// Copyright 2017 The Wuffs 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
//
//    https://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 cgen

import (
	"fmt"
	"strconv"
	"strings"

	a "github.com/google/wuffs/lang/ast"
	t "github.com/google/wuffs/lang/token"
)

func (g *gen) writeStatement(b *buffer, n *a.Node, depth uint32) error {
	if depth > a.MaxBodyDepth {
		return fmt.Errorf("body recursion depth too large")
	}
	depth++

	if n.Kind() == a.KAssert {
		// Assertions only apply at compile-time.
		return nil
	}

	if (n.Kind() == a.KAssign) && (n.AsAssign().LHS() != nil) && n.AsAssign().RHS().Effect().Coroutine() {
		// Put n's code into its own block, to restrict the scope of the
		// tPrefix temporary variables. This helps avoid "jump bypasses
		// variable initialization" compiler warnings with the coroutine
		// suspension points.
		b.writes("{\n")
		defer b.writes("}\n")
	}

	if g.genlinenum {
		filename, line := n.AsRaw().FilenameLine()
		if i := strings.LastIndexByte(filename, '/'); i >= 0 {
			filename = filename[i+1:]
		}
		if i := strings.LastIndexByte(filename, '\\'); i >= 0 {
			filename = filename[i+1:]
		}
		b.printf("// %s:%d\n", filename, line)
	}

	switch n.Kind() {
	case a.KAssign:
		n := n.AsAssign()
		return g.writeStatementAssign(b, n.Operator(), n.LHS(), n.RHS(), depth)
	case a.KChoose:
		return g.writeStatementChoose(b, n.AsChoose(), depth)
	case a.KIOBind:
		return g.writeStatementIOBind(b, n.AsIOBind(), depth)
	case a.KIf:
		return g.writeStatementIf(b, n.AsIf(), depth)
	case a.KIterate:
		return g.writeStatementIterate(b, n.AsIterate(), depth)
	case a.KJump:
		return g.writeStatementJump(b, n.AsJump(), depth)
	case a.KRet:
		return g.writeStatementRet(b, n.AsRet(), depth)
	case a.KVar:
		return nil
	case a.KWhile:
		return g.writeStatementWhile(b, n.AsWhile(), depth)
	}
	return fmt.Errorf("unrecognized ast.Kind (%s) for writeStatement", n.Kind())
}

func (g *gen) writeStatementAssign(b *buffer, op t.ID, lhs *a.Expr, rhs *a.Expr, depth uint32) error {
	if depth > a.MaxExprDepth {
		return fmt.Errorf("expression recursion depth too large")
	}
	depth++

	needWriteLoadExprDerivedVars := false
	if (len(g.currFunk.derivedVars) > 0) &&
		(rhs.Operator() == t.IDOpenParen) {
		method := rhs.LHS().AsExpr()
		recvTyp := method.LHS().MType().Pointee()
		if (recvTyp.Decorator() == 0) && (recvTyp.QID()[0] != t.IDBase) {
			n := len(*b)
			if err := g.writeSaveExprDerivedVars(b, rhs); err != nil {
				return err
			}
			needWriteLoadExprDerivedVars = n != len(*b)
		}
	}

	couldSuspend, skipRHS := false, false
	if rhs.Effect().Coroutine() {
		if err := g.writeBuiltinQuestionCall(b, rhs, 0); err == nil {
			skipRHS = true
		} else if err != errNoSuchBuiltin {
			return err
		} else if op != t.IDEqQuestion {
			if err := g.writeCoroSuspPoint(b, false); err != nil {
				return err
			}
			b.writes("status = ")
			couldSuspend = true
		}
	}

	if err := g.writeStatementAssign1(b, op, lhs, rhs, skipRHS); err != nil {
		return err
	}
	if needWriteLoadExprDerivedVars {
		if err := g.writeLoadExprDerivedVars(b, rhs); err != nil {
			return err
		}
	}
	if couldSuspend {
		b.writes("if (status.repr) {\ngoto suspend;\n}\n")
	}
	return nil
}

func (g *gen) writeStatementAssign1(b *buffer, op t.ID, lhs *a.Expr, rhs *a.Expr, skipRHS bool) error {
	lhsBuf := buffer(nil)
	opName, closer, disableWconversion := "", "", false

	if lhs != nil {
		if err := g.writeExpr(&lhsBuf, lhs, 0); err != nil {
			return err
		}

		if lTyp := lhs.MType(); lTyp.IsArrayType() {
			b.writes("memcpy(")
			opName, closer = ",", fmt.Sprintf(", sizeof(%s))", lhsBuf)

		} else {
			switch op {
			case t.IDEqQuestion:
				opName = cOpName(t.IDEqQuestion)
				if g.currFunk.tempW > maxTemp {
					return fmt.Errorf("too many temporary variables required")
				}
				temp := g.currFunk.tempW
				g.currFunk.tempW++

				b.printf("wuffs_base__status %s%d = ", tPrefix, temp)

				if err := g.writeExpr(b, rhs, 0); err != nil {
					return err
				}
				b.writes(";\n")

			case t.IDTildeSatPlusEq, t.IDTildeSatMinusEq:
				uBits := uintBits(lTyp.QID())
				if uBits == 0 {
					return fmt.Errorf("unsupported tilde-operator type %q", lTyp.Str(g.tm))
				}
				uOp := "add"
				if op != t.IDTildeSatPlusEq {
					uOp = "sub"
				}
				b.printf("wuffs_base__u%d__sat_%s_indirect(&", uBits, uOp)
				opName, closer = ", ", ")"

			case t.IDPlusEq, t.IDMinusEq:
				if lTyp.IsNumType() {
					if u := lTyp.QID()[1]; u == t.IDU8 || u == t.IDU16 {
						disableWconversion = true
					}
				}
				fallthrough

			default:
				opName = cOpName(op)
				if opName == "" {
					return fmt.Errorf("unrecognized operator %q", op.AmbiguousForm().Str(g.tm))
				}
			}
		}
	}

	// "x += 1" triggers -Wconversion, if x is smaller than an int (i.e. a
	// uint8_t or a uint16_t). This is arguably a clang/gcc bug, but in any
	// case, we work around it in Wuffs.
	if disableWconversion {
		b.writes("#if defined(__GNUC__)\n")
		b.writes("#pragma GCC diagnostic push\n")
		b.writes("#pragma GCC diagnostic ignored \"-Wconversion\"\n")
		b.writes("#endif\n")
	}

	n := len(*b)
	b.writex(lhsBuf)
	b.writes(opName)
	if g.currFunk.tempR != g.currFunk.tempW {
		if g.currFunk.tempR != (g.currFunk.tempW - 1) {
			return fmt.Errorf("internal error: temporary variable count out of sync")
		}
		b.printf("%s%d", tPrefix, g.currFunk.tempR)
		g.currFunk.tempR++
	} else if skipRHS {
		// No-op.
	} else if err := g.writeExpr(b, rhs, 0); err != nil {
		return err
	}
	b.writes(closer)
	if n != len(*b) {
		b.writes(";\n")
	}

	if disableWconversion {
		b.writes("#if defined(__GNUC__)\n")
		b.writes("#pragma GCC diagnostic pop\n")
		b.writes("#endif\n")
	}

	return nil
}

func (g *gen) writeStatementChoose(b *buffer, n *a.Choose, depth uint32) error {
	recv := g.currFunk.astFunc.Receiver()
	args := n.Args()
	if len(args) != 1 {
		return fmt.Errorf("TODO: multiple choice")
	}
	id := args[0].AsExpr().Ident()
	suffix := ""
	if n.Name() == id {
		suffix = "__choosy_default"
	}
	b.printf("self->private_impl.choosy_%s = &%s%s__%s%s;\n",
		n.Name().Str(g.tm), g.pkgPrefix, recv.Str(g.tm), id.Str(g.tm), suffix)
	return nil
}

func (g *gen) writeStatementIOBind(b *buffer, n *a.IOBind, depth uint32) error {
	if g.currFunk.ioBinds > maxIOBinds {
		return fmt.Errorf("too many temporary variables required")
	}
	ioBindNum := g.currFunk.ioBinds
	g.currFunk.ioBinds++

	e := n.IO()
	prefix := vPrefix
	if e.Operator() != 0 {
		prefix = aPrefix
	}
	cTyp, end, qualifier := "reader", "meta.wi", "const "
	if e.MType().QID()[1] == t.IDIOWriter {
		cTyp, end, qualifier = "writer", "data.len", ""
	}
	name := e.Ident().Str(g.tm)

	// TODO: do these variables need to be func-scoped (bigger scope)
	// instead of block-scoped (smaller scope) if the coro_susp_point
	// switch can jump past this initialization??
	b.writes("{\n")
	{
		if n.Keyword() == t.IDIOBind {
			b.printf("wuffs_base__io_buffer* %s%d_%s%s = %s%s;\n",
				oPrefix, ioBindNum, prefix, name,
				prefix, name)
			b.printf("%suint8_t *%s%d_%s%s%s = %s%s%s;\n",
				qualifier, oPrefix, ioBindNum, iopPrefix, prefix, name,
				iopPrefix, prefix, name)
			b.printf("%suint8_t *%s%d_%s%s%s = %s%s%s;\n",
				qualifier, oPrefix, ioBindNum, io0Prefix, prefix, name,
				io0Prefix, prefix, name)
			b.printf("%suint8_t *%s%d_%s%s%s = %s%s%s;\n",
				qualifier, oPrefix, ioBindNum, io1Prefix, prefix, name,
				io1Prefix, prefix, name)
			b.printf("%suint8_t *%s%d_%s%s%s = %s%s%s;\n",
				qualifier, oPrefix, ioBindNum, io2Prefix, prefix, name,
				io2Prefix, prefix, name)
			b.printf("%s%s = wuffs_base__io_%s__set("+
				"\n&%s%s,\n&%s%s%s,\n&%s%s%s,\n&%s%s%s,\n&%s%s%s,\n",
				prefix, name, cTyp,
				uPrefix, name,
				iopPrefix, prefix, name,
				io0Prefix, prefix, name,
				io1Prefix, prefix, name,
				io2Prefix, prefix, name)
			if err := g.writeExpr(b, n.Arg1(), 0); err != nil {
				return err
			}
			b.writes(");\n")

		} else {
			b.printf("%suint8_t *%s%d_%s%s%s = %s%s%s;\n",
				qualifier, oPrefix, ioBindNum, io2Prefix, prefix, name, io2Prefix, prefix, name)
			b.printf("wuffs_base__io_%s__limit(&%s%s%s, %s%s%s,\n",
				cTyp,
				io2Prefix, prefix, name,
				iopPrefix, prefix, name)
			if err := g.writeExpr(b, n.Arg1(), 0); err != nil {
				return err
			}
			b.writes(");\n")
			b.printf("if (%s%s) {\n%s%s->%s = ((size_t)(%s%s%s - %s%s->data.ptr));\n}\n",
				prefix, name,
				prefix, name, end,
				io2Prefix, prefix, name,
				prefix, name)
		}
	}

	for _, o := range n.Body() {
		if err := g.writeStatement(b, o, depth); err != nil {
			return err
		}
	}

	{
		if n.Keyword() == t.IDIOBind {
			b.printf("%s%s = %s%d_%s%s;\n",
				prefix, name,
				oPrefix, ioBindNum, prefix, name)
			b.printf("%s%s%s = %s%d_%s%s%s;\n",
				iopPrefix, prefix, name,
				oPrefix, ioBindNum, iopPrefix, prefix, name)
			b.printf("%s%s%s = %s%d_%s%s%s;\n",
				io0Prefix, prefix, name,
				oPrefix, ioBindNum, io0Prefix, prefix, name)
			b.printf("%s%s%s = %s%d_%s%s%s;\n",
				io1Prefix, prefix, name,
				oPrefix, ioBindNum, io1Prefix, prefix, name)
		}
		b.printf("%s%s%s = %s%d_%s%s%s;\n",
			io2Prefix, prefix, name,
			oPrefix, ioBindNum, io2Prefix, prefix, name)
		if n.Keyword() == t.IDIOLimit {
			b.printf("if (%s%s) {\n%s%s->%s = ((size_t)(%s%s%s - %s%s->data.ptr));\n}\n",
				prefix, name,
				prefix, name, end,
				io2Prefix, prefix, name,
				prefix, name)
		}
	}
	b.writes("}\n")
	return nil
}

func (g *gen) writeStatementIf(b *buffer, n *a.If, depth uint32) error {
	// For an "if true { etc }", just write the "etc".
	if cv := n.Condition().ConstValue(); (cv != nil) && (cv.Cmp(one) == 0) &&
		(n.ElseIf() == nil) && (len(n.BodyIfFalse()) == 0) {

		for _, o := range n.BodyIfTrue() {
			if err := g.writeStatement(b, o, depth); err != nil {
				return err
			}
		}
		return nil
	}

	for {
		condition := buffer(nil)
		if err := g.writeExpr(&condition, n.Condition(), 0); err != nil {
			return err
		}
		// Calling trimParens avoids clang's -Wparentheses-equality warning.
		b.printf("if (%s) {\n", trimParens(condition))
		for _, o := range n.BodyIfTrue() {
			if err := g.writeStatement(b, o, depth); err != nil {
				return err
			}
		}
		if bif := n.BodyIfFalse(); len(bif) > 0 {
			b.writes("} else {\n")
			for _, o := range bif {
				if err := g.writeStatement(b, o, depth); err != nil {
					return err
				}
			}
			break
		}
		n = n.ElseIf()
		if n == nil {
			break
		}
		b.writes("} else ")
	}
	b.writes("}\n")
	return nil
}

func (g *gen) writeStatementIterate(b *buffer, n *a.Iterate, depth uint32) error {
	assigns := n.Assigns()
	if len(assigns) == 0 {
		return nil
	}
	name0 := assigns[0].AsAssign().LHS().Ident().Str(g.tm)
	b.writes("{\n")

	// TODO: don't assume that the slice is a slice of base.u8. In
	// particular, the code gen can be subtle if the slice element type has
	// zero size, such as the empty struct.
	for i, o := range assigns {
		o := o.AsAssign()
		name := o.LHS().Ident().Str(g.tm)
		b.printf("wuffs_base__slice_u8 %sslice_%s = ", iPrefix, name)
		if err := g.writeExpr(b, o.RHS(), 0); err != nil {
			return err
		}
		b.writes(";\n")
		b.printf("%s%s = %sslice_%s;\n", vPrefix, name, iPrefix, name)
		if i > 0 {
			b.printf("%sslice_%s.len = ((size_t)(wuffs_base__u64__min(%sslice_%s.len, %sslice_%s.len)));\n",
				iPrefix, name0, iPrefix, name0, iPrefix, name)
		}
	}
	// TODO: look at n.HasContinue() and n.HasBreak().

	round := uint32(0)
	for ; n != nil; n = n.ElseIterate() {
		length, err := strconv.Atoi(n.Length().Str(g.tm))
		if err != nil {
			return err
		}
		advance, err := strconv.Atoi(n.Advance().Str(g.tm))
		if err != nil {
			return err
		}
		unroll, err := strconv.Atoi(n.Unroll().Str(g.tm))
		if err != nil {
			return err
		}
		for {
			if err := g.writeIterateRound(b, assigns, n.Body(), round, depth, length, advance, unroll); err != nil {
				return err
			}
			round++

			if unroll == 1 {
				break
			}
			unroll = 1
		}
	}

	b.writes("}\n")
	return nil
}

func (g *gen) writeStatementJump(b *buffer, n *a.Jump, depth uint32) error {
	jt, err := g.currFunk.jumpTarget(g.tm, n.JumpTarget())
	if err != nil {
		return err
	}
	keyword := "continue"
	if n.Keyword() == t.IDBreak {
		keyword = "break"
	}
	b.printf("goto label__%s__%s;\n", jt, keyword)
	return nil
}

func (g *gen) writeStatementRet(b *buffer, n *a.Ret, depth uint32) error {
	retExpr := n.Value()

	if g.currFunk.astFunc.Effect().Coroutine() ||
		(g.currFunk.returnsStatus && (len(g.currFunk.derivedVars) > 0)) {

		isComplete := false
		b.writes("status = ")
		if retExpr.Operator() == 0 && retExpr.Ident() == t.IDOk {
			b.writes("wuffs_base__make_status(NULL)")
			isComplete = true
		} else {
			if retExpr.Ident().IsDQStrLiteral(g.tm) {
				msg, _ := t.Unescape(retExpr.Ident().Str(g.tm))
				isComplete = statusMsgIsNote(msg)
			}
			if err := g.writeExpr(
				b, retExpr, depth); err != nil {
				return err
			}
		}
		b.writes(";\n")

		if n.Keyword() == t.IDYield {
			return g.writeCoroSuspPoint(b, true)
		}

		if n.RetsError() {
			b.writes("goto exit;\n")
		} else if isComplete {
			g.currFunk.hasGotoOK = true
			b.writes("goto ok;\n")
		} else {
			g.currFunk.hasGotoOK = true
			// TODO: the "goto exit"s can be "goto ok".
			b.writes("if (wuffs_base__status__is_error(&status)) {\ngoto exit;\n} " +
				"else if (wuffs_base__status__is_suspension(&status)) {\n" +
				"status = wuffs_base__make_status(wuffs_base__error__cannot_return_a_suspension);\ngoto exit;\n}\ngoto ok;\n")
		}
		return nil
	}

	if g.currFunk.derivedVars != nil {
		for _, o := range g.currFunk.astFunc.In().Fields() {
			o := o.AsField()
			if _, ok := g.currFunk.derivedVars[o.Name()]; ok {
				if err := g.writeFinalSaveDerivedVar(b, o); err != nil {
					return err
				}
			}
		}
	}

	b.writes("return ")
	if g.currFunk.astFunc.Out() == nil {
		b.writes("wuffs_base__make_empty_struct()")
	} else {
		couldBeSuspension := false
		if retExpr.MType().IsStatus() && !n.RetsError() {
			couldBeSuspension = true
			if s := g.tm.ByID(retExpr.Ident()); (len(s) > 1) && (s[0] == '"') {
				couldBeSuspension = s[1] == '$'
			} else if (retExpr.Operator() == 0) && (retExpr.Ident() == t.IDOk) {
				couldBeSuspension = false
			}
		}

		if couldBeSuspension {
			b.writes("wuffs_base__status__ensure_not_a_suspension(")
		}
		if err := g.writeExpr(b, retExpr, depth); err != nil {
			return err
		}
		if couldBeSuspension {
			b.writeb(')')
		}
	}

	b.writes(";\n")
	return nil
}

func (g *gen) writeStatementWhile(b *buffer, n *a.While, depth uint32) error {
	if n.HasContinue() {
		jt, err := g.currFunk.jumpTarget(g.tm, n)
		if err != nil {
			return err
		}
		b.printf("label__%s__continue:;\n", jt)
	}
	condition := buffer(nil)
	if err := g.writeExpr(&condition, n.Condition(), 0); err != nil {
		return err
	}
	// Calling trimParens avoids clang's -Wparentheses-equality warning.
	b.printf("while (%s) {\n", trimParens(condition))
	for _, o := range n.Body() {
		if err := g.writeStatement(b, o, depth); err != nil {
			return err
		}
	}
	b.writes("}\n")
	if n.HasBreak() {
		jt, err := g.currFunk.jumpTarget(g.tm, n)
		if err != nil {
			return err
		}
		b.printf("label__%s__break:;\n", jt)
	}
	return nil
}

func (g *gen) writeIterateRound(b *buffer, assigns []*a.Node, body []*a.Node, round uint32, depth uint32, length int, advance int, unroll int) error {
	for _, o := range assigns {
		name := o.AsAssign().LHS().Ident().Str(g.tm)
		b.printf("%s%s.len = %d;\n", vPrefix, name, length)
	}
	name0 := assigns[0].AsAssign().LHS().Ident().Str(g.tm)
	b.printf("uint8_t* %send%d_%s = %sslice_%s.ptr + ",
		iPrefix, round, name0, iPrefix, name0)
	if (length == 1) && (advance == 1) && (unroll == 1) {
		b.printf("%sslice_%s.len;\n",
			iPrefix, name0)
	} else if length == advance {
		b.printf("((%sslice_%s.len / %d) * %d);\n",
			iPrefix, name0, length*unroll, length*unroll)
	} else {
		b.printf("wuffs_base__iterate_total_advance(%sslice_%s.len, %d, %d);\n",
			iPrefix, name0, length*unroll, advance*unroll)
	}
	b.printf("while (%s%s.ptr < %send%d_%s) {\n", vPrefix, name0, iPrefix, round, name0)
	for i := 0; i < unroll; i++ {
		for _, o := range body {
			if err := g.writeStatement(b, o, depth); err != nil {
				return err
			}
		}
		for _, o := range assigns {
			name := o.AsAssign().LHS().Ident().Str(g.tm)
			b.printf("%s%s.ptr += %d;\n", vPrefix, name, advance)
		}
	}
	b.writes("}\n")
	return nil
}

func (g *gen) writeCoroSuspPoint(b *buffer, maybeSuspend bool) error {
	const maxCoroSuspPoint = 0xFFFFFFFF
	g.currFunk.coroSuspPoint++
	if g.currFunk.coroSuspPoint == maxCoroSuspPoint {
		return fmt.Errorf("too many coroutine suspension points required")
	}

	macro := ""
	if maybeSuspend {
		macro = "_MAYBE_SUSPEND"
	}
	b.printf("WUFFS_BASE__COROUTINE_SUSPENSION_POINT%s(%d);\n", macro, g.currFunk.coroSuspPoint)
	return nil
}

func trimParens(b []byte) []byte {
	if len(b) > 1 && b[0] == '(' && b[len(b)-1] == ')' {
		return b[1 : len(b)-1]
	}
	return b
}