package asm

import (
	"maps"

	"git.urbach.dev/cli/q/src/config"
	"git.urbach.dev/cli/q/src/data"
	"git.urbach.dev/cli/q/src/dll"
)

// Assembler contains a list of instructions.
type Assembler struct {
	Data         data.Data
	Instructions []Instruction
	Libraries    dll.List
}

// Append adds another instruction.
func (a *Assembler) Append(instr Instruction) {
	if a.Skip(instr) {
		return
	}

	a.Instructions = append(a.Instructions, instr)
}

// Last returns the last instruction.
func (a *Assembler) Last() Instruction {
	return a.Instructions[len(a.Instructions)-1]
}

// Compile compiles the instructions to machine code.
func (a *Assembler) Compile(build *config.Build) (code []byte, data []byte, libs dll.List, labels map[string]int) {
	data, dataLabels := a.Data.Finalize()

	c := compiler{
		patcher: patcher{
			code:         make([]byte, 0, len(a.Instructions)*8),
			earlyPatches: make([]*patch, 0, len(a.Instructions)/8),
			latePatches:  make([]*patch, 0, len(a.Instructions)/8),
			labels:       make(map[string]int, 32),
		},
		build:      build,
		data:       data,
		dataLabels: dataLabels,
		libraries:  a.Libraries,
	}

	switch build.Arch {
	case config.ARM:
		armc := compilerARM{compiler: &c}

		for _, instr := range a.Instructions {
			armc.Compile(instr)
		}
	case config.X86:
		x86c := compilerX86{compiler: &c}

		for _, instr := range a.Instructions {
			x86c.Compile(instr)
		}
	}

	c.ApplyPatches(c.earlyPatches)
	c.AddDataLabels()
	c.ApplyPatches(c.latePatches)
	return c.code, c.data, c.libraries, c.labels
}

// Merge combines the contents of this assembler with another one.
func (a *Assembler) Merge(b *Assembler) {
	skip := 0

	for a.Skip(b.Instructions[skip]) {
		skip++
	}

	a.Instructions = append(a.Instructions, b.Instructions[skip:]...)

	if a.Data.Immutable == nil {
		a.Data.Immutable = b.Data.Immutable
	} else {
		maps.Copy(a.Data.Immutable, b.Data.Immutable)
	}

	if a.Data.Mutable == nil {
		a.Data.Mutable = b.Data.Mutable
	} else {
		maps.Copy(a.Data.Mutable, b.Data.Mutable)
	}

	for library := range b.Libraries.All() {
		for _, fn := range library.Functions {
			a.Libraries.Append(library.Name, fn)
		}
	}
}

// SetLast sets the last instruction.
func (a *Assembler) SetLast(instr Instruction) {
	a.Instructions[len(a.Instructions)-1] = instr
}

// Skip returns true if appending the instruction can be skipped.
func (a *Assembler) Skip(instr Instruction) bool {
	if len(a.Instructions) == 0 {
		return false
	}

	// Call to os.exit + anything is skipped if it's not a label
	call, isCall := a.Last().(*Call)

	if isCall && call.Label == "run.exit" {
		switch instr.(type) {
		case *Label:
		default:
			return true
		}
	}

	switch instr := instr.(type) {
	case *Label:
		// Jump + Label can be replaced by just the Label if both addresses are equal
		jump, isJump := a.Last().(*Jump)

		if isJump && jump.Label == instr.Name {
			instr.Align = 0
			a.SetLast(instr)
			return true
		}
	case *Move:
		// A move following a move with inverted operands is unnecessary
		i := len(a.Instructions) - 1

		for i >= 0 {
			previous := a.Instructions[i]
			move, isMove := previous.(*Move)

			if !isMove {
				return false
			}

			if instr.Destination == move.Source {
				if instr.Source == move.Destination {
					return true
				} else {
					return false
				}
			}

			i--
		}
	case *Return:
		// Call + Return can be replaced by a single Jump
		call, isCall := a.Last().(*Call)

		if isCall {
			a.SetLast(&Jump{Label: call.Label})
			return true
		}

		// Jump + Return is unnecessary
		jump, isJump := a.Last().(*Jump)

		if isJump && jump.Condition == None {
			return true
		}

		// Return + Return is unnecessary
		_, isReturn := a.Last().(*Return)

		if isReturn {
			return true
		}
	}

	return false
}