package build

import (
	"git.akyoto.dev/cli/q/src/build/arch/x64"
	"git.akyoto.dev/cli/q/src/build/asm"
	"git.akyoto.dev/cli/q/src/build/os/linux"
)

// Result contains all the compiled functions in a build.
type Result struct {
	Main             *Function
	Functions        map[string]*Function
	InstructionCount int
}

// Finalize generates the final machine code.
func (r *Result) Finalize() ([]byte, []byte) {
	// This will be the entry point of the executable.
	// The only job of the entry function is to call `main` and exit cleanly.
	// The reason we call `main` instead of using `main` itself is to place
	// a return address on the stack, which allows return statements in `main`.
	final := asm.Assembler{
		Instructions: make([]asm.Instruction, 0, r.InstructionCount+4),
	}

	final.Call("main")
	final.RegisterNumber(asm.MOVE, x64.SyscallRegisters[0], linux.Exit)
	final.RegisterNumber(asm.MOVE, x64.SyscallRegisters[1], 0)
	final.Syscall()

	// This will place the main function immediately after the entry point
	// and also add everything the main function calls recursively.
	r.EachFunction(r.Main, map[*Function]bool{}, func(f *Function) {
		final.Merge(f.assembler)
	})

	code, data := final.Finalize()
	return code, data
}

// EachFunction recursively finds all the calls to external functions.
// It avoids calling the same function twice with the help of a hashmap.
func (r *Result) EachFunction(caller *Function, traversed map[*Function]bool, call func(*Function)) {
	call(caller)
	traversed[caller] = true

	for _, x := range caller.assembler.Instructions {
		if x.Mnemonic != asm.CALL {
			continue
		}

		name := x.Data.(*asm.Label).Name
		callee, exists := r.Functions[name]

		if !exists {
			continue
		}

		if traversed[callee] {
			continue
		}

		r.EachFunction(callee, traversed, call)
	}
}

// Write write the final executable to disk.
func (r *Result) Write(path string) error {
	code, data := r.Finalize()
	return Write(path, code, data)
}