// Copyright 2020 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package shaderir

import (
	"fmt"
	"strings"
)

func (p *Program) structName(t *Type) string {
	if t.Main != Struct {
		panic("shaderir: the given type at structName must be a struct")
	}
	s := t.serialize()
	if n, ok := p.structNames[s]; ok {
		return n
	}
	n := fmt.Sprintf("S%d", len(p.structNames))
	p.structNames[s] = n
	p.structTypes = append(p.structTypes, *t)
	return n
}

func (p *Program) Glsl() string {
	p.structNames = map[string]string{}
	p.structTypes = nil

	var lines []string
	for i, t := range p.Uniforms {
		lines = append(lines, fmt.Sprintf("uniform %s;", p.glslVarDecl(&t, fmt.Sprintf("U%d", i))))
	}
	for i, t := range p.Attributes {
		lines = append(lines, fmt.Sprintf("attribute %s;", p.glslVarDecl(&t, fmt.Sprintf("A%d", i))))
	}
	for i, t := range p.Varyings {
		lines = append(lines, fmt.Sprintf("varying %s;", p.glslVarDecl(&t, fmt.Sprintf("V%d", i))))
	}
	for _, f := range p.Funcs {
		lines = append(lines, p.glslFunc(&f)...)
	}

	var stLines []string
	for i, t := range p.structTypes {
		stLines = append(stLines, fmt.Sprintf("struct S%d {", i))
		for j, st := range t.Sub {
			stLines = append(stLines, fmt.Sprintf("\t%s;", p.glslVarDecl(&st, fmt.Sprintf("M%d", j))))
		}
		stLines = append(stLines, "};")
	}
	lines = append(stLines, lines...)

	return strings.Join(lines, "\n") + "\n"
}

func (p *Program) glslVarDecl(t *Type, varname string) string {
	switch t.Main {
	case None:
		return "?(none)"
	case Image2D:
		panic("not implemented")
	case Array:
		panic("not implemented")
	case Struct:
		return fmt.Sprintf("%s %s", p.structName(t), varname)
	default:
		return fmt.Sprintf("%s %s", t.Main.Glsl(), varname)
	}
}

func (p *Program) glslFunc(f *Func) []string {
	var args []string
	var idx int
	for _, t := range f.InParams {
		args = append(args, "in "+p.glslVarDecl(&t, fmt.Sprintf("l%d", idx)))
		idx++
	}
	for _, t := range f.InOutParams {
		args = append(args, "inout "+p.glslVarDecl(&t, fmt.Sprintf("l%d", idx)))
		idx++
	}
	for _, t := range f.OutParams {
		args = append(args, "out "+p.glslVarDecl(&t, fmt.Sprintf("l%d", idx)))
		idx++
	}
	argsstr := "void"
	if len(args) > 0 {
		argsstr = strings.Join(args, ", ")
	}

	var lines []string
	lines = append(lines, fmt.Sprintf("void %s(%s) {", f.Name, argsstr))
	lines = append(lines, p.glslBlock(&f.Block, f, 0, idx)...)
	lines = append(lines, "}")

	return lines
}

func (p *Program) glslBlock(b *Block, f *Func, level int, localVarIndex int) []string {
	idt := strings.Repeat("\t", level+1)

	var lines []string
	for _, t := range b.LocalVars {
		lines = append(lines, fmt.Sprintf("%s%s;", idt, p.glslVarDecl(&t, fmt.Sprintf("l%d", localVarIndex))))
		localVarIndex++
	}

	var glslExpr func(e *Expr) string
	glslExpr = func(e *Expr) string {
		switch e.Type {
		case Literal:
			return e.Value
		case VarName:
			switch e.Variable.Type {
			case Uniform:
				return fmt.Sprintf("U%d", e.Variable.Index)
			case Attribute:
				return fmt.Sprintf("A%d", e.Variable.Index)
			case Varying:
				return fmt.Sprintf("V%d", e.Variable.Index)
			case Local:
				return fmt.Sprintf("l%d", e.Variable.Index)
			default:
				return fmt.Sprintf("?(unexpected variable type: %d)", e.Variable.Type)
			}
		case Ident:
			return e.Value
		case Unary:
			return fmt.Sprintf("%s(%s)", e.Op, glslExpr(&e.Exprs[0]))
		case Binary:
			return fmt.Sprintf("(%s) %s (%s)", glslExpr(&e.Exprs[0]), e.Op, glslExpr(&e.Exprs[1]))
		case Call:
			// TODO: Take multiple args
			return fmt.Sprintf("(%s).(%s)", glslExpr(&e.Exprs[0]), glslExpr(&e.Exprs[1]))
		case Selector:
			return fmt.Sprintf("(%s).%s", glslExpr(&e.Exprs[0]), glslExpr(&e.Exprs[1]))
		case Index:
			return fmt.Sprintf("(%s)[%s]", glslExpr(&e.Exprs[0]), glslExpr(&e.Exprs[1]))
		default:
			return fmt.Sprintf("?(unexpected expr: %d)", e.Type)
		}
	}

	for _, s := range b.Stmts {
		switch s.Type {
		case ExprStmt:
			lines = append(lines, fmt.Sprintf("%s%s;", idt, glslExpr(&s.Exprs[0])))
		case BlockStmt:
			lines = append(lines, idt+"{")
			lines = append(lines, p.glslBlock(s.Block, f, level+1, localVarIndex)...)
			lines = append(lines, idt+"}")
		case Assign:
			lines = append(lines, fmt.Sprintf("%s%s = %s;", idt, glslExpr(&s.Exprs[0]), glslExpr(&s.Exprs[1])))
		case If:
			panic("not implemented")
		case For:
			panic("not implemented")
		case Continue:
			lines = append(lines, idt+"continue;")
		case Break:
			lines = append(lines, idt+"break;")
		case Return:
			lines = append(lines, idt+"return;")
		case Discard:
			lines = append(lines, idt+"discard;")
		default:
			lines = append(lines, fmt.Sprintf("%s?(unexpected stmt: %d)", idt, s.Type))
		}
	}

	return lines
}

// TODO: Distinguish regular functions, vertex functions and fragment functions. e.g., Treat gl_Position correctly.