   (state.instructions[len(state.instructions)-1].op != .Return &&
	    state.instructions[len(state.instructions)-1].op != .Return_Void) {
		if function.result.kind == .Void {
			append_instruction(&state, ir.Instruction{op=.Return_Void, type=types.VOID, target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION, diagnostic=source.INVALID_DIAGNOSTIC})
		} else {
			value := append_instruction(&state, ir.Instruction{
				op=.Const,
				type=function.result,
				integer=sentinel(function.result),
				target=ir.INVALID_REF,
				a=ir.INVALID_INSTRUCTION,
				b=ir.INVALID_INSTRUCTION,
				diagnostic=source.INVALID_DIAGNOSTIC,
			})
			append_instruction(&state, ir.Instruction{op=.Return, type=function.result, target=ir.INVALID_REF, a=value, b=ir.INVALID_INSTRUCTION, diagnostic=source.INVALID_DIAGNOSTIC})
		}
	}
	return state.instructions[:]
}

lower_global_initializer :: proc(hir_module: ^hir.Module, global: hir.Global, allocator: mem.Allocator) -> []ir.Instruction {
	state := State{hir_module=hir_module, allocator=allocator}
	state.instructions.allocator = allocator
	state.expr_stack.allocator = allocator
	defer delete(state.expr_stack)
	value := lower_expr(&state, global.expr)
	append_instruction(&state, ir.Instruction{
		op=.Return,
		type=global.type,
		target=ir.INVALID_REF,
		a=value,
		b=ir.INVALID_INSTRUCTION,
		diagnostic=source.INVALID_DIAGNOSTIC,
	})
	return state.instructions[:]
}

lower :: proc(hir_module: ^hir.Module, allocator := context.allocator) -> ir.Module {
	module := ir.init_module(allocator)
	for global in hir_module.globals {
		_ = ir.global_id(len(module.globals))
		append(&module.globals, ir.Global{
			name=global.name,
			type=global.type,
			is_static=global.is_static,
			static_value=global.static_value,
			initializer=nil if global.is_static else lower_global_initializer(hir_module, global, allocator),
			problematic=global.problematic,
			diagnostic=global.diagnostic,
		})
	}
	for function in hir_module.functions {
		param_types := make([]types.Type, len(function.params), allocator)
		for local_id, index in function.params {
			param_types[index] = function.locals[local_id].type
		}
		_ = ir.function_id(len(module.functions))
		append(&module.functions, ir.Function{
			link_name=fmt.aprintf("%s", function.link_name, allocator=allocator),
			calling_convention=.C if function.calling_convention == .C else .Brolang,
			implementation=.Declaration if function.implementation == .Declaration else .Definition,
			linkage=.External if function.linkage == .External else .Internal,
			is_main=function.is_main,
			param_types=param_types,
			result=function.result,
			instructions=nil if function.implementation == .Declaration else lower_body(hir_module, function, allocator),
			problematic=function.problematic,
		})
	}
	return module
}